Chapter Five Structural Geology of the Central

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is 775 metres, en route to the Mackenzie River valley at about 70 metres above ..... Michael Pope, Washington State University; ...... eventually returned (as the Yukon-Tanana Terrane) to be accreted. Ogilvie ...... storm- and fair-weather wave-base (Turner et al., 1997). ...... The Coates Lake Group exhibits strong evidence of.
NORTHWEST TERRITORIES

GEOSCIENCE OFFICE

Geology of the central Mackenzie Mountains of the northern Canadian Cordillera Sekwi Mountain (105P)

Mount Eduni (106A)

map-areas, Northwest Territories

northwestern Wrigley Lake (95M)

This is ESS Contribution # 20110306 | Corresponding editor’s address: E. Martel Northwest Territories Geoscience Office | P.O. Box 1500 | Yellowknife, Canada, X1A 2R3 [email protected] | www.nwtgeoscience.ca Recommended Citation: Martel, E., Turner, E.C. and Fischer, B.J. (editors), 2011. Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories. NWT Special Volume 1, NWT Geoscience Office, 423 p. Copyright © 2012.

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Table of contents

Table of Contents Preface................................................................................ 7 Summary............................................................................. 8

Chapter 1. Introduction 1.0. Introduction............................................................... 9 1.1. Location and Access................................................. 9 1.2. Physiography...........................................................11 1.2.1. Drainage.................................................................11 1.2.2. Climate....................................................................11 1.3. Previous Geological Work....................................11 1.4. Current Geological Work......................................13 1.4.1. First field season (2005)......................................14 1.4.2. Second field season (2006).................................14 1.4.3. Third field season (2007).....................................15 1.4.4. Fourth field season (2008)..................................15 1.4.5. Progress reports and accompanying publications..................................................................15 1.4.6. Coordinate systems used in this volume..........17 1.5. Acknowledgements...............................................17

Chapter 2. Regional Setting 2.0. Introduction.............................................................18 2.1. Depositional and Intrusive Framework............18 2.1.1. Proterozoic.............................................................18 Paleo- and Mesoproterozoic........................................18 Early Neoproterozoic....................................................18 Late Neoproterozoic Laurentian margin and breakup of Rodinia.......................................................22 2.1.2. Early to mid-Paleozoic..........................................23 2.1.3. Devonian - Carboniferous - far-field effects of extension and orogeny on the Laurentian margin......................................................24 2.1.4. Late Paleozoic-Mesozoic......................................25 2.1.5. Mesozoic plutonism..............................................26 2.2. Structural Framework...........................................27

Chapter 3. Stratigraphy 3.0. Introduction.............................................................31 3.1. Early Neoproterozoic Epicratonic Basin – Mackenzie Mountains Supergroup........................31 3.1.1. “H1 unit”.................................................................34 Description.....................................................................34 Age and correlation......................................................35 Interpretation................................................................39 3.1.2. Tsezotene Formation...........................................39 Description.....................................................................39 Age and correlation......................................................39 Interpretation................................................................39 3.1.3. Katherine Group....................................................39

Age and correlation......................................................40 Unit K1............................................................................41 Unit K2............................................................................42 Unit K3............................................................................42 Unit K4............................................................................46 Unit K5............................................................................49 Unit K6............................................................................51 Unit K7............................................................................52 3.1.4. Little Dal Group.....................................................55 Mudcracked formation.................................................56 Basinal assemblage......................................................57 Platformal assemblage................................................58 Grainstone formation...................................................62 Gypsum formation........................................................63 Rusty Shale formation..................................................66 Upper Carbonate formation........................................70 3.1.5. Economic potential of the Mackenzie Mountains supergroup..............................................71 3.1.6. Conclusions............................................................71 3.2. Middle Neoproterozoic Volcanic Succession “Little Dal Basalt”......................................................79 3.2.1. Description.............................................................81 3.2.2. Age and correlation..............................................82 3.2.3. Interpretation........................................................82 3.2.4. Economic potential...............................................83 3.2.5. Conclusions............................................................83 3.3. Middle to Late Neoproterozoic Extension- and Rift-Related Successions Windermere Supergroup..........................................83 3.3.1. Coates Lake Group................................................83 Thundercloud Formation.............................................86 Redstone River Formation...........................................90 Coppercap Formation...................................................96 3.3.2. Rapitan Group.....................................................100 Mount Berg Formation...............................................104 Sayunei Formation......................................................104 Shezal Formation........................................................106 Economic potential.....................................................109 Conclusions..................................................................110 3.3.3. Hay Creek Group.................................................110 Twitya Formation.......................................................110 Keele Formation..........................................................112 Ice Brook Formation...................................................116 “Tepee dolostone” map unit......................................117 3.3.4. Unnamed “upper group” of the Windermere Supergroup.........................................122 Sheepbed Formation..................................................122 Gametrail Formation..................................................123 Blueflower Formation................................................127 Risky Formation..........................................................130

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Table of contents 3.4. Lower to Middle Paleozoic Mackenzie Platform......................................................................131 3.4.1 Lowest Paleozoic siliciclastic succession.........131 Backbone Ranges Formation, lower member.........131 Backbone Ranges Formation, middle member.......133 Backbone Ranges Formation, upper member; “Backbone Ranges Formation”...............................135 Ingta Formation..........................................................141 3.4.2. Lower Cambrian carbonate succession..........142 Sekwi Formation.........................................................142 3.4.3. Cambro-Ordovician carbonate succession.....150 Franklin Mountain Formation...................................150 Broken Skull Formation.............................................154 Sunblood Formation...................................................155 3.4.4. Upper Ordovician to Middle Silurian carbonate succession................................................156 Mount Kindle Formation; Whittaker Formation.....156 3.4.5. Upper Silurian to Lower Devonian carbonate succession (Delorme Group)...................................157 Tsetso Formation........................................................158 Camsell Formation......................................................159 3.4.6. Lower and Middle Devonian carbonate succession..................................................................160 Sombre Formation......................................................160 Arnica Formation........................................................161 Bear Rock Formation..................................................162 Grizzly Bear Formation..............................................163 Landry Formation.......................................................164 Hume Formation (Headless and Nahanni formations)................................................................165 3.5. Lower to Middle Paleozoic Selwyn Basin and Misty Creek Embayment.....................166 3.5.1. Cambrian to Lower Devonian siliciclastic basin.........................................................167 Vampire Formation.....................................................167 Hess River Formation.................................................170 Rockslide Formation...................................................170 Rabbitkettle Formation.............................................171 Duo Lake Formation...................................................172 Steel Formation...........................................................173 3.5.2. Late Ordovician to Middle Devonian carbonate units..........................................................173 Sapper Formation.......................................................173 Hailstone Formation...................................................174 3.6. Middle Paleozoic Siliciclastic Basin – Earn Group...................................................175 3.6.1 Earn Group............................................................175 Portrait Lake Formation............................................175 ‘Itsi formation’.............................................................176 Prevost Formation......................................................177 3.6.2. Time-equivalent siliciclastic units....................178 Misfortune Formation................................................178 Thor Hills Formation...................................................178

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Hare Indian Formation...............................................179 Canol Formation.........................................................179 Imperial Formation.....................................................180 3.7. Upper Paleozoic Siliciclastic/ Carbonate Shelf - Tsichu Group............................181 Hawthorne Creek Formation....................................181 Heritage Trail Formation...........................................182 Keele Creek Formation...............................................183 Fourway Formation....................................................183 Mount Christie Formation.........................................183 3.8. Late Permian Chert Basin...................................184 Fantasque Formation.................................................184 3.9. Mesozoic Foreland Basin....................................184 Un-named Cretaceous unit........................................184

Chapter 4. Igneous Rocks 4.0. Introduction...........................................................193 4.1. Tsezotene Sills.......................................................193 4.1.1. General geology..................................................193 4.1.2. Geochronology, geochemistry, and paleomagnetism........................................................193 4.1.3. Summary...............................................................196 4.2. Volcaniclastic Diatremes....................................196 4.2.1. General geology..................................................197 4.2.2. Classification........................................................200 4.2.3. Geochronology....................................................200 4.2.4. Correlation...........................................................201 4.2.5. Summary...............................................................201 4.2.6. Economic considerations...................................201 4.3. Cretaceous Intrusions.........................................202 4.3.1. General geology..................................................202 4.3.2. Geochronology and geochemistry..................202 Crystallisation age......................................................202 Inheritance...................................................................204 Geochemistry...............................................................204 4.3.3. Summary...............................................................205 Petrogenesis of the intrusions..................................205 Economic considerations...........................................207

Chapter 5. Structural Geology of the Central Mackenzie Mountains 5.0. Introduction...........................................................215 5.1. Regional Setting - Northern Cordillera..........215 5.1.1. Pre-Mesozoic tectonism....................................215 5.1.2. Mesozoic-Tertiary structures............................217 Inner foreland belt......................................................217 Outer foreland belt.....................................................217 Outer foreland belt (frontal zone)...........................219 5.1.3. Geophysical constraints.....................................219 5.2. Structure of Central Mackenzie Mountains..220 5.2.1. Previous work......................................................220 5.2.2. Present work.......................................................222

Table of contents 5.2.3. Pre-Mesozoic tectonism....................................222 Introduction.................................................................222 Listric and transfer faults in the Mackenzie Mountains supergroup.............................................222 5.2.4. Outer foreland belt - structural domains.......223 Fold domain.................................................................223 Ten Stone Range structural complex.......................227 Ramp-flat domain.......................................................236 Fold-fault domain.......................................................242 5.2.5. Inner foreland belt.............................................248 5.2.6. Age of deformation............................................248 5.2.7. Structural synthesis............................................249 Regional setting..........................................................249 Structural domains and levels of detachment........249 Plateau fault detachment - sedimentary versus structural ramps........................................................249

Chapter 6. Metamorphism and Thermal Maturity 6.0. Introduction...........................................................251 6.1. Thermal Maturity..................................................251 6.2 Regional Metamorphism......................................254

Chapter 7. Mineral Deposits and Prospects 7.0. Introduction...........................................................255 7.1. Exploration History of Significant Mineral Deposits of the Northwest Territories Cordillera...................................................................255 7.1.1. Coates Lake..........................................................255 7.1.2. Jay..........................................................................255 7.1.3. Gayna River..........................................................258 7.1.4. Bear-Twit...............................................................258 7.1.5. Howard's Pass......................................................258 7.1.6. Crest......................................................................258 7.1.7. Mactung................................................................259 7.1.8. Lened.....................................................................259 7.2. Mineral Deposit Types in the Sekwi Project Area.............................................................................259 7.2.1. Intrusion-related tungsten-skarn....................259 7.2.2. Carbonate-hosted Zn-Pb (± Ag, Cu, Ba) and carbonate-hosted Cu (± Ag, Zn)............................260 Carbonate-hosted Zn (± Pb)......................................260 Carbonate-hosted Cu (±Ag, Zn) ...............................264 7.2.3. Kupferschiefer-type Cu (+Ag)...........................264 7.2.4. Other mineral prospects...................................265 Coal...............................................................................265 Barite............................................................................266 Siltstone-hosted Zn.....................................................266 Intrusion-related Au and other mineralisation.......266 7.3. New Mineral Occurrences..................................267

Chapter 8. Hydrocarbons 8.0. Introduction...........................................................269 8.1. Source Rocks..........................................................269 8.2. Reservoir Rocks....................................................269 8.3. Seals.........................................................................269 8.4. Hydrocarbon Shows.............................................269 8.5. Play Types...............................................................270

Chapter 9. Highlights and Recommendations 9.1. Highlights of Sekwi Project...............................271 9.2. Future Work...........................................................271 9.3. Knowledge Gaps and Outstanding Questions...271

References. .............................................................274 Appendices. ............................................................295 Appendix A: Stratigraphic sections through Paleozoic strata and Little Dal Group..................295 Appendix B: Detailed stratigraphic sections through the Tsezotene Formation, Katherine Group, and Cretaceous unnamed unit.................324 Appendix C: Detailed stratigraphic sections through the Little Dal and Coates Lake groups.... 355 Appendix D: Detailed stratigraphic sections through the Sekwi Formation...............................364 Appendix E: Petrographic analyses on coal-bearing strata of Cretaceous age preserved in central NTS 105P......................................................396 Appendix F: Paleontological data for the Sekwi Project............................................................398 Appendix G: Rock-Eval pyrolysis and total organic carbon data.................................................407 Appendix H: Mineral showings in the Sekwi project area...............................................................413

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Preface This report describes the tectonic evolution, stratigraphy, structure, and igneous history of part of the Mackenzie Mountains in the northern Canadian Cordillera, Northwest Territories. The project focussed on the Sekwi Mountain, Mount Eduni, and northwestern Wrigley Lake map-areas, which are covered by Canada’s National Topographic System (NTS) map sheets 105P, 106A and northwestern 95M, respectively. Mineral showings are described in the context of their regional geological settings. The data-set provides a geological framework that is critical to the search for and assessment of mineral deposits and petroleum potential, as well as other geological studies in the area. This volume is complemented by eight appendices, which include measured sections (Appendices A, B, C and D), total organic carbon and Rock-Eval data (Appendix E and G), macrofossil and microfossil identifications, and palynological data (Appendix F), new assay results, and descriptions of new and previously known mineral showings (Appendix H). Nine bedrock geology maps at 1:100,000 scale and 3 cross-sections were generated along with this volume and are published separately as NWT Open Files 2010-09 to 19. The bedrock geology maps have also been compiled at 1:250,000 scale and published as GSC Open Files 6592 and 6594. 7

Summary Late Proterozoic to Cretaceous, mostly unmetamorphosed sedimentary rocks underlie most of the Sekwi Mountain (NTS 105P), Mount Eduni (NTS 106A), and northwestern Wrigley Lake (NTS 95M) mapareas. The stratigraphic succession has been divided into nine assemblages, which correspond to episodes of distinct depositional environments and/or tectonic regimes. Volcanism was a minor component in the Late Proterozoic and Ordovician, and in mid-Cretaceous time, small subalkaline plutons intruded along the axis of the orogen. The nine assemblages include: • Early Neoproterozoic epicratonic basin; • Middle Neoproterozoic volcanic succession; • Middle to Late Neoproterozoic extension and rift-related successions; • Lower to Middle Paleozoic Mackenzie Platform; • Lower to Middle Paleozoic Selwyn Basin and Misty Creek Embayment; • Middle Paleozoic siliciclastic basin; • Upper Paleozoic siliciclastic/carbonate shelf; • Late Permian chert basin, and; • Mesozoic foreland basin. 8

Chapter One

Chapter One Introduction Citation: Martel, E., 2011. Chapter 1. Introduction; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 9 to 17.

1.0. Introduction The Sekwi Mountain mapping project (referred to throughout this volume as the Sekwi project) study area is in the western Northwest Territories of Canada, in the Mackenzie Mountains. The project addressed the Sekwi Mountain map-area (NTS 105P) between latitudes 63°and 64°N and longitudes 128 ° and 130°W; the Mount Eduni map-area (NTS 106A) between latitudes 64° and 65°N and longitudes 128° and 130°W; and the northwestern part of the Wrigley Lake map-area (NTS 95M) between latitudes 63° and 64°N and longitudes 126° and 128°W (Fig. 1-1). The study area is in the Mackenzie and Selwyn mountains (Fig. 1-2), and includes well-exposed sedimentary, plutonic, and minor volcanic rocks of Proterozoic, Paleozoic, and Cretaceous ages. The stratigraphy, structural evolution, and metallogenic setting of this part of the Canadian Cordillera have been poorly documented until now. The previous lack of geoscience data reflects the logistical and budgetary challenges historically encountered by those working in the Mackenzie Mountains from the Northwest Territories’ side of the drainage divide. This report describes the existing stratigraphic nomenclature, provides stratigraphic correlations across three NTS map-areas, and presents an improved understanding of the

Figure 1-1. Physiographic relief map of the Northwest Territories, Canada, showing the location of the Sekwi Mountain project study area (outlined in red). Communities in the Sahtu Land Claim settlement area (black outline) and elsewhere are shown by red stars. Seasonal and permanent road access through the Northwest Territories is shown.

sedimentary, structural, and tectonic development of a part of the Cordilleran orogen exposed in the central Mackenzie Mountains. The four-year, multidisciplinary Sekwi Project was initiated by the Northwest Territories Geoscience Office (NTGO) in collaboration with the Geological Survey of Canada (GSC). Mapping and thematic studies were carried out from 2005 to 2008. In 2004, prior to the field campaign, the NTGO conducted a regional stream sediment and water sampling program, using the National Geochemical Reconnaissance protocols of the Geological Survey of Canada, in the Sekwi Mountain map sheet (105P) and the Northwest Territories part of the Niddery Lake map sheet (105O). This survey was followed in 2005 and 2006 by two airborne magnetic and radiometric surveys that covered a northeast-trending swath across NTS 105P and parts of 105O and 106A (Carson et al., 2006a-f; NTGO, 2006).

1.1. Location and Access The Sekwi Mountain, Mount Eduni and Wrigley Lake mapareas are located in the Northwest Territories between 100 and 300 km southwest of Norman Wells. Only the southwestern corner of the Sekwi Mountain map-area is in the Yukon Territory (Fig. 1-1). There

Figure 1-2. Physiographic subdivisions of the study area and adjacent parts of the northern Canadian Cordillera, Northwest Territories. Communities in the Sahtu Land Claim settlement area (black outline) and elsewhere are shown by red stars.

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Chapter One is no road access to the study area from the Northwest Territories. Aircraft can be chartered from the communities of Norman Wells and Wrigley. Road access from Yukon Territory (Yukon) is provided by a summer-only road (Canol Road) that extends from Ross River to Macmillan Pass (which is on the watershed divide and the Yukon-Northwest Territories border). This was the service road for a wartime-era pipeline project and receives episodic maintenance (Canol Road - North), from Macmillan Pass to Mile 222. In the Northwest Territories, the road is passable during dry weather. Allterrain vehicles drive from Mile 222 north towards Norman Wells along the Canol Heritage Trail (Fig. 1-1) but the many river crossings, swamps and eroded parts of the trail limit motorised travel. Unsurfaced airstrips (Fig. 1-3) in the area are of variable quality. Some are maintained by outfitting and mineral exploration companies for private use. Airstrips at Mile 222, McClure Lake, Shale (Palmer) Lake, and Willow Handle (Mountain) Lake are short. Longer airstrips are present at Godlin Lakes, on the Keele River (Shell airstrip), and on the Stone Knife River (Welcome airstrip). Float-equipped aircraft can land on Godlin Lakes, McClure Lake, Shale (Palmer) Lake, Willow Handle Lake, Cache Lake, and Boomerang Lake. For most of the study area, the only viable access is by helicopter. During this project the town of Norman Wells (Fig. 1-1) provided food and field supplies, and helicopter and aircraft were chartered there.

the project area (~170 km from the headwaters), where base level is 775 metres, en route to the Mackenzie River valley at about 70 metres above sea-level.

1.2. Physiography

An index map (Fig. 1-4) shows references to previous regional geological mapping in and adjacent to the study area. Early investigations of the Mackenzie Mountains by the GSC were restricted to river routes (Keele, 1910) and to the Canol pipeline service road. Later, helicopter-supported, bedrock reconnaissance mapping (Operation Selwyn of the GSC, 1963-1967) culminated in 1:250 000 scale maps of the Wrigley Lake map-area (NTS 95M; Gabrielse et al., 1973a, b, c) and the Sekwi Mountain maparea (NTS 105P; Blusson 1972). To the north and northeast of NTS 105P, GSC Operation Norman (1969-1970) resulted in

The study area encompasses parts of the Selwyn Mountains and the Mackenzie Mountains (Fig. 1-2). The central and northeastern parts of the study area (NTS 106A, 95M, and northeastern 105P) are characterised by resistant, folded carbonate and siliciclastic strata that form sharp ridges (up to 2300 metres in elevation) and rugged topography (Fig. 1-3). The Redstone Plateau is at an average elevation of 1700 metres (Fig. 1-3). The southwestern part of the Sekwi Mountain map-area (NTS 105P) is in the Selwyn Mountains, and is less rugged; it consists of a high plateau (~1300 metres) with isolated hills (average altitude 1700 metres) and is underlain by recessive siliciclastic strata that weather into rubble-covered ridges and slopes. The highest peaks (over 2400 metres) consist of granitic rocks surrounded by hornfelsed strata. In such areas, permanent ice fields and steep cirques are present.

1.2.1. Drainage The study area is drained by five main river systems that generally flow northeast, perpendicular to the topographic grain of the mountain ranges (Fig. 1-3). These rivers are, from south to north, the Natla, Keele (including its northern tributaries, the Ekwi and Godlin), Twitya, Mountain and (Stone Knife) rivers. The headwaters of these rivers are at the Northwest Territories border with Yukon; the southwestern corner of NTS 105P extends across the divide into the South Macmillan drainage. Many of the headwaters areas are open highlands around 1500 metres elevation. The tributaries flow in flat-floored valleys among peaks that are between 1775 and 1975 metres high, with highest points between 2225 and 2500 metres. Rock units that are resistant to erosion (particularly the Cambrian sandstone and Ordovician dolostone) form northwest-trending ridge systems that are cut through by the rivers. Rapids and valley scarps are few, indicating that river downcutting has kept pace with tectonic uplift. The valleys open out where the rivers exit the mountains in the northeastern part of

1.2.2. Climate The Mackenzie Mountains have a dry, continental climate. Snow cover is reduced to north-facing cirques by early July. Weather during July and August is generally good. Field work can usually continue into early September, at which time snow, fog, and cold can become a hindrance. Summers vary between those characterised by week-long intervals of cool, wet weather, often in succession, and those under long-lived (several weeks) high-pressure cells, with sunny, clear mornings, becoming cloudy by noon and with rain showers in late afternoon or evening. Weather fronts bringing low cloud and rain can occur anytime, and typically come from the southwest. In 2006 (60-day field season) two full days were lost owing to poor flying conditions; in 2007 (60-day field season) four full days were lost; and in 2008 (30-day field season) eight full days were lost. Daytime temperatures reach the low 20s (°C), and nighttime temperatures only begin dipping below 0°C towards the end of August. Precipitation is generally moderate, with rain showers typically in the afternoon.

1.3. Previous Geological Work

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Cecile 2000 GSC Bulletin 553

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Gordey and Irwin, 1987 GSC Map 19-1987

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Figure 1-4. Index map showing coverage of previous regional geological maps. Yukon-Northwest Territories border is shown in white.

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Chapter One

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Regional Geology

Mesozoic Foreland Basin Cretaceous Intrusions Upper Paleozoic Siliciclastic/ Carbonate Shelf Upper Paleozoic Siliciclastic Basin Lower Paleozoic Selwyn Basin Lower Paleozoic Mackenzie Platform Neoproterozoic Extension and Rift-related Sucessions (Windermere Supergroup) Proterozoic Epicratonic Basin (Mackenzie Mountains supergroup) Fault NWT - Yukon border

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Figure 1-6. Outlines of areas where detailed mapping, supported by foot traverses and helicopter spot-landings, was undertaken during the 2006 to 2008 field seasons of the Sekwi Mountain project.

1:250 000 scale maps for Carcajou Canyon map-area (NTS 96D; Aitken and Cook, 1974a) and Mount Eduni and Bonnet Plume map-areas (NTS 106A and B; Aitken and Cook, 1974b; Blusson, 1974). Geological maps at 1:250 000 scale for the Upper Ramparts River (NTS 106G) and Sans Sault Rapids (NTS 106H) map-areas were produced by Aitken et al. (1979a, b). Cecile (1984a, b; 1986a, b), and Cecile and Abbott (1992) completed re-mapping of the Niddery Lake map-area (105O); coloured GSC Open-File maps at 1: 50 000 scale are available for the northeastern quadrants. Abbott’s (1983) investigations into the setting of lead-zinc deposits at Macmillan Pass involved 1:50 000-scale mapping and structural and stratigraphic studies, and included the southwestern corner of the Sekwi Mountain (105P) map-area. Colpron and Jefferson (1998), Colpron and Augereau (1998), and Jefferson and Colpron (1998) produced 1:50 000 maps for southeastern Wrigley Lake (95M/2) and northeastern Glacier Lake (95M/10, 15) map-areas. Gordey and Anderson (1993) revised the 1:250 000-scale map of Little Nahanni map-area (105I) and published an accompanying memoir. The stratigraphic nomenclature for Paleozoic units used in Gordey and Anderson (1993) has been adopted wherever possible in the present report. Detailed stratigraphic work has been conducted and numerous stratigraphic sections have been measured in the study area and surroundings (references throughout Chapter 3). Structural cross-sections and interpretations of the south and central Mackenzie Mountains have been published by Cecile and Cook (1981) and Gordey (1981). During the 1970s, the mineral exploration industry was active in this region, exploring for copper, lead, zinc, tungsten,

0

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40 Kilometres

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!

Figure 1-7. Locations of stations that provided ground control for geological maps.

and diamonds (see Chapter 7.1 for details). Activity resumed recently, during the field component of the Sekwi project, when exploration was concentrated on zinc, copper, and emeralds. The NTGO houses an archive of historic and recent assessment reports, which are submitted by exploration companies for assessment credit pursuant to federal regulations, and which contain the results of exploration programs. These reports are available for download on NTGO’s Gateway website at http:// www.nwtgeoscience.ca/. These reports and other sources have been mined for information on mineral showings in the Northwest Territories, and this collected information is stored in the online, queryable NORMIN Showings database at the same address. Appendix H includes locations and descriptions of known showings in the Sekwi project area. Assay results for new mineral showings discovered during mapping are provided in Table 7.3-1.

1.4. Current Geological Work The primary objective of the Sekwi Project was to provide updated geological maps of the central Mackenzie Mountains, Northwest Territories. Figure 1-5 provides a simplified, updated geology of the Sekwi project area. The project also aimed to improve the knowledge of the structural, stratigraphic, metallogenic and tectonic setting of this poorly documented area. The region was also assessed for its mineral and hydrocarbon potential. This report draws from four field seasons (2005-2008). Framework mapping started in 2006. Strategic areas were selected for mapping at 1:50 000-scale (Fig. 1-6), and a structurally complex area was mapped at 1:25 000-scale by a

13

Chapter One 130°0'0"W

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Figure 1-8. Location of samples collected in 2006, 2007 and 2008. See Appendices for results.

M.Sc. student (see Chapter 5). The mapping was accomplished using a contract helicopter from fixed base camps to support an eight- to 12-person field crew. Numerous four- to eight-day fly camps were located in isolated areas. Figure 1-7 shows the station locations that provided ground control for the geological maps. Stratigraphic sections were measured (Appendices A, B, C, and D) to establish regional variations in thickness and stratigraphic control for paleontological determinations, as well as to provide detailed stratigraphic information for thesis projects. Appendix E provides results of petrographic analyses on coal-bearing strata of Cretaceous age. Fossil determinations and microfossil samples (conodonts) provided control on age and correlation (Appendix F). Samples were collected for Total Organic Carbon and/or thermal maturity (Rock Eval; Appendix G) and samples were collected for palynological analysis (Appendix F). Numerous samples were collected for assay (Appendix H). Selected samples were collected for geochronological analysis (see Chapter 4). Over 500 representative samples were collected and are archived at the Northwest Territories Geoscience Office. Figure 1-8 shows the location of all samples collected for the various analyses. All paleontological and chronostratigraphic age determinations are cited in the text of this volume as they were provided in the respective original published papers and reports; no effort has been made to accommodate amendments that have been made to the geological time scale in the time since the age determinations were made.

14

1.4.1. First field season (2005) Geophysical, stream-sediment and water geochemical surveys, and reconnaissance mapping were undertaken in 2005. The geophysical survey covered a 20 km-wide, northeast-trending transect across NTS 105P (Fig. 1-9). Magnetic and radiometric maps were published (NTGO, 2006; Carson et al., 2006a-f). Regional stream-sediment and water sampling program was undertaken in NTS 105P and the Northwest Territories part of NTS 105O (Day et al., 2005). Visits to previously known Pb-Zn mineral occurrences and reconnaissance mapping were conducted for ten days each (Martel et al., 2005; Dewing et al., 2006)

1.4.2. Second field season (2006) Two months of framework mapping in the Sekwi Mountain map-area (NTS 105P) and parts of map-areas adjacent to its northeastern corner (NTS 96D, 95M and 106A) were undertaken. Four areas were selected for 1:50 000-scale mapping: Caribou Pass, Godlin Lakes, the Ramp and the Four Corners map-areas (Fig. 1-6). Mapping along the Plateau fault in the southern part of NTS 95M, and thematic studies in NTS 105P, were carried out by GSC and NTGO researchers, as well as by university-based colleagues. These studies include: • Stratigraphy of the Little Dal Group and basal Mackenzie Mountains supergroup; Elizabeth Turner, Laurentian University • Stratigraphy of the Katherine Group; Darrel Long, Laurentian University

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1.4.3. Third field season (2007) Two months of mapping in NTS 106A along a northeasttrending transect across, and partly along, the Plateau fault (Fig. 1-6) was completed. Thematic studies and M.Sc. thesis research initiated in 2006 continued. Additional studies include the stratigraphy of the Cretaceous siliciclastic rock preserved in NTS 105P by Darrel Long and Steve Gordey, and interpretations of listric and transfer faults as a solution to unusual facies and thickness distributions in the Mackenzie Mountains supergroup by Darrel Long and Elizabeth Turner (Turner and Long, 2008). A regional stream sediment and water geochemistry program was undertaken in NTS 106B, and the Northwest Territories part of NTS 106C (Falck and Day, 2008). A B.Sc. thesis was initiated during the 2007 field season: • Mineralogical investigation of a new green beryl occurrence on Mount Eduni map sheet (NTS 106A); Mélanie Mercier under supervision of André Lalonde, University of Ottawa.

1.4.4. Fourth field season (2008)

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Figure 1-9. Footprint of magnetic and radiometric surveys (NTGO, 2006; Carson et al., 2006a-f). Coloured grid is the ratio of equivalent U concentration to equivalent Th concentration. High values are magenta to red, lowering through yellow and green to blue and dark blue, representing a range of values from about 1.2 to 0.001.

• Field checks of geophysical anomalies; Ken Ford, GSC; • Stratigraphy of Ordovician and Silurian carbonate rocks; Michael Pope, Washington State University; • Stratigraphy and hydrocarbon potential of the Devonian siliciclastic succession (Hare Indian, Canol and Imperial formations); Willem Zantvoort, NTGO; • Assay sampling of lower Paleozoic deep-water strata and mineral occurrences identified during regional mapping; Luke Ootes, NTGO; • Structural study of the Plateau fault and hydrocarbon potential of underlying rocks; Karen Fallas and Robert MacNaughton, GSC; and • Stratigraphic studies of the Windermere Supergroup; Robert MacNaughton, GSC. Three MSc theses were initiated: • Investigation of the structural, stratigraphic and lithological controls on Zn-Pb mineralisation in the Sekwi Formation; Beth Fischer under supervision of Elizabeth Turner, Laurentian University. • Inferences of the isotopic character of crystalline basement beneath the Mackenzie Mountains (Nahanni Terrane) to establish a geochemical and geochronological framework for the mafic volcanic rocks of the Marmot Formation; Christopher Leslie under the supervision of Jim Mortensen, University of British Columbia. • Deformation in the footwall of the Plateau fault and structural evolution of associated splays in the Mount Eduni NTS sheet (106A); Justin MacDonald under supervision of Shoufa Lin, University of Waterloo.

One month of mapping was undertaken to fill in gaps and revisit problematic areas, and to complete thematic studies in NTS 105P, 106A and 95M. Gaps in the current published maps of NTS 106A [differences between Blusson (1972) and Aitken and Cook (1974b)] were addressed through 1:50 000-scale mapping. Further mapping along the Plateau fault in the southwestern corner of NTS 106A was completed. Several stratigraphic sections were measured to document in detail the entire stratigraphy of the study area and to establish regional variations in thickness. Regional stream sediment and water geochemistry programs were undertaken by the NTGO in collaboration with the GSC in NTS 106A and parts of 106F, G and H. Figure 1-10 shows the locations of these surveys.

1.4.5. Progress reports and accompanying publications Reports of progress and preliminary maps published after each field season include: (1) a provisional map of the Sekwi Mountain map sheet (NTS 105P) at 1:250 000 scale with detailed areas at 1:125 000 scale, accompanied by a report with lithological descriptions and regional correlations (Roots and Martel, 2008); and (2) a provisional map at 1:100 000 scale of the Mount Eduni map sheet (NTS 106A) (Gordey et al., 2008). A map of the geology around the Plateau fault in Wrigley Lake map sheet (NTS 95M) was also published (MacNaughton et al., 2008a). Final publications include nine bedrock geology maps at 1:100,000 scale and 3 crosssections designed to accompany this volume, published separately as NWT Open Files 2010-09 to 19 (see Figure and Table 9-1 for full citations). Geological data generated by the project are available in ESRI shapefile format, published as NWT Open Report 2012-002. Simplified bedrock geology maps are also published at 1:250,000 scale as GSC Open Files 6592 and 6594. Publications of results from thematic studies undertaken concurrently with bedrock mapping include: • Proterozoic-Cambrian lithostratigraphy (MacNaughton et al., 2008b); • Qualitative assessment of the Plateau fault (MacNaughton et al., 2008a); • Assay results (Ootes et al., 2007; Ootes and Martel, 2010); • Metallogeny of northern Cordillera (Ootes and Falck, 2008); • Geology and mineralogy of the Mountain River beryl

15

Fort Chapter One Good Hope

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Stream Sediment Sampling Programs

1

2

Day, S.J.A., Lariviere, J.M., Friske, P.W.B., Gochnauer, K.M., MacFarlane, K.E., McCurdy, M.W., and McNeil, R.J., 2005. National Geochemical Reconnaissance, Regional Stream Sediment and Water Geochemical Data, Macmillan Pass - Sekwi Mountain Northwest Territories (NTS 105O east and 105P); Geological Survey of Canada, Open File 4949 / Northwest Territories Geoscience Office, Contribution 0014. 1 CD-ROM.

3

4

Ozyer, C.A., 2010. Ts' udenilineTu' eyeta (Ramparts River and Wetlands) Candidate Protected Area Phase II Non-renewable Resource Assessment – Minerals, Northwest Territories, Canada; Northwest Territories Geoscience Office, NWT Open File 2010-07, 47 p. and 1 CD. Day, S.J.A., Falck, H., McCurdy, M.W., and McNeil, R.J., 2010. Regional Stream Sediment and Water Geochemical Data, Cranswick River Area, Northwest Territories (parts of NTS 106F and G); Geological Survey of Canada, Open File 6721 / NWT Geoscience Office, NWT Open Report 2010010. 1 CD-ROM.

6

Day, S.J.A., Falck, H., Friske, P.W.B., Pronk, A.G., McCurdy, M.W., McNeil, R.J., Adcock, S.W., and Grenier, A.G., 2009. Regional Stream Sediment and Water Geochemical Data, Mount Eduni area, northern Mackenzie Mountains NT (NTS 106A and part of 106B); Geological Survey of Canada, Open File 6312 / Northwest Territories Geoscience Office, NWT Open Report 2009-004. 1 CD-ROM.

en

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iv tR

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Falck, H. and Day, S.J.A., 2008. Preliminary Regional Stream Sediment and Water Geochemical Data, Backbone Ranges area, west-central Northwest Territories (parts of NTS 106B and C); Northwest Territories Geoscience Office, NWT Open Report 2008013, 12 p. McCurdy, M.W., McNeil, R.J., Friske, P.W.B., Day, S.J.A, and Wilson, R.S., 2007. Stream Sediment Geochemistry in the Proposed Extension to the Nahanni Park Reserve, in Mineral and Energy Resource Potential of the Proposed Expansion to the Nahanni National Park Reserve, North Cordillera, Northwest Territories, (ed.) D.F. Wright, D. Lemkow, and J. Harris; Geological Survey of Canada, Open File 5344, p. 75-98.

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McCurdy, M.W., Day, S.J.A., Friske, P.W.B., McNeil, R.J., and Hornbrook, E.H.W., 2009. Regional Stream Sediment and Water Geochemical Data, Frances Lake area, southeastern Yukon (NTS 105H); Geological Survey of Canada, Open File 6043 / Yukon Geological Survey Open File 2009-1. 1 CDROM.

8

McCurdy, M.W., Friske, P.W.B., McNeil, R.J., Day, S.J.A., and Goodfellow, W.D., 2009. Regional Stream Sediment and Water Geochemical Data, eastern Yukon and western Northwest Territories (NTS 105I); Geological Survey of Canada, Open File 6271 / Yukon Geological Survey Open File 2009-26. 1 CD-ROM.

9

Ozyer, C., 2012. Shúhtagot’ine Néné Candidate Protected Area,Phase II Nonrenewable Resource Assessment – Minerals, Northwest Territories, Canada; Northwest Territories Geoscience Office, NWT Open File 2012-01. (includes increased sample density over approx. footprints of 1 and 6)

Figure 1-10. Map showing footprints and citations for the regional stream sediment and water geochemistry surveys in the Mackenzie Mountains undertaken by the NTGO in collaboration with the GSC.

16

Chapter One occurrence (Mercier et al., 2008); • Syndepositional fault activity during deposition of the Neoproterozoic Mackenzie Mountains supergroup (Turner and Long, 2008); • An educational brochure of the geology along the Canol Heritage Trail (Roots et al., 2008); • Application of gamma-ray spectrometry data for lithological mapping in the Cordillera (Harris et al., 2008); • Field, petrological and geochemical study of the 780 Ma Tsezotene sills (Ootes et al., 2008); • Results regional stream sediment and water geochemistry (see Fig. 1-10 for complete citations); • Source and reservoir potential of the Devonian Hare Indian, Canol and Imperial formations (MacNaughton et al., 2008a); • Stratigraphy and isotope geochemistry of the Gypsum formation, Little Dal Group (Turner, 2009); • Early Neoproterozoic origin of metazoans in the Little Dal Group (Neuweiler et al., 2009); • Geochemical, geochronological, isotopic, and apatite study of Cretaceous magmatism (Rasmussen, 2009). Five graduate and undergraduate theses were supported through the Sekwi project. Each thesis has been (or will be) available through its host university. • Mid-Cretaceous magmatism; Ph.D. Kirsten Rasmussen, University of British Columbia; • Diatremes and related volcanic rocks of the Marmot Formation; M.Sc. Christopher Leslie, University of British Columbia (Leslie, 2009); • Controls on Zn-Pb mineralisation in the Sekwi Formation; M.Sc. Beth Fischer, Laurentian University; • Deformation in the footwall of the Plateau fault; M.Sc. Justin MacDonald, University of Waterloo (MacDonald, 2009); • Mineralogy of the Mountain River beryl occurrence; B.Sc. Mélanie Mercier, University of Ottawa (Mercier, 2008).

1.4.6. Coordinate systems used in this volume Spatial coordinates in this volume are presented as either latitude and longitude, or easting and northing. The latter are for a Universal Transverse Mercator (UTM) projection in zone 9 using North American Datum 1983 (NAD83).

1.5. Acknowledgements Assistance in the field was provided by Beth Fischer, Christopher Leslie, Justin MacDonald, Andrew Parmenter, and Kirsten Rasmussen (2006); by Beth Fischer, Christopher Leslie, Justin MacDonald, Mélanie Mercier, Ryan Pippy, Danielle Thomson, Christopher Carver and Robert Morden (2007); and

by Beth Fischer, Ben Borkovic, Danielle Thomson, and Peter van Walraven (2008). We thank NTGO researchers (Hendrik Falck, John Ketchum, Yvon Lemieux, Hamish Sandeman, and Willem Zantvoort), GSC and GSC emeritus researchers (Mike Cecile, Don Cook, Ken Ford, Dave Morrow, and Andy Okulitch) and university professors (Mario Coniglio, Andre Lalonde, Shoufa Lin, and Jim Mortensen) for their time in the field and/or for sharing their expertise. Discussions with these individuals have clarified many aspects of the stratigraphy, structure, intrusive and tectonic history, and economic potential of the Mackenzie Mountains. Many of the authors contributed insights and improvements to each others’ sections. Accommodation and excellent food was provided by Ramhead Outfitters and Phelps Dodge Ltd. in 2006; by Mackenzie Mountain Outfitters and Gana River Outfitters in 2007; and by Ramhead Outfitters, Mackenzie Mountain Outfitters and Gana River Outfitters in 2008. Aircraft were chartered from North Wright Airways (2006-08) and Ursus Aviation (2005 and 2008). Helicopter support was provided for the duration of each field season by Sahtu Helicopters (2006) and Canadian Helicopters (2007 and 2008). The enthusiastic co-operation and logistical help provided by Eagle Plains Resources Ltd., Phelps Dodge Ltd. (now Freeport McMoRan Copper and Gold, Inc.), and Aurora Geosciences Ltd. are gratefully acknowledged. Kelly Pierce and Kyle Rentmeister provided GIS expertise. The primary funding for the Sekwi project was provided by the Strategic Investments in Northern Development program of Indian Affairs and Northern Development, Canada (INAC) and administered by the Department of Industry, Tourism and Investment (ITI), Government of the Northwest Territories. ITI and INAC also provided some funding and in-kind support through their regular programming. Support for GSC personnel involved in the project was provided by the GSC’s Mackenzie Corridor Assessment Secure Energy Supply Project and their Northern Mineral Resources Development Program. Additional support for thesis projects was provided by NSERC grants to E.C. Turner, J. Mortensen, and S. Lin, by University of Ottawa funding to A. Lalonde, by an INAC Northern Scientific Training Program grant to B. Fischer, and by INAC/NTGO funds to C. Leslie. Additional funding was provided by the federal Polar Continental Shelf Program (Natural Resources Canada). All authors sincerely appreciate the critical reviews of Tammy Allen, Mike Cecile, Keith Dewing, Jim Dixon, Craig Hart, Federico Krause, Yvon Lemieux, Dave Lenz, Bernie Maclean, Dan Marshall, Andrew Okulitch, Lee Pigage, Leanne Pyle, Derek Thorkelson, Hamish Sandeman, Robert Sharp, and especially Thomas Hadlari who reviewed the entire volume. Tiffany Chevrier is gratefully acknowledged for her contribution to the technical redaction of the volume. Dave Watson and Erin Palmer provided useful advices on formatting.

17

Chapter Two

Chapter Two Regional Setting Citation: Gordey S.P. and Roots, C.F., 2011. Chapter 2. Regional Setting; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 18 to 30.

2.0. Introduction Sedimentary and intrusive rocks in the central Mackenzie Mountains span the history of the northwestern Laurentian margin (ancestral North America; present coordinates) from about 1.0 Ga (Neoproterozoic) to ~80 Ma (Cretaceous), and are well exposed by the rugged, mountainous terrain of the Cordilleran foreland fold and thrust belt. Because of the area’s low metamorphic grade, stratigraphic relationships, depositional fabrics, and fossils are well preserved. In chronological order, highlights of the protracted geological history of the area include: (a) an epicratonic basin containing fartravelled, late Proterozoic fluvial deposits related to the Grenville orogeny, succeeded by a partly segmented carbonate basin; (b) the Cryogenian breakup of the supercontinent Rodinia and establishment of an expansive Paleozoic siliciclastic-carbonate passive margin; (c) far-field effects of orogeny and extension of the Laurentian margin beginning in the Middle Devonian; (d) reestablishment of passive margin sedimentation in the Carboniferous; and (e) accretion of western terranes in the Jurassic-Cretaceous, resulting in Cretaceous plutonism, sedimentation and development of the Cordilleran foreland fold and thrust belt. The following discussion provides a Cordillera-wide context for later descriptions of stratigraphy, igneous rocks, structure, metamorphism, and hydrocarbon and mineral resources. Figure 2-1 provides a schematic stratigraphic column and summary of tectonic assemblages for the Sekwi project area. Lithologies of rock units are summarised in Table 2-1. Figure 2-2 and 2-3 show the geographic distribution and stratigraphic relationships of units in NTS 105P and 106A. Figures 2-4 to 2-8 depict regional assemblages and structures for selected time intervals and Figures 2-9 and 2-10 outline the main structural divisions of the Cordilleran foreland belt.

2.1. Depositional and Intrusive Framework 2.1.1. Proterozoic Older Proterozoic strata in the Canadian Cordillera form discrete successions that are generally separated by large hiatuses and exposed in geographically isolated areas (Fig. 2-1). Young et al. (1979) subdivided the Proterozoic succession of northern Canada into three broadly correlative, unconformity-bounded “sequences”: sequence A (Wernecke Supergroup and equivalent); sequence B (Mackenzie Mountains supergroup and equivalents; includes Pinguicula Group); and sequence C (Windermere Supergroup). The scheme was widely applied in subsequent literature (e.g., Rainbird et al., 1996a), and MacLean and Cook (2004) correlated seismic subsurface and surface regional information to refine sequence A into four unconformity-bounded successions (A1-A4). Dating and redefinition of the Pinguicula Group in Yukon (Thorkelson et al., 2005; Medig et al., 2010; Turner, 2010) led to recognition of its lower half as a separate succession from the upper half. In the 1980s, Eisbacher (1985) and Bell and Jefferson (1987)

18

used sub-continent-scale correlation of Late Proterozoic successions to propose a global plate-tectonic reconstruction. Their ideas on the Neoproterozoic proximity of the western Laurentian margin to eastern Australia (the SWEAT hypothesis) remain influential (e.g., Li et al., 2008).

Paleo- and Mesoproterozoic The oldest stratigraphic succession in the Cordillera, the Wernecke Supergroup (sequence A1; Fig. 2-4), contains two siliciclastic-carbonate “grand cycles” deposited after 1.6 Ga (Furlanetto et al., 2009). Distant, correlative strata may include the Muskwa assemblage of British Columbia (e.g., Ross et al., 2001). The accumulation of these thick successions has been related to Paleoproterozoic continental breakup and subsidence that formed a crustal ramp with dramatically thinned continental crust to the west and south (Cook et al., 1991; Cook and Erdmer, 2005). In the Yukon, after an interval of polyphase deformation, differential uplift and erosion (Racklan orogeny; Thorkelson et al., 2005), a succession dominated by mudstone and mud-grade carbonate [A3; lower Pinguicula Group and correlatives (Fig. 2-4), 1003 Ma; Medig et al., 2010] covered a broad area under extension. In the subsurface of the Northwest Territories, beneath a putatively correlative orogenic-related unconformity (Forward orogeny), MacLean and Cook (2004) recognised strata that are not preserved in Yukon sections, including basinal shale and platform carbonate (A2) that are correlated with the Hornby Bay Group. The Coppermine basalt (A4) correlates with the Bear River dykes in Yukon, which are part of the Mackenzie dyke swarm (Thorkelson et al., 2005). None of these rocks is exposed at surface in the Sekwi project area. The thick Belt-Purcell Supergroup of the southern Canadian Cordillera (~1.47-1.37 Ga) has no known counterpart in the Sekwi project area.

Early Neoproterozoic The Mackenzie Mountains supergroup (sequence B, Figs. 2-1 and 2-4; 0.78 Ga), the oldest strata in the Sekwi project area, accumulated in a large, epicratonic basin (Rainbird et al., 1996; Long et al., 2008; Turner and Long, 2008). The oldest exposed unit (informal “H1 unit”) appears to have been a carbonate ramp. Overlying clastic strata reflect a shallowing muddy shelf (Tsezotene Formation) overlain by fluvial, deltaic and shallowmarine settings (Katherine Group). Sediment was in part supplied by an extensive Neoproterozoic river system draining the Grenville orogen (Rainbird, 1992; Rainbird et al., 1997) from which detrital zircons in the Katherine Group (Fig. 2-1) indicate a maximum depositional age of 1005 Ma (Leslie, 2009). Uppermost strata (Little Dal Group) are carbonate-dominated. Much of the lower Little Dal Group was deposited in basinal (northwest) and shallow-water (southeast) settings with giant microbial reefs in the former (Aitken, 1989b; Turner et al., 1997, 2000a). The upper part of the group includes carbonate and siliciclastic rocks and a widespread gypsum unit. The gypsum played a key role as a regional detachment during Mesozoic deformation.

Chapter Two

AGE CRETACEOUS JURASSIC TRIASSIC PERMIAN

UNNAMED CLASTIC ROCKS

SELWYN PLUTONS

FOURWAY FM KEELE CREEK FM HERITAGE TRAIL FM

THOR HILLS FM

EARN GROUP

PREVOST FM

?

?

?

IMPERIAL FM

MISNAHANNI FM FORTUNE HUME FM FM HEADLESS FM

LOWER

GRIZLANDRY FM ZLY BEAR FM HAILARNICA STONE FM BEAR FM ROCK FM SOMBRE FM SAPPER FM CAMSELL FM STEEL FM TSETSO FM

LAKE FM

HAY- SUNBLOOD WIRE FM BROKEN FRANKLIN RABBITSKULL KETTLE MT FM FM FM

HESS RIVER FM

SEKWI FM

VAMPIRE FM

BACKBONE RANGES FM

(unnamed)

RISKY FM

(middle)

BLUEFLOWER FM

(lower)

SHEZAL FM SAYUNEI FM

? LITTLE DAL GP KATHERINE GP

?

TONIAN

?

MACKENZIE MTNS SUPERGROUP

?

COPPERCAP FM REDSTONE R. FM ‘LITTLE THUNDERCLOUD FM DAL BASALT’ ‘UPPER CARBONATE FM’ ‘RUSTY SHALE FM’ ‘GYPSUM FM’ ‘GRAINSTONE FM’ ‘BASINAL ASSEMBLAGE’ ‘MUDCRACKED FM’ UPPER DIVISION MIDDLE DIVISION LOWER DIVISION TSEZOTENE FM

(SEQUENCE C)

HAY CREEK GP

SHEEPBED FM ‘TEPEE DOLOSTONE’ ICEBROOK FM KEELE FM TWITYA FM

COATES LAKE GP

(Sturtian Glaciation)

(upper)

GAMETRAIL FM

RAPITAN GP

CRYOGENIAN

WINDERMERE SUPERGROUP

INGTA FM

(Marinoan Glaciation)

SELWYN BASIN

ROCKSLIDE FM

CAMBRIAN

EDIACARAN

MACKENZIE PLATFORM

MT KINDLEWHITTAKER FMS

DUO

ORDOVICIAN

ed

SILICICLASTIC BASIN

MISCANOL FM FORTUNE HARE FM INDIAN FM

PORTRAIT LAKE FM

fault

HAWTHORNE CREEK FM

MIDDLE

SILURIAN

SILICICLASTIC/ CARBONATE SHELF

EXTENSION AND RIFT-RELATED SUCCESSIONS

VOLCANIC SUCCESSION

(SEQUENCE B)

PALEOZOIC

DEVONIAN

UPPER

MESOZOIC FORELAND BASIN

FANTASQUE FM

'ITSI' FM

NEOPROTEROZOIC

IGNEOUS ROCKS

MT. CHRISTIE

CARBONIFEROUS

?

TECTONIC AFFINITY

FORMATION

TSICHU GROUP

MESOZOIC

Central Mackenzie Mountains 105P, 106A, 95M NW

EPICRATONIC BASIN

Figure 2-1. Schematic stratigraphic column of strata exposed in the Sekwi project area, central Mackenzie Mountains, and tectonic affinity of the main successions.

19

ERA

PERIOD/ EPOCH

Mesozoic

Chapter Two

mid-Cretaceous

GROUP/ SUITE

FORMATION (THICKNESS)

Selwyn

Permian

quartz monzonite and granodiorite

Mount Christie (690 m) Fourway (220+ m) Keele Creek (345 m)

Carboniferous

Tsichu

Heritage Trail (220 m) Hawthorne Creek (330 m)

Upper Devonian to Mississippian Earn

Paleozoic

Upper Devonian Lower to Middle Devonian Silurian to Lower Devonian Silurian Lower Ordovician to Lower Silulrian Upper Cambrian to Lower Ordovician Middle Cambrian Lower Cambrian Ediacaran and Lower Cambrian

LITHOLOGY

‘Itsi’ Prevost

Thor Hills

Portrait Lake

Misfortune

(300 m)

(900 m)

(40-880 m)

Hailstone (190 m)

(340-440 m)

(270 m)

Grizzly Bear (200 m)

shale, siltstone and chert; minor quartz sandstone calcarenite and calcsiltite; minor quartzite or chert interbeds shale, interstratified with crinoidal limestone; chert beds and nodules near top quartz sandstone and pebble conglomerate; interbedded with shale shale; minor sandstone and siltstone, calcareous shale with limestone beds shale, chert granule- to pebblesandstone, chert-arenite, conglomerate; minor siltstone, shale siltstone, shale sandstone and siliceous shale shale, siltstone, chert-arenite, chert-pebble conglomerate, shale, chert, sandstone, minor cherty argillite and minor chert-pebble conglomerate banded chert limestone, minor limey limestone, silty limestone mudstone

Sapper (80-850 m)

limestone, shale, lenses of massive limestone

Steel (100 m)

mudstone

Duo Lake (200 m)

shale, shaly limestone

Rabbitkettle (437-840 m)

limestone, shale, dolostone

Hess River (115-1270 m)

shale; local chert, minor limestone

Sekwi (700 m)

limestone, dolostone, sandstone, minor variegated shale sandstone, siltstone, shale, minor argillaceous sandstone, minor interbedded orthoquartzite, local thick carbonate member upper mbr: quartz sandstone, minor siltstone and shale middle mbr: dolostone, minor quartz sandstone and shale lower mbr: quartz sandstone and siltstone

Vampire (390 m) Backbone Ranges

(700-1800) (150 m) (68-270 m)

NOTE: unit thicknesses shown are approximate and regionally representative; they are not based on data solely within the project area

UNCONFORMITY RELATION UNCERTAIN INTRUSIVE CONTACT EQUIVALENCE

Table 2-1 (a). Stratigraphic units exposed in the southwestern part of the Sekwi project area, central Mackenzie Mountains. Lateral facies relationships are complicated and only partially depicted in this table.

(Table 2.1a and 2.1b layout on facing pages left and right respectively)

20

Chapter Two

ERA Meso -zoic

PERIOD/EPOCH

GROUP

LITHOLOGY shale and sandstone, quartz and chert pebble and cobble conglomerate; coal seams

mid-Cretaceous

unnamed (1300+ m)

Permian

Fantasque (< 55 m)

chert, siliceous shale

Imperial (400-1850 m)

sandstone, siltstone, shale, minor limestone upper mbr: shale, siltstone lower mbr: shale, rare beds of sandstone and chert pebble conglomerate shale, siltstone, minor limestone

Upper Devonian

Canol (23-400 m) Hare Indian (400 m), Tsezotene Formation (~1.5 km), Katherine Group (~1.5 km), and Little Dal Group (~2 km). Collectively, these strata record deposition in an extensional basin that developed on Laurentian continental crust during the early to middle Neoproterozoic (Turner and Long, 2008), at a relatively low paleolatitude (Park and Jefferson, 1991; Evans, 2006). The configuration of the basin beyond its exposure area in the Mackenzie Mountains is uncertain. The exposure area of the MMSG in the Northwest Territories spans about 500 kilometres of strike-length, from NTS 106D (Yukon border) in the northwest to 96L (Northwest Territories) in the southeast, and occupies a prominent, arcuate deviation in the structural grain of the Canadian Cordillera that mimics the inferred margin of the Neoproterozoic basin (Fig. 3.1.1-1; Aitken, 1981). In the Northwest Territories, exposures of the lower three-quarters of the MMSG [“H1 unit”, Tsezotene Formation, Katherine Group and lower Little Dal Group (Mudcracked, Basinal, and Grainstone formations)] are largely limited to the folded zone east of the Plateau fault, which represents the eastern limit of significant MesozoicTertiary thrusting. The upper one-quarter of the MMSG [upper Little Dal Group (Gypsum, Rusty Shale and Upper Carbonate formations)] is predominantly exposed in the immediate hangingwall of the Plateau fault. Northwest and southeast of the MMSG exposure area, rocks of similar age are not exposed. At least part of the MMSG is presumed to be present in the subsurface west of the Plateau fault, as shown on accompanying cross-sections (NWT Open File 2010-18; Fig. 9-1). Parts of both the Katherine and the Little Dal groups are exposed in isolated areas in southeastern NTS 106A (see accompanying maps, NWT Open Files 2010-09 to 17; Fig. 9-1). Several units originally included in the upper part of the Pinguicula Group in Yukon by Eisbacher (1981) are now known to belong to the MMSG (Yukon; Abbott, 1997; Thorkelson, 2000; Thorkelson et al., 1998, 2001, 2005; Turner, 2010). The basal contact and lowermost formations of the MMSG are exposed in the Wernecke Mountains, providing stratigraphic information for the lowermost MMSG that is not available in the Mackenzie Mountains (Turner, 2010). Parts of the Fifteenmile and Tindir groups are also possible correlatives, although firm lithostratigraphic correlations remain elusive. Seismic data indicate that equivalent rocks are present in the subsurface of the interior plains east of the Mackenzie Mountains (Cook and MacLean, 2004). Structural studies by Aitken and Pugh (1984), Cook (1992), and Cook and MacLean (2004) indicate that the supergroup is underlain by several kilometres of older sedimentary rocks that are probably equivalent to Sequence A (~1.7-1.2 Ga), which, in turn, may be underlain by metamorphic and plutonic rocks similar to those exposed to the east in the Thelon - Wopmay belt (Parrish, 1991). This configuration is supported by

31

Chapter Three

˚

˚

Figure 3.1.1-1. Geographic distribution of the major units of the Mackenzie Mountains supergroup, and locations of sections measured in the Mackenzie Mountains supergroup during the Sekwi project. See Appendices B and D for details.

32

Chapter Three

Figure 3.1.1-2. Generalised stratigraphic column for the Mackenzie Mountains supergroup (after Turner and Long, 2008).

33

Chapter Three analysis of zircons in a granitic clast recovered from an Ordovician diatreme near Coates Lake by Jefferson and Parrish (1989), which yielded an inherited age of at least 1.75 Ga. The Shaler Supergroup of Victoria Island and the adjacent mainland is directly correlative to the MMSG (Rainbird et al., 1996a; Long et al., 2008). The Coates Lake Group (Aitken, 1981; Morris and Aitken, 1982; Jefferson 1978a,b, 1983; Jefferson and Ruelle, 1986) was originally included in the MMSG by Young et al. (1979, 1982), but was re-assigned to the Windermere Supergroup by Gabrielse and Campbell (1991), based on its close tectonostratigraphic relationship with overlying strata of the Rapitan Group (Yeo, 1981; Eisbacher, 1985). The maximum depositional age of the Katherine Group is ~1,005 Ma, based on detrital zircons (Rainbird et al., 1996b, 1997; Leslie, 2009). Stromatolite “biostratigraphy” suggested a depositional age of 1350 Ma for the “H1 unit” and 950 Ma for the Upper Carbonate formation of the Little Dal Group (Aitken et al., 1978b). Paleomagnetic data from red mudstone in the Little Dal Basinal assemblage (Park, 1981) suggested a depositional age of 900-950 Ma for that unit. The apparent polar wander pattern for the MMSG post-dates the “Grenville loop”, implying a depositional age of 1.5 km. The principal reference section for the red member (see below) is in the Sekwi project area, on the south face of Mount Eduni (NTS 106A: 64°13’30”N, 128°03’W; Section 019; Appendix B). In NTS 106A and adjacent parts of 96D, the Tsezotene Formation crops out in the core of the Tigonankweine anticline south of Mount Eduni, and in the core of major anticlines in the frontal ranges of the Mackenzie Mountains in the Sans Sault

Rapids (NTS 106H), Mount Eduni (NTS 106A) and Carcajou Canyon (NTS 96D) map-areas (Aitken et al., 1973; Aitken and Cook 1974a, 1974b, 1974d, 1975; Narbonne and Aitken 1995; Fig. 3.1.1-1). Detailed descriptions of the Tsezotene Formation are limited to papers by Gabrielse et al. (1973a) and Aitken et al. (1973). Paleomagnetic studies of the formation were published in Park and Aitken (1986a) and a preliminary sedimentological analysis was made by Long (1991). Rock-Eval data for material from the Tsezotene Formation are provided in Appendix G.

Description Siliciclastic strata of the Tsezotene Formation generally coarsen up-section (Long, 1991; Long et al., 2008; Turner and Long, 2008), and are divided into two informal members (Aitken et al., 1978a; Fig 3.1.1-2). The lower part of the formation (grey member; 5901105 m thick) is characterised by dark grey to greyish-black mudrock (N3 to N2 on the Munsell colour chart), with minor siltstone, very fine sandstone and carbonate rock (Fig. 3.1.2-2). The upper part of the formation (red member; 165-470 m thick) is characterised by varicoloured mudstone and siltstone, with dusky red (5R 3/4), greyish-green (2G 5/2) and dark grey (N3 to N5) colours (Figs. 3.1.2-3 to -7). Minor rock types include abundant thin beds of very fine sandstone and carbonate rock (Fig. 3.1.2-5). The lower part of the red member is locally characterised by an interval of interlayered siliciclastic rocks and stromatolitic limestone of variable thickness and lateral continuity (Figs. 3.1.2-6 and -7), which was first recognised by Aitken and Cook (1974a).

Age and correlation There is no equivalent of the Tsezotene Formation in the Amundsen Basin, Victoria Island, owing to an unconformity between the Mikkelsen Islands Formation (putative equivalent of the “H1 unit”) and the Nelson Head Formation (equivalent of Katherine Group). In the Wernecke Mountains, a shallow-water mudstone – siltstone succession (Tarn Lake Fm.) in the revised Hematite Creek Group (Turner, 2010; formerly unit D of the Pinguicula Group) is probably equivalent to the Tsezotene Formation (Thorkelson, 2000; Long et al., 2008).

Interpretation The Tsezotene Formation is thought to record progradation of a muddy shelf (Long, 1991). Evidence of emergent conditions, including desiccation cracks, is abundant in the red member but scarce to absent in the grey member.

3.1.3. Katherine Group D.G.F. Long The Katherine Group (Figs. 3.1.1-2 and 3.1.2-1) was defined by Hume and Link (1945) based on extensive exposures in the frontal ranges of the Mackenzie Mountains near Mount Katherine, southwest of Norman Wells, as initially investigated by Link (1921). Gabrielse et al. (1973a), working in the Wrigley Lake and Glacier Lake map-areas, named equivalent strata the Tigonankweine Formation, with a type section in the Glacier Lake map-area (NTS 95L) at 62°38’N, 126°32.5’W. This name was later discarded once the unit’s continuity with strata to the north was confirmed by mapping (Aitken et al., 1973; Aitken and Cook, 1974a, 1974b). The general trend from deeper-water to shallower-water lithofacies in the Tsezotene Formation continues into the Katherine

39

Chapter Three

Figure 3.1.2-1. Location of selected measured sections in the Tsezotene Formation and Katherine Group (U-11, U-13 and MQ-33 are from Aitken et al. (1973); 77AC15 is from Aitken’s unpublished field notes; other sections measured by D.G.F. Long). Sections 035-038 were measured as part of the Sekwi project. Sekwi project areas mapped in detail are outlined in blue. Green = map unit H1; black = Tsezotene Formation; yellow = Katherine Group; blue = Little Dal Group. Location of Mount Katherine indicated by white star.

Group, which is dominated by arenite of fluvial, deltaic and shallowmarine origin (Aitken et al., 1978a; Long, 1978, 1982; Long et al., 2008). The group is divided into seven units of formational rank, informally named K1 to K7, with an aggregate thickness of up to 1,600 m (Aitken et al., 1978a; Long et al. 2008). Much of the outcrop belt is covered by an extensive felsenmeer of pinkweathering boulders, such that Gabrielse et al. (1973) divided the group into three mappable units (equivalent to units K1 to K5, K6, and K7) in the Glacier Lake (NTS 95L) and Wrigley Lake (NTS 95M) map-areas. Aitken and Cook (1974a, 1974b) divided the group into two mappable units, the lower Katherine (units K1 to K5) and the upper Katherine (units K6 and K7). During the Sekwi project, the Katherine Group was subdivided into a lower ({K1; K1 to K5), middle ({Km; K6), and upper ({Ku: K7) subdivision. As part of the Sekwi project, four sections (035, 036, 037 and 038; Fig. 3.1.2-1 and Appendix B) were measured, in order to confirm the sense of synsedimentary displacement on the Fort Norman Structure (Turner and Long, 2008).

40

The Katherine Group is not known to be of any direct economic importance. Hydrocarbon content of muddy and carbonate samples is typically low (0.01 to 0.52%) with an average TOC content of 0.13% (see Appendix G). All samples examined were over-mature with respect to hydrocarbon generation.

Age and correlation The Katherine Group is present in the Wernecke Mountains (Yukon), as part of the (revised) Hematite Creek Group (Turner, 2010). The Katherine Group is also thought to be equivalent to unit D1 in the Hart River Inlier (Abbott, 1997), and unit R5 in the Coal Creek Inlier (Abbott, 1997). The Katherine Group is equated with the Nelson Head, Aok and Grassy Bay formations in the Amundsen Basin (Rainbird et al., 1996a). Unit K6 is directly correlative with the Aok Formation in the Shaler Supergroup (Jefferson and Young, 1988; Rainbird et al., 1996a; Long et al., 2008), which, like unit K6, includes at least two stromatolitic dolostone horizons in most sections.

Chapter Three

Figure 3.1.2-3. Shoaling succession of red silty mudstone and sandy mudstone in the red member of the Tsezotene Formation in Section 005 (NTS 106A; approximately 493700E, 7195500N). Each cycle coarsens upwards and some have a discontinuous cap of medium- to coarse-grained sandstone. Inset shows a pumice clast at the top of one of these cycles.

Figure 3.1.2-2. Typical thin- to thick-laminated silty mudrocks of the grey member, Tsezotene Formation, in Section 015 in the Imperial River Canyon (NTS 106H; approximately 543500E, 7217100N.

Unit K1

Description Unit K1 (Aitken et al., 1978a) is sandstone-dominated, with a thickness of 300 to 600 m in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-1 and -2). It thins northwestward to as little as 126 m in the front ranges immediately north of Mount Katherine (Fig. 3.1.3-1). Its lower contact with mudrocks of the Tsezotene Formation is typically sharp, with local evidence of erosion (up to 1.5 m relief). The principal reference section for unit K1 is on the south face of Mount Eduni, at 64°13’30”N, 128°03’W (Section 019; Figs. 3.1.2-6, 3.1.3-1 and -3, and Appendix B). In this section, which is typical of much of the unit, 87% of the section is light pinkweathering fine- to very fine-grained sandstone (quartz arenite), and 3% is black and red mudstone and siltstone. Medium- to largescale planar cross-stratification, with an average bed thickness of 50 cm (Fig. 3.1.3-4) is present in 77% of the sandstones. Low-angle or sinusoidal cross-stratification, and local current lineation is present in 9% of the section. The remaining sandstones are either ripple- or plane-laminated (Figs. 3.1.3-5 and -6). Mudstone intraclasts are rare. Most of the sandstone beds represent sheet elements (Fig. 3.1.3-7). Local channels are up to 8 m deep and several hundred metres wide (Figs. 3.1.3-8 and -9).

Figure 3.1.2-4. Soil features in mudstone at base of a red coarsening-upwards cycle, Section 005 (NTS 106A; approximately 493700E, 7195500N).

Interpretation Sandstones in K1 are predominantly fluvial (ephemeral and perennial shallow sandy-braided rivers, and minor meandering sand-bed rivers). Mudstone intervals include inter-fluvial deposits (overbank), abandoned channel-fills and minor intertidal incursions.

Figure 3.1.2-5. Orange-weathering domal stromatolites in the red member, Tsezotene Formation, Section 005 (NTS 106A; approximately 493700E, 7195500N).

41

Chapter Three

Figure 3.1.2-7. Columnar stromatolites at base of red member (Section 019; NTS 106A; approximately 545600E, 7153100).

Interpretation Figure 3.1.2-6. Exposure of the red member of the Tsezotene Formation south of Mount Eduni (Section 019; NTS 106A; approximately 545600E, 7153100). White unit at base is a stromatolitic limestone (C) that separates the grey (Tg) and red (Tzr) members.

Unit K2

Description Unit K2 (Aitken et al., 1978a) consists of interlayered thinbedded sandstone and mudstone, and is 25 to 138 m thick in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-10 and -11). It thins northwestward to as little as 11 m in the Stony Anticline in NTS 106H (Fig. 3.1.3-11 inset). The lower contact with K1 sandstone is typically sharp but non-erosive. Sandstone content typically increases up-section, and the upper contact with unit K3 appears to be transitional. The principal reference section for unit K2 is on the north side of a tributary of the Mountain River, in the Tawu Anticline at 64°46’N, 129°54’W (Section 002; Figs. 3.1.2-1 and 3.1.3-11, and Appendix B) where it is 142 m thick. This section has ~ 40% thin, plane-laminated, grey-weathering mudstone, 20% thin to thick, planar-laminated, orange-weathering dolostone (some with microbial lamination), and 40% thick-laminated, wavy-laminated and ripple cross-laminated dull red to pink-weathering very fineand fine-grained sandstone, with minor mudstone intraclasts (Figs. 3.1.3-12 and -13). In this and other sections there is a general upsection increase in sandstone content. Carbonate rocks are absent from sections in the Stoney, MacDonald, and Foran anticlines in the front ranges, and in the Tigonankweine anticline.

42

The base of unit K2 is interpreted as a third-order sequence boundary (Long et al., 2008). This represents a flooding surface associated with a short-wavelength tectonic and eustatic relative sea-level change, with a duration of 1-11 Ma, reflecting coupling between intraplate stress, basin-scale tectonics and rates of spreading at oceanic spreading centres (Krapez, 1997). Most of the strata can be interpreted as shallow-marine shelf deposits, shoaling to intertidal in sandstone-dominated parts of the succession.

Unit K3

Description Unit K3 (Aitken et al., 1978a) is sandstone-dominated, with a thickness of 72 to 619 m in the Shattered Range and Tigonankweine anticlines (Section 016; Figs. 3.1.3-10 and -11, and Appendix B). This unit is 368 to 454 m thick in the Tawu Anticline and 63 to 276 m thick in the Stony and Foran anticlines in the front ranges (Fig. 3.1.3-10 inset). The lower contact with mudrock and sandstone of unit K2 is sharp or gradational, and is marked by the appearance of planar cross-stratified sandstones and the absence of mudstone. As with units K1, K5 and K7, most of the exposure areas are covered with boulder-rubble; this unit can be readily distinguished only when sub- and superjacent, recessive, mud-rich units can be identified (Fig. 3.1.3-14). The principal reference section for unit K3 is in the north limb of the Stoney Anticline, in the Carcajou ranges at 65°03’30”N, 127°47’40’W (Section 016; Fig. 3.1.3-11 and Appendix B). At this location, which is typical of much of the unit, 98% of the section is light pink-weathering fine- to very fine-grained sandstone (quartz arenite), and 2% is black and red mudstone and siltstone. Mediumto large-scale planar cross-stratification is present in 85% of the

Chapter Three

Figure 3.1.3-1. Northwest-southeast stratigraphic panel for unit K1. Inset map shows measured section locations for unit K1 as red stars labelled with measured thicknesses in metres; see Fig. 3.1.2-1 for locations labelled with section number. The inset map also shows line of cross-section in green. Areas mapped in detail are outlined in blue. Possible K1 isopachs are shown as red lines (labelled in metres with outlined italic font), and possible transfer faults are indicated by grey dashed lines (see Turner and Long (2008) for further details). Tzr = Tsezotene Formation, red member.

43

Chapter Three

Figure 3.1.3-2. West-east section in unit K1 (see Fig 3.1.3-1 for legend and other details). Tzr = Tsezotene Formation, red member.

Figure 3.1.3-3. View of Mount Eduni, Section 019 (NTS 106A; approximately 545600E, 7153100N), showing prominent cliffs of unit K1 sandstone. Lower, smaller cliff is the carbonate unit at the base of the red member of the Tsezotene Formation, shown in Fig. 3.1.2-6.

44

Figure 3.1.3-4. Stacked sets of planar cross-stratified fine-grained sandstone in basal 10 m of unit K1, Section 015 (NTS 106H; approximately 543500E, 7217100N).

Chapter Three

Figure 3.1.3-7. Typical sheet-like geometry of planar cross-stratified sandstones, Section 010 (NTS 96D; approximately 550300E, 711400N), 1170 m level.

Figure 3.1.3-5. Thin-bedded sandstone and massive mudstone of overbank or interfluvial origin in unit K1, Section 015 (NTS 106H; approximately 543500E, 7217100N). Note sand-filled cracks at top of the 1.5 m-high staff, indicating soil development. Wavy to ripple-laminated sand above this may be of splay origin.

Figure 3.1.3-6. Plane-laminated, fine- to very fine-grained sandstones of upper-flow regime sheet-flood origin, at 536 m level in Section 016 (NTS 96E; approximately 556700E, 7215500N). Scale is 1.5 m.

Figure 3.1.3-8. Composite bar-forms (2-4 m thick) near base of K1 in Section 015 (NTS 106H; approximately 543500E, 7217100N), developed by lateral migration of meandering sand-bed rivers.

Figure 3.1.3-9. Liquefaction structures at base of channel-fill sandstone unit, Section 016 (NTS 96E; approximately 556700E, 7215500N). These may record bank collapse or seismic activity. Scale in centimetres.

45

Chapter Three

Figure 3.1.3-10. Stratigraphy of units K2 and K3 along a NW-SE line (green on inset map), in the Shattered Range and Tigonankweine anticlines. Inset shows thickness and isopach data for unit K3. For legend and further explanation see Fig 3.1.3-1.

sandstones, and 2% are characterised by trough cross-stratification (average thickness = 64 cm). Low-angle or sinusoidal crossstratification, with local current lineation is exhibited by 15% of the sandstones. The remaining sandstones are either ripple- or planelaminated. Mudstone intraclasts are common in some of the wavyand ripple-laminated sandstones, and locally are concentrated at the base of channel-fill sequences. Downward-tapering sand-filled cracks are common in some of the finer-grained intervals. Most polygonal forms are interpreted as desiccation cracks, although orthogonal systems (Fig. 3.1.3-15) are locally present. The latter are more difficult to interpret and may be of seismic origin. Most of the sandstone beds represent sheet elements. Local channels are up to 12 m deep and several hundred metres wide.

Interpretation As in unit K1, most of the sandstones in this unit are deposits of ephemeral and perennial, shallow, sandy-braided rivers, with minor evidence of meandering sand-bed rivers. Mudstone intervals include both inter-fluvial deposits (overbank), abandoned channelfills and possible minor intertidal incursions.

Unit K4

Description Unit K4 (Aitken et al., 1978a) consists of interlayered, thinbedded sandstone and mudstone with a thickness of 16 to 92 m in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-

46

16 and -17). The unit is 51 to 91 m thick in the Tawu Anticline and thins to 37 to 59 m in the Stony and Foran anticlines in the front ranges (Fig. 3.1.3-17 inset). The lower contact with unit K3 sandstone is typically sharp but non-erosive. Where sandstone is present near the base of the unit, the succession appears to be transitional (e.g., Section 016). Sandstone content typically increases up-section, and the upper contact, which can be transitional or sharp, is arbitrarily placed at the base of the first thick cross-stratified sandstone in unit K5 (Fig. 3.1.3-18). The principal reference section for unit K4 is on the south side of a tributary of the Mountain River, in the Tawu Anticline at 64°46’N, 129°51’W (Section 003; Figs. 3.1.3-16 and -17, and Appendix B) where it is 91 m thick. The section is dominated (65%) by thin to thick, plane-laminated grey to black mudrock. Most of the very fine- to fine-grained sandstones are confined to the upper part of the unit. Of these fine-grained sandstones, 55% are characterised by large-scale planar cross-stratification, and 35% by thin plane-lamination (with abundant current lineation). The remaining 10% are characterised by wavy and ripple crosslamination. Intraclast horizons are rare. Carbonate rocks are present locally in Sections 006, 013 and 039 (Appendix B) as thin, flaggy beds of orange-weathering dolostone with flat to wavy lamination and abundant polygonal mudcracks, and as thicker units of microbially laminated dolostone (Fig. 3.1.3-19).

Chapter Three

Figure 3.1.3-11. Stratigraphy of units K2 and K3 along a W-E line (green on inset map), across the Mackenzie Mountains Fold Belt. Inset shows thickness and isopach data for unit K2. For further explanation see Fig 3.1.3-1.

47

Chapter Three

Figure 3.1.3-12. Small-scale fining-upwards cycle in a finer-grained interval in unit K3, south of Keele River in Section 016 (NTS 96E; approximately 556700E, 7215500N). Cycle grades from fine sand at the base, through red, plane- and ripplelaminated very fine-grained sandstone, to mudstone with minor interbeds of ripplelaminated sandstone.

Figure 3.1.3-13. Thin-bedded plane-laminated and ripple cross-laminated sandstone overlying interbedded wavy-bedded sandstone and thinly laminated mudstone of intertidal to shallow subtidal origin. Unit K3, Section 003 (NTS 106A; approximately 459600E, 7184200N), 175 m level.

48

Figure 3.1.3-14. Typical exposure of the Katherine Group (facing Section 003, adjacent to a tributary of the Mountain River; NTS 106A; approximately 459600E, 7184200N), showing rubble cover. Sandstone-dominated units can be distinguished with confidence only when finer, recessive units are recognised.

Figure 3.1.3-15. Orthogonal sets of sand-filled cracks in finer interval in unit K3, 200 m level in Section 003 (NTS 106A; approximately 459600E, 7184200N; z9). Top of scale in centimetres.

Chapter Three Interpretation The base of unit K4 is interpreted as a third-order sequence boundary (Long et al., 2008). Most of the unit is interpreted as shallow-marine shelf deposits, shoaling to intertidal and possibly distal fluvial settings in sandstone-dominated parts of the succession. Thicker, planar cross-stratified sandstones (sheet elements) near the top of the unit may be of braided fluvial origin. The presence of current lineation and rare swash marks in some of the planelaminated sandstone co-sets suggests that these are beach deposits.

Unit K5

Description

Figure 3.1.3-16. Stratigraphy of units K4 and K5 along a NW-SE line (green on inset map), coincident with the Shattered Range and Tigonankweine anticlines. Inset shows thickness and isopach data for unit K5. For further explanation see Fig 3.1.3-1.

Unit K5 (Aitken et al., 1978a) is sandstone-dominated, with a thickness of 124 to >300 m in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-16 and -17). It is 154 to 222 m thick in the Tawu Anticline and 180 to 222 m thick in the Stony and Foran anticlines in the front ranges (Fig. 3.1.3-16 inset). The lower contact with mudrock and sandstone of unit K4 can be sharp and possibly erosional, with relief up to 1.5 m, or gradational (Fig. 3.1.3-20). The base is typically marked by thick-bedded, massive or planar cross-stratified sandstones and an absence of mudstone units. As with units K1, K3, and K7, most of the exposure areas are covered with boulder-rubble, such that K5 can be distinguished only when sub- and superjacent, recessive, mud-rich units can be identified (Fig. 3.1.3-14). The principal reference section for unit K5 is in the Shattered Range Anticline at 64°46’N, 129°54’W (Section 002; Fig. 3.1.3-16 and Appendix B). In this section, which is typical of much of the unit, 97% of the section is light pink-weathering fine- to very fine-grained sandstone (quartz arenite), and 3% is black and red mudstone and siltstone. Medium- to large-scale planar cross-stratification is present in 81% of the sandstones (Fig. 3.1.3-21), and 2% are characterised by trough cross-stratification (average thickness = 59 cm). Low-angle or sinusoidal cross-stratification, with local current

Figure 3.1.3-17. Stratigraphy of units K4 and K5 along a W-E line (green on inset map), across the Mackenzie fold belt. Inset shows thickness and isopach data for unit K4. For further explanation see Fig 3.1.3-1.

49

Chapter Three

Figure 3.1.3-18. Interbedded sandstone and mudstone of unit K4 in Section 003 (NTS 106A; approximately 459600E, 7184200N). White sandstone near top of photo marks the base of unit K5.

Figure 3.1.3-19. Thin- to thick-bedded, orange-weathering carbonate rocks in unit K4 in the core of the Shattered Range Anticline (south of Section 029), in the headwaters of the Little Keele River (NTS 106A; approximately 534500E, 7166200N). Resistant sandstone in the lower third of the photograph is the upper part of unit K3.

Figure 3.1.3-20. Scour at base of unit K5 in Section 008 (NTS 106A; approximately 488900E, 7175000N).

50

Figure 3.1.3-21. Planar cross-stratified sandstone, 435 m level of Section 003 (NTS 106A; approximately 459600E, 7184200N).

Chapter Three

Figure 3.1.3-22. Low-angle cross-stratified fine-grained sandstone interpreted as an ephemeral stream deposit, 359 m level of Section 003 (NTS 106A; approximately 459600E, 7184200N). Scale is 1.5 m.

Figure 3.1.3-25. Necks of sand volcanoes on the upper surface of unit K5 in Section 035 (NTS 95M; approximately 564700E, 7090500N). These features may have been formed by syndepositional faulting along the Fort Norman structure (Turner and Long, 2008).

lineation, is present in 6% of the sandstones (Fig. 3.1.3-22 and -23). The remaining sandstones are either ripple- or plane-laminated. Mudstone intraclasts are common in some of the wavy- and ripplelaminated sandstones, and locally are concentrated at the bases of channel-fill sequences. Downward-tapering sand-filled cracks are common in some of the finer-grained intervals. Most of the sandstone beds represent fluvial sheet elements. Local channels are 4-8 m deep and several hundred metres wide (Fig. 3.1.3-24). Waterescape structures (sand volcanoes) are present in the uppermost sandstone units of Section 035 (Fig. 3.1.3-25).

Interpretation As in units K1 and K3, most of the sandstones of this unit are deposits of ephemeral and perennial shallow sandy-braided rivers, with minor evidence of meandering sand-bed rivers. Mudstone intervals include inter-fluvial deposits (overbank), abandoned channel-fills, and possible minor intertidal incursions. Figure 3.1.3-23. Detail of lower contact of low-angle cross-stratified unit in Fig. 3.1.3-22.

Unit K6

Figure 3.1.3-24. Channelised and sheet sandstone elements exposed in the south face of Mount Eduni (Section 019, NTS 106A; approximately 545600E, 7153100N). Note low-angle element boundaries in units immediately below the obvious channel. These represent point-bar surfaces of a sandy meandering fluvial system.

Unit K6 (Aitken et al., 1978a) consists of interlayered thinbedded mudstone, dolostone and sandstone, and is 201 to 253 m thick in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-26 and -27). It is 150 to 219 m thick in the Tawu Anticline and thins to 123 m in the MacDougal Anticline at Dodo Canyon (Section 014, Fig. 3.1.3-27 inset). The lower contact with sandstone of unit K5 is typically sharp but non-erosive. Sandstone is locally present in the upper part of the unit, suggesting a transitional contact with unit K7. The upper contact is at the base of the first thick, cross-stratified sandstone of K7. The principal reference section for unit K6 is in the Tawu Anticline at 65°43’30”N, 128°41’W (Section 023; Fig. 3.1.3-26 and Appendix B), where it is 116 m thick. The section is dominated (68%) by thin to thick plane-laminated grey-green to black mudrock. Dolostone forms 21%, and very fine-grained sandstone (quartz arenite) about 1% of the section. Sandstone is more abundant in other sections, and tends to be concentrated near the top of the unit. Large- and small-scale domical and branching columnar stromatolites (Inzeria) locally form up to half of the carbonate beds (Figs. 3.1.3-28 and -29). Inter-stromatolitic beds commonly contain abundant intraformational conglomerate and large oncoids (Fig. 3.1.3-30). Most of the stromatolitic beds are underlain by,

Description

51

Chapter Three

Figure 3.1.3-26. Stratigraphy of units K6 and K7 along a NW-SE line (green on inset map), in the Shattered Range and Tigonankweine anticlines. Inset shows thickness and isopach data for unit K7. LD = Little Dal Group. For further explanation see Fig. 3.1.3-1.

and interbedded with, thin to thick plane-laminated dolostone and siliciclastic mudstone, with local gutter casts, 3D ripples and hummocky cross-stratification (Figs. 3.1.3-31 and -32). Molar-tooth structure is present in one massive dolostone bed in Section 035 (Fig. 3.1.3-33). Rare sandstone is dominated by thin, very fine-grained co-sets, with flat to wavy lamination and few ripples. Some units contain polygonal mudcracks (Fig. 3.1.3-34). Interbedded mudrock locally contains synaeresis cracks (Fig. 3.1.3-35).

Interpretation The base of unit K6 is interpreted as a third-order sequence boundary (Long et al., 2008). Most of the unit is interpreted as shallow-marine shelf deposits, with evidence of repeated shoaling that produced laterally extensive stromatolite biostromes. Minor storm influence is indicated by hummocky cross-stratification. The increase in sand content near the top of the unit in many sections indicates shoaling to shallow subtidal to intertidal conditions, and suggests a transitional contact with unit K7.

52

Unit K7

Description Unit K7 (Aitken et al., 1978a) is sandstone-dominated, with a thickness of 85 to 270 m in the Shattered Range and Tigonankweine anticlines (Figs. 3.1.3-26 and -27). It thins northwestward to as little as 15 to 39 m in the front ranges of the Mackenzie Mountains (Fig. 3.1.3-26 inset). The lower contact with unit K6 is sharp, and marked by the first appearance of large-scale cross-stratification, or gradational, where it is dominated by wavy- and ripple-laminated sandstone, with few to no mudstone intervals. The principal reference section for unit K7 is in the Tawu anticline at 65°43’30”N, 128°41’W (Section 023; Fig. 3.1.3-26 and Appendix B). In this section, which is typical of much of the unit, 96% of the rock is light pink-weathering fine- to very fine-grained sandstone (quartz arenite), and 4% is red mudstone and siltstone. Medium- to large-scale planar and trough cross-stratification, with an average thickness of 25 cm, is present in 77% of the sandstone

Chapter Three

Figure 3.1.3-27. Stratigraphy of units K6 and K7 along a W-E line (green on inset map) across the Mackenzie fold belt. Inset shows thickness and isopach data for unit K6. LD = Little Dal Group. For further explanation see Fig. 3.1.3-1.

