petrology, mineral chemistry and HFSE concentration processes of the nepheline syenite pegmatites of ...... Igneous and metamorphic petrology.2nd edition.
Chemical variations and textural relationships of the wöhlerite mineral group in the Larvik Plutonic Complex syenite pegmatites, Vestfold and Telemark County: Implications for Zr, Nb and Ti mobility, concentration and distribution in the alkaline pegmatite zirconosilicates of the Langesundsfjord and Larvik areas of southern Norway Submitted by Paul Sotiriou to the University of Exeter as dissertation towards the degree of Master of Science in Mining Geology, September 2013
I certify that all material in this dissertation, which is not my own work has been identified and that no material is included for which, a degree has previously been conferred on me. Signed:
ABSTRACT Optical microscope, cathodoluminescence, SEM and EPMA work and fieldwork were carried out on 10 nepheline syenite pegmatites across the Larvik Plutonic Complex (LPC) in the Vestfold and Telemark counties of southern Norway. The mineralogy, petrology, mineral chemistry and HFSE concentration processes of the nepheline syenite pegmatites of Langesundsfjord and Larvik areas were the focuses of this project and were investigated during the course of the project. The minerals of focus in this dissertation were the wöhlerite mineral group, and to a far lesser extent, the rosenbuschite mineral group. The wöhlerite and rosenbuschite group minerals were some of the first minerals to crystallize being preceded only by apatite, zircon, pyrochlore and zircon. The feldspars and nepheline occur adjacent to wöhlerite group minerals more than any other mineral and are the most common minerals in the pegmatites. Wöhlerite is often found at the base or margins of the pegmatites and can be found as crystals adjacent to crystals of amphibole, aegirine and biotite. The mineral assemblages found and the parental magmatic compositions were deemed to be transitional to medium agpaitic. The chemistry of the wöhlerite and rosenbuschite group minerals shows both localized and regional variations in the pegmatites studied. The apfu composition in wöhlerite vary from Zr0.92. Nb0.71 and Ti0.09 to Zr0.95, Nb0.78 and Ti0.14, the hiortdahlite apfu composition vary from Zr1.12, Nb0.20 and Ti0.10 to Zr1.03, Nb0.14 and Ti0.04 and the rosenbuschite apfu composition vary from Zr1.75, Nb0.10 and Ti1.21 to Zr1.15, Nb0.08 and Ti0.94. The final wöhlerite group mineral to be analysed, låvenite, has the following apfu composition Zr1.78, Nb0.13 andTi0.20. These chemical variations and the mobility of Zr, Nb and Ti can be explained by element substitution mechanisms such as Zr4+↔Ti4+, Nb5++O2- → Zr4++F- and Nb5++O2- → Ti4++F-, which are the atomic scale manifestations of magmatic processes. The substitution mechanisms observed in the wöhlerite and rosenbuschite mineral groups are governed by factors such as the element’s valency and ionic radius as well as the coexisting mineral assemblage. The coexisting mineral assemblage governs the availability and element mobility of Zr, Nb and Ti as well as Fe, Mn, Na and F. The varying coexisting mineral assemblages, and the presence of the wöhlerite and rosenbuschite mineral groups themselves, is governed by the evolution of the parental agpaitic nepheline syenite pegmatite magmas. Therefore, the wöhlerite group minerals were only stabilized when the HF activity was high enough to stabilize these minerals. The alkali activities and volatile activities control the stability of minerals such as wöhlerite, hiortdahlite, låvenite, rosenbuschite and hainite with high HF activities and medium Na activities being required to stabilize the wöhlerite mineral group in the LPC pegmatites studied. In addition to these findings, new occurrences of hainite and hiortdahlite were found at Arøyskjærene and AS Granit quarry respectively based on the composition of the analyses. Furthermore, in Arøyskjærene some of the analyses also resembled the composition of kochite based on the Zr and Nb contents; however, the Ca content was more akin to rosenbuschite, which tentatively suggests a composition intermediate between rosenbuschite and kochite. Lastly, there are cores and rims of wöhlerite crystals from the Skutesundskjær and Sagåsen that have compositions intermediate between wöhlerite and marianoite, which has never been found in any wöhlerite hosted nepheline syenites before. 1
ACKNOWLEDGEMENTS I would like to thank my wonderful supervisors Dr Frances Wall and Dr. Henrik Friis for all their support and advice throughout my project. Additionally, I would like to thank the NGU (Norwegian Geological Survey) for their financial support, their supply of literature and their advice and encouragement. I would particularly like to thank Julian Schilling as he has supported me throughout as has Marianne Engdal. Thanks must be given to Grete Henriksen at the NGU library who helped me track down some references. Sampling from the Sagåsen quarry would not have been possible without the permission of Ole Petter Nyhagen at Lundhs AS who own the Sagåsen quarry from which some of the samples were taken. I also carried out fieldwork at Arent quarry and I am grateful for the access granted. Ole and Lundhs’ support of my project has been immense. To both the NGU and Lundhs AS I say tusen takk og takk for hjelpen for their support and encouragement. I would like to thank Henrik Friis for granting me access to samples at the Oslo Naturhistorisk Museum (NHM) as well as being an awesome and thorough supervisor. I would like to thank Gina Nygard and Svein Erik Nygard at the Torpevannet campsite in Tvedalen, Vestfold, who let me stay in a very spacious cabin throughout my stay in my fieldwork area. Alf Olav Larsen was particularly supportive of my project and provided many useful insights into the Langesundsfjord area and allowed me to go on the Kongsberg Mineral Symposium excursion to the. Paula Piilonen deserves a thank you for offloading some knowledge on the pegmatites of the Langesundsfjord. I would also like to thank Gavyn Rollinson, Sharon Uren and Peter Frost for their respectful services, advice and support whilst I carried out my CL, OM, and SEM analytical and petrographical work. I especially want to thank Steve Pendray for making all those polished sections and polished blocks for me. Ben Snook gave me some very good advice about taking samples from pegmatites. Henrik Friis and Muriel Erambert are sincerely thanked for letting me use the EPMA and helping me with my project. I am obliged to thank my fellow CSM Mining Geology MSc 2013 classmates for their support, advice, encouragement and awesomeness. Lastly, I would like to thank my mum Christine, my stepdad Clemente, my sister Anastasia and the rest of my family for their support and encouragement.