Figure 3.1.3-28. Necks of sand volcanoes on the upper surface of unit K5 in Section 035 (NTS 95M; approximately 564700E, 7090500N). These features may have been formed by syndepositional faulting along the Fort Norman structure (Turner and Long, 2008).

Figure 3.1.3-29. Necks of sand volcanoes on the upper surface of unit K5 in Section 035 (NTS 95M; approximately 564700E, 7090500N). These features may have been formed by syndepositional faulting along the Fort Norman structure (Turner and Long, 2008).

53

Chapter Three

Figure 3.1.3-30. Oncolitic dolorudstone, unit K6, 122 m level of Section 035 (NTS 95M; approximately 564700E, 7090500N).

Figure 3.1.3-31. Interbedded laminated dolostone and siliciclastic mudstone, with prominent gutter cast, unit K6, Section 014 (NTS 96D; approximately 584500E, 71995700N). Scale in centimetres.

Figure 3.1.3-32. Modified 3-D ripples (swaley cross-stratification), unit K6, 45 m level of Section 035 (NTS 95M; approximately 564700E, 7090500N).

Figure 3.1.3-34. Laminated, dolomitic, very fine-grained sandstone with intraclastfilled polygonal cracks of possible intertidal origin, unit K6, 515 m level of Section 036 (NTS 96D; approximately 554800E, 7103900N). Scale in centimetres.

Figure 3.1.3-33. Dolomitised molar-tooth structures (carbonate-cement-filled cracks), unit K6, 440 m level of Section 036 (NTS 96D; approximately 554800E, 7103900N).

54

Chapter Three

Figure 3.1.3-35. Interbedded, thick, planar- to wavy-laminated very fine-grained sandstone and mudstone, with synaeresis cracks, unit K6, 550 m level of Section 003 (NTS 106A; approximately 459600E, 7184200N). Scale in centimetres.

thickness. Eight percent of the sandstones exhibit low-angle or sinusoidal cross-stratification, with local current lineation (Figs. 3.1.336 and -37). The remaining sandstones are either ripple-, plane- or wavy-laminated (Figs. 3.1.3-38 and -39). Mudstone intraclasts are common in wavy-laminated units.

Interpretation Sandstones in this unit are predominantly fluvial (ephemeral and perennial shallow sandy-braided rivers, and minor meandering sand-bed rivers). Mudstone intervals include both inter-fluvial deposits (overbank) and abandoned channel-fills. Where thick intervals of planar- and wavy-laminated very fine-grained sandstones are present, these probably represent nearshore or beach deposits. The base of the unit appears to be gradational, reflecting a facies transition from shallow-marine deposits of unit K6. The upper contact of the formation with the Mudcracked formation of the Little Dal Group is typically sharp, and represents a third-order sequence boundary.

Figure 3.1.3-36. Low-angle cross-stratified sandstone of channel origin, capped by a succession of channel-fill or overbank fines, unit K6, Section 003 (NTS 106A; approximately 459600E, 7184200N).

3.1.4. Little Dal Group E.C. Turner Gabrielse et al. (1973a) established the Little Dal Formation, which was promoted to group status by Aitken et al. (1978b), and its seven informal, formation-scale stratigraphic units described by Aitken (1981). The group, approximately 2-2.5 km thick and dominated by carbonate rocks, also contains subordinate, generally fine terrigenous clastic rocks and a thick sulphate-facies evaporite unit. The formation-scale units (Fig. 3.1.1-2) remain informal and have no type sections, although Gabrielse et al. (1973a) proposed a type section for the (then) Little Dal Formation south of Coates Lake (formerly Little Dal Lake) in NTS 95L. Numerous field sections are available in Aitken et al. (2011). In early mapping, the term “Little Dal” was in some cases limited to what is now known as the “Upper Carbonate formation” of the Little Dal Group, and the underlying units (from Mudcracked to Rusty Shale formations) was mapped together as the “H5” unit. This usage was soon abandoned once the relationships among stratigraphic units that predominate on either side of the Plateau fault were understood (Mudcracked to Grainstone formations generally exposed east of the fault; Gypsum to Upper Carbonate formations generally exposed west of the fault), and the group’s stratigraphy informally established (Aitken, 1981). Analysis of unusual thickness and facies patterns in the lower

Figure 3.1.3-37. Current lineations and small obstacle-scours on surface of planelaminated bed, Section 004 (NTS 106A; approximately 454100E, 7189000N). Compass for scale.

Little Dal Group provided constraints on tectonostratigraphic evolution of the basin during the group’s deposition (Turner and Long, 2008). Isopachs for the lowermost Little Dal Group are provided in Turner and Long (2008) and for the uppermost Little Dal Group by Jefferson (1983) and Jefferson and Parrish (1989). The Little Dal Group is correlative to the Boot Inlet, Fort

55

Chapter Three

Mudcracked formation

Figure 3.1.3-38. Heavy-mineral concentrations in laminated very fine sandstone, with soft-sediment deformation, Section 008 (NTS 106A; approximately 488900E, 7175000N).

The Mudcracked formation (Aitken, 1981) is a thin (10-68 m) terrigenous unit that, depending on location, conformably (Turner et al., 1997) to slightly unconformably (Batten et al., 2004) overlies the Katherine Group (Aitken, 1981). Numerous sections through this formation have been measured by Aitken (1981), Turner (1999) and Batten (2002); this is probably the best-documented unit in the Little Dal Group. For isopachs, see Aitken (1981) and Turner and Long (2008), and for paleocurrents, see Aitken (1981). The Mudcracked formation is present on the flanks of all anticlines east of the Plateau fault, although it is erosionally truncated beneath the Cambro-Ordovician Franklin Mountain Formation in the extreme northeast of the Sekwi project area (NTS 106A). One detailed section was measured for the Sekwi project, on a creek tributary of the Imperial River in north-easternmost NTS 106A, an area for which no stratigraphic data was hitherto available (Section 08-ECT-IR; Appendix C). Sekwi project sections 07-CLS1 and 07-RAS-S1 and S2 included the Mudcracked formation (Appendix A).

Description In the northwestern part of the MMSG exposure area (Sekwi project area), the conformable contact of the Mudcracked formation with Katherine Group quartz arenite is overlain by dark-weathering, decimetre- to metre-scale beds of grey, red and green siltstone and quartz arenite with subordinate carbonate layers. Shallow-marine sedimentary structures are ubiquitous, and include synaeresis cracks, halite casts, hummocky cross-stratification, gutter casts, tool marks, tempestites with graded shale chips, trough cross-bedding and both asymmetrical and symmetrical ripple cross-lamination (Figs. 3.1.4-1 to -3). Many bedding surfaces have a black veneer that is probably a microbial mat residue. Morphologically distinct, macroscopic organic remains are locally present as the carbonaceous compressions Morania and Beltina on bedding planes. A ubiquitous uppermost unit in the Mudcracked formation is an orange-weathering oncoid grainstone, typically one to 10 m thick, rarely with small bioherms of columnar stromatolites (Figs. 3.1.4-4 and -5). The upper contact of the Mudcracked formation was placed at the top of the oncoid grainstone, which acts as a conspicuous marker unit (Aitken, 1981). The only significant lateral variation in the study area is more conspicuous red and green siltstone and mudstone colours in the more easterly (inboard) areas (e.g., section 08-ECT-IR; Fig. 3.1.4-1 and Appendix C).

Age and correlation

Figure 3.1.3-39. Inter-fluvial deposits with synaeresis cracks, Section 008 (NTS 106A; approximately 488900E, 7175000N).

Collinson, Jago Bay, Minto Inlet and Wynniatt Formations of the Shaler Supergroup, Amundsen Basin (Rainbird et al., 1996a; Long et al., 2008). The lower Little Dal Group is equivalent to unit F of the upper Pinguicula Group (revised Hematite Creek Group; Turner, 2010) in the Wernecke Mountains (Thorkelson et al., 2001, 2005). The Little Dal Group may also be equivalent to units D2 and D3 in the Hart River Inlier (Abbott, 1997) and unit F1a in the Coal Creek Inlier (Abbott, 1997).

56

The Mudcracked formation is correlated with the lower part of the Boot Inlet Formation (Reynolds Point Group, Shaler Supergroup) in the Amundsen Basin (Rainbird et al., 1994, 1996a). Although a thin stratigraphic interval that is probably equivalent to the Mudcracked formation is present in the Hematite Creek Group (former upper Pinguicula Group, Wernecke Mountains, Yukon) above Katherine Group strata, the interval does not contain similar lithofacies (Turner, 2010).

Interpretation The basal contact of the Mudcracked formation represents a third-order flooding surface, and marks the transition from fluvialdominated conditions of the Katherine Group to fully marine conditions of the Little Dal Group (Aitken, 1981; Long et al., 2008). The formation, up to the oncoid marker unit, represents the first

Chapter Three

Figure 3.1.4-1. Interbedded mudstone, siltstone and quartz arenite of the Mudcracked formation. near Etagochile Creek, south side of Tawu Anticline (NTS 106A; approximately 525900E, 7166800N). Exposure is approximately 15 m high.

Figure 3.1.4-2. Halite casts in the Mudcracked formation, near 64°48’16”N/129°41’17”W. Scale in cm.

Figure 3.1.4-4. Orange-brown-weathering oncoid grainstone marker at top of the Mudcracked formation (as defined by Aitken, 1982), near Etagochile Creek, south side of Tawu Anticline, at 64°37.5’N/128°27.5’W.

Figure 3.1.4-5. Iron-stained contact (arrow) between oncoid marker of Mudcracked formation (sensu Aitken, 1982) and Cambro-Ordovician Franklin Mountain Formation, south flank of Stony Anticline near Imperial River (Section 08-ECT-IR; NTS 106A; approximately 545583E, 7202165N).

(LD0) in a series of third-order transgressive-regressive cycles that can be discerned through most of the Little Dal Group (Turner and Long, 2008). Physical sedimentary structures in the Mudcracked formation record deposition in a storm-dominated, terrigenous shelf environment that was intermittently or locally hypersaline. The oncoid unit at the top of the formation records transgression throughout the basin, and in this map-area heralds deepening into the first transgressive-regressive cycle (LD1) of the overlying Basinal assemblage (Turner and Long, 2008).

Basinal assemblage

Figure 3.1.4-3. Synaeresis cracks and shale-chip conglomerate, Mudcracked formation near Etagochile Creek, south side of Tawu Anticline, in NTS 106A (approximately 525900E, 7166800N).

The Basinal assemblage (Aitken, 1981; Turner et al., 1997; Turner, 1999; Turner and Long, 2008) is a 143-622 m-thick unit present east of the Plateau fault on the flanks of the Shattered Range, Tigonankweine and Tawu anticlines, and locally on the flanks of the Stony and Foran anticlines. It is laterally equivalent to the Platformal assemblage in locations northwest of a northeasttrending line that passes through approximately 63°55’N, 127°30’W (Aitken, 1981; Turner and Long, 2008). For isopachs, see Turner and Long (2008), and for detailed sections, see Turner (1999, appendix).

57

Chapter Three The Basinal assemblage is generally erosionally truncated and overlain by Paleozoic strata in all but the westernmost anticline (Shattered Range Anticline) east of the Plateau fault. In the Sekwi project area, the Basinal assemblage is an important and easily recognised stratigraphic marker east of the Plateau fault. Part of the Basinal assemblage (equivalent to members 1-3) was once referred to informally as the “dead-end shale” in the mineral exploration literature, whereas carbonate rocks of member 4 were referred to as the “lower limestone” and “sharpstone breccia” (e.g., Hewton, 1982). In the Gayna River area (NTS 106B), molar-tooth carbonates of the uppermost Basinal assemblage host Zn mineralisation (Hewton, 1982), and subtle deformation structures associated with the giant Little Dal reefs of the Basinal assemblage have been proposed as a factor controlling metal concentration at a local scale (Turner, 2007). For the Sekwi project, two detailed sections were measured through the Basinal assemblage, on the west side of Cranswick River at the Yukon – Northwest Territories border in southeastern NTS 106F, and on the southwest flank of the Tigonankweine Range, in southwestern NTS 96D (Sections 08-ECT-CR and 07-ECT-TG; Appendix C). Sekwi project sections 07CL-S1 and 07RAS-S1, -S2, and -S3 included parts of the Basinal assemblage (Appendix A).

Description The conformable basal contact of the Basinal assemblage was placed above the oncoid marker unit at the top of the Mudcracked formation (Aitken, 1981). The upper contact with the Grainstone formation is conventionally placed where molar-tooth lime mudstone passes gradationally upward to dolomitic ooid-intraclast grainstone. See Turner (1999; appendix) for detailed sections. The Basinal assemblage consists of four shale-to-carbonate cycles (LD1 to 4; Figs. 3.1.4-6 to -8) that define informal members, also numbered B1 to B4 or member 1 to member 4 (Turner et al., 1997), each with laterally variable thicknesses between 16 and 400 m. In member 1 (16 to >91 m), recessive, green-grey siltstone and shale are overlain by a distinctive, ubiquitous, resistantly weathering stromatolite biostrome that varies from isolated domes of columnar stromatolites 1 m thick to multi-storey biostromes >20 m thick. In most localities, the stromatolite unit is 485 m thick, and locally exposed throughout the Mackenzie arc just east of the Plateau fault and in its immediate hanging-wall. The Gypsum formation is of considerable importance: it is a major décollement surface for the Plateau fault (see Chapter 5), and may have contributed to the sulphur content of base-metal sulphides in spatially associated showings in the Mackenzie Mountains zinc district. In the course of this project, three almost complete sections were measured, at widely spaced locations in the footwall of the Plateau fault on NTS 106B, 106A and 95M (06-ECT-FC; 07-ECTSK; 08-ECT-NB; Figs. 3.1.4-25 to -28; Turner, 2009).

Description The lower contact is placed where distinctive, recessive, peritidal dolostone of the uppermost Grainstone formation is abruptly overlain by white-weathering, current-rippled, subtidal, sulphate-facies evaporites (Figs. 3.1.4-29 to -32), with possible disconformity (see Grainstone formation, above). The upper contact is placed where white-weathering evaporites are abruptly overlain by siltstone or dolostone of the lower Rusty Shale formation, with

63

Chapter Three

Figure 3.1.4-18. Simplified stratigraphic section for the Grainstone formation at Keele River (Section 08-ECT-KR; NTS 95M; approximately 553000E, 7091800N).

64

Chapter Three

Figure 3.1.4-19. Exposure of Basinal assemblage and overlying Grainstone formation on east side of Keele River. Section 08-ECT-KR followed creek tributary in centre of photo. View to NE. Elevation differential between river and cliff-top is approximately 600 m; Grainstone formation exposed (incomplete) is ~335 m thick. NTS 95M; approximately 553000E, 7091800N.

Figure 3.1.4-20. Molar-tooth dolomudstone and intraclast dolorudstone in lower Grainstone formation, Keele River (section 08-ECT-KR; NTS 95M; approximately 553000E, 7091800N). Hammer for scale.

Figure 3.1.4-21. First of two recessive, argillaceous, platy dolostone units in the Grainstone formation at Keele River (section 08-ECT-KR; NTS 95M; approximately 553000E, 7091800N). Hammer for scale.

65

Chapter Three seeming conformity. No section documented to date exposes both lower and upper contacts. The formation possesses a distinctive though subtle stratigraphy that appears to be fairly consistent throughout the exposure area. The thick, dazzling, white-weathering evaporites contain minor interlayered dolostones as well as two distinctively pink-weathering argillaceous units (Figs. 3.1.4-25 to -28). A ~10-5 m-thick, resistant, widespread carbonate member near the top of the formation (Figs. 3.1.4-25 to -28 and -33) locally contains molar-tooth structure, an indication of normal marine conditions near storm wave-base.

Age and correlation The Gypsum formation is directly equivalent to the evaporitic Minto Inlet Formation of the Shaler Supergroup (Rainbird et al., 1994, 1996a; Long et al., 2008). There is no proposed equivalent in the Wernecke Mountains (Yukon). Figure 3.1.4-22. Cross-bedded and partly silicified ooid dolograinstone in the upper massive oolite of the Grainstone formation, Keele River (section 08-ECT-KR; NTS 95M; approximately 553000E, 7091800N). Hammer for scale.

Figure 3.1.4-23. Argillaceous, quartz-silty, recessive dolomudstone of the upper platy dolostone unit, just below the contact with the Gypsum formation at Stone Knife River (section 07-ECT-SK; NTS 106A; approximately 466700E, 7184000N).

Interpretation As first suggested by Aitken (1981), the abrupt transition from supratidal dolostone of the uppermost Grainstone formation to deep-water, lagoonal evaporite rocks of the Gypsum formation indicates a sudden and probably tectonically induced flooding of the basin, accompanied by its restriction from full exchange with global ocean water (Turner, 2009). The basin floor was characterised in some intervals by particulate evaporites that accumulated on a sea floor that was at least intermittently near storm wave-base, as suggested by possibly tempestite-related current-ripple crosslamination. Episodic water freshening is recorded by subtle carbonate interlayers throughout the section, and minor influxes of terrigenous material by slightly elevated clay content and attendant colour variation. Terrigenous clay content increases southeastward, indicating its probable source area (Fig. 3.1.4-25; Aitken, 1981; Aitken and McMechan, 1991). The carbonate marker indicates a temporary and probably tectonically induced return to open-ocean circulation. Stable isotope values for both carbonate and evaporite units are typical for rocks of this age (Fig. 3.1.4-25; Turner, 2009).

Rusty Shale formation The Rusty Shale formation (Aitken, 1981) is a conspicuous, dark-brown-weathering, slightly recessive unit that is well exposed in the hanging-wall of the Plateau fault in NTS 106A, B and 95M (Figs. 3.1.4-34 to -36), and locally in its footwall (Fig. 3.1.4-37). It is not known to be of economic relevance. For isopachs, see Aitken (1981). One section was measured in the course of this study (08-ECT-TR; Fig. 3.1.4-35) and conforms closely to the typical composition and stratigraphy as described below. The basal contact was also examined on NTS 95M (08-ECT-NB; Fig. 3.1.4-25).

Description

Figure 3.1.4-24. Quartz sandy, cross-laminated dolostone with desiccation cracks, from the upper platy dolostone unit of the Grainstone formation at Stone Knife River (section 07-ECT-SK; NTS 106A; approximately 466700E, 7184000N). Pencil for scale.

66

The lower contact is generally abrupt, where dolostone, or locally, thin siltstone or sandstone, overlies recessive evaporite rocks of the Gypsum formation (Fig. 3.1.4-37); this contact is seldom well exposed. The upper contact is placed where resistant, buff-weathering intraclastic, “molar-tooth”, and stromatolitic dolostones gradationally overlie argillaceous carbonate rocks of the uppermost Rusty Shale formation. As described and depicted by Aitken (1981), the Rusty Shale formation is typically ~200-250 m thick, and has a distinctive, regionally valid, five-part stratigraphy (see 5 members in Fig. 3.1.435). (A) A lower, yellow-buff-weathering dolostone dominated

Chapter Three

Figure 3.1.4-25. Simplified stratigraphy and stable isotopic composition of the Gypsum formation at Fugue Creek (06-ECT-FC); Stone Knife River (07-ECT-SK) and Nidhe Brook (08-ECT-NB). Isotopic analyses were performed at G.G. Hatch Laboratory, University of Ottawa; see Turner (2009).

67

Chapter Three

Figure 3.1.4-26. Gypsum formation exposure at Fugue Creek [377 m (incomplete); near Gayna River; 06-ECT-FC]. NTS 106B; approximately 413200E, 7205400N). Red lines indicate section location. View to S.

Figure 3.1.4-27. Gypsum formation exposure at Stone Knife River [482 m (incomplete); 07-ECT-SK; NTS 106A; approximately 466700E, 7184000N]. Red line indicates line of section. View to W.

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Chapter Three

Figure 3.1.4-28. Gypsum formation exposure at Nidhe Brook [250 m (incomplete); 08-ECT-NB; NTS 95M; approximately 552800E, 7093500)]. Red line indicates line of section. View to NE.

Figure 3.1.4-29. Weakly banded gypsum is the most common lithofacies in the Gypsum formation. Section 07-ECT-SK (NTS 106A; approximately 466700E, 7184000N).

Figure 3.1.4-30. Multi-directional ripple cross-lamination is locally present in both gypsum and interlayered dolostone lithofacies of the Gypsum formation. Section 07-ECT-SK (NTS 106A; approximately 466700E, 7184000N).

69

Chapter Three by mechanical lamination, desiccation cracks, symmetrical and asymmetrical cross-lamination, minor molar-tooth structure, local chert, and quartzose sand to silt (Fig. 3.1.4-38) is overlain by (B) locally ripple cross-laminated siltstone, mudstone and shale, with rare stromatolites (Fig. 3.1.4-39 and -40), (C) interbedded quartz arenite and siltstone, with desiccation cracks, grading, and asymmetrical and symmetrical ripples (Figs. 3.1.4-41 and -42), (D) grey shale and siltstone, and (E) dolostone and limestone with shaly interlayers, molar-tooth structure, intraclasts, grading, and local stromatolites and oolite (Fig. 3.1.4-43). In addition to this overall composition, section 08-ECT-TR examined for the Sekwi project exhibited numerous, 4 to 25 m-thick shallowing cycles grouped into a larger-order cyclic pattern.

Age and correlation The Rusty Shale formation is thought to be correlative to the lower Wynniatt Formation of the Shaler Supergroup (Rainbird et al., 1996a; Long et al., 2008).

Interpretation The Rusty Shale formation records the abrupt termination of restricted, evaporitic lagoonal conditions, and a return to storm-dominated open -marine circulation. The abrupt nature of the transition suggests a tectonic influence. Influxes of fineto medium-grained terrigenous material indicate progradation of sandy peritidal systems over offshore carbonate facies. The presence of two orders of shallowing cycles suggests that eustatic patterns were superimposed on steady regional subsidence during deposition of this formation. Aitken and McMechan (1991) indicated a probable sediment source area to the southeast.

Upper Carbonate formation The Upper Carbonate formation (Aitken, 1981; Jefferson, 1983; Jefferson and Ruelle, 1986; Jefferson and Parrish 1989) is a thick (locally in excess of 850 m) cliff-forming dolostone exposed in the hanging wall of the Plateau fault and in the hanging wall of subsidiary faults immediately east of the Plateau fault. The formation was first described by Aitken (1981) as having four members; Jefferson (1983) and Jefferson and Parrish (1989) subsequently recognised 13 informal members (UC1 to 13), of which the thirteenth is a volcanic unit (the “Little Dal basalt”) now considered to be a separate entity (Table. 2-1). For isopachs, see Aitken (1981), Jefferson (1983) and Jefferson and Parrish (1989). The Upper Carbonate formation locally contains minor fracturehosted copper sulphides both in the area of the Redstone copper belt and elsewhere. For this project, one section (section 55 of Jefferson, 1983, southeast of Boomerang Lake on NTS 95M) was examined (not measured) in detail (Figs. 3.1.4-44 and -45).

Description

Figure 3.1.4-31. Nodular and chicken-wire fabrics are rare in the Gypsum formation. Section 07-ECT-SK (NTS 106A; approximately 466700E, 7184000N). Pencil for scale.

Figure 3.1.4-32. Thin-bedded to laminated, locally ripple cross-laminated, grey dolostone (upper part of photo) forms sparse interlayers in the Gypsum formation. Section 07-ECT-SK (NTS 106A; approximately 466700E, 7184000N). Hammer for scale.

70

The gradational basal contact with the Rusty Shale formation is placed above the uppermost of the thin shale interlayers present in the Rusty Shale formation’s upper carbonate member. The Upper Carbonate formation is almost exclusively carbonate and contains only minor intercalations of terrigenous mud. The lower six members (UC 1-6) are composed of grey and tan, poorly preserved stromatolitic to oolitic dolostone and limestone (Figs. 3.1.4-46 to -56), whereas the upper six members (UC 7-12) are poorly

Figure 3.1.4-33. Carbonate marker of the upper Gypsum formation, as exposed at section 08-ECT-SK (NTS 106A; approximately 466700E, 7184000N).

Chapter Three

Figure 3.1.4-34. A typical exposure of the Rusty Shale formation, in the hangingwall of the Plateau fault. View to west across Stone Knife River. NTS 106A; approximately 467000E, 7168000N).

preserved, discontinuous stromatolitic carbonate units separated by grey to brown nodular lime mudstone (Figs, 3.1.4-57 to -62; Table 3.1.4-1; see Jefferson (1983) for detailed descriptions of the 12 members of the Upper Carbonate formation). Minor siltstone and shale units are present. The Upper Carbonate formation is unconformably overlain by a variety of middle Neoproterozoic to Paleozoic units. The oldest unit to overlie the Upper Carbonate formation is the “Little Dal basalt”. Jefferson (1983) and Jefferson and Parrish (1989) note that this contact has very little stratigraphic variability: it is almost always at the level of unit UC12. However, subtle angularity is evident in some locations (Fig. 3.1.4-63). The unconformity at the base of the Coates Lake Group is similarly subtle, cutting only as low as UC7 (Jefferson, 1983; Jefferson and Parrish, 1989). Evidence of significant karstification or exposure is not present at or near the upper contact of the Little Dal Group. The Upper Carbonate formation hosts Cu showings in the Sekwi project area (Appendix H).

Interpretation The Upper Carbonate formation records transgression followed by cyclic members that shallow from shale through carbonate mudstone to molar-tooth carbonate, ooid dolograinstone, and stromatolitic dolostone. Isopachs provided in Jefferson (1983) and Jefferson and Parrish (1989) depict syndepositional embayments that may presage those that controlled depositional patterns in the overlying Coates Lake Group, and that may be related to syndepositional faulting that affected thickness and facies patterns of the lower Little Dal Group (Turner and Long, 2008).

3.1.5. Economic potential of the Mackenzie Mountains supergroup Base-metal showings are present in several of the carbonate units in the Mackenzie Mountains supergroup. Such showings include major Zn-Pb deposits hosted predominantly by the Grainstone formation at Gayna River (NTS 106B; subordinate showings in reefs and lime mudstone of the Basinal assemblage), minor Zn-Pb showings in the Basinal assemblage and Grainstone formation in the Sekwi project area, and Cu showings in the Upper Carbonate formation (see Chapter 7 and Appendix H for details). Most or the entire Mackenzie Mountains supergroup is overmature with respect to hydrocarbon generation (Table 3.1.5-1), and it does not represent a viable hydrocarbon exploration target, even where buried by the Plateau fault. Analysis of 48 samples from the lower part of the supergroup indicates a maximum preserved TOC of 0.52%, in the grey member of the Tsezotene Formation. Average values for individual units are 0.22% to 0.06%. Tmax values range from 202 to 502° C, with an average of 406° C. See Appendix G for details.

3.1.6. Conclusions A major advance that resulted in part from Sekwi project initiatives is a new appreciation of the tectonostratigraphic dynamics of the basin in which the MMSG accumulated. Turner and Long (2008) demonstrated that although eustasy was the

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Figure 3.1.4-35. Simplified stratigraphic section for Rusty Shale formation showing 5 members, at Twitya River (section 08-ECT-TR; NTS 106A; approximately 527100E, 7109100N).

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Chapter Three

Figure 3.1.4-36. Rusty Shale formation exposure at Section 08-ECT-TR, where the formation is approximately 200 m thick. NTS 106A; approximately 527100E, 7109100N.

Unit

Thickness & erosional profile

Description

UC1

~50 m; resistant

2-15 m cycles of stromatolites/oolite/intraclast grainstone, molar-tooth carbonate, black shale & laminated, desiccation-cracked dolostone or domal stromatolites

UC2

~50 m; recessive

Rhythmically bedded oolite, Baicalia bioherms and argillaceous dolostone

UC3

~50 m; resistant

Baicalia, Boxonia and Collenella biostromes

UC4

~50 m; resistant

Partly silicified domal stromatolites and Gymnosolen biostromes

UC5

~50 m; recessive

Basal glauconitic oncolite marker; shaly orange dolostone with grey limestone nodules grading up to black, calcareous shale

UC6

~50 m; resistant

Massive, vuggy, grey dolostone; most prominent cliff-maker in the formation

UC7

~10 m; recessive

Buff dolostone containing broad columnar stromatolites; minor shaly limestone

UC8

~10 m; resistant

Orange dolostone with grey limestone nodules

UC9

~10 m; resistant

Gymnosolen and Boxonia biostromes

UC10

~10 m; resistant

Buff-pink dolostone containing partly silicified Acaciella; desiccationcracked red and green shale

UC11

~10 m; recessive

Buff-grey biostromal dolostone with Gymnosolen, oolite and calcareous shale

UC12

~10 m; recessive

Inzeria biostrome

Table 3.1.4-1. Lithostatigraphic composition of the Upper Carbonate formation (from Jefferson, 1983).

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74

Figure 3.1.4-37. At Nidhe Brook, 4.5 m of red and green siltstone and mudstone separate evaporite rocks of the upper Gypsum formation and dolostone typical of the lower Rusty Shale formation. Section 08-ECT-NB; NTS 95M; approximately 552800E, 7093500. Hammer for scale.

Figure 3.1.4-40. Typical exposure of lower siltstone/shale member of Rusty Shale formation at Section 08-ECT-TR (NTS 106A; approximately 527100E, 7109100N). Hammer for scale.

Figure 3.1.4-38. Mechanical lamination and slight silicification in lower carbonate member, Rusty Shale formation at section 08-ECT-TR (NTS 106A; approximately 527100E, 7109100N).

Figure 3.1.4-41. Synaeresis and desiccation cracks are common in lower siltstone/shale member, Rusty Shale formation at Section 08-ECT-TR. NTS 106A; approximately 527100E, 7109100N. Hammer tip for scale.

Figure 3.1.4-39. Baicalia in lower siltstone/shale member, Rusty Shale formation at Section 08-ECT-TR. NTS 106A; approximately 527100E, 7109100N.

Figure 3.1.4-42. Cross-bedded quartz arenite with shale chips in Sandstone member of Rusty Shale formation at Section 08-ECT-TR (NTS 106A; approximately 527100E, 7109100N).

Chapter Three predominant control on the disposition of paleoenvironments and lithofacies, striking changes in thickness and lithofacies are present in strike-parallel correlation panels. The MMSG basin can no longer be seen as a simple passive margin in an epicratonic sag basin, but instead was characterised by pronounced subbasins with striking facies and thickness variability associated with bathymetric changes imposed by synsedimentary fault displacement. A further considerable advance has been the collection of stratigraphic descriptions for units that were previously next to unknown (the “H1 unit” and the Gypsum formation of the Little Dal Group). The overall configuration of this early Neoproterozoic epicratonic basin remains poorly constrained: although its eastern margin, preserved as the MMSG in the Northwest Territories, is now adequately described, it is uncertain how these units correlate to putative equivalents in the Yukon (Wernecke Mountains, Hart River Inlier, and Coal Creek Inlier; Rainbird et al., 1996a; Long et al., 2008). Investigation of the northwestern-most exposures of the MMSG in the vicinity of the Northwest Territories-Yukon border as well as of other proposed equivalents in the Yukon may shed light on (a) the nature of the basin farther west; (b) proposed correlations with the Shaler Supergroup of the northern Canadian mainland and Victoria Island, and (c) intercontinental correlation with Neoproterozoic units that may have been contiguous with the MMSG basin at the time of deposition.

Figure 3.1.4-43. Columnar stromatolites with inter-column cortoids in unit upper carbonate member of Rusty Shale formation at Section 08-ECT-TR (NTS 106A; approximately 527100E, 7109100N). Pencil for scale.

Figure 3.1.4-44. Lower part of the Upper Carbonate formation, south of Boomerang Lake in northwestern NTS 95M [approximately 576400E, 7073800N; near section 55 of Jefferson (1983)].

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Chapter Three

Min Tmax

n

Little Dal Gp.

0.06

0.6

0.06

436

Unit K7

0.06

0.15

0.01

434

489

325

3

Unit K6

0.14

0.37

0.05

470

502

391

7

Unit K5

0.22

0.43

0.13

417

498

337

4

Unit K3

0.14

0.41

0.01

405

453

335

8

Tz red

0.06

0.21

0.01

339

491

302

13

Tz grey

0.21

0.52

0.07

360

439

302

11

Table 3.1.5-1. Organic carbon data for Mackenzie Mountains supergroup.Ave = average. n = number of samples. See also Appendix G.

76

Max Tmax

Ave Tmax

Min TOC

Max TOC

UNIT

Ave TOC

Figure 3.1.4-45. Upper part of the Upper Carbonate formation south of Boomerang Lake. Same general location as Figure 3.1.4-44.

1

Chapter Three

Figure 3.1.4-46. Intraclast dolofloatstone at gradational contact between Rusty Shale formation and basal Upper Carbonate formation at Section 08-ECT-TR (NTS 106A; approximately 527100E, 7109100N). Figure 3.1.4-49. Diagenetically altered molar-tooth structure from unit UC2 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-47. Cement-rich stromatolites with unusual morphology, from dolostone of unit UC1. South of Boomerang Lake, same general location as Figure 3.1.4-44.

Figure 3.1.4-50 Typical banded dolostone of unit UC2 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-48. Banded, graded dolostone tempestites of unit UC1 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-51. Partly silicified intraclast dolofloatstone from unit UC2 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

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Figure 3.1.4-52. Graded intraclast tempestites from dolostone unit UC3 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-53. Columnar stromatolites typical of dolostone unit UC3 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-54. Partly silicified, mechanically laminated dolostone from unit UC3 of Jefferson (1983). Same general location as Figure 3.1.4-44.

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Figure 3.1.4-55 Lime mudstone lenses in dolostone form a distinctive lithofacies of unit UC5 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-56 Vuggy grey dolostone typical of unit UC6 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-57 Columnar stromatolites in dolostone unit UC7 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Chapter Three

3.2. Middle Neoproterozoic Volcanic Succession - “Little Dal Basalt” E.C. Turner

Figure 3.1.4-58. Lime mudstone lenses in dolostone are typical of unit UC8 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-59. Thin terrigenous mudstone units are present in the Upper Carbonate formation, but seldom are well exposed. This one is at the base of unit UC9 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

A thin, discontinuous succession of volcanic rocks separating the Little Dal and Coates Lake groups was first noted by Gabrielse et al. (1973a), and has been informally termed the “Little Dal basalt”. This volcanic unit represents the initiation of the “Hayhook extensional event” (Young et al., 1979), and is considered by some to be the first record in the northern Cordillera of incipient, episodic rifting of the supercontinent Rodinia (Heaman et al., 1992; Harlan et al., 2003), although there are other views of this early rifting (e.g., Li et al., 2008). This unit is accepted by many as the basal unit of the Windermere Supergroup in the Mackenzie Mountains, but see Jefferson (1983), Jefferson and Parrish (1989) and Colpron et al. (2002) for other views. As the early stratigraphic understanding of the Neoproterozoic in the Mackenzie Mountains progressed, this unit was included in several different established stratigraphic entities. Some considered it part of the Redstone River Formation (prior to the identification of the Thundercloud Formation; Gabrielse et al., 1973a; Ruelle, 1982; Armstrong et al., 1982). Aitken (1981) recognised the existence of a basal mixed terrigenouscarbonate unit in the Coates Lake Group (later named the Thundercloud Formation; Jefferson, 1983), and, attributing the influx of terrigenous material and onset of basaltic volcanism to a common tectonic cause, assigned the basalt to the (eventual) Coates Lake Group. This configuration was contested on the basis of conspicuous weathering features at the top of the basalt (Jefferson, 1983), interpreted to represent a significant unconformity. In this view, the basalt would be best assigned to the Mackenzie Mountains supergroup, and was designated the uppermost member (UC13) of the Upper Carbonate formation of the Little Dal Group. Given that no direct geochronological data are available to demonstrate an affinity to either the MMSG or the Coates Lake Group, this chapter treats the “Little Dal basalt” as an independent entity. The unit has not been established formally, nor a type section designated. The basalt is discontinuously distributed over ~100 km of strike length, as a conspicuous black ridge in the hangingwalls of the Plateau and Thundercloud faults. There are three areas in which the basalt is extensive and well exposed: in the Thundercloud Ranges (NTS 95L; south of the Sekwi project area; Fig. 3.2.1-1), near Dal Lake (southeastern NTS 95M) and in the Keele River area (northwestern NTS 95M; within the Sekwi project area; Fig. 3.2.1-2). It is unclear whether the basalt is absent beyond these areas as a function of its original distribution, later erosion, or both. Although the preserved thickness and areal extent of the basalt are small, Dudas and Lustwerk (1997) pointed out that large volumes of basaltic detritus in the overlying Coates Lake and Rapitan groups suggest that extensive erosion through the late Neoproterozoic could have redistributed much of the basalt’s original volume. These rocks were not examined in detail for the Sekwi project; the descriptions and interpretations below are predominantly from previous work (Jefferson, 1983; Jefferson and Parrish, 1989; Dudas and Lustwerk, 1997).

Figure 3.1.4-60. Columnar stromatolites from dolostone unit UC10 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

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Chapter Three

Figure 3.1.4-61. Partly silicified branching columnar stromatolites from dolostone unit UC12 of Jefferson (1983). Same general location as Figure 3.1.4-44. Hammer for scale.

Figure 3.1.4-62. Mechanically laminated dolostone from unit UC12 from 4 metres below the contact with the “Little Dal basalt”. Same general location as Figure 3.1.444. Hammer for scale.

Figure 3.1.4-63. Contact of Upper Carbonate formation with “Little Dal basalt”; note subtle angularity of contact relationship. Same general location as Figure 3.1.4-44. Base of basalt – black dotted line; layering in Upper Carbonate formation = white dotted lines. The basalt is ~30 m thick at this location.

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Chapter Three

3.2.1. Description Jefferson (1983) measured detailed sections through the basalt at numerous locations. In the Thundercloud Range (Fig. 3.2.11), where the basalt reaches its maximum thickness of 92 m, he reported nine flows with thicknesses of 1 to 26 m; in the area east of Keele River (in northwestern NTS 95M; in Sekwi project area; Fig. 3.2.1-2), the basalt succession is considerably thinner (~30 m), with individual flows up to 12 m thick. The nature of the basal contact of the “Little Dal basalt” (Figs. 3.2.1-1 to -3) is contentious. Aitken (1981) described the basal contact with underlying dolostone of the Upper Carbonate formation (Little Dal Group) as conformable, and described characteristics that suggest that the lava had been extruded onto wet sediment. Jefferson (1983) also described the basal contact as conformable, and noted that its position is no lower than the uppermost carbonate unit in the Upper Carbonate formation (UC12). Outcrop-scale examination during Sekwi project traverses, however, indicates that the contact is at least locally subtly angular and clearly unconformable (Figs. 3.1.4-63 and 3.2.1-2). Reddened clasts of the underlying carbonate are present in the lowest 3 m of the basal, amygdaloidal flows (Figs. 3.2.1-4 and -5), and greater vesicularity is not evident in the vicinity of carbonate

Figure 3.2.1-1. The “Little Dal basalt” expresses its maximum known thickness (92 m) on the west flank of the Thundercloud Range (NTS 95L; approximately 634672E, 6922851 N), in the steeply dipping hanging-wall of the Thundercloud Fault, near sections 1 and 2 of Jefferson (1983). View to east.

Figure 3.2.1-2. The basal contact of the “Little Dal basalt” is subtly erosional at this section south of Boomerang Lake (NTS 95M; 576713E, 7074441N), near section 55 of Jefferson (1983).View to south.

surfaces, as would be expected if they had been partly digested, waterlogged, unlithified carbonate sediment at the time of basalt deposition. The upper surface of the basalt is described as an erosional unconformity characterised by oxidation, jasper-filled fractures extending down into the basalt, and a detrital lag (basal Thundercloud Formation) containing jasper pebbles (Fig. 3.2.1-6) and heavymineral concentrates (Jefferson, 1983; Jefferson and Parrish, 1989). The oldest unit to overlie the weathered unconformity surface is the Thundercloud Formation of the Coates Lake Group. As described by Jefferson (1983) and Dudas and Lustwerk (1997), the basalt is very dark grey or green, and locally buffand red-weathering. The rocks are subophitic, plagioclase- and clinopyroxene-phyric, lack olivine or orthopyroxene, contain traces of volcanic glass, and are locally amygdaloidal. Primary iron-titanium oxides with dendritic textures are locally replaced by hematite and titanite. Plagioclase is predominantly albitic. A range of alteration minerals is present, and amygdules are filled with calcite, chlorite and chalcedony. Pillows and breccias are locally present. No feeder structures for the basalt flows have been documented. Geochemical analysis indicates a tholeiitic basalt composition (Dudas and Lustwerk, 1997). Two petrogenetic lineages have been identified: these may represent different degrees of partial melting in the source rock, and cannot represent different degrees of fractional crystallisation. The two lineages dominate separate geographic areas, one in the Thundercloud Range, and the other in the Keele River area. Each lineage, however, exhibits geochemical variation that is probably a function of fractional crystallisation. The amount of fractionation decreases upward stratigraphically. Paleomagnetic work on “Little Dal basalt” from the Thundercloud and Keele River areas was reported by Morris and Aitken (1982). Magnetic remanence patterns for the two locations do not concur, and coherent results were obtained only from the Keele River material, where results define a stratigraphically lower, unweathered part, and an upper, extensively weathered part. According to Morris and Aitken (1982), magnetism associated with the basalt is significantly different from that reported from strata in the Basinal assemblage of the lower Little Dal Group (Park, 1981), indicating either that the basalt is significantly younger than the Little Dal rocks, or that significant plate movement took place between deposition of the two. Remanence directions from the basalt also differ from those for the Tsezotene sills, suggesting that the basalt may not be coeval with and related to them (Morris and Aitken, 1982).

Figure 3.2.1-3. Basal contact of “Little Dal basalt” south of Boomerang Lake in northwest NTS 95M. Same approximate location as Figure 3.2.1-2.

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Chapter Three

Figure 3.2.1-4. Basal few centimetres of the “Little Dal basalt” (immediately left of hammer head) contain angular, pebble-sized carbonate clasts in steeply dipping hangingwall of Thundercloud Fault (NTS 95L). Same location as Figure 3.2.1-1; view to north.

Figure 3.2.1-6. Thin basal lag of Thundercloud unit 1 consists of jasper and basalt pebbles in a volcanic clastic matrix. Same approximate location as Figure 3.2.1-2. Hammer shaft for scale.

connection between them can be demonstrated. Two sills were dated at 766±24 and 769 ±27 Ma (Rb-Sr; Armstrong et al., 1982), and a quartz diorite intrusion presumed to be related to them at 777.7 +2.5/-1.8 Ma (U-Pb zircon; Jefferson and Parrish, 1989). More recent dating of the gabbro sills has yielded a date of ~779.5 ±2.3 Ma (Pb-Pb baddeleyite; Harlan et al., 2003). These bodies belong to the newly identified, regional Gunbarrel igneous event of western North America (Harlan et al., 2003). Park and Jefferson (1991) reported similar paleomagnetic poles for the basal Thundercloud Formation and Tsezotene sills, indicating that they were roughly coeval, which further strengthens the probable ~780 Ma age for the basalt, and suggests that depositional ages of the basalt and overlying Thundercloud Formation may be similar. Given the probable ~780 Ma depositional age for the basalt, resolution of the conflict over its temporal and tectonic relationship with overlying and underlying units may be most satisfactorily achieved if both it and the sub- and superjacent units can be directly dated.

3.2.3. Interpretation

Figure 3.2.1-5. Basal 3 metres of the “Little Dal basalt” [contact with Upper Carbonate formation (Little Dal Group) is at base of photo] contain reddened, irregular, partly digested carbonate clasts. South of Boomerang Lake (NTS 95M), near section 55 of Jefferson (1983); same location as Fig. 3.2.1-1. Hammer for scale.

3.2.2. Age and correlation The “Little Dal basalt” has not been directly dated. Its majorelement geochemistry (Armstrong et al., 1982; Jefferson, 1983) favours a relationship with the Tsezotene sills (see Chapter 4.1), which intrude rocks low in the Mackenzie Mountains supergroup (~4 km below the basalt). Sills and basalt are exposed in distinct geographic areas separated by ≥75 km, and no direct physical

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Basalt was erupted into subaerial and subaqueous environments of an incipient intracratonic rift system that probably represented the earliest phase of intermittent, protracted middle to late Neoproterozoic rifting (Colpron et al., 2002). Its evolved, continental tholeiitic basalt composition is typical of intracratonic extension (Jefferson and Parrish, 1989; Dudas and Lustwerk, 1997). An upward decrease in fractionation probably indicates that with continued volcanic activity, less-evolved material became available. Post-depositional alteration, including oxidation, silicification and addition of carbonate, probably took place as a result of interaction with sinking brine from overlying Coates Lake Group basins (Dudas and Lustwerk, 1997). The major-element composition reported by Dudas and Lustwerk (1997) is highly modified from that of fresh continental flood basalt, showing an unusually high weight percent of Na2O (~4-5%). This type of high-temperature alteration (spilitisation) is common in hot basalt on the sea-floor. Albitisation of more anorthitic plagioclase probably took place as Na diffused out of glass and into plagioclase, where it replaced Ca. The fracture-filling jasper reported by Jefferson (1983) and Jefferson and Parrish (1989) is also probably the product of such early, high-temperature alteration. Given that the underlying two kilometres of strata are dominated by carbonate rocks, the silica for fracture-filling jasper and vesicle-

Chapter Three filling silicates was also probably liberated by comparatively hightemperature leaching of basaltic glass as the hot basalt pile bathed in convecting, locally derived fluid. Alteration by albitisation and jasper precipitation in fractures were probably high-temperature phenomena, rather than the products of protracted subaerial exposure and weathering. Subsequent weathering and erosion would be required, however, to liberate jasper clasts that then accumulated as a lag, and for hematitic alteration of basalt and its detritus. The amounts of time represented by the contacts at the base and top of the basalt are critical questions in resolving the tectonostratigraphic relationships of the volcanic unit with underlying and overlying strata, as well as their possible correlation into the Amundsen Basin (Victoria Island). Jefferson (1983) and Jefferson and Parrish (1989) argued that conspicuous weathering at the top of the basalt unit records a protracted interval of exposure that is compatible with interpretation of the surface as an unconformity; this argument would indicate that the basalt has a closer stratigraphic affinity with underlying carbonates of the Little Dal Group than with the overlying Coates Lake Group. The basal contact of the basalt is with carbonate rocks, which in general do not show conspicuous weathering evidence except under moist climatic conditions. Both the underlying Little Dal Group and overlying Coates Lake Group have thick evaporite units, attesting to a protracted interval of aridity during the early to midNeoproterozoic in this area. Carbonate rocks such as the Upper Carbonate formation of the Little Dal Group do not weather by oxidation or hydrolysis as basalt does; the only type of chemical weathering able to affect them significantly is dissolution by meteoric water. Significant meteoric diagenesis and karstification are not expected under an arid climatic regime such as that recorded by either the MMSG or the Coates Lake Group. Under such conditions, and particularly if no significant deformation or differential uplift took place, a brief depositional hiatus and a protracted one could leave similarly minimal evidence on a carbonate rock surface. In contrast, basalt weathers rapidly by oxidation even in arid settings. For example, pronounced weathering surfaces commonly develop on basalt flow-tops during geologically brief intervals between emplacement of successive flows. In a basalt, conspicuous weathering could, therefore, be the product of either trivial or protracted exposure, such that the two conditions could be indistinguishable from one another in the rock record. This argument suggests that the nature of weathered surfaces does not necessarily reflect exposure duration, and cannot help to resolve the temporal relationships in question here, particularly given that the two weathered surfaces concerned (basal and upper contacts of the basalt) developed on completely different rock types. Furthermore, no information is available regarding the state of weathering on the upper surfaces of the successive flows that constitute the “Little Dal basalt”, and so it is unclear whether the upward increase in weathering through the entire unit reported by Dudas and Lustwerk (1997) is the product of decreased volcanism through the upper part of the succession (i.e., greater opportunity for inter-flow weathering) or of weathering that entirely post-dated volcanic activity.

3.2.4. Economic potential The “Little Dal basalt” is of economic relevance in that it is almost certainly the source of copper for the deposits of the Redstone copper belt, which is hosted by the immediately overlying Coates Lake Group. Although copper minerals are not abundant or concentrated in the basalt, it is thought that copper liberated during hematisation of the high-Fe basalt or its detritus in overlying red-beds in the shallow subsurface was transported by brines and

then reduced at the host horizon at the base of the Coppercap Formation (Ruelle, 1982; Chartrand and Brown, 1985; Lustwerk and Wasserman, 1986; Jefferson and Ruelle, 1987; Chartrand et al., 1989). The basalt is present only locally along the length of the Coates Lake Group’s exposure, and copper mineralisation in the Coppercap Formation seems to be limited to the general vicinity of areas where the basalt is known to be present today. If this association is valid, this would imply that the present-day distribution of the basalt is roughly the same as its distribution during Coates Lake Group deposition, and that no significant erosional removal of basalt took place after the sub-Coates Lake hiatus. In addition to mineralisation in Coates Lake Group strata, fracture-hosted copper showings are also present in the Upper Carbonate formation of the underlying Little Dal Group and in the overlying Sayunei Formation (Rapitan Group) in the vicinity of the basalt.

3.2.5. Conclusions Numerous questions remain regarding the nature, age, and stratigraphic relationships of the “Little Dal basalt”. Foremost among these are: (1) its age, which remains to be validated directly; (2) its temporal and tectonostratigraphic relations with immediately sub- and superjacent units; (3) how (1) and (2) will affect correlation of the upper Shaler Supergroup in Amundsen Basin with Little Dal and Coates Lake groups, as well as contribute to inter-continental correlations; and (4) the detailed evolution of basalt flows and their alteration history.

3.3. Middle to Late Neoproterozoic Extension- and Rift-Related Successions - Windermere Supergroup 3.3.1. Coates Lake Group E.C. Turner The middle Neoproterozoic Coates Lake Group represents the base of the Windermere Supergroup (Fig. 3.3.1-1). Strata of the Coates Lake Group are exposed only in the hanging wall of the Plateau and Thundercloud faults and in subsidiary footwall structures, along a strike length of approximately 300 km that spans the Sekwi project area. The Coates Lake Group was deposited in rift basins and consists of three units: the Thundercloud Formation, the Redstone River Formation and the Coppercap Formation (Fig. 3.3.1-2). The Coppercap Formation hosts red-bed copper of the Redstone copper belt (~37 Mt at ~4% Cu; Eisbacher, 1977; Helmstaedt et al., 1979; Ruelle, 1982; Chartrand and Brown, 1985; Lustwerk and Wasserman, 1986; Jefferson and Ruelle, 1987; Chartrand et al., 1989). The group unconformably overlies the early Neoproterozoic Little Dal Group, or locally the “Little Dal basalt”, and is unconformably overlain by the middle Neoproterozoic Rapitan Group or other, still younger units. The Coates Lake Group was deposited in a series of embayments that formed as grabens and half-grabens during the “Hayhook extensional event” (Young et al., 1979; Young, 1995). The 20 to 60 km-wide embayments are preserved in the hanging wall and footwall of the Plateau fault. Each sub-basin deepened centripetally near its margins, and the system deepened to the west overall. The initial fill of the embayments was a heterolithic succession (shale, carbonate rocks, sandstone and evaporite rocks of the Thundercloud

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Chapter Three Formation) that displays pronounced variation in lithofacies and thickness over short lateral distances. This succession is overlain by evaporite rocks, red terrigenous mudrocks, conglomerates and minor carbonate rocks of the Redstone River Formation, which has pronounced lateral variability in lithofacies and thickness patterns. The upper Coates Lake Group is represented by a suite of unusual carbonate lithofacies belonging to the Coppercap Formation; this unit expresses more uniform lithofacies and thickness patterns than do the underlying two formations. Nothing is known of the subsurface distribution of the Coates Lake Group west of its surface exposures along the Plateau fault, but it is interpreted to dip shallowly to the southwest parallel to the interpreted subsurface trace of the Plateau fault, as shown on accompanying cross-sections (NWT Open File 2010-18; Fig. 9-1). The basins were at comparatively low paleolatitude (Park and Jefferson, 1991) as indicated by their conspicuous evaporite content. The Coates Lake Group was first recognised by Gabrielse et al. (1973a) at which time only the Redstone River and Coppercap formations were identified. These strata were termed the “copper cycle” by Aitken (1981), at which time it became clear that mixed terrigenous and carbonate units overlying the Upper Carbonate formation of the Little Dal Group (to which they had originally been assigned), bore greater lithostratigraphic affinity to overlying rather than underlying units, and deserved to be identified as the basal unit in the “copper cycle”. This basal unit eventually came to be known as the Thundercloud Formation (Jefferson, 1983; Jefferson and Ruelle, 1987). The group was formalised and named after Coates Lake (the former Little Dal Lake) in NTS 95L (Jefferson, 1983), and its constituent units described in detail by Jefferson (1983), Jefferson and Ruelle (1987) and Jefferson and Parrish (1989), from which publications most of the descriptions below are summarised. Some authors included the Coates Lake Group in the Mackenzie Mountains supergroup (Jefferson, 1983; Jefferson and Ruelle, 1987). This view was based on the similarity in isopach patterns between the Coates Lake Group and the Upper Carbonate formation of the Little Dal Group, and the poor development of relief along the subtle, basal unconformity. Other workers, considering the Coates Lake Group’s distinctly extension-related nature, thought it exhibited closer tectonostratigraphic affinity to the rift-related, overlying Windermere Supergroup (Aitken, 1981; Morris and Aitken, 1982; Park and Aitken, 1986a; Ross, 1991; Narbonne et al., 1994; Narbonne and Aitken, 1995; Thorkelson et al., 2005; Long et al., 2008). Uncertainty remains over the tectonostratigraphic and temporal relations of the Coates Lake Group with the underlying Little Dal Group and “Little Dal basalt”, and with the overlying Rapitan Group. The maximum depositional age of the Coates Lake Group is 780 Ma, as delimited by a U-Pb date for the Tsezotene sills (see Chapter 4.1) and a related quartz diorite intrusion in the underlying Mackenzie Mountains supergroup (Jefferson and Parrish, 1989; Heaman et al., 1992; Harlan et al., 2003). These intrusive bodies belong to the Gunbarrel igneous province (Harlan et al., 2003) and are presumed to be contemporaneous with and related to an undated extrusive unit known as the “Little Dal basalt” (Chapter 3.2), which lies between the Little Dal Group and the Coates Lake Group. A minimum depositional age for the Coates Lake Group is indirectly provided by the age of Franklin dykes and sills (U-Pb zircon ~723 Ma, Heaman et al., 1992; U-Pb zircon, ~716 Ma; Macdonald et al., 2010), which have a paleomagnetic pole (and inferred age) similar to that from an iron-formation in the Sayunei Formation (Park, 1997), which overlies the Coates Lake Group. The age of a tuff interbedded with glacial deposits that are tentatively correlated with the lower Rapitan Group is ~716 Ma (U-Pb zircon;

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Figure 3.3.1-1. Summary of group and formation nomenclature for the Windermere Supergroup in the Sekwi Project study area. Large black arrow indicates position of “Tepee dolostone” map unit.

upper Mount Harper Group, western Yukon; Macdonald et al., 2010). If correlation of the Rapitan Group and the upper Mount Harper Group is validated, the minimum depositional age of the Coates Lake Group would be ~716 Ma. The Coates Lake Group was deposited on an eroded and faulted surface atop Little Dal Group carbonate rocks. The “Hayhook extensional event” (Young et al., 1979; Young, 1995), is the term used to encompass extension that post-dated deposition of sequence B strata, but pre-dated rifting associated with deposition of the upper Windermere Supergroup. Localised flood basalt (“Little Dal basalt”, of uncertain age and stratigraphic affinity; Chapter 3.2) probably marks the onset of extension. The basalt is apparently preserved only in the southern part of the exposure belt (south of Twitya River), reflecting either its original extent or its erosional limit, or a combination of both. The basal contact with the underlying Upper Carbonate formation of the Little Dal Group (Aitken, 1981) is described by Jefferson and Parrish (1989) as a very low-angle unconformity that truncates no more than the uppermost 6 (discounting the basalt) members of the Upper Carbonate formation, producing a maximum of 160 m of relief (including possible erosional removal of any basalt). The presence of an unconformity between the Little Dal and Coates Lake groups has been documented paleomagnetically (Morris and Aitken, 1982), but the lack of significant relief along the unconformity led Jefferson and Parrish (1989) to conclude that the exposure interval was probably brief.

Chapter Three

Figure 3.3.1-2. Generalised stratigraphy of the Coates Lake Group, with paleoenvironmental interpretations. The units depicted in each formation are not always present, nor necessarily in the order indicated. Thundercloud and Redstone River formations have pronounced lateral thickness changes.

West of the Sekwi project area, in Yukon (NTS 106C), Eisbacher (1981) and Thorkelson (2000) described thrust and reverse faults, inclined to overturned folds, and later west-trending normal faults, all affecting strata equivalent to and older than the Mackenzie Mountains supergroup, but not the overlying Rapitan Group. A conspicuous, angular unconformity marks the base of the Windermere Supergroup in that area, in contrast to the apparent subtlety of the unconformity in the Mackenzie Mountains. The contractional event, termed the Corn Creek Orogeny (Thorkelson, 2000; Thorkelson et al., 2005), may have taken place during deposition of the Coates Lake Group in the Mackenzie Mountains, or during the hiatuses that separate it from the underlying Little Dal Group or overlying Rapitan Group. This suggests that the unconformity between the Mackenzie Mountains supergroup and the Windermere Supergroup may represent a lengthier and more tectonically active interval than has hitherto been assumed. It is unclear whether the contractional Corn Creek orogeny in the Wernecke Mountains predates, coincides with, or postdates the “Hayhook extensional event” in the Mackenzie Mountains, but the cross-cutting normal faults in the Wernecke Mountains indicates that extension followed contraction in the Yukon. In addition to problems associated with the structural and stratigraphic differences between these areas, understanding the geological evolution of the northern Cordillera after deposition of sequence B is confounded by a lack of geochronological control on the main stratigraphic units. The Coates Lake Group exhibits strong evidence of syndepositional extension (Eisbacher, 1981; Jefferson, 1983; Jefferson and Parrish, 1989). The group is preserved in a series of half-grabens exposed along the length of the Plateau fault. Consequently, the strata (especially the lower two formations) are discontinuously exposed and show great variability in thickness (Fig. 3.3.1-3), lithofacies and paleocurrent directions. Some of the halfgrabens are separated by narrow horsts, whereas others appear to be separated by a single fault that experienced marked subsidence on one side but gradual rotation on the other. This configuration is indicated by half-graben stratigraphy with marked asymmetry:

generally abrupt southern embayment margins reflect north-down subsidence on faults separating grabens, but northern graben regions pinch out, recording a hinge-like behaviour on the south side of faults. The half-grabens also experienced internal displacement on subsidiary faults throughout their depositional histories, which strongly affected lithofacies distribution and unit thicknesses. In the Sekwi project area, embayments corresponding to the rift half-grabens are, from north to south, the Mountain River, Hay Creek, and Keele River embayments (Fig. 3.3.1-4). Coates Lake Group strata are not known to be exposed northwest of the Mountain River Embayment (i.e., northwest of approximately 64°45’N, 130°W), but continue south of the Sekwi project area into the heart of the Redstone copper belt in NTS 95L. In NTS 106A (Hay Creek and Mountain River embayments), Coates Lake Group exposures are divided into western (in Plateau fault hanging-wall; Figs. 3.3.1-5, -6, and -8) and eastern (in hanging-wall of a subsidiary fault; Fig. 3.3.1-7) panels that expose graben-centre and grabenmargin strata, respectively, permitting limited reconstruction of graben configuration across strike (Figs. 3.3.1-9 and -10). It has been suggested that the Plateau fault, which separates these two paleogeographic zones, may have been a major Proterozoic normal fault that defined the eastern part of the graben systems (Jefferson and Parrish, 1989). The Plateau fault is of unknown but probably small Mesozoic-Tertiary displacement (at most several tens of kilometres), suggesting that the graben margins and centres were not separated by great distances at the time of deposition. The Coates Lake Group has been loosely correlated with the Kilian Formation of the Shaler Supergroup (Amundsen Basin; Rainbird, 1991; Rainbird et al., 1996a), but this suggestion remains to be tested with geochronological, chemostratigraphic and sequence-stratigraphic data (Long et al., 2008). In contrast to the Mackenzie Mountains supergroup - “Little Dal basalt” - Coates Lake Group succession, the upper part of the Shaler Supergroup is not known to contain any significant hiatus, and such a correlation, if validated, might suggest important differences in basin evolution between the two areas.

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Chapter Three

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The Coates Lake Group is economically important because it hosts the Redstone copper belt (Eisbacher, 1977; Helmstaedt et al., 1979; Ruelle, 1982; Chartrand and Brown, 1985; Lustwerk and Wasserman, 1986; Jefferson and Ruelle, 1987; Chartrand et al., 1989). Copper is concentrated in lower CP1 (the stratigraphic “transition zone” between Redstone River and Coppercap formations), but is also present as fracture-controlled concentrations higher in the Coppercap Formation stratigraphy, in carbonates of the Thundercloud Formation, and locally in the lower Rapitan Group. Although the stratigraphic, lithologic, diagenetic and geochemical controls on deposits in the Coates Lake area have been outlined, much remains to be understood at all levels, and the deposits in the Keele River area remain poorly known. Temporal relationships with the underlying “Little Dal basalt” as well as possible correlative relationships with the upper Shaler Supergroup in the Amundsen Basin, Victoria Islands remain to be confirmed. Study of the unusual carbonate lithofacies and geochemistry of the Coppercap Formation could provide greater insight into the controls on copper distribution, and into the nature of the unusual basins and water chemistry in which the upper Coates Lake Group was deposited. For the Sekwi project, three formal sections were measured. Section 07-ECT-HC (Appendix C) was measured through the Thundercloud Formation east of Hay Creek, in southern NTS 106A (Hay Creek Embayment). Section 2008-J113 (Appendix C) was measured through Redstone River and lower Coppercap formations east of Stone Knife River, in the western panel (hangingwall of Plateau fault) in northwestern NTS 106A (Mountain River Embayment). Section 08-ECT-RS (Appendix C) was measured through the Thundercloud and Coppercap formations east of Stone Knife River in the eastern (footwall) panel, Ten Stone Range, NTS 106A, Mountain River Embayment. Numerous other sections were examined in detail. The reader is referred to the descriptions and figures of Jefferson (1983) for greater stratigraphic detail.

TH1 (0-40 m) consists of siliciclastic rocks that disconformably overlie the “Little Dal basalt” or Upper Carbonate formation of the Little Dal Group, have extreme lateral thickness variability, and consist of two facies: laterally discontinuous volcanic detritus and laterally discontinuous hematitic chert conglomerate. It has significant thickness only where it overlies basalt, and is represented by a lag deposit elsewhere. This unit is, therefore, not generally present in NTS 106A (where the “Little Dal basalt” is absent), but it is locally present in NTS 95M. TH2 (0-250 m) is the most conspicuous and consistent of Thundercloud Formation units (Figs. 3.3.1-11 to -15). This lithofacies consists of maroon (locally buff, green or grey) mudstone and buff dolostone that are collectively 100 m; Fig. 3.3.1-19; Section 07-ECT-HC: Appendix C) in the western exposure panel, depending on location relative to embayment limits, but are generally thin to absent in the eastern panel (Figs. 3.3.1-10 and -20; Appendix C). Minor Cu occurrences are known from this unit in the Sekwi project area.

Thundercloud Formation The Thundercloud Formation (0 to >300 m; Jefferson, 1983; Jefferson and Ruelle, 1987) consists of terrigenous clastic and carbonate strata that are present at the base of the Coates Lake Group in some localities. This unit was originally considered to be part of the Upper Carbonate formation of the Little Dal Group (Aitken, 1977). The type section is south of the Sekwi project area in the Thundercloud Ranges (62°24’N, 126°21’W; NTS 95L), and a reference section is designated in the Keele River area (63°47’N, 127°27’W; Jefferson, 1983; Jefferson and Ruelle, 1987). For the Sekwi project, one detailed section covered the Thundercloud Formation where it is thick in the western panel of the Hay Creek Embayment (07-ECT-HC; Appendix C).

The depositional age of the Thundercloud Formation may be indirectly inferred by paleomagnetic data that indicate similar primary paleopoles for both it and the Tsezotene sills (Park and Jefferson, 1991); the latter have been dated at ~780 Ma (Harlan et al., 2003) and have an inferred relationship with the “Little Dal basalt”, which immediately underlies the Thundercloud Formation. These relationships suggest that the depositional age of the Thundercloud Formation is similar to that of the basalt, and could also imply a related tectonic origin for the two. The Thundercloud Formation is a geographically constrained unit whose distribution is controlled by the presence of rift-related scarps, and so it is not known to have any direct correlatives in the Canadian Cordillera, or in the mainland or Arctic Islands to the northeast.

Description

Interpretation

The basal, unconformable contact of the Thundercloud Formation is at the upper, weathered surface of the “Little Dal basalt”, or at an abrupt contact with dolostone of the Upper Carbonate formation (Little Dal Group; Fig. 3.3.1-8). The upper contact with the Redstone River Formation is variously described as conformable (Jefferson, 1983) to unconformable (Eisbacher, 1978b). Jefferson (1983) divided the Thundercloud Formation into four lithofacies assemblages (TH1 to 4) that represent local paleoenvironments that both grade laterally to one another and succeed one another vertically, generally (but not always) in stratigraphic order as numbered.

Conglomeratic and arenitic facies of the Thundercloud Formation record the deposition of alluvial fans in the vicinity of newly formed graben margins. Localised, volcanic clastic facies TH1 was sourced by erosion of “Little Dal basalt” from elevated fault blocks in areas south of 64°N, whereas chert-clast-dominated TH1 accumulated through weathering of underlying cherty carbonates (Little Dal Group) in areas where basalt was absent. Localised accumulation of this coarse material was followed by more widespread deposition of medium to fine clastic material of the remaining subaerial (terrigenous) to subaqueous (carbonate) Thundercloud Formation (TH2) units in shallowly flooded,

Age and correlation

Chapter Three

Figure 3.3.1-3. Sedimentary geometry of half-graben fills of the Hay Creek and Mountain River embayments (NTS 106A). Colours as in Fig. 3.3.1-1. Pink toothed line indicates separation of basin-ward facies exposed in hanging-wall of Plateau fault (above) and marginal facies exposed east of the Plateau fault (below). After Jefferson, 1983.

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Chapter Three

Figure 3.3.1-4. Interpreted embayment configuration along the length of the Coates Lake Group’s exposure belt during deposition of the Redstone River Formation. After Jefferson and Ruelle (1987).

Figure 3.3.1-5. Coates Lake Group exposed in the hanging-wall of the Plateau fault (=western panel) in NTS 106A, between Mountain and Stone Knife rivers, approximately 473000E, 7163400N. View to southwest.

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Chapter Three

Figure 3.3.1-6. Coates Lake Group exposed in the hanging-wall of the Plateau fault (=western panel) in NTS 106A, immediately west of Stone Knife River (approximate location of section 117 of Jefferson (1983). Base of Thundercloud Formation is at approximately 465900E, 7167660N. View to northwest.

Figure 3.3.1-7. Coates Lake Group exposed in the footwall of the Plateau fault, in the Ten Stone Range, north of Abandoned Creek (NTS 106A). Thundercloud Formation is thin, and Redstone River Formation is absent. View to northwest. Abandoned Creek flows to the right (northeast) in the photo and creek junction in mid-ground is at approximately 507300E, 7144600N.

Figure 3.3.1-8. Basal contact of Thundercloud Formation with Upper Carbonate formation of Little Dal Group, east of Hay Creek (NTS 106A). Karst features are not evident at this surface. Section 07-ECT-HC (base at approximately 511000E, 7122100N), Appendix C.Abandoned Creek flows to the right (northeast) in the photo and creek junction in mid-ground is at approximately 507300E, 7144600N,

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Chapter Three

Figure 3.3.1-9. Exposure of Coates Lake Group strata in NTS 106A, showing western and eastern panels, and locations of Jefferson’s (1983) sections. After Jefferson (1983).

restricted embayments. Units TH2 and TH4 record interfingering of subaerial mudstones and subaqueous carbonate facies along broad, low-energy, sabkha-like coastal zones, locally interrupted by influxes of compositionally immature to mature sandy material (TH3) associated with beach or delta progradation.

Redstone River Formation The Redstone River Formation (Gabrielse et al., 1973a; Fig. 3.3.1-2) consists of evaporitic and fine clastic rocks; its thickness and lithofacies change dramatically along strike. The type section of the formation was established on the east flank of Coppercap Mountain, immediately east of Little Dal Lake (now Coates Lake) in NTS 95L. The Redstone River Formation evaporite unit is locally a décollement surface for the Plateau fault or its splays, in which locations ductile deformation has structurally enhanced or reduced the evaporite unit’s apparent thickness. One detailed section measured during the Sekwi project included evaporite-dominated rocks of the upper Redstone River Formation in the western panel of the Mountain River Embayment (08-ECT-J113; Appendix C).

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Description Jefferson (1981) divided the Redstone River Formation into five lithofacies assemblages (RR1 to RR5). Not all are present at any given locality, and they are commonly laterally equivalent to one another (Fig. 3.3.1-10). Lithostratigraphic descriptions indicate that basal units both overlie and are interfingered with Thundercloud Formation lithofacies: contacts are generally gradational in embayment centres, but more abrupt at their margins. The upper contact with the Coppercap Formation is gradational through an interbedded “transition interval”. RR1 (0 - >215 m) is an evaporite unit dominated by pink- to white-weathering gypsum with brecciated, red mudstone clasts and maroon mudstone interlayers (Figs. 3.3.1-21 to -23). Other evaporite minerals are also present, particularly in the Keele River area, where Na- and Mg-evaporite minerals such as glauberite, magnesite and talc dominate over Ca-sulphates (Ruelle, 1982), particularly in the lowest part of the succession. RR1 evaporites are gradational with underlying Thundercloud Formation carbonate rocks in embayment centres, but pinch out toward their margins. Evaporite rocks are overlain by any of the other Redstone River Formation lithofacies.

Chapter Three

Figure 3.3.1-10. Diagrammatic depiction of Coates Lake Group embayment fill from graben margin (right; equivalent to eastern panel of Coates Lake Group in NTS 106A) to graben centre (west; equivalent to western panel of Coates Lake Group in NTS 106A). After Jefferson (1983).

Figure 3.3.1-11. Graben-margin boulder conglomerate of Thundercloud Formation at contact with underlying Upper Carbonate formation, in eastern panel of Coates Lake exposures (footwall of Plateau fault). Ten Stone Range, immediately east of Mountain River (approximately 64°33’N/129°14’W). Marker for scale is 15 cm long.

Figure 3.3.1-12. Dolostone of Thundercloud Formation (TH2), in eastern panel of Coates Lake Group exposures in Ten Stone Range, east of Stone Knife River in NTS 106A (approximately 477700E, 7169500N).

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Figure 3.3.1-13. Interlayered red mudstone and buff dolostone of Thundercloud Formation (TH2), eastern panel of Coates Lake Group exposure, NTS 106A (same location as Fig. 3.3.1-12). Hammer for scale.

Figure 3.3.1-16. Interbedded red mudstone and quartz arenite of the Thundercloud Formation (TH3) east of Hay Creek in western panel of Coates Lake Group exposures (hanging-wall of Plateau fault) in NTS 106A (approximately 510900E, 7122100N). Section 07-ECT-HC, Appendix C.

Figure 3.3.1-14. Dolostone of the Thundercloud Formation (TH4), south of Boomerang Lake in northwestern NTS 95M [approximately 576400E, 7073800N, near section 55 of Jefferson (1983)]. Hammer for scale.

Figure 3.3.1-17. Stromatolite layer enclosed by TH3 arenite and siltstone. Same location as Fig. 3.3.1-15.

Figure 3.3.1-15. Cherty dolostone of the lowermost Thundercloud Formation (here, TH2), south of Boomerang Lake in northwestern NTS 95M [approximately 576400E, 7073800N, near section 55 of Jefferson (1983)]. Hammer for scale.

Figure 3.3.1-18. Interlayered, rusty-weathering arenite and siltstone of TH3. Same location as Fig. 3.3.1-15. Hammer for scale.

Chapter Three

Figure 3.3.1-19. Coates Lake Group exposed south of Boomerang Lake in hanging-wall of Plateau fault (NTS 95M; approximately 576000E, 7073600N). View to south. Note sharp and subtly angular contact between Coppercap Formation (Coates Lake Group) and Sayunei Formation (Rapitan Group).

RR2 (0-30 m) consists of red, hematitic mudstone, or locally a mudstone–dolostone breccia. RR3 (0-1000 m) is a conspicuous red mudstone with minor sandstone and siltstone, grading, ripple crosslamination, thin gypsum interbeds and scattered gypsum laths, and desiccation cracks; it generally forms the bulk of Redstone River Formation thickness (Figs. 3.3.1-24 and -25). Hematite is present predominantly as detrital specularite concentrates in ripple crosslamination, and as clay-grade, disseminated hematite. RR4 (20 m) that are the graben-margin equivalents of RR3 mudstone and RR4 pebbly sandstone (Figs. 3.3.1-27 to -29). The conglomerate is massive and ungraded, with sparse sandstone and mudstone interbeds. The predominant clast type is carbonate material from the underlying Little Dal Group. The transition between the Redstone River Formation and the Coppercap Formation is the main host of Cu mineralisation in the Redstone Copper belt (south of Sekwi project area) and along strike into the Sekwi project area (See Chapter 7 and Appendix H).

Age and correlation The depositional age of the Redstone River Formation is no better constrained than that of the Coates Lake Group as a whole (723 Ma; see above). Although lithostratigraphy

indicates a generally gradational contact with the underlying Thundercloud Formation, paleomagnetic work has suggested the possibility of a disconformity between the RR3 and underlying Thundercloud Formation units (Park and Jefferson, 1991). It is possible that the evaporitic facies of the Redstone River Formation correspond to evaporites of the Kilian Formation (Shaler Supergroup; Rainbird, 1991; Rainbird et al., 1996a), but a lack of geochronological data prohibits confirmation of such a relationship.

Interpretation Local faulting continued episodically during deposition of the Redstone River Formation, as inundation of the embayments became more widespread. Subaqueous evaporites of the lower Redstone River Formation (RR1) were deposited in spatially limited, low-lying, lagoonal, evaporative basins in half-graben centres. Deposition of thick lagoonal evaporite units was limited to the deeper parts of embayments, whereas shallower areas were dominated by mudstone deposition. A marine setting for the evaporites is more probable than a lacustrine setting, based on the water volumes required to produce the impressive thickness of evaporites present in embayment centres. This may be contraindicated by evidence of local variability in evaporite minerals present: high Mg and Na in evaporites in the Keele River area (Ruelle, 1982) were probably contributed by weathering of mafic rocks and basaltic glass from nearby “Little Dal basalt” exposures. Basalt is absent from the areas north of the Keele River (Hay Creek and Mountain River embayments).

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Figure 3.3.1-20. Coates Lake Group exposed in Ten Stone Range (eastern panel of Coates Lake exposures) in NTS 106A. Redstone River Formation is absent at this embayment-margin location. View up-section across basal contact of Thundercloud Formation to southwest. Same location as 3.3.1-12. Helicopter and geologists (circled) for scale.

Figure 3.3.1-23. Cross-bedded, granule-grade evaporite particles in Redstone River Formations unit RR1 at Hutch Mountain (same general location as Fig. 3.3.121). Hammer for scale.

Figure 3.3.1-21. Thick Redstone River Formation exposed on northeast flank of Hutch Mountain, east of Keele River in northwestern NTS 95M (approximately 563200E, 7077200N). Abbreviations indicate lithofacies of Jefferson (1983). See Figure 3.3.1-2 for details.

Figure 3.3.1-24. Thick red mudstone of Redstone River Formation (RR3) at Coppercap Mountain (location of the Redstone copper deposits), in NTS 95L. Little Dal Group (right) and lower Coates Lake Group (foreground) also shown. View to north. Abbreviations indicate lithofacies of Jefferson (1983).

Figure 3.3.1-22. Redstone River evaporite rocks exposed in western panel of Coates Lake Group exposures (hanging-wall of Plateau fault) [NTS 106A; approximately 473100E, 7163500N; near sections 112-114 of Jefferson (1983)]. View to southeast.

Figure 3.3.1-25. Fine sandstone of Redstone River Formation (RR3-4); same location as Fig. 3.3.1-22.

Chapter Three

Figure 3.3.1-26. Sandstone interbedded with mudstone in Redstone River Formation (RR3-4), hanging-wall of Plateau fault west of Stone Knife River [NTS 106A; approximately 464900E, 7167800N) on valley slope between sections 117 and 118 of Jefferson (1983)]. Hammer for scale.

Figure 3.3.1-29. Redstone River Formation conglomerate (RR5) with a carbonatedominated matrix. Same general location as Fig. 3.3.1-14.

Figure 3.3.1-27. Conglomerate and cross-bedded sandstone (RR5 and 4) of Redstone River Formation. Same area as Fig. 3.3.1-26.

Figure 3.3.1-30. Buff-weathering “transition zone” between the Redstone River and Coppercap formations (arrowed). Coppercap Formation unit CP1 here is approximately 15 m thick. Same location as Fig. 3.3.1-22.

Figure 3.3.1-28. Polymictic conglomerate of Redstone River Formation (RR5) consists largely of boulder- to pebble-grade carbonate clasts from Upper Carbonate formation of Little Dal Group, in a matrix containing terrigenous sand. Same area as Fig. 3.3.1-26.

Figure 3.3.1-31. Buff-weathering dolostone in the “transition zone” (CP1). Same location as Fig. 3.3.1-22. Hammer for scale.

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Figure 3.3.1-34. Oxidised hardground or exposure surface overlain by graded tempestite bed from Coppercap Formation unit CP1. Same general area as Fig. 3.3.1-26. Figure 3.3.1-32. Buff-weathering dolostone sparsely interlayered with red mudstone in the “transition zone” (=CP1) between Redstone River and Coppercap formations. Same location as Fig. 3.3.1-22. Hammer for scale.

Figure 3.3.1-35. Contorted microbial lamination from Coppercap Formation CP1. Same area as Fig. 3.3.1-26.

C), and one section covered the thin “transition zone” between the Redstone River and Coppercap formations in the western panel of the Mountain River Embayment (2008-J113; Appendix C).

Description Figure 3.3.1-33. Sparse copper minerals coating a fracture in the “transition zone” between Redstone River and Coppercap formations. Same location as Fig. 3.3.1-22.

RR2 represents thin alluvial fans near graben margins. Fine siliciclastics of the upper Redstone River Formation (RR3) record fault-scarp-derived expansion of distal alluvial fans and floodplains that interfingered with playa lake evaporites or possibly sabkhas; coarser clastics of the Redstone River Formation. RR4 and 5 are associated only with proximal, graben-margin alluvial fans. Both are presumed to be largely derived from weathering of the iron-rich “Little Dal basalt” (Lustwerk and Wasserman, 1986).

Coppercap Formation The Coppercap Formation (Gabrielse et al., 1973a; Fig. 3.3.12) consists of medium grey-weathering carbonate rocks. The type section is south of the Sekwi project area (62°43’N, 126°37’W), on the east flank of Coppercap Mountain (NTS 95L). This formation’s lateral thickness and lithofacies changes are not as pronounced as those of the underlying two formations, and it has a greater plan extent perpendicular to strike, extending eastwards to lie near the Coates Lake Group’s basal unconformity in exposures east of the Plateau fault in NTS 106A (Jefferson, 1983). For the Sekwi project, one section included the lower Coppercap Formation in the eastern panel of the Mountain River Embayment (08-ECT-RS; Appendix

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The Coppercap Formation is characterised by medium to dark grey-weathering dolostone with minor argillaceous interbeds. Its base is gradational with the Redstone River Formation, through a “transition zone” (Figs. 3.3.1-31 to -34) that is the main host to copper concentrations in the Redstone copper belt. The following descriptions are summarised from Jefferson (1983), who identified six lithofacies assemblages (CP1 to CP6 that generally succeed one another in numerical order). Lithofacies assemblage CP1 (0-100 m) consists of buff to grey or red, microbially laminated, desiccation-cracked carbonates with mudstone (southern area only) and minor evaporites (Figs. 3.3.1-30 to -40). This unit forms the upper part of the “transition zone” through which Redstone River Formation mudstone grades into overlying Coppercap Formation carbonate rocks. The remainder of the Coppercap Formation (0-470 m) consists of two shallowing-upwards successions, each capped by stromatolites. Lithofacies assemblage CP2 (10-70 m) is described as thin-bedded shaly limestone to calcareous shale, and generally lacks distinct sedimentary structures (Figs. 3-3.1-41 and -42). Lithofacies assemblages CP3 to 5 (1->160 m; Figs. 3.3.1-43 to -49) are subtly turbiditic, mixed siliclastic-carbonate arenites and siltstones (up to 30% terrigenous material), locally with dark grey shaly interbeds, and are arranged in two coarseningupwards successions, each generally with a stromatolite biostrome at its top (Fig. 3.3.1-50). Lithofacies assemblage CP6 (to 20 m) consists

Chapter Three

Figure 3.3.1-39. Cross-bedding and grading in tempestite from Coppercap Formation unit CP1. Same area as Fig. 3.3.1-26. Hammer for scale. Figure 3.3.1-36. Cracks in lower Coppercap Formation described as dewatering structures by Lustwerk and Wasserman (1986) and reputed to be of importance to the movement of mineralising fluids. Note sulphide specks in the cracks. Same area as Fig. 3.3.1-26.

Figure 3.3.1-37. Tepee structure of Coppercap Formation unit CP1. Same location as Fig. 3.3.1-15.

Figure 3.3.1-40. Intraclast rudstone from Coppercap Formation unit CP1. Same area as Fig. 3.3.1-26. Hammer for scale.tempestite bed from Coppercap Formation unit CP1. Same general area as Fig. 3.3.1-26.

Figure 3.3.1-38. Cross-lamination and healed synsedimentary faults from Coppercap Formation unit CP1. Same area as Fig. 3.3-26. Hammer for scale.

Figure 3.3.1-41. Recessive shaly limestone (approximately 15 m thick) of unit CP2 of the Coppercap Formation. Same location as Fig. 3.3.1-22.

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Figure 3.3.1-42. Argillaceous carbonate of Coppercap Formation unit CP2. Same location as Fig. 3.3.1-22. Hammer shaft for scale.

Figure 3.3.1-45. Soft-sediment deformation developed after formation of black chert lenses in laminated CP3-5 facies of the Coppercap Formation. Same area as Fig. 3.3.1-22. Hammer for scale.

Figure 3.3.1-43. Laminated facies from Coppercap Formation interval CP35, with fitted, synsedimentary breccia. Western panel of Coates Lake Group exposures (hanging-wall of Plateau fault) north of Abandoned Creek in NTS 106A at approximately 64°22’N/129°00’W (slightly NW of section 103 of Jefferson 1983).

Figure 3.3.1-46. Unusual, possibly microbially laminated fabric with sediment-filled, geopetal interstices in the upper Coppercap Formation. Same area as Fig. 3.3.1-22. Hammer for scale.

Figure 3.3.1-44. Microbially laminated Coppercap Formation unit CP3-5 with synsedimentary ductile deformation. Western panel of Coates Lake Group exposures in NTS 106A, immediately north of Abandoned Creek [approximately 500800E, 7138800N; z9; same location as section 103 of Jefferson (1983)]. Hammer handle for scale.

Figure 3.3.1-47. Faintly laminated carbonate with pale chert bands in Coppercap Formation unit CP3-5. Same location as Fig. 3.3.1-44. Hammer for scale.

Chapter Three

Figure 3.3.1-48. Thin-bedded (pale) and microbially laminated (dark) carbonate with miniature slump scar overlain by chaotic intraclast rud/floatstone in the upper Coppercap Formation. Eastern panel of Coates Lake Group exposures in NTS 106A, southeast of Abandoned Creek at approximately 468300E, 7144500N. Hammer for scale.

Figure 3.3.1-51. Dolostone- and chert-clast conglomerate with dolomitic matrix, presumably Coppercap Formation facies CP6 of Jefferson (1983). This unit underlies a biostrome like that depicted in Fig. 3.3-49, very near the upper contact of the Coppercap Formation with the Sayunei Formation. Same area as Fig. 3.3.1-44.

Figure 3.3.1-49. Very thin-bedded to laminated CP3-5 facies of the Coppercap Formation with faint grading and very small, healed synsedimentary faults (upper centre). Same area as Fig. 3.3.1-44.

Figure 3.3.1-52. Contact of Coppercap Formation (grey and orange) and overlying Sayunei Formation (maroon; Rapitan Group) is regionally disconformable but possibly locally gradational. Note greenish colour of recessive basal Sayunei Formation. Same area as Fig. 3.3.1-44. View to west.

of dark- and light-grey speckled intraformational breccias with local silicification and possible evaporites (Fig. 3.3.1-51). The upper contact of the Coppercap Formation with the Rapitan Group (Windermere Supergroup) is a low-angle unconformity with coarse lag deposits (Figs. 3.3.1-52 and -53). Early descriptions of the contact as locally gradational were later dismissed as being based on gradational colour changes that are probably diagenetic and entirely within lowermost Rapitan Group strata (Jefferson and Parrish, 1989). The Coppercap Formation is tha main host of Cu mineralisation in the Redstone copper belt (south of Sekwi project area) and in along-strike equivalents in the Sewki project area (see Chapter 7 and Appendix H).

Age and correlation Figure 3.3.1-50. Microbial buildup in Coppercap Formation unit CP3-5; darker patches are silicified. Same area as Fig. 3.3.1-43.

The depositional age of the Coppercap Formation is no better constrained than that of the Coates Lake Group as a whole (723 Ma; see above). This formation is not known to have any direct correlatives in the Canadian Cordillera or in the mainland or Arctic Islands to the northeast, although the Coates Lake Group has been

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3.3.2. Rapitan Group E.C. Turner

Figure 3.3.1-53. Contact of Coppercap Formation and overlying Sayunei Formation. Carbonate unit in foreground is a stromatolite biostrome (approximately 2 m thick) like that depicted in Fig. 3.3.1-49. Resistant units in basal Sayunei Formation are dolomite-clast conglomerate with dolomitic matrix in lowermost few metres, but with entirely terrigenous mud-silt matrix higher up. Same area as Fig. 3.3.1-44.

loosely correlated with the Kilian Formation (Shaler Supergroup; Rainbird et al., 1996a). Stable isotopic data from carbonate rocks may suggest equivalence of Coates Lake Group strata with uppermost strata of the lower Tindir Group (Alaska) and lower Mount Harper Group (western Yukon; Macdonald et al., 2010).

Interpretation During the transition to the west-deepening Coppercap Formation, fault activity diminished, terrigenous and evaporite rock deposition ceased, and lateral facies variation became more subdued. The “transition zone” at the base of the Coppercap Formation records incremental flooding of the formerly subaerial embayment floors and attendant broadening of the overall area of deposition; this is particularly noticeable in the eastern exposure panel in NTS 106A, where Coppercap Formation rocks overlie the Upper Carbonate formation separated by at most a thin interval of Thundercloud Formation strata. The resulting, early, generally littoral environments (CP1) are characterised by microbial lamination, desiccation cracks, and fine detrital carbonate material deposited in a low-energy but not conspicuously evaporative intertidal to supratidal environment, alternating with red mudstone in 1-20 m thick cycles to form the “transition zone”. Ensuing, widespread and pronounced embayment deepening initially produced regionally extensive stagnant basinal conditions (CP2), eventually followed by deposition of two cycles of progradational, shoaling-upward, carbonate-dominated turbidites into elongate, trough-like embayment centres (CP3-5). Turbiditic and laminated dolostone of these units are the predominant lithofacies of the Coppercap Formation in the Sekwi project area. It is unclear whether carbonate basins of the Coppercap Formation were lacustrine or marine. It is also unclear where the carbonate production area that provided material to be resedimented as turbidites was; perhaps it was significantly farther east than the present-day exposure area, or perhaps most of this deeper-water carbonate was produced as water-column precipitates that were then resedimented according to local graben-floor paleotopography. Features of CP6 indicate that embayments eventually filled and/ or became emergent, leading to weathering and silicification of the underlying carbonates.

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The Rapitan Group is a thick (up to 1500 m; Yeo, 1981) middle Neoproterozoic succession of red- and grey-green-weathering diamictites, maroon turbidites, and local iron-formation that overlies the Little Dal and Coates Lake groups in the vicinity of the Plateau fault and related Mesozoic-Tertiary structures. The outcrop belt follows for ~630 km the crescentic grain of the Mackenzie Mountains, from NTS 106F in the northwest to NTS 95L in the southeast (Figs. 1-5 and 3.3.2-1). This glacially influenced succession is assigned to the lower part of the Windermere Supergroup, a riftdrift succession that forms “sequence C”, which is the youngest of the post-Hudsonian unconformity-bounded sedimentary packages of northwestern Canada (Young et al., 1979). The Rapitan Group is the first of two Cryogenian glacial successions preserved in northwestern Canada, and represents the ~700 Ma Sturtian glaciation (Narbonne and Aitken, 1995). The Rapitan Group is named after Rapitan Creek in NTS 106E/F (Yukon). The earliest mention of rocks belonging to this succession is from the northwestern Mackenzie Mountains. Keele (1906) reported iron ore float in the drainages of the Peel, Rackla, and Stewart rivers (Yukon). Keele (1910) reported ~30 m of iron-formation on the Keele River (then named the Gravel River) in the Sayunei Range (NTS 105P/95M). Significant early contributions include the work of Ziegler (1959), in which the glaciogenic origin of the succession was recognised and the Snake River tillite established, and Green and Godwin (1963), in which the Rapitan Group was established. The Crest iron deposit was discovered in the Snake River area in 1961, with exploration activity following in 1962 (Stuart, 1963). See Chapter 7.1.3 for details. The Rapitan Group was divided into informal lower, middle and upper units (equivalent to today’s Sayunei, Shezal and Twitya formations; Upitis, 1966; Gabrielse et al., 1973a; Aitken et al., 1973), and a formal nomenclature for the formation-scale units of the succession was established (Eisbacher, 1978b). A major study of the Rapitan Group (Yeo, 1981, 1984a) was completed as part of a GSC field program in the 1970s. The Rapitan Group consists of three formations. The Mount Berg Formation is limited to the southern part of the Rapitan Group exposure area, whereas the Sayunei and Shezal formations are exposed extensively along the length of the Plateau fault (see accompanying maps NWT Open Files 2010-09 to -19). Use of the term “Rapitan Group” today differs from that of some earlier papers. For example, based on the concept that Rapitan Group and overlying units formed a shallowing cycle (Eisbacher, 1976), Eisbacher (1978b) and others included in the Rapitan Group the overlying Twitya and Keele formations, which are now part of the Hay Creek Group (Yeo, 1978). The Mount Berg Formation was not recognised until comparatively late (Yeo, 1978). The diamictite and turbidite units have not received significant attention since the 1970s, but further work was undertaken in the 1980s on jasperhematite iron-formation (Klein and Beukes, 1993). A maximum age for the Rapitan Group is furnished by a granite dropstone from the lower Sayunei Formation with a U/Pb zircon date of 755± 18 Ma (Ross and Villeneuve, 1997). This age was deemed to be typical of Windermere-aged intrusive events in the Cordillera, and the clast was tentatively interpreted as the product of as-yet unproven rift-related magmatism and unroofing. Young (1992) suggested that the Rapitan Group, which overlies both the Mackenzie Mountains supergroup and the Coates Lake Group, was necessarily younger than 723 Ma (Heaman et al., 1992), based on the age of intrusive rocks of the Franklin event, near the top of the

Chapter Three

Figure 3.3.2-1. Distribution of the Sayunei and Shezal formations in the Sekwi project area (outlined in red), and of iron-formation in the Sayunei Formation. Exposure areas and iron-formation locations after Yeo (1984).

Shaler Supergroup (Victoria Island), which is equivalent to the Mackenzie Mountains supergroup. These rocks are now dated at ~717 Ma (Macdonald et al., 2010), which would dictate an even younger maximum age. Paleomagnetic poles for the Sayunei Formation are identical to those of the Franklin igneous event, strongly suggesting that the Sayunei Formation was deposited at approximately the same time (Park, 1997). If confirmed, a suggested correlation of the Rapitan Group with glacial deposits of the upper Mount Harper Group (western Yukon) would provide a depositional age of ~716 Ma for the lower Rapitan Group (Macdonald et al., 2010). Correlation with similar strata in the upper Tindir Group

(Alaska) and with glaciogenic successions on other continents has been suggested (e.g., Young, 1992; Hoffman and Li, 2009), but controversy remains over the synchronicity of the late Neoproterozoic glacial events, and such correlations remain tentative; see Hoffman and Li (2009) for a summary of geochronological data for Sturtian glacial deposits. The Rapitan Group is exposed in the Mackenzie and Wernecke mountains over a strike length of ~600 km. In the Northwest Territories, its exposure is almost exclusively in the hanging-wall of the Plateau fault (Figs. 3.3.2-2 to -3) and along strike west of the fault’s northern terminus. Exposure is discontinuous in the southern

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Figure 3.3.2-2. Sharp, disconformable contact of Sayunei Formation (maroon) on Coppercap Formation (grey; Coates Lake Group), hanging-wall of Plateau fault, between Mountain and Stone Knife rivers (NTS 106A; approximately 473100E, 7163500N).

and central Mackenzie Mountains, but is thick and laterally continuous along strike in the Sekwi project study area (Fig. 3.3.2-1 and -4). Exposure in Yukon is structurally complex, and the Rapitan Group succession is both sedimentologically and stratigraphically different from the succession in the Mackenzie Mountains; Yukon exposures will not be addressed here. As is the case for many of the older Neoproterozoic units in the northern Cordillera, lateral extent of exposures perpendicular to strike is limited, but isopach maps (Yeo, 1981) indicate that thickness diminishes both eastward, owing to depositional onlap onto paleotopographically elevated areas, and westward, by thinning of depositional units (Fig. 3.3.2-4). For this reason, the subsurface extent of the Rapitan Group west of the Plateau fault is probably limited (see Chapter 5 and accompanying cross-sections NWT Open File 2010-18; Fig. 9-1). Previous work defined two main areas of Rapitan Group exposure: the Snake River basin (northwesternmost Mackenzie Mountains, at Northwest Territories – Yukon border) and the Mountain River – Redstone River basin (Yeo, 1981). Isopach maps (Fig. 3.3.2-4) not only depict a narrow depositional zone of glaciomarine Rapitan Group strata in these two areas, but also indicate that the fault-controlled troughs in which it accumulated were divided into sub-basins, a configuration that is supported by paleocurrent data (Yeo, 1981). Yeo (1981) interpreted these subbasins to have been controlled by the same fault system that formed the graben-like embayments of the Coates Lake Group, which

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Figure 3.3.2-3. Thin, steeply dipping Sayunei and Shezal formations overlying Coates Lake Group in hanging-wall of Plateau fault immediately west of Stone Knife River (NTS 106A; approximately 465700E, 7167300N).

the Rapitan Group overlies along a considerable strike length. Depocentres for the Sayunei and Shezal formations coincide in some areas but contrast strongly in others. Possible evidence of syndepositional tectonic activity includes synsedimentary faults and slump folds (Eisbacher, 1981; Yeo, 1981).

Chapter Three

Figure 3.3.2-4. Isopach maps for Sayunei and Shezal formations, from Yeo (1981), compared with embayments of underlying Coates Lake Group, from Jefferson and Parrish (1989). Sekwi project area is outlined in red.

The Rapitan Group was deposited in an extensional environment, as were the underlying Coates Lake Group and overlying Hay Creek Group. Extension that predated and accompanied deposition of the Rapitan Group is termed the “Hayhook extensional event” (Young et al., 1979; Young, 1995), but the degree to which extensional episodes prior to and during deposition of sequence C strata are related to one another is unclear owing to poor age constraints on deposition of most of the Neoproterozoic units in the Mackenzie Mountains.

Eisbacher (1978a, 1981) and Helmstaedt et al. (1979, 1981) presented evidence of local, northeast-directed contractional deformation that affected Coates Lake Group and Sayunei Formation strata during deposition of the lower Sayunei Formation and produced an intra-formational unconformity (NTS 105P). Yeo (1978) and Aitken et al. (1981) reinterpreted these structures to be either syndepositional slump folds or structures of MesozoicTertiary origin, based in part on their similarity to nearby structures assigned to the Laramide orogeny. In view of evidence of earlier

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Chapter Three contractional deformation during the middle Neoproterozoic elsewhere in the northern Cordillera (NTS 106C; Eisbacher, 1981; Thorkelson, 2000), it is possible that the tectonic evolution of this area after deposition of sequence B (Mackenzie Mountains supergroup) is more complex than has hitherto been acknowledged. The Rapitan Group basins were at low latitude during sedimentation, as demonstrated by a complex paleomagnetic remanence resulting from subtle thermal events associated with rifting (approximately 25° paleolatitude for the Mount Berg Formation, and approximately 6° and 4° for the Sayunei and Shezal formations, respectively; Park, 1997). In the Mackenzie Mountains, the Rapitan Group is regionally unconformable on strata of the Little Dal or Coates Lake groups, although some observations have suggested that the lower contact is locally conformable with the Coates Lake Group, particularly in basin-ward locations (Eisbacher, 1978b, 1981; Fig. 3.3.2-5). The Rapitan Group is abruptly and seemingly conformably overlain by deep-water, fine-grained siliciclastics and local, basal carbonate rocks of the Twitya Formation (Eisbacher, 1978b; Yeo, 1981). The Rapitan Group is known not only because it is the lowest of the late Neoproterozoic glacial successions in northwestern Canada, but also because it contains a large iron deposit in the form of jasperhematite iron-formation. The area best known for thick and areally extensive iron-formation (the Snake River or Crest deposit) is in the Snake River and Cranswick River area of the northern Mackenzie Mountains and northern Yukon. Historical reserves at the Crest deposit were loosely estimated at >10 billion tons at 47% Fe for the region as a whole (Stuart, 1963; Gross, 1965; Yeo, 1984b). See Chapter 7.1.6 for details. Iron-formation is also present in the Sekwi project area (Fig. 3.3.2-1). Iron-formation exposures have been reported from both the Sayunei and Shezal formations, although it is unclear how these reported occurrences are related to one another stratigraphically, if at all. With the recent growth in understanding of the “snowball Earth” episode, it has become clear that carbonate units that immediately overlie Neoproterozoic glaciogenic units were deposited during deglaciation. For the Rapitan Group succession, this terminal deglaciation event is identified with the turbiditic to stromatolitic carbonate succession that is locally present at the base of the Twitya Formation (Hay Creek Group; Chapter 3.3.3). Previous work used the terms “mixtite” or “tillite” for some of the major lithofacies of the Rapitan Group. Controversy over the use and implications of these terms has been avoided by using the descriptive classification scheme of Hambrey (1994), and in the present work, “diamictite” is preferred for most of the Rapitan Group lithofacies that consist of unsorted mixtures of mud-, silt-, sand- and gravel-grade material. Although numerous traverses included the Rapitan Group in the course of the Sekwi project, no detailed study was undertaken on this group. This review is based on the work of previous authors.

Mount Berg Formation The Mount Berg Formation (Yeo, 1981; upgraded from Mount Berg Member of Yeo, 1978) is exposed only in NTS 95L and is not present in the Sekwi study area. It is described here for completeness, and because issues of stratigraphic correlation in the Rapitan Group require its inclusion. Its type section is on the south side of Mount Berg (NTS 95L) in the Thundercloud Range of the Mackenzie Mountains (62°31' N; 126°15' W).

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Description The Mount Berg Formation was first described in a B.Sc. thesis (Condon, 1964). As described by Yeo (1981), it consists of greygreen diamictite, with lesser siltstone, conglomerate and sandstone. The formation unconformably overlies rocks of the Coates Lake and Little Dal groups, and is gradationally overlain by red turbidites of the Sayunei Formation. This recessive unit is locally in excess of 300 m, and thins westward beneath the Sayunei Formation. Yeo (1981) describes the Mount Berg Formation as consisting largely of grey-green diamictite in which angular to subrounded clasts of carbonate rock, intraformational siltstone and volcanic rock are suspended in a silty to sandy matrix. No sedimentary structures or clast orientation data are reported. Diamictite is locally interbedded along sharp contacts with 2 m-thick layers of recessive, silty mudstone with massive to faintly laminated structure, fine- to medium-grained sandstone, and conglomerate.

Age and correlation No part of the Rapitan Group has been directly dated. As outlined above, a maximum depositional age for the Rapitan Group is 755± 18 Ma, the crystallisation age of a leucogranite dropstone in the Sayunei Formation (U/Pb zircon; Ross and Villeneuve, 1997). Young (1992) suggested that the Rapitan Group, which overlies both the Mackenzie Mountains supergroup and the Coates Lake Group, was necessarily younger than 723 Ma (Heaman et al., 1992), the age of the Franklin intrusive event. Paleomagnetic poles for the Sayunei Formation are identical to those of the Franklin igneous event, strongly suggesting that the Sayunei Formation was deposited at approximately the same time (Park, 1997).

Sayunei Formation The Sayunei Formation, established by Eisbacher (1978b) using a 125 m-thick type section 11 km west of Hayhook Lake in NTS 95M (63°31’N/127°W), consists largely of maroon turbidites, mudstones, and diamictites. The name comes from the Sayunei Range in NTS 105P and 106A, from a traditional name meaning “mountain sheep” (Keele, 1910).

Description This unit conformably overlies the Mount Berg Formation in the southern Mackenzie Mountains (NTS 95L), but unconformably overlies strata of the Little Dal or Coates Lake groups elsewhere in the Northwest Territories, including the Sekwi project study area. Some descriptions suggest that it locally exhibits a conformable basal contact with the Coates Lake Group (Eisbacher, 1978b, 1981; Yeo, 1981, 1984a; Fig. 3.3.2-5). It is abruptly but conformably overlain by diamictite of the Shezal Formation (Fig. 3.3.2-3). The Sayunei Formation appears to thicken westward to an axis, then thin, defining an irregular, narrow depositional zone that is roughly parallel to the Plateau fault. The Sayunei Formation is 0 to ~600 m thick. Isopach maps (Yeo, 1981, 1984a; Fig. 3.3.2-4) for the Sayunei Formation depict thickness variations that define several depocentres along the length of this trough in NTS 106A, 95M and 95L. The unit pinches out northwestward; in the Snake River area (NTS 106F) the Sayunei Formation is absent and the basal Rapitan Group is represented by the Snake River Tillite Member of the Shezal Formation. The Sayunei Formation is regionally maroon-coloured, although other colours are locally present, particularly near

Chapter Three the formation’s base and top. Five lithofacies were described by Yeo (1981) from the Sayunei Formation. Graded, centimetric to decimetric siltstone-mudstone turbidites and massive, hematitic mudstones predominate, with no evidence of shallow-water deposition. Turbidites (Fig. 3.3.2-6) are generally marked by pale colour in the coarser, lower parts of layers (lithic to quartzose arenite to siltstone) and a pronounced red colour in the finest parts (hematitic mudstone). The turbidites are characterised by sharp contacts, locally loaded or fluted bases (Fig. 3.3.2-7), and crosslamination. Dropstones (Fig. 3.3.2-8) and aggregate sediment clots (“till pellets”) are common. Coarse turbidites with conspicuous, sand-grade bases are locally present, as are thin stringers to thick beds of framework-supported conglomerate with sharp, irregular contacts. Synsedimentary microfaults are locally present (Fig. 3.3.29). Diamictite layers up to several metres thick, with local beddingparallel clast orientation, are common in the uppermost part of the formation. Eisbacher (1978b) also described units of “sharpclast siltstone”, which consist of coarse, angular carbonate clasts embedded randomly in siltstone, and which were inferred to have been deposited in the immediate vicinity of syndepositionally active normal faults. Paleocurrents from turbidites have diverse orientation but in general depict westward transport in the Sekwi project area (Eisbacher, 1978b, 1981; Yeo, 1981). Jasper-hematite iron-formation in the Sekwi project area (Fig. 3.3.2-10) was first reported by Keele (1910) in the Keele River area. Later work revealed similar material near the top of the Sayunei Formation (Fig. 3.3.2-14), in up to three distinct layers, each with several kilometres of lateral extent (Yeo, 1978; 1981; 1984a, b). Ironformation has also been reported from the Sayunei Formation south of the Sekwi project area (NTS 95L; Condon, 1964). Sayunei ironformation is dominated by laminated and nodular jasper-hematite (±magnetite?) rock with dropstones. Yeo (1981, 1984a, 1986) suggested that hematitic mudstone in turbidites and in diamictite matrix of the Sayunei Formation should also be considered a variety of iron-formation.

Figure 3.3.2-6. Composite graded layers (probable distal turbidites) are typical of the Sayunei Formation in the hanging-wall of the Plateau fault between the Mountain and Stone Knife rivers (NTS 106A; approximately 474800E, 7161200N).

Age and correlation Paleomagnetic poles for the Sayunei Formation are identical to those of the Franklin igneous event, strongly suggesting that the Sayunei Formation was deposited at approximately the same time (Park, 1997). If correlation of the Sayunei Formation and the upper

Figure 3.3.2-5. Basal contact of Sayunei Formation with the Coppercap Formation appears to be gradational rather than sharp in some locations. Hanging-wall of Plateau fault, north of Abandoned Creek (NTS 106A; approximately 500600E, 7138900N).

Figure 3.3.2-7. Creep-folded and loaded bed bases in graded beds of the Sayunei Formation (NTS 105P; approximately 541854E, 7075936N).

Figure 3.3.2-8. Large and small cobble-grade dropstones in basal Sayunei Formation mudstone, in hanging-wall of Plateau fault north of Abandoned Creek (NTS 106A; approximately 500600E, 7138900N).

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Figure 3.3.2-9. Sedimentary microfaults and creep-folds (arrow) in Sayunei Formation turbidites, in hanging-wall of Plateau fault between Mountain and Stone Knife rivers (NTS 106A; approximately 474800E, 7161200N).

Figure 3.3.2-12. Red, clast-rich, intermediate diamictite of the Mountain River member of the Shezal Formation, in the hanging-wall of the Plateau fault between Mountain and Stone Knife rivers (NTS 106A; approximately 474800E, 7161200N). The abundant carbonate clasts have chloritised rims. Note jasper clast (arrow).

Figure 3.3.2-10. Iron-formation of uncertain stratigraphic position in central NTS 95M (approximately 604753E, 7031577N).

Figure 3.3.2-13. Yellow-grey, “scaly-weathering”, clast-rich intermediate diamictite of the Bonnet Plume Member of the Shezal Formation; northeastern NTS 105P (approximately 525918E, 7089334N).

Mount Harper Group is substantiated, the depositional age of the latter (~716 Ma, U-Pb zircon; Macdonald et al., 2010) would also be also valid for the Sayunei Formation.

Shezal Formation The Shezal Formation (Eisbacher, 1978b) consists of ~0-800 m of green-grey diamictite. Its type section is 13 km west of Hayhook Lake in NTS 95M (63°33’N/127°04’W), where it is 235 m thick. The Shezal Formation is named for Shezal Canyon, a tributary of the Keele River in NTS 95M.

Description

Figure 3.3.2-11. Sharp but conformable contact of the Shezal and overlying Twitya formations in northeastern NTS 105P (approximately 524020E, 7082275N).

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The Shezal Formation is discontinuously exposed throughout the Mackenzie Mountains and in the northeastern Wernecke Mountains (Yukon). In the Sekwi project area it is extensively exposed in the hanging wall of the Plateau fault. The Shezal Formation conformably overlies the Sayunei Formation with a gradational, interlayered relationship (although

Chapter Three

Figure 3.3.2-14. Two different correlation schemes for the Rapitan Group. Simplified from (A) Yeo, (1981, 1984, and 1986) and (B) Klein and Beukes (1993).

some previous workers have proposed an erosional contact; Gabrielse et al., 1973a; Young, 1976; Yeo, 1978), or lies unconformably on strata of the Little Dal or Coates Lake groups. Its upper contact with pyritic siltstone of the Twitya Formation is sharp but conformable (Fig. 3.3.2-11). Like the underlying Sayunei Formation, the Shezal Formation was deposited in a linear basin, but exhibits along-strike thickness variation that defines local depocentres. Relationships between Sayunei and Shezal depocentre locations (Fig. 3.3.2-4) vary from strongly similar (central NTS 106A) to contrasting (northeastern 105P and northwestern 95M). According to Yeo (1981), Shezal thickness maxima are west of those for the underlying Sayunei Formation in the Sekwi project area. The Shezal Formation has three members defined on the basis of colour and structure (Yeo, 1981). In the Northwest Territories, the lower part of the Shezal Formation, the Mountain River Member (Yeo, 1981), is deemed to be laterally equivalent to green-grey diamictites of the Snake River Tillite (Ziegler, 1959) of the northwesternmost Mackenzie Mountains (Yeo, 1981, 1984a). In the Sekwi project area, the Mountain River Member consists of up to ~362 m of typically red-coloured, recessive, massive, blocky-weathering to friable diamictite with minor conglomerate, sandstone and mudstone (Fig. 3.3.2-12). In the Sekwi project area, the upper Bonnet Plume Member consists of up to 824 m of “scaly-weathering” grey-green diamictite that is interlayered with underlying red diamictite (Fig. 3.3.2-13). Subsidiary mudstone, sandstone, and conglomerate are also present, and authigenic pyrite is present in the matrix (Yeo, 1978). Green and Goodwin (1963) reported the presence of tuff in the Rapitan Creek area (Yukon), but this has not been substantiated.

Diamictites of the Shezal Formation are massive to weakly stratified at a metre- to decametre-scale. Massive diamictite predominates, and is characterised by a lack of structure other than local sub-parallel clast alignment and local slickenside surfaces in the matrix (Eisbacher, 1978b). Some of the stratified diamictite exhibits centimetre-scale interlayering with muddy to sandy interbeds, some of which are red. Subangular to rounded, pebble- to bouldergrade clasts commonly exhibit striated or faceted surfaces, and are dominated by carbonate compositions, with lesser volumes of quartz arenite, jasper, volcanic and mafic intrusive clasts, and rare metamorphic clasts. Eisbacher (1978b; 1985) reported that clast size increases upward with a concomitant increase in compositional diversity to include gneissic, volcanic and mafic-intrusive clast compositions. Diamict matrix is calcareous or dolomitic, depending on the dominant clast type. Mud-grade matrix is hematite-cemented in the Mountain River Member. Mudstone layers up to several metres thick are interbedded along sharp to gradational contacts with diamictite, and are identical in composition to the diamictite’s matrix. Sandstone layers up to several metres thick exhibit sharp, loaded bases, and local grading and ripple cross-lamination. Conglomerate lenses have irregular contacts and are generally less than one metre thick. Paleocurrents from cross-bedded sandstones depict generally westward transport in the Mountain River – Redstone River basin (Sekwi project area), but more complex distributions in the Snake River basin. The Shezal Formation is renowned for its thick hematite-jaspilite iron-formation in the Snake and Cranswick river areas (NTS 106F), first reported by Keele (1906) and Camsell (1906). The Crest deposit of the Snake River Basin was explored extensively in the 1960s (see

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Chapter Three Stuart, 1963 and Green and Goodwin, 1963), resulting in historical reserves estimated at >10 billion tonnes for the region as a whole (Stuart, 1963; Gross, 1965; Yeo, 1984a). Minor exploration activity also took place in the southern Mackenzie Mountains (Condon, 1964), where minor amounts of jasper-hematite (and possibly magnetite; Yeo, 1981, 1984a) iron-formation are locally present at the base of the Shezal Formation (including Sekwi project area). Stratigraphic sections of Yeo (1984) indicate several localities where nodular (sometimes misleadingly referred to as “pisolitic”) to irregular jasper-hematite (±magnetite) iron-formation are exposed in the lower Bonnet Plume River Member and Mountain River Member diamictites in and near the Sekwi project area (Fig. 3.3.2-10). Reworked fragments of ironformation are also locally present in diamictite. Geochemistry and stratigraphy of the Snake River ironformation were investigated based predominantly on archived core (Klein and Beukes, 1993). Interlayered clastic units were considered to be laterally continuous, but increase in stratigraphic proportion both eastward and upward. Iron-formation overlies a variety of clastic deposits, including diamictite, sandstone and shale, most of which are the product of mass flow. Vague cyclicity in iron-formation lithofacies was noted, and slumped iron-formation described in the lower part of the unit. Phosphorus and iron content vary inversely with organic carbon content and uranium and thorium concentrations. The REE composition of the iron-formation differs from that of Archean iron-formations, and closely resembles that of modern ocean water. It is unclear whether scattered exposures of iron-formation throughout the Rapitan Group exposure area represent a single unit that is disrupted by patchy deposition and later erosion, or whether they represent independent, localised depositional systems. Whether any or all of the known iron-formation horizons in the Mountain River – Redstone River basin should be considered stratigraphically equivalent to the Crest iron-formation in the Cranswick River – Iron Creek area in the Snake River Basin remains to be assessed.

Age and correlation No part of the Rapitan Group has been directly dated. See this chapter’s introduction and Sayunei Formation for depositional age constraints.

Interpretation Although it was recognised quite early that the Rapitan Group was glaciomarine (Ziegler, 1959), some early workers attributed the Rapitan Group’s diamictites to mass-flow (Upitis, 1966; Stewart, 1972; Gabrielse et al., 1973a). Yeo (1981) and Young (1988, 1995) interpreted the Rapitan glaciation as a response to uplift along the margins of new, rifted seaways. The majority of previous workers has interpreted Rapitan Group diamictites as resedimented glaciomarine deposits associated with the melting of floating glacier ice, although Yeo (1981) attributed some features to locally grounded ice, and Eisbacher (1978b) disputed the widely accepted origin of most lonestones in the Sayunei Formation as glacial dropstones. Many workers have attributed the change from diamictites to turbidites and back to diamictites as the record of glacial and interglacial intervals, although Young (1976) suggested instead that this pattern may reflect differences between the marine effects of dry- versus wet-based glaciers. With the emergence of the “snowball Earth” hypothesis in the 1990s (Kirschvink, 1992; Hoffman et al., 1998), under which almost all of Earth would have been ice- or slush-covered, many of the confounding attributes of the Rapitan succession, such as low-latitude glaciation and iron-formation

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deposition, have become easier to explain. The “snowball Earth” hypothesis is by no means universally accepted, and its voluminous and controversial literature is beyond the scope of this review. The Rapitan Group generally onlaps eastward onto an unconformity and thins westward depositionally from an axial zone of greatest thickness (Yeo, 1986). This configuration was interpreted to reflect rifting to form a small Red-Sea-type basin (Yeo, 1981; Young, 1984). Deposition of the Rapitan Group was, therefore, confined to a long (>600 km) and narrow zone (10 Gt iron reserve at the Crest deposit of the Snake River basin (Snake and Cranswick River area), northwest of the Sekwi project area (see Chapter 7.1.6 ). Subsurface

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Chapter Three distribution of thick iron-formation southwest of the Crest deposit exposure area is unknown, and may be limited by general outboard thinning of the Rapitan Group as demonstrated using isopachs (Yeo, 1981). Although exposures of iron-formation in the MountainRedstone basin (Sekwi project area) are thin and discontinuous, defining their temporal and paleoenvironmental relationships with the Crest succession would be an important contribution. Although the potential of the Crest deposit as a source of iron ore has been established, the presence and distribution of other valuable elements that are commonly associated with iron-formation remain to be reassessed in both depositional basins using current geochemical methods. Copper showings are also known from the Sayunei Formation in areas where mineralisation is present in the underlying Coates Lake Group (e.g., Helmstaedt et al., 1979).

Conclusions Numerous questions remain regarding the origin and implications of the Rapitan Group, which is an important part of the middle Neoproterozoic glacial record and contains a significant iron reserve. Important details regarding paleoenvironmental interpretation are contested; for example, how much (if any) of the succession was of subglacial origin, and how much of the significant mass-flow evidence was related to tectonic activity (rifting) versus meltwater influxes. The physical sedimentology and configuration of depositional basins during the critical time of iron-formation deposition have yet to be addressed. The question of whether ironformation intervals were deposited simultaneously or diachronously should be addressed in the context of a re-evaluated regional correlation scheme. Regional and global correlations remain unclear. Tectonostratigraphic evolution in the context of breakup of Rodinia and Neoproterozoic basin succession remain poorly understood.

3.3.3. Hay Creek Group R.B. MacNaughton Windermere Supergroup strata that overlie the Rapitan Group consist of three “grand cycles” (Aitken, 1989a), each with a lower half-cycle that is dominated by fine-grained siliciclastic strata and an upper half-cycle that generally is dominated by carbonate rocks. Interpretation of this packaging is complicated by controversy regarding the correlation of the uppermost grand cycle (see below). Fossil constraints on age are sparse and units are not amenable to direct determination of age by radiometric dating. Carbon-isotope chemostratigraphy aids in correlating these strata beyond the Mackenzie Mountains (e.g., Kaufman et al., 1997). The lowest grand cycle and its associated glacial deposits are part of the Hay Creek Group, which is exposed in the Sekwi project area (Fig. 3.3.1-1). As originally defined (Yeo, 1978), the Hay Creek Group consisted of the Twitya and Keele formations. Subsequent work demonstrated that the Ice Brook Formation (Aitken, 1991) is a distal equivalent of parts of the Twitya and Keele formations, and so it is included in the Hay Creek Group in the present description. Also included is the “Tepee dolostone” map unit, originally considered a member of the Keele Formation (Gabrielse et al., 1973a) but now treated as a unit of formation rank (e.g., James et al., 2001). Some workers previously treated the Twitya Formation (Gabrielse et al., 1973a) or Twitya and Keele formations (Eisbacher, 1978b) as part of the Rapitan Group, but these usages have been abandoned (Eisbacher, 1985; Narbonne and Aitken, 1995). The Hay Creek Group (Twitya, Keele, Ice Brook formations and “Tepee dolostone”) is exposed extensively in the hanging-wall

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panel of the Plateau fault in NTS 95M, 105P, and 106A. In parts of NTS 106A the Hay Creek Group crops out in structural panels to the southwest and northeast of the Plateau fault (Fig. 3.3.3-1).

Twitya Formation The Twitya Formation is a dark-weathering map unit dominated by fine-grained siliciclastic lithofacies (Fig. 3.3.3-2). In early reports that provided measured sections, (Upitis, 1966; Gabrielse et al., 1973a; Aitken et al., 1973) the Twitya Formation was an unnamed, upper division of the Rapitan Group. Eisbacher (1978b, p. 13) named the formation, with a type section “along a ridge 15 km west of Hayhook Lake” in NTS 95M (63º33’30” N, 127º03’30” W). Additional measured sections were presented in that report. One detailed section was measured during the Sekwi project (08MWB-S1; Fig. 3.3.3-3). The Twitya Formation is exposed extensively in the Sekwi project area as far east as and along the Plateau fault, as well as in at least one fault panel to the northeast. It is not exposed at surface southwest of the Sayunei Range. Southeast of the project area, Gabrielse et al. (1973a) mapped probable Twitya Formation strata (as upper Rapitan Group) between the Plateau and Hayhook faults in NTS 95M and 95L (see also Eisbacher, 1981).

Description The base of the Twitya Formation is sharp in all exposures but commonly is recessive and covered (Fig. 3.3.3-2). In northwestern NTS 95M, basal beds of the Twitya Formation downlap locally onto the underlying Shezal Formation. The contact with the overlying Keele Formation is conformable and gradational (Figs. 3.3.3-2 and -3). In the vicinity of Shale (Palmer) Lake in NTS 106A, the contact is clearly visible from a distance, whereas in northwestern NTS 95M the contact is subtly gradational and less distinct. The contact with the Ice Brook Formation is dealt with in the treatment of that unit. Siltstone and shale are the dominant lithofacies through large thicknesses of the Twitya Formation, although sandstone also is a significant component (Fig. 3.3.3-4a); these lithofacies commonly contain detrital mica. Conglomerate (Fig. 3.3.3-4b) and limestone also are present at some levels. Fresh colours include dark grey, brownish-grey, and grey. Finer-grained siliciclastic lithofacies weather dark grey, olive-brown, maroon-brown, and grey, though sandstone locally weathers light orange-brown. Conglomerate weathers pale grey and light tan. Carbonate rocks weather grey to light grey. Most lithofacies are laminated to thin-bedded; conglomerate is a notable exception, being thick-bedded in some localities (Fig. 3.3.3-4b). Conglomerate is also present as recognisable channel fills, some of which cross-cut each other. Siltstone beds are variably massive, parallel-laminated, and/or current-ripple cross-laminated. Sandstone beds are sharp-based and generally normally graded. Depending on the locality, such beds may contain ripple crosslamination, low-angle cross-lamination, or possible hummocky cross-stratification; mud clasts are common. Conglomerate beds generally have erosional bases and are massive to normally graded. Some sections contain intervals with abundant, well-developed slump masses and slump-folded beds. Limestone with dark grey to black shale partings is present locally at the base of the formation; it is fetid and fine-grained, with poorly developed Bouma sequences and thin intraclast horizons. Higher in the formation, especially near the top, thin beds of stromatolitic limestone are locally present, in association with probable shallowwater facies. Beds consisting of transported pebbles, cobbles, and

Chapter Three

Figure 3.3.3-1. Distribution of the Hay Creek Group in NTS 105P, 106A, and northwestern 95M.

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Chapter Three

Figure 3.3.3-2. View of Rapitan Group (Sayunei and Shezal formations) and lower part of Hay Creek Group (Twitya and Keele formations). Note generally recessive character of Twitya Formation, with three subtly developed upward-coarsening cycles reflected in weathering profile. Keele Formation displays intertonguing with dark-weathering siliciclastic lithofacies previously reported by Eisbacher (1979) and Aitken (1991). View is of first ridge to north of measured section 08MWB-S1, seen from the base of the section. Location is southeast of Shale (Palmer) Lake in NTS 106A.

small boulders of orange-weathering dolostone, some with relict microbial textures, are present locally near the top of the formation. Macrofossils have been documented at only one locality, near Bluefish Creek, where discoidal sole impressions may be small, primitive Ediacaran organisms (Hofmann et al., 1990). The Twitya Formation is up to at least 900 m thick. It coarsens up at many localities near the Plateau fault. This apparently is due to upward shoaling, based on sections where a sandy upper interval contains hummocky cross-stratification and other evidence of shallow-water deposition. Upward shoaling is less apparent in sections farther west and southwest, which were deposited more distally (Eisbacher, 1981). Viewed at a distance, many sections can be subdivided into three, large-scale upward-coarsening successions (Fig. 3.3.3-2). The Twitya Formation is known to contain at least one basemetal sulphide occurrence in the Sekwi project area (Appendix H). It also hosts the Mountain River Beryl occurrence (emerald) discovered as during the Sekwi project (see Chapter 7.3 and Appendix H).

Age and correlation The Twitya Formation lies between two major glacial deposits: the Shezal and Ice Brook formations. The Shezal Formation is considered to be a product of Sturtian glaciation and the Ice Brook Formation a product of Marinoan glaciation. The Twitya Formation thus is well constrained as Cryogenian-aged. No microfossils have been reported.

Interpretation Eisbacher (1978b, p. 14) suggested that the Twitya Formation was deposited “on a gravitationally unstable shelf ”. In the Sekwi project area, the depositional paleoslope dipped to the southwest or west (Eisbacher, 1981). More recent work (MacNaughton et al., 2001; this report) point to deposition in depths ranging from slope to shelf to shoreface. Evidence for relatively shallow-water deposition includes the presence of low-angle and hummocky cross-stratification. Slope deposition is suggested by the presence of slump-folds and turbidites at some levels.

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Keele Formation The Keele Formation is a resistant, pale-weathering formation that commonly is carbonate-dominated but locally contains significant volumes of siliciclastic material (Fig. 3.3.3-2). The unit was briefly described by Upitis (1966) and was formalised by Gabrielse et al. (1973a), with a type section near Sheepbed Creek in the central part of NTS 95L (63°37’00” N, 127°17’30” W). In the Sekwi project area, the Keele Formation is well exposed in the hanging-wall panel of the Plateau fault, but to the southwest it is absent, apparently by non-deposition (Aitken, 1991). The Keele Formation was not a focus of detailed study during the Sekwi project and no complete sections were measured through it; section 08MWB-S1 (Fig. 3.3.3-3) includes the lower part of the formation. Measured sections have been published by Gabrielse et al. (1973a), Aitken et al. (1973), Eisbacher (1978b), Aitken (1991), Day (2002) and Day et al. (2004). Unpublished sections by J.D. Aitken also exist in GSC-Calgary archives. Sekwi project section 07CL-S4 included the Keele Formation (Appendix A).

Description The Keele Formation lies conformably and gradationally upon the Twitya Formation. A satisfactory definition for the base of the formation has been elusive. Gabrielse et al. (1973a), examining strata in NTS 95M and southward, emphasised the sand content of the Keele Formation and indicated that the base was marked by cross-bedded sandstone. Eisbacher (1978b) placed the base at the first carbonate layer above mudrocks of the Twitya Formation. This definition was not fully satisfactory, because olistostromes were used to mark the base of the Keele in some sections, with the result that Twitya-like lithofacies made up much of the Keele Formation in some areas. (The later recognition of the Ice Brook Formation has clarified this issue; see below.) Day et al. (2004; p. 226) considered the base to be “marked by the abrupt appearance of oolitic carbonate and/or quartz arenite”. For regional mapping, the contact is readily recognised at a distance in places where the transition from recessive-weathering Twitya Formation to resistant Keele Formation is relatively abrupt, but is much harder to pick where the transition

Figure 3.3.3-3a

17

400

Chapter Three

08MWB-S1

16 14, 15

13

10

9

8 7

200

T WITYA FORMATION

CRYOGENIAN

11

300

12

6

4

100

5

Legend

3

Sandstone with lesser siltstone and shale.............

Siltstone and Shale.........................................................

Siltstone and shale with lesser sandstone.............

Quartz wackle..................................................................

Accessory sand...................................................

Parallel lamination.......................................................

Accessory silt......................................................

Load casts....................................................................

2

1 0

Current ripples and/or ripple crosslamination...... Normal Grading........................................................

Accessory conglomerate.....................................

Figure 3.3.3-3 (a). Graphic log of measured section 08MWB-S1, through Twitya Formation and lower part of Keele Formation, southeast of Shale (Palmer) Lake in NTS 106A. Base of section is at 489347E/7147757N and top is at 487940E/7147661N (UTM, Nad 83, zone 9). From base to top of section.

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36

900

KEELE FORMATION

38

KEELE FM.

Chapter Three Figure 3.3.3-3b

08MWB-S1

35

800

37

34 33

32 31

700

30

29

28 27

600

25 24 23

22

500

CRYOGENIAN T WITYA FORMATION

26

Legend Dolostone...........................................................................

Thick-bedded dolostone............................................

Quartz wackle..................................................................

Siltstone and shale with lesser sandstone.............

Conglomerate....................................................................

Sandstone with lesser siltstone and shale.............

Dolostone breccia............................................................

Siltstone and Shale.........................................................

Stromatolites........................................................................ Convolute bedding or lamination.................................

Calcareous....................................................................

21

Accessory conglomerate.....................................

Microbial lamination...................................................

20

Shale lithoclasts..................................................

Accessory sand...................................................

Mudstone and/or siltstone partings....................

Accessory silt......................................................

19

18 400

Parallel lamination.......................................................

17

Current ripples and/or ripple crosslamination......

Load casts....................................................................

Figure 3.3.3-3 (b). Graphic log of measured section 08MWB-S1, through Twitya Formation and lower part of Keele Formation, southeast of Shale (Palmer) Lake in NTS 106A. Base of section is at 489347E/7147757N and top is at 487940E/7147661N (UTM, Nad 83, zone 9). From base to top of section.

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1100

KEELE FORMATION

Chapter Three

08MWB-S1 43 42 41

Legend

1000

40

Dolostone.........................................................................

Siltsone and shale with lesser sandstone.............

Sandstone with lesser siltstone and shale.............

Shale lithoclasts..................................................

Convolute bedding or lamination.................................

Mudstone and/or siltstone partings....................

Parallel lamination..............................................................

ES

39

38

900

Load casts............................................................................... Current ripples and/or ripple crosslamination......

Old Elephant Skin................................................................

ES

Figure 3.3.3-3 (c). Graphic log of measured section 08MWB-S1, through Twitya Formation and lower part of Keele Formation, southeast of Shale (Palmer) Lake in NTS 106A. Base of section is at 489347E/7147757N and top is at 487940E/7147661N (UTM, Nad 83, zone 9). From base to top of section.

is more gradual. The Keele Formation is sharply overlain by the Ice Brook Formation or “Tepee dolostone” map unit. Southwest of the outcrop belt of the Keele Formation, its basinward equivalent (in terms of stratigraphic position) is the Ice Brook Formation, although much of the Ice Brook Formation is younger than the Keele Formation. The transition takes place across a “breakaway scarp” (Eisbacher, 1978b; Aitken, 1991). The composition of the Keele Formation is highly variable. It is dominated by limestone and dolostone (Fig. 3.3.3-5a and b) in some areas but by siliciclastic strata elsewhere. Lithofacies have been described in detail by Eisbacher (1981) and, particularly, Day et al. (2004). The main carbonate lithofacies are microbial laminite, intraclast grainstone, and ooid to peloid grainstone. Less commonly present are lime mudstone, finely crystalline limestone, ribbon-bedded limestone, and rudstone/floatstone of debrisflow origin. Stromatolites are present at some levels and, with microbial lamination, are the only biogenic material known from the formation. Some lithofacies contain siliciclastic sand or silt, or have been extensively dolomitised. Common fresh colours are grey, light grey, and light tan. The main weathering colours are light tan or light grey; some of the less common lithofacies weather dark grey to black. Dolomitisation has destroyed primary textures in many carbonate beds but cross-bedding, parallel-lamination, waveand current-ripple cross-lamination, and microbial lamination are locally discernable. Beds are thin to thick. Siliciclastic lithofacies are shale, siltstone, sandstone (including quartz arenite, subarkose, and lithic arenite to sublitharenite), and granule to pebble conglomerate (Fig. 3.3.3-5c). On fresh and weathered

surfaces, shale is grey, green-grey, brownish-grey, or black, siltstone is grey, black, or brown, and sandstone and conglomerate are brown, tan, yellow, white, or green-grey. Sandstone is fine- to coarse-grained, thin- to thick-bedded and preserves parallel lamination, current- and wave-ripple cross-lamination, swaley cross-stratification, hummocky cross-stratification, and trough and tabular cross-stratification. Slumpfolds, slide surfaces, and sole marks also are present. Thickness of the Keele Formation ranges from 300 to 600 m (Day et al., 2004). In some sections, the Keele Formation is carbonate-dominated through its entire thickness. A strongly developed cyclicity characterises some sections, where laminated, commonly shaly carbonate alternates with thicker-bedded, ooid grainstone facies (Eisbacher, 1978b). Day et al. (2004) identified depositional sequences and correlated them from Stone Knife River (NTS 106A) to Glacier Lake (NTS 95L). Regionally, the Keele Formation can be subdivided into a lower, carbonate-dominated member and an upper, siliciclastic-dominated member (Aitken, 1991; Day et al., 2004). The upper member has been informally referred to as the “Keele clastic wedge”. Near the “breakaway scarp” (east of Shale (Palmer) Lake), a tongue of shale resembling Twitya Formation or Ice Brook Formation (Delthore Member) divides the lower, carbonate-dominated Keele Formation into three submembers: a lower, carbonate-dominated interval with abundant carbonate conglomerate: a middle interval consisting mainly of fine-grained siliciclastic rocks; and an upper interval dominated by typical Keele Formation carbonate lithofacies (Figs. 3.3.3-2 and -3). These submembers were documented by Aitken (1991; see also Fig. 3.3.3-3). The so-called “Keele clastic wedge” is present here as well.

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Chapter Three

Figure 3.3.3-4. Outcrop photographs of Twitya Formation, showing characteristic lithofacies. In both photographs, markings on hammer handle are 10 cm apart. (A) Interbedded sandstone (quartz wacke), siltstone, and shale; NTS 106A. (B) Thick-bedded, coarse-grained sandstone and conglomerate, NTS 106A.

In addition to the basinward transition into siliciclastic units, the Keele Formation preserves major along-strike facies changes in the Sekwi project area. Around Shale (Palmer) Lake (NTS 106A), the formation is carbonate-dominated, whereas in parts of northwestern NTS 95M, siliciclastic facies are generally dominant (Eisbacher, 1978b; Day et al., 2004; present work).

Age and correlation The Keele Formation preceded the main deposition of glacial deposits in the Ice Brook Formation. It thus is older than the Marinoan glaciation and, consequently, is of Cryogenian age. Negative carbon isotope values from the Keele Formation are comparable to other units of this age globally (Narbonne et al., 1995; Narbonne and Aitken, 1995). The Keele Formation is known to extend into the Wernecke Mountains, Yukon (Eisbacher, 1981).

Interpretation Sedimentological study of the Keele Formation suggested that carbonate lithofacies were deposited in environments ranging from outer ramp (below storm wave-base) to peritidal, whereas siliciclastic lithofacies record shelf, shoreface, and continental (including fluvial) deposition (Day et al., 2004).

Ice Brook Formation The Ice Brook Formation of Aitken (1991) is best known for preserving the deposits of a post-Rapitan glacial event. It occupies the same stratigraphic level as the Keele Formation but is present either outboard (southwest) of that unit or as patchily distributed, thin accumulations on top of it. It is exposed at least as far southwest as the Sayunei Range in NTS 106A and Sekwi Brook in NTS 105P, and was mapped by Blusson (1972) as his map unit 8. The formation is subdivided into, in ascending order, the Durkan, Delthore, and Stelfox members (Aitken, 1991; Fig. 3.3.3-6). Aitken (1991) acknowledged that the members were not all mappable, and they were not mapped during the present work. During the Sekwi project, one section was measured through the Ice Brook Formation (08MWB-S6; Fig. 3.3.3-7). Aitken (1991) published several sections, including type sections for the formation (in the Sayunei Range, south central NTS 106A) and its members (all in a reference section northwest of Stelfox Mountain). Strata now assigned to the Ice Brook Formation were assigned to the Keele Formation in sections by Eisbacher (1978b, his section 6; 1981; his section 4).

116

Description The Ice Brook Formation is best described in terms of its three members, which are presented in ascending order. Depending on which member is present at its base, the Ice Brook Formation lies with sharp or gradational contact upon the Twitya Formation. Its upper contact is sharp. The Durkan Member consists essentially of a single olistostrome. It is a relatively resistant diamictite, consisting of limestone and dolostone boulders, as well as “rafts” of transported carbonate strata, in a mudstone matrix. Clasts are pale grey and weather orange; matrix is dark-weathering. Internally the olistostrome is chaotic, massive, and unsorted. Its lower and upper contacts are sharp. Along the platform margin of the Keele Formation, the Durkan Member can be mapped as a single tongue of carbonate debris derived from the lower part of the Keele Formation (Eisbacher, 1978b; Aitken, 1991). Distribution and thickness of this member are discontinuous. Near the “breakaway scarp” of the lower Keele Formation, the Durkan Member is tens of metres thick but it thins drastically basinward to 3 m or less over a few kilometres (Aitken, 1991). Horizons of scattered clasts (mainly pebbles and cobbles) of orange-weathering carbonate present in the upper Twitya Formation at some localities may be the most distal expression of the Durkan Member. Overlying the Durkan Member, with a sharp contact, is the semi-resistant Delthore Member. It is up to 60 m thick, but because it resembles the Twitya Formation it cannot be delimited reliably where the Durkan Member is not present (Aitken, 1991). It consists of siltstone, mudstone, sandstone (including quartz arenite), and minor diamictite, and locally contains lonestones. The member is pale grey to grey on fresh surfaces and weathers brown or grey. Siltstone and very fine sandstone typically are laminated to very thin bedded, although quartz arenite is locally very thick bedded. Sandstone beds have sharp to erosional bases, in some cases with load casts, flutes, or groove casts. Ripple cross-lamination is present, and Aitken (1991) reported the presence of Tbc and Tabc type Bouma sequences. Soft-sediment deformation, including slumpfolds, is common. The most widely mappable subdivision of the Ice Brook Formation is the Stelfox Member. Most strata mapped as Ice Brook Formation during the Sekwi project belong to this member. It is a resistant-weathering cliff-former that is up to 300 m thick in basinal sites (though it is locally as thin as a few metres in such settings) but generally less than 20 m thick where it overlies the Keele Formation. In outboard sections, the base of the Stelfox Member is sharp to

Chapter Three gradational but apparently conformable upon rocks mapped either as Delthore Member or Twitya Formation. Where it overlies the Keele Formation, the contact is locally karstic and probably disconformable. The Stelfox Member is dominated by carbonate-clast diamictite (Fig. 3.3.3-8), with lesser shale, siltstone, and sandstone. Fresh colours include light grey, grey, and pale brown; the member weathers greyish orange to tan. Diamictite consists mainly of pebbles in a calcareous siltstone matrix (Fig. 3.3.3-8). The Stelfox Member is commonly massive, and bedding is generally indistinct; a weak bedding-parallel fabric is locally produced by preferential orientation of clasts. A small number of beds preserve normal grading (Aitken, 1991) or are contorted. Rare striated clasts have been documented. Sandstone and siltstone preserve parallel lamination, starved ripples, normal grading and cross-lamination. Pebble lags, lonestones (dropstones), and till pellets were reported from these lithofacies by Aitken (1991). The Ice Brook Formation has yielded no fossils.

Age and correlation The Stelfox Member is considered to have been deposited during the 660-635 Ma Marinoan glacial interval (Knoll et al., 2006). Lonestones in the Delthore Member may also point to deposition during this event. The Durkan Member evidently was derived from the “lower Keele” platform (see above), and so it is broadly coeval with the Keele Formation. If the Delthore Member correlates with the tongue of Twitya Formation that overlies carbonate olistostromes shed from the lower Keele Formation near Shale (Palmer) Lake, then it also may be broadly coeval with the Keele Formation. Stratigraphic relationships indicate that the Stelfox Member post-dated deposition of the Keele Formation (Fig. 3.3.3-6).

Interpretation Aitken (1991) discussed the probable depositional mechanisms for the Ice Brook Formation. The Durkan Member is considered to be an olistostrome shed from the “lower Keele” platform, a view also shared by Eisbacher (1978b) and supported by observations during the Sekwi project. In the Delthore Member, the presence of slump structures, probable turbidites, and minor debris flows suggests deposition on a slope. Poorly sorted to chaotic diamictites in the Stelfox Member are demonstrably of debris-flow origin. The unit largely is of glaciomarine origin, indicated by dropstones, till pellets, and rare striated clasts.

“Tepee dolostone” map unit

Figure 3.3.3-5. Outcrop photographs of Keele Formation, showing characteristic lithofacies. In all photographs, markings on hammer handle are 10 cm apart. (A) Grey, thin-bedded limestone and mudstone, northwest NTS 95M. (B) Pale grey-weathering carbonate in NTS 106A. (C) Cross-bedded quartz arenite and conglomerate in NTS 106A.

Gabrielse et al. (1973a) documented a distinctive orange-buff weathering dolostone (Fig. 3.3.3-9) that was considered to be the uppermost member of the Keele Formation. This unit has proven to be a useful marker horizon, because it forms a light-weathering, prominent rib below the dark-weathering Sheepbed Formation. Eisbacher (1981) referred to it as the “Tepee dolostone” member of the Keele Formation. Aitken (1991) pointed out that this name is inappropriate, because the map unit contains limestone as well as dolostone, and does not contain “tepee” structures, sensu stricto, such as those documented from peritidal settings. Aitken (1991) also demonstrated that the “Tepee dolostone” was separated from the Keele Formation by the Ice Brook Formation or an unconformity, depending on the location, and thus should not be part of the Keele Formation.

117

Chapter Three Tepee dolostone

ox telf

S

Keele Formation

Sheepbed Formation

r.

Mb

br.

re M

ho Delt

Ice k o Bro Twitya Formation Durkan Mbr. Legend

Figure 3.3.3-6. Stratigraphic relationships among the members of the Ice Brook Formation and adjacent units. Diagram reproducedFigure from Aitken (1991). 3.3.3-6

Limestone......................................................................

Shale..............................................................................

Diamictite.....................................................................

Siltstone........................................................................

Sandstone....................................................................

James et al. (2001) provided a detailed description of the “Tepee dolostone” and assigned the lower, dolostone part of the unit to an informal “Ravensthroat formation” and an upper, limestone interval to an informal “Hayhook formation”. Regrettably, these formations, which are being increasingly adopted in the literature, were not formalised in accordance with the North American Code of Stratigraphic Nomenclature, nor were type sections established. Additionally, the subdivision of the “Tepee dolostone” into two formations is unsatisfactory from a mapping perspective. In many places, the entire “Tepee dolostone” is barely resolvable on 1:100 000 scale geological maps of the Mackenzie Mountains produced during the Sekwi Project (NWT Open File 2010-09 to 17). The thickest accumulation of the Ravensthroat formation measured by James et al. (2001) is 18 m, and that of the “Hayhook formation” 15 m. As a result, the two “formations” of James et al. (2001) are better treated as members of a single map unit. Resolution of these lithostratigraphic difficulties is beyond the scope of this report. During mapping for the Sekwi project, all strata in this interval were mapped as “Tepee dolostone” map unit. It would be desirable to adopt a better, formal name for this interval in future work. The “Tepee dolostone” map unit is present in the hanging-wall panel of the Plateau fault. In NTS 106A, it is present at least as far southwest as the Sayunei Range. In northwestern NTS 95M, it is extensively exposed southwest of the Plateau fault. The “Tepee dolostone” map unit was included in one section measured during the Sekwi project (08MWB-S6; Fig. 3.3.3-7). It is also present in sections presented by Gabrielse et al. (1973a), Eisbacher (1981), and Aitken (1991). James et al. (2001) presented ten detailed measured sections through the unit.

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Description The basal contact of the “Tepee dolostone” map unit commonly is covered, but, where exposed, is sharp. Aitken (1991) suggested that there may have been erosion of the Stelfox Member prior to “Tepee dolostone” deposition. The overlying Sheepbed Formation lies sharply on the “Tepee dolostone”, possibly with minor, local erosional relief (Aitken, 1991). The contact between the lower (dolostone) and upper (limestone) intervals of the “Tepee dolostone” is a karstic surface with erosional relief. The most detailed description of the “Tepee dolostone” was provided by James et al. (2001). The lower member of the map unit (informal “Ravensthroat formation”) is dominated by microcrystalline dolostone that is pale grey or pale tan and weathers yellow, cream, peach, and pinkish yellow (Fig. 3.3.3-9). Layering is very thin- to medium-bedded. Much of this interval is laminated, although massive-looking beds also are present. Corrugated (stromatolitic) bedding and elongate, tepee-like structures are common in some sections. The upper member of the map unit (informal “Hayhook formation”) is limestone that is dark grey on fresh surfaces and weathers grey. Quartz siltstone laminae are present locally. Layering is thin- to mediumbedded and peloidal facies are common. Some intervals have been dolomitised. A distinctive feature of this member in many sections is the presence of crystal bundles and laminated sea-floor precipitates that resemble stromatolites; both are neomorphic after aragonite (James et al., 2001). Both members of the “Tepee dolostone” generally thin basinward. In the most outboard exposures, only the dolomitic lower member is present (e.g., Fig. 3.3.3-9).

400

Chapter Three

08MWB-S6

300

13

200

SHEEPBED FORMATION

EDIACARAN

14

12

11

10

Legend

9

8 5, 6, 7

100

ICE BROOK FM., STELFOX MEMBER

CRYOGENIAN

TP

4 3

Sandstone with lesser siltstone and shale.............

Quartz wackle..................................................................

Siltstone and Shale.........................................................

Quartz arenite...................................................................

2

Diamictite........................................................................

Accessory sand...................................................

Carbonate lithoclasts...........................................

1

Calcareous....................................................................

Parallel lamination.......................................................

0

T WITYADELTHORE

Dolostone...........................................................................

Figure 3.3.3-7 (a). Graphic log of measured section 08MWB-S6. Base of section is at 533347E/7070891N and top is at 532431E/7069738N (UTM, Nad 83, zone 9). Section includes uppermost Twitya Formation (or possibly Delthore Member of Ice Brook Formation), Stelfox Member of the Ice Brook Formation, “Tepee dolostone” map unit, Sheepbed Formation, and the lower member of the Backbone Ranges Formation. Section is in NTS 106A. (a), (b), and (c) are from base to top of section.

119

Figure 3.3.3-7b

19

800

Chapter Three

08MWB-S6

py

17

16

py

600

EDIACARAN SHEEPBED FORMATION

700

py

18

15

500

py

Legend Black shale.........................................................................

Sandstone with lesser siltstone and shale.............

Siltstone and shale with lesser sandstone.............

Siltstone and Shale.........................................................

Pyrite..........................................................................

400

14

Figure 3.3.3-7 (b). (continued).

120

py

Accessory sand...................................................

Parallel lamination.......................................................

Accessory conglomerate.....................................

Normal Grading........................................................

B. R. FM., middle mbr.

Figure 3.3.3-7c

Chapter Three

08MWB-S6

Thickness estimated.

23

1000

EDIACARAN BACKBONE RANGES FM; lower member

1100

Viewed at a distance

py

22

Legend 900

20

19

Conglomerate.................................................................

Quartz arenite..................................................................

Dolomitic sandstone.....................................................

Dolostone...........................................................................

Sandstone with lesser siltstone and shale.............

Calcareous....................................................................

Tectonic folding..........................................................

Mudstone and/or siltstone partings....................

Pyrite................................................................................

T

Parallel lamination.......................................................

Current ripples and/or ripple crosslamination......

Load casts....................................................................

py

800

SHEEPBED FORMATION

21

Figure 3.3.3-7 (c). (continued).

121

Chapter Three Age and correlation The “Tepee dolostone” is considered to correlate with other “cap carbonates” that were deposited globally following the Marinoan glaciation. The base of these distinctive carbonates correlates with the base of the Ediacaran System, which has been dated as ca. 635 Ma (Knoll et al., 2006). Thus, the “Tepee dolostone” is the oldest Ediacaran map unit in the Mackenzie Mountains. It has been recognised (as “Ravensthroat formation”) in the Wernecke Mountains, Yukon (Pyle et al., 2004).

Interpretation The origin of Neoproterozoic post-glacial “cap carbonates” has been caught up in controversies about the “snowball Earth” hypothesis, but such matters are beyond the scope of this report. Readers are referred to James et al. (2001) for a thorough discussion of the probable depositional and diagenetic history of the “Tepee dolostone”. In summary, these authors interpreted the lower, dolostone member (their “Ravensthroat formation”) as predominantly deposited by chemical precipitation from seawater following a major glacial event, whereas the upper, limestone member (“Hayhook formation”) reflects carbonate deposition under more normal-marine conditions.

3.3.4. Unnamed “upper group” of the Windermere Supergroup R.B. MacNaughton Strata above the Hay Creek Group make up an informal “upper group” within the Windermere Supergroup (Fig. 3.3.11). Formations generally accepted as belonging to this interval in the study area are, in ascending order, the Sheepbed, Gametrail, Blueflower, and Risky formations. Of these, the Sheepbed and Gametrail formations are universally considered to be present in the hanging-wall panel of the Plateau fault, and to extend well to the west. By contrast, the Blueflower and Risky formations were considered by Aitken (1989a) to be absent east of sections exposed around Sekwi Brook, whereas Fritz (1982; Fritz et al., 1983,1991) considered these formations to correlate with strata in the hangingwall panel of the Plateau fault. These issues will be addressed later in this report, as part of the discussion of basal Cambrian siliciclastic

Figure 3.3.3-8. Outcrop photograph of Stelfox Member of Ice Brook Formation. Note characteristically abundant, unorganised carbonate clasts in tan to brown, calcareous, silty matrix. Marks on hammer handle are 10 cm apart, in NTS 106A.

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units (see Chapter 3.4.1). The present part of the report will discuss only those formations defined by Aitken (1989a) as belonging to the Windermere Supergroup in the Mackenzie Mountains. These units are present in the hanging-wall of the Plateau fault and in smaller exposures west of the fault in NTS 105P (Fig. 3.3.4-1).

Sheepbed Formation The Sheepbed Formation is a dark-weathering, shaledominated, recessive map unit (Fig. 3.3.4-2) that is present extensively west of the Plateau fault. It was named by Gabrielse et al. (1973a), with a type section >750 m thick at Sheepbed Creek in NTS 95L. At one time, it was considered to be the uppermost formation of the Windermere Supergroup in the Mackenzie Mountains (e.g., Eisbacher, 1981, 1985), although subsequent work by Aitken (1989a) caused this view to be abandoned. At least one lead-zinc-silver deposit (Majesty) is hosted by the Sheepbed Formation (Aitken, 1991). During the Sekwi project, MacNaughton et al. (2008b) included the upper part of the Sheepbed Formation in one measured section (section MWB07-02; Fig. 3.3.4-2), and it was measured in its entirety as part of section 08MWB-S6 (Fig. 3.3.3-7). Other published sections include those of Gabrielse et al. (1973a), Aitken et al. (1973), Eisbacher (1981), Aitken (1989a), Narbonne and Aitken (1990), Dalrymple and Narbonne (1996), and Shen et al. (2008).

Description The base of the Sheepbed Formation is sharp in all exposures and marks a notable difference in weathering character relative to underlying resistant formations. The contact with the overlying Gametrail Formation is gradational (Figs. 3.3.4-2 and -3; see also Aitken, 1989a; MacNaughton et al., 2000, 2008b). Where the Gametrail Formation is absent at some localities along the hangingwall panel of the Plateau fault (Gabrielse et al., 1973a; Aitken, 1989a), the Sheepbed Formation is overlain, presumably with erosional disconformity, by the lower member of the Backbone Ranges Formation (Fig. 3.3.3-7). Shale is the dominant rock type in the Sheepbed Formation, and is dark grey, brown, or black on fresh and weathered surfaces (Fig. 3.3.4-4a). Black, pyritic shale is common in the lower part of the formation, whereas siltstone is prevalent in the upper part. Shale and siltstone commonly are laminated; siltstone contains rare current

Figure 3.3.3-9. Outcrop photograph of dolostone facies of “Tepee dolostone” map unit. Note characteristic orange-tan weathering tone, NTS 106A.

Chapter Three ripples. In some exposures, bedding in mudstone-dominated intervals is obscured by cross-cutting cleavage. Thin, sharp-based, normalgraded beds of very fine- to fine-grained sandstone are common at some levels and locally contain current ripples. Such beds are generally pale brown to brown (fresh and weathered). In the upper parts of some sections along the Plateau fault (e.g., MacNaughton et al., 2008b), pale brown, light grey, or white, quartz-rich sandstone is increasingly common in the upper part of the formation (Fig. 3.3.44b). Local features of such units include cross-bedding, parallel lamination, hummocky cross-stratification, thin to thick bedding, and lenticular caps of maroon-weathering quartz granule to pebble conglomerate. In exposures at Sekwi Brook, massive channel-fills that include coarse-grained sandstone and pebble conglomerate are present at several horizons (Dalrymple and Narbonne, 1996). Also at Sekwi Brook, Dalrymple and Narbonne (1996) reported minor volumes of parted to ribbon-bedded limestone, some as rafted blocks, as well as debrites of reworked siliciclastic mudrocks and sandstone. Soft-sediment deformation, including slump-folds and slump masses, is prevalent, particularly in more outboard exposures. Ediacaran body fossils from the Sheepbed Formation were described by Narbonne and Aitken (1990) and Narbonne (1994). A low-diversity assemblage of acritarchs was recovered from the upper part of the formation (Baudet et al., 1989). Rare structures originally assigned to the simple burrow ichnogenus Planolites montanus by Narbonne and Aitken (1990) have been reinterpreted as dubiofossils or pseudofossils (G.M. Narbonne, pers. comm., 1998). No formal subdivisions of the Sheepbed Formation have been proposed, but Dalrymple and Narbonne (1996) considered it to consist of three informal members (lower, middle, and upper), each progressively more sandy than those beneath. Upwardcoarsening (and shallowing) of the formation is well documented in both proximal and distal sections (Gabrielse et al., 1973a; Fritz, 1982; MacNaughton et al., 2008b). The formation thickens to the southwest, away from the Plateau fault (e.g., Shen et al., 2008).

Age and correlation The position of this unit directly above the “Tepee dolostone” map unit indicates an early Ediacaran age (see discussion above). This is supported by the presence of body fossils of the Ediacara fauna in the Sheepbed Formation. Correlation of the Sheepbed Formation in the Sekwi project area is relatively straightforward. The formation is known to extend into the Wernecke Mountains, Yukon (Eisbacher, 1981; Pyle et al., 2004).

Interpretation Dalrymple and Narbonne (1996) interpreted the Sheepbed Formation at Sekwi Brook as a continental-slope deposit, based on the presence of turbidites, debrites, slumps, and submarine channels, as well as probable contourites. No comparably detailed studies have been done for the entire formation nearer the Plateau fault. There, shale-dominated lower parts of the formation could be of deep-shelf or slope origin (Narbonne and Aitken, 1995; Shen et al., 2008) but the upper part of the formation preserves evidence of wave action (Shen et al., 2008; MacNaughton et al., 2008b) and of shoreface and possibly fluvial deposition (MacNaughton et al., 1999, 2008b).

Gametrail Formation The Gametrail Formation is dominated by resistant-weathering dolostone or limestone and forms cliffs at many localities. It is present only west of the Plateau fault and is notable for preserving a well-

developed lateral transition from carbonate platform to carbonate slope deposits. The Gametrail Formation is probably present as an unnamed carbonate at the contact between the Sheepbed and Backbone Ranges formations in a section presented by Gabrielse et al. (1973a). It was shown in a cross-section, but not discussed, by Eisbacher (1981, his Figure 11), and was referred to by Aitken (1984) as the “Sheepbed carbonate”. Aitken (1989a) named the formation and presented a log of its type section near Sekwi Brook (~320 m), as well as stylised sections from several other localities. Similarly simplified sections were presented by Baudet et al. (1989). MacNaughton et al. (2000) remeasured the type section and examined other sections in the same vicinity (Fig. 3.3.4-5). In the course of the Sekwi project, sections were measured near Godlin River (MacNaughton et al., 2008b; Fig. 3.3.4-3 and -6) and south of Moose Horn River.

Description The base of the Gametrail Formation is in gradational contact (Fig. 3.3.4-3) with the underlying Sheepbed Formation (Aitken, 1989a; MacNaughton et al., 2008b). Along the Plateau fault, the Gametrail Formation is overlain sharply or erosionally by the lower member of the Backbone Ranges Formation (Fig. 3.3.4-6). Karst features (including karst pipes) have been documented in the upper Gametrail Formation (Aitken, 1989a). To the southwest, at Sekwi Brook, the contact with the overlying Blueflower Formation is gradational (Aitken, 1989a; MacNaughton et al., 2000). Aitken (1991) considered the Gametrail Formation to contain two broad lithofacies associations, a conclusion supported by the present work. The platformal association is dominated by particulate (ooids, peloids) dolostone and sandy dolostone that is pale grey to grey on fresh surfaces and weathers grey to pale grey (Fig. 3.3.47a). It is thin- to thick-bedded (Fig. 3.3.4-7b), commonly with welldeveloped trough cross-bedding, low-angle cross-bedding, or sharply defined parallel lamination (Fig. 3.3.4-7c). Carbonate breccia layers are locally present (Fig. 3.3.4-7b). The basinal association is characteristically pale grey to grey or dark grey, well-bedded limestone (locally dolomitised) that weathers grey, pale grey, or pale greyish-tan (Fig. 3.3.4-8a). Thin to medium beds are massive, parallel-laminated, or current-ripple crosslaminated, and contain Bouma sequences. Bases and tops of beds are sharp. Sedimentary micro-faults and slump-folds are common and layering locally is cut by arcuate intraformational truncation surfaces. This lithofacies contains rare Ediacaran body fossils, as well as the oldest trace fossils reported from the Mackenzie Mountains (MacNaughton et al., 2000). Another important lithofacies in the basinal assemblage is chaotic intraclast rudstone (“megabreccia”), which is present as thin to very thick, massive beds containing clasts that are up to boulder-sized (Figs. 3.3.4-5 and -8b). In some sections along the Plateau fault, notably south of Moose Horn River, both assemblages are present, with the platformal overlying the basinal (Aitken, 1989a; this work). To the southwest, as at Sekwi Brook, only the basinal assemblage is present, implying that the platform deepened to the southwest. Near Shale (Palmer) Lake, the exhumed margin of the Gametrail platform is visible in mountainside exposures (see discussion in Aitken, 1989a). Rudstone (“megabreccia”) facies are most characteristic of the basinal assemblage, but also are present at least locally at the top of the Gametrail Formation along the Plateau fault. The Gametrail Formation locally has been removed beneath the lower member of the Backbone Ranges Formation along the Plateau fault (Aitken, 1991). At some localities north of Shale (Palmer) Lake, the Gametrail Formation was extensively brecciated, presumably by

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Figure 3.3.4-1. Distribution of the unnamed “Upper group” of the Windermere Supergroup in NTS 105P, 106A, and northwest 95M. This unnamed “upper group” includes the Sheepbed, Gametrail, Blueflower, and Risky formations.

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Figure 3.3.4-2. Sheepbed to Backbone Ranges formations, viewed looking southwest from a site 2 km southeast of Godlin River. Recessive, dark-weathering shale in foreground is all part of the Sheepbed Formation, whereas overlying, more resistant map units (Gametrail and Backbone Ranges formations) form the ridge. Measured section MWB07-S2 (see Figure 3.3.4-3) is shown.

Figure 3.3.4-4. Outcrop photographs of Sheepbed Formation, taken along route of Section MWB07-S2 (Figure 3.3.4-3). (A) Shale and siltstone from interval 1 of section MWB07-S2; hammer handle is 30 cm long. These are the characteristic lithofacies through much of the Sheepbed Formation. Strata young to left. (B) Siltstone and overlying, increasingly sandy beds defining an upward-coarsening package near the top of the Sheepbed Formation (interval 10 of section MWB07-S2). Geologist for scale. Strata young to top.

post-depositional karst weathering, and forms distinctive pinnacles today (Fig. 3.3.4-9). Dolomitisation has been pervasive in much of the Gametrail Formation in the hanging-wall panel of the Plateau fault. Farther outboard, dolomitised zones are both parallel to and at a high angle to primary layering. “Presquilite” veins of white, baroque dolomite are common in many exposures of the Gametrail Formation, notably in its type area (Aitken, 1991).

Age and correlation Stratigraphic position and the presence of Ediacaran body fossils constrain the Gametrail Formation to an Ediacaran age. The

geographic distribution of this formation extends into the Wernecke Mountains, Yukon (Pyle et al., 2004).

Interpretation The platformal assemblage of the Gametrail Formation was deposited in shallow water on a marine platform, probably in relatively energetic conditions (Aitken, 1991; MacNaughton et al., 2008b). Basinal assemblage strata were deposited in deeper water, on a carbonate slope (MacNaughton et al., 2000). Chaotic accumulations of intraclast rudstone (“megabreccia”) in basinal sections were deposited as debris flows (MacNaughton et al. 2000)

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Figure 3.3.4-3. Graphic log of measured section MWB07-S2, through uppermost Sheepbed Formation and basal Gametrail Formation; note gradational contact between formations, and general upward coarsening of Sheepbed Formation. For a view of this section, see Figure 3.3.4-2. Section is near Godlin River in northeastern NTS 105P. Base of section is at 515916E/7088569N and top is at 515630E/7088366N (UTM, Nad 83, zone 9). Reproduced from MacNaughton et al. (2008).

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Chapter Three and probably reflect failure of oversteepened platform margins. Rudstone accumulations nearer the Plateau fault (i.e., in relatively shallow water) may be related to karst development. The Gametrail Formation’s platformal assemblage was extensively karstified at some sites. The origin of the hydrothermal dolomite (“presquilite”) veins that have been noted at many localities has not been established, and could be a profitable subject for future work.

Blueflower Formation The Blueflower Formation is a semi-resistant to recessively weathering map unit dominated by shale and siltstone (Fig. 3.3.410), locally with a mixed carbonate-siliciclastic lower member (Fig. 3.3.4-5). It was originally mapped as part of Map unit 10b of Blusson (1972) and was formally named by Aitken (1989a), with a type section near Sekwi Brook (~450 m). It has been studied in detail only in the Sekwi Brook area and June Lake anticline of NTS 105P, but probably is present to the west of those areas. Possible tongues of Blueflower Formation lithofacies have been noted between the Gametrail Formation and lower member of the Backbone Ranges Formation near Shale (Palmer) Lake (NTS 106A). The Blueflower

Formation was not studied in detail during the Sekwi project and no sections were measured. Measured sections including the Blueflower Formation have been published by Aitken (1989a), Narbonne and Aitken (1990), and MacNaughton et al. (2000); see Figure 3.3.4-5. Baudet et al. (1989) also presented a simplified section through the formation.

Description The conformable contact of the Blueflower Formation with the clean carbonates of the Gametrail Formation is marked by the introduction of shale and sandstone (Aitken, 1989a; MacNaughton et al., 2000). At Sekwi Brook, the contact is gradational and corresponds to a change in weathering profile from the resistant, cliff-forming Gametrail Formation to the semi-resistant, carbonaterich lower member of the Blueflower Formation. In the June Lake anticline, the lower member is not present and the contact is sharp, with mudrock lying upon carbonate. The contact with the overlying Risky Formation is gradational. Lithological descriptions of the Blueflower Formation are based on Aitken (1989a) and MacNaughton et al. (2000). Through

Figure 3.3.4-5. Measured sections through Gametrail Formation (“basinal assemblage”), Blueflower Formation, and Risky Formation, at the type area of these units near Sekwi Brook. Diagram is modified from MacNaughton et al. (2000).

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Figure 3.3.4-6. Graphic log of measured section MWB07-S3 through Gametrail Formation. For a view of this section, see Figure 3.3.4-7a. Fault in interval 4 does not noticeably affect section thickness. Section is near Godlin River in northeastern NTS 105P. Base of section MWB07-S3 is at 512452E/7091700N and top is at 512354E/7091668N. B.R.F. (lwr.) = Lower member, Backbone Ranges Formation. S.F. = Sheepbed Formation. Reproduced from MacNaughton et al. (2008).

much of its thickness, the Blueflower Formation is dominated by shale, siltstone, and very fine- to fine-grained sandstone (Fig. 3.3.410). The shale is dark grey to black, weathering to black, grey, or brown. Sandstone is tan, brown, grey, or pale grey to white on fresh surfaces, and weathers tan, grey, brown, or, less commonly, orange to (for sandstone only) tan. Mudrocks are laminated and sandstone is very thin- to thick-bedded. In much of the formation, sandstone beds are sharp to erosionally based, commonly with sole marks, and display Bouma subdivisions, including massive, parallel-laminated, and current-ripple cross-laminated intervals. In the upper part of the formation, sandstone beds tend to be both thicker than below, and dolomitic. Soft-sediment deformation features include loadcasts, flames, and slump-folds. Slump masses and intraformational truncation surfaces are present. At Sekwi Brook, the lower third of the formation is dominated by limestone that is grey on fresh surfaces and weathers pale to medium grey. Very thin to thin beds of lime mudstone, wackestone, or packstone commonly are interstratified with partings or thin interbeds of dark grey mudstone or shale, producing ribbonbedded limestone. Such beds contain Bouma subdivisions (massive, parallel-laminated, or current-ripple cross-laminated intervals). Also present are thick beds of grey, massive or, rarely, trough cross-

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bedded packstone, with up to 30% quartz sand, minor rudstone, and intervals of sandstone and shale (as described above). Carbonate interbeds are much less prevalent farther west in the June Lake anticline, although some intervals of ribbon-bedded limestone were recorded by Aitken (1989a). At Sekwi Brook, the upper, siliciclastic interval of the Blueflower Formation contains several horizons of massive, chaotic, breccia or conglomerate (Fig. 3.3.4-10). Such intervals are up to several metres thick, with clasts up to boulder size in a mudstone matrix that weathers dark grey or brown. Clasts include reworked dolostone, shale, and sandstone; dolostone clasts commonly weather orange or brown. Thrombolite mounds have been recovered from these beds (Aitken and Narbonne, 1989). House-sized dolostone olistoliths also are present. At Sekwi Brook, the Blueflower Formation is capped by a sharp-based package of up to several tens of metres of cross-bedded to swaley cross-stratified quartz sandstone. Fossils in the Blueflower Formation include Ediacaran bodyfossil impressions (Narbonne and Aitken, 1990; Narbonne, 1994; MacNaughton et al., 2000), horizontal trace fossils (Narbonne and Aitken, 1990; MacNaughton et al., 2000), and acritarchs (Baudet et al., 1989).

Chapter Three

Figure 3.3.4-7. Outcrop photographs of platformal assemblage of Gametrail Formation, all from Section MWB07-03. Reproduced from MacNaughton et al. (2008). (A) View of Section MWB07-03; note resistant character of Gametrail Formation. Described intervals in section (Fig. 3.3.4-6) are labelled. Strata young to left. Helicopter provides scale. (B) Well-bedded dolostone to sandy dolostone (interval 3 in (A)), some with low-angle to parallel lamination. Hammer rests on carbonate rudstone (breccia). Stratigraphic top is to left. Hammer handle is approximately 30 cm long. (C) Physical sedimentary structures preserved in a talus block (probably from interval 4 in Figure 3.3.4-7a). Note presence of scours, cross-bedding, and well-developed parallel bedding. Top of photograph corresponds to stratigraphic top of block. Clasp knife is approximately 10 cm long.

Age and correlation

Interpretation

The presence of Ediacaran body fossils indicates an Ediacaran age for the Blueflower Formation. Among these is Windermeria aitkeni, the only dickinsoniid reported from northwestern Canada (Narbonne, 1994), which suggests an age younger than ca. 560 Ma (Narbonne, 2005). As will be discussed below, the Blueflower Formation may correlate, at least in part, with the lower member of the Backbone Ranges Formation. The name has been applied to similar, Ediacaran-fossil-bearing strata in the same stratigraphic position in the Wernecke Mountains (Yukon; Pyle et al., 2004).

The prevalence of probable turbidites (carbonate and siliciclastic) and abundant slump structures suggests deposition on the continental slope (MacNaughton et al., 2000). Chaotic conglomeratic deposits are probably debrites derived from an adjacent, exposed carbonate platform, which is also the probable source of the carbonate olistoliths. Increasing prevalence of sandstone upward suggests upward shallowing through the formation, as does the presence of evidence for shoreface deposition (i.e., swaley crossstratification) in the uppermost, sandstone-dominated interval of the formation.

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Risky Formation The Risky Formation is currently considered to be the uppermost formation in the Windermere Supergroup in the Mackenzie Mountains (Narbonne and Aitken, 1995). It is a resistantweathering map unit dominated by dolostone, sandy dolostone/ dolomitic sandstone, and quartz arenite (Fig. 3.3.4-5). It was formalised by Aitken (1989a), with a type section near Risky Peak (~115 m). Its presence in NTS 105P was documented by Blusson (1972), who referred to it as Map unit 11, but included it in his Map unit 10 in several areas. In NTS 105P, the Risky Formation extends at least as far southwest as the east limb of the June Lake anticline, but according to Aitken (1989a), it is absent in the west limb. If the Risky Formation correlates with the middle member of the Backbone Ranges Formation (Fritz, 1982; Fritz et al., 1983, 1991), then it is present in the hanging-wall of the Plateau fault. If these units are not correlative, as in the view favoured by Aitken (1989a), then the Risky Formation is not known to be present northeast of the Sekwi Brook area. Measured sections including Map unit 11 or the Risky Formation have been presented by Fritz et al. (1983), Aitken (1984, 1991), Baudet et al. (1989), Narbonne and Aitken (1990); sections previously measured by MacNaughton et al. (2000) are shown in Figure 3.3.4-5. No detailed study was done on this unit for the Sekwi project.

Description

Figure 3.3.4-8. Probable basinal assemblage lithofacies of the Gametrail Formation. In both photographs, hammer handle is marked with 10 cm divisions; top of photograph is stratigraphic top. (A) Very thin to thin-bedded dolostone. In some localities, such lithofacies preserve evidence of turbidites. (B) Carbonate dolorudstone. In the basinal assemblage, rudstone locally forms intervals up to tens of metres thick and records deposition from debris flows or other grain-rich sedimentgravity flows. Other thick accumulations of carbonate breccia in the Gametrail Formation are the result of extensive karstification.

Figure 3.3.4-9. Thick accumulations of karst-related carbonate breccia in the Gametrail Formation, now weathering as pinnacles. Site pictured is north of Shale (Palmer) Lake in NTS 106A.

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The Risky Formation’s contact with the underlying Blueflower Formation is gradational to abrupt but conformable. It was placed by Aitken (1989a, p. 20) at the level where thick-bedded dolostone or sandstone assumes “clear dominance over mudrocks”, although MacNaughton et al. (2000; their Figure 5) implicitly placed the contact at the level where carbonate rocks assumed dominance. Either approach corresponds to a marked change in weathering character, from the recessive upper member of the Blueflower Formation to the resistant, cliff-forming Risky Formation. At most localities, the contact with overlying map units is sharp and erosional (e.g., Fig. 3.4.1-10). At Sekwi Brook, the contact is karstic (including sand-filled grykes) and erosional relief is present at the contact at several localities.

Figure 3.3.4-10. Lower part of upper member of Blueflower Formation near Sekwi Brook (NTS 105P), showing dark-weathering shale and siltstone and brownweathering, thin-bedded sandstone. At centre of photograph is a polymictic debrite containing abundant carbonate clasts. Photograph along route of section B illustrated in Figure 3.3.4-5.

Chapter Three The dominant rock types of the Risky Formation are dolostone, sandy dolostone, dolomitic sandstone, and quartz sandstone. Such lithofacies are light grey, light tan, or grey on the fresh surface and weather cream, orange, tan, or light grey. Limestone and shale are less common, and commonly are grey on both fresh and weathered surfaces. The formation is well bedded and commonly blocky weathering. Thick to very thick bedding is characteristic, but medium and thin bedding are also present. Where primary fabrics can be observed in dolomitised carbonates, the rocks are packstones, grainstones, or less commonly rudstones; the main allochems are ooids, oncoids, and peloids, commonly with some fine quartz sand. Both carbonate and quartz-sandy lithofacies contain trough crossbedding, swaley cross-stratification, hummocky cross-stratification, and parallel lamination. Stromatolites are common at Sekwi Brook but much less so in the June Lake anticline (Aitken, 1989a). Vuggy porosity is common at some sites. Rare, poorly preserved trace fossils are present but no body fossils have been reported. The Risky Formation apparently thins to the west before disappearing between the east and west limbs of the June Lake anticline, presumably due to non-deposition. The formation is increasingly sandy to the west (Aitken, 1989a). MacNaughton et al. (2000) discussed the probable sequence-stratigraphic packaging of the formation at Sekwi Brook. The Risky Formation is known to contain at least one Zn-PbCu occurrence in the Sekwi project area (Appendix H).

Age and correlation The age of the Risky Formation is established by its stratigraphic context. It lies conformably upon the Blueflower Formation, which preserves Ediacaran body fossils, but beneath the Ingta Formation, which preserves an Ediacaran-Cambrian boundary. Thus, the Risky Formation must be of late Ediacaran age. It also is present in the Wernecke Mountains, Yukon (Nowlan et al., 1985; Pyle et al., 2004).

Interpretation The Risky Formation has been considered to be mainly of shallow-marine (platformal) origin (Aitken, 1989a; MacNaughton et al., 2000). This is based on the presence of sedimentary structures pointing to significant wave action (swaley and hummocky crossstratification) and other high-energy structures (high-angle crossbedding, parallel lamination in sandstone). Cross-bedded oolitic dolograinstone presumably was deposited on high-energy ooid shoals in shallow water, and much of the sandstone was deposited at shoreface depths.