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LIST OF CONTENTS Abstract..................................................................................................................................................................1 Acknowledgements...........................................................................................................................................2 Definitions...........................................................................................................................................................13 Chapter 1: Introduction................................................................................................................................14 1.1: Introductory statement........................................................................................................................14 1.2: Scope of the project................................................................................................................................14 1.3: Aim of the project...................................................................................................................................15 1.4: Objectives of the project......................................................................................................................15 Chapter 2: Background.................................................................................................................................17 2.1: Regional geologic and tectonic setting of Vestfold’s and Telemark’s nepheline syenite pegmatites..........................................................................................................................................17 2.2: Summary of the geological evolution of southern Norway..................................................18 2.3: The Oslo Rift..............................................................................................................................................20 2.3.1: Extrusive and intrusive lithologies of the Oslo Rift.............................................................................. 21
2.3.1.1: Extrusive lithologies.......................................................................................................................................21 2.3.1.2: Intrusives............................................................................................................................................................22 2.3.1.3: Summary of the petrogenesis of the intrusive rocks of the Oslo Rift.......................................23 2.3.2: The wider tectonic framework of the Oslo Rift......................................................................................23
2.4: The Larvik Plutonic Complex (LPC)................................................................................................24 2.4.1: Intrusive history of the LPC............................................................................................................................26 2.4.2: Geological framework of the Langesundsfjord area............................................................................26
2.5: The nepheline syenite pegmatites of the Langesundsfjord and Larvik areas......................................................................................................................................................................27 2.5.1: Pegmatite types of the Langesundsfjord and Larvik areas............................................................... 27
2.5.1.1: The Stavern type..............................................................................................................................................28 2.5.1.2: The Tvedalen type........................................................................................................................................... 28
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2.5.1.3: The Langesundsfjord type........................................................................................................................... 28 2.5.2: Mineralogy of the nepheline syenite pegmatites of the Langesundsfjord area and the LPC..........................................................................................................................................................................................29
2.6: The wöhlerite group..............................................................................................................................32 2.6.1: Occurrence............................................................................................................................................................. 32 2.6.2: Locality Occurrence............................................................................................................................................32 2.6.3: Crystal structure..................................................................................................................................................33
2.7: Petrological, mineralogical and economic significance of agpaitic nepheline syenites................................................................................................................................................................34 Chapter 3: Fieldwork and sampling........................................................................................................36 3.1: Sampling strategy...................................................................................................................................36 Chapter 4: Analytical procedures.............................................................................................................37 4.1: OM (and Photomicrograph OM) and CL observations methodology......................................................................................................................................................37 Chapter 5: Fieldwork observations.........................................................................................................39 5.1: Sagåsen quarry........................................................................................................................................39 5.2: Arent quarry..............................................................................................................................................41 5.3: Barkevik......................................................................................................................................................42 5.4: Låven............................................................................................................................................................43 5.5: Arøyskjærene............................................................................................................................................44 5.6: AS Granit quarry......................................................................................................................................45 Chapter 6: Petrography.................................................................................................................................48 Chapter 7: Semi quantitative and quantitative microbeam results...........................................62 7.1: SEM and EPMA methodology......................................................................................................................................................63 7.1.1: SEM............................................................................................................................................................................ 63 7.1.2: EPMA........................................................................................................................................................................64
7.2: SEM observations...................................................................................................................................64 7.3: EPMA data results and observations..............................................................................................64
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Chapter 8: Discussion....................................................................................................................................92 8.1: Discussion of results and observations.........................................................................................92 8.2: Discussion and comparison of previous work on the wöhlerite group minerals............................................................................................................................................................110 8.2.1: Discussion and comparison of the chemical compositions, variations and cause of variations of the wöhlerite group minerals and rosenbuschite group minerals..............................111 8.2.2: Brief discussion of the chemical indicators of magmatic evolution in nepheline syenites..............................................................................................................................................................................122
Chapter 9: Conclusion.................................................................................................................................123 References........................................................................................................................................................125 Appendices.......................................................................................................................................................134 Appendix 1- Microscope qualitative and semi quantitative observations...........................134 Appendix 2 –Apfu variations traverse graphs..................................................................................157 Appendix 3 –Apfu chemical relationship plots................................................................................160 Appendix 4 –Field photos..........................................................................................................................164 Appendix 5 – Data analysis calculations.............................................................................................169 Appendix 6 –OM photomicrographs (all at x5 magnification)..................................................171 Appendix 7 - CL photomicrographs (all at x4 magnification)...................................................180 Appendix 8 – SEM and EPMA BSE images..........................................................................................182 Appendix 9 – SEM EDS spectra...............................................................................................................187 Appendix 10 – Scans of polished sections..........................................................................................188 Figures Figure 2.1- Simplified geological map of the Oslo Graben (After Larsen et al. 2008)....................................................................................................................................................................17 Figure 2.2 – Simplified tectonic map showing an overview of Western Europe with the Variscan front, the Tornquist fault system and the Oslo Rift shown in the context of the pre rift configurations with the Caledonian structures and the boundary of the Fennoscandian Craton (After Larsen et al. 2008).............................................................................18 Figure 2.3 – Geological sketch map of the geology of Scandinavia in a Proterozoic context. The map shows how the Oslo Rift is related to the Proterozoic rocks that surround it (After Binden et al. 2008a).................................................................................................19
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Figure 2.4 – Geological map (1:250,000) of the bedrock of southern Norway showing the regional geology of the study area. The key to the map is located on right hand side (After NGU 2013). The area of study is indicated by the red rectangle and is located in the western half of the LPC with its monzonites and syenites shown in pink-red and pink........................................................................................................................................................................20 Figure 2.5 – Schematic of the architecture of the Oslo Rift including the graben segments and the master faults (After Larsen et al. 2008)................................................................................21 Figure 2.6 – A diagram showing how the intrusives of the Oslo Region were thought (by Barth 1944 – ‘Barth’s family tree’ based on range in modal minerals) to have developed by fractional crystallization of a monzonitic magma which was derived from a alkali basaltic magma of mantle origin (After Barth 1944 & Segalstad and Raade 2003)..........22 Figure 2.7 - Map showing the distribution of Late Carboniferous to Early Permian magmatic rocks and Late Permian sedimentary basins of northern Europe (After Heeremans et al. 2004).................................................................................................................................24 Figure 2.8–Schematic close up geological map of the Larvik Plutonic Complex and its environs (After Petersen 1978; Berthelsen et al. 1996; Dahlgren 2010; Andersen et al. 2012).....................................................................................................................................................................25 Figure 2.9 – Some of the HFSE and REE minerals present in the nepheline syenite pegmatites of the Langesundsfjord (After Andersen et al. 2010)..............................................30 Figure 2.10 - Some of the Zr, Nb, Ti and REE minerals present in the Larvik Plutonic Complex (After Andersen et al. 2012)....................................................................................................31 Figure 2.11 – Crystal structure of wöhlerite. The left hand diagram shows the crystal structure of the wöhlerite group whilst the right hand diagram show the octahedral walls of wöhlerite seen down [010](After Biagoni et al. 2012)..................................................33 Figure 2.12 – Members of the wöhlerite, rosenbuschite and mosandrite groups with their chemical formulae and physical properties (After Biagoni et al. 2012).....................................................................................................................................................................34 Figure 3.1 – Google Map showing the locations of the samples from the Langesundsfjord-Larvik area studied with locations being approximate (Google Maps 2013).....................................................................................................................................................................36 Figure 5.1 – Google Map showing the location of the Sagåsen quarry, near Mørje, Telemark County, Norway. Sample locations are shown and are approximate (Google Maps 2013)........................................................................................................................................................39 Figure 5.2 – Blocks of coarse fresh pegmatite at Sagåsen quarry showing the macroscopic textures prevalent in the pegmatites at Sagåsen near Mørje and the dominance of nepheline, albite and microcline..................................................................................40 Figure 5.3 – Map of the Arent quarry near Tvedalen, Vestfold County, Norway (Google Maps 2013)........................................................................................................................................................41
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Figure 5.4 – Partially altered coarse grained pegmatite at Arent quarry with hammer for scale. The hammer is 30cm high...............................................................................................................42 Figure 5.5 – Shows the textures on display at Barkevik. The two images focus on wöhlerite and its relation to biotite and microcline. The image on the right shows a zoomed out image of the left hand image.............................................................................................43 Figure 5.6 – Pegmatite textures on Låven. Left: Big crystals of aegirine with wöhlerite, nepheline and microcline. Right: Zoomed out view of part of the nearby pegmatite. Notebook and author’s hand and pencil for scale.............................................................................44 Figure 5.7 – Pegmatites at Arøyskjærene. Left: A flat lying pegmatites intruding into the larvikite country rock. Right: Multiple pegmatites cutting across larvikite in the Arøyskjærene....................................................................................................................................................45 Figure 5.8 – AS Granit quarry in near Tvedalen, Vestfold County, Norway (Google Maps 2013).....................................................................................................................................................................45 Figure 5.9 – Pegmatites cutting through the larvikite host rocks at the AS Granit quarry near Tvedalen....................................................................................................................................................46 Figure 5.10 – Wöhlerite crystals set in a feldspar-nepheline dominated pegmatite mass with biotite and fluorite also occurring. This was taken at the base of the pegmatite.............................................................................................................................................................46 Figure 6.1 - Close up of the mafic minerals in contact with wöhlerite and surrounded by feldspars, feldspathoids and zeolites at Barkevik. The pegmatite is not in situ...................49 Figure 6.2 –Mafic minerals and wöhlerite exposed in a not in situ pegmatite at Barkevik...............................................................................................................................................................49 Figure 6.3 – Coarse grained fresh pegmatite at Sagåsen quarry near Mørje with rucksack for scale. The photo shows a contact between the pegmatite and the larvikite country rock. Note: this is not an in situ outcrop, it is a block of pegmatite and larvikite that has been quarried....................................................................................................................................................50 Figure 6.4 – Photo of a finer grained, smaller pegmatite at Arent quarry near Tvedalen. Note the notebook for scale........................................................................................................................50 Figure 6.5 – Altered coarse grained pegmatite at Arent quarry with notebook for scale.......................................................................................................................................................................51 Figure 6.6 – Photograph of the base/margin of a pegmatite at Arøyskjærene showing mafic minerals (such as amphibole, biotite, magnetite, ilmenite and aegirine), wöhlerite, rosenbuschite and hiortdahlite. The pegmatite is not in situ but would have been horizontal with the way up being in the opposite direction to where the pencil (for scale) is pointing..............................................................................................................................................51 Figure 6.7 – Coarse grained fresh pegmatite at Arent quarry which shows the textural relationships in the pegmatite and the accumulation of mafic minerals at the base and margins of the pegmatite. Plant is about 50cm high........................................................................52