3.4. Lower to Middle Paleozoic Mackenzie Platform 3.4.1 Lowest Paleozoic siliciclastic succession R.B. MacNaughton In the Sekwi project area, lowest Paleozoic siliciclastic formations are preserved only west of the surface trace of the Plateau fault (Fig. 3.4.1-1); east of the fault, they have been removed over the Redstone Arch. Discussion of these formations is complicated by uncertainties in correlation. Identifying the top of the Windermere Supergroup and tracing the Backbone Ranges Formation westward from its type area are related problems that bedevil the lithostratigraphy of this interval. The upper limit of the terrigenous clastic interval is much

better constrained, and is defined by the appearance of carbonaterich strata that contain Lower Cambrian trilobites. Figure 3.4.1-2 summarises the salient issues. The interval between the top of the Gametrail Formation and the base of trilobite-bearing Cambrian strata records significant westward lithofacies changes. In the hanging-wall of the Plateau fault, this interval is represented by three thick members of the Backbone Ranges Formation. Westward, at Sekwi Brook and June Lake, the same interval contains (in ascending order) the Blueflower, Risky, Ingta (at June Lake and farther west), “Backbone Ranges”, and Vampire formations. (In this report, the designation “Backbone Ranges Formation” is used to distinguish the more restricted usage (in western exposures) from the tripartite Backbone Ranges Formation in the hanging-wall of the Plateau fault.) Some workers (Aitken, 1989a; Baudet et al., 1989) have considered the “Backbone Ranges” and Vampire formations successions in the west to correlate with the entirety of the Backbone Ranges Formation near the Plateau fault, and all formations below the “Backbone Ranges Formation” to belong to the Windermere Supergroup. Inherent in this view is the interpretation of the Backbone Ranges Formation as entirely of Early Cambrian age (Figure 2 of Aitken, 1991). Other workers (Fritz, 1982; Fritz et al., 1983, 1991; MacNaughton et al., 2008b) have correlated the Ingta-to-Vampire formations succession in the west with only the upper member of the Backbone Ranges Formation in the east, viewing the Risky Formation [formerly Map unit 11 of Blusson (1972)], as equivalent to the middle member of the Backbone Ranges Formation. This interpretation underlies the correlations adopted in the present report, although correlation issues have not been decisively settled as of this writing. A key implication of this correlation is that the lower two members of the Backbone Ranges Formation near the Plateau fault are probably of Ediacaran age and correlate with Windermere formations (sensu Aitken, 1989a). Notwithstanding this, these lower two members are described in this part of the report for the sake of clarity. Map units included in this succession are as follows. Along the hanging-wall of the Plateau fault, the Backbone Ranges Formation consists of three mappable, informal members: a lower member of sandstone, siltstone, and minor dolostone; a middle member dominated by dolostone; and an upper member dominated by quartz sandstone (Fig. 3.4.1-3). Farther west, the succession treated herein is probably equivalent only to the upper member. There, the basal unit, the Ingta Formation, is dominated by siltstone and shale. The overlying “Backbone Ranges Formation” is dominated by quartz sandstone but contains notable volumes of siltstone. Above this, the Vampire Formation is dark-weathering siltstone and shale (Fig. 3.4.1-4). Basinward, the “Backbone Ranges Formation” passes into a sand-rich, siltstone-dominated succession assigned to a thickened Vampire Formation. Owing to its presumed lateral equivalence to basinal strata in Yukon (Gordey and Anderson, 1993) the Vampire Formation is described in this report among those formations assigned to the Selwyn Basin succession (Chapter 3.5.1).

Backbone Ranges Formation, lower member The Backbone Ranges Formation was defined by Gabrielse et al. (1973a), who also described its three informal members. The type section of the formation and members is near Sheepbed Creek in NTS 95L. Each of the three members is of formation-scale thickness in the study area. The lower member of the Backbone Ranges Formation (~500 m thick) is a mixed unit of quartz sandstone, siltstone, and dolostone

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Figure 3.4.1-1. Distribution of basal Cambrian map units in NTS 105P, 106A, and northwestern 95M. Because of problems in correlation, some uppermost Ediacaran strata may also be included in this diagram.

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Chapter Three (Fig. 3.4.1-5). It is exposed in the hanging-wall panel of the Plateau fault throughout the study area and is most conspicuous southwest of the Plateau fault in NTS 106A Measured sections that include the lower member have been published by Gabrielse et al. (1973a), Aitken et al. (1973), Fritz (1982), and MacNaughton et al. (2008b; Fig. 3.4.1-5). MacNaughton et al. (1999) provided a preliminary redescription of the lower member at the type section.

Description The base of the lower member is sharp and commonly erosional (Aitken, 1989a). Basal layers locally contain reworked dolostone clasts derived from the underlying Gametrail Formation (Fig. 3.4.1-6a). The Gametrail Formation is absent owing to erosion at some locations (Aitken, 1989a), including the type section of the Backbone Ranges Formation (Gabrielse et al., 1973a; Fritz, 1982); there, the lower member is in contact with the Sheepbed Formation. The contact is presumably erosional, but is difficult to recognise where the upper part of the Sheepbed Formation is also sandy. The contact with the overlying middle member is sharp. The lower member is heterolithic (Figs. 3.4.1-5 and -6b), but generally is dominated by sandstone, with lesser (though still abundant) siltstone and shale, and minor dolostone. Sandstone generally is quartz arenite or less commonly quartz wacke. Some quartz sandstone layers contain quartz granules and pebbles. Quartzose sandstone is grey, light grey or pale tan on fresh surfaces and weathers white, pale grey, tan, pink, or maroon. Silty sandstone is brown or tan on fresh surfaces and generally weathers brown. Mudrocks are tan, light brown or deep maroon on fresh or weathered surfaces. Iron staining is common in siliciclastic facies at some levels. Dolostone is light tan or light grey on the fresh surface and weathers orange, tan, grey, or brownish grey. Bedding thickness is variable; thin to medium bedding is very common but thick and very thick beds of sandstone are present. Cut-and-fill packaging is locally well developed. Sedimentary structures include trough crossstratification, low-angle cross-stratification, parallel bedding and parallel lamination, desiccation cracks, and synaeresis cracks. The lower member has yielded no body fossils but simple trace fossils were collected from the type section. The thickness of the lower member decreases by an order of magnitude between its type section (269.5 m; Fritz, 1982) and Godlin River (67.5 m; MacNaughton et al., 2008b), approximately 160 km to the northwest. Regional variations in facies and stratigraphic packaging have not been studied.

Age and correlation The presence of simple trace fossils implies that the unit is not older than the Gametrail Formation, which is the oldest unit in the Mackenzie Mountains to contain trace fossils (MacNaughton et al., 2000). It also is consistent with the correlation between the lower member and part or all of the Blueflower Formation, implied by Fritz et al. (1991).

Interpretation No detailed account of the lower member’s sedimentology has been published. MacNaughton et al. (1999, 2008b) noted that the range of lithofacies and sedimentary structures preserved in the lower member is consistent with deposition in a range of shallowmarine and continental environments.

Backbone Ranges Formation, middle member The middle member of the Backbone Ranges Formation (~150 m) is a resistant, cliff-forming unit of well-bedded, brightly coloured carbonate rocks (Figs. 3.3.4-2 and 3.4.1-3). It is exposed in the hanging-wall panel of the Plateau fault throughout the study area. The following authors have included the middle member in published sections: Gabrielse et al. (1973a), Aitken et al. (1973), Fritz (1982), and MacNaughton et al. (2008b). MacNaughton et al. (1999) re-described the middle member at the type section, but did not publish section notes.

Description The base of the middle member is sharp in all studied exposures and presumably represents a marine flooding surface. Locally, reworked siltstone of the lower member is present in the basal bed of the middle member. The upper contact is sharp throughout the study area and may be locally erosional. At the type section in NTS 95L, the top of the middle member is a major karst horizon marked by carbonate breccia and solution pipes (Fritz, 1982; MacNaughton et al., 1999). The middle member is dominated by well-bedded, micro- to finely crystalline dolostone and limestone. Fresh colours are light grey, grey, or light tan. Weathering colours are highly variable, including light grey, maroon, pink, tan, and orange (Fig. 3.4.1-6c and 6d). Distribution of weathering tones lends a banded appearance to many cliff exposures (Figs. 3.3.4-2 and 3.4.1-3). Some parts of the middle member preserve well-developed, maroon mudstone partings (Fig. 3.4.1-6c). The carbonate rocks are very thin- to mediumbedded, but predominantly thin-bedded. They commonly exhibit parallel lamination, intraclast (flat-pebble) rudstone, and microbial lamination. In the type section, MacNaughton et al. (1999) reported soft-sediment slump-folds and a capping unit of 60 m of stromatolite boundstone. No body or trace fossils have been reported. The middle member is best-documented in the hanging-wall of the Plateau fault, where it extends from the type area at least as far northwest as Mountain River (Gabrielse et al., 1973a; Aitken et al., 1973). In NTS 106A, it is present in structural panels southwest of the Plateau fault. It may be laterally equivalent southwestward to the Risky Formation in NTS 105P. Significant lateral and vertical variations in colour, noted in the middle member during mapping, are not consistent or systematic.

Age and correlation The age of the middle member is constrained only by its stratigraphic position. If correlation with the Risky Formation is accepted, then it is of late Ediacaran age.

Interpretation Preliminary discussions of the middle member’s sedimentology were presented by MacNaughton et al. (1999; 2008b). In the Sekwi project area, the regular, well-laminated character of much of the middle member indicates deposition in quiet, marine settings. Intraclast rudstone suggests the influence of episodic storms.

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Figure 3.4.1-2. Ediacaran-Cambrian lithostratigraphy in the study area. Both Godlin River and Sheepbed Creek regions are in the hanging-wall of the Plateau fault; Sheepbed Creek is the type area of the Sheepbed and Backbone Ranges formations in NTS 95L. Note the marked change in lithostratigraphy to the west, typified by exposures around Sekwi Brook and June Lake in NTS 105P.

Figure 3.4.1-3. Overview photograph of Backbone Ranges Formation, displaying the characteristic subdivision into three members that exists along the hanging-wall of the Plateau fault. View is to southeast, from coordinates 518626E/7084434N in northeastern NTS 105P. Stratigraphic top is to the right. Abbreviations are: GT = Gametrail Formation; lBR = lower member, Backbone Ranges Formation; mBR = middle member, Backbone Ranges Formation. At this site, the top of upper member may have been removed by faulting. Photograph reproduced from MacNaughton et al. (2008).

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Figure 3.4.1-4. Sekwi Mountain, as viewed from the south, with exposed formations labelled. Bedding is overturned to the right; oldest formations are to the left. Here, the Ingta Formation lies unconformably upon the Risky Formation of the Windermere Supergroup (barely visible at extreme left of photograph). Note recessive-weathering character of Ingta and Vampire formations relative to much of the “Backbone Ranges Formation”. Photograph taken by G.M. Narbonne in 1991.

Backbone Ranges Formation, upper member; “Backbone Ranges Formation” The resistantly weathering upper member of the Backbone Ranges Formation (~760 m) is responsible for the castellated appearance of many cliffs in the hanging-wall and to the west of the Plateau fault (Fig. 3.4.1-3). The formation generally is dominated by quartz sandstone, much of which is thick-bedded. The following authors have included the upper member in published sections: Gabrielse et al. (1973a), Aitken et al. (1973), and Fritz (1982). Two sections were measured during the Sekwi project; one through the upper member near Moose Horn River (Section 08MWB-S2; Fig. 3.4.1-7) and one through the basal beds of the upper member near Godlin River (Fig. 3.4.1-5; MacNaughton et al., 2008b). In treating the upper member of the Backbone Ranges Formation, it is necessary to discuss the status of Map unit 12 of Blusson (1971). In northeastern NTS 105P, in the hanging-wall of the Plateau Fault, Map unit 12 includes the three characteristic members of the Backbone Ranges Formation (MacNaughton et al., 2008). Farther southwest of the Plateau fault, the situation is less straightforward. There, Map unit 12 lacks the tripartite subdivision typical of the Backbone Ranges Formation. It generally is sandstone dominated, although Blusson (1971) may have included the underlying, shale-dominated Ingta Formation (see below) in Map unit 12 in the June Lake anticline. Aitken (1989) applied the name Backbone Ranges Formation to the sandstone-dominated portion of Map unit 12, and considered it to contain strata equivalent to the lower, middle, and upper members. In the present report, sandstonedominated exposures of Map unit 12 southwest of the hanging-wall

of the Plateau Fault are considered to be equivalent to the upper member only (see discussion above) and are referred as “Backbone Ranges Formation”. MacNaughton et al. (1997a,b) referred to this sandstone-dominated interval as the Backbone Ranges Formation, and divided it into lower and upper members based on the relative proportion of sandstone and siltstone. These informal members can be confused with the members defined by Gabrielse et al. (1973a) and should not be propagated in the literature. If the correlations described above are correct, strata assignable to the upper member are present from the hanging-wall of the Plateau fault west to the shale-out into the Vampire Formation (see below), approximately along-strike from the confluence of the Keele and Ingta rivers. Measured sections that include Map unit 12 or “Backbone Ranges Formation” were published by Fritz (1979b, 1980), Fritz et al. (1983), and MacNaughton et al. (1997a, b).

Description The lower contact of the “Backbone Ranges Formation” is conformable, or possibly mildly erosional (Aitken, 1989a) in the east limb of the June Lake anticline, and presumably is conformable to the west. To the east and northeast, the contact between the “Backbone Ranges Formation” and the Risky Formation (Aitken, 1989a; MacNaughton et al., 2000) or between the upper member and the middle member (Fritz, 1982; MacNaughton et al., 1999) is erosional and commonly karstic. The “Backbone Ranges Formation” is overlain sharply but conformably by shale of the Vampire Formation (Figs. 3.4.1-4 and -8), recording an apparently abrupt marine transgression (MacNaughton et al., 1997b). In the Sekwi project area, the upper member is overlain gradationally by carbonate rocks or shale of the Sekwi Formation (Gabrielse et al.,

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Figure 3.4.1-5. Measured section MWB07-S4, through lower and middle members of Backbone Ranges Formation. Section is near Godlin River in northeastern NTS 105P. Base is at 520768E/7083234N and top is at 520618E/7083113N. Reproduced from MacNaughton et al. (2008).

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Figure 3.4.1-6. Outcrop photographs of lower and middle members of Backbone Ranges Formation; all photographs are from Section MWB07-S4 (see Fig. 3.4.1-5 for location) and are reproduced from MacNaughton et al. (2008). (A) Erosional base (at arrows) of Backbone Ranges Formation. At left of hammer point is a reworked clast of dolostone from the underlying Gametrail Formation (below arrows). Beds are upright. Hammer is approximately 30 cm long. (B) Outcrop exposure of lower member, Backbone Ranges Formation. Lower and upper parts of outcrop are interbedded sandstone, siltstone, and shale, with orange-weathering sandy dolostone at geologist’s feet. To the right of the geologist is medium- to thick-bedded quartz sandstone. Beds are upright. (C) Pink- to maroon-weathering, thin-bedded carbonate in middle member, Backbone Ranges Formation. Block indicated by arrow is about 30 cm long. Beds young to right. (D) Cream-weathering dolostone, middle member, Backbone Ranges Formation. Marks on hammer handle are 10 cm apart. Beds young to right.

1973a; Fritz, 1981). In the type area, the upper member is overlain disconformably by Middle Cambrian strata of the Avalanche Formation (Gabrielse et al., 1973a; Fritz, 1982). The dominant rock type in this map unit is thin- to very thickbedded, very clean, well-sorted quartz sandstone (Figs. 3.4.1-4, -8 and -9), which ranges from very fine-grained to conglomeratic. Fresh colours are white, pale grey, pale tan, and pale pink; weathered colours are white and pale grey, locally pink, deep maroon, or ironstained. Common sedimentary structures include trough and planar cross-bedding, locally of very large scale. Compound cross-bedding, overturned foresets, flaggy parallel bedding and parallel lamination, conglomeratic lags, and rare adhesion structures have also been documented. Cut-and-fill stratigraphy and channel cross-sections are present at numerous levels in the quartz arenite packages. A second common lithofacies is very thin- to medium-bedded, very fine- to fine-grained quartz arenite to wacke that is light brown to tan on fresh and weathered surfaces. Such layers locally exhibit hummocky or swaley cross-stratification; where interbedded with mudrocks, they are locally current-rippled, including starved ripples.

Bases of beds are sharp to erosional, commonly with tool marks and flute-modified burrows. Siltstone and shale are also common; these are tan, brown, olive, or maroon or fresh and weathered surfaces and commonly are laminated. Mudrocks in the formation commonly preserve synaeresis or desiccation cracks. Light grey crystalline dolostone to quartz-sandy dolostone, weathering orange, cream, or light grey, is also present. No body fossils or microfossils have been recovered from this unit. Trace fossils, including many that were probably produced by arthropods, are abundant in the siltstone-rich intervals (MacNaughton and Narbonne, 1999), as are problematica that may be assignable to a trace-fossil origin (Hofmann, 1983). MacNaughton et al. (1997a) documented both upwardcoarsening and upward-fining packages in the “Backbone Ranges Formation” in the June Lake anticline (Fig. 3.4.1-8); preliminary study of other sections suggests that such patterns may be preserved elsewhere. The larger-scale stratigraphic packaging of this unit varies notably from east to west. In the hanging wall of the Plateau fault, thick beds of quartz sandstone generally dominate, and

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Figure 3.4.1-7

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Figure 3.4.1-7. Measured section 08MWB-S2 through upper member of Backbone Ranges Formation, south of Moose Horn River in northwestern NTS 95M. Base is at 571593E/7034881N and top is at 571364E/7035559N. Section illustrates sandstone-dominated character of the upper member along the hanging-wall of the Plateau fault.

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Figure 3.4.1-8. Detailed measured section through the Ingta, “Backbone Ranges”, and Vampire formations at Sekwi Mountain in central NTS 105P. For a photograph of these strata, see Figure 3.4.1-6. Reproduced from MacNaughton et al. (1997a).

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Figure 3.4.1-9. Thick-bedded, resistant-weathering quartz arenite in upper member of Backbone Ranges Formation. Photograph is of interval 4 in measured section 08MWB-S2 (Figure 3.4.1-7; see Fig. 3.4.1-7 for location).

Figure 3.4.1-10. Type section of Ingta Formation, viewed from the south. Bedding is overturned to the right; oldest formations are to the left. Risky Formation is part of the Windermere Supergroup. In this section, Ingta Formation has a well-developed capping member of pale-weathering, stromatolitic limestone.

Figure 3.4.1-11. Platy, well-indurated siltstone and very fine-grained sandstone in the Ingta Formation, southwestern NTS 105P. Beds are upright.

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Chapter Three siltstone-dominated intervals are relatively minor (Fig. 3.4.1-7). At Sekwi Brook, this unit consists of a basal quartz sandstone interval, overlain in turn by a recessive-weathering siltstone package, and a thick package of quartz sandstone. In the June Lake anticline, it consists of the lower, siltstone-dominated and upper, quartz-arenitedominated interval (informal members of MacNaughton et al., 1997a) referred to above (Fig. 3.4.1-8). The formation becomes increasingly fine-grained to the west and southwest, passing laterally into the much siltier lithofacies of the Vampire Formation. This is consistent with paleocurrent data presented by MacNaughton et al. (1997a), which indicated that seaward transport by rivers was to the present-day west and southwest.

Age and correlation Trace fossils place the “Backbone Ranges Formation” in the subtrilobite Cambrian Rusophycus avalonensis Zone (MacNaughton and Narbonne, 1999). If the upper member correlates with the Ingta, “Backbone Ranges”, and Vampire formations, it ranges in age from latest Ediacaran to Early Cambrian (Fallotaspis Zone).

Interpretation MacNaughton et al. (1997a) studied the sedimentology of the “Backbone Ranges Formation” in the east limb of the June Lake anticline, and concluded that it records marine to continental deposition in a braid-delta system. Sub-environments included mid-shelf, shoreface, beachface, delta front and delta plain, fluvial channel/distributary, and eolian dune fields. Comparable studies have not been done elsewhere in the upper member. MacNaughton et al. (1999) suggested that much of the upper member was of braided-fluvial origin in its type section. Given the prevalence of thick, trough-cross-bedded sandstone, and the presence of desiccation features, this interpretation probably applies to much of the upper member in the Sekwi project area as well.

Ingta Formation The Ingta Formation, named by Aitken (1989a), is a variegated, siltstone- to shale-dominated map unit, capped by a limestone member. The type section (Fig. 3.4.1-10) is in the east limb of the June Lake anticline (63° 21’ 10” N, 128° 30’ 00” W). Blusson (1971) mapped the Ingta Formation as the basal part of his Map unit 12; Fritz (1982; Fritz et al., 1983) considered it a “lower sub-member” of Map unit 12, whereas Aitken (1984) referred to it as the “Variegated formation”. During the Sekwi project, the Ingta Formation was included on traverses but was not a subject of detailed study. The Ingta Formation has been documented only in NTS 105P, where is present in both limbs of the June Lake anticline (Aitken, 1989a) and probably extends to the west to form part of Map unit 10a of Blusson (1972). It is not known to extend east of Natla River and its northward and southward extents are not known. No sections were measured in the Ingta Formation during the Sekwi project. Measured sections were published by Fritz et al. (1983; “lower submember” of Map unit 12 in their sections 11 and 12), Aitken (1989a), and MacNaughton et al. (1997a, b). All published sections are from the east limb of the June Lake anticline.

Description In the east limb of the June Lake anticline, the Ingta Formation overlies the Risky Formation with a disconformable contact (Fig. 3.4.1-10) that shows local development of karst (Aitken, 1989a;

MacNaughton et al., 1997b). The contact may be conformable in the west limb. The upper boundary was interpreted as erosional by Aitken (1989a), who noted lateral changes in the thickness of the limestone member that caps the formation. Much of this relief, however, is probably due to the presence of microbial bioherms in the limestone member. Laminated to thin-bedded siltstone and mudstone dominate the Ingta Formation (Fig. 3.4.1-11). These rock types are strikingly variegated, including tones of maroon, apple-green, tan, brown, and grey, and are locally iron-stained. Sandstone is much less common, consisting mainly of very thin to thin, sharp-based beds of very fine-grained sandstone, with well-developed current ripples or, less commonly, hummocky cross-stratification. Locally, the basal few metres of the formation consists of sandstone containing hummocky or swaley cross-stratification. At some localities, the siltstone-dominated lower part of the formation contains scattered, very thin beds of lime mudstone or intraclast (flat-pebble) rudstone. The Ingta Formation is capped by up to 40 m of grey-weathering limestone that is locally stromatolitic or oolitic (Figs. 3.4.1-8, -10). No macroscopic body fossils are known from the Ingta Formation, but trace fossils are common (Aitken, 1989a; MacNaughton and Narbonne, 1999). Carbonate beds yield a depauperate assemblage of small shelly fossils as well as phosphatic microproblematica (Conway Morris and Fritz, 1980; Nowlan, 1993, 1995, 2002). Carbonate strata assigned to Blusson’s (1972) map unit 11 (=Risky Formation of Aitken, 1989a) by Conway Morris and Fritz (1980) are now considered to belong to the limestone member of the Ingta Formation (Narbonne and Aitken, 1995). Aitken (1989a) reported a thickness of 256 m for the Ingta Formation at its type section, and 220 m in the west limb of the June Lake anticline. It thickens southward from the type section (MacNaughton et al., 1997b). The siltstone-dominated part of the formation records subtle upward fining in its lower half, followed by equally subtle upward coarsening. The formation is generally finergrained to the south and (probably) west, and the capping carbonate member thins northward, westward, and southward away from the type section (MacNaughton et al., 1997b).

Age and correlation Trace fossil assemblages (MacNaughton and Narbonne, 1999) delineate a conformable Ediacaran-Cambrian boundary (base of Treptichnus pedum Zone) in the upper part of the Ingta Formation. Thin carbonate beds low in the formation record a strong negative excursion in carbon isotopic values that correlates with a similar latest Ediacaran excursion (Narbonne et al., 1994). Detailed correlation of the Ingta Formation beyond the June Lake anticline is uncertain. Observations on traverses in the western part of NTS 105P suggest that Blusson’s Map unit 10a locally contains facies like those of the Ingta Formation, and Aitken (1989a) commented on similarities between the Ingta Formation and the “Grit unit” to the west (cf. Gabrielse et al., 1973a). Whether the Ingta Formation correlates with basal Cambrian strata east of Natla River is a subject for further study. Aitken (1989a) considered the Ingta Formation to be the uppermost formation of the Windermere Supergroup. Subsequent workers (MacNaughton and Narbonne, 1999; MacNaughton et al., 2000) removed it from the Windermere Supergroup on the grounds that it lies unconformably upon Windermere strata, contains a conformable Ediacaran-Cambrian boundary, and appears to be overlain conformably by Cambrian strata.

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Chapter Three Interpretation The Ingta Formation records predominantly subtidal deposition in settings from distal shelf (siltstone, current-rippled sandstone) to lower shoreface (hummocky cross-stratified sandstone), although the basal sandstone, which contains swaley cross-stratification, probably accumulated in shallower water (MacNaughton et al., 1997a).

3.4.2. Lower Cambrian carbonate succession B.J. Fischer and M.C. Pope

Sekwi Formation The Sekwi Formation (Handfield, 1968) consists of lithologically diverse limestone and dolostone with subordinate siliciclastic rock and a geographically restricted component of volcanic rock. The type section (63°33’N, 128°44’W) is 5 km northwest of June Lake in central NTS 105P. The Sekwi Formation in and near the Sekwi project area was described by Gabrielse et al. (1973a), Aitken et al. (1973, 1982), Fritz (1975, 1976, 1978, 1979a, 1979b, 1981, 1992), and Gordey and Anderson (1993). The sedimentology and stratigraphy of the Sekwi Formation were described by Krause (1979) and Krause and Oldershaw (1978, 1979). The sequence stratigraphic evolution of the Sekwi Formation is presented in Dilliard (2006) and Dilliard et al. (2010), and a stable isotope chemostratigraphy of the formation has been established (Dilliard et al., 2007). Three Early Cambrian trilobite biozones (Fallotaspis, Nevadella and BonniaOlenellus) were established based on Sekwi Formation specimens and correlated globally (Fritz, 1972). The Sekwi Formation was the focus of a M.Sc. thesis during the Sekwi project (Fischer et al., 2009). Published sections of the Sekwi Formation in the Sekwi project area are listed in Appendix D. Sections through part of the Sekwi Formation at the Palm, AB, and TIC zinc showings are illustrated in Figure 3.4.2-2 and described in Appendix D. The Sekwi Formation is exposed along the western margin of the Mackenzie fold belt, reflecting its paleo-position along the shelf and slope of the Mackenzie Platform (Fig. 3.4.2-1). The formation is noted for both its prolific trilobite fauna and its abundant zinc(-lead) showings (see Chapter 7.2.2).

Description The lower contact of the Sekwi Formation is gradational with fine siliciclastic strata of the underlying Vampire Formation throughout most of NTS 105P and 105I, and is defined by the first appearance of pure carbonate beds. Where the Vampire Formation is absent, the Sekwi Formation conformably overlies quartz sandstone of the upper member of the Backbone Ranges Formation (Fig. 3.4.2-2). In the Sekwi project area (Fig. 3.4.2-1), the formation ranges from 518 m thick in the southeastern part of NTS 105P to 1149 m in the western part of NTS 105P, averaging about 700 m. Thicknesses in NTS 106A fall between these extremes. The formation is not exposed in northwestern NTS 95M. Outside the Sekwi project area, the formation is 800 to 1300 m thick in NTS 106B and 106C to the northwest, 30 m thick to the east in southwestern NTS 95M, and 90-800 m thick to the south and southeast, in NTS 105I, 95E, and 95L. Figure 3.4.2-2 depicts the regional stratigraphy of the Sekwi Formation based on work undertaken during the Sekwi project and the work of previous authors.

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The Sekwi Formation is overlain conformably by Middle Cambrian black calcareous shale and minor limestone of the Hess River Formation (which is as old as Early Cambrian farther west, where the basin was deeper). In easternmost positions, increasingly deep, lower Phanerozoic erosion permitted younger units to be deposited disconformably on top of the Sekwi Formation. These younger rocks consist of thinly bedded, basinal strata (silty limestone and shale) of the Late Cambrian to Early Ordovician Rabbitkettle Formation, platformal strata (dolostone and oncoidal dolostone) or transitional strata (silty dolostone, siltstone, and dolostone conglomerate) of the Cambro-Ordovician Franklin Mountain Formation, and basinal, black calcareous shale of the OrdovicianSilurian Duo Lake Formation. In eastern 105P and south of the Sekwi project area in NTS 95L, 95M (Gabrielse et al., 1973a), and 105I (Fritz, 1979b, 1981; Gordey and Anderson, 1993), the Sekwi Formation is conformably overlain by nodular limestone and shale of the Middle Cambrian Rockslide Formation, and locally by dolostone and oncolitic dolostone of the Avalanche Formation, both lateral equivalents of the upper Hess River Formation. In the northwesternmost extent of the basin, in NTS 106C, OrdovicianDevonian dolostone unconformably overlies the Sekwi Formation. The Sekwi Formation is notable for abrupt lithological changes, both horizontally and vertically. A widespread quartzsandy interval is present near the middle of the Sekwi Formation across most of the Sekwi project area and environs (Fritz, 1976, 1978, 1979a). For the purposes of this study, the Sekwi Formation is divided into three informal members whose boundaries are the top and bottom of the quartz-sandy interval: the lower carbonate member, the quartz-sandy member, and the upper carbonate member (Fig. 3.4.2-2). The quartz-sandy member is a quartz arenite marker unit in most of NTS 105P and 105I, but loses its distinction to the north and west. These informal member designations may not be applicable to the southeasternmost extents of the Sekwi Formation, in NTS 95E and 95L, where up to 120 m of mafic volcanic rocks are included in the formation. The lower carbonate member of the Sekwi Formation in western NTS 105P, and south of the Sekwi project area in NTS 105I, is dominated by deep-water deposits that shallow upward into an ooid (-oncoid) grainstone. The most widespread lithofacies of the lower carbonate member is wavy-bedded, nodular, silty limestone (Fig. 3.4.2-3) with centimetre-scale bands of dolomitic siltstone surrounding elongate, bedding-parallel limestone nodules. Other deep-water rock types common in the lower carbonate member are laminated, thinly and planar-bedded, brownish grey to black calcisiltstone, shale, and lime mudstone (Fig. 3.4.2-4). Glauconitic limestone is locally present at the base of the Sekwi Formation and a number of hardgrounds of limited lateral extent are present in the lower carbonate member. Slumping, soft-sediment folding, penecontemporaneous breccias, and debrites are common in the lower carbonate member of basinal sections in western NTS 105P and 105I. Debrites from 0.20 m to 30 m thick and up to several kilometres long form resistant, light grey bands that stand out on hillsides (Fig. 3.4.2-5). Individual debrites are typically overlain by a turbidite cap (Krause and Oldershaw, 1979). Clasts are tabular, range from centimetres to tens of metres long (usually 2-30 cm), and consist of lime mudstone, laminated calcisiltstone, and less commonly ooid grainstone, archeocyathan boundstone, or rippled quartz arenite, in a finely crystalline limestone matrix (Fig. 3.4.2-6). The origin of these units is discussed by Krause and Oldershaw (1979) and Dilliard et al. (2010). Large allochthonous blocks (up to several hundred metres long) are present in syndepositionally folded lime mudstone, calcisiltstone,

Chapter Three 131°0'0"W

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Figure 3.4.2-1. Distribution of Sekwi Formation exposures in Sekwi project area (NTS 105P, 106A, and northwestern 95M) and adjacent map sheets.

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Chapter Three and shale in the westernmost parts of NTS 105P. The upper part of the lower carbonate member in NTS 105P consists of ooidoncoid grainstone to dolograinstone and a range of quartz-sandy rock types. The grainstone is similar to that present in the upper carbonate member (described below). The lower carbonate member is 150-300 m thick except in northeastern exposures (NTS 106A/SW), where it consists of less than 100 m of thick-bedded dolostone, limestone bioherms, thin beds of dolomitic arenite, and minor breccia. In northwestern exposures (NTS 106B and 106C), siliciclastic shale and thinly bedded dolostone (locally quartz-rich) are as common as nodular limestone. Shoreward sections in NTS 105P are dominated by nodular limestone, and although they lack debrites, they do contain the occasional allochthonous block. The quartz-sandy member in NTS 105P and 105I consists of thinly to thickly bedded dolomitic arenite, thickly bedded orangeweathering dolostone with floating quartz grains of sand to granule grade, thick beds of pure quartz arenite that weathers white with a concealing cover of black lichen, and orange-, green-, and maroonweathering siltstone. Sedimentary structures in the quartz-sandy units include tabular and trough cross-bedding derived from 2D and 3D ripples and small, 3D dunes (Krause, 1979), parallel lamination and ripple cross-lamination, starved ripples, and ichnofossils including Skolithos isp. and Rosellia isp. (Figs. 3.4.2-7 and -8). The base of the quartz-sandy member in 105P/SE is locally a karstic surface in the underlying dolostone (Krause, 1979; Fritz, 1979a). The quartz-sandy member in NTS 106A, and northwest of the Sekwi project area in NTS 106B and 106C, consists primarily of brown-weathering siltstone and dolomitic siltstone, with subordinate dolomitic quartz arenite and limestone, including trilobite and archeocyathan rudstone. Orange-grey-weathering, microbial ± archeocyathan boundstone mounds up to 15 m high (Fig. 3.4.2-9) and limestone bioherms of unidentified composition (Fig. 3.4.2-10) are present in the lower and upper carbonate members, typically within 200 m of the quartz-sandy member. The upper carbonate member of the Sekwi Formation is dominated by shallow-water, subtidal to peritidal lithofacies, including recessive intervals of shale to calcareous shale, mudstone, and siltstone that weather bright red, orange or yellow (Fig. 3.4.211). A distinctive interval of yellow- and orange-weathering siltstone, averaging 50-100 m thick, is 100-200 m above the base of the upper carbonate member and is traceable across most of the Sekwi project area and areas to the northwest (Fritz 1976, 1978, 1979a). Grey to orange-grey weathering, thickly to thinly bedded, variably dolomitised ooid, oncoid, intraclast, and composite-clast grainstone and rudstone units range from centimetres to tens of metres thick (Figs. 3.4.2-12 and -13). Oncoid rudstone commonly grades vertically or laterally into ooid grainstone; both lithofacies are resistant and form prominent cliffs. Ooid and skeletal grainstones locally are ripple cross-stratified on a centimetre- to decimetrescale. Skeletal wackestone, packstone, and floatstone and their dolomitic equivalents are generally less resistant, thinner bedded, orange-brown weathering, and contain trilobite and brachiopod fragments, Salterella, archeocyathans, hyolithids, and centimetrescale thromboids in a lime mudstone to dolostone matrix (Fig. 3.4.214). Mottling in dark, finely crystalline dolostone and limestone is defined by amorphous, centimetre-scale variations in colour, crystal size, and organic or carbonate content, reflecting diagenetically modified differences in original composition and texture caused by burrowing. Up to 20% siliciclastic component is common in these rocks. Bioturbation and burrowing are common in skeletal and mottled lithofacies (Fig. 3.4.2-15). Local penecontemporaneous

144

deformation produced thin, polymictic dolostone debrites and softsediment folds. Pale yellowish grey weathering, microcrystalline to very finely crystalline dolostone preserving fine-scale peritidal fabrics is common in the upper carbonate member. Microbially laminated dolomudstone, dolosiltstone, and stromatolitic dolostone contain desiccation cracks, tepee structures, millimetre-scale mudstone intraclasts, pseudomorphs after evaporites, and a variety of trace fossils (Figs. 3.4.2-16 and -17). Stromatolites are unbranched, columnar and hemispherical varieties up to 40 cm high. Pale to medium grey weathering fenestral limestone (Fig. 3.4.2-18) is associated with mottled or burrowed carbonate mudstone and microbially laminated dolostone. Fenestrae in yellowish greyweathering dolostone locally contain pyrite, sphalerite and galena (Palm and Tee-1 showing areas, Appendix H). Thin, locally brecciated paleosol intervals of bright red-brown shale or siltstone are interspersed with peritidal rocks, especially in eastern sections. Skeletal metazoans preserved in the Sekwi Formation include abundant trilobites (Fritz, 1972, 1973) and fragmented brachiopods; whole inarticulate brachiopod shells are rare. Salterella specimens are concentrated in packstone beds. Hyolithids and solitary archeocyathans form wackestone and floatstone beds in the upper carbonate member. Chancelloriid sclerites are present in skeletal wackestone in the lower carbonate member (Randell et al., 2005). Archeocyathans and the “corallomorph” species Tabulaconus (Handfield, 1969; Murphy et al., 2003) locally contribute framework support to microbial (Renalcis, Girvanella, and Epiphyton) boundstone bioherms (Fig. 3.4.2-9). Stromatolitic and thrombolitic growth forms also are present in evenly layered strata outside of bioherms. A wide range of trace fossils is present in siliciclastic and muddy to silty carbonate rocks deposited in shallow to deep-water (slope and basinal) settings (Hasiotis et al., 2003). Traces include escape burrows (Fig. 3.4.2-7), dwelling burrows, trilobite resting and crawling traces, horizontal burrows in winding to straight, non-branching forms (Fig. 3.4.2-8), and vertical burrows up to 10 cm in diameter. Bioturbation is common and ichnofabric indices range from 1 to 5. Facies variations in the Sekwi Formation are significant at both local and regional scales. Local changes in depositional environment (for example, from carbonate shoal to lagoon) are reflected by lateral changes in lithofacies on a scale of metres to decametres. Regional variations are most marked in the lower carbonate and quartzsandy members, where thick intervals of deep-water lithofacies thin and become sandier to the east, near the paleo-shoreline (Krause, 1979; Dilliard et al., 2010). Two shoreward sections in NTS 106B contain a thick interval of quartz arenite near the top of the upper carbonate member. The upper carbonate member in southern NTS 105P and south of the Sekwi project area, in NTS 105I, contains abundant purple-weathering siltstone and more quartz-sandy rock than elsewhere (Gabrielse et al., 1973a; Fritz, 1981; Gordey and Anderson, 1993). Depositional rate in NTS 106B and 106C, to the northwest, increased during deposition of the quartz-sandy and upper carbonate members, whereas in NTS 105P it decreased during that time (Fritz, 1979a). In the southeastern corner of NTS 105I and in NTS 95E and 95L, mafic volcanic flows, breccias, and tuffs overlie and are intercalated with Sekwi Formation carbonate and siltstone. The volcanic interval is overlain locally by a distinctive, bright orange and yellow weathering unit of limestone and silty dolostone (the Brintnell member), which itself is overlain by more-typical rocks of the Sekwi Formation (Gabrielse et al., 1973a). The Brintnell member may be correlative with the yellow- and orange-weathering siltstone in the upper carbonate member in the Sekwi project area, based on lithological descriptions and gross stratigraphic position, but Fritz (1979a) did not comment on this possibility.

Northwest Composite

Hess River Fm.

(compiled from Fritz (1976) sections 1 & 2 and Krause (1979) Arctic vRed River section)

10

9k

m

North Composite (compiled from Fritz (1976) section 4, Fritz (1979) section 31, and Krause (1979) Mountain River section)

TIC (this study) transitional Franklin Mountain Fm.

Rabbitkettle(?) Fm.

white & laminated 4

S4-6

dark 3 & laminated 3

28 km

TIC

dark 2 & laminated 2

Cloudy(?) Fm.

vuggy 2 dark 1

Duo Lake(?) Fm.

µ

µ

laminated 1

Sekwi Fm. upper

Franklin Mountain Fm.

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carbonate member

storm & quartz-rippled

member 4

dune

mbr 3

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µ

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member 2

30 km

4 km

thicky bedded fenestral unit

AB

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Southeast South

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UTM z9N NAD83

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200 m

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Chapter Three

64−N

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Fallotaspis

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Legend carbonate lithologies limestone dolostone lime mudstone dolomudstone calcisiltstone dolosiltstone wackestone packstone grainstone Ÿoatstone rudstone boundstone modiÿers

siliciclastic lithologies

siliciclastic-silty

shale or mudstone siltstone sandstone

quartz-sandy sparsely quartz-sandy nodular sparsely nodular conglomerate breccia black weathering hardground

member

unconformity

Emily

informal member boundary

calcareous shale

biozone boundary

dolomitic shale

lus

correlation line

calcareous siltstone dolomitic siltstone calcareous sandstone dolomitic sandstone nodular shale

µ

µ

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fenestral fabric

mud cracks vugs sphalerite +/- galena cemented breccia

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ooids oncoids intraclasts skeletal fragments trilobites Salterella sp. hyolithids stromatolites archeocyathans microbial chert

S4 S3 S2

fault

siliciclastic-dominated lithologies

thin-bedded medium-bedded thick-bedded wavy-bedded with shale partings with siltstone partings resistant recessive karst surface bioturbated/mottled wavy laminated microbially laminated cross-stratiÿed

upper carbonate

formation boundary

bedding modiÿers argillaceous

Renalcis mounds

Palm (this study)

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Red Arctic

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Location Map

65−N

mudcracked unit (orange marker at base) mottled unit

108 km

Backbone Ranges Fm.

AB (this study)

quartz arenite unit

Vampire Fm.

Southeast Composite (compiled from Fritz (1976) section 10, Krause (1979) June Lake section, and Dilliard (2006) section 10)

South Composite (compiled from Fritz (1976) section 7, Fritz (1978) section 25, Krause (1979) Ingta River section, and Dilliard (2006) section 1)

Figure 3.4.2-2 Fence diagram for the Sekwi Formation in the Sekwi Project area and areas to the northwest provides temporal (sequence-stratigraphic and biostratigraphic), providing a paleoenvironmental context for this unit and the Zn-Pb showings it contains (stars). Third-order sequence-stratigraphic units (S0 to S6, coloured fences) are those of Dilliard et al. (2010) in southern areas, and have been tentatively projected to northern composite sections (see text). Composite sections are based on previous work as noted for each section, whereas detailed sections at AB, TIC and Palm showings were compiled from measured sections and mapping during Sekwi-project field work. Stratigraphic positions of base-metal showings other than AB, TIC, and Palm are from measured sections in assessment reports (Brock, 1973a; Helmstaedt and McGregor, 1974); stratigraphic position of ARN and TEE uncertainty is indicated by vertical bars. Correlation of members is based on Fritz’s (1976, 1978, 1979a) lithological correlations, which were guided by the assumption that the Nevadella - Bonnia-Olenellus biozone boundary remains within one lithological unit.

145

Chapter Three

Figure 3.4.2-3. Nodular to banded silty limestone typical of the lower carbonate member of the Sekwi Formation. Pale grey-weathering nodules and bands are limestone. Yellow-brown-weathering bands are quartz-silty limestone. Wrist band of glove is 5 cm across. (NTS 105P/11, 497450 E, 7063936 N).

Figure 3.4.2-6. Clast-supported breccia formed by a debris flow in the lower carbonate member of the Sekwi Formation. Clasts are dominantly lime mudstone and calcisiltstone. Hammer for scale is approximately 30 cm long. (NTS 105P/6, 481424 E, 7034611 N).

Figure 3.4.2-7. Escape burrows in cross-bedded quartz arenite of the upper part of the lower Sekwi Formation. (NTS 105P/11, 491186 E, 7052095 N). Figure 3.4.2-4. Interbedded, grey-weathering lime mudstone and brown-weathering, laminated lime siltstone from the lower carbonate member of the Sekwi Formation. Width of hammer handle is 2.5 cm. (NTS 105P/11, 788326 E, 7065640 N).

Figure 3.4.2-5. Debrites in the lower carbonate member of the Sekwi Formation. Pale grey-weathering, resistant layers stand out on hillside. Prominent grey layer in middle of photo is ~15 m thick. (NTS 105P/6, 493732 E, 7031010 N).

146

Figure 3.4.2-8. Trace fossils in rippled, desiccation-cracked fine sandstone and siltstone in the quartz-sandy member of the Sekwi Formation. Scale bar in centimetres. (NTS 105P/6, 481424 E, 7034611 N).

Chapter Three

Figure 3.4.2-9. Dolomitised microbial (Renalcis?) boundstone from a 7 m-high mound near the Palm showing. Saccate structure is visible in some of the microbial clots (e.g., to right of pen tip; inset). Pen cap is 1.3 cm wide at its base. (NTS 106A/05, 750589 E, 7152399 N)

Figure 3.4.2-11. Recessive siliciclastic to calcareous shale and mudstone units in the upper carbonate member of the Sekwi Formation weather bright yellow and orange. In foreground is ooid grainstone. Resistant grey band in mid-photo is a bioturbated skeletal wackestone. (NTS 105P/11, 787731 E, 7066245 N)

fronts locally cross-cut bedding planes and are spatially associated with faults. Dolomitisation is more intense in shoreward sections and preferentially affects the upper carbonate member, where complete dolomitisation is recorded in a number of sections. Dolomitisation in the lower Sekwi Formation is typically restricted to strata less than 100 m below the quartz-sandy member; deep-water facies are characteristically undolomitised. The Sekwi Formation is a major host of Zn-Pb mineralisation in the Sekwi project area (Appendix H). Brecciation, void-filling cementation, dolomitisation, and sulphide mineralisation in the Sekwi Formation are spatially interrelated. Breccia textures range from mosaic to rubble, cemented float- to packbreccias (sensu Morrow, 1982a) with angular to rounded clasts. Cement phases include iron, zinc, lead, and copper sulphides, dolomite, barite, calcite, and quartz. Replacement sphalerite and galena mineralisation is spatially related to the void-filling style, typically occurring in the same deposits (see Chapter 7.2.2). Mineralised areas are surrounded by a halo of pervasively dolomitised rocks. The detailed stratigraphic successions at three Zn±Pb showings in the Sekwi Formation are illustrated in Figure 3.4.2-2. The Palm showing is in NTS 106A, whereas the TIC and AB showings are 7 km and 105 km west of the Sekwi project area, respectively. The Palm section was measured in detail, the TIC column is a compilation of four measured sections, and the AB column was compiled from a measured section and property-scale mapping. The showings were placed in stratigraphic context by comparison with composite sections compiled from previously measured sections through the full Sekwi Formation (referenced in Figure 3.4.2-2).

Age and correlation Figure 3.4.2-10. A 20 m-high microcrystalline limestone bioherm. Note preferential dolomitisation of the underlying rocks. Geologist for scale. (NTS 105P/11, 785705 E, 7062978 N)

Dolomitisation in the Sekwi Formation was discussed briefly by Krause and Oldershaw (1978) and Krause (1979). Fabricpreserving, very finely crystalline dolomitisation of microbially laminated, peritidal lime mudstones was interpreted to be of shallow, eogenetic origin (Fig. 3.4.2-16). Pervasive, fine to mediumcrystalline dolomite ranges from fabric-retentive to fabricdestructive. Selective dolomitisation is illustrated by preferentially dolomitised allochems (Fig. 3.4.2-12) or matrix. Dolomitisation

The lowermost Sekwi Formation in western sections was deposited in the Early Cambrian during the latter part of the Fallotaspis trilobite biozone (Fritz 1976, 1978, 1979a). The bulk of the lower carbonate member and most of the quartz-sandy member were deposited during the Nevadella biozone. The Fallotaspis zone is missing in shoreward sections, which begin in the Nevadella zone. The upper Sekwi Formation was deposited during the BonniaOlenellus biozone. In most sections in and south of the Sekwi project area, the top of the Sekwi Formation is near the top of the BonniaOlenellus zone, and is overlain conformably by shale containing Middle Cambrian fossils (Fritz, 1981; Dilliard, 2006). West of the

147

Chapter Three

Figure 3.4.2-12. Ooid grainstone. Preferentially dolomitised ooids (yellow) in a pale to dark grey dolomitic ooid grainstone. Scale in centimetres. (NTS 105P/10, 500361 E, 7051159 N)

148

Figure 3.4.2-15. Bioturbated pale grey lime mudstone and yellow, nodular dolomudstone from the upper carbonate member of the Sekwi Formation. Scale in centimetres. (NTS 105P/11, 490182 E, 7047005 N)

Figure 3.4.2-13. Oncoid dolorudstone with large, spherical oncoids, from upper carbonate member of the Sekwi Formation. Pen cap is 1.3 cm wide at its base. Near Palm showing. (NTS 106A/05, 750779 E, 7152346 N)

Figure 3.4.2-16. Yellow-weathering, microbially laminated dolostone from the upper carbonate member of the Sekwi Formation. Small intraclasts and disrupted laminations are visible in a narrow band above and to the right of the pen tip. Pen cap is 1.3 cm wide at its base. (NTS 106A/05, 750691 E, 7152289 N)

Figure 3.4.2-14. Dolomitic Salterella grainstone from the upper carbonate member of the Sekwi Formation. Cut surface etched with 15% HCl. Near Palm showing. (NTS 106A/05, 750582 E, 7152403 N)

Figure 3.4.2-17. Bedding-plane view of desiccation-cracked dolomudstone from the upper carbonate member of the Sekwi Formation. Irregular and elongate voids are pseudomorphs after gypsum and possibly anhydrite. Scale bar in centimetres. (NTS 105P/11, 491186 E, 7052095 N)

Chapter Three

Figure 3.4.2-18. Fenestral limestone. Pale grey-white, laminar to irregular, calcitefilled fenestrae in darker grey lime mudstone matrix. Larger vugs and veins are also filled by white calcite cement. Scale in centimetres. (NTS 105P/11, 491186 E, 7052095 N)

Project area, in NTS 106B and 106C, deposition ended earlier and the formation top is near the middle of the Bonnia-Olenellus zone (Fritz, 1976, 1978, 1979a, 1992). Deposition of the Sekwi Formation took roughly 10 to 15 million years, with the bulk of this time accounted for by its lower part (Dilliard et al., 2010). Three samples taken from the lower carbonate member of the Sekwi Formation during the Sekwi project were dated based on macrofossils as late Early Cambrian and Early Cambrian (Appendix F). The Gull Lake Formation, which consists of up to one kilometre of fine-grained, terrigenous clastic rock and minor carbonate rock, accumulated outboard of the Sekwi shelf in the Selwyn Basin, west of the Sekwi project area. The lower part of the Gull Lake Formation is correlative with the Sekwi Formation (Fritz, 1992). South-southeast of the Sekwi project area, in NTS 95E, Lower Cambrian strata show a marked facies change from orangeweathering, sandy dolostone of the Sekwi Formation north of the Flat River, to dark brown-grey-weathering, pyritic, calcareous shale and argillite with minor, thin-bedded, argillaceous, archeocyathanbearing limestone south of the Flat River (Gabrielse et al., 1973a).

Interpretation The Early Cambrian shoreline trended north between the present-day latitudes of 64°N and 62°30’N. Above 64°N its trend was northwest to west, and below 62°30’N its trend was southeast. Exposures of the Sekwi Formation in northern NTS 106B, NTS 106A/SW, eastern NTS 105P, and NTS 95M/SW represent shoreward, shallow-shelf locations, whereas exposures in southwestern NTS 106B and central and western NTS 105P represent deeper shelf and slope environments. Exposures southsoutheast of the Sekwi project area (NTS 105I, 95E, 95L) represent deeper shelf and slope environments near a volcanic centre (Gabrielse et al., 1973a). The transgressive systems tract (TST) and highstand systems tract (HST) of a second- or third-order sequence (S0) correspond to the lower carbonate member of the Sekwi Formation (Fig. 3.4.22; Dilliard et al., 2010). Fritz (1975, 1976, 1978, 1979a, 1992) previously identified two grand cycles (sensu Aitken, 1966) in the Vampire and Sekwi formations. Sequence S0 correlates with halfcycle A2, which is the upper, carbonate-rich part of grand cycle A. Five third-order sequences overlie S0 (Dilliard, 2006). The lowstand systems tract (LST) of S1 is the quartz-sandy member and correlates with half-cycle B1, the siliciclastic-rich, lower part of grand cycle B. The top of S1 and S2-S6 form the upper carbonate member and are

correlative with half-cycle B2. The orange and yellow weathering siltstone interval in the upper carbonate member corresponds to Fritz’s subordinate half-cycle B2b, as well as the lower part of S2. Sequence boundaries in NTS 105P are discussed by Dilliard et al. (2010). Placement of sequence boundaries in the northern composite sections (Fig. 3.4.2-2) makes use of Krause’s (1979) sedimentological descriptions. The boundary between S0 and S1 in the North composite section is placed between an underlying interval of dolomitic microbial mounds and laminations, oolitic dolostone, and bioturbated, dolomitic quartz arenite, and an overlying interval of trough cross-bedded quartz arenite in coarsening-upward cycles. In the Northwest composite section, quartz arenite and siltstone overlie nodular limestone, thinly bedded dolostone, and argillaceous dolostone. The boundary in both cases is taken to represent an influx of nearshore siliciclastic sediments into a shallow marine environment. The composite sequence S1-3 consists of shallow water deposits that can be divided into three or four higher-order sequences in the North composite section, but data for the Northwest composite section are not as detailed. In general, a siliciclastic-dominated interval (the quartz-sandy member) is overlain by a succession of subtidal-peritidal cycles which have successively greater peritidal components upwards. The boundary between S1-3 and S4-6 is placed between the peritidal cap of a shallowing-upward cycle and the overlying, thinly interbedded limestone and shale (in the North section) or oncoid dolorudstone and skeletal packstone (in the Northwest section) that formed in deeper water. S4-6 is dominated by shallow water deposits and consists of two shallowingupward cycles followed by a deepening-upward trend which may represent the TST of S6. The Sekwi Formation was deposited on an initially shallowly inclined, homoclinal ramp. At least in western 105P, this ramp steepened during the highstand stage of S0, and then returned to a gently dipping state during the highstand of S1 (Dilliard et al., 2010). Steepening of the ramp was related to syndepositional, down-to-the-basin faulting (Dilliard et al., 2010), a conclusion that is consistent with evidence of protracted extensional tectonism in the region (Cecile et al., 1997). Slumps, sediment gravity-flows, and the deep-water setting of large, allochthonous blocks of shallowwater origin provide evidence of a steep and/or tectonically active slope. Shoreward parts of the ancestral ramp are expressed by a thin lower Sekwi Formation and the absence of deep-water facies. Shallowing of the ramp and filling of accommodation space at the end of lower Sekwi time are recorded by prograding ooid shoals and peritidal flats, and microbial bioherms. Local emergence of this prograding carbonate led to karsting, followed by deposition of widespread intertidal sandstone (the quartz-sandy member) that blanketed most of the shelf during the lowstand of S1 (Dilliard et al., 2010). The upper carbonate member of the Sekwi Formation records maturation of the ramp into a low-relief feature with spatially intermittent shoals of ooids and oncoids. Five cycles of submergence and filling, with intermittent emergence in shoreward sections, created vertical successions of subtidal shelf or shoal and intertidal inner-ramp facies, capped by peritidal facies and local paleosols. The pervasive and selective styles of dolomitisation noted above may be locally of burial diagenetic origin but elsewhere arose in conjunction with faulting and mineralising events, as interpreted from their close spatial relationship. The origin and pathways of dolomitising fluids are not understood. Brecciation and sulphide mineralisation are present in both the lower and upper carbonate members of the Sekwi Formation (Fig. 3.4.2-2; Appendix H).

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Chapter Three

3.4.3. Cambro-Ordovician carbonate succession C.F. Roots, E. Martel and S.P. Gordey The upper Cambrian to Devonian geologic record in the Sekwi project area (Fig. 3.4.3-1) is represented by three transgressiveregressive cycles that roughly correspond to the upper Sauk, Tippecanoe and lower Kaskaskia sequences of Sloss (1963). The lowermost sequence (cycle A) began with transgression in the Late Cambrian and is represented by the Upper Cambrian - Lower Ordovician Franklin Mountain Formation, and to the southeast, the Broken Skull and Sunblood formations. These units have lateral equivalents in deeper water to the west, described in Chapter 3.5 (Selwyn Basin). Cycle A strata are unconformably overlain by rocks of cycle B, the Upper Ordovician to Lower Silurian Mount Kindle Formation, and its lateral equivalent, the Whittaker Formation. The Cambro-Ordovician carbonate units (cycle A) of the Mackenzie Platform (Figs. 3.4.3-2 and -3) are exposed in a broad belt flanking the high ranges of the Mackenzie Mountains, and in the northern Ogilvie Mountains (Yukon).

Franklin Mountain Formation Buff- and pale grey-weathering, locally stromatolitic, thickbedded dolostone was first described by Williams (1922, 1923) 180 km east of NTS 105P, and redefined by Norford and Macqueen (1975). The formation is widespread in the subsurface of the northern interior plains as well as beneath the Anderson and Peel plateaus north of the Sekwi project area. The Franklin Mountain Formation is exposed in the Mackenzie and Ogilvie mountains, including the flanks of box-anticlines in northeastern NTS 106A, and in the southwestern quadrant of NTS 106A, where it includes a transitional facies into its basinal equivalent, the Rabbitkettle Formation.

Figure 3.4.3-1. succession.

150

Exposure area of Cambrian to Devonian Mackenzie Platform

In the Peel-Mackenzie Platform of northern Yukon (north of 65°N), the Franklin Mountain and Mount Kindle formations have been referred to as the Ronning Group (Pugh, 1983; redefined by Morrow, 1999). The southeastern limit of the Ronning Group is in the Sekwi project area, where it is a monotonous dolostone succession (Fig. 3.4.3-4). Five Sekwi project measured sections included parts of the Franklin Mountain Formation: 07CL-S1, -S2 -S3 and -S4, and 07RAS-S2 and -S3 (Appendix A).

Description At the type section, the Franklin Mountain Formation is conformable and gradational with the underlying Saline River Formation and is unconformably overlain by the Mount Kindle Formation. In central NTS 106A, the Franklin Mountain Formation unconformably overlies Lower Cambrian (Backbone Ranges Formation) strata. Eastward, the sub-Franklin-Mountain hiatus increases, so that in the northeastern part of NTS 106A the Franklin Mountain Formation directly overlies the lowermost part of the Little Dal Group. North of McClure Lake (NTS 106A) the basal contact is difficult to identify, because the reddish mudstone of the basal Franklin Mountain Formation (Fig. 3.4.3-5) is similar to underlying Little Dal Group strata (e.g., 07-RAS-S1; Appendix A). In the Sekwi project area, the upper contact exhibits a sharp change from pale grey, relatively planar beds of the Franklin Mountain Formation, to overlying, dark grey-weathering, irregular beds of the Mount Kindle Formation (Figs. 3.4.3-6 and -7). In south-central NTS 106A, a mid-Silurian unconformity truncates the Mount Kindle Formation so that the Tsetso Formation directly overlies the Franklin Mountain Formation. At the type section east of the Mackenzie River (NTS 95O; 63°21’N, 123°12’W), the Franklin Mountain Formation is 310 m thick, but to the east, beneath the northern interior plains, drill intersections are locally two to three times thicker. In NTS 106A, the formation generally thins westward, from 380 m (07RAS-S2; all cited sections in Appendix A), and 298 m (07RAS-S3) in the east, to 209 m (08RAS-S1). At the western side of the Sekwi project area, east of the Mountain River, the formation is 38 m thick (07CL-S2) and decreases westward through a transitional facies to shaly strata of the Rabbitkettle Formation. Early descriptions of the Franklin Mountain Formation identified four informal members (Aitken et al., 1973; Aitken and Cook, 1974b; Norford and Macqueen, 1975): (1) a basal “redbed” unit (siltstone, quartz sandstone, dolostone) that is present only near the Mackenzie Arch; (2) a lower “cyclic” member (shale, intraclast rudstone, stromatolites) that is laterally equivalent to the “redbed” member east of the Mackenzie Arch, where the Franklin Mountain Formation overlies the Saline River Formation; (3) a “rhythmic” member that overlies (1) or (2) (cycles of pale grey-weathering, finely crystalline dolostone and brownweathering, medium crystalline oolitic or stromatolitic dolostone); and (4) a “cherty” member, in which chert becomes increasingly conspicuous eastward from the edge of the Mackenzie Platform into the northern interior plains. These subtle members can be difficult to identify, particularly when outcrop is poor. A fifth, “porous dolostone” member is also locally present (Mackenzie, 1974; Pugh, 1983). Reddish mudstone with siltstone interbeds generally characterise the basal 15-50 m of the Franklin Mountain Formation (Fig. 3.4.35). In the northeastern quadrant of NTS 106A (McClure Lake area), the formation is dominated by medium- and thick-bedded dolostone and lacks distinct members. A basal member is present but

Chapter Three W

E

Mountain River (CL07 S2, GGA07-400 Morrow, 1991; Section #11)

NE of McClure Lake (Section RAS07-S2)

~130km Cache Lake

[Canol Fm]

[Hare Indian and Canol fms] Nahanni Fm

[Misfortune Fm]

40m

138m

100m

Hume Fm

Landry Fm

156m

300m

Bear Rock Fm

80m

40m

Arnica Fm

301m

Sombre Fm

Mount Kindle Fm

Tsetso Fm

280m

375m 270m

oooooooooooo

Camsell Fm

534m

Franklin Mountain Fm Franklin Mountain Fm - basal red beds

o oo oo oo oo oo oo oo oo ooo oooooooooooo o

270m

Mount Kindle Fm

[Backbone Ranges Fm]

100m

Rabbitkettle Fm

[Little Dal Group 'basinal assemblage']

Lateral facies transition

Numbers are thickness in metres

197m

oooooooo oooo oooooo

46m

286m

ooooo Erosional uncomformity

[Sekwi Fm]

[Unit] Formations above and

below Mackenzie Platform

Figure 3.4.3-2. Schematic stratigraphic diagram for Paleozoic Mackenzie Platform units in northern half of NTS 106A. W (Morrow, 1991; Section #7) [Misfortune Fm] Hume Fm 112m 83m

40km

E (Section RAS-08-S2)

[Hare Indian and Canol fms] Nahanni Fm Landry Fm Arnica Fm

Sombre Fm

Camsell Fm

80m

Headless Fm 150m 120m

Sombre Fm

488m

950m 39m Tsetso Fm 429m 337m

205m 20m

Mount Kindle Fm Sunblood Fm

205m

Broken Skull Fm

150m

[Sekwi Fm]

100m

Numbers are thickness in metres

200m [Backbone Ranges Fm]

Lateral facies transition Limit of exposure [Unit] Formations above and below Mackenzie Platform

Figure 3.4.3-3. Schematic stratigraphic diagram for Paleozoic Mackenzie Platform units in 105P and 95M.

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Chapter Three

Figure 3.4.3-4. The Franklin Mountain Formation consists generally of pale grey-weathering dolostone, locally with red mudstone to sandstone at its base. Here, the Franklin Mountain Formation is overlain by dark grey Mount Kindle Formation at the top right of the ridge. View northeastward in NTS 106A/13 (vantage point: 459980E, 7204558N).

Figure 3.4.3-5. In the vicinity of the Mackenzie arch, the basal unit of the Franklin Mountain Formation is maroon calcareous mudstone and siltstone. View northward in NTS 106A/7 (520099E, 7136359N).

difficult to distinguish from the underlying Basinal assemblage of the Little Dal Group: both consist of reddish calcareous mudstone and siltstone interbedded with carbonate rocks. At section 07RAS-S3, the basal member, about 152 m thick, consists of brick-red-weathering, medium- to fine-grained sandstone (Fig. 3.4.3-8). This member is locally conglomeratic (dolostone and white sandstone pebbles), and olive-grey shaly dolostone and yellow-orange-weathering dolostone are locally present. This member is overlain by 198 m of poorly bedded, pale grey-weathering, medium-crystalline dolostone and locally parallel-bedded, laminated and mottled dolostone (Fig. 3.4.3-9). Columnar stromatolites 5-15 cm in diameter (Fig. 3.4.3-10) are common.

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In section 07RAS-S2 the basal red unit is thinner (68 m), and is overlain by thin, rhythmically bedded dolostone and coarsely crystalline, medium-bedded dolostone. The latter strata commonly contain intraclasts, irregular bed-tops and channels up to 20 cm deep. Approaching the edge of the Mackenzie Platform (south of Cache Lake in central NTS 106A) the Franklin Mountain Formation is dominated by thin, regular beds (section 08-RAS-S1; Appendix A). The basal member, 87 m thick, consists of orangebrown, dolomitic siltstone and sandstone, overlain by green-grey to light brown (upward) and dark red mixed with yellow-brown lime mudstone. The overlying 112 m include a rubble-covered interval and intervals of finely crystalline dolostone ranging from light orange-brown to grey-white (Fig. 3.4.3-11). The upper contact with the Tsetso Formation is sharp and unconformable. The Franklin Mountain Formation in western NTS 106A is 38 m thick and consists of grey chert-breccia interbedded with yellowweathering finely crystalline dolostone (sections 07CL-S2 and -S3; Appendix A). In the western part of the Sekwi project area near the edge of the Mackenzie Platform, the upper part of the formation has been referred to as the “transitional facies” by Cecile (1982) and redefined by Morrow (1999). This transitional zone includes purple silty dolostone interbedded with coarsely crystalline orange dolostone, pink calcareous sandstone and microbially laminated dolostone. Minor conglomerate and possible burrow-mottling are present. The formation is 366 m thick in section 07CL-S3. The upper part of the Franklin Mountain Formation is typically white, sucrosic dolostone that splinters with a conchoidal fracture. In this stratigraphic interval, quartz-lined vugs and white quartz patches are common, and sedimentary textures are difficult to discern. Stromatolites, thrombolites, gastropods and burrows have been reported from the Franklin Mountain Formation.

Chapter Three

Figure 3.4.3-6. Transition between Franklin Mountain and Mount Kindle formations is subtly indicated by an increase in bioturbation. View east in NTS 106A/9; (541464E, 7161249N); grey scale bar (top right quadrant) is 2 cm.

Figure 3.4.3-7. The Franklin Mountain Formation (lower half) is overlain by Mount Kindle Formation (darker dolostone in upper right). In some places the contact is visible from a distance. NTS 106A/01 (547304E, 7103670N).

Figure 3.4.3-9. The Franklin Mountain Formation is characterised by thick beds of laminated dolostone. NTS 106A/5 (472485E, 7127316N).

Figure 3.4.3-10. The upper part of the Franklin Mountain Formation locally contains columnar stromatolites. NTS 106A/7 (521876E, 7148200N).

Figure 3.4.3-8. The Franklin Mountain Formation locally has a lower member characterised by reddish sandy dolostone. NTS 106A/7 (515237E, 7122980N). Figure 3.4.3-11. North of Hay Creek, the upper part of the Franklin Mountain Formation contains thin-bedded dolomitic siltstone and brown-weathering mediumbedded dolostone (background). View southwest at Interval 4 of section 08RAS-S1, NTS 106A/2; (515755E, 7122951N).

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Chapter Three The Franklin Mountain Formation is a minor host of Zn-Pb±Cu, Ag showings in and beyond the Sekwi project area (Appendix H). Although a basal red sandstone is locally conspicuous, the amount of hematite required to colour the beds is economically insignificant. Locally, pyrite-filled vugs are common. Bedding surfaces are iron-stained near the top of the unit. Secondary silicification is typical in dark-weathering members, including vugs rimmed with quartz crystals.

Age and correlation

Figure 3.4.3-12. In the eastern part of the Sekwi project area the Broken Skull Formation is represented by a brown-weathering cliff-band and rubble. It unconformably overlies the Proterozoic Katherine Group (pink, in centre). The ridge is capped by Mount Kindle (Whittaker) Formation, which produces grey talus. The cliff-band is about 30 m thick. View to northwest in the Tigonankweine anticline, NTS 95M/13 (561963E, 7091091N).

The Franklin Mountain Formation is Late Cambrian to Early Ordovician (Norford and Macqueen, 1975) but the “transitional” strata are as young as latest Middle Ordovician close to the basin, due to non-erosion of strata (Cecile, 1982). A sample from transitional Franklin Mountain Formation strata in southwestern NTS 106A yielded Late Cambrian (Sunwaptan –Proconodontus? Zone) conodonts. A sample from a tongue of Franklin Mountain Formation in the overlying mixed unit of Rabbitkettle, Duo, and Marmot formations contained Early Ordovician (late Tremadocian to Floian) conodonts (Appendix F). The Franklin Mountain Formation is time-correlative and lithologically similar to the lower part of the Bouvette Formation, which underlies much of the northern Ogilvie Mountains as far west as the Yukon-Alaska border. South of the Sekwi project area, the monochromatic and relatively thick Franklin Mountain Formation passes southwestward into the more colourful Broken Skull and Sunblood formations. Temporally equivalent strata in the Misty Creek Embayment belong to the Rabbitkettle Formation (Cecile, 1982).

Interpretation

Figure 3.4.3-13. The Sunblood Formation consists of about 120 m of thick-bedded dolostone (central, straight part of skyline, between snow patches). View to east, about 12.5 km northwest of Mount Delthore, NTS 105P/9 (533894E, 7059706N).

The locally conspicuous cyclic aspect of the Franklin Mountain Formation reflects oscillation of sea-level in a relatively shallow-water environment (Morrow, 1999). The red-weathering basal member records clastic input, with exposure, weathering, deep oxidation and erosion in the vicinity of the Mackenzie Arch. Bottom currents are indicated by intraclasts, flutes and tool-marks throughout the formation (Morrow, 1999). Dolomudstone accumulated at least in part in a peritidal environment, as indicated by desiccation cracks and wave-rippled bedding surfaces.

Broken Skull Formation This tan-, orange- and red-weathering carbonate unit commonly forms a staircase of cliff-bands and talus (Figs. 3.4.312, -14, and -15). Gabrielse et al. (1973a) defined the Broken Skull Formation in the Backbone Ranges, southeast of NTS 105P. This unit is exposed in NTS 105P, mainly in the southeastern quadrant, where it extends northwestward from Mount Delthore along the Sayunei Range. A second exposure area is in northwestern NTS 95M, where it is present on the limbs of the Tigonankweine anticline north of Vanishing Ram Creek. Although the Broken Skull Formation was encountered in the course of the Sekwi project, it was not the subject of focussed study.

Description

Figure 3.4.3-14. Thick-bedded pale grey dolostone of the lower Broken Skull Formation in the Tigonankweine anticline. View to north in 95M/13 (563552E, 7092409N).

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At the type area, Broken Skull Formation unconformably overlies the Middle Cambrian Avalanche Formation; to the east it unconformably overlies the Rockslide Formation (figure 24 of Gordey and Anderson, 1993). In the Tigonankweine anticline the formation unconformably overlies strata of the Little Dal Group. The type section passes transitionally upward into the Ordovician

Chapter Three This unit is considered to be the lateral equivalent of the upper part of the Franklin Mountain Formation (transitional facies of Cecile, 1982) in western NTS 106A.

Interpretation Desiccation cracks, cross-beds and oncoids are common in the upper part of the Broken Skull Formation, signifying a substrate that was intermittently above wave-base or even emergent.

Sunblood Formation The Sunblood Formation was formalised by Kingston (1951) at Virginia Falls on the South Nahanni River, but the base is not exposed there (Douglas and Norris, 1960). A reference section was defined in NTS 95L (120 km southwest of NTS 105P) by Gabrielse et al. (1973a). The Sunblood Formation is exposed in thin outcrop bands in eastern NTS 105P and is widespread in southeastern Yukon (Gabrielse and Blusson, 1969; Pigage, 2008). In the Sekwi project area, this dolostone is buff- to pink-weathering, but south of the project area, it is a thicker, fetid-smelling, dark-grey-weathering limestone that is characterised by red-striped beds near its top.

Description

Figure 3.4.3-15. Rhythmic thin- and medium-bedded limestone with grey shale partings of the upper Broken Skull Formation in the Tigonankweine anticline. View to north in 95M/13 (563552E, 7092409N).

Sunblood Formation. In southern NTS 105P, the formation is truncated beneath the sub-Mount Kindle (Whittaker) Formation unconformity (Gabrielse et al., 1973a). This time interval in the Selwyn Basin is represented by the Rabbitkettle Formation. The type section of the Broken Skull Formation (NTS 95L; 62°21’N, 127°20’W) is 823 m thick (Gabrielse et al., 1973a). South of the study area (in NTS 105I) the formation is 769 m thick (section 29 of Gordey and Anderson, 1993). Its thickness decreases northward to less than 80 m in the Sayunei Range. The Broken Skull Formation consists of a basal quartz-sandy carbonate member 0-103 m thick, and two overlying members (Fig. 3.4.3-12). At Delthore Mountain, the basal unit of comparatively resistant dark red sandstone is 25 m thick, and is overlain by pale to medium grey-weathering thick-bedded dolostone (lower) and dark grey, thin-bedded limestone (upper) members. Both the dolostone and limestone are finely crystalline, with dark grey fresh surfaces. Along strike to the northwest in the Sayunei Range, the Broken Skull Formation consists of vuggy grey dolostone with oncoids, and the division into members is not apparent.

Age and correlation The Broken Skull Formation is sparsely fossiliferous. Trilobites indicate a Late Cambrian (Furongian) to Early Ordovician age (Gabrielse et al., 1973a). In NTS 105I the upper limestone member is as young as late Middle Ordovician (Gordey and Anderson, 1993) and includes an interval that is equivalent to the Sunblood Formation. Echinoderm fragments collected in northeastern NTS 105P during the Sekwi project were not age-diagnostic (Appendix F).

The Sunblood Formation conformably overlies the Broken Skull Formation; the contact is locally gradational. In the Sayunei Range the unit is overlain, possibly unconformably, by the Mount Kindle (Whittaker) Formation, and at the reference section south of the Sekwi project area, it is overlain by dark shale that may belong to the Duo Lake Formation. Morrow (1982b) and Ludvigsen (1975; 1982) disagreed about the significance of a third unit, the Esbataottine Formation, an argillaceous and silty limestone that is locally present between the Sunblood and overlying Whittaker formations in the Nahanni River area. The reference section (Gabrielse et al., 1973a; section 23) at 62°07’W, 126°42’W (NTS 95L) is 1481 m thick. In contrast, in the eastern half of NTS 105P the Sunblood Formation was reported as 150+ m thick by Blusson (1971), although where traversed during the Sekwi project it was less than 120 m thick (08RAS-S2; Appendix A). Faintly mottled, finely crystalline dolostone of the Sunblood Formation is pink-weathering in the Sayunei Range. Exposures north of Vanishing Ram Creek (in the footwall of the Plateau fault) are yellow-weathering (Fig. 3.4.3-13), generally massive, and have rare wavy lamination and stylolitic parting. In the reference section southeast of the Sekwi project area, the Sunblood Formation has four units. Dark grey, fetid dolostone overlain by alternating light buff-grey and dark grey-weathering dolostone beds (“zebra member”) form the lowest unit. This basal unit is overlain by a thick interval of lime mudstone, a quartz-sandy carbonate interval and an uppermost dolostone and limestone interval that is locally cherty (Gabrielse et al., 1973a). From the reference section, the Sunblood Formation thins rapidly northward. This may reflect bevelling of the top by the sub-Mount Kindle (Whittaker) Formation unconformity (e.g., Gabrielse et al., 1973a), although the exposure in the Sekwi project area more closely resembles the upper part of the formation, rather than the lower part. The Sunblood Formation passes westward into dark shale. The Sunblood Formation is known to contain at least one Zn occurrence in the Sekwi project area (Appendix H).

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Chapter Three Age and correlation Receptaculitids in the grey-weathering dolostone and Maclurites in the platy and nodular limestone indicate a Middle Ordovician age; other sparse fossils include trilobites, brachiopods, ostracodes, bryozoans, bivalves, cephalopods and conodonts. Blue-grey shale layers contain graptolites of similar age (Gabrielse et al., 1973a).

Interpretation The Sunblood Formation was deposited on the Mackenzie Platform, buttressed from the open ocean to the west by platformmargin tidal flats and reefs of the Haywire Formation.

3.4.4. Upper Ordovician to Middle Silurian carbonate succession C.F. Roots, E. Martel and S.P. Gordey An episode of global regression and erosion during the late Middle Ordovician (Morrow, 1999) bevelled strata of the Mackenzie Platform. Upper Ordovician to Lower Silurian strata (cycle B) unconformably overlie Middle Ordovician rocks and increasingly older strata eastward (see Figs. 2-2 and -3). The principal unit of this succession is the thick-bedded, porous, fossil-rich Upper Ordovician to Lower Silurian Mount Kindle Formation (~605 m thick; Figs. 3.4.3-2 and -3), and its lateral equivalent, the Whittaker Formation (up to 1000 m thick). These two formations were respectively defined to the north and to the south of the Sekwi project area. For this report, the “Mount Kindle” name is applied for all exposures in the Sekwi project area, and “(Whittaker)” is included after the name to indicate regions where the strata were previously assigned to the Whittaker Formation on maps.

Mount Kindle Formation; Whittaker Formation The Mount Kindle Formation is a brownish-grey, thickbedded, fine- to medium-crystalline dolostone. Its type section near Wrigley (Williams, 1922, 1923) was re-defined by Norford and Macqueen (1975) and further described by Morrow (1999). This formation is present throughout the northern Mackenzie and Ogilvie mountains in Yukon. It is widespread in NTS 106A, forming sharp-edged skylines and dark-grey cliff bands (Fig. 3.4.4-1). The Whittaker Formation, a dark grey-weathering, medium- to thick-

Figure 3.4.4-1. The Mount Kindle Formation contains three cycles of dark grey dolostone and pale grey dolomitic mudstone. The unit overlies the Broken Skull Formation (right) and is capped by Tsetso Formation (left); white dashed lines emphasise the contacts. View to north from east of Natla River in NTS 105P/9 (524187E, 7063329N).

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bedded bioclastic dolostone, was defined by Douglas and Norris (1961). Gabrielse et al. (1973a) mapped most of its distribution in the southern Mackenzie Mountains. The Whittaker Formation trends northwest along the axis of the Sayunei Range in NTS 105P. Given that the Whittaker Formation is the southern equivalent of the northern Mount Kindle Formation, the latter term is used for this interval in the Sekwi project area (northern Mackenzie Mountains), regardless of which formation had originally been identified at any particular location. Seven Sekwi project measured sections included the Mount Kindle Formation (07CL-S3 and S4, 07RAS-S2 and S3, 08EM-S1, 08DT-S1, and 08RAS-S2; Appendix A).

Description The Mount Kindle Formation disconformably overlies the Franklin Mountain Formation or the Duo Lake Formation. The contact is typically a subtle change from crudely bedded, relatively unfossiliferous dolostone to a grey-brown-weathering, bioturbated dolostone with abundant silicified fossil debris. In northern Yukon the contact between these two formations is also subtle, and because of their similar character they are grouped together as the Ronning Group (redefined by Morrow, 1999). In southern NTS 105P, the regional unconformity bevels the underlying Sunblood or Broken Skull formations, and the contact is marked by a pebble pavement, breccia or karst. The upper contact is a disconformity beneath arenaceous carbonate rocks of the Tsetso Formation. At its type section, the Mount Kindle Formation (63°21’N, 123°12’W) is 262 m thick (Norford and Macqueen, 1975). Throughout the Ogilvie Mountains it averages 600 m thick (Morrow, 1999). In western NTS 106A it is 405 m thick (Section 07CL-S3; Appendix A); in northeastern NTS 106A it is 272 and 293 m thick (Sections 07RAS-S2 and -S3; Appendix A). The type section of the Whittaker Formation in the Root River Basin (NTS 95K) is 1240 m thick, but the unit thins rapidly northand westward. Blusson (1972) reported up to 900 m in eastern NTS 105P. At section 08RAS-S3 it is 370 m thick, but in the Sayunei Range it is only 80-100 m thick, and is repeated by thrust faults. The formation appears to increase in thickness southwestward to the shelf edge, which is 5-15 km farther to the southwest than the shelf margin of Middle and Upper Cambrian formations (Cecile, 1982; Morrow, 1991). The Mount Kindle Formation consists of cliff-forming, mediumcrystalline dolostone with >10% silicified macrofossil fragments. Crinoids, nautiloids, and many coral types (all typically fragmented and strewn through the thick beds; Figs. 3.4.4-2 to -4) characterise this formation. The presence of abundant fossils distinguishes this unit from other Ordovician to Silurian platformal carbonate rocks. Stromatoporoids (particularly in the Sayunei Range) and biostromes (northeastern NTS 106A) are particularly common. In the Sayunei Range, cliffs of the Mount Kindle (Whittaker) Formation contain densely fossiliferous, siliceous bands tens of metres thick. Some layers are up to 60% coral and brachiopod fragments; less common are cephalopods, bryozoans, and trilobites. These skeletal rudstone beds are interspersed with mottled lime mudstone and microbial laminite. Typically, fresh surfaces show pale grey limestone with patches of finely crystalline dolostone. Skeletal dolowackestone and brachiopod dolopackstone are common in upper parts of the formation. Locally, thick lime- and dolomudstone beds are intensely bioturbated (Fig. 3.4.4-3), resulting in a mottled texture. The uppermost parts of the formation are typically recrystallised, obliterating sedimentary textures.

Chapter Three

Figure 3.4.4-2. The Mount Kindle Formation is overlain along a very low-angle unconformity, marked by solution pits, by the pale-coloured Tsetso Formation (left). View westward to the Mountain River in NTS 106A/5 (from 472399E, 7129231N).

A transition facies of the Mount Kindle Formation (between platformal dolostone and its basinal equivalent Cloudy Formation of the Misty Creek Embayment) in northwestern NTS 105P and southwestern NTS 106A was documented by Cecile (1982), and has also been noted in north-central NTS 105P during the Sekwi project. The transition facies include massive limestone, skeletalooid grainstone and rudstone, thin-bedded limestone with black chert lenses and nodules and slump features, thin-bedded dolostone, and dolostone mounds several tens of metres thick. The Mount Kindle Formation commonly exhibits a “spiderweb” texture consisting of abundant thread-like veinlets of calcite. In the Sayunei Range, barite veins up to 1.5 m wide are common and are roughly parallel to the lower contact of the Mount Kindle (Whittaker) Formation. The Mount Kindle Formation hosts numerous Zn showings in the Sekwi project area (Appendix H).

Age and correlation Fossils described by Norford and Macqueen (1975) suggest that the Mount Kindle Formation is Late Ordovician to Early Silurian in age. Sekwi project conodont and macrofossil collections from this formation are late Middle Ordovician to Early Silurian. Sekwi project samples from the transitional Mount Kindle Formation yielded Late Ordovician to Early Silurian conodonts (Appendix F). The off-shelf equivalents of the Mount Kindle (Whittaker) Formation are the Cloudy Formation (thin-bedded limestone and shale; Cecile, 1982), and farther southwest, the shale-dominated Duo Lake Formation.

Interpretation

Figure 3.4.4-3. The lower Mount Kindle Formation includes thick, vuggy units (hammer for scale left of centre). Tigonankweine anticline, 6 km east of Keele River in NTS 95M/13 (559023E, 7092219N).

Thick, uneven dolostone beds were probably deposited in highenergy, shallow water, consistent with an unrestricted, open-marine shelf or ramp setting. Extensive silicification locally obliterated delicate features in carbonate mudstone, although primary bedding had already been compromised by bioturbation over large areas. Paradoxically, the quartz selectively preserved the structure of many fossil fragments (Fig. 3.4.4-4).

3.4.5. Upper Silurian to Lower Devonian carbonate succession (Delorme Group) C.F. Roots, E. Martel and S.P. Gordey

Figure 3.4.4-4. The upper Mount Kindle Formation is characterised by abundant coral, brachiopod and sponge fragments in dolomudstone. Location is 5 km east of Mountain River in NTS 106A/6 (472802E, 7129585N).

Pale yellow-weathering silty dolostone of the uppermost Silurian and Lower Devonian Tsetso and Camsell formations of the Delorme Group (up to 1200 m; Cecile and Norford, 1993) represent cycle C. Originally described by Douglas and Norris (1961) as the Delorme Formation, these strata were later revised as two formations (Morrow, 1991): the Tsetso Formation (in large part the formerly unnamed “Silurian-Devonian carbonate”), and the Camsell Formation (or “Camsell breccia”). Both of these formations are present in the eastern half of NTS 105P and as northwest-trending belts across NTS 106A (Figs. 3.4.3-2 and -3). Thickness variations of the Tsetso Formation and timeequivalent Camsell Formation throughout the Mackenzie Mountains were strongly influenced by geographically variable subsidence. Two Siluro-Devonian depocentres (figure 9 of Morrow, 1991) are indicated: the Godlin salient, in north-central NTS 105P and adjacent NTS 106A, is 120 km northwest of the larger ‘Camsell Formation sub-basin’ (Root basin), where the Delorme Group is more than 1600 m thick. The Norman Wells high (northeastern

157

Chapter Three NTS 106A, and northeast of there), Twitya uplift (southeastern NTS 106A), and Redstone arch (western NTS 95M) are areas where the succession is notably thinner.

Tsetso Formation Yellow- to orange-brown-weathering, thin-bedded, impure dolostone [(unit 20 of Blusson (1971), and equivalent to the Delorme Formation of Douglas and Norris (1961)], forms an easily recognised pale tan-weathering band separating the underlying, dark-coloured Mount Kindle (Whittaker) Formation from the equally thickbedded, pale grey dolostone of the Arnica Formation above. Four Sekwi project measured sections included the Tsetso Formation (07CL-S4, 07MM-S1, 08RAS-S1 and -S2; Appendix A).

Description The base of the Delorme Group unconformably overlies the Franklin Mountain Formation in central NTS 106A, but where the latter has a similarly quartz-sandy composition, the two units cannot be distinguished. In northeastern NTS 105P the Tsetso Formation appears to overlie the Mount Kindle (Whittaker) Formation conformably (Fig. 3.4.4-2), but solution pits in the uppermost Mount Kindle Formation are filled by Tsetso Formation material, suggesting that exposure and meteoric diagenesis took place (Fig. 3.4.5-1). The Tsetso Formation is up to 550 m thick in north-central NTS 105P (Morrow, 1991) but tapers northeastward and southwestward. In eastern NTS 105P, 429 m of the unit were measured (section 08RAS-S2). In western NTS 106A, Morrow (1991) measured 46 m of Tsetso Formation overlain by 534 m of Camsell Formation. Tsetso Formation thicknesses of 40 m (section 07RAS-S2) and 22 m (section 08RAS-S1) were recorded in northeastern NTS 106A. The Tsetso Formation is a yellowish-brown-weathering, thinto medium-bedded, argillaceous to silty dolostone with microbial lamination, intraclasts, ripple cross-lamination, desiccation cracks and tepee structures (Fig. 3.4.5-2 to -5). Dolomite-cemented crackle breccia and inferred karst solution pits (Morrow, 1991) are characteristic of the Tsetso Formation. Solution pits in vertical section appear as concave-upward cavities are locally present. Some layers contain yellow-grey-weathering dolomitic clasts and nodules that appear to be supported by the darker grey dolomudstone matrix. Microbially laminated limestone with chert nodules and evidence of bioturbation are locally present. Stromatoporoids, solitary and colonial corals, and brachiopod and cephalopod debris were documented during mapping. A tripartite division of the Tsetso Formation has been recognised in NTS 106A (Aitken and Cook, 1974b; Morrow, 1991); pale yellow and grey dolostone lies between more recessive, orange-weathering, silty and sandy units at the base and top of the formation. These divisions are best developed northeast of the Sekwi project area. Fragments of fish plates collected during the Sekwi project were not identifiable. Blusson (1971) noted the presence of ostracodes and graptolites in the Tsetso Formation.

Figure 3.4.5-1. The Tsetso Formation unconformably overlies the Mount Kindle Formation. Here, grey dolostone infills the irregular surface of oxidised dolomitic sandstone. Pen is 16 cm long. From 5 km east of Mountain River in NTS 106A/6 (472802E, 7129585N).

Figure 3.4.5-2. The Tsetso Formation consists of thin- and medium-bedded dolostone. The formation is also represented in the background by pale yellow rubble at the base of the slope. It overlies steeply dipping dark grey Mount Kindle Formation. View to east, NTS 106A/10 (520269E, 7157315N).

Age and correlation Two conodont collections (Section 8 of Morrow, 1991) yielded Late Silurian (Ludovian to Pridolian) to Early Devonian ages. Early Devonian (Pragian to early Emsian) conodonts were identified in Sekwi project samples (Appendix F). Northeast of the study area, the Tsetso Formation interdigitates with the Camsell Formation (Morrow, 1991). To the west and south, the Tsetso Formation grades into the Duo Lake Formation (Blusson, 1971).

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Figure 3.4.5-3. The Tsetso Formation consists of sandy dolostone beds with crosslamination and rare stylolites. Photo from the head of Vanishing Ram Creek in NTS 95M/13 (581624E, 7078825N).

Chapter Three Interpretation The characteristic yellow colour of the formation results from reduced iron oxide coatings on quartz sand grains and indicates episodic subaerial exposure. The Tsetso Formation contains vugs filled with dolomudstone. These were suggested by Morrow (1991) to be solution pipes that developed during intermittent subaerial exposure after lithification. Intraformational breccias are interpreted to have formed as later dissolution breccias (Morrow, 1991). The Tsetso Formation was deposited on a regional unconformity caused by uplift along a southwest-trending axis (Twitya Uplift of Morrow, 1991) that exhumed the Franklin Mountain Formation and older units. These older quartzose units are believed to be the source of quartz grains in the silty and sandy beds of the Tsetso and Camsell formations (Morrow, 1991), as opposed to sand derived from distant cratonic source areas. An intertidal, supratidal and emergent depositional environment is interpreted based on the presence of desiccation cracks and minor exposure surfaces. Subtidal foreshore units were constructed with sand from the surrounding Twitya uplift and the Norman Wells High (Morrow, 1991). The depositional pattern of the Delorme Group was linked to differential subsidence and comparatively low global sea-level. Because the areas of greater subsidence on the shelf were probably, aridity resulted in deposition of thick evaporite successions (Camsell Formation; below) in subaqueous areas but peritidal land-locked carbonates where subsidence was less pronounced (Tsetso Formation).

Figure 3.4.5-4. Tepee structure in Tsetso Formation dolostone. From 10 km north of Twitya River in NTS 106A/2 (513326E, 7125804N).

Camsell Formation The Camsell Formation was first described by Douglas and Norris (1961) in the Root River map-area (NTS 95K). It consists of pale grey-, yellow- or white-weathering, cliff-forming limestone. In southwest NTS 106A the Camsell Formation cliff band punctuates the interval between the well-bedded, dark-weathering dolostone of the Mount Kindle (below) and Arnica (above) formations, allowing assignment of the more recessive under- and over-lying units to the Tsetso and Sombre formations, respectively. Gabrielse et al. (1973a) based their description on measured sections and wells. No focussed work was undertaken on this unit during the Sekwi Project.

Description The Camsell Formation sharply overlies the Tsetso Formation and is conformably overlain by the Arnica and Sombre formations. The distribution of the Camsell Formation is based on visual mapping of a distinctive, resistant, cavernous and vuggy-weathering limestone (Figs. 3.4.5-6 to -8). As a result, the formation appears to be discontinuously exposed, and lateral variations are obscure. Breccia bodies are also present well below and well above the obvious, mappable Camsell Formation; these zones are in the Tsetso and Sombre formations. These predominantly limestone-matrix breccia bodies are several tens of metres thick and are separated from one another by intervals of regular-bedded dark grey- to yellow-weathering dolostone that are up to tens of metres thick. In the Sekwi project area, exposures trend from southwestern NTS 106A (where the unit exhibits pronounced lateral thickness variation - 30 to 300 m over about 1 km laterally) southeast to the Ekwi River. Morrow (1991) recognised a silty “banded” carbonate facies and an evaporite facies in the Camsell Formation. The banded facies is distinctly layered, with darker lime mudstone intervals grading upward into lighter grey, laminated dolomitic mudstone, which

Figure 3.4.5-5. The Tsetso Formation limestone locally contains mudcracks. Location is in NTS 105P/1, 18 km southwest of Godlin Lakes (493788E, 7065436N).

Figure 3.4.5-6. The Camsell Formation breccia forms 10 m-high pinnacles of variably resistant carbonate with no internal stratification. NTS 106A/9 (535956E, 7145532N).

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Chapter Three

Figure 3.4.5-8. Camsell Formation breccia contains angular, heterolithic carbonate clasts in secondary limestone matrix. Scale bar is 9 cm long. NTS 105P/15; 10 km northeast of Godlin Lakes (578401E, 7082555N).

of the primary sedimentary structure was destroyed, and where layering was inclined, the collapse caused shearing and complex bed dislocations. The internal collapse led to local infilling of space by rubble of overlying units.

3.4.6. Lower and Middle Devonian carbonate succession C.F. Roots, E. Martel and S.P. Gordey Figure 3.4.5-7. The Camsell Formation breccia (including hoodoos at top left) overlies more distinctly layered dolomudstone of the Tsetso Formation (right of centre). View to southeast of 70 m-high canyon wall, 6 km west of McClure Lake, NTS 106A/9 (519033E, 7158730N).

is then abruptly overlain by the next dark interval. The evaporite (breccia) facies consist of meteoric-calcite-cemented limestone-clast pack-breccia, float-breccia and crackle breccia, with clasts that are up to boulder-sized (Morrow, 1991). No halite casts or evidence of the former presence of evaporite layers were confirmed during Sekwi project work.

Age and correlation No faunal indicators were found in the Camsell Formation. An Early Devonian age is implied by the unit’s stratigraphic position between the Tsetso Formation and the overlying Arnica Formation. Although the solution-collapse breccia that characterises the Camsell Formation resembles that of the Bear Rock Formation, the latter is temporally associated with the younger Arnica Formation.

Interpretation The Camsell Formation’s geographically limited depocentres were probably highly restricted; aridity led to evaporite deposition in low-lying areas, but other areas experienced peritidal carbonate deposition (partly equivalent to the Tsetso Formation; Morrow, 1991). The Camsell Formation represents a facies of the Delorme Group that is characterised by the presence of calcite-cemented breccia, which is inferred to have formed by the dissolution of evaporite beds interlayered with carbonate units. Morrow (1991) indicated that the breccia formed after beds were lithified, tilted and exhumed. Groundwater dissolved the uplifted anhydrite layers, leading to collapse of carbonate layers into the open spaces. Much

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A shallow, open-marine setting resulting from Early to Middle Devonian sea-level rise led to the deposition of a platformal carbonate succession (Morrow and Cook, 1987). Devonian strata of the Mackenzie Platform represent a transgressive succession that records comparatively steady subsidence of the continental margin (Morrow and Cook, 1987), rather than pronounced differential subsidence, as in the underlying Delorme Group. The Mackenzie Platform was at latitude 10°N to 25°N during this time (Smith et al., 1981). A rise in sea-level covered the Norman Wells high and inundated the earlier source-area of terrigenous siliciclastic sediment, resulting in a cleaner carbonate than that of the previous depositional regime. Seven platformal carbonate formations [Sombre, Bear Rock, Grizzly Bear, Arnica, Landry, Headless and Nahanni (together, Hume)] contain more than 2500 m of strata in the Mackenzie Platform (Figs. 3.4.3-2 and -3). These units extend with little change northward from the southern Mackenzie Mountains, where they were defined by Gabrielse et al. (1973a). In the Sekwi project area, the Sombre, Arnica, Landry, Headless and Nahanni (Hume) formations form a westward-thickening wedge. The Bear Rock Formation is exposed in the northeastern part of the Sekwi project area and is interpreted to have resulted from solution-collapse of evaporite rocks that are correlative to Devonian evaporite strata exposed in the Mackenzie Valley. The Grizzly Bear Formation is exposed only in the westernmost part of the Sekwi project area, and defines the western edge of the Mackenzie Platform in the Early Devonian.

Sombre Formation This medium grey-weathering, fine-grained, cherty carbonate unit has a type area at 61°58’N 124°54’W (NTS 95F; Douglas and Norris, 1961). It is distinguished from the laterally equivalent and

Chapter Three overlying Arnica Formation by more uniform colour and a recessive weathering profile. In NTS 105P, the Sombre Formation forms two outcrop bands that extend northwest into the headwaters of the Mountain River in southwestern NTS 106A. Most of the Sombre Formation was erosionally removed from northeastern NTS 106A before deposition of the Hume Formation. Three Sekwi project measured sections included the Sombre Formation (07MM-S2, 07GGA-S1, and 08RAS-S1; Appendix A).

medium-bedded, but thick beds with convolute laminations were encountered on several traverses in the Sayunei Range. Horizontal burrows, bioturbation, and breccia zones with black chert fragments are also present. The Sombre Formation is known to contain at least one Zn occurrence in the Sekwi project area (Appendix H).

Description

A middle Early Devonian age was indicated by conodont faunas in NTS 105I (Gordey and Anderson, 1993). Brachiopods, although common, did not yield a diagnostic age. The western equivalents of the Sombre Formation are the lower part of the Arnica Formation, as well as the Grizzly Bear and Sapper formations.

The base of the Sombre Formation is a sharp contact placed at the top of the highest yellow-weathering bed of the Tsetso Formation (Fig. 3.4.6-1), or a sharp but conformable contact with the Camsell Formation (Morrow, 1991). The abrupt upper contact with the Arnica or Landry formation is marked by a change in weathering colour and bedding character. The Sombre Formation is reported to be 700 m thick in NTS 105P (Blusson, 1971). This appears to be a regional maximum; to the south, in NTS 105I, the formation is 575 m to 635 m thick (Gordey and Anderson, 1993). East of Mount Delthore in NTS 105P the unit is 488 m thick (section 08RAS-S2). In NTS 106B, the formation is 700-1000 m thick (Morrow, 1991). Where first described, and as far north as southern NTS 105P, the Sombre Formation has three divisions. Lowermost thick-bedded crystalline dolostone grades upward to thin-bedded dololaminite and locally quartz-silty dolomudstone. A middle interval of thin, distinctively dark-weathering, fetid, crystalline, stromatoporoid- and coral-bearing dolostone is succeeded by an upper, medium-grey-weathering dolostone with silty interbeds. These subdivisions are not evident farther north (Morrow, 1991), where the Sombre Formation contains cyclic alternations of dark brown-grey-weathering stromatoporoid-bearing dolostone and pale grey-weathering microbially laminated to stromatolitic dolostone. Morrow (1991) indicated that the only significant distinction between the Sombre and Arnica formations in the northern Mackenzie Mountains is a higher proportion of pale grey, microbially laminated strata in the former. In the Sayunei Range of northern NTS 105P, variably greyweathering, dark grey microcrystalline carbonate is the predominant rock type of the Sombre Formation. The unit here is typically

Figure 3.4.6-1. The Sombre Formation is characterised by grey-banded dolostone. It overlies the Tsetso Formation (yellow bands in centre) and dark-weathering Mount Kindle Formation (lower right and background). View northwestward in NTS 105P/15; 10 km northeast of Godlin Lakes (516529E, 7082520N).

Age and correlation

Interpretation The Sombre Formation formed a broad carbonate shoal at the shelf-break, and protected an inner zone of subtidal deposits (Arnica Formation). Dolomitic laminite reflects a quiescent intertidal setting.

Arnica Formation The Arnica Formation is characterised by dark brownish-greyweathering, medium- to thick-bedded, vuggy dolostone in eastern and central NTS 105P and pale grey, thick-bedded dolostone in the Sayunei Range. This unit forms a continuous belt that extends northward from the area where the formation was first defined by Douglas and Norris (1961; southern Mackenzie Mountains), forms multiple outcrop belts in eastern NTS 105P, and extends into southwestern NTS 106A of the Sekwi project area. Two Sekwi project measured sections included the Arnica Formation (07GGA-S1 and 08RAS-S2; Appendix A). No detailed work was undertaken on this formation during the Sekwi project.

Description In the Sayunei Range the Arnica Formation conformably overlies the Sombre Formation (Fig. 3.4.6-2). To the south and east of this locality it overlies the Tsetso Formation. The abrupt basal contact with underlying Delorme Group records the transgression documented by Williams (1975) in the Root River Basin. The upper

Figure 3.4.6-2. The Arnica Formation (DA) overlies Sombre Formation (DS) and is overlain by Landry (DL) and Hume (DH) formations in the Sayunei Range. View to northwest (immediately west of Fig. 3.4.6-1) in NTS 105P/15; 10 km northeast of Godlin Lakes (516529E, 7082520N).

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Chapter Three contact is gradational with the Landry Formation (Morrow, 1991). At its type locality in the First Canyon of the South Nahanni River (NTS 95F; 61°17’N, 124°14’W), the Arnica Formation is 625 m thick. Blusson (1971) reported a maximum thickness of 365 m in NTS 105P, although some exposures mapped by him have been reinterpreted as Grizzly Bear Formation (Cecile, 2000). In NTS 105P, the lower part of the Arnica Formation consists of white dololaminite and dolomitised peloidal and intraclast packstone. The upper beds of the Arnica Formation are thickbedded to massive dolostone. It is locally microbially laminated and cross-bedded. The packstone is a possible hydrocarbon reservoir, particularly at the northeast facies change to evaporite and breccia of the Bear Rock Formation (Gal et al., 2009). The Arnica Formation hosts numerous Zn-Pb showings in the Sekwi project area (Appendix H).

Age and correlation

Description Regionally, the Bear Rock Formation conformably overlies the Tsetso (Fig. 3.4.6-3) and Sombre formations. Its upper contact is interdigitated with the Landry Formation, and it grades westward into the Arnica Formation (Morrow, 1991). In the subsurface, the Bear Rock Formation consists of alternating anhydrite and dolostone layers of uniform thickness. In eastern NTS 106A the Bear Rock Formation forms spires, lumpy palisades and talus rubble (Fig. 3.4.6-4). It is a calcitecemented pack-breccia that forms limestone cliffs, or a floatbreccia that generally underlies recessive slopes. The clasts of lime mudstone vary from cobble- to boulder-sized and are randomly oriented. Breccia textures are diverse (Fig. 3.4.6-5). The breccia is generally indistinguishable from that of the Camsell Formation, although locally the Bear Rock Formation weathers pale grey, rather than yellow.

According to Morrow (1991), the Arnica Formation is Early Devonian. No age-diagnostic fossil samples were collected during the Sekwi project. Pale-weathering carbonate exposures in the western part of NTS 105P (unit 22c of Blusson, 1971) were reassigned to the Grizzly Bear Formation in accordance with the adjacent map-area (Cecile, 2000). In eastern NTS 105P, the less uniform, white exposures are in part facies-equivalent to, or are interdigitated with, the Bear Rock Formation, which is the dominant facies of this age east of the Mackenzie Mountains. The Arnica Formation merges eastward into the Bear Rock Formation and westward into Grizzly Bear Formation, which undergoes a facies change westward into Hailstone and eventually basinal Misfortune formations. North of NTS 106A the Arnica Formation was described by Morrow (1999). It is equivalent to the upper Stone Formation in the northern Rocky Mountains.

Interpretation The Arnica Formation represents a platformal facies, whereas the Grizzly Bear Formation represents the platform edge. The breccia of the Bear Rock Formation represents the hypersaline, inboard equivalent of the Arnica Formation (Morrow, 1991; Gal et al., 2009). Light grey, microbially laminated dolostone is interpreted as an intertidal deposit; dark fossiliferous bands indicate intermittent subtidal conditions. The cross-beds of detrital carbonate grains could record beach deposition. Dolomitisation has completely destroyed primary sedimentary structures throughout much of the Arnica Formation.

Figure 3.4.6-3. Bear Rock Formation breccia (DBR) forms a pale-weathering band between Tsetso (lDT) and Landry (DL) formations. Underlying units include Franklin Mountain (`OF) and Mount Kindle (OSK) formations; Hume Formation (DH) overlies Landry Formation. Aerial view to west in NTS 106A/9; 10.5 km west of McClure Lake (519028E, 7158695N).

Bear Rock Formation This medium- and dark-grey, irregularly weathering carbonate breccia was first defined at the eponymous mountain near Wrigley on the Mackenzie River (Hume and Link, 1945). The type section near Tulita is 154 m thick (Morrow and Meijer Drees, 1981). This unit is a possible hydrocarbon reservoir, and its subsurface extent is well documented in the Mackenzie Valley and Root River Basin. In the Mackenzie Mountains, the Bear Rock Formation extends into NTS 96D (Carcajou) 95N (Dahadinni) and NTS 95M (Wrigley Lake) map-areas, as well as into northeastern NTS 105P and NTS 106A. No detailed work was done on this unit during the Sekwi project, but two measured Sekwi project sections included this unit (07CL-S4 and 07MM-S3; Appendix A).

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Figure 3.4.6-4. The Bear Rock Formation forms hoodoos of grey dolostone clasts in a porous, lime-cemented matrix. Exposure is about 10 m high. View to southeast in NTS 96D/4, 6 km east of Keele River (554402E, 7099182N)

Chapter Three Age and Correlation The Bear Rock Formation is Early to Middle Devonian (Eifelian) age, based on ostracode data from a correlative unit in the Colville Hills (Cook and Aitken, 1971). An early Eifelian (Middle Devonian) age for the upper part of the formation was determined from conodonts by Chatterton (1978) south of the Peel River. The Bear Rock Formation is equivalent to shelf-margin limestone in the Northern Ogilvie Mountains (Cranswick Formation of Norris, 1968), and to the Arnica and Landry formations (Morrow, 1999; Gal et al., 2009).

Interpretation The evaporite rocks in the subsurface of the Mackenzie Valley record peritidal cycles in which anhydrite layers were overlain by thin, mudcracked dolo-laminite layers (Meijer Drees, 1980). The breccia exposed in the Mackenzie Mountains developed where these layers were uplifted and erosionally breached so that the interbedded anhydrite was dissolved by groundwater. After evaporite removal, the remaining layers were converted to breccia through collapse and layer-parallel slip along inclined bedding planes (Morrow, 1991).

Grizzly Bear Formation This thick-bedded to massive carbonate succession forms impressive, pale grey-weathering cliffs in the northwestern quadrant of NTS 105P (Fig. 3.4.6-4). The Grizzly Bear Formation was initially described by Gabrielse et al. (1973a) in NTS 95L. The formation’s exposure area was extended northwest by Gordey and Anderson (1993), and Cecile (2000) extended usage to NTS 105O. This formation is the marker unit in the Caribou Pass syncline, and was initially mapped as a member of the Arnica Formation (Blusson, 1972).

Description

upper contact of the Grizzly Bear Formation with Devonian-aged shale of the Canol and Misfortune formations is locally erosional, and has been demonstrated to be unconformable in NTS 105O (Cecile, 2000) and NTS 105I (Gordey and Anderson, 1993). At the type section (62°42N, 127°50’W in NTS 95L), the Grizzly Bear Formation consists of 256 m of pale grey-weathering carbonate rock. In NTS 105I the formation varies from very thin to 200 m thick (Gordey and Anderson, 1993). In northeastern NTS 105O the formation is estimated to be more than 200 m thick (Cecile, 2000). The Grizzly Bear Formation weathers yellow-brown to pale grey and is medium grey on fresh surfaces. In parts of western NTS 105P, the formation consists predominantly of skeletal packstone, and less commonly, biostromal boundstone, and is massive to thickbedded. Dark grey-weathering beds contain amphiporids and thamnoporid colonial corals, as well as crinoids with twin axial canals. The unit locally consists of interlayered dark and pale grey limestone with shaly partings and sparse dolostone interbeds (Fig. 3.4.6-7). Convolute or wavy bedding is common, as are slightly darker grey-weathering parallel beds 1-30 cm thick. In one location, fine-grained quartz sandstone interbeds with low-angle crossbedding are present. In the core of the Caribou Pass syncline, four cliff-forming units are present in the Grizzly Bear Formation, each tens of metres thick (Fig. 3.4.6-8). The lower part of the formation consists of thick dolostone, with wispy black laminations that locally define planar cross-beds, and pyrite and chert nodules. The upper part of the Grizzly Bear Formation on the northeast side of the Caribou Pass syncline consists of thin-bedded, nodular limestone with shaly interbeds. Among them is a 5-15 m-thick bed with abundant brachiopods in a dark grey, silty limestone matrix (Fig. 3.4.6-9). This layer also contains intraclasts derived from the underlying bed. At the top of the unit at the southern end of the syncline, a 25 m-thick pinkish-grey-weathering dolostone and dark grey limestone unit exhibits abundant vugs containing pyrobitumen.

The Grizzly Bear Formation unconformably overlies Duo Lake Formation shale in NTS 105P, but the contact is structurally disrupted. South of the Sekwi project area and away from the edge of the platform, the Grizzly Bear Formation overlies the Sapper Formation and interdigitates with the Sombre Formation, with which it shares a conodont zone (Gordey and Anderson, 1993). The

Age and correlation

Figure 3.4.6-5. Bear Rock Formation breccia has a distinctive, porous weathering style resulting from dissolution of evaporite beds and collapse of interlayered carbonate beds. NTS 106A/7, 12 km south of Cache Lake (510417E, 7132974N).

Figure 3.4.6-6. The Grizzly Bear Formation is anticlinally folded and overlain by brown Canol Formation. View to southeast near northwest corner of NTS 105P/13 (452900E, 7092450N).

Crinoid packstone in the Grizzly Bear Formation contains ossicles with twin axial canals, indicating latest Early to earliest Middle Devonian age. Sekwi project samples yielded conodonts with ranges spanning the late Early to Late Devonian (late Emsian

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Chapter Three to early Givetian). One sample contained a Silurian (Pridoli) to Early Devonian (Lochkovian) conodont fauna (Appendix F). Southwest of the Stew and Caribou Pass synclines, the Grizzly Bear Formation thins abruptly to a single limestone band enclosed by shale, which together represent part of the Hailstone Formation. Towards the platform (northeastward from western NTS 105P) the Grizzly Bear Formation is broadly correlative with the Arnica Formation, and perhaps uppermost(?) Sombre and overlying Landry formations.

Interpretation

Figure 3.4.6-7. The Grizzly Bear Formation contains thin beds of nodular limestone with shaly partings, overlain by thicker beds of laminated limestone. View to west in NTS 105P/11, 10 km northwest of Caribou Pass (482744E, 7054114N).

The distribution of the Grizzly Bear Formation defines the western edge of the Mackenzie Platform (as used herein) during the Early Devonian. Cecile (2000) interpreted the Grizzly Bear Formation as a shallow-water platformal depositional environment, but the thick beds and coral debris appear to represent deposits of the upper continental slope. Skeletal floatstone debrites are interbedded with shale that represents background, deeper-water sedimentation.

Landry Formation This thick-bedded, pale grey-weathering, conspicuously recessive limestone unit was described by Douglas and Norris (1961) and Gabrielse et al. (1973a). In the southern Mackenzie Mountains, the Landry Formation is widespread in NTS 95L and NTS 95M, as well as parts of NTS 96D. In NTS 105P the Landry Formation is exposed in a narrow belt from the Natla River in the southeast to the Twitya River in the northwest. One Sekwi project measured section included the Landry Formation (07GGA-S1).

Description

Figure 3.4.6-8. The Grizzly Bear Formation forms cliffs and towers that outline the Caribou Pass syncline. Bands of medium- and thick-bedded limestone are separated by thin, dark, shaly limestone beds. Aerial view is tilted downward, looking south, in southwestern NTS 105P/11, 7.5 km west-northwest of Caribou Pass (482460E, 7046950N).

Figure 3.4.6-9. Basal layers of the Grizzly Bear Formation contain brachiopod rudstone. Tool is 12 cm long. View to north in NTS 105P/11, 10 km northwest of Caribou Pass (484768E, 7051538N).

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The Landry Formation conformably overlies the Arnica Formation in the northeastern half of the Sekwi project area. Where the Landry Formation overlies the Sombre Formation, the contact is defined by the lowest thick, blue-grey-weathering limestone (Morrow, 1991). The upper contact of the Landry Formation with the Natla Formation (NTS 105I) and Hume Formation (NTS 95M) is placed above the highest sooty, recessive limestone layer. Regionally, the unit thickens from Norman Wells westward to the shelf edge. In general its thickness varies inversely with the thickness of the underlying Sombre and Arnica formations (Morrow, 1991). In NTS 105P, Blusson (1972) reported a maximum thickness of 520 m. and a thickness of 505 m was measured previously in the area (section 8 of Morrow, 1991). In NTS 106A the Landry Formation is 150 m thick (section GGA07-S1; Appendix A), similar to that of Morrow’s (1991) Section 11. Where the formation is exposed in the Tigonankweine anticline it is 23 m thick. The predominant rock type of the Landry Formation is thickbedded to massive, locally mottled lime mudstone (Figs. 3.4.6-10 and -11). Lesser amounts of medium to dark grey dolostone, siltstone, fossiliferous limestone and calcareous shale are also present (Williams, 1975). Fenestral fabric, channels, and ripple-drift cross-stratification are common. Brachiopods, trilobites, bryozoans, branching corals, and minor ostracodes have been found in the Landry Formation. In northern Yukon and along the Yukon-Northwest Territories border, the Landry Formation is a resistant (“rib-forming”) bluegrey-weathering unit (Morrow, 1999). It is generally poor in fossils, possibly as a function of the hypersalinity of the adjacent Bear Rock Formation deposition. The Landry Formation is known to contain at least one Zn-Pb occurrence in the Sekwi project area (Appendix H).

Chapter Three

Figure 3.4.6-10. The Landry Formation (pale rubble in foreground) overlain by Headless (brown) and Nahanni (ridge-former) formations. Field of view at horizon is 80 m. NTS 95M/13 (588713E; 7073812N).

Age Morrow’s (1991) paleontological collections from the Godlin salient are late Early Devonian (late Emsian). The conodont fauna from one Sekwi project sample has an Early to Middle Devonian range (Emsian to Eifelian; Appendix F).

Interpretation Where the Landry Formation consists of thick, fossiliferous lime mudstone, it is interpreted to have been deposited in an openmarine environment. The presence of brown lime mudstone and peloidal limestone (recessive-resistant) couplets records cyclic regressive episodes of deposition (Morrow, 1991).

Hume Formation (Headless and Nahanni formations) The Hume Formation was defined at the northeastern front of the Mackenzie Mountains in NTS 106H by Bassett (1961) at 65°20.5’N 129°58’W), coincident with formalisation of the Nahanni and Headless formations in the southern Mackenzie Mountains by Douglas and Norris (1961). Tassonyi (1968) recognised the equivalence of the units, and Morrow (1991) proposed use of the term “Hume Assemblage” to encompass them. This arrangement is necessary because the distinction between the Headless and Nahanni formations is not always clear north of 65°N . In central and northeastern NTS 106A, massive, pale greyweathering limestone is referred to as the Hume Formation. It differs from the characteristic Hume, which is dark grey, argillaceous, fossiliferous limestone with minor shale interbeds (Morrow, 1991). Because the formation is pale-weathering and massive in the Sekwi project area, its lower contact is hard to distinguish from the similar lithology of the Bear Rock Formation. A pale grey, palisade-forming limestone in southwestern NTS 105A and extending southeastward across NTS 105P is called the Nahanni Formation, and is underlain by recessive, light brown-weathering silty limestone of the Headless Formation. Both the Nahanni and the Hume formations are abruptly overlain by recessive, dark-weathering Devonian-Mississippian siliciclastic units. One Sekwi project measured section included the Hume Formation (07CL-S4), two included the Headless Formation (07GGA-S1 and 08RAS-S1), and one included the Nahanni Formation (08RAS-S1; Appendix A).

Figure 3.4.6-11. The Landry Formation contains brachiopods with geopetal indicators. NTS 105P/10, 8 km south of Godlin Lakes (506922E, 7066668N).

Description Hume Formation strata overlie the Landry Formation abruptly and conformably (Morrow, 1991). The basal contact is diachronous, becoming younger westward (Noble and Ferguson, 1971). The upper contact is a sharp depositional regime-change to shale and siltstone of the Hare Indian and Canol formations (Fig. 3.4.6-12). This contact is generally gradational over 2-5 metres. In southern NTS 106A, the Headless Formation is 95 m thick and the Nahanni Formation is approximately 20 m thick (section 08RAS-S1; Appendix A). The Hume Formation is regionally at least 138 m thick north of this area (Morrow, 1991). In NTS 105P, the Headless Formation is 850 m thick and is overlain by about 60 m of Nahanni Formation (Blusson, 1971). The Hume Formation can locally be divided into a recessive lower member and a resistant upper member, which correspond to the Headless and Nahanni formations, respectively (Morrow, 1991). Most of the unit consists of orange-brown-weathering, thickbedded, biostromal limestone. Yellow-brown-weathering skeletal rudstone is less common. The top of the Hume Formation contains a brachiopod- (Atrypa sp.) and coral-rich limestone that grades upward into Canol Formation by abrupt decrease in limestone bed thickness and abundance over a thickness of 2 to 5 metres. Where two formations can be discerned, the Headless Formation consists of dark grey argillaceous limestone interbedded with calcareous shale (Fig. 3.4.6-13). The Headless Formation is a relatively incompetent unit and is typically tightly folded in thrust panels. The formation contains common burrow-mottling, and is characteristically petroliferous with oil stains. Locally, lime mudstone interbeds contain coral and crinoid fragments. In contrast to the Headless Formation, the overlying Nahanni Formation consists of relatively clean, bluish-grey-weathering, thickbedded to massive skeletal wackestone and packstone. Well-bedded, finely crystalline dolomitic limestone is present at the top of the unit. Near the Mountain River, where beds dip steeply, it forms a resistant wall, or a pinnacle-studded palisade. This unit contains skeletal wackestone and rudstone with crinoid, brachiopod and ostracode fragments. Argillaceous material forms partings between limestone beds and patches within beds (Fig. 3.4.6-14).

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Chapter Three

Figure 3.4.6-12. The Hume Formation is a pale brownish-grey limestone (left) in contact with dark grey calcareous shale of the Hare Indian-Canol formations (right). View to northeast in NTS 106A/9, 5 km northwest of McClure Lake (529313E, 7159015N).

Figure 3.4.6-14. Nahanni Formation limestone beds are 1-2 m thick and interlayered with recessive, calcareous shale. View to east in NTS 106A/9, 10 km west of McClure Lake (519327E, 7158992N).

Figure 3.4.6-13. The Headless Formation consists of skeletal grainstone (rubble-covered saddle to right in mid-ground). It is overlain by the cliff-forming Nahanni Formation, which is more than 25 m thick. View to southwest in 106A/5, 3 km east of Mountain River (457979E, 7126967N).

Age and correlation A conodont collection from 22 m above the formation’s base yielded an early Eifelian age (Morrow, 1991), and late Eifelian to early Givetian ages were reported elsewhere (Chatterton, 1978; Morrow, 1999). Conodont collections from the Sekwi project have Middle Devonian ranges (late Eifelian – early Givetian; Appendix F). The Nahanni Formation is laterally equivalent to, or interbedded with, the “Manetoe facies”, an important gas reservoir unit in the southwestern Northwest Territories (Morrow et al., 1990). See Chapter 8 for details.

Interpretation The Headless and Nahanni formations (=Hume Formation) were deposited in a subtidal environment during transgression. The lower member of the Hume Formation contains thin skeletal packstone beds whose surfaces are well cemented and stained orange (Morrow, 1991). These surfaces are probably hardgrounds, and imply intervals of sediment-starvation.

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3.5. Lower to Middle Paleozoic Selwyn Basin and Misty Creek Embayment A large area of eastern Yukon and adjacent Northwest Territories is underlain by dark, fine-grained siliciclastic strata. This basinal area was named the “Selwyn Basin” by Gabrielse (1967) after the Selwyn Valley, which parallels the Northwest Territories-Yukon border near 65°N. He noted that the basinal strata thinned eastward. During the next decade the term became synonymous with a “shale basin” (i.e., a depositional feature), of Early Cambrian to Middle Devonian age (Tempelman-Kluit and Blusson, 1977). The term “Selwyn Basin” as used in this report encompasses all siliciclastic and slope carbonate deposits immediately west of the Mackenzie Platform (following the usage of Gordey and Anderson, 1993). This definition specifically excludes the younger Earn Group strata (described here in Chapter 3.6; a separate, mid-Paleozoic siliciclastic basin) that host stratiform zinc-lead deposits in the Macmillan Pass area; some industry reports do not make this distinction.

Chapter Three The Misty Creek Embayment, defined by the distribution of basinal strata, is a broad embayment that is parallel to the YukonNorthwest Territories border, and opens southward into the Selwyn Basin (figure 2 of Cecile, 1982). Its southeast-trending axis is west of the Sekwi project area, straddling the Northwest Territories-Yukon border in NTS 105I and 106B, and the eastern border of the deepwater area trends northwest across west-central NTS 106A and northeastern NTS 106B. The southern end of the embayment is in north-central NTS 105P. The Misty Creek Embayment is relevant to this project because transitional or slope deposits on its eastern flank are exposed in western NTS 105P and in the southwestern corner of NTS 106A (Figs. 3.5.1-1 and -2). This region contains southeasttrending cylindrical folds that provide exposure of sections through Devonian-Mississippian siliciclastic strata and the overlying Upper Paleozoic shelf (described here in Chapter 3.7; Tsichu Group and Mount Christie Formation).

3.5.1. Cambrian to Lower Devonian siliciclastic basin C.F. Roots, R.B. MacNaughton, E. Martel and S.P. Gordey

The correlation of and stratigraphic nomenclature for the deeper-water strata associated with the Selwyn Basin have been controversial. The Vampire Formation is an outboard equivalent of part of the shallow-water Backbone Ranges Formation in the Mackenzie Mountains and is equivalent to the Narchilla Formation of the Selwyn Basin. Both Cecile (1982) and Gordey and Anderson (1993) outlined problems with the Road River Formation/Group nomenclature in the Selwyn Basin area. Usage in this volume follows Cecile (1982), without reference to the Road River Group, of which the constituent formations remain ambiguous.

Vampire Formation The Vampire Formation is a recessive-weathering unit that consists of dark-weathering siltstone (Fig. 3.5.1-3) interbedded with quartzose sandstone. It was established by Fritz (1982), with a type section in Nahanni map-area (105I), near where the South Nahanni River crosses the Nahanni anticline. In the Sekwi project area, this unit corresponds to strata previously assigned to Map unit 13 by Blusson (1971). It is absent in the hanging-wall panel of the Plateau fault, but is widespread southwest and west of the junction of the Keele and Ingta rivers. In NTS 105P, the Vampire Formation extends at least as far east as Risky Peak and Blueflower Mountain, as a tongue between the “Backbone Ranges Formation” and the Sekwi Formation. In the central and western parts of NTS 105P, the formation is progressively thicker as it replaces the “Backbone Ranges Formation” basinward. It almost certainly forms some part of Blusson’s (1971) Map unit 10a in southwestern NTS 105P. The Vampire Formation has not been mapped in NTS 106A, but Fritz (1982) recognised it in the central and western parts of NTS 106B. The name has also been applied to basal Paleozoic strata in the Wernecke Mountains (Yukon; e.g., Nowlan et al., 1985; Osborne et al., 1986). Prior to the unit’s formalisation (Fritz, 1982), several sections measured by Fritz (1976, 1978, 1979a, b; 1981) included siltstone- or shale-rich strata below the Sekwi Formation, which today would be assigned to the Vampire Formation. In an unpublished thesis, Krause (1979) presented several sections that included strata assigned to an informal “June Lake formation”, a unit superseded by the Vampire Formation. More recently published Vampire Formation sections

Figure 3.5.1-1. Distribution of Selwyn Basin (Misty Creek Embayment) and transitional strata.

from the Mackenzie Mountains are those of Fritz et al. (1983) and MacNaughton et al. (1997a, b). The Vampire Formation is not known to contain economic mineralisation. It was not a focus of study during the Sekwi project and no sections were measured in it.

Description Where the Vampire Formation overlies the “Backbone Ranges Formation” in NTS 105P, its base is sharp but conformable and records a major marine transgression (MacNaughton et al., 1997b). Where the Vampire Formation overlies the Risky Formation or the middle member of the Backbone Ranges Formation, its base may be disconformable. Basinward of the shale-out of the Risky Formation (Aitken, 1989a), the contact between the Vampire Formation and underlying units is presumably a shale-on-shale surface. The Vampire Formation is conformably and commonly gradationally overlain by the Sekwi Formation (Fig. 3.5.1-4). Detailed descriptions of the Vampire Formation were provided by Fritz (1982) and MacNaughton et al. (1997a,b). Siltstone and shale are the dominant rock types of the Vampire Formation (Fig. 3.4.1-8). Fresh and weathered colours are generally dark grey, brownish-grey, or greenish-grey; rusty-weathering colours are also present. These lithofacies generally are laminated and locally preserve slump-folds. Sandstone is present in lesser volumes. It is more prevalent in distal sections (where the Vampire Formation is the distal equivalent of quartz-arenite-rich intervals; Fig. 3.5.1-3) than in sections where the Vampire Formation is a tongue between the “Backbone Ranges” and Sekwi formations. Vampire Formation sandstone is quartzose and very fine- to fine-grained. Fresh surfaces are medium grey, light brownish-grey, tan, greenish-grey, or rarely pale grey or white. Weathering colours include rust, medium brownish-grey, and

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Chapter Three W

40km Caribou Cry River

E

[Misfortune Fm] 500m

Grizzly Bear Fm [Portrait Lake Fm]

70m

Hailstone Fm Arnica Fm

500m

Duo Lake Fm 300m

Rabbitkettle Fm

Hess River Formation

100m

Numbers are thickness in metres

Mount Kindle Fm

600m

150m

Lateral facies transition

[Unit] Formations above and

below Mackenzie Platform

Figure 3.5.1-2. Schematic stratigraphy of deep-water, lower to middle Paleozoic units in western Mackenzie Mountains. Adapted from Gordey and Anderson (1993) and Cecile (2000), with additional Sekwi project data.

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Chapter Three medium to pale grey. Sandstone beds are very thin to thick, sharp to erosionally based, and locally lenticular. Common sedimentary structures in sandstone include parallel lamination, hummocky cross-stratification, load casts, slump structures, ripple marks, and tool marks. Also present are pot casts (horizons with pot-holes) and rare swaley cross-stratification and trough cross-bedding. Blusson (1971) estimated that the Vampire Formation (his Map unit 13) is about 150 m thick in NTS 105P. Krause (1979), however, determined that the “June Lake formation” is up to at least 386 m thick in the Sekwi project area. The Vampire Formation is 930 m thick in its type area (Fritz, 1982). Regional trends in the internal stratigraphic packaging of the Vampire Formation are not well understood. MacNaughton et al. (1997b) suggested that the formation could be subdivided into seven small-scale depositional

Figure 3.5.1-3. Hillside exposure of Vampire Formation in southwestern NTS 105P. Interbedded silty sandstone, siltstone, and shale at this location are probably the distal equivalent of the “Backbone Ranges Formation” exposed farther east. Photograph taken looking southeast from 483833E/ 7022922N. Beds are upright. Geologist for scale (centre).

sequences in the east limb of the June Lake anticline, but the regional significance of these packages is uncertain.

Age and correlation In its type section (Fritz, 1982) trace-fossil evidence indicates that at least the upper two-thirds of the Vampire Formation is of Cambrian age. The type section is a distal equivalent of the upper member of the Backbone Ranges Formation. In the June Lake anticline, the Vampire Formation tongue contains trace fossils that delineate the boundary between the sub-trilobite Cambrian Rusophycus avalonensis and Cruziana tenella zones (MacNaughton and Narbonne, 1999). The uppermost beds of the Vampire Formation in the Sekwi project area have generally been considered to be in the Cambrian Fallotaspis Zone (e.g., Fritz, 1980). In the western part of NTS 105P, the Vampire Formation includes sandstone-rich intervals that are the distal equivalent of the “Backbone Ranges Formation”. These strata underlie the Sekwi Formation, which contains Early Cambrian trilobites, and have yielded the trace fossil Psammichnites, confirming their Early Cambrian age; Appendix F). Body fossils have been collected near the top of the formation and include hyolithids, brachiopods, and Volborthella(?) sp. (Fritz, 1980), as well as fragmentary trilobite carapaces. Trace fossils are common to abundant and include well-developed arthropod traces (MacNaughton and Narbonne, 1999; MacNaughton, 2009). Terreneuvian (late early Cambrian) acritarchs have also been recovered (Baudet et al., 1989). According to the correlation of Gordey and Anderson (1993), the outboard equivalent of the Vampire Formation in the Yukon is the Narchilla Formation (Hyland Group), which is there considered to be an early unit in the Selwyn Basin succession. For this reason, and even though the Vampire Formation in the Sekwi project area exhibits only subtle outboard deepening and fining, it is here included in the Selwyn Basin succession. Understanding the relationships of the Vampire Formation with its inboard and outboard equivalents, and the tectonostratigraphic implications thereof, would be a subject worthy of further study.

Figure 3.5.1-4. The Hess River Formation consists of dark-weathering shale and siltstone. It conformably overlies brown-weathering dolostone of the Sekwi Formation. View to southwest in NTS 105P/11, 7.5 km northwest of Caribou Pass (487200E, 7052483N).

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Chapter Three Interpretation Fritz (1982) considered the Vampire Formation to be a slope deposit, at least in its type area. Although the dominance of siltstone and shale suggests a relatively low-energy setting, the presence of hummocky cross-stratification, and even possible fluvial channelfills, in sections in the June Lake anticline suggests that at least parts of the formation were deposited in shallow- to marginal-marine settings (MacNaughton et al., 1997a). Exposures in the southwestern part of NTS 105P have not been studied in detail but presumably record more distal deposition.

Hess River Formation This unit of thin-bedded black shale, calcareous mudstone and limestone, was defined by Cecile (1982) 50 km northwest of NTS 105P. It forms a recessive interval that sharply contrasts with underlying, orange-weathering carbonate of the Sekwi Formation, and overlying tan- to grey-weathering, banded Rabbitkettle Formation (Fig. 3.5.1-4). One Sekwi project measured section included the Hess River Formation (08BF-S1; Appendix A).

Description The basal contact of the Hess River Formation with the Sekwi Formation is sharp but conformable. The contact is typically covered but forms a prominent topographic break between orangeweathering carbonate rock and dark grey shale (Fig. 3.5.1-4). The upper contact with the Rabbitkettle Formation is covered, but to the west it is gradational (Cecile, 1982, 2000). At the type section (62°42’N 130°47’W in NTS 105O) along the axis of the Misty Creek Embayment, the Hess River Formation is 420 m thick. On the flanks of the embayment the formation attenuates to as little as one-tenth that thickness (Cecile, 1982). The Sekwi project area includes the eastern flank of the Misty Creek Embayment in northwestern NTS 105P, where the Hess River Formation is 99 m thick (section 08BF-S1; Appendix A). The lower part of the Hess River Formation consists of friable, parallel-laminated calcareous black siltstone with medium blue-grey weathering, dark grey thin-bedded, nodular limestone interbeds. Local thin intraclast beds containing trilobite fragments, sponge spicules and phosphatic granules (section 08BF-S1) are present. The siltstone and shale are locally calcareous. Pyritic nodules up to 1 cm in diameter are present. The Hess River Formation typically includes increasing volumes of calcareous shale upwards; the upper half of the Hess River Formation is characterised by fissile, grey- and brown-weathering, pale tan-grey, calcareous shale. Locally, very thin-bedded silty limestone is present, or a 10 m-thick limestone band is overlain by 8-10 m of graptolitic shale (presumably Duo Lake Formation). The carbonate-rich strata are topographically prominent. Secondary calcite veinlets, although a volumetrically minor feature, are prominently white against the dark host. Minor barite was reported by Cecile (1982).

Age and correlation Trilobite fragments are the only body fossils described from this formation. In the axis of the Misty Creek Embayment, trilobites indicate a latest Early Cambrian to latest Middle Cambrian age (Cecile, 1982). The Hess River Formation may be as young as Late Cambrian on the flanks of the embayment; this is the same age as the oldest strata of the overlying Rabbitkettle Formation.

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The slope facies-equivalent of the Hess River Formation is the Rockslide Formation (Cecile, 1982; Gordey and Anderson, 1993), located in the southeastern quadrant of NTS 105P.

Interpretation This fine siliciclastic succession records a deep-water depositional environment. The sharp base overlying the carbonatedominated Sekwi Formation indicates an abrupt transgression. Debrites and other collapse deposits are lacking, so this change was probably the result of eustatic sea-level rise, rather than regional block-faulting.

Rockslide Formation The Rockslide Formation consists of recessive, dark grey- to black-weathering limestone. It was first described by Gabrielse et al. (1973a) east of the Sekwi project area. At the type section (63°20’N, 127°32’W), 2.4 km north of Rockslide Pass in west-central NTS 95M, it is 500 m thick. This formation was traversed during measurement of section 08EM-S1 (Appendix A) in northeastern NTS 105P. The description below is based on the descriptions by Gabrielse et al. (1973a) for NTS 95M and by Gordey and Anderson (1993) for NTS 105I, immediately south of NTS 105P.

Description At the type section, the Rockslide Formation is underlain by the Backbone Ranges Formation and overlain by the Broken Skull Formation (Gabrielse et al., 1973a). South of the study area in NTS 105I the formation is laterally equivalent to the Avalanche Formation, grading through several to a few tens of metres of increasing bed thickness and proportion of dolostone to the northwest (Gordey and Anderson, 1993). Where the Rabbitkettle Formation overlies the Rockslide Formation, the base of the former is defined by the lowest fine-grained sandstone. In NTS 105I, the contact with the underlying Sekwi Formation is sharp and conformable. In the Sekwi project area, the Rockslide Formation is consistently underlain by the Sekwi Formation and overlain by the Rabbitkettle Formation. In NTS 105I, the Rockslide Formation is described as thin- to medium-bedded dark grey-weathering, commonly planar-laminated limestone. Medium grey- to brownish-grey-weathering nodular siltstone, oolitic limestone, and silty limestone are locally abundant rock types. Syndepositional slump-folds are also locally present. In NTS 95M, the formation is a highly fossiliferous (trilobites, brachiopods; Gabrielse et al., 1973a), recessive, platy, nodular, black to orange-buff-weathering, dark grey, fine-grained argillaceous limestone and calcareous siltstone. In the one Sekwi project measured section (08EM-S1; Appendix A), the Rockslide Formation consists of recessive, dark grey- to brown-grey-weathering, laminated, platy, calcareous shale and silty, argillaceous, dark grey, finely crystalline to crypto-crystalline limestone, with minor thin beds of dark, platy, crypto-crystalline limestone and buff dolostone.

Age and correlation The Rockslide Formation contains abundant trilobites that collectively represent all Middle Cambrian trilobite zones (appendix 4 of Gordey and Anderson, 1993). Fossils collected during the Sekwi project were not age-diagnostic. The Rockslide Formation correlates with dolostone of the Avalanche Formation west of the type section in NTS 95M (Gabrielse et al., 1973a). The transition zone between the two formations migrated southeastward through time (S. Gordey, pers. comm., 2008).

Chapter Three Interpretation Compared to dolostone of the Avalanche and underlying Sekwi formations, the Rockslide Formation was deposited in relatively deep water and perhaps on a slope, as indicated by local slump structures (Gordey and Anderson, 1993).

Rabbitkettle Formation Interbedded limestone and shale of the Rabbitkettle Formation form a tan to dark grey-weathering, prominently banded interval in the Sekwi project area. The type section (Gabrielse et al., 1973a) is at 62°31’N, 127°17’W, about 200 km southeast of the Sekwi project area. The formation was also described by Gordey and Anderson (1993) in NTS 105I, immediately south of the project area, and by Cecile (1982) in northeastern NTS 105O (reference section in the Misty Creek Embayment is 437 m thick; Cecile, 2000). In the Sekwi project area, the Rabbitkettle Formation is exposed in western NTS 105P and in the southwest quadrant of NTS 106A. The Rabbitkettle Formation hosts SEDEX mineralisation of the Anvil District (Yukon). Five Sekwi-project measured sections included the Rabbitkettle Formation (07CL-S2 and -S3, 08EM-S1, 08BF-S1, and 08DT-S1; Appendix A).

the formation is of Middle Cambrian to Early Ordovician age. A Middle Ordovician conodont age was reported by Gordey and Anderson (1993) in NTS 105I, where the Rabbitkettle Formation contact with the overlying Duo Lake formation is diachronous. Sekwi project conodont collections from northern NTS 105P have ranges of Early or Middle Ordovician and Middle Ordovician to Middle Devonian, and one from NTS 106A is Cambrian (Appendix F). Tetragraptid and trilobite samples collected during the Sekwi project are Early to Middle Ordovician. The Rabbitkettle Formation is widespread throughout the Selwyn Basin area. In the Richardson Mountains, equivalent strata are referred to as the lower part of the Road River Formation (e.g., Cecile and Morrow, 1981), and in northeastern British Columbia, equivalent strata are known as the Kechika Formation (Cecile and Norford, 1979). The Mackenzie Platform correlatives of the Rabbitkettle Formation are the Broken Skull and Franklin Mountain formations.

Description The base of the Rabbitkettle Formation is conformable but poorly exposed in the Sekwi project area. The contact with the Sekwi Formation is placed at the base of the first thick interval of silty limestone (Cecile, 1982). Where documented, the basal strata consist of quartz-sandy limestone interbedded with platy limestone and dark grey calcareous shale (section 08BF-S1). The upper contact with the overlying Duo Lake Formation is conformable and probably diachronous, and is locally as young as Early Ordovician (Cecile, 1982). In the Sekwi project area, the Rabbitkettle Formation is 560 m (section 08BF-S1; Appendix A) and 524 m (section 08DTS1; Appendix A) thick. The Rabbitkettle Formation is a thick succession of interlayered thin-bedded nodular limestone, platy limestone, laminated calcareous siltstone and concretionary calcareous shale (Figs. 3.5.1-5 and -6). The pale grey to brown, finely crystalline limestone is laminated and locally argillaceous. Recessive shale predominates locally, and lime mudstone is typically interlayered with thin-bedded, wispy-laminated grey and fissile black shale. The yellow-grey-weathering limestone layers are 2 to 40 cm thick and form 20-50% of the unit. Locally they contain intraclasts and chert pebbles as well as chert concretions and slump-folds. Near the eastern limit of its range (north-central NTS 105P), an overturned succession that contains the Rabbitkettle Formation includes tan and grey, platy carbonate rhythmites overlain by lime mudstone. Most of the unit consists of recurring, sharp-based, 20-50 m-thick couplets of limestone grading upward into calcareous shale. Grading, ripple cross-lamination and nodular bedding are common. Macrofossils are rare in the Rabbitkettle Formation, but trace fossils are abundant on shaly bed surfaces.

Figure 3.5.1-5. The Rabbitkettle Formation is characterised by bands of paleweathering limestone interlayered with dark shale and calcareous siltstone. View to southwest of about 80 m of strata on the southwestern flank of the Caribou Pass syncline; southeastern corner of NTS 105P/12, 15 km west-southwest of Caribou Pass (474008E, 7044109N).

Age and correlation Trilobites with Late Cambrian ranges have been documented in the Rabbitkettle Formation in NTS 105P and NTS 105I (Pratt, 1992); in adjacent NTS 106B, trilobites in the Rabbitkettle Formation are Late Cambrian to Early Ordovician. Based on trilobite faunas (Pratt, 1992; Westrop, 1995) and the ages of fossiliferous limestone units below and laterally adjacent to the Rabbitkettle Formation,

Figure 3.5.1-6. The Rabbitkettle Formation consists of interbedded shale and nodular grey limestone. Grey talus at the base of the cliff obscures the contact with the underlying Hess River Formation; brown shale at top of ridge belongs to Duo Lake Formation. View to northwest in NTS 105P/11, 10 km northwest of Caribou Pass (483482E, 7055174N).

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Chapter Three Interpretation The dark colour, fine grain-size and lack of shallow-water features denote deposition in a quiet, sub-wave-base setting. Rhythmic deposition indicates slow background sedimentation with episodic sediment influxes. Cecile (2000) speculated upon periodic submergence of adjacent platformal environments or periodic influx of siliciclastic or lime mud controlled by climate, currents, tectonics, or eustatic sea-level change.

Duo Lake Formation The Duo Lake Formation is a shaly, recessive, dark-weathering interval that contains graptolites (Fig. 3.5.1-7). The formation is present in the southern half of the project area (central and western NTS 105P), and is generally distinguished from a distance because of the underlying, banded Rabbitkettle Formation, and the resistant, pale, massive carbonate rocks of the overlying Grizzly Bear Formation (Fig. 3.5.1-8). The Duo Lake Formation was described by Cecile (1982) in the axis of the Misty Creek Embayment, with a type section immediately west of the Sekwi project area. Five Sekwi project measured sections included the Duo Lake Formation (07CLS2, 08EM-S1, 08BF-S1, and 08DT S1 and S2; Appendix A).

Figure 3.5.1-7. The Duo Lake Formation, particularly in its upper 20 m, contains graptolites in black shale. Slabs are 10 cm long. NTS 105P/11, 16 km northwest of Caribou Pass (480498E, 7059949N).

Description The Duo Lake Formation conformably overlies the Rabbitkettle Formation. Its lower contact is the boundary between limestone-dominated (below), and shale-dominated (above) recessive successions. The upper boundary is at an abrupt lithological change to massive, pale grey carbonate rocks (Fig. 3.5.1-8), although both contacts are sheared and generally poorly exposed. In the Sekwi project area the Duo Lake Formation is overlain by the Steel Formation in southwestern NTS 105P, by the Grizzly Bear and Hailstone formations in northwestern NTS 105P, and by the Mount Kindle Formation in central NTS 105P. The project area encompasses the northeastern flank of the Misty Creek Embayment. At the type section (64°42’N 130°47’W; in NTS 106B) the Duo Lake Formation is 316 m thick. Thickness measurements made during the Sekwi project are 356 m (section 08DT-S1) in north-central NTS 105P, and 197 m (section 08DT-S2) southwest of Caribou Pass syncline (Appendix A). In the Sekwi project area, the Duo Lake Formation consists of carbonaceous (locally calcareous) mudstone that weathers grey-brown. Centimetre-thick layers of pale grey wavy-laminated limestone are locally present. The limestone is locally nodular, although parallel bedding and prominent fissility are typical. Chert nodules and bands are common. Rare siltstone and sandstone beds are present. In southwestern NTS 106A, Duo Lake Formation is interstratified with Rabbitkettle, Franklin Mountain, and Marmot formations; this succession has been mapped in that area as Rabbitkettle Formation (section 07CL-S2; Appendix A). At the type section (Cecile, 1982), the Duo Lake Formation consists of two units. The lower 240 m consists of interlayered silty limestone and graptolitic shale, and the upper 76 m consists of graptolitic siliceous shale with minor chert. The formation exhibits a pronounced lateral variation in composition. The Duo Lake Formation contains sedimentary structures such as cross-lamination and ripple-casts, as well as synsedimentary deformation (Fig. 3.5.1-9). Fossil debris is abundant in siltstone layers (Fig. 3.5.1-10). Fragments of corals, brachiopods and crinoids are common. Graptolites are common in the Duo Lake Formation and are especially common in the upper half of the unit. Stream beds in

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Figure 3.5.1-8. The Duo Lake Formation (OSD) is about 70 m thick on the northwest limb of the Caribou Pass syncline. It overlies the Hess River Formation (`HR) and Rabbitkettle Formation (`OR), and is overlain by grey limestone of the Grizzly Bear Formation (DGB). View to southeast in western NTS 105P/11, 16 km northwest of Caribou Pass (480771E, 7060133N).

headwaters north of Caribou Pass are rust-coloured as a result of the oxidation of groundwater percolating through the metal-rich shale.

Age and correlation Conodont and macrofossil collections from the Sekwi project (Appendix F) range from Early Ordovician (late Tremadocian to Floian) to Silurian (late Llandovery to early Wenlock). Cecile’s (1982) collections from the northwestern Misty Creek Embayment included graptolite faunas that are as old as earliest Early Ordovician; the youngest collection is latest Middle Ordovocian. Duo Lake Formation strata are the off-shelf equivalent of the upper Franklin Mountain Formation (Cecile, 1982) in southwestern NTS 106A, and of the Middle Ordovician Sunblood Formation in south-central NTS 105P.

Interpretation Duo Lake Formation strata in the western part of the Sekwi project area are fine-grained, but coeval shallow-water carbonate rocks are present less than 15 km to the northeast. This margin of the Misty Creek Embayment is interpreted to have been a gentle slope. Thin-bedded dark grey shale and chert signify a comparatively deep-water environment that was probably below the carbonate compensation depth.

Chapter Three to the Sapper Formation locally intervening (in southeastern 105O; Gordey and Anderson, 1993). The Steel Formation consists of siliceous, light- to dark-grey mudstone, in 10 to 80 cm-thick beds that weather orange, yellowishbrown, dull olive-grey, or dark yellowish-brown. The mudstone is variably dolomitic and typically contains pyrite. Dark grey to black wispy discontinuous lamination is common in paler lithofacies throughout the formation. In southwestern NTS 105P, the orange mudstone reaches 50 m in thickness, but it interfingers with black shale and is locally absent.

Age and correlation

Figure 3.5.1-9. The Duo Lake Formation contains increasing carbonate interbeds eastward, away from the Selwyn Basin. Here, silty mudstone displays soft-sediment deformation, enclosed by grey limestone beds. Location is 15 km southwest of Godlin Lakes, in northeastern NTS 105P/12 (496382E, 7067995N).

The age of the Steel Formation is poorly constrained. According to Gordey and Anderson (1993) a graptolite collection from the formation is of Silurian (Late Ludlow) age. Based on graptolite collections from below and above the formation, it may range from late Wenlock (Silurian) to earliest Devonian in age.

Interpretation Lack of current-related structures and the formation’s distribution west of time-equivalent shallow-water carbonate strata suggest deposition in a sub-wavebase setting. The ubiquitous wispylaminated texture may have been caused by disruption of bedding by burrowing organisms. The presence of burrows suggests that the bottom-waters were oxygenated.

3.5.2. Late Ordovician to Middle Devonian carbonate units C.F. Roots, E. Martel and S.P. Gordey

Sapper Formation

Figure 3.5.1-10. The Duo Lake Formation contains dark-coloured silty beds with abundant graptolite debris. Black bars in scale at bottom are 1 cm long. From Section EM07-S1, interval 4, in the northeast corner of NTS 105P/12, 16 km southwest of Godlin Lakes (496206E, 7066845N).

Steel Formation The Steel Formation is a thin, orange-weathering mudstone between the Duo Lake Formation and the overlying Earn Group (Chapter 3.6). It was defined by Gordey and Anderson (1993) in NTS 105I. At the type section (62°19’N 129°27’W; NTS 105I) the formation is 143 m thick and consists of wispy-laminated, siliceous, pale to dark grey mudstone. The Steel Formation was not identified in the Sekwi project area prior to this study, and was not encountered in traverses during the Sekwi project. It is, however, present in southwestern NTS 105P where it was mapped as the middle division of unit OSDpt of Abbott (1983; later correlated with Steel Formation; G. Abbott, pers. comm., 2010). The description below is based on Gordey and Anderson (1993) and Abbott (1983).

Description The basal contact with the Duo Lake Formation is gradational over 2 m. The Steel Formation is overlain conformably by the Portrait Lake Formation, with a tongue of silty limestone assigned

Black limestone that weathers blue-grey (lower part) and tan to buff (upper part) characterises the Sapper Formation. The unit was defined about 30 km south of NTS 105P by Gordey and Anderson (1993). Exposure of this unit trends northward into NTS 105P west of the Natla River. The formation was not identified in NTS 105P prior to this study. The tan-weathering, thin-bedded, black to dark grey “silty limestone unit” (Abbott, 1983) in the Macmillan Pass area is correlated with the Sapper Formation (G. Abbott, pers. comm., 2010) and extends northwest in NTS 105O (Cecile, 1996). The Sapper Formation was not examined during the Sekwi project.

Description At the type section, the formation’s base is conformable with underlying grey-weathering cherty dolostone of the Haywire Formation. In southwestern NTS 105P, silty limestone of the Sapper Formation directly overlies orange-weathering mudstone of the Silurian Steel Formation (Abbott, 1983). The upper contact is an unconformable, abrupt change to the Grizzly Bear Formation, whose basal layer is a limestone breccia with subrounded grey limestone clasts and abundant coral and crinoid debris (Gordey and Anderson, 1993). The unconformity cuts progressively down through older strata northward. At the type section in NTS 105I (62°42’N 128°25.6’W) the Sapper Formation is 362 m thick (Gordey and Anderson, 1993). At the type section (Gordey and Anderson, 1993) the lower member, 107 m thick, consists of blue-grey to grey-weathering, black, lime mudstone. The thin beds show wavy partings and centimetre-

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Chapter Three Description

Figure 3.5.2-1. The Hailstone Formation is the pale yellow-grey limestone unit overlain by dark shale forming the peak (Duo Lake Formation). View to southeast, NTS 105P/11, 12 km northwest of Caribou Pass (482100E, 7057200N).

sized limestone nodules. The upper, 255 m-thick member comprises thin-bedded grey-black, laminated, argillaceous to silty limestone. In outcrop, the upper part of the formation has resistant bands formed by limestone beds.

Age and correlation At the type section, collections of conodonts, graptolites and shelly fossils collectively range from Late Ordovician to Middle Devonian (late Eifelian; Gordey and Anderson, 1993). A conodont collection from the silty limestone in the Macmillan Pass area yielded an Early Devonian (Pragian) age (Abbott, 1983). In northeastern NTS 105O, the Sapper Formation is Late Silurian (Ludlow) to Middle Devonian (Emsian; Norford et al., 1993). In northwestern NTS 105P, a conodont collection from a unit tentatively identified as the Sapper Formation but undivided on the map was Early Devonian (Pragian) in age (Appendix F). The Sapper Formation is a relatively recent addition to the Selwyn Basin nomenclature. In earlier work, these strata were included in the upper part of the Road River Formation or as the Funeral Formation (e.g., Gabrielse et al., 1973a). In the Misty Creek Embayment, the Sapper Formation is of the same age as the Cloudy Formation (Cecile, 1982), but was later recognised as an independent unit (e.g., Cecile, 2000). In the Selwyn Basin, the correlative unit is the Duo Lake Formation; on the Mackenzie Platform, the correlative unit is the Mount Kindle Formation.

Interpretation The flat lamination, lack of wave- or traction-produced structures, and position west of the carbonate shelf suggest a belowwave-base depositional environment for the Sapper Formation (Gordey and Anderson, 1993).

Hailstone Formation The Hailstone Formation is a thin succession of platy limestone that weathers tan-grey. It is stratigraphically equivalent to the Grizzly Bear Formation. In west-central NTS 105P, it is present as a tongue within the Grizzly Bear Formationon on the eastern limb of the Caribou Pass syncline, and as its lateral equivalent on the southwestern limb. The type locality defined by Cecile (2000) is in NTS 106B. Two Sekwi project measured sections included the Hailstone Formation (08BF-S1 and 08DT-S2; Appendix A).

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The Hailstone Formation is 82 m thick on the southwestern limb of the Caribou Pass syncline (section 08DT-S2) and 348 m thick on the northeastern limb (section BF08-S1). On the western flank of the Caribou Pass syncline it is about 30 m thick. At the type section in NTS 106B, it is 190 m thick (Cecile, 2000). Cecile (2000) described three members in the type section. The lower contact of the formation is not exposed at the type section. Near the base is poorly sorted cobble conglomerate or breccia, overlain by 80 m of calcareous black shale interlayered with greywhite bioclastic limestone. The middle member is grey- to whiteweathering, thin-bedded limestone. The upper unit, 70 m thick, is black shale with bioclastic limestone. Where the Hailstone Formation is exposed on-trend to the southeast in NTS 105P (section 08DT-S2), it consists of interlayered, calcareous black shale and laminated yellow-grey limestone. The limestone is fetid and contains abundant crinoid ossicles with twin canals. The lower 9 m contains lenses of limestone-cobble conglomerate and channel-fills of crinoid rudstone. On the eastern limb of the Caribou Pass syncline (section 08BF-S1), the Hailstone Formation consists of thinly laminated, finely to micro-crystalline limestone and argillaceous lime siltstone, covered intervals presumed to be underlain by shale, and near the top, a 13 m-thick interval of dark grey weathering skeletal wackestone and floatstone with brachiopds and crinoids, including a bed of brachiopod packstone. Because the black shale upper member described by Cecile (2000) was not distinguished from the overlying Misfortune Formation, only the resistant, light-coloured limestone was routinely attributed to this unit (Fig. 3.5.2-1) during mapping by the Sekwi project. In areas of low topographic relief this unit is indicated by beds of resistant limestone 1 to 5 m thick. The lower contact of the Hailstone Formation is rarely exposed. At the reference locality in NTS 105O/16 (UTM 432100 E, 7089450 N), the contact with the Duo Lake Formation is disconformable, and marked by a onemetre-thick conglomerate bed (Cecile, 2000).

Age and correlation Crinoids from the Hailstone Formation in northeastern NTS 105O indicate an early Early Devonian (late Lockhovian to Pragian) and possibly late Early Devonian age (Cecile, 2000). Age-ranges of conodont collections from the Hailstone Formation in the Sekwi project area are as old as Late Silurian to Early Devonian (Pridoli to Lochovian) and as young as early Middle to early Late Devonian (Eifelian to Frasnian; Appendix F). The Hailstone Formation is the slope-facies equivalent of the Grizzly Bear Formation of the Mackenzie Platform. The Hailstone Formation thins abruptly and disappears basinward. The limestone tentatively assigned to the Natla Formation by Cecile (1982) exposed along the eastern flank of the Misty Creek Embayment should be assigned to the Hailstone Formation (Cecile, pers. comm., 2008).

Interpretation The thin, parallel bedding in part of the formation suggests deposition below wave-base. According to Cecile (2000), coarser parts of the Hailstone Formation reflect deposition on a westwarddeepening debris-fan with clasts derived from Grizzly Bear Formation platformal carbonate rocks.

Chapter Three

3.6. Middle Paleozoic Siliciclastic Basin – Earn Group C.F. Roots, E. Martel and S.P. Gordey

A thick succession of black shale, chert, conglomerate and brown sandstone of Middle and Late Devonian and Carboniferous age unconformably overlies strata of the Mackenzie Platform and Selwyn Basin of northwestern Canada. The succession varies in lithology and thickness from place to place. The composition and source of the clastic sediment are important, and serve to distinguish two laterally equivalent successions. In Yukon and westernmost Northwest Territories, the coarse clasts are predominantly chert, which were probably derived from Duo Lake and older formations in the Selwyn Basin. Paleocurrent data indicate source regions to the west and north. The units in that region are collectively called the Earn Group. The second succession, consisting chiefly of dark shale overlain by brown silt- and sandstone, underlies western Northwest Territories (northern Interior Plains), northern Yukon and Alaska. The clasts are principally quartz. This regional sedimentary apron is a distal reflection of the Ellesmerian orogeny, which took place northeast of this region. Three successions (Portrait Lake, Itsi and Prevost formations; Misfortune and Thor Hills formations; Hare Indian, Canol and Imperial formations) are described here. They represent Middle Devonian to earliest Mississippian strata from southwest to northeast across the Sekwi project area. Distribution and schematic stratigraphic relations are shown in Figures 3.6.1-1 and 3.6.1-2.

3.6.1 Earn Group

Figure 3.6.1-1. Distribution of the Earn and Tsichu groups in the western part of the Sekwi project area.

Portrait Lake Formation

relationship with extensional faulting (Gordey and Anderson, 1993). These faults may have been conduits for hydrothermal springs on the seafloor, and provided barium in the water column.

“Gunsteel-blue”-weathering, black siliceous shale and chert, quartz arenite and conglomerate of Early to Late Devonian age (Fig. 3.6.1-3) are included in the Portrait Lake Formation, defined by Gordey and Anderson (1993). This formation is widespread in the eastern Selwyn Basin, particularly in the Macmillan Pass area. This unit was not examined during the Sekwi project, and its distribution reflects previous mapping, which included southwestern NTS 105I (Abbott, 1983; G. Abbott, pers. comm., 2010). The type section of the Portrait Lake Formation is in the Macmillan Pass area (63°08’N 130°1.5’W; 1 km west of NTS 105P) where the unit is 897 m thick (Gordey and Anderson, 1993). This locality is interpreted to be a fault-controlled subbasin (Abbott and Turner, 1991). North and south of these faults the total thickness is much less, although accurate measurement is typically thwarted by layer-parallel thrusts and folds. The Portrait Lake Formation is the regional host of stratiform zinc-lead±barite deposits in the Macmillan Pass area in the southwestern corner of the Sekwi project area (Goodfellow and Rhodes, 1990; Abbott and Turner, 1991). See Chapter 7 for details. These deposits spatially coincide with voluminous conglomerates containing chert pebbles and granules derived from older Selwyn Basin strata. Many of the barite occurrences are near the top of the formation, several metres above muddy chert-quartz sandstone and conglomerate (Morganti, 1979). Bedded barite, small barite concretions in carbonaceous mudstone, streaky white barite, and barite veins have been documented. A regional barite unit of Late Devonian (mid-Frasnian; Dawson and Orchard, 1982) age, and several zinc-lead-silver-barite occurrences, have a synchronous

Description The base of the Portrait Lake Formation is diachronous. Southwest of the type section, in NTS 105I, the Portrait Lake Formation unconformably overlies Mackenzie Platform transitional and slope carbonate units, above an unconformity that cuts downward through the Nahanni, Grizzly Bear and Haywire formations (Gordey and Anderson, 1993). At the type section, the Portrait Lake Formation is difficult to distinguish from black, silty limestone of the underlying Sapper Formation (Gordey and Anderson, 1993). The basal contact is defined at the base of the lowest unit of gunsteel-blue- to grey-weathering, siliceous siltstone, shale and chert. In NTS 105I, the Portrait Lake Formation is unconformably overlain by uppermost Devonian to mid-Mississippian shale, sandstone and chert conglomerate of the Prevost Formation (Gordey and Anderson, 1993). In the Macmillan Pass area (southwestern 105P) the formation is overlain by the upper Devonian ‘Itsi Formation’ (Abbott and Turner, 1991; G. Abbott, pers. comm., 2010). The type section of the Portrait Lake Formation has three members (Gordey and Anderson, 1993). The formation’s base is at the top of the underlying silty limestone (Sapper Formation). The lower member consists of a basal 90 m of bluish-greyweathering black platy siltstone overlain by brown-weathering silty shale and shale. The middle member consists of massive chert-pebble conglomerate. Clasts are entirely well-rounded chert and siliceous siltstone, mostly grey, with less off-white or black, in

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Chapter Three SW Macmillan Pass

Caribou Cry River

40km

NE Godlin Lakes

45km

Fourway Fm

Keele Creek Fm

Heritage Trail Fm

220m

330m

Prevost Fm

555m

345m

Hawthorne Creek Fm

Thor Hills Fm

Imperial Fm

300m

200m

Itsi fm

300m Misfortune Fm 300m

Hare Indian and Canol fms

300m

419m Portrait Lake Fm

100m

Lateral facies transition Numbers are thickness in metres

Limit of exposure

Figure 3.6.1-2. Schematic relationships among Earn Group (and equivalent units) and Tsichu Group in the western Mackenzie Mountains. Adapted from Gordey and Anderson (1993) and Cecile (2000), with additional Sekwi Project data.

a matrix of chert and quartz grains. The upper member consists of black platy siltstone (261 m thick) with rare black limestone beds. Siliceous shale and chert become prominent constituents southwest of the type section and the coarse clastic components are correspondingly diminished.

Age and correlation Conodonts in the Portrait Lake Formation range in age from Early Devonian to late Late Devonian (mid-Famennian). At the type section, the conodonts are no younger than late Frasnian (Gordey and Anderson, 1993), suggesting that the formation’s upper contact may be diachronous. In southeastern NTS 105O, the Misfortune Formation is lithologically similar to the lower 90 m of the lower member of the Portrait Lake Formation (Cecile, 2000). The Canol Formation is time-equivalent to the Portrait Lake Formation, but of northeastern provenance (Cecile, 2000).

Interpretation The Portrait Lake Formation accumulated in a sub-wave-base setting favouring deposition of black shale and chert. It represents a “starved-basin” facies that accumulated prior to block faulting and the development of submarine channels that funnelled clastic input from uplifted areas.

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Both the Portrait Lake Formation and overlying Prevost Formation contain sediment gravity flow deposits that accumulated in a submarine fan setting. On a regional scale, the irregular distribution of coarse clastic deposits reflects the numerous inferred distributary channels of this submarine fan. Furthermore, with increasing distance from depocentres, the proportion of clastic detritus diminishes relative to the background sedimentation (chiefly siliceous shale and chert in the Portrait Lake Formation; shale, siltstone and finegrained sandstone in the Prevost Formation). The chert-pebble conglomerate facies of the Portrait Lake Formation is abundant in the Macmillan Pass area, but is minor to the southeast in NTS 105I. In the Prevost Formation the opposite is the case. Submarine channels funnelled clastic material from uplifted areas north and west of the region (Blusson, 1974; Gordey and Anderson, 1993. The conglomerate formed paleo-highs on the basin floor, indicated by pinch out-of adjacent carbonaceous mudstone (Goodfellow and Rhodes, 1990)

‘Itsi formation’ Brown-weathering sandstone, siltstone and shale of Late Devonian age in the Macmillan Pass area were named the Itsi member of the Portrait Lake Formation (Abbott and Turner, 1991; Goodfellow and Rhodes, 1990). With additional mapping,

Chapter Three it became clear that the unit should be considered a formation, although it has not yet been formalised (J.G. Abbott, pers. comm., 2010). No detailed study was made during the Sekwi project.

Description The ‘Itsi formation’ disconformably and locally unconformably overlies the Portrait Lake Formation. The top of the unit is overlain by locally preserved siliceous shale that is correlated with the Prevost Formation. Both units are unconformably overlain by the Mississippian Tsichu Group (J.G. Abbott, pers. comm., 2010). Three subdivisions were described by Abbott (1983) in the Macmillan Pass area. The lowest comprises dark brown-weathering, medium- to thick-bedded, ripple cross-laminated and parallellaminated sandstone and siltstone with silty shale. This subdivision was described in further detail (units 4a and 4b of Carne, 1979): near the base are cyclic alternations of black mudstone or shale with red-brown siltstone. The shale contains millimetre- to centimetrescale nodules of anhydrite to barite with textures indicating that the latter replaced the former during diagenesis. Local intraclast conglomerate beds, bioturbation and possible fecal pellets are also present (Carne, 1979). Thickness of the ‘Itsi formation’ decreases southwestward, from hundreds of metres thick south of Macmillan Pass, to tens of metres west of the southwestern corner of NTS 105P (J.G. Abbott, pers. comm., 2010). The southern extent of the ‘Itsi formation’ (63°55’N; northwestern NTS 105I) is laterally equivalent to, and probably overlain by, blue-weathering shale described by Abbott and Turner (1991) as upper Portrait Lake Formation. Thus the ‘Itsi formation’, although a mappable formation in the northern area, is only a member of the Portrait Lake Formation in the south.

Age and correlation The ‘Itsi formation’ is Late Devonian in age (Abbott and Turner, 1991). It overlies siliceous shale of the Portrait Lake Formation, which contains conodonts as young as late Frasnian, and is overlain by similar blue-weathering shale containing conodonts as old as early middle Famennian. The ‘Itsi formation’ is the same age as the Imperial Formation (Chi and Hills, 1974) of the Mackenzie Mountains and northern Yukon and has similar sedimentological characteristics. A separate terminology is preferred here because the unit is physically distinct from the Imperial Formation.

Interpretation Deposition by normal bottom currents is suggested by the interbedded sand-silt beds, and ripple cross-laminated fabric, but the possibility of deposition by turbidity flows cannot be excluded without detailed examination (J. G. Abbott, pers. comm., 2010).

Prevost Formation Brown-weathering sandstone, siltstone and shale, overlain by blue- and brown-weathering shale of Mississippian age, are exposed in the Macmillan Pass area (southwestern NTS 105P). The resistant weathering profile of the sandstone distinguishes it from underlying, recessive, grey shale of the Portrait Lake Formation. The formation was introduced by Gordey and Anderson (1993) south of the project area. No detailed work was done on this formation during the Sekwi project.

Description The base of the Prevost Formation is mapped as an unconformity. The formation overlies various lithofacies of the Portrait Lake Formation, but farther to the west it rests directly on the Proterozoic-Cambrian Hyland Group. Typically, a sharp change in weathering colour and lithology separates the grey to gun-blue shale-dominated Portrait Lake Formation from the brownweathering, sandy Prevost Formation. The top of the Prevost Formation is a presumed unconformity, indicated by the local absence of the middle and top subdivisions beneath the Mississippian Heritage Trail Formation (reported in two places by Gordey and Anderson, 1993). The type section of the Prevost Formation (62°26’N / 129°18’W) is 555 m thick (Gordey and Anderson, 1993). The proportion of coarse to fine clastic material varies from place to place, but the basal 100 m of the Prevost Formation is generally dominated by shale and siltstone. The type section contains three members. According to Gordey and Anderson (1993), the lower member is 160 m thick and consists of grey-weathering chertquartz sandstone with minor chert granule to pebble conglomerate beds. The middle member, comprising brown-weathering, thinbedded and laminated shale and siltstone, is 90 m thick. The upper member comprises apparently massive, coarse-grained chert-quartz sandstone and chert-pebble conglomerate. The top 14 m includes thinly interbedded shale and ripple-cross-laminated sandstone.

Age and correlation The age of the Prevost Formation is poorly constrained as latest Devonian to earliest Mississippian (Gordey and Anderson, 1993). This unit is partly correlative with the Frasnian to early midFamennian Imperial Formation (Chi and Hills, 1974) and the Early Mississippian Thor Hills Formation.

Interpretation

Figure 3.6.1-3. The Portrait Lake Formation is dominated by thin-bedded black chert (blocky beds) and interbedded shale. NTS 105P/12, 2.5 km northwest of Caribou Cry River, 35 km north of Mile 222 airstrip, Canol Heritage Trail (466197E, 7053664N).

A sub-wave-base setting is interpreted for background deposition of siliceous shale, siltstone and fine-grained sandstone. Chert-pebble conglomerate, cherty quartz arenite and wacke were deposited by sediment gravity-flows that transported immature clastic debris far outward on the submarine fan (Gordey and Anderson (1993). Meagre paleo-flow evidence indicates a source area to the northwest.

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Chapter Three

3.6.2. Time-equivalent siliciclastic units Misfortune Formation Limonite-stained black shale, minor siltstone and sandstone, overlain by white-weathering, siliceous shale and chert-pebble conglomerate in northwestern NTS 105P is ontrend with exposures of the Misfortune Formation as established by Cecile (2000) in northeastern NTS 105O. One Sekwi project measured section included the Misfortune Formation (08DTS2; Appendix A).

Description The lower contact of the Misfortune Formation forms a prominent topographic and lithologic break at the top of the calcareous Grizzly Bear Formation and Hailstone Formation. Vegetation and debris obscure contact relations, but Cecile (2000) reported a sharp break, although the contact is diachronous into the Hailstone Formation southwest of the study area. North of the Mactung pluton, an area mapped as Misfortune Formation overlies undifferentiated Hess, Rabbitkettle and Duo Lake formations strata; the contact is not exposed. The top of the unit is marked by a distinct colour change from pale-brown-weathering Misfortune Formation to darker brownweathering Thor Hills Formation, a contact that Cecile (2000) interpreted as conformable. In western NTS 105P, the colour change between the units is subtle, and the position of the contact is extrapolated from regional bedding attitudes. The Misfortune Formation is overlain toward the northwest by the Thor Hills Formation in the same way that the Canol Formation is overlain by the Imperial Formation. At Cecile’s (2000) type section (63°37’N, 130°06’W), the lower member is 170 m thick and the upper member is >100 m thick. During Sekwi project field work, 423 m of this unit was measured near the southeastern axis of the Caribou Pass syncline (section 08DT-S2; Appendix A). In northwestern NTS 105P, the lower Misfortune Formation consists of interlayered, non-calcareous black shale and rustyweathering, clast-supported conglomerate. Long ridge-spurs across the unit in the southwestern limb of the Caribou Pass syncline expose dark shale with less than 10% yellow-brownweathering, thin-bedded, bioturbated sandstone. Sandstone beds thicker than 60 cm are rare. Misfortune Formation strata exhibit ripple cross-stratification. Barite nodules are abundant in Cecile’s (2000) type section. The upper Misfortune Formation is white-weathering black siliceous shale with minor (centimetre- to metre-scale) lithic sandstone and chert-pebble conglomerate (Cecile, 2000). In westcentral NTS 105P, this unit consists of greenish-grey to dark greyweathering, parallel-bedded sandstone with irregularly spaced, brown- to yellowish-green-weathering chert-pebble conglomerate to coarse or granular sandstone beds typically 1-3 m thick). Decimetrescale cross-beds and erosive contacts beneath sandstone beds are common. The moderately sorted and rounded conglomerate clasts are 35-90% chert (section 08DT-S2)

Age and correlation Early Middle to Late (Famennian) Devonian conodonts were recovered from the Misfortune Formation (Cecile, 2000).

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The Misfortune Formation is homotaxial with the basal 90 m of the lower member of the Portrait Lake Formation to the south, and laterally equivalent to the Canol Formation to the north and east. Compared to the latter, the Misfortune Formation contains more lithic sandstone and chert-pebble conglomerate. The transition between the Misfortune and Canol formations is near the axis of the Stew syncline (Cecile, 1996) at 63°42’N, 130°09’W, where the relatively homogeneous Misfortune Formation expands into distinct mappable divisions of the lower Canol Formation.

Interpretation Thin bedding and dark colour reflect a deep-water depositional environment. This interpretation is strengthened by increasing chert content to the west (along the axis of the Misty Creek Embayment; Cecile, 2000). The conglomerate lenses and their erosive bases are consistent with an interpretation of submarine channels through which coarse lithic material was episodically transported into the quiescent, deep-water environment, probably as sediment gravity flows.

Thor Hills Formation Brown-weathering, dark grey shale, overlain by blue-greyweathering black shale and uppermost grey shale and siltstone that weathers brown constitute the Thor Hills Formation. The type section is near the east edge of NTS 105O (63°38’N, 130°02’W), 2 km northwest of the Sekwi project area (Cecile, 2000). One Sekwi project measured section included the Thor Hills Formation (08DTS2; Appendix A).

Description The base of the Thor Hills Formation is at the base of the lowest brown-weathering shale and quartz-rich sandstone overlying whiteweathering chert and siliceous shale of the underlying Misfortune Formation. The lower contact is conformable or gradational. The upper contact with the Hawthorne Creek Formation is indicated by a colour change from brown- to grey-weathering shale. The formation is estimated to be between 330 and 400 m thick (Cecile, 2000). The Thor Hills Formation consists of three units (from bottom to top): brown weathering shale, blue-grey-weathering black shale, and brown-grey-weathering shale and siltstone (Cecile, 2000). The unit also includes an exposure that consists entirely of chert-pebble conglomerate and chert-lithic sandstone 8 km southwest of the type section. In the Sekwi project area, in western NTS 105P, the Thor Hills Formation extends along-strike directly from the area of the type section. It consists of black, rusty-weathering shale and medium- to thick-bedded fine-grained quartz sandstone that is relatively resistant to erosion. Between the Caribou Cry and Ingta rivers, minor synclines contain erosional outliers of chert-pebble conglomerate and chert-lithic sandstone that are assigned to the Thor Hills Formation.

Age and correlation Cecile (2000) interpolated a Late Devonian age based on fossil collections from the underlying Misfortune Formation and overlying Tsichu Group. Although it is possible that the conglomerate facies may be younger, Cecile noted a similar stratigraphic relationship to shale and sandstone as seen in Middle to Late Devonian units in southern NTS 105O.

Chapter Three The Thor Hills Formation is coeval with the laterally equivalent Imperial Formation, but is distinguished from it by the presence of chert clasts, and the chert’s northwestern source. The unit correlates with the upper Portrait Lake Formation and possibly the Prevost Formation (Cecile, 2000).

of the Hare Indian Formation was deposited below deep, euxinic waters. The interbedded shale and limestone of the upper member northeast of the Sekwi project area represent turbidite deposition.

Interpretation

The Canol Formation consists of dark grey to black, thinbedded, locally calcareous shale. The unit is widespread beneath the northern Interior Plains and extends across northern Yukon (Richardson and Northern Ogilvie mountains). At Norman Wells the Canol Formation is the hydrocarbon source rock for the Kee Scarp Reef oil-field. In the Sekwi project area this unit occupies broad synclinal keels in NTS 106A and 95M, and tight synclines in northwestern NTS 105P. The type section of the Canol Formation is at the northeastern Mackenzie Mountains front (65°10.5’N, 128°46.5’W) about 15 km north of the Sekwi project area (Bassett, 1961). One Sekwi project measured section included the Canol Formation (07-MM-S3; Appendix A). Rock-Eval data for material from the Canol Formation are provided in Appendix G.