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Figure 6.8 – Close up of the mafic minerals and wöhlerite accumulated at the base of one of the splays of the pegmatites at Arent quarry. Photo is about 50cm across....................................................................................................................................................................52 Figure 6.9 – Crystals of wöhlerite located towards the bottom of the pegmatite.............................................................................................................................................................53 Figure 6.10– Diagram showing a mineral paragenesis of the studied nepheline syenite pegmatite localities. The placement of the lines is only an estimate based on optical petrography and hand specimen petrography work. This paragenesis agrees with observations by Larsen et al. (2010)......................................................................................................54 Figure 6.11– Sku-N3. SEM-BSE image of rosenbuschite crystals that have grown into the biotite space with aegirine formed in between the rosenbuschite crystals. The biotite crystallized after the rosenbuschite based on the textures observed......................................55 Figure 6.12 – Sagå-N5. SEM-BSE image showing the apatite-fluorite-pyrochlore-zircon mass in at the contact between the wöhlerite and the microcline. It appears as though the wöhlerite has been altered to zircon, fluorite and pyrochlore. Pyrochlore and zircon are the brighter minerals. The scale bar is 100μm across.............................................................56 Figure 6.13 – Sagå-N5. Top left: SEM-BSE image of calcite-zircon-fluorite-pyrochlore vein through a crystal of wöhlerite (grey). Top right: Close up of part of the calcite vein. Bottom: Another part of the calcite (dark) vein with more zircon and pyrochlore (bright).................................................................................................................................................................57 Figure 6.14- SEM-BSE image of Sku-N1 with microcline, albite, wöhlerite, fluorite and zircon. The fluorite and zircon forms as the result of alteration around the rim of the wöhlerite crystal..............................................................................................................................................57 Figure 6.15 – Wöhlerite under XPL from Saga-N3 and Bark-N1. The top left and top right images are of twinned wöhlerites from Saga-N3. The bottom left image is of twinned and non twinned wöhlerites from Bark-N1. The top images show wöhlerite with microperthite and aegirine (r) and microperthite (l). The scale bar length equates to 500μm...................................................................................................................................................................60 Figure 6.16 – OM photomicrograph image of the textures present in a wöhlerite from Sagå-N5 in XPL. The textures seen include wöhlerite lamellar twinning, fractures and veins. The scale bar length equates to 500μm....................................................................................61 Figure 6.17 – OM photomicrograph image of calcite veinlet present in a wöhlerite from Sagå-N5 in XPL. Alteration has taken place adjacent to the veinlet with secondary zircon and pyrochlore present in addition to fluorite. The scale bar length equates to 500μm...................................................................................................................................................................61 Figure 6.18 – OM photomicrograph image of the microfractures present in a wöhlerite crystal from Sagå-N5 in XPL. The scale bar length equates to 500μm.....................................61 Figure 7.1 – Geological map of the Langesundsfjord area showing the variations in the chemistry of rosenbuschite from Arøyskjærene (Arøy-N1) and Låven (Låv-N4 (2) and Låv-N4 (1))(After NGU 2013)..................................................................................................................71 8
Figure 7.2 – Geological map of the Langesundsfjord area showing the variations in the chemistry of hiortdahlite from Arøyskjærene (Arøy-N1), Låven (Låv-N4 (2) and Låv-N4 (1)), Øst Stokkøya (Østok-N1) and Skutesundskjær (Sku-N4)(After NGU 2013)..................................................................................................................................................................71 Figure 7.3– Geological map of the Langesundsfjord area showing the variations in the chemistry of hiortdahlite from Sagåsen quarry (Sagåsen 4) and AS Granit quarry (GranN1)(After NGU 2013)..................................................................................................................................72 Figure 7.4 – Geological map of the Langesundsfjord area showing the variations in the chemistry of hiortdahlite from Sagåsen quarry (Sagåsen 4 and Sagå-N5), Saga I (SagaN3), Håkestad (Tjølling) quarry (Håke-N1), Skutesundskjær (Sku-N1 and Sku-N4), Barkevik (Bark-N1) and Øst Stokkøya (Østok-N1)(After NGU 2013).....................................72 Figure 7.5 – Apfu variations plot of Ti, Fe and Mn across Traverse D in a wöhlerite in Sku-N1..................................................................................................................................................................82 Figure 7.6 – Apfu variations plot of Zr and Nb across Traverse D in a wöhlerite in SkuN1...........................................................................................................................................................................83 Figure 7.7 - Apfu variations plot of Zr and Nb across Traverse A in a wöhlerite in SagaN3...........................................................................................................................................................................83 Figure 7.8 - Apfu variations plot of Ti, Fe and Mn across Traverse C in a wöhlerite in Sku-N1..................................................................................................................................................................84 