Dark colour, thin beds and lack of carbonate rocks suggest a deep-water depositional environment for the Thor Hills Formation. The chert clasts were probably eroded from the Duo Lake Formation, and the conglomerate distribution and paleocurrent measurements suggest source areas to the west (Gordey and Anderson, 1993).

Hare Indian Formation The Hare Indian Formation consists of calcareous shale and limestone. The type section is at the Ramparts Gorge (Mackenzie River south of Fort Good Hope; 66°11’N 128°55’W), approximately 200 km northeast of the Sekwi project area (Bassett, 1961).

Description The basal contact of the Hare Indian Formation is gradational. In central NTS 106A, where the Hare Indian Formation cannot be differentiated from the overlying Canol Formation, the shale is interbedded with limestone beds that are similar to those of the underlying Hume Formation but diminish in thickness upward. The Hare Indian Formation northeast of the Mackenzie Mountains is gradational with, and partly equivalent to, shale and carbonate of the Ramparts Formation (Pyle et al., 2007). In the Sekwi project area (northeastern NTS 106A), however, the Ramparts Formation is absent and the shaly Canol Formation conformably overlies the Hare Indian Formation, although the contact is subtle and poorly exposed. For this reason, an undifferentiated Hare Indian and Canol formation map-unit is used for this area. At the type section (Bassett, 1961), the Hare Indian Formation consists of 250 metres of green-grey shale with thin beds of limestone, silty limestone and siltstone. An equivalent thickness is present along a north-south axis extending from the type locality. At the Mackenzie Mountain front the formation is 190 m thick (Pyle et al., 2007), but the formation thins westward and southward from there to a zero-edge near 132°W. In the northeastern Sekwi project area, the Hare Indian Formation is a thin-bedded dark grey to black, slightly calcareous shale with local limestone beds. Immediately north of this area, the base of the formation (Bluefish Member) is locally identifiable owing to the characteristic presence of Tentaculites, decimetre-scale limestone concretions and pyrite nodules (Pyle et al., 2007). RockEval data for material from the Hare Indian Formation are provided in Appendix G. The Hare Indian Formation was not studied in detail during Sekwi project field work.

Age The Hare Indian Formation is Middle Devonian (Givetian), based on brachiopod and tentaculitid fauna (Bassett, 1961).

Interpretation The unconformable base of the Hare Indian Formation suggests an episode of exposure of the shelf carbonate prior to drowning in the siliciclastic basin. Black, organic-rich and calcareous shale

Canol Formation

Description The Canol Formation overlies a regional unconformity. In the Mackenzie Mountains, the Hare Indian Formation has been eroded; for example in northwestern NTS 105P, the Canol Formation overlies the Grizzly Bear Formation limestone with about 40 m of topographic relief. Cecile (2000) reported a shale-clast lag at this contact in northeastern NTS 105O. The sharp upper contact of the Canol Formation with the overlying Imperial Formation is defined by the appearance of more resistant, fine-grained brown-weathering sandstone. In the southwestern corner of the Sekwi project map-area, the contact is a disconformity where Canol Formation is overlain by the Hawthorne Creek Formation (the Imperial Formation, or equivalent Thor Hills Formation, was not deposited or has been entirely eroded). At the type section, the Canol Formation is 23 m thick (Bassett, 1961). The formation is 122 m thick at Norman Wells, and in the mountains it is several hundred metres thick. The Canol Formation was not measured during this study, but in adjacent northeastern NTS 105O it is 182 m to 400 m thick (Cecile, 2000). The Canol Formation is a yellowish-, bluish-, and rusty-brownweathering shale that is locally siliceous and contains abundant large dm- to m-scale concretions throughout the formation. Northeast of the Sekwi project area, this formation is approximately 4 to 20 metres thick, but its thickness reaches >100 m going west toward the basin. In adjacent NTS 105O, the Canol Formation consists of thinbedded, black, siliceous shale, papery black shale with limestone nodules, and rare thin beds of limestone and sandstone. Sandstone and a lens of chert-pebble conglomerate were noted near the formation’s base (section 14 in figure 39 of Cecile, 2000). In western NTS 105P, the Canol Formation consists of a lower, recessive, shale-dominated member, and an upper, relatively resistant chertshale member (Fig. 3.6.2-1). Medium grey-to maroon-weathering calcareous shale contains rare laminae of light-brown-weathering fine sandstone and sole marks (Fig. 3.6.2-2). Locally the blue-black shale contains nodules of dark brown limestone. The Canol Formation hosts numerous barite showings (Appendix H). Modern, perennial upper tributaries sourced in this unit have stream bottoms coloured by bright orange or white precipitates.

179

Chapter Three Age and correlation

Description

The Canol Formation is Late Devonian (Frasnian) in age. A Sekwi project collection from the Canol Formation in northwestern NTS 95M yielded spores of possible Late Devonian (Frasnian to early Famennian) age (Appendix F). The Canol Formation is equivalent to the Misfortune Formation in western NTS 105P, and the Portrait Lake Formation to the southwest. In NTS 106B (northwest of the Sekwi project area), Blusson (1974) mapped a unit similar to the Canol Formation as equivalent to the Besa River Formation of the northern Rocky Mountains.

The Imperial Formation conformably overlies the Canol Formation (Cecile, 2000). It is generally distinguished by the lowest appearance of brown-weathering sandstone beds (Fig. 3.6.2-3). In the Peel area (immediately north of the Sekwi project area), a 10 to15 m-thick interval of recessive, dark-grey shale, lacking the pyrite and chert of the Canol Formation, indicates the base of the Imperial Formation (Pyle et al., 2007). In the northern and eastern parts of the Sekwi project area, the top of the unit is erosionally absent. In the southwestern part of the Sekwi project area, the Imperial Formation is overlain by the Hawthorne Creek Formation and is about 400 m thick. The Imperial Formation is typically hundreds of metres thick. It forms a cyclic, 600 m-thick succession that underlies much of the Mackenzie Valley. In the Richardson Mountains (Yukon), it is 1909 m thick (Pugh, 1983). It is over 700 m thick in the western part of the Sekwi project area (western NTS 105P) and tapers to approximately 300 m in the east (NTS 106A and northwestern NTS 95M), due to pre-Cretaceous erosion. The Imperial Formation is composed of very fine- to finegrained sandstone with interbedded silty mudstone. The lower 300

Interpretation The Canol Formation is a deep-water, black, organic-rich shale deposited during the early stage (starved-basin facies) of foredeep basin development (Cecile, 2000).

Imperial Formation Rhythmically bedded, brownish-green quartz sandstone and brown-weathering shale in the Sekwi project area are assigned to the Imperial Formation (Fig. 3.6.2-3, -4, and -5). The type section of the Imperial Formation (Hume and Link, 1945) is located on the Imperial River at the Mackenzie Mountain front (65°07’N, 127°51’W). Two sections of the Imperial Formation were measured (306 m and 66 m) during the Sekwi project (07WZ-S1 and 07MM-S3; Appendix A). These sections are incomplete because the upper Imperial Formation is erosionally absent where measured.

Figure 3.6.2-3. The Imperial Formation is characterised by thin sandstone layers (resistant, pale layer) interbedded with dark shale. View to north, overlying dark Canol Formation shale (lower left corner). NTS 106A/9, 3 km northwest of McClure Lake (528304E, 7159346N). Figure 3.6.2-1. The upper Canol Formation consists of brown-weathering calcareous siltstone and dark shale, overlain by pale grey-weathering black shale. View to east, NTS 105P/11, 15 km west-northwest of Caribou Pass (474669E, 7054158N).

Figure 3.6.2-2. Bed base from the Canol Formation, with load casts and tool marks that are preserved where black chert is interbedded with shale. NTS 105P/11, 6.5 km northwest of Caribou Pass (483095E, 7050082N).

180

Figure 3.6.2-4. The lower Imperial Formation contains brown-weathering sandstone and dark, thin-bedded shale. View to south, NTS 106A/10, 7.5 km west of McClure Lake (523179E, 7157689N).

Chapter Three m consists of pale to medium grey silty mudstone and very finegrained sandstone. Above this is approximately 200 to 400 m of very fine- to fine-grained greenish-grey sandstone with interbedded silty mudstone. The Imperial Formation can be crudely described as three thick cliff-forming sandstone units, which are separated by less-resistant to recessive, thick silty shale packages (Fig. 3.6.2-4). The sandstones contain horizontal and vertical burrows near bed bases. Bioturbation decreases up-section, and sedimentary structures are better preserved. The Imperial Formation sandstone is locally fossiliferous, containing solitary rugose corals, colonial corals, and brachiopods.

Age and correlation A Late Devonian to Early Mississippian (Frasnian to early Tournasian) age was established based on conodont and spore collections (Chi and Hills, 1974; 1976; Cecile, 2000). Palynomorphs from Imperial Formation samples collected during Sekwi project field work yielded a Late Devonian (Frasnian to early Famennian) age (Appendix F). The Imperial Formation is laterally equivalent to the Thor Hills Formation (Earn Group) to the southwest.

Interpretation Rhythmic bedding, graded bedding, sole-marks and flutecasts indicate that the Imperial Formation should be interpreted as a turbidite succession. In the Stew syncline, sedimentary structures indicate eastward transport (Section 3 of Cecile, 2000). Flutes indicate traction currents towards the southwest in the Misty Creek Embayment. The presence of burrowing organisms is indicated by horizontal trails, vertical tubes and abundant bioturbation in the sandstone intervals. Abrupt tops to the sandstone beds overlain by layer-parallel shale were interpreted as flooding surfaces (Pyle et al., 2007). In the Richardson Mountains (Yukon), the general facies architecture is consistent with an eastern, shelf-edge, source with deeper-marine conditions to the west.

3.7. Upper Paleozoic Siliciclastic/ Carbonate Shelf - Tsichu Group C.F. Roots, E. Martel and S.P. Gordey

The Tsichu Group was formalised as a group with five formations in northeastern NTS 105O, adjacent to the Sekwi project map-area (Cecile, 2000). The term was originally introduced by Gordey and Anderson (1993) for a succession of quartz sandstone, chert and carbonate of mostly Mississippian age that overlies the Earn Group. In western NTS 105P, the Sekwi project extended contacts from the eastern limit of mapping by Cecile (2000) using marker horizons of distinctive lithology. Rusty black shale and sandstone are lithologies common to several formations; thus isolated exposures are assigned to units that best fit the structural interpretation. Because Cecile’s (2000) formations are in part laterally equivalent, their depositional environments are discussed together.

Hawthorne Creek Formation Black shale and lesser sandstone, and calcareous shale interbedded with yellow-weathering limestone, form a darkweathering, easily recognised unit that overlies the Imperial Formation sandstone. In some places, erosional outliers form conspicuous black hills (Fig. 3.7.1-1). In western NTS 105P, the Hawthorne Creek Formation is exposed on both limbs of the Stew syncline, which trends southeast from the type section in NTS 105O at 63º 38.7’N, 130º 02’W (section 9 of Cecile, 2000), where it is 330 m thick.

Description The Hawthorne Creek Formation conformably overlies the Canol and time-equivalent Thor Hills formations (Cecile (2000). Rusty-weathering, black-lichen-coated cherty shale is typical of the Hawthorne Creek Formation. A 20 m-thick basal interval consists of thin-bedded carbonaceous siltstone, and grades upward into fine-grained black sandstone with pods of brown limestone (Fig. 3.7.1-2). In the Macmillan Pass area, the equivalent unit (unit Csp of Abbott, 1983) consists of recessive brown, blue-brown and dark blue silty shale, shale and siliceous shale with beds of sandstone and quartzite. This formation typically weathers more darkly than the underlying ‘Itsi formation’ sandstone. One exposure of the Hawthorne Creek Formation (not visited during the Sekwi project) appears to be capped on a ridge by a more resistant unit that is probably sandstone of the Heritage Trail Formation.

Age and Correlation During the Sekwi project two conodont collections from the Hawthorne Creek Formation in western NTS 105P yielded Late Devonian (middle and late Famennian) ages (Appendix F) that are older than those from the type section (Early Mississippian; early to middle Tournasian and probable Viséan, Cecile, 2000). The unit is equivalent to unit DMsh2a of Cecile and Abbott (1992) and probably correlates with parts of units Dp3, Dp4 and Csp of Abbott (1983; J. G. Abbott, pers. comm., 2010) in the Macmillan Pass area. Figure 3.6.2-5. The upper Imperial Formation is dominated by sandstone. NTS 106A/9, 3 km northwest of McClure Lake (528304E, 7159346N).

181

Chapter Three

Figure 3.7.1-1. The Hawthorne Creek Formation is a conspicuous, dark brown-weathering sandstone unit (centre), stratigraphically overlying pale brown-weathering Canol Formation shale. The background mountain at far left shows stratigraphy of the Tsichu Group: Heritage Trail, Fourway and (top) Keele Creek formations. View to northwest, NTS 105P/12, midway between Caribou Cry and Twitya rivers, 47 km north of Mile 222 airstrip on the Canol Heritage Trail (464650E, 7063450N).

Description

182

Figure 3.7.1-2. The Hawthorne Creek Formation consists of dark-weathering shale and siltstone. View southwest, NTS 105P/12, 9 km northwest of Caribou Cry River, 55 km north-northeast of Mile 222 airstrip on the Canol Heritage Trail. Eastern NTS 105P/12 (468700E, 7062000N).

In the Macmillan Pass area (Cecile and Abbott, 1992), the base of the Heritage Trail Formation is an unconformity where the Hawthorne Creek Formation has either been eroded or was not deposited. North and east of the Macmillan Pass are, however, exposures of the Hawthorne Creek Formation are abundant, and its bedding attitude is similar to that of the overlying Heritage Trail Formation, although a slight disconformity is probable, considering the coarse grain-size of this unit. The Heritage Trail Formation is conformably overlain by the Keele Creek Formation, at a contact that appears to be gradational over several metres where examined (Fig. 3.7.1-4). Thick-bedded quartz arenite (referred to as quartzite by Cecile, 2000), with less common shaly and calcareous interbeds, characterises the Heritage Trail Formation. The base of the formation contains 30 m of dark quartzose wacke. In west-central NTS 105P, the unit is 40-50 m thick, with a granular conglomerate at the base (08BB-1266). At that location, the coarse-grained, thickbedded sandstone is white-and orange-weathering.

Heritage Trail Formation

Age and correlation

The Heritage Trail Formation consists of massive to blocky, grey-white quartz sandstone (Fig. 3.7.1-3). It is on-trend with the Heritage Trail Formation in northeastern NTS 105O, forming a prominent ridge extending northwestward from the Caribou Cry River. The formation is also present as thin, high-standing synclinal keels on adjacent ridges. The type section is shared with the Hawthorne Creek Formation (63º 38.7’N, 130º 02’W in NTS 105O; section 9 of Cecile, 2000), 1.2 km west of the Sekwi project area.

The age of the Heritage Trail Formation is interpolated from conodonts recovered from over- and underlying units. It is broadly Mississippian (Cecile, 2000) and correlates with the “Tsichu quartzite member” of Gordey and Anderson (1993) and unit Mg and the lower of two MPqs map units in the Macmillan Pass area (Cecile and Abbott, 1992). In NTS 105P, its distribution is equivalent to that of Unit 27 of Blusson (1971). In both age and lithology, the Heritage Trail Formation is equivalent to the Mattson Formation (Richards, 1989) in the southern Mackenzie Mountains and the Keno Hill quartzite (e.g., Roots et al., 1995; Roots, 1997) across central Yukon.

Chapter Three

Fourway Formation The Fourway Formation is a pale-weathering calcareous sandstone and siltstone succession that caps two ridges in western NTS 105P. The type locality (Cecile, 2000) is a ridge-top (63º 39.5’N, 130º 02’W) immediately west of the Sekwi project area.

Description Figure 3.7.1-3. The Heritage Trail Formation consists of quartz sandstone (colonised by black lichen) that forms relatively resistant hills and cliffs among shaly units. View to west on the southwestern flank of the Middlecoff anticline, NTS 105P/12, 26 km north of Mile 222 airstrip on the Canol Heritage Trail (462384E, 7044976N).

The conformable lower contact of the Fourway Formation is a sharp lithologic transition from limestone of the Keele Creek Formation to siliciclastic strata. This formation is the highest stratigraphic unit in the Sekwi project area; its upper contact is not preserved. At the type locality, a prominent peak exposes over 220 m of white to buff siliceous carbonate and calcareous siltstone. In western NTS 105P, a few tens of metres of strata in erosional remnants consist of light grey- to buff-weathering quartz sandstone, dolostone, shale and minor chert. The limestone contains silicified crinoids and brachiopods.

Age and correlation

Figure 3.7.1-4. The Keele Creek Formation consists of brown- and dark greyweathering shale and limestone. View to southeast, NTS 105P/12, 40 km north of Mile 222 airstrip on the Canol Heritage Trail (453926E, 7060968N).

Keele Creek Formation

Early Pennsylvanian (Bashkirian) conodonts were recovered from the type locality, but the full age range of the unit is unknown. Originally attributed to the Mount Christie Formation (Blusson, 1972), this unit was re-defined as Fourway Formation by Cecile (2000). It is an areally confined units, in contrast to timeequivalent strata to the south and east of the study area which are dominated by green argillite and orange- and green-hued chert of the Mount Christie Formation (Gordey and Anderson, 1993).

Interpretation of the Tsichu Group

This conspicuously dark-weathering (and locally light grey) shale and limestone succession occupies synclinal keels near the western limit of NTS 105P, and occupies the core of the Stew syncline. The unit can be difficult to distinguish from other dark shaly strata, but its position above the arenaceous Heritage Trail Formation is diagnostic. At the type section (63º 38’N, 130º 02’W in eastern NTS 105O; 2 km west of the Sekwi project area), the Keele Creek Formation is 325 m thick (Cecile, 2000).

The four formations of the Tsichu Group indicate a complex paleogeography featuring both shallow-water limestone and siliciclastic rocks, and deeper-water facies. Cecile (2000) summarised them as follows: the Heritage Trail and Fourway formations are interpreted as relatively shallow-water deposits because of the dominance of bioclastic material and clean quartz sand. The Hawthorne Creek and Keele Creek formations are interpreted as deeper-water deposits that accumulated around the peripheries of the shallow-water units.

Description

Mount Christie Formation

In western NTS 105P, the Keele Creek Formation overlies the Heritage Trail Formation (gradational over several metres), and is conformably overlain by the Fourway Formation. In western NTS 105P, the Keele Creek Formation consists of recessive, medium- to pale-grey-weathering, dark grey siltstone with thick laminae of light grey-weathering limestone (08BB-1267). At the type section, the basal 20 m of the Keele Creek Formation is black, recessive shale, overlain by more than 300 m of dark shale (70%) interbedded with tan- to grey-weathering crinoidal limestone (30%). Chert nodules and layers are abundant at the top of the unit.

The Mount Christie Formation consists of resistant, dark orange-brown-weathering, interbedded green-grey siliceous shale and recessive green shale. It is exposed in three localities near the southern boundary of NTS 105P. The largest exposure extends southward into NTS 105I and is 24 km north of the type section (at 62º48.2’N, 129 º 42.0’W) where it is 687 m thick (Gordey and Anderson, 1993). No exposures of the Mount Christie Formation were visited during the Sekwi project.

Age and Correlation

At the type section, the formation’s base is described (Gordey and Anderson (1993) as a sharp change from uppermost quartz sandstone of undifferentiated Tsichu formation (now Group) to shale. The top of the Mount Christie Formation is the highest chert bed, unconformably overlain by Triassic shale of the Jones Lake Formation. The strata exposed in NTS 105P were not examined, but extrapolated from exposures to the south.

Conodonts collected from the type section of the Keele Creek Formation indicated a Late Mississippian to Early Pennsylvanian age (Cecile, 2000) as did two samples from the Sekwi project (Bashkirian; Appendix F). The Keele Creek Formation is laterally equivalent to bioclastic limestone of the Caribou Pass Formation.

Description

183

Chapter Three Age and Correlation In NTS 105I, a conodont collection indicates a Late Mississippian to Permian age for the Mount Christie Formation (Gordey and Anderson, 1993).

Interpretation According to Gordey and Anderson (1993) the composition and lack of wave- or traction-produced sedimentary structures suggest that the Mount Christie Formation was deposited below wave-base. Precipitation of chert occurred during lulls in terrigenous clastic input. The quartz sandstone probably reflects pulses of coarse clastic material into this relatively quiescent environment, or a temporary decrease in water depth.

3.8. Late Permian Chert Basin D.G.F. Long and S.P. Gordey

Fantasque Formation Small, isolated exposures of black, laminated chert are present as structurally isolated blocks and as locally contiguous sedimentary units (typically less than 500 m strike-length) exposed immediately west of Cretaceous strata exposed in NTS 105P/10 (for location see Chapter 3.9; Fig. 3.9.1-1). In the southern part of this area, Morrow (unpublished field notes for section MTA-79-32 at 63°35’N, 128°39’W) recorded about 28 m of black, silicified mudstone, which was interpreted as occupying a karstic depression on the top of the Devonian Landry Formation. The upper contact with Cretaceous mudstone and minor sandstone at this location appears to be erosional (Fig. 3.9.1-2). Farther north, structurally isolated blocks of chert (up to 200 m thick) appear to be structurally interleaved with carbonate rocks of the Landry Formation, and are in fault-contact with Cretaceous strata.

Age and correlation Chert bodies in NTS 105P/10 might be interpreted as silicified mudstones equivalent to parts of the lower Paleozoic deep-water succession, except that they are clearly younger than the Devonian Landry Formation. A more plausible explanation is that they are lateral equivalents of the Late Permian Fantasque Formation (Yukon; Wignall and Newton, 2003). This correlation is supported by the presence of chalcedony-filled spheroids, here interpreted as recrystallised radiolaria.

Interpretation The Fantasque Formation is extensively exposed in southeastern Yukon and adjacent parts of Northwest Territories and British Columbia, but has not previously been recorded in NTS 105P (MacNaughton, 2002). This stratigraphic unit forms part of a widespread interval of deep-water chert deposition that extends from the Western Canada Sedimentary Basin to the Arctic Islands (Murchey and Jones, 1992; Beauchamp, 1994; Henderson 1997; Beauchamp and Baud, 2002). It is suggested here that the chert unit was originally far more extensive, but was largely eroded during the Mesozoic-Tertiary orogeny, providing much of the black chert detritus present in strata of the Cretaceous foreland basin.

3.9. Mesozoic Foreland Basin D.G.F. Long

Description

Unnamed Cretaceous unit

One sample of the formation was examined in thin section (Fig. 3.8.1-1) and proportions of its sedimentary components established by point-counting (500 points). This sample has distinct, thin

Over 1.3 km of highly deformed, steeply dipping, predominantly muddy, organic-rich, post-Berriasian to Campanian strata are preserved between two high-angle faults, in a 1.5 to 2 km-wide, 20 km-long panel located immediately south of the Canol Heritage Trail in the Sekwi Range (NTS 105P/10; Fig. 3.9.1-1). Blusson (1971) was the first to record the presence of coal in this unnamed succession [his Unit 30, shown as KTR on Figure 3.9.1-1 and on maps of Roots and Martel (2008); and as Ksp on accompanying map Open File 2010-14]. This succession was subsequently investigated by Ricker (1973), who measured three sections along ridge-crests, and recorded up to five coal seams, each at least 1.5 m thick, with possible lateral extent on the order of 450 m. Three sections were measured during the Sekwi project (sections 1, 2 and 3; Fig. 3.9.1-1 and Appendix B), with data from an additional section to the south (section 5) provided by D.W. Morrow (GSC Calgary, unpublished field notes 1979, section MTA-79-32; Appendix B). The objectives of the Sekwi project study of these rocks were to describe the stratigraphy, sedimentology and hydrocarbon potential of this isolated exposure of Cretaceous strata, which is about 150 km west of the nearest Cretaceous marine strata in the Mackenzie Valley, and 400 km east of terrestrial strata in the Whitehorse Trough.

Figure 3.8.1-1. Laminated chert of the Fantasque Formation, NTS 105P/10, base of section 2 (Fig. 3.9.1-2). A = 0.04 mm diameter chalcedonic spherule representing a recrystallised radiolarian test; B = siliceous silt grains; C = cryptic wavy lamination (? stylo-bedding) outlined by clay minerals. D = bubble defect in mountting media. Plane-polarised light.

184

lamination, outlined by minor concentrations of silt-sized, bladed phyllosilicate (illite? = 5.0 %). Anhedral, microcrystalline quartz makes up 87.6% of the sample, with 4.2% equant, detrital, silt-grade minerals and 2.8% opaques (hydrocarbons and iron sesquioxides). Small (>aug granite; K>P>/=Q; perthite present; minor to moderate ser in plag; access. zircon (c-gr), apatite, allanite, titanite

Additional Notes P>Q; perthite present; bt granite moderate ser-ms in plag; most qtz very f-gr; chl-ms locally after bt as euhedral grains and finer-grained clots (spotted); access. zircon, apatite, allanite, titanite

also sampled: pegmatitic vein; finer-grained and more leucocratic phase

Logan

CL-06-35

481576

6994804

0.31

R

f-m-gr. equigr. en- f-gr. equigr. bt>hbl>>aug-en granodiorite; P>K>Q; minor ser in aug-bt granite plag and minor clay speckling in Ksp; large euhedral plag and abundant small euhedral are complexly zoned; bt-rich (20-25%); access. zircon, apatite, allanite, pyrite

sub-cm rounded clots of finergrained bt-rich xenoliths(?)

Mt. Christie

CL-06-36

478575

6986329

1.60

O

m-gr. crowded (fine)-m-gr. Ksp-phyric (aug>bt; K>P>Q; perthite Ksp-phyric bt-aug- and tartan twins (microcline) present; minor to moderate clay hbl monzonite speckling in Ksp; minor to moderate ser in plag; moderate chl (blue after bt; access. zircon, apatite, allanite, titanite (VERY c-gr. and abundant), pyrite

also sampled: aplite (pegmatitic pods, disseminated sulphides); pegmatite (trm pods); very similar to O'Grady pluton texture but f-gr.

Christie Pass

CL-06-37

470564

6988698

0.96

O

m-gr. nearcrowded Kspphyric aug-bt-hbl granite

fine-m-gr. Ksp-phyric (mm to ~1cm; may be zoned) also sampled: trm matrix hosted hbl>>bt>>aug qtz monzonite to qtz syenite; K>>P=Q; mostly bt to breccia (rich in sulphides and chl (blue) unless an inclusion; minor ser and moderate calcite in granite clasts) plag; perthite present; access. zircon, apatite, allanite, titanite (very c-gr and VERY abundant), pyrite

Ross River CL-06-38

450948

6991241

0.15

R

m-gr. equigr. moderately leucocratic bt granite

fine-m-gr. equigr. bt granite; Q=P>K; qtz is typically c-gr. and inclusion-free (almost qtz-phyric); perthite and scattered Kspphenocrysts (bt>>aug qtz monzonite to granite; K>P>/=Q; perthite and minor to moderate clay speckling present; complexly zoned plag with zone-controlled ser; minormoderate ser-chl (blue) after bt; access. zircon, apatite, allanite, titanite, pyrrhotite

Mile 222

CL-06-40

456525

7009761

0.49

R-O

f-m-gr. Ksp-phyric f-m-gr. Ksp-phyric (~0.5 cm) hbl>bt>>aug qtz monzonite; K=P>Q; aug-bt-hbl granite perthite and local tartan twins (microcline) present; complexly zoned plag with zone-controlled ser; moderate chl (blue) after bt; access. zircon, apatite (can be c-gr w/hbl), allanite, titanite>>magnetite, pyrite

very f-gr. bt-hbl rich cm-scale xenoliths (~50% mafic); also sampled: N-S trending 20-cm wide mafic dyke

Table 4.3-1. General descriptions of representative intrusive samples that underwent geochemical and geochronological analysis; coordinates are for the UTM projection using NAD 83 datum, zone 9. MS = magnetic susceptibility (x103 SI units); RS = redox state; R = reduced; O = oxidised. Abbreviations are as follows: f = fine; m = medium; c = coarse; gr. = grained; equigr. = equigranular; phyric = phenocrystic; crystic = megacrystic; Ksp (K) = K-feldspar; plag (P) = plagioclase; qtz (Q) = quartz; bt = biotite; hbl = hornblende; aug = augite; en = enstatite; ms = muscovite; chl = chlorite; ser = sericite; trm = tourmaline; access. = accessory.

American Shale Composite (Gromet et al., 1984), the samples display a slight enrichment in LREEs (La to Gd and La to Sm, respectively) but otherwise appear to be very close in composition to typical supracrustal rocks (Fig. 4.3-8b). Finally, when normalised to the primitive mantle of Sun and McDonough (1989), the profile for the samples has pronounced negative anomalies associated with high-field-strength elements (Nb, Ta, P, Ti; Fig. 4.3-8c). The above data suggest that the intrusions are largely crustally derived, or have undergone high degrees of crustal contamination combined with some fractional crystallisation processes (indicated by increased SiO2 with peraluminosity, depleted Eu-Nb-Ta-P-Ti, and relatively low HREE). The enrichment in LREEs is evidence for some input from a more enriched source, possibly lithospheric mantle as suggested for the Mayo and Tombstone suites (Hart et al., 2004b). It has already been proposed that partial melting in an enriched mantle, combined with partial melting, assimilation, and/or contamination in the middle to upper crust, could be an explanation for the geochemical compositions exhibited by both the Tombstone and Mayo plutonic suites (Hart et al., 2004b). Further evidence for some mantle-melt input is the moderate to very high chromium concentrations of most of the intrusions (20-120 ppm; Table 4.3-2). Overall, the major and trace element geochemistry is more consistent with the Tombstone and Mayo plutonic suites than it is with the Tungsten suite, when compared to data from Hart et al. (2004b), Heffernan (2004), and Rasmussen et al. (2007a).

4.3.3. Summary The eight intrusive bodies sampled in NTS 105P range from fine-grained equigranular to medium-grained K-feldspar-phyric to weakly K-feldspar cumulate textures, and are of sub-alkaline, metaluminous to weakly peraluminous, reduced to oxidised, intermediate to felsic monzonitic compositions. The trace element geochemistry of these bodies is consistent with derivation of the parent magma from melting of middle to upper crustal rocks with some input from a LREE-enriched source, possibly the lithospheric mantle as suggested by Hart et al. (2004a). Geochronologically, the intrusions were emplaced over a short interval from approximately 97 to 92 Ma, and evidence for inheritance is commonly but not always present in all of the samples, generally in the form of rounded xenocrystic to irregular, partially resorbed cores; wellzoned older magmatic cores are most common. Based on these data, the intrusions in NTS 105P may be classified into the Mayo plutonic suite as previously described in detail by Hart et al. (2004b).

Petrogenesis of the intrusions The Tungsten and Mayo suites of intrusions have been interpreted to have been derived by crustal melting, either associated with contractional deformation and thickening of the rift- and continental-margin-related rocks (e.g., Woodsworth et al., 1991; Gordey and Anderson, 1993), and/or due to post-orogenic collapse

205

Chapter Four

Figure 4.3-3. Macroscopic features of intrusions (pen and rock hammer as scales). (A) K-feldspar megacrysts (Mile 222 pluton). (B) Metasedimentary xenolith (Dechen’La pluton). (C) Pervasive jointing and shallowly dipping aplite dyke swarm (Dechen’La pluton). (D) Aplite dyke with pegmatitic core (Mt. Christie pluton). (E) Tourmaline-filled miarolitic cavity (Mt. Christie pluton). (F) Quartz vein (Ross River pluton). (G) Mafic dyke (red dashed borders) cross-cutting K-feldspar megacrystic phase (Ross River pluton). (H) Mafic xenolith with irregular boundary indicates mixing of mafic and intermediate-felsic magma (Dechen’La pluton).

206

Chapter Four

Figure 4.3-4. Representative images of polished and stained hand sample slabs for the intrusive samples that underwent geochemical and geochronological analysis; note the white 1cm scale bar for each sample.

and decompression melting of these rocks (Hart et al., 2004a; Mair et al., 2006). The Tombstone suite differs from all other Cretaceous plutonic suites in that Tombstone suite intrusions are weakly to strongly alkalic and include abundant intermediate and minor mafic components, as well as silica-undersaturated phases, suggesting that these magmas were derived from melting of the mantle (Mortensen et al., 2000; Hart et al., 2004b). Trace element abundances suggest that an enriched or lithospheric mantle source has affected the essentially crustally derived Mayo suite intrusions through contamination processes, but that the Tombstone suite was probably largely derived from partial melts sourced in lithospheric mantle that underwent high degrees of crustal contamination during ascent to upper-crustal levels (Hart et al., 2004b). The setting envisaged for the combination of crustal melts and alkalic mantle-derived melt influx has been described as a post-collisional back-arc environment that may have undergone post-orogenic relaxation or very limited extensional deformation during the emplacement of the intrusions (Hart et al., 2004a). The geochronological and geochemical overlaps between Mayo and Tombstone suite intrusions in this area could be due to a gradual change in petrogenetic conditions, from crustally derived but enriched mantle-contaminated Mayo suite intrusions to increasingly enriched mantle-derived melts with time, resulting in Tombstone suite intrusions.

The classification of these intrusions as Mayo and/or Tombstone suite plutons has implications for the northern extent of Tungsten suite intrusions located farther south of NTS 105P (Rasmussen et al., 2007a), and suggests that the Mayo intrusions extend farther south and west in the Northwest Territories than previously thought. Furthermore, the emplacement of only one, petrologically distinct Tombstone suite intrusion (O’Grady) in the immediate vicinity of the study area, and the scattered exposures of Tombstone suite plutons farther to the southwest (e.g., Charlie, McLeod; Heffernan, 2004) and to the northeast (e.g., Emerald Lake; Coulson et al., 2002) in areas dominated by magmatism from other plutonic suites (e.g., Tay River and Mayo, respectively) require an explanation.

Economic considerations Metallogenically, the three plutonic suites of the TTB are associated with a range of mineralisation types typical of magmatism inboard of a continental magmatic arc (Chapter 7.2). The Tungstensuite plutons have a W-Cu-(Zn-Bi-Au-Mo) and Pb(Ag)-Zn metal tenor, expressed in the form of skarn, manto, and vein occurrences (e.g., Mactung: 33.0 Mt at 0.88% WO3 indicated and 11.3 Mt at 0.74% WO3; Cantung: 1.51 Mt grading 1.27% WO3 indicated,

207

Chapter Four

Figure 4.3-5. Representative back-scattered electron (BSE; upper) and cathodoluminescence (lower) images of zircons displaying typical grain sizes, morphologies, zoning, and core and rim characteristics for each sample examined; note that both examples for CL-06-34 are BSE images. Significant resorption surfaces are outlined by a dashed white line, which is thicker for core outlines: XC = xenocrystic core; MC = magmatic core; MR = magmatic rim; ? = uncertain.

including 1.02 Mt at 1.08% WO3 probable; 6.21 Mt at 1.56% WO3 recovered as of 2009; LaCroix and Cook, 2007; Reid et al., 2009; Rasmussen et al., 2011). Mayo suite plutons are associated with Au-Bi-Te-W mineralisation (e.g., Dublin Gulch: 4.19 Moz Au; Ray Gulch: 7.26 Mt at 0.87% WO3; Hart et al., 2000) and possibly AsAg-Pb mineralisation (e.g., Keno Hill deposits), that generally forms vein-style deposits in the intrusions and the country rock, with local skarn and greisen occurrences (Hart et al., 2004b). Tombstone suite plutons are associated with Au-Cu-Bi skarn and vein mineralisation (e.g., Brewery Creek: 0.676 Moz Au; Marn: 0.33 Mt at 8.6 g/t Au, 1% Cu, 0.1% W, 17 g/t Ag; Hart et al., 2000; Galambos, 2004), or with disseminated to vein-style U-Th-F enrichments (Hart et al., 2004b). In NTS 105P, no known ore-bodies are associated with the intrusions sampled for this study, but several mineral occurrences are spatially associated with these and other similar intrusions in the general area (NORMIN, 2010; Yukon Minfile, 2004). Nearby,

208

intrusion-related, base and precious mineral occurrences and deposits include skarn and/or manto with various combinations of W, Cu, Ag, Zn, Pb, (rare Mo, Au), and abundant “vein” showings with various combinations of Cu, Ag, Pb, Zn, Au, Sb, Mo, Sn (some of these may be mis-classified; Gordey and Anderson, 1993; Yukon Minfile, 2004; Rasmussen et al., 2007a; NORMIN, 2010). In particular, Au skarns/veins, As-Ag-Pb veins, Sb veins, and W skarns have a close spatial association with several of the intrusions examined in NTS 105P (e.g., Gordey and Anderson, 1993; Yukon Minfile, 2004), and these metal tenors are reasonably consistent with those described for Mayo suite intrusions in Yukon. However, based on the presence of several ca. 92-94 Ma intrusions, mineralisation more typical of Tombstone suite magmatism (e.g., Au-Cu-Bi, or U-Th-F; Hart et al., 2004b) is also possible in NTS 105P (Chapter 7.1.7).

Chapter Four

Figure 4.3-6. 238U/206Pb crystallisation age weighted-mean plots (y-axis) with 2-sigma error bars for representative samples; white error bars represent analyses that were rejected by Isoplot3, and horizontal black line is the calculated weighted mean for each sample reported in Table 4.3-3. (A) Samples with relatively simple zircon systematics compare to Figure 4.3-6 (b).

209

Chapter Four

Figure 4.3-6. (continued). (B) Samples with older (Mayo age) magmatic cores and younger (Tombstone age) magmatic rims, compare to Figure 4.3-6 (a), that may or may not be separated by partial resorption surfaces.

210

Chapter Four

Radial Fractures

1

2

25

18

2

28

1

1

3

CL-06-35

34

23

1

1

30

3

3

3

1

CL-06-36

41

24

1

1

39

1

2

2

2

ap thick well-zoned magmatic rims and partially resorbed wellzoned magmatic cores; at least 1 significant resorption surface in rim

CL-06-37

21

15

18

2

1

1

ap thick well-zoned magmatic rims and partially resorbed wellzoned magmatic cores; at least 1 significant resorption surface in rim

CL-06-38

52

23

9

5

18

35 13 13 13

1

ap well-zoned magmatic rims with partially resorbed magmatic cores; porous/unzoned xenocrystic and intensely resorbed cores are abundant

CL-06-39

44

31

1

2

35

8

6

8

1

ap thick well-zoned magmatic rims with partially resorbed magmatic cores; at least 1 significant resorption surface in rim

CL-06-40

53

28

3

46

8

8

8

CL-06-34

INCLUSIONS

Porous

2

XENOCRYSTS

Resorbed

28

Unzoned (BSE)

Magmatic ± Partially Resorbed

3

n 32

Porous

Radial Fractures

CORES:

20

Sample CL-06-33

Partially Resorbed

RIMS:

Summary of Typical Zircon Textures ap thick well-zoned magmatic rims with partially resorbed wellzoned magmatic cores ap very small grains with well-zoned magmatic rims and partially resorbed well-zoned magmatic cores; at least 1 significant resorption surface in rim

(ap) thick well-zoned magmatic rims with partially resorbed magmatic cores; multiple small resorption surfaces and at least 1 significant resorption surface in rim

ap thick well-zoned magmatic rims with partially resorbed wellzoned magmatic cores; at least 1 significant resorption surface in rim

Table 4.3-2 (a). Zircon data for representative samples. Summary of zircon textures evident in back-scattered electron and cathodoluminescence images of polished zircon cross-sections, where n = number of grains used for textural compilation, and ap = apatite (bolded = particularly abundant; bracketed = rare).

206 238

Pb/

U Age (Ma) 93.7

Magmatic

2-δ error (Ma) 0.53

2-δ error (%) 0.56

206

n 9

MSWD 1.9

Pb/238U Inheritance (Ma) 95.68

Xenocrystic 2-δ error (Ma) 0.66

2-δ error (%) 0.66

n MSWD 12 3.1

206 Pb/238U Inheritance (Ma) nd

Plutonic Suite Tombstone (Mayo) Tombstone

Sample CL-06-33

Pluton Dechen’La

CL-06-34

Natla

92.33

0.55

0.59

13

5.1

nd

1807, 1901

CL-06-35

Logan

96.16

0.97

1.0

12

4.6

nd

129.1, 106.6

Mayo

CL-06-36

Mt. Christie

96.24

0.51

0.53

14

3.6

nd

nd

Mayo

CL-06-37

Christie Pass

96.73

0.58

0.6

14

2.5

nd

139.7, 137.4

Mayo

CL-06-38

Ross River

92.99

0.92

0.99

7

4.3

95.25

0.49

0.99

9

1.8

1207

CL-06-39

Keele River

93.13

0.31

0.33

16

1.09

95.96

0.71

0.75

7

0.6

nd

CL-06-40

Mile 222

96.50

0.51

0.52

13

1.6

nd

Tombstone (Mayo) Tombstone (Mayo) Mayo

nd

Table 4.3-2 (b). Zircon data for representative samples. B) LA-ICP-MS 238U/206Pb geochronological results where nd = not determined, n = number of ablations used for the weighted mean calculation, r = number of ablations rejected by Isoplot3 for the weighted mean calculation, MSWD = mean square of weighted deviates for the weighted mean calculation, and data for older magmatic cores plotted in Figure 4.3-6b are bracketed.

211

Chapter Four Sample SiO2 Al2O3 Fe-OTotal Fe2O3 FeO Fe2O3 / FeO CaO MgO Na2O K2O TiO2 MnO P2O5 SrO BaO LOI Total Ba Ce Co Cr Cs Cu Dy Er Eu Ga Gd Hf Ho La Lu Nb Nd Ni Pb Pr Rb Sm Sn Sr Ta Tb Th Tl Tm U V W Y Yb Zn Zr

CL-06-33 66.26 15.34 3.79 0.65 2.82 0.23 3.55 2.17 2.43 4.76 0.47 0.07 0.171 0.05 0.11 0.61 99.79 937 86.9 9 80 9.11 5 3.26 1.77 1.38 17.4 5.55 8.5 0.62 44.6 0.25 12.7 37.8 16 36 10 210 6.69 3 446 1 0.66 24.4 1.1 0.24 7.34 71 2 17.2 1.55 54 339

CL-06-34 69.14 15.13 2.91 0.35 2.30 0.15 2.15 1.07 2.34 5.46 0.33 0.05 0.177 0.04 0.07 0.99 99.85 611 106 4.6 20 22.2 15 km-thick Wernecke Supergroup (sequence A1), which Cook et al. (1991) extended along the length of the Cordillera. Interpretation of both of the above datasets led previous authors to recognise a compressional orogenic event (Forward orogeny; MacLean and Cook, 2004), which predated deposition of sequence A3 (Pinguicula Group), and which they equated with the pre-Pinguicula-Group Racklan deformation recognised in Yukon. North of the Mackenzie Mountains, this deformation is intracratonic or thick-skinned, with broad folds and faults, both having several kilometres of relief and affecting crystalline basement. Deep seismic reflection and refraction experiments along the SNORCLE transect (Cook and Erdmer, 2005), southwest of the Sekwi project area (Fig. 5-2), were aimed at deciphering deep crustal structure, and provide little information on stratigraphic successions (Fig. 5-2b). Creaser and Spence (2005) attributed a deep crustal reflector along the SNORCLE line (Fig. 5-2, line 3) at the same depth as the top-of-basement position indicated by Clarke and Cook (1992) (Fig. 5-2, line 6x) with the same significance, as modified and extended North American crystalline basement that extends westward to the Tintina fault (Fig. 5-2b). It is uncertain what may lie beneath Mackenzie Mountains (see Fig. 5-2b, position of red vertical line). Deep geophysical data indicate that the Moho is at 35-40 km depth and is probably overlain by extended North American basement that is about 10

219

Chapter Five km thick, which is in turn overlain by about 30 km of sedimentary rocks. Shallower reflection data to the northeast indicate about 20 km of sequence A strata, overlain by a combination of sequence B (Mackenzie Mountains supergroup), sequence C (Windermere Supergroup) and Phanerozoic rocks totalling about 10 km of thickness. Given that the sequences are unconformity-bounded, it is unknown in what proportion each is preserved, particularly the relative amounts of sequence A1 versus A2. In addition, the extension of uniformly thin basement west of the basement ramp is simplistic. Younger extensional events probably modified this basement (e.g., basal Windermere Supergroup extension; fault indicated diagrammatically in Fig. 5-2b). It is unclear whether the effects of the Racklan-Forward orogenies extend southward to the latitude of the project area.

5.2. Structure of Central Mackenzie Mountains 5.2.1. Previous work The Mackenzie Mountains have received relatively little structural interpretation. Most of this region was mapped in reconnaissance during the early 1970s. Cross-sections that accompany the regional maps (1:250,000 scale, locally 1:125,000 scale) depict the structural style at surface but do not portray interpretations at depth. Although it was considered by early workers that décollement surfaces were probably fundamental to development of the foreland belt (e.g., Gabrielse et al., 1973a), it was not until the early 1980s that cross-sections depicted this. As at present, a lack of seismic control means that determination of depth to detachment(s) is qualitative or crudely estimated from the geometry of structures at surface. Deep seismic profiling through adjacent areas in the late 1990s (see above), combined with regional gravity data, provide limited insight on depth to crystalline basement and on thickness and character of the succession above basement and below the oldest exposed Mackenzie Mountains supergroup unit in the Northwest Territories (informal “H1 unit”). Norris (1972) provided the first regional analysis of the structure of the northern Cordillera fold and thrust belt. He noted that en-echelon fold bundles possessed an asymmetry relative to their position around the arc of the Mackenzie Mountains, and that the arcuate shape was inherited from an ancient, persistent and fundamental shape of the margin. Gabrielse et al. (1973a-c) were the first to map and describe the Plateau fault, and recognised it as one of the most significant structures in Mackenzie Mountains. They observed that the fault maintains a relatively constant stratigraphic position, and that, although it is moderately west-dipping at surface, it flattens with depth and merges with a décollement surface beneath the Redstone Plateau. They suggested that crustal shortening of at least 10 km across the fault would be consistent with regional average amounts of shortening (20%), and that considerable shortening was required to explain contrasts in formation thicknesses between hanging-wall and footwall. They also mentioned that in general the faulting and folding in the region would be facilitated by deformation above surfaces of décollement, and that the entire stratigraphic succession exposed may be allochthonous above crystalline basement. By the mid-1970s, Aitken et al. (1982) had mapped the Plateau fault from its type area (Gabrielse et al., 1973a-c) to its northwest termination and recognised that its immediate hanging-wall is consistently in the Gypsum or Rusty Shale formations of the Little Dal Group. They concluded that the fault is rooted in a detachment in the Gypsum formation. Like Gabrielse et al. (1973a-c), they noted

220

that the juxtaposition of different stratigraphic successions across the fault suggested large horizontal displacement (tens of kilometres). They suggested an alternative interpretation, based on stratigraphic arguments, in which offset could be as little as a few kilometres, and that the dramatic differences in stratigraphy across the fault were attributable to the “Selwyn Basin” hinge line (Mackenzie arch of the present report). Aitken et al. (1982) recognised that the flat-topped anticlines northeast of the Plateau fault were related to shortening above a detachment that is much deeper than the Gypsum formation of the Little Dal Group. In the early 1980s, Gordey (1981) constructed a crosssection of the Mackenzie Mountains, making the fundamental assumptions that the northern foreland belt (as in the Rocky Mountains) was thin-skinned, and that a basal detachment extended beneath the entire foreland belt. Using a crude areabalance method, he estimated a detachment depth of 11 km (beneath Redstone Plateau) and drew surface structures down to this level. Total shortening across the Mackenzie and Franklin mountains was estimated at 53 km (~14%). Coincidentally, the line of section passed near the southern termination of the Plateau fault, which led him to suggest that in this area, the Plateau fault had minimal offset; the structural elevation of Proterozoic rocks (i.e., Redstone Plateau) could not be attributed to displacement along the fault, but instead, deflection of the basal detachment above a deeper (perhaps basement) ramp accounted for structural elevation of Proterozoic strata. For comparison, Cecile and Cook (1981) constructed a northern section that crossed an area where the Plateau fault and its detachment are well exposed. Using the same area-balance method, they portrayed a depth to basal detachment of about 18 km (beneath the Plateau fault), and showed shortening of about 60 km across the Mackenzie Mountains (their segment A-F). Cecile and Cook (1981) portrayed the Plateau fault as a flat structure at shallow depth, and drew it to overlap a wide extent of flat-lying, organic-rich, possible hydrocarbon host rocks of Devonian to Mississippian age. The implication was that a possible hydrocarbon trap beneath the Plateau fault could be as large as 4,000 km2 (Cecile et al., 1982). In contrast to Gordey (1981), Cecile and Cook (1981) presumed that the basal detachment for the fold and thrust belt was at the interface of sedimentary rocks and crystalline basement. Cook and MacLean (1999) described the Imperial anticline in the northern Franklin Mountains, and related its development to translation across a stratigraphically controlled ramp from a deep detachment in the Mackenzie Mountains to a much shallower level in Upper Cambrian evaporite strata in the northern Franklin Mountains, as previously inferred by Aitken et al. (1982). Based on seismic information, they implied at least 1.5 km of basal Mackenzie Mountains supergroup, which provided a crude estimate of depth to detachment under the northern Mackenzie Mountains of about 12 km. To assess the entrapment of hydrocarbon source rocks beneath the Plateau fault, as suggested by Cecile et al. (1982), MacNaughton et al. (2008) undertook sampling and bedrock mapping to establish thermal maturation, source rock potential and fault geometry. They concluded that there was only limited trapping potential, and that such potential was confined to the leading edge of the Plateau fault. Devonian-Mississippian strata do not extend regionally beneath the footwall as indicated by Cecile and Cook (1981). MacNaughton et al. (2008) presented two possible structural interpretations of the Plateau fault and its footwall along a section that touches the easternmost part of the Sekwi project area.

Chapter Five Figure 5-4. Structural cross-sections A, B, and C across Sekwi Mountain (NTS 105P) and Mount Eduni (NTS 106A) map areas (locations shown in Fig. 5-3). Sections are simplified from those presented at larger scale as accompanying NWT Open File 2010-18. At times during the Paleozoic, basinal facies (Selwyn Basin) migrated across the platform (Mackenzie Platform) leading to the apparent interfingering of the two elements. Selected formation tops shown in grey. Numbered features are referenced in the text. On the index map, the boundary between Inner (IB) and Outer (OB) belts (Figs. 5-1 and 5-2) is indicated by black dashed line.

221

Chapter Five

5.2.2. Present work The Sekwi project area displays a range of structural styles. Based on similarities in the geometry and orientation of structures, these styles can be geographically grouped into several informal domains (Fig. 5-3). From northeast to southwest, these include a region dominated by continuous, large-amplitude, flat-topped anticlines and intervening synclines (fold domain), a structurally complex zone in the footwall of the Plateau fault (Ten Stone structural complex), a large, relatively undeformed region in the hanging-wall of the Plateau fault (ramp-flat domain), and farther southwest, a domain of regional-scale, en-echelon or discontinuous folds broken by a complex array of faults (fold-fault domain). The southwestern part of the Sekwi project area includes the transition to penetratively deformed strata of the inner belt. For each domain, a description of the structural geometry is followed by a discussion of factors that may have controlled development of that geometry and implications for depth to detachment. Unless otherwise indicated, the names for structural features have been adapted from contiguous, previously named structures in adjacent areas. Three annotated cross-sections (accompanying cross section sheet NWT Open File 2010-18; simplified in Fig. 5-4) illustrate subsurface geometry, based on surface distribution of rock units, structural attitudes, and consistency with fold and thrust belt geometry. Formation thicknesses were conserved; where thickness changes are present, they were presumed to be uniform between control provided by surface exposure and dip. Thrust faults were drawn to cut up-section in the direction of transport, emplacing older over younger strata. Stratigraphic cut-offs in the hangingwall of thrust faults should match those in the footwall. Rigorous balancing using bedding line length and palinspastic restoration were not undertaken. A caveat is that such interpretation becomes increasingly ambiguous with depth, and without constraints provided by subsurface information such as seismic or drilling, the interpretation provided may not be unique. Despite the uncertainty, levels of detachment are fundamental to interpreting structural geometry in a fold and thrust belt such as the Mackenzie Mountains, and a first attempt is made to illustrate these here. During the present work, the Ten Stone Range structural complex was mapped in detail by J. MacDonald (2009) as part of an M.Sc. study in order to assess the structural geometry and depth to detachment. The Plateau fault was the focus of regional and detailed mapping by Karen Fallas, and has been reported elsewhere (MacNaughton et al., 2008). Although Mesozoic-Tertiary structures dominate the project area, the presence of Proterozoic syndepositional listric and normal faults that affected sedimentary dynamics of the Mackenzie Mountains supergroup was inferred (see below), based on detailed thickness and facies variations.

(by domain) below. However, the Neoproterozoic listric and transfer faults are newly recognised, partly through this project, and so a summary is presented below.

Listric and transfer faults in the Mackenzie Mountains supergroup Strata of the ~4 km-thick Mackenzie Mountains supergroup (Chapter 3.1; Fig. 3.1.1-2) were deposited in a broad, elongate, arcuate basin that appears to have developed over a late Mesoproterozoic to early Neoproterozoic failed rift (Aitken and Long, 1978; Aitken and McMechan, 1991; Young, 1992; Rainbird et al., 1996a, 1997). Early reconstructions, based on poorly constrained formation- to groupscale thickness patterns, indicated that it may have been deposited along a passive margin with a strong degree of primary curvature (Norris, 1973; Aitken and Long, 1978; Park et al., 1989; Aitken and McMechan, 1991). The apparent oroclinal curvature of the outcrop belt (Fig. 5-5) was considered to have been inherited from the underlying basement structure, rather than being an artefact of Cretaceous-Tertiary deformation. New data (this study) have confirmed irregular thickness distribution patterns of formation- and member-scale intervals in the Katherine and Little Dal groups both normal and parallel to the craton margin (Chapter 3.1). The thickness trends indicate that the basin was segmented into sub-basins by a series of listric and transfer faults (Fig. 5-5; Long et al., 2008; Turner and Long, 2008). Using this model, based on Lister et al. (1986), the entire Mackenzie Mountains supergroup was deposited in a broad embayment along the western margin of Rodinia that developed above a lower-plate segment of an extensional margin. The absence of strata equivalent to the Mackenzie Mountains supergroup anywhere in the Canadian Cordillera south of 62º indicates that the area south of the Liard Line (Cecile et al., 1997) was a promontory that probably represents an upper-plate segment of the craton margin. From thickness data, lithofacies variations, and isopachs, Turner and Long (2008) were able to demonstrate repeated reactivation of several transfer faults in the Sekwi project area (Figs. 5-5 and 5-6).

5.2.3. Pre-Mesozoic tectonism Introduction Pre-Mesozoic structures documented or inferred by previous workers in the Mackenzie and Wernecke mountains have been summarised above. Field observations made during the present project are consistent with the previous studies and include steep faults with pre-Cambro-Ordovician (Franklin Mountain Formation) displacement, as well as those with probable Neoproterozoic (preor syn-Rapitan Group) movement. These latter, rare structures are discussed in the context of the cross-sections or area of occurrence

222

Figure 5-5. In the Sekwi project area, the main (proposed) northeast-trending transfer faults have been named the Fort Norman Structure, and the Godlin, Mountain River, Sammon’s Creek and Stone Knife faults (discussed in text). Coloured background indicates regional distribution of Mackenzie Mountains supergroup, from base to top including H1 unit (green), Tsezotene Formation (black), Katherine Group (yellow) and Little Dal Group (blue). Units K1 to K7 are divisions of the Katherine Group. Units LD0 to LD4 are divisions of the Little Dal Group (see Chapter 3.1.4 for further details). Stratigraphic unit symbols adjacent to pins indicate timing of down-dropping events along that structure. After Turner and Long (2008).

Chapter Five

5.2.4. Outer foreland belt - structural domains Fold domain Geometry

Figure 5-6. Lithofacies and thickness variations in the Tsezotene Formation and Katherine Group (section identified by number across top of figure). Stratigraphic sections plotted relative to locations of transfer faults in Figure 5-5. Transgressiveregressive cycles are formed by pairs of formation-scale units: A = Tsezotene Formation and K1; B = K2 and K3; C = K4 and K5; D = K5 and K6. Red arrows indicate demonstrated sense and timing of movement; grey arrows indicate suspected sense of movement. Each sequence is hung from its top surface. Modified from Turner and Long (2008).

The main proposed northeast-trending transfer faults in the Sekwi project area have been named the Fort Norman Structure (Cecile et al., 1982), and the Godlin, Mountain River, Sammon’s Creek and Stone Knife faults (Fig. 5-5). The suggested orientation and location of the Fort Norman Structure (Aitken and Pugh, 1984) coincides with a basement feature that truncates the southeasttrending Neoproterozoic “Great Bear Arch” to the northeast, and with the Platformal-Basinal transition in the Little Dal Group in the map-area (Aitken, 1981). In the northeast, the structure is further constrained by geophysical data, including a marked deflection of seismic thickness contours of the Mackenzie Mountains supergroup beneath the Mackenzie Valley (Cook and MacLean, 2004). There is no clear evidence for or against development of an ocean basin to the west of the Mackenzie margin during the early Neoproterozoic. The Mackenzie Mountains supergroup was subject to mild tectonic adjustment prior to extrusion of the “Little Dal basalt” at the start of the Hayhook extensional event at around 779 to 770 Ma (Gunbarrel event of Harlan et al., 2003). Reactivation of transfer and listric faults may have directly influenced the shape of rift basins during deposition of the Coates Lake and Rapitan groups, and also during the transition to drift, marked by deposition of the overlying slope deposits in the Twitya Formation. Reactivation of some transfer faults took place during development of the Phanerozoic Cordilleran margin, and during final closure of the margin in the Cretaceous. The location of the Mackenzie Mountains supergroup on a thinner and weaker lower-plate margin adjacent to inferred upper-plate margins to the south and north may have exaggerated the basin margin’s original eastward convexity during Cretaceous-Tertiary deformation. Finally, Turner and Long (2008) have suggested that the northeast-trending transfer faults may have played a significant role in channelling the later movement of ore-bearing fluids.

The fold domain underlies the northeastern half of the Mount Eduni (NTS 106A) map sheet (Fig. 5-3) and comprises northwesttrending anticlines cored by quartz arenite of the Mackenzie Mountains supergroup (Shattered Range, Tawu and Stony anticlines) and flanked by intervening synclines (Bolstead, McDermott, Houdini, and Cache Creek synclines) that expose shale and fine-grained sandstone of the Devonian Imperial Formation. In the northeastern part of the Sekwi project area, the Stony anticline is bifurcated near its southeastern end by the Stony syncline (Fig. 5-3). In the central part of the area, the Tigonankweine anticline is the en-echelon continuation of the Shattered Range anticline. The folds of this domain are impressive in their regional continuity, extending well to the north and northwest of the project area, and in the consistency of the stratigraphic levels they expose. For example, the Shattered Range anticline is approximately 180 km long and the Tawu anticline is about 300 km long. The Stony anticline is approximately 180 km long, but considering that it is semi-continuous with the Foran anticline (Fig. 5-3) the combined anticlinal structure has a total length of about 230 km. Likewise, the intervening synclines (Bolstead synclinorium, Cache Creek synclinorium and McDermott syncline) also display remarkable continuity. At their northwestern terminations, the anticlines plunge out abruptly near the Mackenzie Mountains front (Lemieux et al., 2009). The anticlines become tighter to the southeast, with less structural relief, and expose predominantly Paleozoic strata. The anticlines are conjugate concentric folds in which flat-lying strata in the fold cores are flanked, across sub-angular hinges, by moderately outward-dipping monoclines defining the fold limbs (Figs. 5-4 and 5-7). The across-strike width of the flat-topped part of the folds generally varies from 4 to 6 km, but locally narrows to about 2 km. Rarely, the monocline hinge-lines merge to form a single anticlinal fold axis, as along the Tawu anticline. The strata in the anticline cores are devoid of small-scale folds. Although structural measurements are not available for areas beyond the borders of the present work, measured bedding attitudes along the anticline limbs typically range from about 40º to 60º. The scarcity of values in the 20º to 30º range is presumed to result from local warping. Based on the available data, the folds appear to be symmetrical. Structural relief, or the difference in stratigraphic level of a horizon between a syncline and the adjacent anticline, is as much as 3800 m (Tawu anticline, cross-section C in Fig. 5-4; accompanying NWT Open File 2010-18). The anticlines are broken by numerous north- to northwesttrending, steeply dipping faults of relatively small stratigraphic offset (2 km. As in cross-section E-E’, the latter fault roots in the Gypsum formation. The Cache Lake fold is a complex structure whose fold nose is bifurcated by a chevron-style syncline, and which features a folded thrust fault on its northeast side. Offset on the folded thrust is 1-2 km, and the thrust cuts up at a high angle through the Paleozoic section, placing its hanging-wall strata above Devonian clastic rocks. Displacement on the fault at its leading edge is probably completely absorbed by folding and minor shearing in the Devonian strata. On its own, displacement along this fault would have resulted in a faultbend anticline. However, continued shortening accentuated this anticline, folded the thrust fault, and led to propagation of another thrust out of the core of the growing anticlinal structure. As in cross-section E-E’, evidence of pre-Upper-Cambrian (pre-Franklin-Mountain-Formation) erosion is significant, in that both the Twitya Formation and the Little Dal Group Upper

Figure 5-16. Detailed map of Cache Lake fold reproduced from MacDonald (2009, his Fig. 3.6; reduced to 60% of original size). Cross-section lines added for location reference. Origin of fold and significance of faults numbered 1 to 5 are discussed in text. Legend on Figure 5-12.

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Chapter Five Carbonate formation are absent in the Cache Lake fold, but are present to its southwest. Cross-section G-G’ (Figs. 5-12 and 5-13c) is close to and resembles section F-F’, and structures can be traced from the latter into this line of section. Southwest of the section’s mid-point, a syncline exposing Devonian clastic rocks is flanked by thrust faults. The southwestern fault truncates the southwestern limb of the syncline and parts of a footwall anticline. Dip-slip displacement along this fault is about 2.5 km. The northeastern fault follows a bedding glide zone in the Gypsum formation (Little Dal Group) and emplaces it above the Franklin Mountain Formation. Offset along this structure is at least 1.0 km, depending on where hanging-wall cut-offs are extrapolated. A small amount of duplication beneath the core of the syncline is indicated by the slightly higher structural elevation of Devonian clastic strata here, as compared to adjacent areas (e.g., northeast end of section). As in cross-section F-F’, the Cache Lake fold contains a folded thrust fault. Significant erosion beneath the Cambro-Ordovician Franklin Mountain Formation is indicated by the absence of Little Dal Group Upper Carbonate formation in the area of the Cache Lake fold. Cross-section H-H’ (Figs. 5-12 and 5-13b) shows the geometry of the structures in the southeastern part of the Ten Stone Range complex, where faulting is more deeply rooted, as indicated by the involvement of Proterozoic Katherine Group strata. There are three main faults in this section, all of which are present in cross-sections F-F’ and G-G’. The fault on the southwest is a continuation of the “out-of-syncline” fault in the previous sections, except that here, it has cut down-section in its hanging-wall to include Katherine Group strata. Offset along this structure may amount to about 6 kilometres, but there is little control on projected hanging-wall cutoffs or on the dip of deep footwall strata. This fault has a small splay that repeats the Little Dal Group Upper Carbonate formation. The second fault is a continuation of the Cache Lake fault from previous sections, and here cuts down-section in its hanging-wall through the Katherine Group, repeating Katherine Group and Little Dal Group strata. The third fault probably connects with the Cache Lake fault. Dip-slip along this structure is at least 5 km, with a stratigraphic separation of about 2.5 km, because the fault emplaces Proterozoic strata above Devonian clastic rocks. In this vicinity, the Cache Lake fold is not present. The Little Dal Group Grainstone formation is only tens of metres thick in this section, compared to hundreds of metres in the sections to the northwest.

Regional cross-section In addition to the detailed sections summarised above, MacDonald (2009) constructed a 50 km-long section extending beyond the area mapped (Fig. 5-12) both to the southwest (16.25 km), to include the Plateau fault, and to the northeast (17.6 km), across the Shattered Range anticline. With minor modification, this work has been integrated into regional cross-section B (as segment B3B4 of Fig. 5-4; accompanying cross-sections NWT Open File 201018) of the regional cross-sections. For details of the construction of segment B3-B4, estimates of shortening, and presentation of fault trajectories in a stratigraphic framework, see MacDonald (2009).

Interpretation Based on measured bedding-line length at the top of the Little Dal Group Basinal assemblage, shortening across the Ten Stone structural complex is calculated at 7.35 km or about 14.8 percent

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across the regional section (excluding Plateau fault; cross-section B (segment B3-B4; Fig. 5.4; accompanying NWT Open file 2010-18). In the Ten Stone Range complex, multiple detachments are required to explain the geometry of surface structures. Using a profile of the Shattered Range anticline, MacDonald (2009) calculated a depth to detachment beneath the northeast end of his section of about 11 km below sea-level. This would place the detachment beneath the extrapolated Tsezotene(?) Formation. The detachment in the Gypsum formation, which carries the Plateau fault and some other faults in the Ten Stone Range complex, is at a much higher stratigraphic and structural level, about 3 km below sea-level, beneath the western end of the profile. It is evident that the Plateau fault or splays from it played only a minor role in the formation of the Ten Stone Range complex; many structures in the complex root not in the Gypsum formation but at deeper stratigraphic levels such as the lower Little Dal Group, the Katherine Group, or even deeper. Stratigraphically, the restored section of MacDonald (2009) displays evidence for the Mackenzie arch, first proposed by Gabrielse (1967) and supported by Aitken et al. (1982), whereby Proterozoic units thicken and have a steepening dip toward the southwest [as much as 7-13o as indicated on the restored section of MacDonald (2009)], and thin to the northeast by progressive truncation beneath the sub-Upper Cambrian unconformity. It is possible that localisation of the complex structures of the Ten Stone Range complex may have been influenced by this pre-existing dip prior to Cretaceous-Tertiary shortening (MacDonald, 2009). The Ten Stone Range complex is unique in that it features folding of an earlier thrust fault (the Cache Lake fault). The Cache Lake fold is the only fold of such complexity in the Mount Eduni map-area, and possibly in the Mackenzie Mountains.

Ramp-flat domain Geometry A large region immediately west of the Plateau fault (collective term used herein for north and south Plateau faults, described below) consists of weakly folded and faulted strata that are divided into numerous subdomains or zones based on structural attitude. Structures in the domains are either sub-horizontal (termed flats) or southwest-dipping (termed ramps). Moderate dips in the immediate hanging-wall of the Plateau fault, including the fault itself (zone 1; Fig. 5-3; 3-6 km across) give way southwest-ward to a broad region of sub-horizontal and structurally elevated strata (zone 2; 52 km at widest), which in turn changes abruptly to a narrow band with moderate to steep southwest dips (zone 3; 6 to 8 km wide; Figs. 5-17, 5-18 and 5-19). In the western Mount Eduni map-area (NTS 106A), this pattern is complicated by the Shale Lake fault, in which the hanging-wall forms a band of variable extent comprising subhorizontal strata (zone 4; up to 9 km wide) flanked by strata with shallow southwest dip (zone 5; Fig. 5-20). In the southern Mount Eduni map-area, the ramp-flat geometry previously described (i.e., zones 2 and 3) is flanked by another flat (zone 6; 16 km wide) and narrow ramp (zone 7; 90° bend in structural trend outlined by fold trends in the southwestern Sekwi Mountain map-area (NTS 105P) is dramatically displayed across the central Niddery Lake map-area to the west (NTS 105O). Southeast-trending structures appear to be refolded along east-west axes. Cecile (2000) attributed this geometry to right-lateral drag along the Macmillan-Hess strikeslip fault system (Abbot and Turner, 1991; Roots, 2003) and indicates post-Triassic to possibly Tertiary displacement. Abbott (1982) first suggested Devonian fault control of depositional patterns in the same region. A fundamental basement(?) weakness, expressed as faulting in the Devonian, may have been reactivated during Mesozoic contraction to produce the Hess River strikeslip fault system and the peculiar re-folded geometry. To the west, the strain is expressed as faults at the surface. To the east, in the Sekwi Mountain map-area, where the strain decreases as the bend in structural trend diminishes, such faults (if at depth) do no penetrate the cover.

5.2.6. Age of deformation In general, pulses of sedimentation in the foreland basin of the fold and thrust belt can be a proxy for timing of structural deformation and elevation of topography in the belt. In the northern Canadian Cordillera, two main pulses, in mid-Cretaceous and latest Cretaceous to Paleocene time, were separated by an episode of quiescence [Wheeler and McFeely (1991), cf. Dixon (1999)]. If the associated sediment is fluvial and immature, one might assume a closer proximity to the mountain front than if they are marine. At specific localities, the age of deformation can be bracketed between the age of youngest involved strata and that of any cross-cutting relationships. In the inner belt, deformation is bracketed as post-Triassic, based on exposure of involved Upper Triassic strata in nearby areas (Cecile, 2000; Gordey and Anderson, 1993), and pre-midCretaceous, by the truncation of thrust faults and folds by midCretaceous plutons (southwestern Sekwi Mountain map-area; NTS 105P). The plutons have K-Ar cooling ages with a mean of about 92 Ma (approx. Turonian) and a range of about 100-86 Ma (Cenomanian to Coniacian; Canadian Geochronology Database, 2010)2. In the inner belt, about 140 km to the southwest, rare occurrences of Lower Cretaceous strata, disconformably overlying Triassic and older rocks, suggest that deformation can be more tightly bracketed to before the late Early Cretaceous (Gordey, 2008). In the outer belt, 65 km northeast of the mid-Cretaceous plutons, tightly folded Cretaceous rocks in the central Sekwi Mountain map-area (Fig. 5-27) are confined to a fault-bounded panel. Identification of a combination of pollen and leaves suggests a post-Berriasian, probably Barremian to Albian age for most of the section (Chapter 3.9). Regional considerations suggest that the section is part of a mid-Cretaceous pulse of sedimentation, which began abruptly in Late Aptian time (cf. Dixon, 1999). Within these constraints, the Cretaceous sedimentary units in the central Sekwi Mountain map-area were deposited immediately before or synchronously with intrusion and cooling of the Cretaceous plutons. Deformation and uplift had reached the margin of the inner belt by Aptian-Albian time. The fluvial origin of the Cretaceous sedimentary units (Chapter 3.9) also suggests that the mountain front was nearby to the west, or perhaps that the area was in an intermontane setting. It is probable that at about this same time (i.e., Aptian-Albian), low-angle extensional faulting produced structural conditions favourable for sedimentation(?) and preservation of the Cretaceous strata. The younger age limit of the folded Cretaceous section in central Sekwi Mountain map-area is not well constrained. A single collection of leaves from high in the section suggests an age no younger than Campanian, and probably not as old as Cenomanian (Chapter 3.9). It can only be said with confidence that deformation had passed through the central Sekwi Mountain map-area by post-Albian time. There is no suggestion of earlier deformation. For example, where Cretaceous sedimentary units (Fig. 5-27) rest unconformably above thin-bedded chert correlated with the Permian Fantasque Formation, the contact is concordant. Aitken et al. (1982) related coarse clastic Paleocene strata near the present front of the Mackenzie Mountains [Carcajou Canyon (NTS 96D) and Fort Norman (NTS 96C) map-sheets] to Late Cretaceous - Paleocene formation and rise of the fold mountains of the ‘outer belt’ (fold domain of this report).

2 Based on sample 51 isotopic ages on granitic rocks from Geological Survey of Canada’s Canadian Geochronology Knowledgebase, for the region 62.30°-63.35° N and 128.50°-130.3° W (from NTS 105I, 105J and 105O) immediately southwest and south of Sekwi Mountain map-area, March 2010.

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Chapter Five In summary, contractional deformation had progressed eastward to the edge of the ‘inner belt’ by mid-Cretaceous time (approximately 92 Ma) but did not affect the fold domain until latest Cretaceous-Paleocene time. Deformation in the intervening fault-fold and ramp-flat domains is crudely constrained to have occurred after the Albian, up to and including the latest Cretaceous to Paleocene. If deformation was episodic rather than continuous, it is possible that deformation in the fault-fold and ramp-flat domains was entirely of latest Cretaceous-Paleocene age. The Cretaceous extension inferred above would fit between the contractional pulses. As Aitken et al. (1982) noted, the rise of the Plateau sheet has left no stratigraphic record by which the timing of its displacement may be definitively determined.

5.2.7. Structural synthesis Regional setting The central Mackenzie Mountains are underlain by Neoproterozoic and Paleozoic strata that were deposited along the western ancestral margin of North America, which subsequently formed part of the northern Cordilleran foreland fold and thrust belt. Eastward-migrating deformation in latest Early Cretaceous to Paleocene time was driven by accretion of exotic terranes that now overlap the western preserved parts of the margin. Paleozoic paleogeographic elements include expanses of variably subsiding shallow platforms flanked to the west and north by deeper-water basins. The platforms include competent clastic and carbonate strata that have generally been deformed into open to locally tight folds or cut by thrust faults. Basinal areas accumulated thinnerbedded, incompetent, fine clastic rocks and chert that are commonly cleaved and tightly folded. In the central Mackenzie Mountains, metamorphic grade is sub-greenschist facies, sedimentary structures and fossils are well preserved, and cleavage is generally lacking. Deformation was accommodated through bed-parallel slip.

Structural domains and levels of detachment The dominant structure of the central Mackenzie Mountains is the east-verging Plateau fault, which developed along a weak regional detachment in gypsum and shale of the Proterozoic Little Dal Group. To the northeast, in its footwall, is a narrow, relatively complicated zone of folds and thrust faults, the Ten Stone structural complex. Still farther to the northeast, regional structure is dominated by large-scale, symmetrical, flat-topped, box anticlines with strike-lengths of up to several hundred kilometres. Limb dips approach 60°. The intervening synclines are cored by thin-bedded Devonian clastic and carbonate rocks that display small-scale, locally tight folds. Southwest of the Plateau fault is a broad plateau, which is more pronounced in southern sections, of sub-horizontal Proterozoic to lower Paleozoic strata (Redstone Plateau) flanked to the southwest by a ramp of steeply west-dipping Paleozoic rocks. Southwest of the plateau and ramp, structures are dominated by regional synclinoria (Godlin Lakes and Caribou Pass synclinoria) that flank a central anticlinorium (June Lake anticlinorium). These regional folds are cut by numerous east- and west-dipping thrust faults with offsets of up to 6 km, and with vergence consistent with structural position (i.e., faults dip towards cores of synclinoria). The unique preservation of a

narrow panel of Cretaceous strata in the Godlin Lakes synclinorium is attributed to low-angle extensional faulting that accompanied Cretaceous-Tertiary contraction or that occurred during an interval of relaxation within the overall contractional regime. Several levels of detachment are suggested in the conceptual parts of the cross-sections (i.e., beyond limits of coloured fills). On the northeast, a basal detachment for deformation is indicated at about 12 to 7 km below sea-level (cross-sections A and B, respectively, of Fig. 5-4) based on excess-area calculations for the Shattered Range and Tawu anticlines. The results, although imprecise, suggest that the detachment is relatively deeper beneath section A than B, which is in keeping with the narrower width and lower amplitude of structures in the latter. This detachment is projected sub-horizontally westward (with the exception of the ramp discussed below). Given that crystalline basement is substantially deeper (?30 km; Fig. 5-2b), the detachment is not at the crystalline basementsedimentary rock interface (as in Cecile and Cook, 1981), but within the sedimentary succession. The base of the Pinguicula Group (sequence A3, Fig. 5-2b) may be near the appropriate depth, and if Racklan deformation is present, would provide a flat horizon for detachment, as opposed to deformed beds beneath. The next structurally higher detachment is in the Proterozoic Tsezotene Formation. This would accommodate folds and thrust faults in the Ten Stone structural complex that affect strata of the Katherine and Little Dal groups (MacDonald, 2009). Still higher is that in the Rusty Shale/Gypsum formations of the Proterozoic Little Dal Group, which form the immediate hanging-wall of the Plateau fault. A still higher detachment, perhaps in incompetent shale of the Proterozoic Twitya or Sheepbed formations, is proposed to accommodate shortening that formed the Godlin Lakes and Caribou Pass synclinoria. The intervening, northwest-diminishing, June Lake anticlinorium may have formed at a ramp joining this detachment with that in the Little Dal Group. In the southwestern parts of the sections, higher detachment(s) in incompetent lower Paleozoic strata seem to be required to accommodate the relatively tighter structures present in those areas.

Plateau fault detachment sedimentary versus structural ramps The Plateau fault is unique in the Mackenzie Mountains for its great strike length, its postulated offset, and its possibly related features (i.e., the ramp and plateau). Its origin and significance are enigmatic [e.g., Cecile and Cook (1981); Gordey (1981); MacNaughton et al. (2008a)]. The Plateau fault has been termed an overthrust with overlaps of up to 35 km, and features such as the ramp and plateau are implicitly related (Cecile and Cook, 1981; Cecile et al., 1982). The controversy over the amount of offset or overlap is partly based on how strata in the footwall of the fault are projected westward to intersect the west-dipping hanging-wall in the subsurface. The sections presented here provide a new interpretation that has several regional implications. It is suggested that the initial stratigraphic configuration before deformation played a fundamental role in development of the Plateau fault. The Mackenzie arch (Fig. 2-5) is the locus of coalescing unconformities and dramatic thinning of late Proterozoic to mid-Paleozoic formations. The Gypsum and Rusty Shale formations of the Proterozoic Little Dal Group (i.e., the Plateau fault detachment) were therefore originally at much deeper levels to the southwest than to the northeast, at the position of the Mackenzie

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Chapter Five arch. These incompetent formations formed a favourably oriented, westdipping “sedimentary ramp” that accommodated regional detachment. Where displacement along the detachment reached the Mackenzie arch, dip of the “sedimentary ramp” flattened markedly and displacement broke through overlying units to be expressed as the Plateau fault. Minor displacement continued along the detachment to form some structures of the Ten Stone structural complex. Based on this interpretation, offset along the Plateau fault may be much less than previously proposed. However, in the absence of known stratigraphic cutoffs in the hanging-wall, only a minimum (about 6 km) can be suggested for the sections as drawn. In contrast, Cecile and Cook (1981) projected Devonian strata westward for long distances beneath the Plateau fault. Geometric constraints along all sections (particularly section A) show this interpretation to be implausible, as indicated also in MacNaughton et al. (2008). The present interpretation implies that the ramp and plateau geometry (Redstone Plateau) are unrelated to the Plateau fault detachment.

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In a situation where a detachment maintains a constant depth and a fault cuts upward from it to emplace older over younger strata, a flat plateau may develop. The structural height of the plateau is equal to the thickness of duplicated strata (stratigraphic separation). For the Redstone Plateau, however, there is minimal stratigraphic separation or structural elevation related to the Plateau fault detachment. Therefore, eastward translation across a deeper ramp (probably in the basal detachment) must have occurred to account for the structural elevation of thick Paleozoic strata ‘up-and-over’ the Redstone Plateau. The projected eastward dip and taper of the Paleozoic wedge (projected lines in cross-section C in Fig. 5-4) are an artefact of inversion of the originally west-dipping “sedimentary ramp” after eastward translation. Gordey (1981) noted that shortening across the Mackenzie Mountains east of the Mackenzie arch was of an amount sufficient to restore the position of the Mackenzie arch to this ramp, and suggested that this ramp may ultimately be basement-controlled.

Chapter Six

Chapter Six M  etamorphism and Thermal Maturity Citation: Martel, E., MacNaughton, R.B. and Fischer, B.J., 2011. Chapter 6. Metamorphism and Thermal Maturity; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 251 to 254.

6.0. Introduction Rocks in the study area are predominantly of sub-greenschist facies. In terms of regional metamorphism, metamorphic mineral assemblages (with the possible exception of sheet silicates, which are difficult to assess) are poorly developed. Evidence for contact metamorphism is present around Cretaceous granodiorite plutons (Chapter 4.3). The relatively low metamorphic grade of much of the study area leaves open the possibility of a viable hydrocarbon system (e.g., Cecile et al., 1982). One activity of the Sekwi project dealt with the hydrocarbon potential of the Plateau fault (Chapter 8). It was also considered important to constrain the thermal maturity of strata in the study area and in surrounding map sheets.

6.1. Thermal Maturity Published data on the thermal maturity of the study area are sparse. A small suite of samples (Arnica, Bear Rock, and Headless formations) was analysed by Cecile et al. (1982) for pristane/nC17 and saturate/aromatic ratios. The results suggested that the samples were mature to over-mature with respect to oil, but were equivocal due to storage and weathering effects. Rock-Eval pyrolysis yields poor results for most units in the study area. In their study of the hydrocarbon potential of the Plateau fault, MacNaughton et al. (2008a) reported that over half of the Proterozoic to Middle Devonian samples they analysed returned TOC values lower than 0.3%, rendering the resulting Tmax values suspect (e.g., Fowler et al., 2003). Most samples with sufficiently high TOC values were deemed unreliable because they returned S1 or S2 values lower than 0.2 mg HC/g rock, or displayed a bimodal S2 peak (e.g., Peters, 1986; Fowler et al., 2003). For explanation on abbreviations used in this Chapter and detailed results see Appendix G. Upper Devonian strata fared somewhat better under Rock-Eval pyrolysis. Although MacNaughton et al. (2008a) reported that Hare Indian and Imperial formation samples all returned S2 values too low for reliable Tmax determination, the Canol Formation yielded Tmax values suggesting that it has reached the dry-gas-generating zone in NTS 95M and 105P. Feinstein et al. (1988, 1991) reported a single analysis from the Imperial Formation in the northwest corner of NTS 95M, which indicated that the sample (Tmax > 464; %Ro >1.40) was overmature with respect to oil generation but not gas generation. Data from fossils help significantly to constrain the thermal maturity of the region. Ediacaran and earliest Cambrian acritarchs (organic-walled microfossils) documented by Baudet et al. (1989) from sections near Shale (Palmer) Lake, June Lake, and Sekwi Brook (Fig. 1-3) were re-examined by Utting (2007b). The acritarchs are uniformly black and metallic, indicating Ro% equivalent values of 4-5, and thus a maximum temperature of >360°C for these strata. MacNaughton et al. (2008a) presented a preliminary compilation of thermal maturity data from conodonts and palynomorphs in the

central Mackenzie Mountains, compiled from unpublished GSC paleontology reports and published sources. In their report, thermal maturity data from conodonts (CAI), palynomorphs (TAI), and acritarchs (AAI) were converted to equivalent vitrinite reflectance (Ro%) values. The compilation included some data generated during the early part of the Sekwi project. The compilation for Upper Cambrian to Middle Devonian strata (Fig. 6-1) illustrates the main regional trends, with thermal maturity increasing to the west and south. In NTS 95M, Ro% values are above 1.2 and less than 2.0, suggesting Tmax not greater than 300° C and possibly less than that. In northeastern NTS 105P, Ro% values do not exceed 2.0, but in the southwestern and southern parts of the map-area Ro% values approach 4.0 (indicating Tmax 360°-500° C). Some conodont samples from NTS 106A (M. Orchard, pers. comm.) have yet to be incorporated into the earlier compilation. These suggest that temperatures affecting Upper Cambrian to Middle Devonian strata in the southwestern part of that map-area exceeded the dry gas preservation limit (i.e., Ro% equivalent values >3.0) but that thermal maturity northeast of the Sayunei Range (Fig. 1-3) is lower (Ro% equivalent values of 2.0 or less, and in the dry gas zone). MacNaughton et al. (2008a) also presented a regional compilation of fossil-derived thermal-maturity data for Upper Devonian strata (Fig. 6-2). The compilation showed similar trends in thermal maturity to those displayed by older strata, with higher maturity to the west and south, but sample control was lacking in the southern part of NTS 95M and 105P and for most of 106A. To some extent, however, these regional trends are supported by the work of Feinstein et al. (1988, 1991), who reported Rock-Eval results for a small number of samples from NTS 96D and 106A that suggested the thermal maturity of Upper Devonian strata decreased to the north. Focussing on the Sekwi project area, participants collected 53 conodont and six palynomorph samples that provided both age and maturity data (Appendix F; Fig. 6-3). These samples were all from the Mackenzie Platform or from strata of the overlying clastic basin (position of the Mackenzie Platform margin is shown in Figures 6-1 and 6-2). Devonian and older samples in the Sekwi project area typically have CAI values of 4 to 5.5 (5 of 51 have lower values, reported as 3-4, and one has a surprisingly low value of 1.5; blue circle on Fig. 6-3a). A late Fammenian (latest Devonian) sample returned a CAI value of 2.75 (large green circle). Two Bashkirian (late Carboniferous) samples have CAI of 2.5 (blue circle) and 2.75 (dark green circle). These results are similar to those presented by Morrow et al. (1990) from southeast of the project area (NTS 95F and 95G), where Devonian conodonts have CAI values of 4 to 5 but Carboniferous conodonts have CAI equal to 1.5, and Carboniferous palynomorphs show TAI equivalent to CAI of 3 or less. Morrow et al. (1990) inferred a late Devonian (post-Nahanni Formation) regional thermal event, which is supported by the Sekwi project data. Sekwi project data may constrain the timing of this event more tightly as post-middle Fammenian and pre-late Fammenian, although the younger age limit is defined by only one sample.

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Chapter Six

Figure 6-1. Thermal maturity, based on fossil data, of Upper Cambrian to Middle Devonian strata of Mackenzie Platform and Selwyn Basin. Thermal maturity beyond the dry gas preservation limit is indicated by %Ro values greater than 3.00. Values between 1.36 and 2.99 are within the dry gas zone but are overmature with respect to oil. Values less than 1.35 may have remaining oil potential. Conversion of conodont alteration index (CAI) and palynological thermal alteration index (TAI) data to %Ro values was based upon equivalencies determined by Utting et al. (1989). Figure reproduced from MacNaughton et al. (2008).

Figure 6-2. Thermal maturity, based on fossil data, of Upper Devonian map units (Hare Indian, Canol, and Imperial formations and time-equivalent strata). See Figure 6-1 for explanation of %Ro values. Figure reproduced from MacNaughton et al. (2008).

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Chapter Six

Figure 6-3 (a). Thermal maturity data from Sekwi project, of Ordovician to Carboniferous strata in the Mackenzie Platform and Selwyn Basin. Sample locations symbolised by conodont alteration index (CAI) or palynomorph thermal alteration index (TAI), as appropriate, and labelled with fossil age determinations.

253

Chapter Six

Figure 6-3 (b). The same samples as Figure 6-3a at a scale comparable to that of Fig. 6-1 and 6-2, symbolised by maximum equivalent vitrinite reflectance, which was calculated from CAI and TAI according to the equivalencies determined by Utting et al. (1989).

6.2 Regional Metamorphism The regional metamorphic grade is low and rocks in the Sekwi project area are of sub-greenschist facies. The maximum depth of burial just south of the Sekwi project area (NTS 105I) was estimated at less than 5 km for the Silurian-Devonian Steel Formation and less than 10 km for the Precambrian to Lower Cambrian Hyland Group, the latter correlating to a maximum pressure of about 2.8 kbar (Gordey and Anderson, 1993). Although the southwestern part of NTS 105P was not mapped during this project, observations there showed that siliciclastic rocks of the Earn Group and Lower Paleozoic units are locally foliated. The fabric varies from a slaty cleavage to a dissolution cleavage defined by pressure solution and growth of fine-grained mica. Cretaceous intrusive rocks (Chapter 4.3) are exposed in the southwestern corner of NTS 105P. No mapping was conducted in the vicinity of these plutons during this study. The following description is based on Blusson (1971), Turner (1981), Anderson et al. (1983), and Gordey and Anderson (1993). The plutons intrude the Lower Cambrian Vampire Formation, the Lower Ordovician to Lower Silurian Duo Lake Formation, and the Upper Devonian to

254

Mississippian Prevost and Portrait Lake formations. These rocks are mainly siliceous and calcareous shale and siltstone. Contact aureoles in these non-calcareous country rocks extend up to 3 km from the plutons and are rusty due to oxidized pyritiferous alteration. The first appearance of andalusite ± biotite is within the rusty zone, 500 m or less from the contact. Where the plutons intrude carbonate rocks 10 to 50 km south of the Sekwi project area (NTS 105I), a rusty contact zone has developed within the pluton, and aureoles appear to preserve primary layering as alternating green diopsidic layers and brown garnetiferous layers, although rare diopsidegarnet-plagioclase skarns cross-cut primary layering. The presence of andalusite and the known stratigraphic thicknesses in NTS 105I indicate an epizonal to mesozonal emplacement depth of 3.3 to 11.6 km. Pressure during pluton emplacement was no greater than 3.5 kbar (Gordey and Anderson, 1993).

Chapter Seven

Chapter Seven M  ineral Deposits and Prospects Citation: Ootes, L., Fischer, B.J., Rasmussen, K.L., Borkovic, B., Long, D.G.F. and Gordey, S.P., 2011. Chapter 7. Mineral Deposits and Porspects; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) mapareas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 255 to 268.

7.0. Introduction

7.1.1. Coates Lake

There are over 300 known mineral deposits and prospects in the Mackenzie and Selwyn mountains of the Northwest Territories (NORMIN, 2010). This chapter reviews the exploration history of some of the most significant of these, then provides detailed descriptions of the various deposit types known to be present in the study area. At least five end-member deposit types are known in the Mackenzie and Selwyn mountains of the Northwest Territories: (1) intrusion-related (including tungsten and base-metal skarns and gem minerals); (2) sedimentary exhalative (SEDEX) Zn-Pb; (3) carbonate-hosted Zn-Pb; (4) red-bed or Kupferschiefer-type Cu; and (5) stratiform iron in iron formation (Ootes and Falck, 2008). Of these, showings of three deposit types are present within the Sekwi study area: intrusion-related skarn (tungsten), carbonatehosted Zn-Pb (+ Cu and other metals), and Kupferschiefer-type Cu (Chapter 7.2). In addition, subordinate types of mineralisation (Chapter 7.2) and a newly discovered occurrence of green beryl (Mercier et al., 2008; Chapter 7.3) are present in the study area (Figs. 7.1-1 and -2; NORMIN, 2010). NORMIN ID numbers are from the NTGO's NORMIN Showings database and can be can be used with the Showings search utility in the GoMap or GoData application at www. nwtgeoscience.ca, to access the publicly available industry exploration reports (“assessment reports”) and published references pertinent to each mineral showing. Yukon MINFILE numbers are from a database of mineral showings available on request from the Yukon Geological Survey (www.geology.gov.yk.ca).

The Kuperschiefer-type Cu (+Ag) Coates Lake prospect (NORMIN ID 095LNE0007) is significantly south of the project area, approximately 190 km west of the community of Wrigley. It was first discovered and staked in September 1961 by prospectors W.J. Mackenzie and D. Munro, employees of Redstone Mines Limited (Jory, 1962). The showing was found by tracking soil geochemistry samples along the streams (Jory, 1962). Redstone Mines conducted detailed mapping of the claims and drilled 45 diamond drill holes totalling about 7,000 m. Exploration also included geophysical surveys, a geochemical drainage survey and soil and silt sampling programs (NORMIN, 2010). Dr. J.A. Coates was integral in identifying the significance of the copper deposits, but was killed in a plane crash in 1968. In 1970, the property was optioned to Cerro Mining Company of Canada Limited, which conducted further exploration and drilled three holes, but ultimately dropped the option (NORMIN, 2010). In 2005, Lumina Resources Corporation (Lumina) completed a GIS-based compilation of all available relevant data pertaining to the Redstone copper belt and specifically the mining leases at Coates Lake (Lumina, 2006). In addition, Lumina completed a regional geological evaluation of the Redstone copper belt that included a structural and stratigraphic assessment of the broader Coates Lake area and sampling of the copper-bearing unit from Coates Lake north to the Keele River. This work culminated in the staking of 55 new claims in 2005 and 2006 (Lumina, 2006). In November 2006 Lumina was acquired by Western Copper Corporation, which now holds 100% of the Coates Lake claims (Western Copper Corp., 2008). The historic mineral resource estimate for Coates Lake made by Shell Canada Resources Ltd. in 1977 is 33.6 million tonnes grading 3.92% Cu and 9 grams/tonne Ag (Hitzman et al., 2005).

7.1. Exploration History of Significant Mineral Deposits of the Northwest Territories Cordillera B. Borkovic

The geological history of the Mackenzie Mountains has been documented by Gabrielse and Yorath (1991). The first geological information regarding the northern Cordillera was provided when G.M. Dawson and R.G. McConnell led a reconnaissance survey into the area in 1887-88. In 1908, Joseph Keele traversed the Mackenzie Mountains along what is now the Keele River, providing the only transect of the Mackenzie Mountains until the GSC conducted Operation Mackenzie, a regional mapping project directed by R.J.W. Douglas in 1957 (Price, 2007). The construction of the Canol Road in the early 1940s provided access to the Mackenzie and Selwyn mountains and opened up this frontier to mineral exploration. The following is a brief overview of the mineral exploration history of significant deposits in or near the Sekwi project footprint.

7.1.2. Jay The Kuperschiefer-type Jay copper prospect (NORMIN ID 095LNE0001) is in the Sekwi project area and is in the same belt of copper mineralisation that hosts the Coates Lake deposit, but 140 km farther north (Ruelle, 1976; Hitzman et al., 2005; Ootes and Falck, 2008). In 1963 and 1965-66, reconnaissance geological mapping by the GSC discovered local copper mineralisation in the Redstone River Formation in NTS 95M/13 (Ruelle, 1976). This resulted in Shell pursuing an exploration program at the Keele River. In 1975, Shell conducted a stratigraphic mapping program on Prospecting Permit 361 and was successful in identifying the Jay and June Creek showings. In 1976, Shell drilled 13 holes on the Jay showing and 5 holes on the June Creek showing as part of a 9,626 m, 41diamond drill-hole program on the property, and encountered only minor copper mineralisation (NORMIN, 2010). The permit lapsed but the ground was re-acquired in the mid-2000s by Freeport-McMoRan Inc. A historic resource estimate of 1.2 million tonnes at 2.7% Cu is reported for the Jay prospect (Hitzman et al., 2005).

255

Chapter Seven

132°W

130°W

66°N

128°W Norman Wells

Crest

65°N 126°W Tulita

Gayna River

T W N T Y

Bear-Twit

64°N 124°W

Jay Wrigley

Mactung

63°N

Howard's Pass Lened

Coates Lake 122°W 62°N

Geology Cretaceous to Tertiary sedimentary rocks Cretaceous plutonic rocks

Fort Simpson

Tungsten

Carboniferous sedimentary rocks Undivided Devonian to Carboniferous sedimentary rocks Devonian sedimentary rocks Undivided Cambrian to Devonian sedimentary rocks Cambrian sedimentary rocks

Nahanni Butte 61°N

Undivided Proterozoic to Paleozoic sedimentary rocks Undivided Proterozoic to Cambrian sedimentary rocks T NW T Y

Neoproterozoic sedimentary rocks Mesoproterozoic to Neoproterozoic sedimentary rocks Mineral Occurrences Fault: normal; thrust; undefined (pendant on hanging-wall side)

Community Canol Heritage Trail

0

20

40

60

80 100

Fort Liard

Kilometres

Figure 7.1-1. Geological map of the Mackenzie Mountains on shaded relief map with known mineral prospects indicated. Showings discussed in chapter 7.1 are highlighted by orange star. Note that only showings from the northern part of the mountains are discussed and highlighted.

256

Chapter Seven 132° 65°

128° 65°

Mineral Occurrences Carbonate-hosted Zn-Pb Shale-hosted Barium (SEDEX?) Coal Red-bed/kupferschiefer-type Cu New mineral occurrence Regional Geology Mesozoic Foreland Basin Cretaceous Intrusions Upper Paleozoic Siliciclastic/ Carbonate Shelf Upper Paleozoic Siliciclastic Basin Lower Paleozoic Selwyn Basin Lower Paleozoic Mackenzie Platform Neoproterozoic Extension and Rift-related Successions (Windermere Supergroup) Proterozoic Epicratonic Basin (Mackenzie Mountains supergroup) Fault, undefined NWT - Yukon border

64°

64°

10

5

0

10

20

Kilometres

63° 132°

63° 128°

Figure 7.1-2. Geological map of the Sekwi study area with known mineral prospects highlighted, including those discovered during the Sekwi mapping project. See Table 7.3-1 and Appendix H for detailed descriptions and locations.

257

Chapter Seven A number of other Cu-bearing prospects are present throughout the region in an arcuate belt stretching north from Coates Lake to the Keele River, and significant prospecting work throughout the 1960s and 1970s helped to drive interest in the potential value of this district (NORMIN, 2010).

7.1.3. Gayna River Gayna River (also referred to as RT; NORMIN ID 106BNE0014) is one of a number of carbonate-hosted Zn-Pb showings to the northwest of the Sekwi project area. During the exploration boom of the 1970s, numerous zinc-lead showings were discovered in a 250 x 50 km “zinc belt” of Proterozoic to Devonian carbonate rocks in the Backbone Ranges of the Mackenzie Mountains (Sharp et al., 2005; Dewing et al., 2006). The most significant of these discoveries was the Gayna River zinc-lead deposit. Rio Tinto Canadian Exploration Ltd. (Rio Tinto) prospected and geologically mapped the property in 1975 (Sanguinetti et al., 1975; Hewton, 1982), and drilled 28,000 m in over 177 holes between 1975 and 1979 (Sharp et al., 2005). Typical breccia zones, still open in most directions, include historical resource estimates of: 56,300 tonnes of 14.52% Pb-Zn, 95,300 tonnes of 9.85% Pb-Zn, and 1,066,800 tonnes of 4.51% Pb-Zn (Hewton, 1982), but this cannot be properly evaluated without modern reserve estimates. Welcome North Mines Ltd. was also active in the region at that time and discovered many of the Gayna River showings (Sharp et al., 2005). Despite promising results, interest in the zinc belt waned in the 1980s as commodity prices declined, leading to the abandonment of all mineral titles by the original owners (Sharp et al., 2005). Eagle Plains Resources Ltd re-staked the Gayna River deposit in 2000. In 2004, Eagle Plains acquired five prospecting permits and staked several claim groups to secure mineral titles to many of the showings in the belt (Sharp et al., 2005). During 20052008, Eagle Plains undertook field work to re-examine the major showings. Prospecting and geophysics uncovered new exploration targets (R.J. Sharp, personal communication, 2008).

7.1.4. Bear-Twit The carbonate-hosted Bear-Twit Zn-Pb (+Ag) showing (NORMIN ID 106ASW0002) was discovered in 1972. Following prospecting work by Pete Risby, the BEAR claims were optioned by Arrow Inter-America Corporation in 1972 and then by Welcome North Mines Ltd. in 1973 (Brock, 1973b). The adjoining TWIT claims were also acquired by Welcome North to cover the possible extension of mineralisation present on the Bear claims (Brock, 1973b). Both blocks were optioned to Cominco Ltd. in the spring of 1973. Cominco prospected, mapped, sampled, and drilled the showings on the main zone (NORMIN, 2010) and deeper drilling in 1974 led to the discovery of significant zones of mineralisation at depth. The property was optioned by Bethlehem Copper Corporation in 1975, who conducted further drilling before dropping the option in 1976. Twenty-one drill holes through the main showing in 1973-1976 intersected numerous high-grade zones, including 23 m of 15.75% Zn, 11.16% Pb, and 4.16 oz/T Ag (Bagshaw, 1974), but the mineralisation was deemed too patchy to warrant further work (Bellamy, 1976). The Bear-Twit property was visited in 2005, when it was assessed as an attractive exploration target (Dewing et al., 2006).

258

7.1.5. Howard’s Pass The Howard’s Pass SEDEX Zn-Pb (NORMIN ID 105ISW0018, Yukon MINFILE ID 105I 012) district is southwest of the study area, in the Selwyn Basin. Geochemical surveying and geological mapping programs in 1968, 1971, and 1972 identified possibly significant lead-zinc mineralisation in the Howard's Pass area that was staked by Canex Placer Ltd. (Canex) in 1972 as the X claims in Yukon and the Y claims in Northwest Territories (NORMIN, 2010). In late 1972, Canex constructed a winter access road, airstrip and tote roads, and conducted extensive trenching, mapping, grid soil testing, and geophysical work. In 1973-74 Canex drilled 38 holes totalling 6241 m (Yukon MINFILE, 2008). In 1975 Canex entered a joint venture with Essex Minerals, drilling 61 holes totalling 14,960 m over the next two years (NORMIN, 2010). Underground drilling in the early 1980s led to the delineation of a historical indicated resource at the XY deposit of 59 million tonnes grading 2.1% lead and 5.4% zinc, including a high-grade zone of 8.2 million tonnes grading 5.5% lead and 10.6% zinc (NORMIN, 2010). A historical resource estimate of 55.4 million tons grading 5.3% zinc and 1.8% lead was given for the Anniv deposit. In 2005 Selwyn Resources Ltd. acquired the Howard’s Pass property and between then and 2008, spent more than $45 million on exploration, including over 88,000 m of drilling. Selwyn Chihong Mining Ltd., the owner as a result of a 2010 partnership, puplished an indicated resource for their property, consisting of several deposits, of 180.69 Mt @ 5.25% Zn and 1.83% Pb (Falck and Gochnauer, 2011).

7.1.6. Crest The Crest stratiform iron formation and associated iron deposit (NORMIN ID 106FSE0002, Yukon MINFILE ID 106F 008) straddles the Northwest Territories - Yukon border in the far northwestern Mackenzie Mountains, approximately 290 km west of Norman Wells and significantly northwest of the Sekwi project area. The Rapitan iron formation is exposed over a strike length of 51 km, with stratigraphic thickness varying from 30 m in the Northwest Territories to up to 150 m in Yukon (NORMIN, 2010). A historic resource estimate of 5.6 billion tonnes of ~47% Fe has been made for the Iron Creek area in the Yukon, and there is a historic estimate of more than 10 billion tonnes for the region as a whole (Stuart, 1963; Gross, 1965; Yeo, 1984b). California Standard Company Ltd. discovered Crest in 1961, although hematite float in glacial till was well known in the area prior to the discovery (Yukon MINFILE, 2008). A total of 862 claims covering an area of about 240 square km were staked in June 1962 and transferred to a new subsidiary company, Crest Exploration Ltd., which conducted significant exploration work on the property and constructed an airstrip to facilitate the transportation of materials and personnel into and out of the site (Yukon MINFILE, 2008). The entire property was surveyed and taken to lease, and a feasibility study was carried out by Canadian Bechtel Ltd. in 196364. Two bulk samples totalling about 110 tonnes were shipped out for metallurgical tests. Sometime in the late 1970s to early 1980s, the property was transferred to Chevron Resources Canada, which holds Crest under mineral lease until at least 2014.

Chapter Seven

7.1.7. Mactung The Mactung tungsten property (NORMIN ID 105OSE0001) is located in the Selwyn Mountain Range and covers the area around Mt. Allan on the Yukon-Northwest Territories border, approximately eight km northwest of MacMillan Pass. The deposit is a Late Cretaceous intrusion-related tungsten skarn and contains a NI-43101 compliant resource measurement of 33 million tonnes @ 0.88% WO3; making Mactung the largest known tungsten deposit in the western world (North American Tungsten Corporation Ltd, 2008). Mactung was discovered in 1962 by James Allan, a geologist with Southwest Potash Corporation (Amax), during the course of the Ogilvie Reconnaissance Project (Allan, 1963). In the 1960s, Amax conducted surficial exploration work on the property and then in 1970 built an 11 km access road from the Canol Trail to improve access to the site, and drilled 61 holes over the next two years (NORMIN, 2010). By 1973 Amax began underground developments and collected a 272 tonne bulk sample for metallurgical testing (Brophy et al., 1984). Falling tungsten prices caused work on the project to stop in 1985. North American Tungsten Corporation Ltd. emerged as the owner of the Mactung deposit and Cantung mine in October 1997 after a series of sales and mergers throughout the late 1980s and 1990s. In the summer of 2008, North American Tungsten conducted a $3.2 million exploration program, which included infill, surface, and geotechnical drilling programs, as well as aerial photography and environmental surveys (North American Tungsten Corporation Ltd., 2008). The Mactung deposit is currently undergoing feasibility studies.

7.1.8. Lened The Lened (NORMIN ID 105ISE0003) skarn-related showing was first staked in 1960 by two geologists working for Canex Aerial Exploration Limited, who eventually allowed the claims to lapse after a two-hole diamond drill program returned sub-economic metal grades (Allen and Adie, 1960). Through the 1960s and 1970s, the property and several adjoining claims were held by a series of companies and prospectors, ultimately coming to be held by the Union Carbide Exploration Company, and by the end of 1982 a total of 168 holes (23,000 m) had been drilled, delineating an estimated historical resource of 750,000 tonnes grading 1.17% WO3 and 0.15% Cu (NORMIN, 2010). In 1996 Ron Berdahl re-staked the showing as the LENED 1-16 claims and TOY 1-12 claims. In 1997 colourless to pale "commongreen" beryl (emerald) crystals and more rare emerald-green beryl was discovered on the property. Sampling elsewhere returned gold values up to 1.023 g/tonne (Walton, 1998).

7.2 Mineral Deposit Types in the Sekwi Project Area Three major deposit types are known from the literature to be present in the Sekwi study area. Each is represented by numerous showings. Intrusion-related skarn (tungsten), carbonate-hosted Zn-Pb (+Cu and other metals), and Kupferschiefer-type Cu are discussed below. Subordinate types that are also discussed below

are coal, barite, shale-hosted zinc, and skarn-related gold. A deposit type newly discovered during this project, green beryl (emerald), is discussed in the next section.

7.2.1. Intrusion-related tungsten skarn L. Ootes and K.L. Rasmussen

The single most important mineral deposit in the Sekwi project area is Mactung (Fig. 7.1-1; Table 7.2-1), an intrusion-related tungsten (+ Cu) skarn deposit. Mactung, which straddles the YukonNorthwest Territories border, is the only intrusion-related mineral deposit or prospect identified in the Sekwi project area. It has an indicated resource of 33 million tonnes @ 0.88 WO3 (LaCroix and Cook, 2007) and an additional inferred resource of 11.3 Mt at 0.74% WO3 (North American Tungsten), and is therefore considered the largest tungsten deposit in the western world. Mactung is currently in the mine feasibility stage and, should it move to the mine stage, most of the operations would be conducted in Yukon. Mineralisation at Mactung is adjacent to, or above, typical Tungsten suite (94-98 Ma) intrusions: small, peraluminous, medium-grained, K-feldspar porphyritic, biotite-muscovite(garnet)-bearing monzogranite intrusions and associated marginal leucogranite, and aplite-pegmatite dykes (Fig. 7.2-1; Dick and Hodgson, 1982; Gerstner et al., 1989; Selby et al., 2003; Hart et al., 2004b; Rasmussen et al., 2007a; Yuvan et al., 2007). These intrusions are thought to have formed in a post-collisional, distal back-arc scenario, related to subduction-accretion on the western edge of North America (Mair et al., 2006; Rasmussen et al., 2007a). The skarn is hosted by Paleozoic (Lower Cambrian) carbonatedominated strata of the Sekwi Formation, and has been subdivided into scheelite-bearing anhydrous (pyroxene-garnet-pyrrhotite) and hydrous skarn facies (amphibole-pyrrhotite and biotite+/-pyrrhotite) by previous workers (Dick and Hodgson, 1982; Mathieson and Clark, 1984; Gerstner et al., 1989). Fluid inclusion results from mineralised samples indicate that mineralisation and anhydrous skarn began at temperatures of 410-470°C and evolved to hydrous skarn mineralisation at 360-415°C occurring between five to ten kilometres depth, with skarnification and mineralisation occurring simultaneously (Gerstner et al., 1989). This is similar to, although slightly cooler than, the temperature of mineralisation estimated for similar ore at the Cantung mine to the south (Yuvan et al., 2007). Other significant tungsten deposits and showings in the region, south of the Sekwi project area, include the high-grade Cantung mine deposit (1.51 Mt grading 1.27% WO3 indicated, including 1.02 Mt at 1.08% WO3 probable; 6.21 Mt at 1.56% WO3 recovered as of 2009; Fig. 7.2-1; Reid et al., 2009; Rasmussen et al., 2011) and the Lened deposit (0.75 Mt at 1.17% WO3; NORMIN, 2008), in addition to the Rudi, Cac, Clea, and Ivo mineral occurrences (NORMIN, 2010). The shared feature of these tungstenmineralised systems is their association with typically 96.5-98.5 Ma, multi-phase biotite ± muscovite monzogranitic rocks with leucocratic marginal phases (biotite-poor, with muscovite ± garnet or tourmaline) and abundant late-stage aplitic ± pegmatitic dykes of the Tungsten plutonic suite (Fig. 7.2-1). Aside from Cantung and parts of Lened, these mineral occurrences are reported to consist solely of anhydrous skarn mineral assemblages, mostly of garnet-

Name

NORMIN ID

Latitude

Longitude

NTS

Development Stage

Commodities

Host rock

Type

Mactung

105OSE0001

63.2850

-130.1608

105O08

Advanced Exploration

W-Cu-Zn

Monzonite

Skarn

Table 7.2-1. Skarn-tungsten in the Sekwi study area. Extracted from NORMIN (2008).

259

Chapter Seven

Figure 7.2-1. Intrusion-related skarn (A) Schematic illustration of skarn-associated mineralisation related to Cretaceous plutons. (B) Photograph of pyrrhotite-scheelite skarn mineralisation cut by aplitic dyke in the E-Zone at Cantung. Although this photograph is from Cantung, the mineralisation at Mactung is similar.

diopside with scheelite ± pyrrhotite-chalcopyrite mineralisation along the margins of the intrusions and commonly in contact with fine-grained, equigranular, leucocratic, muscovite ± tourmaline, or garnet-bearing marginal phases. The less significant prospects appear to lack these hydrous, higher-grade skarn assemblages (as is seen at Cantung in the retrograde amphibole-pyrrhotite skarn and particularly in the biotite skarn; Mathieson and Clark, 1984); this apparent absence of higher-grade minerals may be due to a lack of exploration work, or perhaps may reflect a mineralising system that was not particularly long-lasting.

7.2.2. Carbonate-hosted Zn-Pb (± Ag, Cu, Ba) and carbonate-hosted Cu (± Ag, Zn) B.J. Fischer

Carbonate-hosted Zn (± Pb) showings are by far the most common showing type in the study area (Fig. 7.1-2; Table 7.22), representing 80% of the known showings (NORMIN, 2010). Carbonate-hosted Cu-rich showings are transitional with both carbonate-hosted Zn-rich showings of the Mackenzie Platform and stratiform, Kupferscheifer-type Cu-rich showings of the Redstone copper belt. A rigid separation of showings into these types is not always possible with the available information; for example, numerous carbonate-hosted Zn showings and two of the Kupfershiefer-type showings (Day-Noon and Nite) share affinities with the carbonate-hosted Cu-rich type.

Carbonate-hosted Zn (± Pb) A summary of recent discussions surrounding classification and origin of carbonate-hosted Pb-Zn deposits is provided by Leach et al. (2005). In general, the deposit type is characterised by simple mineralogy of epigenetic (replacement and space-filling), strata-bound character in platformal carbonate successions. Metals

260

and sulphur from crustal sources carried by basinal brines were deposited between 75° and 200ºC. Spatial controls are faults and fractures, dissolution collapse breccias, and lithological transitions. Topographically derived hydraulic head and thermohaline convection are both accepted as driving mechanisms of fluid flow, whereas mixing of two fluids is a preferred stimulus for deposition of metals. There are no universally accepted criteria for distinguishing the Irish subtype from classic Mississippi Valley type (MVT) deposits. Irish-type fluids were somewhat higher temperature (up to 240 ºC) and circulated deeply in extensional margin settings, precipitating ore minerals early during diagenesis (Wilkinson, 2003), whereas MVT fluids were on average lower temperature and in most cases circulated more shallowly in foreland basins, precipitating ore after or late during diagenesis. Pre-ore dissolution is a major ore control for classic MVT deposits, but is of subordinate importance in Irishtype deposits (Leach et al., 2005; Hitzman and Beaty, 1996). Carbonate-hosted zinc-rich showings in the Sekwi project area occur predominantly in Lower Paleozoic platformal carbonate rocks, and there are numerous documented examples in the regional syncline in north-central NTS 105P and southwestern 106A (Fig. 7.1-2; Table 7.2-2). The greatest preponderance of recorded showings is in three stratigraphic intervals: the Lower Cambrian Sekwi Formation, the Ordovician-Silurian Whittaker Formation and its lateral equivalent (Mount Kindle Formation), and the Middle Devonian Arnica and immediately overlying Landry formations. The host rock is thoroughly dolomitised, except where it is Landry Formation. Hosts include bioturbated, argillaceous, sandy, fenestral, skeletal, oolitic, and intraclastic lithologies, and are commonly vuggy, fractured, or brecciated. References for this information, unless otherwise noted, are publicly available records of exploration work submitted to government by exploration companies. Ore minerals typically are sphalerite, its alteration products smithsonite and hydrozincite, and galena. Lead carbonates and sulphates (cerussite, angelsite) and minor amounts of copper sulphides and carbonates (chalcopyrite, tetrahedrite, chalcocite,

Name

NORMIN ID

Development Stage

Commodities

Host Rock

Type

Rank

NITE

105PNE0022

Latitude 63.8206

Longitude

-128.1933 105P16

NTS

Local Examination

Cu-Ag

Conglomerate, Dolostone

Cu-rich / Kupf

Showing

Day-Noon

105PNE0025

63.8403

-128.2283 105P16

Local Examination

Cu

Limestone, Conglomerate

Cu-rich / Kupf

Showing

ZEE

105PNE0037

63.9239

-128.9653 105P15

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

CAL

105PNE0038

63.8400

-128.9278 105P15

Local Examination

Zn

Limestone

Zn-rich

Showing

REEF-3

105PNE0039

63.8531

-128.9469 105P15

Local Examination

Zn-Pb

Breccia, Dolostone

Zn-rich

Showing

REEF-2

105PNE0041

63.8589

-128.9653 105P15

Local Examination

Zn-Pb

Dolostone, Breccia

Zn-rich

Showing

REEF-1

105PNE0042

63.8664

-128.9733 105P15

Local Examination

Zn-Pb

Dolostone, Breccia

Zn-rich

Showing

SCAT-7

105PNE0043

63.8894

-128.9997 105P15

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

KEG

105PNW0001

63.9950

-129.2656 105P14

Drilled

Zn-Cu

Dolostone

Zn-rich

Showing

TAP-1

105PNW0002

63.9547

-129.1814 105P14

Drilled

Zn-Pb

Dolostone

Zn-rich

Showing

105PNW0003

63.9700

-129.1397 105P14

Local Examination

Zn-Pb

Breccia, Dolostone

Zn-rich

Showing

105PNW0004

63.9108

-129.4594 105P14

Local Examination

Pb-Zn-Ag

Breccia, Dolostone

Zn-rich

Showing

TEE EXTENSION

105PNW0005

63.8219

-129.3714 105P14

Local Examination

Pb-Zn

Dolostone

Zn-rich

Showing

Dolostone

TEE-1/T-1,2,3,4,5

105PNW0006

63.7603

-129.3058 105P14

Local Examination

Zn-Pb

LIN-1

105PNW0007

63.8144

-129.3944 105P14

Local Examination

Pb

Snow Zone 2

105PNW0008

63.9594

-129.2581 105P14

Reconnaissance

Pb-Zn

Dolostone

Zn-rich

Showing

Zn-rich

Observed Ore Mineral

Zn-rich

Showing

Snow Zone 1

105PNW0009

63.9650

-129.2767 105P14

Local Examination

Zn

Dolostone

Zn-rich

Showing

Rain Zone 1

105PNW0010

63.9722

-129.2908 105P14

Local Examination

Zn

Dolostone

Zn-rich

Observed Ore Mineral

Rain Zone 2

105PNW0011

63.9861

-129.3244 105P14

Reconnaissance

Zn-Pb

Dolostone, Limestone

Zn-rich

Observed Ore Mineral

Rain Zone 3

105PNW0012

63.9878

-129.3247 105P14

Local Examination

Pb-Zn

Dolostone

Zn-rich

Showing

DICK-1

105PNW0013

63.8467

-129.3781 105P14

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

DICK-3

105PNW0014

63.8386

-129.3719 105P14

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

LAN-1

105PNW0015

63.8458

-129.3525 105P14

Local Examination

Pb-Zn-Ag

Dolostone

Zn-rich

Showing

KEV

105PNW0016

63.8694

-129.3592 105P14

Local Examination

Zn

Dolostone

Zn-rich

Frostheave/Boulder

ART-EKWI No.1

105PNW0018

63.8550

-129.1828 105P14

Drilled

Zn-Pb

Limestone

Zn-rich

Showing

ART-EKWI No.2,3,4

105PNW0019

63.8528

-129.1756 105P14

Drilled

Zn-Pb

Limestone

Zn-rich

Showing

ICE-9

105PNW0020

63.6492

-129.0522 105P11

Drilled

Pb-Zn

Dolostone

Zn-rich

Showing

ARN-6

105PNW0021

63.7508

-129.2856 105P12

Drilled

Pb-Zn

Dolostone

Zn-rich

Showing

Table 7.2-2. Carbonate-hosted Zn-Pb occurrences in the Sekwi study area. Minlzd = mineralized. Brackets in Commodities denote observed ore mineral, no brackets denote anomalous assays of that commodity. Bari = barite. Zn-rich = Carbonate-hosted Zn-Pb type. Cu-rich = Carbonate-hosted Cu type. Kupf = Kupferschiefer-type Cu. Rank of Showing is assigned to occurrences in bedrock. See also NORMIN Showings attribute definitions at http://www.nwtgeoscience. ca/normin/#shattr. Modified from NORMIN (2011).

Chapter Seven

TAP-2 DEE-1

261

262 OS-DA

105PNW0033

63.9769

-129.5564 105P13

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

DEE-3

105PNW0034

63.9208

-129.4628 105P14

Local Examination

Zn-Pb-Ag

Dolostone, Breccia

Zn-rich

Showing

SCAT-5

105PNW0036

63.9058

-129.0203 105P14

Local Examination

Zn-Pb

Dolostone, Limestone

Zn-rich

Showing

ARN-1

105PNW0039

63.7236

-129.2439 105P11

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

Emily-3

105PNW0040

63.6908

-129.1728 105P11

Local Examination

Zn

Dolostone

Zn-rich

Showing

Emily-5

105PNW0041

63.6675

-129.1089 105P11

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

ICE-6

105PNW0042

63.6636

-129.0725 105P11

Local Examination

Pb-Zn

Dolostone

Zn-rich

Talus

TAP-3

105PNW0043

63.9517

-129.1683 105P14

Drilled

Zn-Pb

Dolostone, Vein

Zn-rich

Showing

TAP-4

105PNW0044

63.9611

-129.1836 105P14

Drilled

Zn-Pb

Dolostone

Zn-rich

Showing

SCAT-3

105PNW0045

63.9069

-129.0397 105P14

Local Examination

Zn-Pb

Limestone, Dolostone

Zn-rich

Showing

SCAT-10

105PNW0046

63.9006

-129.0019 105P14

Local Examination

Zn-Pb

Limestone, Dolostone

Zn-rich

Showing

DAR

105PSE0024

63.3528

-128.3822 105P08

Reconnaissance

Zn-Pb-Cu-Ag

Breccia, Dolostone

Zn-rich

Showing

Majesty

105PSE0025

63.2708

-128.4558 105P08

Drilled

Pb-Zn-Ag-Cu

Siltstone, Limestone

Cu-rich / Zn-rich

Showing

105PSW0028

63.4853

-129.2175 105P06

Local Examination

Zn-Pb-Ag

Breccia, Dolostone

Zn-rich

Showing

106ANW0020

64.5533

-129.9767 106A12

Local Examination

Zn-Pb

Limestone

Zn-rich

Showing

JAN No.2

106ANW0021

64.5483

-129.9664 106A12

Local Examination

Zn-Pb

Limestone, Breccia

Zn-rich

Showing

Tet-Rap Showing B

106ASE0011

64.0428

-128.2792 106A01

Local Examination

Cu-Zn-Ag

Breccia, Dolostone

Cu-rich

Showing

Tet-Rap Showing C

106ASE0012

64.0411

-128.2167 106A01

Local Examination

Cu

Breccia, Dolostone

Cu-rich

Showing

RML 3

106ASE0013

64.0706

-128.2194 106A01

Drilled

Cu-Ag-Zn

Breccia

Cu-rich

Showing

Tet-Rap Showing A

106ASE0014

64.0439

-128.2933 106A01

Drilled

Cu-Zn-Ag

Dolostone, Quartz

Cu-rich

Showing

VIC

106ASE0015

64.2856

-128.6167 106A07

Local Examination

Pb-Zn (Bari)

Dolostone, Breccia

Zn-rich

Showing

TOAD

106ASE0016

64.3267

-128.7656 106A07

Local Examination

Zn-Pb (Cu)

Dolostone

Zn-rich / Cu-rich

Showing

Bear-Twit

106ASW0002

64.0389

-129.4225 106A03

Advanced Exploration

Zn Pb Ag

Dolostone

Zn-rich

Showing

PALM East

106ASW0003

64.4033

-129.7447 106A05

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

JUDE

106ASW0004

64.3736

-129.8872 106A05

Local Examination

Zn-Pb

Breccia, Limestone

Zn-rich

Showing

Esau's Fault

106ASW0005

64.1236

-129.2961 106A03

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

PALM West

106ASW0006

64.4111

-129.8469 106A05

Local Examination

Zn-Pb

Dolostone, Quartz

Zn-rich

Showing

REV Main Show

106ASW0007

64.1197

-129.3175 106A03

Drilled

Zn-Pb

Breccia, Dolostone

Zn-rich

Showing

Cirque

106ASW0008

64.1203

-129.3561 106A03

Drilled

Zn-Pb-Ag

Dolostone, Breccia

Zn-rich

Showing

Waterfall

106ASW0009

64.1122

-129.3569 106A03

Local Examination

Zn-Pb

Breccia, Dolostone

Zn-rich

Showing

PALM Main

106ASW0019

64.4040

-129.7946 106A05

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

Palm Waterfall

106ASWNONE

64.4014

-129.7922 106A05

Local Examination

Zn-Pb

Dolostone

Zn-rich

Showing

Table 7.2-2. (continued).

Chapter Seven

Horseshoe JAN No.1

Chapter Seven

A

B

C Figure 7.2-2. Carbonate-hosted Zn(-Pb) mineralisation. (A) Coarse yellow replacement sphalerite (sp) disseminated in a dark grey, mottled dolostone with up to 10% siliciclastic silt. A network of pyrite (py; oxidised and muddy on this weathered outcrop surface) follows organic-rich seams surrounding coarser, siltier, sphalerite-bearing “mottles”. From AB-C zinc showing, Sekwi Formation. Scale in millimetres. (NTS 106C/16, 347439 E, 7210162 N). (B) Sphaleritecemented dolostone breccia of the Bear-Twit zinc-lead showing, Whittaker Formation. Sphalerite is pale yellow to translucent, coarsely crystalline, and coated with a white smithsonite stain on the weathered surface in this photo. Scale is 16 cm long. Photo courtesy Robert J. Sharp. (NTS 106A/03, 479363 E, 7101417 N). (C) Dissolution and space-filling textures in a sample from the Palm zinc showing, Sekwi Formation. Dolostone (host) edges are rounded. Openings are rimmed by pyrite (py) followed by sphalerite (sp) and filled by orange dolomite (dm). (NTS 106A/5, 462079 E, 7142347 N).

malachite, and azurite) are less common. Both space-filling and replacement textures commonly co-occur in the same deposit. Cements of coarse-grained ore and gangue minerals, commonly paragenetically zoned, occupy micropores, larger vugs, veins, and the matrices of crackle, mosaic and rubble floatbreccias and packbreccias (sensu Morrow, 1982a) with dissolution and fittedfabric textures. Replacements are massive, disseminated (Fig. 7.22a), or selective fossil replacements. Pyrite or marcasite is invariably present, though abundances vary widely. Dolomite is ubiquitous as both replacement and recrystallisation of the host rock in a broad zone around most showings and as space-filling, coarse cement that commonly has baroque texture. Barite, calcite, and/or fluorite space-filling phases are normally also present. Quartz is a common, usually minor, late phase. The commodities of economic potential are zinc and lead. In most cases zinc is most abundant; in one showing it is absent entirely. Silver is significantly anomalous in a few of the deposits. The BearTwit showing consists of sphalerite-galena (± tetrahedrite) fracture-fill and minor breccia cement with associated dolomite, calcite, quartz, and barite in silicified, brecciated skeletal dolostone of the Mount Kindle (Whittaker) Formation (Fig. 7.2-2b). Twenty-one drill holes through the main showing in 1973-76 intersected numerous highgrade zones, including 23 m of 15.75% Zn, 11.16% Pb, and 4.16 oz/T Ag (Bagshaw, 1974), but the mineralisation was deemed too patchy to warrant further work. The Rev showing to the northeast, in the same interval of the host formation as Bear-Twit (though designated Mount Kindle Formation), yielded a 22.9 m drill intersection that averaged 8.65% Zn (Brock et al., 1976). The Ice 9 showing of fracture-filling

and disseminated galena and smithsonite in vuggy, orange, sandy dolostone of the Sekwi Formation averaged 8.20% Pb and 12.50% Zn across 9 m from representative grabs every 30 cm (Brock, 1973a). Copper minerals (mainly chalcopyrite and tetrahedrite) were noted in 10 showings, and so Cu may be of significance as a by-product, but it was generally not assayed for. A quartz-dolomite-galena-sphaleritechalcopyrite vein at Keg returned 0.55% Cu (Adamson, 1974). Barite varies in abundance, but is not economically significant in this style of deposit (see Chapter 7.2.4). Most showings of this type have a clear spatial association with faults or fractures, and exhibit fracture-filling textures (e.g., Royle, 1976; Dewing et al. 2006). Some have dissolution textures (Fig. 7.22c) that have not been demonstrated to be significantly pre-ore. The mineralisation at many showings is strata-bound, but lithologic controls are not clear. A limited number of academic studies has focussed on Mackenzie Mountains zinc showings. Two episodes of mineralisation have been proposed on the basis of minor-element chemistry of sphalerite (McLaren and Godwin, 1979) and lead isotope populations (Godwin et al., 1982). Ore-forming fluids were between 100º and 240ºC with salinities of 10 to 34 weight percent NaCl equivalent (Carrière and Sangster, 1999; Gleeson, 2006; Fischer et al., 2009; Wallace, 2009). Mixing of more than one fluid is suggested by the available data (Gleeson, 2006; Fischer et al., 2009; Wallace, 2009). The showings resemble Irish-type deposits in the warmer temperatures of their mineralising fluids, but lack evidence of syndiagenetic precipitation. Their typical relationship to late brittle structures and association with transitional Cu-rich mineralisation types suggests that attempts to classify them as Irish-type or MVT are ill-advised. A recent

263

Chapter Seven study of the Gayna River deposit concluded that the main phase of mineralisation occurred in the Cretaceous or Tertiary, and that the metals had been extracted from underlying shale (Wallace, 2009). Ongoing studies at Laurentian University (Fischer et al., 2009, 2010; Fischer and Pierce, 2011) will provide a clearer basis for interpretation of showings in the Sekwi Formation. Six carbonate-hosted Zn showings in the map-area, including Keg and Bear-Twit, contain copper sulphosalts in trace to minor amounts (e.g., Adamson, 1974; Brock et al., 1976; Dewing et al. 2006), and may be transitional between the zinc-dominated and copperdominated types.

Carbonate-hosted Cu (±Ag, Zn) A related showing type in the map-area is dominated by copper with accessory silver. Zinc content varies widely (Table 7.2-2). There are seven such showings, two of which may also be classified as Kupferscheifer-type. In the literature a case is made for recognition of a class of deposits including Kipushi-type, which is hosted by shallowmarine to lagoonal carbonate rocks, and dominated by Cu-Pb-Zn with accessory Ge, Ag, Ga, As ± Cd, Co, Sb, and V. These deposits are characterised by the discordant nature of the ore bodies, the presence of siliciclastic sedimentary rocks and evaporites in the host succession, and the presence of organic matter with the ore, but otherwise are quite similar to carbonate-hosted Zn-Pb deposits (Bernstein and Cox, 1986; Trueman, 1997). Proximity to a redox boundary and prior opening of the reduced carbonate host by brecciation, faulting, or karsting are cited as primary controls. An early stage of pyrite mineralisation is typically distinguishable from a later, copper mineralising event. In this discussion, the key difference between the Cu-rich and Zn-rich deposit types is mineralogy. Ore minerals of the Cu-rich type are predominantly tetrahedrite, chalcopyrite, bornite, or bournonite, plus the secondary copper minerals malachite and azurite, and rarely covellite, chalcocite, and boulangerite. In some occurrences, sphalerite, secondary zinc minerals, and galena are important. The two showings that are transitional with Kupferscheifer-type mineralisation are dominated by chalcopyrite and bornite, with less volumetrically important tetrahedrite. Gangue minerals are calcite, quartz, pyrite, and dolomite. Ore minerals occur with pyrite in quartz or quartz-calcite veins in parallel fractures in dolostone, and with dolomite-calcite cement in dolostone or limestone breccia. The association with vein quartz or calcite and late faulting is typical. Mineralised zones are pervasively fractured, locally gossanous, and seem to be grossly concordant (e.g., Anderson et al., 1973; Cukor, 1974). A drill-hole through the RML 3 showing cut 32 m of calcitetetrahedrite cementing a dolostone breccia, which averaged 0.9% Cu and 1.1 oz/ton Ag (Kim, 1972). The Majesty showing (Campbell and Hardy, 1981) is characterised by banded, slumped, sheared, and brecciated, stratabound mineralisation in a siltstone-dominated unit, and epigenetic, space-filling, and replacement sulphides in under- and overlying carbonate breccias and slump conglomerates. The major ore minerals are sphalerite, galena, bournonite, and tetrahedrite; despite this, no samples were assayed for Cu. A drill intersection averaged 5.75% Pb, 13.52% Zn, and 20.1 g/t Ag over 3.6 m. The showing has affinities with SEDEX Zn, carbonate-hosted Zn, and carbonate-hosted Cu types. Host strata for these showings are Proterozoic: two are in the upper Coppercap Formation, four are thought to be in the Little Dal Group, and the Majesty showing is in a succession of latest Proterozoic units, which may correlate with the Gametrail, Blueflower, and Risky formations; Aitken (1989a) postulated that the host is the Sheepbed Formation.

264

7.2.3 Kupferschiefer-type Cu (+Ag) L. Ootes

The oldest recognised mineral deposit type in the Mackenzie Mountains is strata-bound copper, hosted by the Coates Lake Group, which wholly defines the Redstone copper belt. The Coates Lake Group is most commonly exposed in the hanging-wall of the Plateau fault (Chapter 3; Fig. 7.1-1) and consists of three formations (Chapter 3.3.1). The conglomerate-dominated alluvial-fan-like Thundercloud Formation grades up into the evaporitic, sabkharelated Redstone River Formation, which is overlain by carbonate rocks of the Coppercap Formation (Fig. 7.2-3; Jefferson and Ruelle, 1986). Disseminated, very low-grade copper mineralisation is widespread, but the most significant copper occurrences are generally strata-bound, or stratiform lenses in the “transition zone” between the Redstone River and Coppercap formations (Fig. 7.23; Jefferson and Ruelle, 1986). The relationship between ore bodies and host rocks (Jefferson and Ruelle, 1986), suggests that these deposits should be classified as Kupferschiefer-type according to the criteria of Hitzman et al. (2005). The Coates Lake Group is restricted in exposure to the central part of the Mackenzie Mountains, and is thickest at Coates Lake (Jefferson and Ruelle, 1986; Colpron and Jefferson, 1998; Jefferson and Colpron, 1998). To the north, in the Sekwi project area (near 64°30’ NTS 106A), the Coates Lake Group pinches out and may have been eroded prior to deposition of the overlying Rapitan Group; the Coates Lake Group has not been documented north or west of this (Eisbacher, 1981; Jefferson and Parrish, 1989). Thickness and lithofacies patterns in the Coates Lake Group define a series of depositional embayments (Jefferson and Parrish, 1989) caused by syndepositional normal faulting in a series of half-grabens that were probably related to continental extension (Eisbacher, 1981; Jefferson and Ruelle, 1986; Jefferson and Parrish, 1989). Some contractional deformation (tilting, folding) of the Coates Lake Group took place prior to deposition of the overlying Rapitan Group (Helmstaedt et al., 1979), but the tectonic cause of this folding remains enigmatic. Of the 25 known Cu (± Ag) occurrences in the Mackenzie Mountains, 8 of these are in the Sekwi project area (Fig. 7.1-2; Table 7.2-3). The economically most significant deposit is at Coates Lake (south of the Sekwi project area) with historic resource estimates of 33.6 million tonnes grading 3.9% Cu and 9 g/t Ag (Hitzman et al., 2005). A thorough review of the mineralisation at Coates Lake is provided by Chartrand and Brown (1985), Jefferson and Ruelle (1986), and Chartrand et al. (1989). Of the eight Coates-LakeGroup-hosted prospects in the Sekwi project area, the Jay prospect is most the significant, with a historic resource estimate of 1.2 million tonnes at 2.7% Cu (Hitzman et al., 2005). Two other prospects, Lisa and June Creek, have been drilled. At a regional scale, the copper mineralisation (bornite, chalcocite, chalcopyrite; Fig. 7.2-3c and d) is believed to be the result of fluid mobilisation in a rifting basin (Fig. 7.2-3a; Jefferson and Ruelle, 1986; Chartrand et al., 1989). Copper and associated metals were liberated by oxidation of metals present in aquifer rocks, transported in either compaction-derived or meteoric-recharge-related chloride brines through sulphate-bearing redbeds, and then interacted with a reducing interface to precipitate sulphides (Fig.7.2-3; Chartrand et al., 1989; Brown, 2005; Hitzman et al., 2005). This interface is the “transition zone” between the Redstone River and Coppercap formations (Fig. 7.2-3). Upward zoning from copper-rich to copperpoor ore minerals indicates sub-vertical fluid flow (Jefferson and Ruelle, 1986). The copper source was suggested by Chartrand et al. (1989) to be the now red and oxidised evaporitic beds of the Redstone

Chapter Seven

Figure 7.2-3. Kupferschiefer-type mineralisation. (A) Photograph of Coates Lake Group east of the Shell airstrip (northwestern NTS 95M), with formations denoted. (B) Schematic model for redbed-hosted copper mineralisation (after Brown, 2005) with regional stratigraphic control added (after Jefferson and Ruelle, 1986). (C)-(D) Photomicrographs of copper mineralisation at June Creek. Brn=bornite; Ccp=chalcopyrite; Cc=chalcocite; ?=unidentified mineral; carbonate host. Plane-polarised reflected light.

River Formation, or the volcaniclastic conglomerates of the underlying Thundercloud Formation. It is probable that the underlying “Little Dal basalt”, between the Mackenzie Mountains supergroup and the Coates Lake Group, provided most of the copper (Dudás and Lustwerk, 1997). The copper was either directly leached from the basalt, or more probably liberated from volcanic detritus in overlying units. Sedimentary and ore textures indicate that the mineralisation event took place during very early diagenesis (Jefferson and Ruelle, 1986; Chartrand et al., 1989).

7.2.4. Other mineral prospects B. J. Fischer, D.G.F. Long, S.P. Gordey and K.L. Rasmussen

Coal Coal was first reported in Cretaceous strata of NTS 105P/10 by Blusson (1971) (Fig. 7.1-2). The coal was subsequently investigated by Ricker (1973) for Welcome North Mines Ltd., who measured three sections along ridge-crests, and recorded up to five coal seams, each estimated as at least 1.5 m thick, with possible lateral extent on the order of 450 m. Analysis of nine channel samples and two bulk samples from this study, from seams with reported thicknesses of 1.25 to 4 m, indicate that on an as-received basis, they have an average freecarbon content of 67.5% (range 61.9-73.5%), with 18.4% volatiles

(range 17.0-20.0%), 12.2% ash (range 4.6-20.4%), 1.9% moisture (range 0.5-2.4%) and 0.45% sulphur (range 0.36-0.59%). Proximate analysis of four coal samples from Section 2 (see Figs. 3.9.1-1 and -2), collected during this study, had a similar range (Table 7.2-4), with an average free-carbon content of 73.9% (range 64.3-779.0%), with 17.1% volatiles (range 15.7-20.1%), 7.0% ash (range 2.9-14.1%), 2.0% moisture (range 1.5-2.4%), and 0.42% sulphur (range 0.31-0.61%). Collectively, these analyses indicate that the coal is predominantly low-volatile bituminous coal using the ASTM classification (based on conversion of dry ash-free volatile content using Table 4 of Stach et al., 1982). This is equivalent to meta-bituminous in the Alpern Coal Classification (Alpern et al., 1989). The reflectance characteristics of three samples from Section 3 (see Figs. 3.9.1-1 and 2) were examined by F. Goodarzi (GSC Calgary), who interpreted them as low-volatile bituminous and semianthracitic coals (Table 7.2-5). All samples were in the catagenic stage of hydrocarbon generation, and are in the dry gas zone. At least seven seams of low-volatile bituminous to semianthracitic coal are known to be present in the Cretaceous strata in NTS 105P/10; others may be hidden in covered intervals. All of the strata in this fault-bounded outlier have steep dips and are highly sheared as a result of intense deformation during the CretaceousTertiary; as a result none appear to have any immediate economic potential, despite their proximity to the Canol Heritage Trail.

265

Chapter Seven Kupferschiefer(?)

Siltstone-hosted Zn

Table 7.2-3. Kupfershiefer-type copper occurrences in the Sekwi study area. Extracted from NORMIN (2008).

Kupferschiefer(?) Conglomerate Cu-Ag

Cu-Ag-Zn

Local Examination

Local Examination

105P16

105P16

-128.1933

-128.2283 Day-Noon

63.8403

105PNE0022

105PNE0025

NITE

63.8206

Barite is present in two settings in the study area: (1) sedimentary exhalative (SEDEX) barite expressed as tabular, stratiform, syngenetic, shale-hosted bodies, and (2) carbonate-hosted barite expressed as space-filling, epigenetic barite in veins and breccias. Occurrences of the second type are abundant in the map-area in association with carbonate-hosted Zn (± Pb) showings, but are too small to be of economic interest. The Alfa showing in northern NTS 105P (Fig. 7.1-2) is a 1.5 m-thick, 90 m-long lens of massive barite with 10000

J

07jdm1305-a 106ASE0021

513556

7131668

K

06ap76A

105PNW047

471505

7046850

3703

chalcopyrite in shale

L

06ap54A

105PNW048

482109

7057646

5360

M

08bf1073A

105PNE0044

545511

7087002

pyrite in sandstone malachite in limestone of Coppercap Fm. at Sayunei Fm. contact

Coppercap Fm. Outcrop

N

06em129B

105PNE0045

520499

7085189

dolostone

Twitya Fm.

O

06ras121D

105PNE0048

504980

7065323

P

08lt57A

095MNW0039

577072

7074301

Q

08lt59A

095MNW0040

576271

7073970 >10000

R

06kr216

095MNW0041

556035

7088855

S

06kr152A

095MNW0042

581745

7078801

T*

06em103A

095MNW0043

562910

7077136

U

06ras217

095MNW0045

576308

7074022 >10000

V

08lt58A

095MNW0044

576347

7074094 >10000

3650

3.3 13100

5570 >5000 351000

Outcrop Emerald Mal; Ccp; Outcrop Py:Brt: Po

malachite mineralization in dolostone

Twitya Fm.

mineralized interlayered dolostone, sphalerite.

Sheepbed Fm. Outcrop Ccp; Sp

boulder from river bed float with copper oxide staining

35.1

malachite chalcocite in quartz vein cutting dolostone Outcrop Mal some copper oxide in large 10-30 cm barite veins, lots of barite (stockwork in places) but very little mineralization, small patch of reddish oxide mineral Bear Rock Fm. Outcrop Mal; Brt

"Teepee dolostone"

Boulder Az; Mal

Little Dal Gp.

Outcrop Az; Mal

4.8

limestone rubble

Hume Fm.

Rubble

2.9

vein hosted mineralization, minor occurrence

Coopercap Fm. Subcrop Az; Brt; Mal Undivided siliclastic rocks Outcrop Ccp; Py

6250 >5000 483000 9750 153

5327 >10000 2826

18.0

Duo Lake Fm.

Az; Mal

Outcrop Py

Outcrop

shale Canol Fm. Outcrop Ba in scree and outcrop of Little Dal Upper Carbonate, from member 6 >200m sparsely in scree along strike, thru Little Dal Gp. Outcrop Mal; Ccp; Az in fractures of Coppercap Fm. member 2 laminate, outcrop and scree Coppercap Fm. Outcrop Mal; Az; Tet? malachite in evaporite

Little Dal Gp.

Outcrop Mal

goethite in dolostone rubble

Tseso Fm.

Rubble

malachite in dolostone rubble

Coppercap Fm. Rubble

dolostone laminated dolostone, pseudomorphous after stellate clusters of acicular crystals

Coppercap Fm. Outcrop Thundercloud Fm. Outcrop Mal; Az

Mal; Az

Table 7.3-1. Mineral occurances discovered during the Sekwi project. * Indicates a new showing within 500m of a previously known showing. Map label refers to the label on Sekwi project maps (NWT Open File 2010-08 to 19; see Figure and Table 9-1). Easting and northing are in UTM Zone 9, NAD 83. Az=azurite; Ba=barite; Brt=bornite; Ccp=chalcopyrite; Mal=malachite; Po=pyrrhotite; Py=pyrite; Sp=sphalerite; Tet=tetrahedrite. After Ootes et al. (2007) and Ootes and Martel (2010).

Chapter Seven

cliff forming dolostone, Little Dal Gp. Upper Carbonate fm.? malachite azurite near veins/fractures

3790

4310

Py; Mal

12.6

3.2

3570

Twitya Fm.

Minerals

Chapter ChapterEight One

Chapter Eight Hydrocarbons Citation: MacNaughton, R.B., Fallas, K.M. and Zantvoort, W., 2011. Chapter 9. Hydrocarbons; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 269 to 270.

8.0. Introduction

8.3. Seals

The central Mackenzie Mountains generally present poor prospects for hydrocarbon exploration (Cecile et al., 1982; MacNaughton et al., 2008a). Petroleum studies were not a major focus of the Sekwi project, but the hydrocarbon potential of the Plateau fault was studied (MacNaughton et al., 2008a), as were the source-rock and reservoir potential of the Devonian siliciclastic Hare Indian, Canol and Imperial formations. See Appendix G for explanations of terminology and abbreviations used in the chapter, and for detailed results.

MacNaughton et al. (2008a) reviewed probable seals in the stratigraphic succession of the study area. Many formations in the study area are shale-dominated or consist of tight, mud-grade carbonate lithofacies; these will not be reviewed here. Three intervals, however, must be noted as of particular significance. The Rusty Shale formation (Little Dal Group), which is a detachment horizon of the Plateau fault at the fault’s leading edge, is probably required as a seal in any Plateau-fault-related play (Cecile et al., 1982; MacNaughton et al., 2008a). The Headless Formation, which consists of shaly carbonate, would serve as a top seal on any play in reservoirs in the Arnica and Landry formations or their diagenetically altered equivalents (Manetoe facies; Bear Rock Formation). The Headless Formation, however, also seals most of the Mackenzie Platform succession from possible Upper Devonian source rocks. The Upper Devonian siliciclastic succession is shaledominated and could be a good seal for stratigraphic and structural traps sourced from the Canol Formation.

8.1. Source Rocks For this discussion, only units with samples that returned total organic carbon (TOC) values of at least 2% are considered to be source rocks (Fowler et al., 2005). Published and unpublished data for Proterozoic map units suggest that there is no remaining source potential, and post-maturity with respect to oil generation (MacNaughton et al., 2008a). Samples from the Cambrian-Devonian Mackenzie Platform succession, analyzed by Rock-Eval 6 pyrolysis, showed no source-rock potential. Shale of Ordovician to Silurian age (e.g., Duo Lake Formation) can preserve up to 8.2% TOC and may have remaining source-rock potential. However, most samples are post-mature with respect to oil generation and those shales are preserved mainly in the Selwyn Basin, where thermal maturity tends to be very high. Upper Devonian siliciclastic formations retain some source potential. Sparse data for the Hare Indian Formation include values up to 4.1% TOC. The Canol Formation returns values of up to 6.52% TOC. For both formations, TOC values are non-prospective in the eastern parts of the study area, but increase to prospective values in the west. Both formations are probably post-mature with respect to oil generation. The Imperial Formation is probably not prospective as a source rock.

8.2. Reservoir Rocks During the Sekwi project, mappers recorded visible porosity as part of outcrop descriptions. MacNaughton et al. (2008a) reviewed potential reservoir units, focusing on units in the footwall of the Plateau fault. Based on that review, there are two main intervals of potential reservoir facies. First, the Mount Kindle (Whittaker) Formation (Fig. 8-1) has been reported to contain vuggy porosity (Gabrielse et al., 1973a; Aitken and Cook, 1974b; Chapter 3.4.4). Second, breccia of the Bear Rock Formation (related to solution collapse of the Sombre and Arnica formations; Morrow, 1991) can be porous and cavernous (Gabrielse et al., 1973a; Aitken and Cook, 1974b; Chapter 3.4.6) and is petroliferous east of the study area, in NTS 96D (Aitken and Cook, 1974b). Vuggy porosity related to Manetoe-facies dolomitisation has been reported from NTS 95M. This, however, is the northern limit of this diagenetic facies and occurrences in the region are relatively thin (Morrow et al., 1990); the Manetoe facies is not known to be present north of about 63° 20' N. North of the Sekwi project area, sandstone beds in the upper Imperial Formation preserve good porosity, but such beds have not been documented in the study area (Zantvoort, 2007; MacNaughton et al., 2008a).

8.4. Hydrocarbon Shows In the Sekwi project area, hydrocarbon shows are limited mainly to pyrobitumen. During the Sekwi project, staining or solid hydrocarbons were noted in the Nahanni, Hume, Arnica, and Bear Rock Formations, as well as in Lower to Middle Devonian carbonate rocks of uncertain identity. Pyrobitumen has been previously reported from the Risky Formation (Aitken, 1989a) and from the Manetoe facies (e.g., Leighton, 1987). During mapping, a fetid odour was noted to be characteristic of outcrops of the Twitya and Mount Kindle (Whittaker) formations. Several other units in the region have previously been reported to be fetid, including the Sunblood, Sombre, Arnica, Natla, and Bear Rock formations (Gabrielse et al., 1973a; Aitken and Cook, 1974a). Rock-Eval analysis of several samples from fetid outcrops

Figure 8-1. Visible porosity in Mount Kindle (Whittaker) Formation in northwestern NTS 95M, near coordinates 582320E, 7078973N. Large pores are associated with stromatoporoids. Marks on hammer handle are 10 cm apart. Photograph reproduced from MacNaughton et al. (2008).

269

Chapter Chapter Eight Four of the Twitya and Mount Kindle (Whittaker) formations found no evidence for elevated TOC in the samples; the smell probably is from relict sulphur compounds.

8.5. Play Types Two conceptual play types have been suggested for the Mackenzie Mountains. Cecile et al. (1982) proposed that the Plateau fault was a large-scale overthrust and that Paleozoic platformal carbonate rocks were preserved extensively in the footwall, raising the possibility of a large-scale gas play. More-recent work (MacNaughton et al., 2008a; Fallas, 2008; this report) indicates that extensive footwall preservation of reservoir facies is improbable and that the Plateau fault is not a large-scale play (see Chapter 5 for detailed discussion of Plateau fault). Recently, MacNaughton et al. (2008a) have argued that large-scale trapping beneath the Plateau fault is very improbable. There may be limited potential for trapping at the fault’s leading edge, where the fault places Little Dal Group upon Imperial Formation (Fig. 8-2), but only if footwall cut-offs have juxtaposed the Canol Formation against porous intervals in the Mackenzie Platform succession and if the Rusty Shale formation acts as a seal (MacNaughton et al., 2008a; Fallas, 2008). Gabrielse et al. (1973a) tentatively suggested that in synclinoria capped by the Imperial Formation, trapping by anticlines may have taken place. Such synclinoria are present in the Sekwi project area, mainly east of the Plateau fault. At present, however, no reservoir is known that could be invoked for this play type.

270

Figure 8-2. A possible geometry for trap formation at the leading edge of the Plateau fault. Scenario requires emplacement of Little Dal Group upon Imperial Formation, and structural juxtaposition of reservoir and source units. Reproduced from MacNaughton et al. (2008).

Chapter Chapter Nine One

Chapter Nine H  ighlights and Recommendations Citation: Martel, E., 2011. Chapter 9. Highlights and Recommendations; in Geology of the central Mackenzie Mountains of the northern Canadian Cordillera, Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map-areas, Northwest Territories; Martel, E., Turner, E.C. and Fischer, B.J. (editors), NWT Special Volume 1, NWT Geoscience Office, p. 271 to 273.

9.1. Highlights of Sekwi Project

9.2. Future Work

During three summers of field work by geoscientists and students from various organisations, the equivalent of nine 1:50 000 maps were ground-truthed. The parts outside of the ground-truthed areas (Fig. 1-7) were extrapolated from ground observations, inferred from aerial photographs and satellite imagery, or updated from previous maps and reports, and unpublished statigraphic sections. Nine maps at 1:100 000 scale have been published to accompany this report (NWT Open File 2010-09 to 2010-17). Three structural cross-sections with annotated explanations depict the inferred stratigraphy and regional structures at depth (NWT Open File 2010-18). A new interpretation for the geometry of the Plateau fault is demonstrated on these cross-sections and explained in Chapter 5 of this volume. A common legend applicable to all nine 1:100 000 maps and cross-sections is published separately as NWT Open File 2010-19. Figure 9-1 is an index map showing the location of published Sekwi project maps and structural cross-sections. Table 9-1 includes the complete citations for each publication. Two simplified maps at 1:250 000 scale (NTS 105P and 106A) have also been published for the Sekwi project as GSC Open Files 6592 and 6594 (Table 9-1). Five theses have been published or are currently underway (Mercier, 2008; MacDonald, 2009; Leslie, 2009; Fischer, in progress; Rasmussen, in progress). An improved geoscience database with assays, geochemistry, geochronology, isotope data, macrofossils, microfossils, TOC, CAI, permeability/porosity, representative archived samples, pictures, and rock descriptions is available in the Appendices to this volume, or by request through the Northwest Territories Geoscience Office. As discussed in Chapter 7.3, a number of new mineral occurrences were discovered during the course of the Sekwi project. Noteworthy are Cu, Pb, Zn, and beryl. The first discovery of beryl in the Mackenzie Mountains was during this project, and highlights the potential for new types of mineralisation in the study area. Carbonatehosted Zn-Pb mineralisation is interpreted to be controlled by both structure and favourable lithologies. This mineralisation type is known from carbonate-dominated formations ranging from Proterozoic to Devonian in age (Little Dal Group, Sekwi, Franklin Mountain, Mount Kindle, Camsell, Landry, Arnica, and Grizzly Bear formations). This project along with other simultaneous research, has stimulated work toward development of a workable model for Mackenzie Mountains carbonate-hosted Zn district. Diatremes and associated mafic volcanic rocks of the Marmot Formation are exposed locally in the study area. Two diatremes have been dated by Ar-Ar techniques (452±2.6 and Ma 460±2.5 Ma) and are thought to represent low degrees of partial melt of a metasomatised garnet-bearing source. Based on ground observations and assay results, the Redstone copper belt may extend northwest of the well-known Coates Lake deposit and Keele River showings. Copper has been found in rocks of the Redstone River Formation and the Coppercap Formation, but also in rocks of the Little Dal and Rapitan groups. The hydrocarbon potential of the area’s strata and of the Plateau fault as a possible conceptual play have been investigated and deemed medium to poor owing to non-favourable burial temperatures and the interpreted geometry of the Plateau fault.

Lack of functional basic geological maps is evident in some parts of the Mackenzie Mountains. Some of these deficiencies have been addressed by the Sekwi project. However, areas without proper 1:250 000 coverage remain, including NTS 106B and C. Future work should focus on the stratigraphy west of the Sekwi Project area, in the Misty Creek Embayment (NTS 106B and C). The transitions from the Mackenzie Platform to the Selwyn Basin and Misty Creek Embayment are essential to understanding basin evolution controls on mineralisation and providing metallogenic models.

9.3. Knowledge Gaps and Outstanding Questions Although numerous facets of geoscience have been investigated during the multidisciplinary Sekwi project, several items remain poorly understood. Some of these knowledge gaps are listed below. 1. The Coates Lake Group depositional setting and stratigraphy remain poorly understood even though they have important implications for metallogenic models for Cu mineralisation. 2. Preliminary studies of granitic xenoliths in the Coates Lake diatreme dated at ca. 1175-1100 Ma (Jefferson and Parrish, 1989) have provided insight on the nature of underlying basement. The search for xenoliths in diatremes of the study area was not successful and therefore the basement remains poorly constrained. 3. The age of deposition of the “Little Dal basalt” and its relationship to under- and overlying strata are poorly constrained. Attempts to date the basalt by U-Pb techniques on baddeleyite were not successful. 4. As discussed in various previous publications, the terminology for the Road River Group has not been adequately explained since the first introduction of the term Road River Formation (see Chapter 3.5.1; Cecile, 1982; Gordey and Anderson, 1993). The stratigraphy remains to be documented with a complete section of the “Road River Formation” and detailed investigations of correlative units (Duo Lake Formation, Steel Formation, and Cloudy/Sapper Formation). 5. Correlation and characterisation of various jasper-hematite iron formations throughout the Rapitan Group requires investigation, as well as the inferred glaciation(s) recorded by this group. 6. The stratigraphy in southwestern NTS 105P consists largely of shale and siltstone preliminarily assigned to the Vampire Formation. However, these rocks were not investigated during the Sekwi Project and require detailed examination to define the transition from the Mackenzie Platform to Selwyn Basin stratigraphy better, and to asses the potential for mineralisation. 7. Significant parts of the areas covered by the 1:250 000 maps produced by this project are based entirely on much earlier maps and should be upgraded to match the level of detail of the mapping performed during the Sekwi mapping initiative.

271

Chapter Nine •

Some of the outstanding questions include: • What is the source of fluid and timing of mineralisation for the Mountain River beryl occurrence? What are the possible vectors to this new type of mineralisation? • What is the undiscovered potential in the study area for SEDEX Pb-Zn-Ba deposits in the Earn Group and Cambrian to Silurian shale exposed in and around the study area? Are the vectors to mineralisation the same as vectors to SEDEX deposits in the Selwyn Basin? • What model best characterises the Cu occurrences of the Redstone copper belt?



A7

130° 65° 106A13

106A14

106A NW NWT Open File 2010-09

106A15

106A NE NWT Open File 2010-10

106A11

106A10

106A9

106A5

106A6

106A7

106A8

106A4

106A3

128° 65°

106A16

106A12

106A SW NWT Open File 2010-11 A1



What is the age(s?) of carbonate-hosted Zn-Pb mineralisation? Was there more than one mineralisation event? Is there a spatial and/or temporal association for mineralising fluids between SEDEX and carbonatehosted Pb-Zn showings? What underlies the Katherine Group in the study area and how does it correlate to the stratigraphy exposed west of the study area in Yukon?

B7

106A SE NWT Open File 2010-12 106A2

106A1

C7 127° 64°

64° 105P13

105P14

105P NW NWT Open File 2010-13 B1

105P12

105P11

105P15

105P16

95M NW NWT Open File 2010-17

105P NE NWT Open File 2010-14 105P10

105P9

95M14

95M13

95M11

95M12

10 105P5

C1

105P SW NWT Open File 2010-15 105P4

63° 130°

105P6

105P3

105P7

5

0

10

20

Kilometres

105P8

105P SE NWT Open File 2010-16 105P2

105P1

63° 128°

Figure 9-1. Index to accompanying Sekwi project bedrock geology maps at 1:100,000 scale and structural cross-sections. A legend common to all 1:100,000-scale maps has also been published, as well as simplified bedrock maps at 1:250,000 scale. See Table 9-1 for full citations.

272

Chapter Nine Open File # NWT Open File 2010-09

type bedrock map

scale 1:100,000

NTS 106A NW

NWT Open File 2010-10

bedrock map

1:100,000

106A NE

NWT Open File 2010-11

bedrock map

1:100,000

106A SW

NWT Open File 2010-12

bedrock map

1:100,000

106A SE

NWT Open File 2010-13

bedrock map

1:100,000

105P NW

NWT Open File 2010-14

bedrock map

1:100,000

105P NE

NWT Open File 2010-15

bedrock map

1:100,000

105P SW

NWT Open File 2010-16

bedrock map

1:100,000

105P SE

NWT Open File 2010-17

bedrock map

1:100,000

95M NW

NWT Open File 2010-18

crosssections

1:100,000

105P 106A

NWT Open File 2010-19

common legend

GSC Open File 6592

bedrock map

1:250,000

105P

GSC Open File 6594

bedrock map

1:250,000

106A

NWT Open report

digital geology data

ESRI shapefile format

105P 106A 95M

105P 106A 95M

Citation Gordey, S.P., Martel, E., MacDonald, J., MacNaughton, R., Roots, C.F., and Fallas, K. (compilers), 2010. Geology of Mount Eduni, NTS 106A Northwest, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-09 (Edition 2). 1 map, scale 1:100,000. Roots, C.F., Martel, E., Fallas, K., Gordey, S.P., and MacNaughton, R. (compilers), 2010. Geology of Mount Eduni, NTS 106A Northeast, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 201010 (Edition 2). 1 map, scale 1:100,000. Gordey, S.P., Martel, E., Fallas, K., Roots, C.F., MacNaughton, R., and MacDonald, J., 2010. Geology of Mount Eduni, NTS 106A Southwest, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 201011 (Edition 3). 1 map, scale 1:100,000. Gordey, S.P., Martel, E., MacDonald, J., Fallas, K., Roots, C.F., and MacNaughton, R., 2010. Geology of Mount Eduni, NTS 106A Southeast, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 201012 (Edition 2). 1 map, scale 1:100,000. Roots, C.F., Martel, E., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Northwest, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-13 (Edition 2). 1 map, scale 1:100,000. Roots, C.F., Martel, E., MacNaughton, R., Fallas, K., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Northeast, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 201014 (Edition 2). 1 map, scale 1:100,000. Roots, C.F., Martel, E., MacNaughton, R., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Southwest, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-15 (Edition 2). 1 map, scale 1:100,000. Roots, C.F., Martel, E., and MacNaughton, R. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Southeast, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-16. (Edition 2) 1 map, scale 1:100,000. Fallas, K., Roots, C.F., Martel, E., and MacNaughton, R. (compilers), 2010. Geology of Wrigley Lake, NTS 95M Northwest, Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-17 (Edition 2). 1 map, scale 1:100,000. Gordey, S.P., MacDonald, J.D., Roots, C.F., Fallas, K., and Martel, E., 2010. Regional cross-sections, detachment levels and origin of the Plateau fault, central Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-18 (Edition 3). 1 sheet, scale 1:100,000. Roots, C.F., Martel, E., Gordey, S.P., MacNaughton, R., and Fallas, K., 2010. Legend for the geology of Sekwi Mountain, Mount Eduni and northwest Wrigley Lake areas (NTS 105P, 106A, and 95M NW), Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open File 2010-19 (Edition 2). 1 sheet. Roots, C.F., Martel, E., MacNaughton, R.B. and Gordey, S.P., 2011. Bedrock geology, Sekwi Mountain (105P), Northwest Territories; Geological Survey of Canada, Open File 6592, 1 sheet. Gordey, S.P., Roots, C.F., Martel, E., MacDonald, J., Fallas, K.M. and MacNaughton, R.B., 2011. Bedrock geology, Mount Eduni (106A), Northwest Territories; Geological Survey of Canada, Open File 6594, 1 sheet. Gordey, S.P., Pierce, K.L., Fallas, K., Martel, E. and Roots, C.F., (compilers), 2012. GIS compilation for the geology of Sekwi Mountain, Mount Eduni, and northwest Wrigley Lake areas (NTS 105P, 106A, and 95M NW), Mackenzie Mountains, Northwest Territories; Northwest Territories Geoscience Office, NWT Open Report 2012-002. Digital files.

Table 9-1. Table of Sekwi project bedrock maps and cross-sections with complete citations. See Figure 9-1 for locations.

273

References

References Abbott, J.G., 1982. Structure and stratigraphy of the Macmillan fold belt; evidence for Devonian faulting; in Yukon Geology and Exploration 1981. Dept. Indian Affairs and Northern Development (Canada). Whitehorse, Yukon. p. 22-33. Abbott, J.G., 1983. Geology of the MacMillan Fold Belt 105O SE and parts of 105P SW; Yukon Geological Survey, Exploration and Geological Services Division, Mineral Resources Directorate, Indian and Northern Affairs Canada, Open File 1983-1, scale 1:50,000, 16 p. Abbott, J.G., 1997. Geology of the upper Hart River area, eastern Ogilvie Mountains, Yukon Territory (116A/10,116A/11); Indian and Northern Affairs Canada, Exploration and Geological Services Division, Yukon Region, Bulletin 9. Abbott, J.G. and Turner, R.J., 1991. Character and paleotectonic setting of Devonian stratiform sedimenthosted Zn, Pb, Ba deposits, Macmillan Fold Belt, Yukon; in Mineral Deposits of the Northern Canadian Cordillera, Yukon - Northeastern British Columbia [Field Trip 14]. Edited by J.G. Abbott and R.J. W. Turner; Geological Survey of Canada, Open File 2169, p. 99-136.

Aitken, J.D., 1991. The Ice Brook Formation and postRapitan, Late Proterozoic glaciation, Mackenzie Mountains, Northwest Territories; Geological Survey of Canada, Bulletin 404, 43 p. Aitken, J.D., 1993. Cambrian and Lower Ordovician Sauk sequence; in Sedimentary Cover of the Craton in Canada (Chapter 4C), Stott, D.F. and Aitken, J.D. (eds.); Geological Survey of Canada, Geology of Canada, no. 5, p. 96-124 (also Geological Society of America, The Geology of North America, v. D-1). Aitken, J.D. and Cook, D.G., 1974a. Effect of antecedent faults on “Laramide” structure, Mackenzie arc; in Report of Activities, part B, November 1973 to March 1974; Geological Survey of Canada, Paper 74-01B, p. 259-264. Aitken, J.D. and Cook, D.G., 1974b. Carcajou Canyon map-area, District of Mackenzie, Northwest Territories; Geological Survey of Canada, Paper 74-13, 28 p. + 1 map. Aitken, J.D. and Cook, D.G., 1974c. Geological maps showing bedrock geology of the northern parts of Mount Eduni and Bonnet Plume Lake map-areas, District of Mackenzie, N.W.T.; Geological Survey of Canada, Open File 221, scale 1:125,000.

Adamson, T.J., 1974. KEG Group-Report on 1973 Field Work; submitted by Dynasty Explorations Limited; Northwest Territories Geoscience Office, NWT Assessment Report 080318.

Aitken, J.D. and Cook, D.G., 1974d. Surface and subsurface geology of the Ontaratue River, Travaillant Lake and Cannot Lake map-areas, District of Mackenzie, Northwest Territories; Geological Survey of Canada, Open File 234.

Aitken, J.D., 1966. Middle Cambrian to Middle Ordovician cyclic sedimentation, southern Rocky Mountains of Alberta; Bulletin of Canadian Petroleum Geology, v. 14, p. 405-441.

Aitken, J.D. and Cook, D.G., 1975. Geology of Upper Ramparts River (106G) and Sans Sault Rapids (106H) maparea, District of Mackenzie; Geological Survey of Canada, Open File 272.

Aitken, J.D., 1977. Redstone River Formation (Upper Proterozoic) in Mount Eduni and Bonnet Plume Lake map - Areas, District of Mackenzie; Report of Activities Part A, Geological Survey of Canada, Paper 77-01A, p.137-138.

Aitken, J.D. and Cook, D.G., 1976. Geology, Norman wells, Mahony Lake, District of Mackenzie; Geological Survey of Canada, Open File 304.

Aitken, J.D., 1981. Stratigraphy and sedimentology of the upper Proterozoic Little Dal Group, Mackenzie Mountains, Northwest Territories; in Proterozoic Basins of Canada, edited by F.H.A. Campbell; Geological Survey of Canada, Paper 81-10, p. 47-72. Aitken, J.D. 1984. Strata and trace fossils near the Precambrian-Cambrian boundary, Mackenzie, Selwyn, and Wernecke mountains, Yukon and Northwest Territories: Discussion; in Current Research, Part B; Geological Survey of Canada, Paper 84-1B, p. 401-407. Aitken, J.D., 1989a. Uppermost Proterozoic formations in central Mackenzie Mountains, Northwest Territories; Geological Survey of Canada, Bulletin 368, 26 p. Aitken, J.D., 1989b. Giant “algal” reefs, middle/upper Proterozoic Little Dal Group (>770, 243m

240m

9

Brick red weathering, red shale, with 3-5cm nodules; some yellowish weathering beds; section terminated abruptly, description incomplete 8

LD, basin 2

220m

200m

28

Base of section

Grey limestone, medium to thick beds except thin bedded from 2-6m above base, planar beds with undulating surfaces, dark partings, very ÿne dark laminations in the thin beds. @21.2m maÿc dyke 60cm thick, medium brown to grey weathering. @34.2m thin bedded with 20cm beds of cross-bedded sandstone every metre. At top, yellow-green.

REC S-REC S-RES RES

Figure A11. (continued).

311

Chapter Appendix Nine A Section 07RAS-S2

19

Tsetso Fm.

Top of section

Section described and measured by C. Leslie, C. Roots and M. Pope on July 15 & 19, 2007.

1029.0m Thin medium bedded lime mudstone. Thickness ~46 m. Lower contact covered.

1000m 18

Medium grey, ÿne to coarsely crystalline sugary dolostone with poorly deÿned bedding and locally laminated; rubbly texture possibly result of extensive bioturbation; @36m fenestral texture and silica-lined vugs; @23m is dark brown and grey weathering dolostone, breaks in clumps; no fossils. Lower contact covered.

Tsetso (Mount 900m Kindle Fm.?)

17

800m

16

Mount Kindle Fm.

Medium grey ÿnely crystalline limestone and lime mudstone. At top is skeletal wackestone but no fossils recognizeable; @20 m is brachipod packstone which is light grey and brown dolostone; base is 1 m layer of crushed brachiopods. Lower contact appears conformable.

W Sil

Sil

700m

15 14

50

Sil

13

Franklin Mt. Fm.

RAS07S2-17

07RAS-S2-16A to 16D

White to light grey, splintery weathering ÿnely crystalline dolostone; barren. Lower contact conformable, gradational.

52

Sil

First slope from end of ridge. Dark and light grey bands several metres of ÿne to coarse crystalline dolostone and silty dolostone, thick uneven bedding with burrowed upper few centimetres, some non-calcareous siltstone layers. @10 m are white siliciÿed patches to 1 m thick; @36 m is horizon of siliciÿed stromatolites; @54 m is curved laminae indicating stromatolitic domes (photo); @66 m is better laminated, uniform grey-brown dolostone with possible thrombolites; @111 m are siliciÿed and coarsely dolomitized dark grey layer 2 m thick (sample 361a). Lower contact conformable, gradational.

Sil

600m

Dark and light grey bands several metres wide of rough weathering medium crystalline dolostone with >10% siliciÿed organisms; including corals, brachiopods, nautiloids, stromatoporoids, gastropods. Entire thickness extensively burrowed. @15 m is a 50 cm band of light grey weathering chert; @45 m is sample and photo of columnar fossi with 4-pointed star cross-section. @75.5 m are zones of white irregular siliciÿcation and domal stromatolites but fewer large fossils. Lower contact sharp, appears disconformable (photos).

RAS07S2-18

RAS07S2-14

37

Sil

Cycles of thin-bedded ÿnely crystalline dolostone abruptly overlain by coarsely crystalline, knobby (bioturbated) medium bedded dolostone; @15m is ÿrst noted siliciÿcation; @32 m is 15 cm layer of domal stromatolites. Lower contact conformable.

Sil

Light grey coarsely crystalline, medium bedded dolostone, porous Yellow ÿnely crystalline, thin bedded lime mudstone, peritidal or tidal ¢at Light grey, coarsely crystalline, medium bedded dolostone, porous

12

500m 11 10 9

Sil

Grey to yellow weathering, thin to medium parallel bedded, mottled, ÿne crystalline grey dolostone; a few yellow weathering thin bedded mudstones suggest a peritidal environment; mechanically

35 laminated with rip-up clasts and convoluted beds; some channels 20 cm thick and up to 20 m wide; @28 m are siliciÿed nodules and lamination; cm-scale bulbous stromatolites; @46 m is ∆361; @87m thin laminae stand out - (vague teepee structure). Lower contact conformable?

400m

8

Red silty nodular dolostone (70%) interbedded with yellow weathering platy dolomitic siltstone (30%); at base is 5 m thick light geenish grey weathering clean sandstone interbeddded with glauconitic (?) sandstone. Lower contact erosional

FM, basal mbr

7

Medium parallel bedded and thinly laminated, orange-grey weathering ÿnely to medium crystalline dolostone with interbedded thinly laminated grey shales; light reddish orange weathering , medium dark grey limestone, parallel bedded, locally wavy contacts / lamination possibly microbial near the base. Lower contact conformable.

300m 6

Light orange brown weathering, dark grey variably medium bedded ÿnely crystalline dolostone, parallel

25 laminations, locally near top are graded beds (sample 6a), rusty red weathering hematized fractures.

07RAS-S2-7A

RAS07S2-6A

Lower contact covered.

200m LD, basin 2

LD, basin 1?

5

4

100m

3

Red shale with nodular bedding , minor siltstone, with nodules developed along bedding (includes cross bedding through nodules; sample 07RAS-S3-4a); green and brown resistant ÿne grained sandstone beds 10-30 cm. Lower contact in gully not exposed. Move section 300 m SE into gully facing southwest: @15 m, covered by stream alluvium; @40 m shales with nodules; no burrows.

07RAS-S2-4A to 4D RAS07S2-4A

Orange-brown weathering, thin to medium bedded, dark grey oncoid and pisoid grainstone/rudstone;

21 5% dolostone rip-up clasts; 5-10% oncolites and pisolites; forms slabby rubble. @15 m, a 2 m resistant

LD, Mudcracked Fm.

1

0m

Base of section

Figure A12. Section 07RAS-S2.

312

RAS07S2-5B

Orange (lower) and grey (upper) weathering ÿnely crystalline dolostone, bedding unknown as mostly chips exposed atop shale in saddle. Lower contact conformable.

2

Kath, K7(w)

Dark greenish-grey weathering, dark grey thin bedded shale (40%), siltstone (40%; sample 5a) and brown weathering sandy limestone beds up to 20 cm thick (sample 5b). Limestone nodules. Lower contact conformable.

REC S-REC S-RES RES

layer forms a scarp. Lower contact conformable. Medium-brown weathering grey siltstone with thin sandstone beds (50%), ÿne-grained, thin black laminations; shale chips abundant and probably bulk of unit but not exposed. @22.5 m is a 14 m thick maÿc intrusion trending 320 and dipping steeply southwest; @25 m is an orange-brown dolostone bed 50 cm thck, and more sandstone toward the top of the unit. Lower contact covered. White weathering, ÿne to medium grained sandstone. All large bouders, locally rusty, and siltstone chips in frost boils may indicate recessive interbeds near contact.

07RAS-S2-2A 07RAS-S2-1A RAS07S2-1A & 1B

Chapter Appendix Nine A Section 07RAS-S3

Section described and measured by C. Roots, K. Fallas and M. Pope on July 16, 2007.