Figure 7.9 - Apfu variations plot of Zr and Nb across Traverse C in a wöhlerite in SkuN1...........................................................................................................................................................................84 Figure 7.10 - Apfu variations plot of Ti, Fe and Mn across Traverse B in a wöhlerite in Saga-N3................................................................................................................................................................85 Figure 7.11 – Compositional variation plot of the wöhlerite and rosenbuschite group minerals from across the Larvik Plutonic Complex with data being plotted using the Triplot program. (Ca+Mg+Mn+Fe) is equal to VI (R2+)......................................................................................................................................................................86 Figure 7.12 - Compositional variation plot of the rosenbuschite group minerals from across the Larvik Plutonic Complex with data being plotted using the Triplot program. (Ca+Mg+Mn+Fe) is equal to VI (R2+)....................................................................................................86 Figure 7.13 – Compositional variation and cation distribution plot of wöhlerite, låvenite, hiortdahlite and rosenbuschite with Nb, Ti and Zr + Hf cation sites plotted using the Triplot program................................................................................................................................................87 Figure 7.14 – Apfu chemical relationship plot that shows the inverse proportional relationship between Mn2+ and Fe2+ in wöhlerites from Saga-N3............................................89 Figure 7.15 – Apfu chemical relationship plot that shows the inverse proportional relationship between Nb5+ and Ti4+ in wöhlerites from Sagå-N5.............................................89
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Figure 7.16 – Apfu chemical relationship plot that shows the inverse proportional relationship between Nb5+ and Zr4+ in wöhlerites from Sagåsen 4..........................................89 Figure 7.17 – Apfu chemical relationship plot that shows the positive correlation relationship between Zr4+ and Ti4+ in wöhlerites from Saga-N3...............................................89 Figure 7.18 – Apfu chemical relationship plot that shows the positive correlation relationship between Ca2+ and Fe2+ in wöhlerites from Saga-N3..............................................90 Figure 7.19 – Apfu chemical relationship plot that shows the inverse proportional relationship between Ca2+ and Mn2+ in wöhlerites from Saga-N3............................................90 Figure 7.20– Apfu chemical relationship plot that shows the inverse proportional relationship between Zr4+ and F- in wöhlerites from Gran-N1...................................................90 Figure 7.21 – Apfu chemical relationship plot that shows the inverse proportional relationship between Na+ and F- in wöhlerites from Låv-N4 (2)...............................................90 Figure 7.22 – Apfu chemical relationship plot that shows the inverse proportional relationship between F- and Nb5+ in wöhlerites from Saga-N3..................................................91 Figure 8.1 – Half a metre thick coarse grained pegmatite at Arøyskjærene showing the feldspar-nepheline dominated core quite nicely. Note the mafic minerals concentrated at the margins. The core is partially altered to various zeolites such as natrolite and analcime...............................................................................................................................................................94 Figure 8.2 – Image showing the core of a pegmatite at Arent quarry near Tvedalen and its textural relationship to the margins and base of the pegmatite which has a far greater concentration of mafic minerals. The photo is about 2m across................................................94 Figure 8.3 – EPMA-BSE image of the 3 wöhlerite group minerals present in the Østok-N1 sample: hiortdahlite, låvenite and wöhlerite. The darker phase is hiortdahlite, whilst the brighter phase is låvenite and the intermediate phase is wöhlerite.........................................96 Figure 8.4 - Compositional variation plot of the wöhlerite and rosenbuschite group minerals from across the Larvik Plutonic Complex with data being plotted using the Triplot program. (Ca+Mg+Mn+Fe) is equal to VI (R2+)..............................................................114 Figure 8.5 - Compositional variation of cuspidine-group minerals expressed in atomic percentage of the major occupants of octahedrally coordinated cation sites, including Ti, Zr + Hf, Nb + Ta and divalent cations (VIR2+ = Ca + Mn + Fe + Mg)(After Chakhmouradian et al. 2008)................................................................................................................115 Figure 8.6 – Triangular composition variation plot showing the distribution of Ti and Zr across the 10 localities sampled by Andersen et al. (2010). The data used was sourced from Andersen et al. (2010).....................................................................................................................116 Figure 8.7 – Shows the most important Zr and Ti mineral assemblages present in the different pegmatite types of the LPC (After Andersen et al. 2012).........................................119
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Figure 8.8 - Shows the stability conditions of the minerals of interest as well as minerals such as zirconolite, catapleiite, lorenzite, astrophyllite, rinkite, mosandrite, eudialyte, zircon and titanite in 2D (top) and 3D (bottom). The HF, H2O and Na activities affect the stability of the all of these minerals and are a function of alkali and volatile activities of the magma and by extension the peralkalinity of the magma...................................................120 Tables Table 6.1 – This shows the minerals identified during the petrography. Mineral formulae are from Andersen et al. (2010, 2012) and Larsen et al. (2010). Hiortdahlite I was identified as opposed to hiortdahlite II (See Merlino and Perchiazzi 1985, 1987).....................................................................................................................................................................48 Table 6.2 – Determination of the agpaicity of the Langesundsfjord nepheline syenite pegmatites studied based on mineral identification. Based on Mitchell (1996) and Khomyakov (1995).........................................................................................................................................59 Table 7.1 – Table with information on the samples taken, the localities sampled, their locations and the type of sample...............................................................................................................62 Table 7.2 – Provides information about the epoxy mount samples, their IDs, their localities and the type of analysis/microscope sample. Due to time constraints, only the Sagåsen 4 and Håke-N1 epoxy samples were analysed..................................................................63 Table 7.3 - Representative individual analyses and apfu compositions of wöhlerites from Saga-N3, Sku-N4, Sagå-N5, Bark-N1, Østok-N1 and Sku-N1..............................................65 Table 7.4 - Representative individual analyses and apfu compositions of wöhlerites, rosenbuschites and hiortdahlites from Arøy-N1, Låv-N4(2), Låv-N4(1), Sku-N1, Sagåsen 4, Gran-N1 and Håke-N1...............................................................................................................................66 Table 7.5 – Shows the average structural formulae of wöhlerite, hiortdahlite, rosenbuschite and låvenite from the pegmatite localities sampled from across the LPC.........................................................................................................................................................................67 Table 7.6 - Average analyses and apfu compositions of wöhlerites from Saga-N3 and Sku-N4 with standard deviations (signified by the number in brackets next to the analyses)..............................................................................................................................................................73 Table 7.7 - Average analyses and apfu compositions of wöhlerites from Sku-N4, Sagå-N5 and Bark-N1 with standard deviations (signified by the number in brackets next to the analyses)..............................................................................................................................................................74 Table 7.8 - Average analyses and apfu compositions of wöhlerites from Bark-N1, ØstokN1 and Sku-N1 with standard deviations (signified by the number in brackets next to the analyses)......................................................................................................................................................75 Table 7.9 - Average analyses and apfu compositions of wöhlerites from Sku-N1, Sagåsen 5 and Håke-N1 with standard deviations (signified by the number in brackets next to the analyses)......................................................................................................................................................76 11
Table 7.10 - Average analyses and apfu compositions of wöhlerites from Håke-N1 and hiortdahlites from Sku-N4 with standard deviations (signified by the number in brackets next to the analyses)...................................................................................................................77 Table 7.11 - Average analyses and apfu compositions of hiortdahlites from Gran-N1, Arøy-N1, Låv-N4 (2) and Låv-N4 (1) with standard deviations (signified by the number in brackets next to the analyses)..............................................................................................................78 Table 7.12 - Average analyses and apfu compositions of hiortdahlites from Låv-N4 (1), Østok-N1 and Sagåsen 4 with standard deviations (signified by the number in brackets next to the analyses)......................................................................................................................................79 Table 7.13 - Average analyses and apfu compositions of hiortdahlites from Sagåsen 4 and rosenbuschites from Arøy-N1, Låv-N4 (2) and Låv-N4 (1) with standard deviations (signified by the number in brackets next to the analyses)..........................................................80 Table 7.14 - Average analyses and apfu compositions of låvenite from Østok-N1, titanite from Låv-N4 (1) and pyrochlore from Sagå-N5 with standard deviations (signified by the number in brackets next to the analyses).....................................................................................81
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DEFINITIONS REE = Rare Earth Elements - LREE, HREE, Y and Sc HFSE = High Field Strength Elements - Zr, Nb, Hf, Ta, Ti, U and Th SEM = Scanning Electron Microscope SEM-BSE = Scanning Electron Microscope – Back Scatter Electron EPMA = Electron probe microanalysis CL = Cathodoluminescence OM = Optical Microscope XPL = Cross Polarized Light PPL = Plane Polarized Light NGU = Norges Geologiske Undersøkelse (the Norwegian Geological Survey) LPC = Larvik Plutonic Complex CSM = Camborne School of Mines UoE = University of Exeter Oslo NHM = Oslo Natural History Museum UiO = University of Oslo WDS = Wave Dispersive Spectra EDS = Energy Dispersive Spectra
apfu = Atoms per formula unit αH2O = water activity αHF = fluorine activity αNds = alkali activity
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CHAPTER 1: INTRODUCTION 1.1: INTRODUCTORY STATEMENT The Langesundsfjord has been studied for its famous mineral rich nepheline syenite pegmatites for 200 years, yet relatively little study has been done on the wöhlerite group minerals: Wöhlerite (Na2Ca4ZrNb(Si2O7)2O3F), hiortdahlite (Na2Ca4Zr(Nb,Ti) (Si2O7)2(F,O)4) and låvenite (Na2(Na,Ca)2(Fe2+,Mn,Ti)2(Nb,Zr)2(Si2O7)2(O,F)4). Låvenite has received the most attention, whilst wöhlerite and hiortdahlite haven’t been investigated in as much detail. Wöhlerite will be focused on in particular to study how and why concentrations of HFSE such as Zr, Nb and Ti vary in zircono- and titanosilicates of the wöhlerite and rosenbuschite mineral groups. Studying samples containing wöhlerite from multiple localities across the LPC will provide information on the mineral chemistry and textural relations of wöhlerite. The mineral chemistry and textural relationships will be used to determine the chemical relationships between the elements of interest (Zr, Nb and Ti in particular) and the coexisting mineral assemblages at each locality which will govern how elements exchange for one another and which can explain any chemical variations. Modern analytical and optical techniques such as OM, CL, SEM and EPMA will be used to study pegmatites from the Langesundsfjord and Larvik areas.