Top of section >743m 12

Yellow and grey, thin bedded silty dolostone. Not examined in detail.

07RAS-S3-12A

Medium grey weathering, medium crystalline, medium to thick bedded dolostone with abundant fossil fragments including brachipods. 10% vugs (2-15 cm open spaces).

07RAS-S3-10A

11

Tsetso Fm.

700m

600m Mount Kindle Fm.

10

9

Sil Cal

Lower half: grey and yellow weathering; upper half: dark grey weathering, dark grey fresh surface. Very ÿnely crystaliline, thick to very thick bedded dolostone; sulphurous odour when broken. Bioturbated; fossil fragments abundant above 100m; hexacorals present: @73m: possible radial coral (photo) near top of bed; crinoid? fragments; @85 m fossil frags abundant; @97 m bedding deformed - possible fault; @120 m bioturbted; ÿlled w/ white silica and calcite.

500m

07RAS-S3-9A & 9B

8

400m

Franklin Mountain Fm.

cht

300m

200m

Brick red, ÿne grained, friable sandstone with calcareous cement in debris at base. Stylolite surfaces common; intraclasts, 2% vugs. Orange, light brown and grey stiped outcrop with thin bedded, platy, laminated limestone ÿning up to lime mustone partings; nodular limestone, rhythmically interbedded with greenish limy shale, very thin bedded; upward is dolomitic and increasingly wavy bedding.

6

100m 5 4 3

LD, basin 1

2

0m

07RAS-S3-8A & 8B

7

FMb

LD, basin 2

Medium brownish gery weathering, grey to white on fesh surface, medium to ÿne crystalline, thick bedded dolostone; beds 0.3-1.3 m, some thin laminated; no interbedded shale. Bioturbated; white chert subcircular spots 2-5 cm. @54m: mottled surfaces; pink grey westhering; @ 70-80 m: domal stromatolites, 30 cm high (photo). @120 m silica encrusted.

1

Base of section

REC S-REC S-RES RES

Light brown weathering, nodular limestone interbedded with greenish lime mudstone, very thin bedded; reddish shale bands (~1m), 0.5 m siltstone and ÿssile shale 3 m above the contact. Micro-to ÿnely crystalline, light brown and rusty weathering; fresh is dark grey thin to medium bedded limestone (50%) and shale (50%). 1.5 m of nodular limestone; top surfaces look stromatolitic but no laminae visible; possible load casts; contact with interval 4 is gradional over 20 cm. Gradational boundaries between beds; parallel laminations and thinning upwards; more medium bedded massive limestone like interval 2; rounded and tabular vugs result from weathering. Dark grey thin to medium bedded limestone with shale partings, westhers light brown-grey; nodular, irregular lam, rare parallel lam lower contact gradational over 30 cm. Interbedded medium to thick bedded limestone, siltstone and shale (70% limestone, 30% shale and siltstone) Red, brown and greenish grey shale, limestone nodules, very thin bedded, hackly mud, more than 10 m exposed; nodular and rhythmic bedding

07RAS-S3-7A 07RAS-S3-6A 07RAS-S3-4A

07RAS-S3-3A 07RAS-S3-2A 07RAS-S3-1A

Figure A13. Section 07RAS-S3.

313

Chapter Appendix Nine A Section 07WZ-S1

top covered

Top of section 306.0m 10

55

300m

Purple weathering, dark grey, thin to medium bedded, resistant, fine grained sandstone with silty mud interbeds, same as interval 8, thin bedded facies.

Section described by W. Zantvoort and measured by M. Mercier on August 10, 2007. WZ07S110A-B

9 Purple weathering, dark grey, shale and silty shale with fine grained sandstone interbeds toward the top; recessive and bioturbated at base; this is same recessive unit as interval 4.

8

Purple green weathering, dark grey, thin to medium bedded, resistant, fine grained sandstone with silty mud interbeds; occasional calcareous beds and brachiopds, strongly bioturbated, outcrop is predominantly interbeds of purple weathering silty mudstone and fine grained sandstone.

7 Green/purple weathering silty shale facies with minor fine grained sandstone interbeds containing shelly debris; fresh surfaces dark brown to purple.

200m

WZ07S17A-C

6

300m

Imperial Fm Rusty orange, very fine to fine grained, thin to medium bedded sandstone, tabular to blocky, thin bedded facies fresh surface is light to medium grey; horizontal traces.

WZ07S16A

Buff brown to dark grey, shale, silty shale, and thin bedded, very fine to fine grained sandstone, thinning and fining up sequence, also coarseninng up.

5 4

WZ07S15A TOC

WZ07S14A

Dark grey to black shale and silty shale, recessive.

WZ07S14A

100m

Orange-brown to black, very fine to fine grained, thin bedded silty mudstone to fine grained sandstone; on small scale (bedding scale) there are fining-up sequences; on outcrop scale there are coarsening and thickening; local shelly debris; truncated low angle cross-beds(HCS?) and ripple cross-beds.

3 2

WZ07S13A-C

Thin bedded, silty mudstone with very fine to fine grained sandstone interbeds; start of red/maroon weathering; resistant bands (some strongly calcareous).

WZ07S12A

1

WZ07S11A

67 Green/grey/brown weathering; dark grey-green on fresh surface; silty mudstone with very fine to fine grained sandstone interbeds; semi-recessive tabular beds.

TOC

base covered

0m

Horizontal scale is grain size: c coarse, f fine, g gravel, m mud, ms medium sand, s sand, v very. m

Figure A14. Section 07WZ-S1.

314

WZ07S11A

vfs

fs

ms

cs

g

Chapter Appendix Nine A Section 08BF-S1

Section described by B.J. Fischer and measured by B. Borkovic on July 19 & 21, 2008. 1000m 23

Top of section 979.5m

Cover. Section ends along strike from top of resistant, grey weathering outcrop not examined. Cover consists of calcareous shale chips possibly washed from stratigraphically and topographically overlying unit.

900m 22 19-21

Barely exposed outcrops: ÿnely crystalline, medium grey weathering, medium dark grey skeletal wackestone and Šoatstone with brachiopods, crinoids, skeletal fragments; brachipods concentrated in 10-20 cm beds, which rust preferentially, brachiopod moulds ÿlled by coarse white calcite.

W F Cal

Cover. From 34.5-36.0 is dull medium grey weathering, medium dark grey, ÿnely crystalline limestone, thin wavy partings of variable thickness.

Hailstone Fm.

800m

18

Thinly interbedded microcrystalline limestone and laminated argillaceous lime siltstone, pale brown vs light grey weathering, light medium grey fresh. 17

08BF-S1-18A

20% outcrop: ÿnely crystalline pale brown weathering, light medium grey lime mudstone.

16

700m

08BF-S1-22A & 22B, 22D to 22F BF08S1-22 08BF-S1-20A

Cli˝ . Thinly bedded, ÿnely parallel laminated, non-parting, ÿne to mircocrystalline, beige weathering,

92 light to medium grey limestone and lime siltstone; locally argillaceous. 15

Cover of mm-scale shale chips and small Šat plates of black limestone; outwash from overlying unit?; at 15m minor subcrop of pale brown weathering, medium grey, laminated limestone. Cli˝ and rubble of ar gillaceous lime mudstone to ÿnely crystalline laminated limestone; very hard laminated limestone with thin limestone interbeds 1-3 cm.

14 13

08BF-S1-14A

Rare black shale chips.

12

600m

08BF-S1-15A

Medium bedded, thinly parting, microcrystalline light tan grey weathering, medium to dark grey lime mudstone; locally laminated, compositionally mottled on mm scale, minor black shale debris, local wavy laminations; dips reverse twice, gentle syncline-anticline pair; thickness is exagerrated. 2 strong cleavages (266/26 and 192/21).

folds 11

Thinly to medium bedded, thinly parallel laminated, ÿnely crystalline, medium grey weathering, dark grey limestone; shale less than 10% as partings and very thin interbeds at base, increasing upwards to 30%.

500m

10

Chips of black calcareous shale.

9

8

Rabitkettle Fm.

Thin to medium bedded, thickly laminated, medium grey calcareous shale and very ÿnely crystalline,

folds

400m 7

32 dark grey limestone and argilleceous limestone; very recessive from 0 to 18m; from 18m to top, more limestone beds, 30% shale.

folds Thin to medium bedded, thinly to thickly laminated, ÿnely crystalline, grey-brown weathering, laminated limestone and dark grey calcareous shale; locally nodular laminated limestone interbedded with shale; grey nodules, laminated grey brown matrix, with wispy non-parallel laminations; elsewhere parallel thick to thin laminations; rare debris Šow; limestone intervals have varying bedding characteristics from platy, parallel-bedded to medium irregular / wavy. 40% shale at base, decreasing to 20% by 57 m; very folded from 60m to top, at 75m is calcite vein, dolomitization, fault?

300m 6

08BF-S1-7A

Very thinly bedded, very ÿne grained, dark grey calcareous shale; rare interebeds platy limestone.

5

Thinly to very thinly bedded, very ÿnely crystalline, brown grey weathering, dark grey, siliciclastic-silty limesone and dark gey calcareous shale; interstratiÿed on m-scale, resistant limestone and recessive black shale; increasing % resistant limestone upwards.

200m 4

Hess River Fm.

Sekwi Fm.

Thickly laminated, thinly parting, ÿnely crystalline, medium brownish grey weathering, medium grey limestone; interstratiÿed quartz-sandy vs platy vs shaly beds; some 4-cm beds of laminated limestone; rubble of phosphate?-granule limestone; also dark grey, mm-scale mudballs and tubes in light grey ÿnely crystalline limestone. From 60-99m: dark brown-grey weathering, dark grey calcareous shale.

Phos

100m

0m

3

Very thinly bedded, platy, very ÿne grained, medium greyish brown weathering, medium brown calcareous siltstone with dark grey shale partings.

2

Rubble of very thinly bedded, platy, very ÿnely crystalline, medium dark grey (weathering and fresh) siliciclastic-silty limestone. Rubble of ÿnely crystalline, thin parting, orange brown weathering, medium dark grey dolomitic limestone; rubbly weathering surfaces.

1

Base of section

40 REC S-REC S-RES RES

08BF-S1-4A

08BF-S1-1A

Figure A15. Section 08BF-S1.

315

Chapter Appendix Nine A Section 08DT-S1

Section described and measured by D. Thompson, B.J. Fischer and B. Borkovic on July 18, 2008.

Top of section 923.5m atypical Mt. Kindle Fm.

9

900m

Sil

Limestone, ÿnely crystalline, light grey weathering, black fresh, medium-bedded; chert lenses and nodules, siliciÿed corals and stromatolites and crinoids, occasional banded chert. Measured to the ÿrst resistant limestone cliŁ. Possibly a tongue of Cloudy Fm. (Cecile,1982). Limestone, ÿnely crystalline, light medium grey fresh, light brown weathering, laminated, occasional calcite veins, irregular partings, shale interbeds; mostly rubble.

cht

8 7

R Sil

Finely crystalline limestone, calcareous shale, skeletal rudstone (very ÿne fragments) with ooid grainstone matrix, thin bedded, weathers light grey to tan, fresh color is medium to dark grey; beginning of interval still has sandy to silty limestone interbedded with calcareous shale, but clastic input decreases upsection; limestone beds are cm-m thick, partings of shale are platy to chippy and irregular, skeletal beds are rare and 1-4 m thick; fossil detritus in rudstone is siliciÿed.

800m R Sil Duo Lake Fm.

6

700m

Sil

Black calcareous shale and dark grey to tan weathering, dark grey microcrystalline limestone, interstratiÿed on approx 1 m scale; local very ÿne quartz grains ‹oa ting in limestone; limestone beds are thick (approximately 1-10m), percent limestone and bed thickness increases up-section, colour lightens; rare 0.5 m thick debris ‹o ws with partly siliciÿed matrix and silica rim around some of the clasts; at top of interval begin to get clastic input, tan weathering sandy limestone, thin to medium bedded, ÿne rounded quartz grains, (approx 30 m interbedded with shale).

600m 5

Muddy black calcareous shale, very thin bedded, very recessive, chippy to shaly partings.

08DT-S1-5A

4

500m

Interbedded laminated, very thin to thin bedded limestone (beds 1-3 cm thick), nodular limestone, and

400m

65 black calcareous shale, rare beds of limestone approximately 30 cm thick; rare debris ‹o w beds within

shale; rare black chert blocks with calcite veins; partings are platy but can be blocky in some parts; rare beds of spherical chert in limestone (2 cm diameter); rare concretionary limestone within black shale.

08DT-S1-4A

300m Rabbitkettle Fm.

3

Fine crystalline to microcrystalline, thin bedded limestone and calcareous shale, light tan brown weathering, dark grey fresh, centimetric composite layering, very well laminated, platy to ‹aggy , black shaly partings, occasional alternating dark and light bands, grades into more shale in a saddle.

200m

08DT-S1-3A

2

Interbedded calcareous shale and limestone, thin to very thin bedded, medium brown grey weathering,

58 dark grey fresh, laminated, platy to papery partings, 60 cm thick beds of black shale; interlaminated

calcareous shale and nodular limestone, decreasing nodules upsection; debris ‹o ws approximatley 60 cm thick; local trace pyrite along laminations.

100m

08DT-S1-2A to 2C

1

cht Cal Dol Qtz

0m

Base of section

Figure A16. Section 08DT-S1.

316

REC S-REC S-RES RES

Base of interval 1 is top of interval 4 of 08EMS1. Interstratiÿied light grey weathering, medium grey

52 nodular limestone and laminated brown limestone, thin to medium bedded, chert nodules (5 cm wide 20 cm long approx) to lenses with orange rinds; shaly partings; debris ‹o w beds 10-20cm thick, clasts elongate, chert matrix, cannibalized clasts; calcite, dolomite and quartz veining.

08DT-S1-1A to 1D

Chapter Appendix Nine A Section 08DT-S2

Section described and measured by E. Martel and D. Thompson on July 21, 2008.

9

Top of section

823m

800m

Thor Hills/ Misfortune (upper) Fm.

700m

Interbedded massive, coarse grained sandstone and chert granule to pebble conglomerate, rusty brown purple and yellowish green (weathered), light grey (fresh), well to moderately sorted, rounded to subrounded, clast supported, 95% chert with quartz occupying other 5%. In general, clasts coarsen upwards (to ~5cm), however very top beds are very coarse sandstone. In some beds clasts appear to be aligned along bedding, rare grading, large scale cross bedding, scoured bases, ¡ut es and grooves on bedding surfaces. Chert can be bright green, yellow, black, white, grey, and on rare occasion laminated.

08DT-S2-9A

600m

500m

8

Interstratiÿed chert granule conglomerate and shale. Colours are rusty brown (weathered conglomerate), medium grey (fresh conglomerate), blue black with white yellow streaks (weathered shale), black (fresh shale). 2 conglomerate packages, 60 and 15 m thick, 2 shale packages, 19 and 6 m thick. Chert conglomerate: well sorted, granule to pebble size (matrix mud size), clast supported, rounded, rare quartz grains, rare ovoid shale clasts, scoured bases. Shale: blocky, looks like Canol Fm.

Misfortune (upper) Fm.

400m

7

Misfortune (lower) Fm.

Argillaceous, very ÿnely crystalline limestone and black calcareous shale, interbedded, yellow grey (weathered), dark grey (fresh). Irregular to small blocky partings, one small channel of skeletal detritus, possible graptolites. Up-interval amount of shale increases and becomes increasingly darker and papery. Limestone and chert conglomerate, crinoid rudstone, shale. Rudstone: brown grey (weathered), dark grey (fresh); conglomerate: yellowish grey (weathered), medium grey (fresh); shale: very dark grey. Base of interval is a ~1m thick bed of criniod rudstone with lime mudstone matrix. Crinoids can be quite large (+2cm in diameter) and compose 90% of fossil detritus. Accessory fossils include bryozoans and brachiopods. Within the rudstone are veins of calcite with anthracite grains. Fetid. Above this bed are lensoid conglomerates interbedded with black calcareous shales. Conglomerate: very poorly sorted, lime mudstone clast dominant, cobble size chert clasts, rudstone clasts, rare quartz clasts, subrounded to subangular, lime mud matrix, occasional siliciÿed fossils within lime mudstone clasts. Conglomerate beds are up to 2m thick, and have lensoid geometry. Near top of interval is a channel ÿll bed of dominantly crinoids, also brachiopods, chert, limestone,and quartz pebble clasts (clast supported, matrix is lime mud) scour base, sharp top, graded, cross bedded. Argillaceous limestone and black calcareous shale. Same as intervals 1 and 3. First 15 meters covered. Occasional lenses of mud within limestone laminae.

300m 6

Hailstone Fm.

200m

08DT-S2-8A to 8D

5 4

R

3

08DT-S2-5A to 5S

65 Duo Lake Fm.

Argillaceous limestone and black calcareous shale. Same as interval 1. Poor exposure (383m

Canol Fm.?

18

380m Nahanni Fm.

Thin bedded, dark grey to black shale and thin siltstone beds.

17

Thick bedded, ÿnely crystalline, medium to dark grey limestone, black on fresh surface; abundant corals, locally boundstone, fetid odor.

B 16

Bitu

360m

Finely crystalline brownish grey limestone; vugs ÿlled with pyrobitumen (5%). Photo 232A looking upsection (S). Photo 233A shows panoramic view looking E from Bear Rock to Backbone Ranges fms. 233B of coral fragments is from upper part of interval.

08RAS232A, 08RAS233A & 08RAS233B RAS08S1-16

Thin to medium bedded, ÿnely crystalline, dark and light grey limestone; brachiopods, stromatoporoids.

RAS08S1-15

Thinly bedded, light grey interbedded with brown grey, dolomitic siltstone; ÿne laminations, graded bedding, convolute bedding.

08RAS231B

15

340m

W Headless Fm.

320m

300m

14

280m

13

260m Massive, medium crystalline, medium grey to brown limestone breccia; rough and rubbly texture, anhydrite moulds, (gradational top). Photo looking NW.

Bear Rock Fm.

240m

12

Tsetso Fm.?

cht

08RAS231A RAS08S1-13

Thick bedded, ÿnely crystalline, medium to dark grey dolstone with rare back chert nodules; Mottled, nodular, burrowed near base.

11

Tsetso Fm.

Thin to medium bedded, ÿnely crystalline, yellow dolomitic silstone and sandstone. Photo looking NW from interval 12.

08RAS230E

220m 10

Franklin Mountain Fm.

200m

continued

REC S-REC S-RES RES

Figure A19. (continued).

321

Chapter Appendix Nine A Section 08RAS-S2

Section described by C. Roots and measured by B.J. Fischer on July 27, 2008. continued

1000m

Sombre Fm.

Cal

900m

800m

7

Massive, medium crystalline, yellow and grey weathering dolostone breccia; 15% pore space. 6

700m

600m Tsetso Fm.

Thin to medium bedded, ÿnely crystalline calcareous siltstone with medium to thick dark grey dolostone bands. At 102 m color becomes yellow weathering, irregular bedding surfaces. At 193.5 m Œaky parting. At 270 m ÿrst breccia. No life in upper part. Sulfurous smell. Lower part has colonial corals, solitary bryozoan-like corals, burrow 3 mm diameter. Gradational with interval 7.

WF

500m

400m 5

Dol

Thin bedded, medium crystalline, light grey dolomudstone; upper half has m-wide dark stripes. Corals. White dolomite cement lines/ÿlls convex-up cavities ~ 4x2 mm along bedding planes (both top and bottom convex-up like crescent moon). 3mm chips or rip-ups of dolostone within dolostone at top of one bed.

08RAS-S2-5A

Thickly and thinly bedded, microcrystalline dolostone and dolomudstone, dark and light grey bands; stromatoporoids, corals, sponges?, tube-like structures that resemble belemnites. Top 10 m is lime mudstone. At 60 m, white band 19 m of laminated dolomustone. At 129 m, alternating medium to thick, light vs dark bands. Dark bands have stromatoporoid fragments. From 157.5 - 171 m is most abundant life and extensive burrowing, white silica / chert.

08RAS-S2-4A to 4C

4

300m

Sil

200m

70

Mount Kindle Fm.

100m

3

Medium bedded, ÿnely crystalline, medium and dark grey weathering, dark to medium grey dolostone, with medium grained dolomitic sandstone at top; bioturbated, colonial coral fragments, brachiopods, crinoids; hairline veinlets of silica in spiderweb pattern.

Sil 2

Thin to thickly bedded, ÿnely crystalline light grey dolostone.

1

Sunblood Fm.

75

0m

Base of section

Figure A20. Section 08RAS-S2.

322

REC S-REC S-RES RES

Thickly bedded, ÿnely crystalline dark grey dolostone; fetid odor, bioturbated, abundant skeletal fragments and cemented breccia.

08RAS-S2-1A

Chapter Appendix Nine A Section 08RAS-S2 (continued)

9

Top of section

1659.0m

WF

1600m

Thickly bedded light grey to dark grey weathering dolostone and skeletal dolowackestone to fio tstone; stromatorporoids, coral (solitary and colonial), microbial? laminations, burrows?. >5% bioclastic. Section ends here; outcrop ahead but no time.

08RAS-S2-9A to 9D

Medium bedded, ÿnely laminated medium to microcystalline dolostone and dolorudstone. No fossils near base. Fine fractures with calcite near base. From 180 - 315 m, abundant tan bands. From 343- 349m dolostone breccia. At 364 m vuggy begins. Interstratiÿed coral? (bryozoan-like) dolorudstone and laminated dolostone. Vugs shaped like those corals? and ÿlled with dolomite and quartz. At 367, 0.5m thick dolostone breccia with aligned quartz-ÿlled vugs. At 382 m, 1-2 cm open vugs lined with calcite and quartz. Arnica above 412m. From 412-460, m-scale dark vs. laminated white bands. From 510-516, coral dolorudstone overlain by vuggy bed (as at 382m). From 547-592, minor dolostone breccia. At 739m, wavy laminations with mm skeletal? fragments replaced by silica. At 757m 30-60 cm beds with 2-4mm laminae. Light grey weathering interval has abrupt lower contact and grades up to darker dolostone.

08RAS-S2-8A to 8K

8

W Sil

1500m

Arnica Fm.

R

1400m

R

1300m

1200m Dol Qtz Cal

R

Sombre Fm.

1100m Cal

1000m

55 continued

REC S-REC S-RES RES

Figure A20. (continued).

323

Chapter Appendix Nine B

Appendix B: Detailed stratigraphic sections through the Tsezotene Formation, Katherine Group, and Cretaceous unnamed unit Measured and drafted by D.G.F. Long; compiled by B.J. Fischer and K. Rentmeister

Contents: Figure B1. Locations of stratigraphic sections through the Tsezotene Formation, Katherine Group, and Cretaceous rocks (unnamed unit)

324

Figure B2.

Legend for measured sections through the Tsezotene Formation and Katherine Group

Figure B3.

Section 019: Mount Eduni, NTS 106A: 64°13’30”N, 128°03’W

Figure B4.

Section 002: Tributary of Mountain River, NTS 106A: 64°46’N, 129°54’W

Figure B5.

Section 016: Carcajou Range, NTS 96E: 65°03’30”N, 127°47’40”W

Figure B6.

Section 003: Mountain River, NTS 106A: 64°46’N, 129°51’W

Figure B7.

Section 023: Tawu Anticline, NTS 106A: 65°43’30”, N 128°41’W

Figure B8.

Section 035: Ram Head Lake, NTS 95M/13; 63°56’08”N, 127°40’52”W

Figure B9.

Section 036: Tigonankweine Range, NTS 96D/4; 64°03’26”N, 127°40’52”W

Figure B10.

Section 037: Backbone Ranges, NTS 96D/3; 64°01’47”N, 127°24’31”W

Figure B11.

Section 038: Tributary of Keele River, NTS 96D/5; 64°15’24”N, 127°41’38”W

Figure B12.

Legend for sections through Cretaceous strata

Figure B13.

Section 1, NTS 105P/10, 63°37’16”N, 128°39’44”W

Figure B14.

Section 2, NTS 105P/10, 63°36’23”N, 128°41’1”W

Figure B15.

Section 3, NTS 105P/10, 63°37’29”N, 128°43’6”W

Figure B16.

Section 5, NTS 105P/10, 63°34’53”N, 128°38’49”W

Chapter Appendix Nine B 130°W

129°W

128°W

127°W

023

Legend Section location Sekwi project area Canol trail

106G

096E

106H

65°N

65°N

016

106B

003

096D

106A

038

019

64°N

036

037

64°N

002

035

105O

095M

105P 3 2 130°W

129°W

1 5

0 128°W

5

10

20 Km 127°W

Figure B1. Locations of stratigraphic sections through the Tsezotene Formation, Katherine Group, and Cretaceous rocks (un-named unit).

325

Chapter Appendix Nine B

LEGEND

1000

Modal grain size (M = mudstone; S = sandstone; G = conglomerate)

M

S

G Mudstone Siltstone

Elevation in metres

Sandstone Conglomerate Covered interval Dolostone Limestone Faint shades indicate inferred lithology

Sharp contact Transitional contact

K1 to K7 are informal subdivisions of the Katherine Group Tz = Tsezotene Formation

Sedimentary structures

Notes Massive - no apparent structure Laminated - planar bedded Ripple cross laminated Wavy bedded Trough cross-stratified Planar cross-stratified Intraclasts Dessication cracks Ooids Stromatolites, biolithites Maximum grain size Paleocurrent, from cross-stratification (north to top) Paleocurrent, from current-lineation Ripple crest Elongation of stromatolite domes Slump structures Load structures (pillows) Syneresis cracks Chert B = 25°145 (bedding = dip/direction)

Bed thickness (Left to right: 0-2 mm thin laminated; 2-10 mm thick laminated; 1-5 cm very thin bedded; 5-60 cm thin bedded; 60-120 cm thick bedded).Where two or more blocks are infilled a range of bed thicknesses or structure is present.

Figure B2. Legend for measured sections through the Tsezotene Formation and Katherine Group (sections 019, 002, 016, 003, 035, 036, 037, and 038).

326

Chapter Appendix Nine B 019 Mount Eduni, 106A, 64°13'30"N, 128°03'W 800

M

S

G not measured above 792 m

600

M

S

G or ? Low angle cross-beds low angle cross-beds

K2 poor exposure 3° low angle cross-beds

poor exposure

550

750

K1

Channel 8 m wide with 15 m wide lip Channel trace heavy minerals minor overturned cross-beds

low angle cross-beds

500

700

low angle cross-beds

450

650

low angle cross-bed

Tz red member Sinusoidal cross -beds 5° low angle cross-beds low angle cross-beds Diabase sill low angle cross-beds

600

400

Figure B3. Section 019: Mount Eduni, NTS 106A: 64°13’30”N, 128°03’W. Principal reference section for the red member of the Tsezotene Formation and unit K1 of the Katherine Group.

327

Chapter Appendix Nine B 019 Mount Eduni (continued) 400

M

S

200

M

S

G

G

150 350

orange weathering dolostone

low angle cross-beds

Tz

Tz

red member

100

red member

300 Limestones

low angle cross-beds

Domal stromatolites

Stratifera sp. teepee structures

50

250 first red mudstone black mudrocks

Tz

0 200

Figure B3. (continued).

328

grey member

Chapter Appendix Nine B 002 Tributary of Mountain River, 106A, 64°46'N, 129°54'W

600

M

S

G

covered, Grey mudrocks

K6

550 740

M

S

G

KATHERINE GROUP

Diabase Sill

Meta-siltstone

500

700 covered, black mudstones trace dolostone

K5

Domal laterally linked hemispherical (LLH) stromatolites

650

K6

450 overturned cross-bed

Quartz pebble conglomerate

Elongate, domal stromatolites

trace swash marks

600

400

Figure B4. Section 002: Tributary of Mountain River, NTS 106A: 64°46’N, 129°54’W. Principal reference section for units K2 and K5 of the Katherine Group.

329

Chapter Appendix Nine B 002 Tributary of Mountain River (continued) 400

M

S

G

200

M

S

G

? aeolian lag

covered, sandstone + trace dolostone

K4

K3 150

350

fluvial

K2

covered, abundant sandstone

300

Red and Pink sandstone and mudstone

100

50

250

K1

covered, abundant sandstone

Covered, sandstone

K3 200

Figure B4. (continued).

330

base of section in stream bed.

0

Chapter Appendix Nine B 016 Carcajou Range, 96E, 65°03'30"N, 127°47'40"W S G M M 1000 1200

S

G

K6

K4

B = 20°004 B = 25°034 B = 17°023

giant cross-beds

950

1150

1100

K5

900

B = 20°025

1050

850

K3 1000

K4

800

Figure B5. Section 016: Carcajou Range, NTS 96E: 65°03’30”N, 127°47’40”W. Principal reference section for unit K3 of the Katherine Group.

331

Chapter Appendix Nine B

016 Carcajou Range (continued) 800

M

S

G

600

M

S

G B = 10°067

K1

large cross-bed large cross-bed or channel

channel macroform large cross-bed

750

B = 17°030

550

B = 28°029

B = 16°67

B = 13°031

500

700

Tz

red member

K2 650

450

B = 16°004

600

Figure B5. (continued, 2 of 3).

332

K1

400

B = 6°056

Chapter Appendix Nine B

016 Carcajou Range (continued) 400

M

S

G

200

M

S

G

B = 11°015

syneresis cracks

350

Tz

red member

150

Tz

grey member

B = 10°020

300

100 B = 14°028

Hummocky cross stratification

250

50

Tz

grey member 200

0

Figure B5. (continued, 3 of 3).

333

Chapter Appendix Nine B 003 Mountain River, 106A, 64°46'N, 129°51'W 800

M

S

G

K7 compound channel fill

900

M

S

G Top of hill at 913 m

Oolite Member

Mudcracked Formation

Abundant heavy minerals

750 covered, abundant mudstone

850

LITTLE DAL GROUP

K7

K6 700

KATHERINE GROUP 800

covered. abundant mudstone

650

50% mudstone

Laterally linked hemisperical mounds 1-1.5 cm heads, 8-10 m mound diameter

600

Figure B6. Section 003: Mountain River, NTS 106A: 64°46’N, 129°51’W. Principal reference section for unit K4 of the Katherine Group.

334

Chapter Appendix Nine B

003 Mountain River (continued) 600

M

S

G

400

M

S

G

gutter cast

covered, black mudstone

Cryptalgal lamination

550

K6

K5 350

covered, mudstone with minor carbonate

swash marks

covered mudstone with minor sandstone

300

500

K5

K4 swash marks

covered, abundant sandstone

? beach facies

covered, mudrocks

250

450 covered, abundant sandstone

minor styolites on bedding

K3 Hummocky cross stratification

covered, abundant sandstone

400

200

Figure B6. (continued, 2 of 3).

335

Chapter Appendix Nine B

003 Mountain River (continued) 200

M

S

G

K3 K2

cryptalgal lamination marine covered, grey mudrocks

150

100

KATHERINE GROUP fluvial erosional contact

50

0

Figure B6. (continued, 3 of 3).

336

K1

Base of section is at a stream on the up-hill side of the base of fan.

Chapter Appendix Nine B 023 Tawu Anticline, 106A, 65°43'30", N 128°41'W 650

M

S

G

450

Little Dal Group

M

S

G

black mudrocks

Inzaria sp. grey-green mudrocks red mudrocks

600

400

K7

Large domes, with Inzaria sp.

Red mudrocks

550

B = 15°258

grey, black mudrocks

350

red mudrocks

Black mudrocks

300

500

green-grey mudrocks

Transition zone

K5

K6 450

K6

250

Figure B7. Section 023: Tawu Anticline, NTS 106A: 65°43’30”, N 128°41’W. Principal reference section for units K6 and K7 of the Katherine Group.

337

Chapter Appendix Nine B

023 Tawu Anticline (continued) 250

M

S

G

50

M

S

G Low-angle cross-bed Red mudrocks

B = 22°220

Low-angle planar cross-beds

B = 18°210

K4

Red mudrocks

0

200 red mudrocks B = 24°228

K5 150

100

50

Figure B7. (continued).

338

B = 25°208

K3

Chapter Appendix Nine B 035 Ramhead Lake, 95M/13, 63°56'08"N, 127°40'52"W M

500

S

G

M

Little Dal Group

S

G

300

K7 250

450

low-angle cross-beds

low-angle cross-bed

200

400

Black mudrocks in scree

Red mudstone with minor carbonate beds Inzaria sp. mounds

350

K7

150

yellow grey grey red

K6

Felsenmeer

300

100

Figure B8. Section 035: Ram Head Lake, NTS 95M/13; 63°56’08”N, 127°40’52”W. Units from the K5 formation to Little Dal Group inclusive.

339

Chapter Appendix Nine B 035 Ramhead Lake (continued) M

S

G

100

Black mudstone in scree

K6 50 Gutters

B=27°019

Medium to light grey mudstones in scree

63°56.092'N, 127°41.262'W

0

Sand volcanos Composite cross-beds Hummocky cross stratification B=32°024

K5 -50 Possibly over 150 m of K5 is covered

-100

Figure B8. (continued).

340

63°56.140'N, 127°40.866'W

Chapter Appendix Nine B 036 Tigonankweine Range, 96D/4; 64°03'26"N, 127°40'52"W M

950

S

G

M

Little Dal Group

G

K7

700

Katherine Group

900

850

S

750

650 trace biofilms

B = 22°193

trace biofilms Black mudrocks in scree

800

K7

600

K6 64°03.300'N, 127°52.027'W

Black mudrocks in scree

750

550

Figure B9. Section 036: Tigonankweine Range, NTS 96D/4; 64°03’26”N, 127°40’52”W. Units from the K5 formation to Little Dal Group inclusive.

341

Chapter Appendix Nine B 036 Tigonankweine Range (continued) M

S

G

M

350

550

S

G

B = 26°158

B = 21°220

500

possible biofilms

300

B = 19°194

64°03.433'N, 127°52.687'W

K6 grey mudrocks

450

gutters

250

gutters gutters Molar-tooth structure B = 20°175

K5 Black mudrocks (20% exposed)

400

200

350

150

Figure B9. (continued, 2 of 3).

342

Chapter Appendix Nine B 036 Tigonankweine Range (continued) M

S

G

150

100

50

0

Figure B9. (continued, 3 of 3).

343

Chapter Appendix Nine B 037 Backbone Ranges, 96D/3, 64°01'47"N, 127°24'31"W M

M

S

S

G

G

200 Little Dal Gp 400

64°01.675'N, 127°23.824'W

K6 150

350

K7

100 64°01.724'N, 127°24.292'W

300

Exposed in cliff-face opposite

64°01.755'N, 127°24.447'W

50

low angle cross-beds Fault zone

250

K5

K6

B = 52°050

B = 36°140 (drag fold) low angle cross-beds low angle cross-beds

0

B = 51°067

64°01.777'N, 127°24.513'W

Figure B10. Section 037: Backbone Ranges, NTS 96D/3; 64°01’47”N, 127°24’31”W. Unit K5 to Little Dal Group inclusive.

344

Chapter Appendix Nine B 038 Tributary of Keele River, 96D/5, 64°15'24"N, 127°41'38"W M

S

G

M

500

S

G

300

64°15.296'N, 127°41.658'W

64°15.399'N, 127°41.626'W elevation 889±21m

450

250 Recessive (poor exposure)

Rubble cover

400

K7

350

K6 200

150

Stratiferer Collenia ?

Hummocky cross stratification

64°15.221'N, 127°42.032'W elevation 737±6m

64°15.334'N, 127°41.523'W elevation 765±20m

300

64°15.296'N, 127°41.658'W

Recessive (poor exposure)

100

Figure B11. Section 038: Tributary of Keele River, NTS 96D/5; 64°15’24”N, 127°41’38”W. Unit K5 formation to Little Dal Group inclusive.

345

Chapter Appendix Nine B 038 Tributary of Keele River (continued) M

100

S

G

64°15.454'N, 127°42.653'W elevation 708±8m

Large scale composite sets

50

K5 Lichen covered

Scoured base

0

Large scale composite sets

64°15.193'N, 127°42.369'W elevation 690±15m

Figure B11. (continued).

346

Chapter Appendix Nine B

Legend for sections 1, 2, 3, 5 through Cretaceous rocks

M S G 400

0 0.2 1 5 60 120

Modal grain size (M = mudstone; S = sandstone; G = conglomerate)

Lithology Coal Organic-rich mudstone Mudstone

Elevation in metres

Sandstone

300

Faint shades indicate inferred lithology

Sedimentary structures

1 2 3 4 5 6 7 8 9 10

Conglomrate Covered interval Dolostone Limestone Sharp contact Transitional contact

plant fossils wood (spars) siderite nodules load structures

Notes

1: Massive - no apparent structure 2: Laminated - planar bedded 3: Ripple cross laminated 4: Wavy bedded 5: Trough cross-stratified 6: Planar cross-stratified 7: Intraclasts 8: Organic rich 9: Coal 10: Plant two roots, soilblocks structures preserved - Where or or more are infilled a range of structure is present - Grey shading indicates minor component

Maximum grain size Paleocurrent, from crossstratification (north to top) Ripple crest 61°

Joints, with strike and direction of dip

B = 25°145 (bedding = dip/direction) Sample number: metres from base C118075; 1089 m Palynology sample (GSC Calgary)

Bed thickness - Left to right: 0-2 mm thin laminated; 2-10 mm thick laminated; 1-5 cm very thin bedded; 5-60 cm thin bedded; 60-120 cm thick bedded; >120 cm very thick bedded.

Figure B12. Legend for sections through Cretaceous strata (un-named unit; sections 1, 2, 3, 5).

347

Chapter Appendix Nine B

400

M S

G

0 0.2 1 5 60 120

Section 1, NTS 105P/10, 63°37'16”N, 128°39'44”W 1 2 3 4 5 6 7 8 9 10

300 B = 16°208

B = 50°200

200

60-80% pebbles of white, fine grained siliceous quartz arenite with 20-40% grey and black chert pebbles

?

100

Cretaceous (unnamed)

B = 63°234 B = 61°223

60% white quartz arenite pebbles

B = 76°233

0

Fault contact Devonian

Landry Formation (Dolostone)

61°

88° 86°

Figure B13. Section 1, NTS 105P/10, 63°37’16”N, 128°39’44”W, through un-named, coal-bearing Cretaceous unit.

348

Joints

Chapter Appendix Nine B

Section 2, NTS 105P/10, 63°36'23”N, 128°41'1”W

400

M S

G

1 2 3 4 5 6 7 8 9 10

300

5 cm Coal Channel, 80% dark chert, 20% sandstone clasts

200

Covered - may include thin coal seams Crevasse - Splay complex

B = 93°066

10 cm dull Coal 50 cm Coal ferns

100

Channel + Splay complex 10 cm Coal Channel 50 cm Coal Splay

B = 81°066 B = 85°053

Splay Channel 45 cm coal Pond Splay trace coal in scree

0

B = 84°085 B = 46°028

Fossil ferns Fault contact

~ 200 m Black chert Permian Fantastque Formation Figure B14. Section 2, NTS 105P/10, 63°36’23”N, 128°41’1”W, through un-named, coal-bearing Cretaceous unit.

349

Chapter Appendix Nine B

0 0.2 1 5 60 120

Section 3, NTS 105P/10, 63°37'29”N, 128°43'6”W

1400

1300

1 2 3 4 5 6 7 8 9 10

C118077: 1293 m

1200

?

1100

C118076: 1089 m - no recovery

1000

900

snow covered

Figure B15. Section 3, NTS 105P/10, 63°37’29”N, 128°43’6”W, through un-named, coal-bearing Cretaceous unit.

350

Chapter Appendix Nine B

900

0 0.2 1 5 60 120

Section 3 (continued) 1 2 3 4 5 6 7 8 9 10

snow covered interval

poor exposure Fossil pine cone

800

700

C118080: 693 m

600

C118079: 529.5 m

500

C118078: 424.5 m trace low volatile bituminous coal 435 m

400 Figure B15. (continued, 2 of 3).

351

Chapter Appendix Nine B

400

M S

G

0 0.2 1 5 60 120

Section 3 (continued) 1 2 3 4 5 6 7 8 9 10

C118075: 394.5 m B = 74°070

Cretaceous (un-named)

300

C-118074: 304.5 m trace coal in scree Coal, max 1 m C-118073: 288 m

Flute to 040°

Black mudrocks, minor coal, and Sst, local channels Fining/thinning up sequence, with channels at base C-118072: 249 m trace Semi-anthracite at 248 m trace Low volatile bituminous coal 245 m Covered, organic rich mudrocks, minor ripple cross -laminated sandstone

200

Covered mudrocks (?) minor sandstone

Covered, minor pebbly sandstone Pebbly sandstone Covered, coal, organic mudrocks Black mudrocks

100

Quartz arenite, thin mudstones near top Covered, mudrocks, minor coal, or carbonaceous mudstone (max 1.5 m) at 203 m level. Small pebble to cobble conglomerate contact framework pebbles of dark grey, white, and black chert

0

Fault contact B = 73°230

Devonian Landry Formation (Dolostones)

Figure B15. (continued, 3 of 3).

352

Chapter Appendix Nine B

400

0 0.2 1 5 60 120

Section 5, NTS 105P/10, 63°34'53”N, 128°38'49”W 1 2 3 4 5 6 7 8 9 10

(Section MTA-79-32 of D. Morrow, unpublished)

300

(No details of structure or bed thickness available)

200

100 15% sandstone / 85% mudstone

0 Silicified mudstone (chert) minor mudstone Fantasque Formation (Late Permian) Dolostone Landry Formation (Devonian)

Figure B16. Section 5, NTS 105P/10, 63°34’53”N, 128°38’49”W, through un-named, coal-bearing Cretaceous unit; drafted from section MTA-79-32 of D. Morrow (GSC Calgary, unpublished field notes 1979).

353

Chapter Appendix Nine B

700

0 0.2 1 5 60 120

Section 5 (continued) 1 2 3 4 5 6 7 8 9 10

600

500 (No details of structure or bed thickness available)

400

Figure B16. (continued).

354

Appendix C

Appendix c: Detailed stratigraphic sections Through the Little Dal and Coates Lake groups Measured and drafted by E.C. Turner; compiled by K. Rentmeister

Contents: Figure C1.

Locations of stratigraphic sections measured by E.C. Turner through the Little Dal and Coates Lake groups

Figure C2.

Section 08-ECT-IR; Imperial section of Mudcracked fm. (Little Dal Gp.) & Franklin Mountain Fm.

Figure C3.

Section 08-ECT-CR; Cranswick River section of Basinal assemblage, Little Dal Gp.

Figure C4.

Section 07-ECT-TG; Tigonankweine section of Basinal assemblage, Little Dal Gp.

Figure C5.

Section 08-ECT-TZ; Tsezotene section of Platformal assemblage, Little Dal Gp.

Figure C6.

Section 07-ECT-HC; Hay Creek section of Thundercloud Fm. (Coates Lake Gp.)

Figure C7.

Section 2008-J113; Section of Redstone River Formation (Coates Lake Group)

Figure C8.

Section 08-ECT-RS; Ten Stone north section of Thundercloud and Coppercap fms. (Coates Lake Gp.)

355

356 132°W

130°W

128°W

126°W

08-ECT-CR

106F

Legend 106G

096E

106H

Section location 096F

65°N

65°N

Sekwi project area Canol trail NWT border

08-ECT-IR

08-ECT-RS

106C

J113

106B

096C

096D

106A

Chapter Appendix Nine C

07-ECT-HC

105N

105O

64°N

64°N

07-ECT-TG

08-ECT-TZ 132°W

130°W

Figure C1. Locations of stratigraphic sections measured by E.C. Turner through the Little Dal and Coates Lake groups.

095N

095M

105P

128°W

0 5 10 126°W

20 Km

Chapter Appendix Nine C

Figure C2. Section 08-ECT-IR; Imperial section of Mudcracked fm. (Little Dal Gp.) & Franklin Mountain Fm.

357

Chapter Appendix Nine C

Figure C3. Section 08-ECT-CR; Cranswick River section of Basinal assemblage, Little Dal Gp.

358

Appendix C

Figure C4. Section 07-ECT-TG; Tigonankweine section of Basinal assemblage, Little Dal Gp.

359

Appendix C

Figure C5. Section 08-ECT-TZ; Tsezotene section of Platformal assemblage, Little Dal Gp.

360

Chapter Appendix Nine C

Figure C6. Section 07-ECT-HC; Hay Creek section of Thundercloud Fm. (Coates Lake Gp.).

361

Chapter Appendix Nine C

Figure C7. Section 2008-J113; Section of Redstone River Formation (Coates Lake Group).

362

Chapter Appendix Nine C

Figure C8. Section 08-ECT-RS; Ten Stone north section of Thundercloud and Coppercap fms. (Coates Lake Gp.).

363

Chapter Appendix Nine D

Appendix d: Detailed stratigraphic sections through the Sekwi Formation Measured and compiled by B.J. Fischer; drafted by K. Rentmeister

Contents: Figure D1.

Locations of stratigraphic sections measured through the Sekwi Formation in the Sekwi project area

Figure D2. Locations of stratigraphic sections measured through the Sekwi Formation beyond the Sekwi project area. Box shows location of Figure D1.

364

Table D1.

Previously published stratigraphic sections measured through the Sekwi Formation

Table D2.

Stratigraphic sections measured through the Sekwi Formation in conjunction with the Sekwi project

Figure D3.

Legend for measured sections, Appendix D

Figure D4.

Section BF06AB

Figure D5.

Section BF06Palm

Figure D6.

Section BF07TIC1

Figure D7.

Section BF07TIC2

Figure D8.

Section BF07TIC3

Figure D9.

Section BF07TIC5

Chapter Appendix Nine D 64°30'N

130°W " )

129°W

128°W

Legend

Fogg

" )

_ [

Fz31

Measured stratigraphic sections

Hawk ) ! ("

64°30'N

_ _

07TIC1 _ [

Previously measured; published Previously measured; thesis _ Sekwi project; thesis [ Sekwi project area Canol trail NWT border 096D Contour elevation (m) 500 1000 1500 2000 ! (

Palm Moun

" )

106B

64°N

64°N

106A

! (

Fz22

! (

Fz21 ! (

" )

105P

H-1

D-4 " )

D-3 Cari

! ( " )

63°30'N

! (

Dahl

D-7 !( Fz32 ! (

" )

! (

Fz7

( !! ( "

) " )

D-1

" )

D-9

D-2

Fz8

D-11

" )

D-12

Fz33

! (

! (

! (

Fz36 Bliz 129°W

" )

Fz10

! (

130°W

June

" )

! (

Fz35

Fz34

095M

" )

Type

! ( ! (

" )

D-14

" )

KeeI " )

Fz24

Fz25 Ingt

D-10

Fz30

63°30'N

Fz23

105O

Fz29

! (

Fz5

Fz9 H-3 ! (

" )

! (

0

5

10

20 Km ! (

128°W

Figure D1. Locations of stratigraphic sections measured through the Sekwi Formation in the Sekwi project area. Previously measured sections are detailed in Table D1. “Previously measured; thesis” sections are from Krause (1979). “Sekwi project; thesis” sections are detailed in Table D2.

365

Chapter Appendix Nine D 132°W

130°W

128°W

Legend Measured stratigraphic sections

106G

! ( 106H Previously measured;096E published

Previously measured; thesis Sekwi project; thesis Sekwi project area Canol trail NWT border

" )

65°N

_ [ _ [

AB

Fz1

! (

! (

! (

Fz28 U-1

! (

Arct

! ( " )

Fz18

! (

106B

! (

Fz3

! (

Fz17

TIC3 TIC2 TIC1

U-7

Fz16 TIC5

! ( ! (

_ [ _ [

_!(") [ " )

! (

Fz19

! (

Fz20

! (

096D

106A

" )

64°N

64°N

106C

Goob ! ( " )

Fz26 ! ( Fz2 Fz11 Fz13 ! ( Fz12 ! ( Fz27 Fz14 Fz15

! (

! (

65°N

106F

Fz6

! (

! (

! (

! ( ! ( ! (

105N

" ) ! ( " )

105O ! ( ! ( " )

" )

" )

! (

! (

" ) ! ( " ) 105P

( " )! ) ! ( "

" ) " )

095M

" )

! (

" )

! (

! (

Gab14

! ( ! (

Fig. D1

( ! ( " )!

Gab18 Gab19

! ( ! (

63°N

63°N

! (

_!( [

Nah3

105K

105J

105I

Nah1 Nah2

H-4

_ [ Gab15

62°N

0 5 10

( !! (

H-5

Gab24

20 Km 132°W

095L

! (

130°W

! (

128°W

Figure D2. Locations of stratigraphic sections measured through the Sekwi Formation beyond the Sekwi project area. Box shows location of Figure D1.Previously measured sections are detailed in Table D1. “Previously measured; thesis” sections are from Krause (1979). “Sekwi project; thesis” sections are detailed in Table D2.

366

Section base Year measured 1973

Section top

Section thickness (m) 1007.0

Thickness of Sekwi Fm. (m) 1007.0

495.4

127.4

Section name U-1

Map label U-1

Latitude Longitude Northing 64.8000 -131.5833 7188668.83

Easting 377295.06

Latitude n/a

1973

U-7

U-7

64.6292 -130.0083 7167510.27

451793.77

n/a

2006

Dilliard 1

D-1

63.4395 -129.3723 7034612.53

481424.54

n/a

Dilliard, 2006

2006

Dilliard 10

D-10

63.5406 -128.7656 7045839.99

511652.32

n/a

Dilliard, 2006

2006

Dilliard 11

D-11

63.5242 -128.4562 7044110.51

527051.21

n/a

Dilliard, 2006

2006

Dilliard 12

D-12

63.5183 -128.1893 7043597.91

540331.78

n/a

Dilliard, 2006

2006

Dilliard 14

D-14

63.6177 -128.6256 7054465.17

518561.89

n/a

Dilliard, 2006

2006

Dilliard 2

D-2

63.4076 -129.1255 7031011.50

493731.90

n/a

Dilliard, 2006

2006

Dilliard 3

D-3

63.5511 -129.1976 7047003.77

490182.41

n/a

Dilliard, 2006

2006

Dilliard 4

D-4

63.5968 -129.1776 7052095.50

491186.32

n/a

Dilliard, 2006

2006

Dilliard 7

D-7

63.5885 -128.9927 7051157.82

500361.20

n/a

Dilliard, 2006

2006

Dilliard 9

D-9

63.4917 -128.8801 7040379.87

505970.31

n/a

1976

Fritz 1

Fz1

64.8333 -132.0000 7193253.16

357690.70

64.8250

1976

Fritz 10

Fz10

63.5278 -128.6958 7044437.00

515127.94

n/a

1976

Fritz 2

Fz2

64.6167 -131.7167 7168517.19

370088.93

64.6292

1976

Fritz 3

Fz3

64.4333 -131.3667 7147426.38

386057.58

64.4583

1976

Fritz 5

Fz5

63.7167 -129.4875 7065534.05

475914.34

1976

Fritz 6

Fz6

63.8667 -130.4500 7082966.13

1976

Fritz 7

Fz7

1976

Fritz 8

1976

Longitude

Full Sekwi? Reference n Aitken et al., 1973 n

Comment

Aitken et al., 1973

Same location as Krause's Caribou Pass and Handfield 1.

Dilliard, 2006 -131.9792

Fritz, 1976

1159.1 704.0

y y

Fritz, 1976

-131.7500

1648.8

1047.0

y

Fritz, 1976

-131.4000

1458.8

929.0

y

Fritz, 1976

63.7125

-129.4612

1445.1

1047.3

y

Fritz, 1976

428744.25

63.8583

-130.4333

964.6

847.3

n

Fritz, 1976

63.4445 -129.3833 7035172.88

480879.09

63.4388

-129.3500

1129.6

1068.6

n

Fritz, 1976

Fz8

63.2792 -128.8417 7016703.57

507943.30

63.2792

-128.8583

738.4

707.9

n

Fritz, 1976

Fritz 9

Fz9

63.2612 -128.6167 7014745.67

519243.06

63.2612

-128.5917

1978

Fritz 11

Fz11

64.5708 -133.0417 7166794.63

306457.54

n/a

927.4 266.2

671.3 144.2

y y

Fritz, 1978

1978

Fritz 12

Fz12

64.5292 -132.3917 7160331.80

337310.56

64.5208

-132.3917

593.0

570.1

y

Fritz, 1978

1978

Fritz 13

Fz13

64.5292 -131.8875 7159134.93

361480.09

64.5125

-131.8917

1284.1

833.8

y

Fritz, 1978

1978

Fritz 14

Fz14

64.4417 -132.9708 7152207.69

308945.52

64.4250

-132.9708

1493.9

1311.0

y

Fritz, 1978

1978

Fritz 15

Fz15

64.3833 -131.8208 7142751.79

363954.65

64.3667

-131.8083

1357.6

1049.7

y

Fritz, 1978

1978

Fritz 16

Fz16

64.5708 -130.1292 7161107.65

445901.71

64.5542

-130.1292

1000.0

780.5

n

Fritz, 1978

1978

Fritz 17

Fz17

64.7000 -130.7208 7176134.94

417950.12

64.6875

-130.8250

1341.5

712.8

y

Fritz, 1978

1978

Fritz 18

Fz18

64.5458 -130.7958 7159058.81

413888.28

64.5125

-130.7792

1802.7

1019.2

y

Fritz, 1978

1978

Fritz 19

Fz19

64.3500 -131.3042 7138033.86

388728.81

64.3750

-131.3167

1494.5

1271.0

y

Fritz, 1978

1978

Fritz 20

Fz20

64.2625 -131.2833 7128251.60

389384.37

64.2792

-131.3042

1640.2

1383.2

y

Fritz, 1978

1978

Fritz 21

Fz21

63.6625 -128.9500 7059407.46

502475.06

63.6667

-128.9125

1269.2

653.4

y

Fritz, 1978

1978

Fritz 22

Fz22

63.6958 -129.2083 7063137.54

489699.36

63.6833

-129.1417

1562.5

910.1

y

Fritz, 1978

1978

Fritz 23

Fz23

63.6250 -129.2083 7055244.79

489673.64

63.6375

-129.2875

1961.9

929.6

y

Fritz, 1978

1978

Fritz 24

Fz24

63.4958 -129.1417 7040843.26

492946.20

63.4833

-129.2167

1808.5

1149.4

y

Fritz, 1978

1978

Fritz 25

Fz25

63.4458 -129.3667 7035316.58

481711.28

63.4833

-129.4583

n

Fritz, 1978

1072.6

930.8

Table D1. Previously published stratigraphic sections measured through the Sekwi Formation. Northing and easting in metres based on NAD83, zone 9.

Fritz, 1976

Chapter Appendix Nine D

2204.3 724.4

367

368 Section base Year measured 1979

Section name Fritz 26

Map label Fz26

Latitude Longitude Northing 64.6417 -132.8958 7174239.77

Section top Easting 313919.03

Latitude n/a

Longitude

Section thickness (m)

Thickness of Sekwi Fm. (m)

217.7

164.0

1608.2

925.6

1979

Fritz 27

Fz27

64.4958 -131.5792 7154785.36

376113.91

64.4792

-131.5708

1979

Fritz 28

Fz28

64.8708 -131.3167 7196068.57

390245.62

64.8417

-131.3125

1596.0

1979

Fritz 29

Fz29

63.7292 -129.1292 7066841.48

493621.10

63.7292

-129.1083

1068.6

1979

Fritz 30

Fz30

63.6042 -128.8417 7052916.30

507853.79

63.6083

-128.8375

763.7

1979

Fritz 31&4

Fz31

64.3792 -129.7333 7139471.03

464618.53

64.3792

-129.7167

1318.6

1979

Fritz 32

Fz32

63.5625 -128.9500 7048264.79

502483.77

63.5708

-128.9333

912.5

1979

Fritz 33

Fz33

63.4917 -128.6917 7040408.16

515354.58

63.4917

-128.6708

1777.1

1979

Fritz 34

Fz34

63.3000 -128.7375 7019041.98

513159.64

63.2750

-128.7583

1473.5

1979

Fritz 35

Fz35

63.3833 -128.6458 7028349.17

517703.74

Fritz 36

Fz36

63.1750 -128.4667 7005198.98

526852.62

-128.5958 -128.4292

2129.6

1979

63.3750 63.1625

1979

Nahanni 1

Nah1

62.4700 -128.4150 6926676.98

530167.36

n/a

881.1 1500.0

1981

Nahanni 2

Nah2

62.4083 -128.2458 6919897.55

538970.88

62.3917

Nahanni 3

Nah3

62.6875 -128.3167 6950957.51

534981.57

62.6917

y

Fritz, 1979a

790.5

y

Fritz, 1979a

786.3

y

Fritz, 1979a

573.5

y

Fritz, 1979a

834.8

y

Fritz, 1979a

880.5

y

Fritz, 1979a

576.2

y

Fritz, 1979a

682.9

y

Fritz, 1979a

624.7

y

Fritz, 1979a

558.5 672.0

y y

Fritz, 1979b

1247.5

504.5

y

403.0 111.3

y y

-128.2625

Fritz, 1981

1973

Gabrielse 14

Gab14 63.1667 -127.1833 7005453.28

591484.73

n/a

1885.0 556.1

1973

Gabrielse 15 Gabrielse 18

Gab15 62.3167 -127.8833 6909957.41

557877.93

n/a

468.0

402.4

y

Gab18 63.1833 -127.2167 7007262.67

589754.85

n/a

420.7

39.6

n

556237.21

n/a

2027.4

38.1

y

584300.04

n/a

1204.3

178.4

n

1968

Gabrielse Gab19 63.1667 -127.8833 7004647.98 19 Gabrielse Gab24 62.1333 -127.3833 6890085.25 24 Handfield 1 H-1 63.5500 -129.2000 7046886.53

490060.56

n/a

984.8

984.8

y

1968

Handfield 3

529071.03

n/a

518.3

518.3

y

1973

1973 1973

Table D1. (continued, 2 of 4).

H-3

63.1803 -128.4225 7005806.25

Fritz, 1979a

Fritz, 1981

-128.3958

Comment

Gabrielse et al., 1973a

Section 21 in Gordey and Anderson, 1993. Section 23 in Gordey and Anderson, 1993. Section 22 in Gordey and Anderson, 1993. Upper Backbone Ranges Fm. of original authors was later assigned to Sekwi by Fritz (1981, p. 152)

Upper Backbone Ranges Fm. of original authors was later assigned to Sekwi by Fritz (1981, p. 152)

Handfield, 1968

Published data are smallscale columns and maps. Same location as Krause's Caribou Pass and Dilliard's 3. Published data are smallscale columns and maps.

Chapter Appendix Nine D

1981

Full Sekwi? Reference Fritz, 1979a y

Section base Year Section measured name 1968 Handfield 4 1968 1968

Section top

Map label H-4

Latitude Longitude Northing 62.6833 -128.2833 6950511.83

Easting 536693.10

Latitude n/a

Handfield 5

H-5

62.3167 -127.8667 6909972.43

558741.72

n/a

Type

Longitude

Section thickness (m) 307.3

Thickness of Sekwi Fm. (m) 307.3

391.8

391.8

Full Sekwi? Reference y Handfield, 1968 y

Type

63.5500 -128.7333 7046898.61

513252.57

n/a

769.8

769.8

y

1979

Arctic Red

Arct

64.6167 -131.7167 7168517.19

370088.93

n/a

1536.0

975.0

y

1979

Blizzard Creek Caribou Pass

Bliz

63.1667 -128.4500 7004277.59

527699.71

n/a

525.0

445.0

n

Cari

63.5500 -129.2000 7046886.53

490060.56

n/a

1319.0

1040.0

y

1979

Dahl Sheep

Dahl

63.5167 -129.0000 7043156.82

500000.00

n/a

823.0

363.0

n

1979

Fogg

64.5167 -129.9500 7154931.12

454394.66

n/a

637.0

389.0

n

Goob

64.7333 -130.7667 7179908.74

415868.77

n/a

626.0

448.0

n

Hawk

64.4167 -129.8167 7143698.76

460651.78

n/a

587.0

533.0

n

1979

Foggy Creek Goober Lake Hawkeye Creek Ingta River

Ingt

63.4333 -129.3667 7033923.79

481703.30

n/a

646.0

646.0

n

1979

June Lake

June

63.5333 -128.6000 7045076.05

519890.41

n/a

1370.0

596.0

y

1979

Keele

KeeI

63.5667 -128.5167 7048818.77

524006.13

n/a

490.0

454.0

n

1979

Mountain R

Moun

64.3833 -129.7167 7139926.15

465427.86

n/a

738.0

669.0

n

1975

I

64.5381 -130.1577 7157489.84

444467.03

64.5446

-130.1519

1975

II

64.5406 -130.1695 7157768.88

443908.06

64.5407

-130.1875

1975

IV

64.5541 -130.2113 7159315.26

441933.68

64.5615

-130.2114

1975

IX

64.5125 -130.1679 7154644.43

443925.43

64.5184

-130.1586

1975

J1

64.5426 -130.1702 7157993.25

443877.66

64.5447

-130.1521

1975

R1

64.5187 -130.1161 7155285.88

446427.02

n/a

1975

R1

64.5167 -130.1041 7155050.00

446997.05

n/a

1975

R1

64.5163 -130.1094 7155017.24

446741.52

n/a

1975

R2

64.5177 -130.1347 7155196.33

445531.56

n/a

1975

R2

64.5168 -130.1277 7155084.95

445863.54

n/a

1975

R2

64.5177 -130.1300 7155183.23

445756.52

n/a

1975

T1

64.5071 -130.1187 7153995.12

446276.85

64.5038

-130.1137

1975

T1A

64.5029 -130.1160 7153523.64

446398.62

64.5025

-130.1141

1975

T2

64.5008 -130.0729 7153253.85

448466.33

64.4994

-130.0741

1975

T2A

64.5005 -130.0765 7153223.44

448291.00

64.4994

-130.0746

1975

T3

64.4982 -130.0890 7152984.58

447686.26

64.4953

-130.0801

1975

V

64.5183 -130.1298 7155253.11

445767.44

64.5174

-130.1343

1979

Table D1. (continued, 3 of 4).

Krause, 1979

Re-measured as Dilliard 3; probably in same location as Handfield 1.

Ronning, 1975 (unpublished industry report)

Not shown on map; located near BF07TICx sections.

Chapter Appendix Nine D

1979

1979

Comment

369

370 Section base Year measured 1975

Section name VI

Map label

Section top

Latitude Longitude Northing 64.5246 -130.1343 7155955.30

Easting 445563.52

Latitude 64.5229

Longitude -130.1480

1975

VII

64.5313 -130.1700 7156738.38

443865.29

64.5332

-130.1442

1975

VIII

64.5465 -130.1696 7158426.52

443915.34

64.5556

-130.1656

1975

X

64.5001 -130.0584 7153172.79

449159.08

64.5025

-130.0587

1975

XI

64.5213 -130.0638 7155533.60

448938.58

64.5221

-130.0849

Section thickness (m)

Thickness of Sekwi Fm. (m)

Full Sekwi? Reference Ronning, 1975 (unpublished industry report)

Comment Not shown on map; located near BF07TICx sections.

Table D1. (continued, 4 of 4).

Section name BF06AB BF06Palm BF07TIC1 BF07TIC2 BF07TIC3 BF07TIC5

Map label Fig. # AB D4 Palm D5 TIC1 D6 TIC2 D7 TIC3 D8 TIC5 D9

Described by whom w/ measured by whom B.J. Fischer w/ E. Turner B.J. Fischer w/ E. Turner B.J. Fischer w/ R. Pippy B.J. Fischer w/ D. Thomson B.J. Fischer w/ D. Thomson B.J. Fischer w/ D. Thomson

Latitude 64.9905900 64.4049377 64.5307933 64.5463583 64.5475983 64.5468383

Section base Longitude Northing -132.3000977 7211468.87 -129.7975929 7142380.09 -130.1711367 7156682.58 -130.1702306 7158416.13 -130.1705417 7158554.58 -130.1605917 7158461.13

Table D2. Stratigraphic sections measured through the Sekwi Formation in conjunction with the Sekwi project.

Easting 344378.98 461554.34 443808.74 443884.20 443871.83 444347.35

Section top Section Thickness of Full Latitude Longitude thickness (m) Sekwi Fm. (m) Sekwi? 64.9892534 -132.3002935 91.0 91.0 n 64.4043152 -129.7923065 183.0 157.8 n 64.5327400 -130.1561033 277.5 277.5 n 64.5559367 -130.1740767 360.9 318.9 n 64.5511817 -130.1679567 160.0 160.0 n 64.5473367 -130.1413150 198.9 179.4 n

Chapter Appendix Nine D

Year measured 2006 2006 2007 2007 2007 2007

Chapter Appendix Nine D

Legend Carbonate rocks limestone

dolostone

skeletal grains

lime mudstone

dolomudstone

oncoids

calcisiltstone

dolosiltstone

ooids

dolomitic limestone /calcareous dolostone

dark grey to black weathering dolostone dolostone conglomerate

Siliciclastic rocks

cm-scale intraclasts cemented breccia

Carbonate rocks with

dolomitic shale siliciclastic component argillaceous siltstone limestone quartz-sandy limestone

quartz arenite

argillaceous dolostone

thinly bedded arenite

siliciclastic-silty dolostone

dolomitic quartz arenite

quartz-sandy dolostone

Symbols

d

argillaceous siliciclastic-silty quartz-sandy peloids ooids oncoids skeletal mm-scale intraclasts cm-scale intraclasts stromatolites parallel laminated wavy laminated microbially laminated cross laminated cross bedded cross bedded (low angle) wave ripple wave dune load cast mud cracks burrows bioturbated heavily bioturbated fenestral dolostone dykelets

W P G F R

B µB

20

Cal cht Dol Py Pyro Qtz Sil

Sp

wackestone packstone grainstone “oa tstone rudstone boundstone microbial boundstone contact gradational contact interstratiÿed bedding strike & dip (N to top) vein vug stylolitic cemented breccia rock-matrix breccia fault calcite chert dolomite pyrite pyrobitumen quartz siliciÿed sphalerite photograph (number follows) representative rock sample (number follows)

Key to page layout formation informal member stratigraphic thickness (m) 180m

34

33

170m

interval number (set at base of interval) covered interval

160m

30, 31

29

Sekwi dark 3

dolomitic siltstone

150m

28

140m

130m

27

120m

weathering proÿle (from left to right: recessive, semi-recessive, semi-resistant, resistant)

Figure D3. Legend for measured sections, Appendix D.

371

Chapter Appendix Nine D Section BF06AB (1 of 2)

continued

Possible fault.

50m 9

RF Dol

8

Intraclast dolofloatstone to dolorudstone, buff weathering, pale grey, finely crystalline, massive. Clasts angular, 10,000 ppm Cu, 4310 ppm Zn, 153 ppm Ag, and 6270 ppm Sb. Little Dal Gp. The Little Dal 3 showing is made up of one grab sample, taken from a malachite-stained quartz vein at an evaporite-dolostone contact; the sample contained 5327 ppm Cu. Tsetso Fm. The Delorme showing is made up of one grab sample taken from rubble of vuggy dolostone. The sample contains >10,000 ppm Zn. Coppercap Fm. The Hutch East 2 showing in from on grab sample of rubble of the malachite and azurite-bearing dolostone of the Coppercap Formation that contains 2826 ppm Cu. Thundercloud The Thundercloud showing is defined by one grab sample Fm. that contains >10,000 ppm Cu and 18 ppm Ag, taken from an outcrop of laminated dolostone.

Table H2. Characteristics of mineral showings in the Sekwi project area (NTS map sheets 95M/NW, 105P, and 106A). Data are from NORMIN (2010); comments have been edited slightly. Showing ID begins with the NTS sheet and quadrant in which the showing lies. The table is sorted by Showing ID. NTS is the 1:50,000 map sheet of the National Topographic System in which the showing lies. Northing and Easting are for the UTM projection, Zone 9, NAD 83. Additional information about each showing can be found in the NORMIN Showings database at http://www.nwtgeoscience.ca/; use the NT GoMap or NT GoData query tool. Original information sources are listed in the database; most of these have been scanned and are available for download. Host unit and location have in some cases been modified from the original sources. Map = identification number on Fig. H1 and the NWT Open File maps associated with this project; Dev = Development stage, Recon = Reconnaisance, Local Exam = Local Examination; T = imperial ton, oz = ounce, m = metre. Further information on the meaning of Development stage values can be found at http://www.nwtgeoscience.ca/normin/ under “Showing Attributes”. Shaded rows indicate showings that were discovered during the Sekwi Project (2006-2009).

Chapter Appendix Nine H

Name

095MNW0001

Map Label 68

415

416 NORMIN ID

Northing

Easting

NTS

Dev

Commodities

Host unit

Comment

CC

7074022

576308

095M14

Recon

Cu

Coppercap Fm.

105PNE0022

52

NITE

7077292

539707

105P16

Local Exam Cu-Ag

Coppercap, Sayunei fms.

105PNE0025

53

Day-Noon

7079442

537957

105P16

Local Exam Cu-Ag-Zn

Coppercap, Sayunei fms.

105PNE0037

54

ZEE

7088542

501707

105P15

Local Exam Zn-Pb

Arnica Fm.

105PNE0038

55

CAL

7079343

503657

105P15

Local Exam Zn-Pb

Landry Fm.

105PNE0039

56

REEF-3

7080643

502607

105P15

Local Exam Zn-Pb

Arnica Fm.

105PNE0040

57

BA

7065844

506357

105P10

Local Exam Ba

Canol Fm.

105PNE0041

58

REEF-2

7081293

501707

105P15

Local Exam Zn-Pb

Arnica Fm.

105PNE0042

59

REEF-1

7082143

501307

105P15

Local Exam Zn-Pb

Arnica Fm.

105PNE0043

60

SCAT-7

7084692

499957

105P15

Local Exam Zn-Pb

Arnica Fm.

The CC showing is defined by one grab sample that contains >10,000 ppm Cu, of dolostone from outcrop. “Bornite, chalcopyrite and tetrahedrite, +/- quartz, calcite and carbonate occur in bedding parallel veins up to 6 inches thick; smaller veins fill fractures of various orientations. Trench samples returned assays up to 1.61% Cu and 0.25 oz/ton Ag over 45 feet. The best-mineralized interval was from DDH-2 which yielded a weighted average assay of 0.33% Cu over 10 feet.” A single trench representative sample across 18 feet of highgrade float and gossan assayed 0.29% Cu; chalcopyrite and copper-carbonate mineralization is hosted in fractures and vugs. Selected grab samples from the area assayed up to 31.8% Cu and 12 oz/T Ag. ZEE 12A and 12B comprise the showing. 12A is described as an irregular two-foot wide mineralized layer containing up to 10% sphalerite, over a strike length that can be traced for 50 feet, while 12B consists of high grade smithsonite in breccia fillings and vugs over a thickness of 30 feet. Selected grab samples assayed up to 0.04% Pb and 49.9% Zn. A talus showing within limestone has been traced over an area of 900 feet wide by 500 feet of vertical relief. A character sample assayed 0.04% Pb and 61.7% Zn. A series of lead-zinc occurrences occur in dolostone over a strike length of 2600 feet; these achieve a maximum thickness of 15 feet. Channel samples, averaging 10 feet in length, were taken at four locations along strike; these returned 0.04 to 0.08% Pb and 0.34 to 1.52% Zn. The barite bed ranges in thickness of 15 to 16 metres and has an outcrop length of approximately 650 metres. The mineralized zone is 1000 to 1500 feet wide and extends up to 1500 feet downslope. Galena and sphalerite and associated alteration (smithsonite and cerussite) fill cavities within the Arnica dolostone A characteristic sample assayed 1.05% Pb and 6.27% Zn. Two samples taken over a 50-foot gossanous zone were assayed: (1) fossilized dolostone replaced by sphalerite assayed 1.18% Zn; and (2) gray dolostone breccia with sphalerite-cemented matrix assayed 6.85% Zn. Both contained trace Pb. The showing consists of the SCAT 7 and 8 occurrences; these are within talus and slumped outcrop that exhibits sphalerite in vug fillings hosted by black weathering dolostone. A sample collected at occurrence 8 assayed 0.01% Pb and 6.24% Zn.

Table H2. (continued, 2 of 9).

Chapter Appendix Nine H

Name

095MNW0045

Map Label U

NORMIN ID

Northing

Easting

NTS

Dev

Commodities

Host unit

Comment

Coppercap 2

7087002

545511

105P16

Recon

Cu

Coppercap Fm.

105PNE0045

N

Twitya 2

7085189

520499

105P15

Recon

Pb

Twitya Fm.

105PNE0046

61

Sekwi

7053092

516307

105P10

Local Exam Coal

unnamed Cretaceous unit

105PNE0047

62

WAC

7051192

518707

105P10

Local Exam Coal

unnamed Cretaceous unit

105PNE0048 105PNE0049

O 63

Bari HA1110

7065323 7067700

504980 545456

105P10 105P08

Recon Recon

Ba Pb-Zn

Canol Fm. Twitya Fm.

105PNW0001

18

KEG

7096492

487007

105P14

Drilled

Zn

Mount Kindle Fm.

105PNW0002

19

TAP-1

7091979

491113

105P14

Drilled

Zn-Pb

Rabbitkettle Fm.?

105PNW0003

20

TAP-2

7093692

493157

105P14

Local Exam Zn-Pb

Mount Kindle Fm.

105PNW0004

21

DEE-1

7087191

477457

105P14

Local Exam Zn-Pb

Mount Kindle Fm.

105PNW0005

22

TEE EXTENSION

7077242

481707

105P14

Local Exam Pb-Zn

Mount Kindle Fm.

The Coppercap 2 showing is made up of one grab sample taken from a limestone outcrop with malachite staining; the sample contained 6250 ppm Cu. The Twitya 2 showing is made up of one grab sample taken from an outcrop of dolostone; it assayed >5000 ppm Pb. Several coal seams were sampled. One sample from the showing returned 69.17% fixed carbon, 20.03% volatiles, 8.6% ash and 2.2% moisture. The width of this seam is 8.7 feet. The sulfur content is 0.36% and a heating value of 12,561 BTU/lb was attained. The A Coal Seam has a thickness of 5.5 feet and a heating value of 11,767 BTU/lb with a sulfur content of 0.43%. There are a total of seven coal seams greater than five feet thick that may be traced discontinuously over a strike of 4500 feet. Barite in thinly bedded shale. The HA1110 showing is defined by a single grab sample of sandstone float containing galena that assayed 0.56 % Pb and 0.37% Zn. The sample is associated with the Lower Rapitan Coppercap contact. In 1973, three holes were drilled on the main showing; the mineralization occurs in slump breccias and the best intersection was 4.18% Zn and 0.05% Pb across 67 feet. Mineralized veins with minor quartz, generally less than 10 cm wide, crosscut dolostone. The veins are abundant over a 60-metre stratigraphic thickness and can be traced intermittently for more than 760 metres. Massive pyrite veins contain up to 50% sphalerite with minor amounts of disseminated galena. Surface samples assayed up to 3.71% Pb and 27.5% Zn. One drill hole resulted in an assay interval of 0.40% Zn over 1.2 m. A 6.5-metre thick, shallowly east-dipping breccia bed with pods of sphalerite and galena in thin-bedded, gray dolostone was sampled. Assays ranged up to 4.28% Pb and 7.92% Zn. Mineralization, which consists of a thin layer of smithsonite capping fine-grained sphalerite- and galena-annealed breccia, is hosted by bleached and brecciated dolostone. In places, massive bands of barite, calcite and fluorite form the matrix. A cross-shaped trench was dug over the showing; assays included 11.9% Pb and 15.2% Zn over 50 feet from the long leg (perpendicular to bedding), and 4.2% Pb and 10.8% Zn over 35 feet. Galena and smithsonite are found along the shale-dolostone contact at the intersection of two faults. Local massive sulphide graded 32.5% Pb and 16.5% Zn across 0.76 m of weathered dolostone. This high-grade section is included in a sample which graded 7.75% Pb and 4.80% Zn across 3 m.

Table H2. (continued, 3 of 9).

Chapter Appendix Nine H

Name

105PNE0044

Map Label M

417

418 NORMIN ID

Northing

Easting

NTS

Dev

TEE-1

7070342

484907

105P14

Local Exam Zn-Pb

105PNW0007

24

LIN-1

7076542

480482

105P14

Recon

Zn-Pb

105PNW0008

25

Snow Zone 2

7092542

487357

105P14

Recon

Zn-Pb

105PNW0009

26

Snow Zone 1

7093142

486457

105P14

Local Exam Zn-Pb

105PNW0010

27

Rain Zone 1

7094242

485407

105P14

Drilled

Zn-Pb

105PNW0011

28

Rain Zone 2

7095496

484033

105P14

Recon

Zn-Pb

105PNW0012

29

Rain Zone 3

7095692

484107

105P14

Drilled

Zn-Pb

105PNW0013

30

DICK-1

7079992

481407

105P14

Local Exam Zn-Pb

105PNW0014

31

DICK-3

7079092

481707

105P14

Local Exam Zn-Pb

Table H2. (continued, 4 of 9).

Commodities

Host unit

Comment

Sekwi Fm.

Galena and sphalerite are found in certain orange weathered dolostone beds within lower Cambrian Sekwi Formation that are up to 30 m wide and can be traced for several kilometres along strike. The best mineralization is associated with vuggy, porous sections of reefoid dolostone breccia. An 18-metre chip sample across the T-1 showing assayed 0.76% Zn, 0.14% Pb, and 1.4 g/ton Ag. Mount Kindle Fm. Fine grained massive galena, found within fractures in Devonian dolostone with an estimated 30-metre width, yielded a sample that assayed 38.25% Zn and 15.25% Pb. Arnica Fm. Two occurrences of sphalerite and galena in irregular hairline fracture fillings within dolostone are exposed in a 4-foot by 1.5foot outcrop. A representative grab sample across 1.5 feet of this outcrop assayed 4.8% Zn and 3.0% Pb. The showings are primarily talus. Arnica Fm. Sphalerite and minor galena together with dolomite, calcite, and quartz commonly occur as irregular blebs and masses in thin crosscutting veinlets and occasionally in breccia zones up to 12 inches wide. Channel sampling over a true thickness of 29 feet returned 1.32% Zn and 0.02% Pb. Two drill holes tested the zone; assays of up to 4.40% Zn and 0.20% Pb over 16 feet were attained. Arnica Fm. Pb-Zn mineralization is exposed discontinuously over 30 metres in a northeast-trending gully. Amber and red sphalerite and galena are in randomly oriented fractures and within breccia cement. Mineralized breccia pods range up to 60 cm wide and 1.5 metres long. Drilling was unsuccessful. Arnica or Sombre, Mineralization is seen in nine separate occurrences of float and Mount Kindle fms. outcrop over a discontinuous strike length of 600 m. Channel sampling across a mineralized calcite vein yielded 22.4% Zn and 1.38% Pb across 0.3 m. Landry Fm. A sphalerite- and galena-bearing calcite vein strikes subparallel to bedding, and pinches and swells to a maximum thickness of 30 cm, along a 40-metre strike length. Assay results from channel sampling averaged 13.75% Zn and 3.65% Pb over 32 inches. Sombre Fm. The showing consists of 15-20 cm wide massive cerussitesmithsonite fracture-filling in limestone related to a northwesttrending fault. A high-grade grab sample assayed 11.05% Pb and 41.20% Zn. Sombre Fm. The showing outcrops on 2 spurs about 300 feet apart with a 100-foot wide, high-grade, cerussite- and anglesite-bearing scree train between. Hand trenching was done within the scree; a ten-foot channel sample returned averaged assays of 3.85% Pb and 43.86% Zn.

Chapter Appendix Nine H

Name

105PNW0006

Map Label 23

NORMIN ID

Northing

Easting

NTS

Dev

LAN-1

7079892

482657

105P14

Local Exam Pb-Zn-Ag

105PNW0016

33

KEV

7082542

482357

105P14

Local Exam Zn

105PNW0017

34

ALFA

7081892

486707

105P14

Recon

Ba-F-Pb

105PNW0018

35

ART-EKWI No.1

7080892

491007

105P14

Drilled

Zn-Pb

105PNW0019

36

ART-EKWI No.2,3,4

7080043

491607

105P14

Drilled

Zn-Pb

105PNW0020

37

ICE-9

7057943

497407

105P11

Drilled

Pb-Zn

105PNW0021

38

ARN-6

7069292

485907

105P12

Local Exam Pb-Zn

105PNW0033

39

OS-DA

7094590

472757

105P13

Local Exam Zn-Pb

105PNW0034

40

DEE-3

7088291

477307

105P14

Local Exam Zn-Pb-Ag

105PNW0036

41

SCAT-5

7086542

499007

105P14

Local Exam Zn-Pb

Table H2. (continued, 5 of 9).

Commodities

Host unit

Comment

Sekwi Fm.

The LAN-1 showing is hosted in Sekwi Formation primarily talus ; it contains fracture fillings and veins of sphalerite and galena. A continuous chip sample across 11.7 metres assayed 6.13% Pb, 2.42% Zn and 1.5 oz/T Ag. Mount Kindle Fm. Lead-zinc mineralized boulders of coarse-grained, brecciated dolostone cover a 200-square meter area on a large scree slope. Four samples representative of low, average and high grades gave Zn values ranging from 5.7 - 31.48%. Headless Fm. The main showing is a lens of massive barite with 10,000 ppm Cu. Coppercap Fm. The showing is made up of one grab sample taken from subcrop. A quartz stockwork in dolostone contains vein-hosted azurite, bornite, malachite, and chalcopyrite and assayed 3570 ppm Cu. Mount Kindle Twenty-four drill holes tested the area and numerous Fm., Delorme Gp. mineralized intersections were cut, such as 8.97% Zn, 6.26% Pb, and 2.4% Ag over 12.5 feet in hole CBT-7. Local high grade massive sulphide and Ag were cut but mineralization was erratic. Sekwi Fm. Lead-zinc sulphide is within dolostone and associated with quartz and calcite veining, vug- and cavity-infilling, disseminations, and replacement along bedding planes. Assays from discontinuous mineralization ranged from 1-10%, but averaged about 2% combined lead-zinc. Mount Kindle Fm. Sphalerite is evenly disseminated within a dark gray dolostone matrix-supported breccia unit estimated to be about 20 feet thick. Two float samples assayed 9.0% and 3.6% Zn, while a sample in limestone below this unit, assayed 9.27% Zn. Mount Kindle Fm. Disseminated sphalerite and minor galena together with calcite, sparry dolomite and minor quartz in microfractures, fractures, crackle and fault breccias in dolostone returned chip sample assays of 0.19-1.84% Zn and trace-0.18% Pb.

Chapter Appendix Nine H

Name

106ASE0013

Map Label 14

NORMIN ID

Name

Northing

Easting

NTS

Dev

106ASW0006

Map Label 7

PALM West

7143114

459182

106A05

Local Exam Zn-Pb

106ASW0007

8

REV Main

7110392

484532

106A03

Drilled

Zn-Pb

106ASW0008

9

Cirque

7110492

482662

106A03

Drilled

Zn-Pb-Ag

106ASW0009

10

Waterfall

7109592

482607

106A03

Local Exam Zn-Pb

106ASW0019

11

PALM Main

7142364

462082

106A05

Local Exam Zn-Pb

106ASW0020

B

Mountain River Beryl

7141024

477188

106A06

Local Exam Emer

106ASW0021

C

Twitya

7141064

477112

106A06

Recon

Cu

106ASW0022

D

Sheep-bed

7135957

491133

106A06

Recon

Zn

106ASW0023

E

River Boulder

7149062

496501

106A06

Recon

Cu-Ag

106ASW0024 F

Tepee

7134392 496962 106A06

Recon

Pb-Ag

“Tepee dolostone”

The Tepee showing is made up of one grab sample taken from a malachite-bearing stockwork in dolostone. The sample assayed >5000ppm Pb, and 35.1ppm Ag.

106ASW0025 G

Bear Rock

7149721 496318 106A06

Recon

Ba

Bear Rock Fm.

This showing is defined by a single grab sample from a barite vein/stockwork (10-30cm wide), cutting through dolostone, which has a small amount of malachite staining and local red oxide material. The sample assayed 35.1% Ba.

Host unit

Comment

Sekwi Fm.

Lead-zinc mineralization is associated with a stockwork of quartz and calcite veining that locally extends for 600 feet along strike. Grab samples returned assays up to 38.0% Zn, 5.4% Pb and 23.0 oz/ton Ag. Mount Kindle Fm. Mineralization is fault- and strata-related, and is exposed over an area of 300 horizontal by 450 vertical feet. Four diamond drill holes intersected zinc and lesser lead sulphides with assays up to 8.65% Zn over 73 feet. Mount Kindle Fm. Sphalerite- and galena-bearing crackle zones, veins, and disseminations can be traced in outcrop and talus of sheared dolostone for several thousand feet along a fault. Chip sample assays returned 0.12-5.88% Zn and 0.05-2.84% Pb. Mount Kindle Fm. Sphalerite and galena with minor tetrahedrite are related to faults and fracture filling, crackle zone and vug filling. Chip samples assayed an average 3.76% Zn and 0.15% Pb. Sekwi Fm. Outcrop chip samples at the Main showing assayed 3.3% Zn over 65 feet. Sphalerite and minor galena are associated with quartz and calcite veining, infilling vugs and cavities, disseminations, as well as replacement along bedding planes in dolostone. Twitya Fm. Beryl is hosted by quartz-andesine-dolomite hydrothermal veins in thinly-laminated to medium-bedded pyritic siltstone and sandstone. The veins are 1 cm to 1 m thick and are present in at least three zones that extend over 20 metres. The emerald compositions, vein petrogenesis and tectonic history are comparable to Columbia-style emerald deposits. Twitya Fm. The showing consists of one grab sample taken from a dolostone outcrop with malachite staining, and disseminated chalcopyrite, pyrite, bornite and pyrrhotite; this assayed 3650 ppm Cu. Sheepbed Fm. The Sheepbed showing is defined by one grab sample taken from a mineralized dolostone outcrop; it contained abundant sphalerite with some chalcopyrite and assayed 13,100 ppm Zn. The showing is defined by a float sample taken from a riverbed. The copper oxide stained boulder assayed 5570 ppm Cu.

Chapter Appendix Nine H

Table H2. (continued, 9 of 9).

Commodities

423