1.2: SCOPE OF THE PROJECT Many publications have been written on the investigation of the pegmatites in the Langesundsfjord area. The seminal work of Brøgger (1890) has set the tone for research on the area. Recent publications (Andersen et al. 2012; Andersen et al. 2010; Larsen et al. 2010) have since continued research on the REE and HFSE mineral bearing nepheline syenite pegmatites of the Langesundsfjord area using modern analytical techniques. To fulfil the objectives set out above using modern analytical techniques is important as this will give modern insights into the petrology, mineral chemistry, and the textural relationships between the minerals to be studied. The wöhlerite group minerals wöhlerite and hiortdahlite will be the main focus of this study. Despite being discovered by Scheerer in 1843 (Scheerer 1843, 1844, 1845a) and 170 years of investigation since this discovery (Brøgger 1890, Andersen et al. 2010, Larsen 2010, 14
Marks et al. 2011, Andersen et al. 2012 and Piilonen et al. 2012), it appears that the chemistry and textural relations of the wöhlerite group minerals have not been studied in a lot of detail by modern analytical and optical methods. These modern methods will shed new light on this fascinating mineral group. The purpose behind this dissertation is to obtain observational and analytical data to find out how the chemical variations and textural relationships of the wöhlerite group minerals varies across the LPC and what these variations reveal about the evolution of the parental nepheline syenite pegmatite magmas. Finding out how and why Zr, Nb and Ti varies in wöhlerite group minerals may could reveal how these elements are concentrated and give insights into the evolution of the parental nepheline syenite magma.
1.3: AIM OF THE PROJECT The aim of this MSc thesis project is to determine the mineralogy, petrology and mineral chemistry of the wöhlerite and rosenbuschite mineral groups of the nepheline syenite pegmatites of the Langesundsfjord and Larvik areas of Vestfold and Telemark in southeastern Norway. The wöhlerite mineral group will be the main focus of this study as well as how the wöhlerite group minerals relate to their adjacently associated common rock forming minerals and Nb-Ti-Zr-REE minerals. The wöhlerite group will be focused on because of the lack of study it has received as well as because any chemical variations could reveal information about the conditions under which the wöhlerite group mineral crystallized.
1.4: OBJECTIVES OF THE PROJECT 1. Determine the mineral chemistry of the wöhlerite group minerals in the nepheline syenite pegmatites to be studied across the Larvik Plutonic Complex 2. Calculate the correct mineral formulae of the wöhlerite group minerals 3. Establish if there are any variations in the mineral chemistry of the wöhlerite group minerals 4. Look into the distribution of Nb, Zr and Ti in wöhlerite group minerals across the Larvik Plutonic Complex 5. Conduct a mineral paragenesis of the wöhlerite group and adjacent associated minerals in the nepheline syenite pegmatites across the Larvik Plutonic Complex 15
6. Try to explain the textural, chemical and mineralogical relationships between the different wöhlerite group minerals and other adjacent minerals 7. Try to establish why wöhlerite occurs at the base and margins of pegmatites adjacent to mafic minerals 8. Establish whether the nepheline syenite pegmatites studied are miaskitic, low/mildly agpaitic, highly agpaitic or hyperagpaitic based on the mineral assemblages present 9. Find substitution mechanisms to explain any compositional variations in the wöhlerite and rosenbuschite group minerals and try to determine what this reveals about the conditions of crystallization. 10. Try to determine the Nb-Zr-Ti mobility between the wöhlerite, rosenbuschite and eudialyte group minerals
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CHAPTER 2: BACKGROUND 2.1: REGIONAL GEOLOGIC AND TECTONIC SETTING OF VESTFOLD’s AND TELEMARK’s NEPHELINE SYENITE PEGMATITES The mineral rich nepheline syenite pegmatites of the Langesundsfjord and Larvik areas occur in the Larvik Plutonic Complex (LPC) which forms part of the PermoCarboniferous aged Oslo Rift of southeastern Norway (Brøgger 1887, 1890; Neumann 1960; Larsen 1996; Bryhni et al. 2006; Larsen et al. 2008; Dahlgren 2010; Andersen et al. 2010; Marks et al. 2011; Andersen et al. 2012; Piilonen et al. 2012). Nepheline syenites and their associated mineral rich pegmatites form in zones of rifting and extension (Sørensen 2003; Bryhni et al. 2006; Larsen 2010; Andersen et al. 2010). Lithospheric stretching north of the Tornquist fault system is thought to be the cause of the rift’s formation (Larsen et al. 2008). The Oslo Rift’s formation was contemporaneous with the last phase of the Variscan orogeny with the main graben forming period starting in the late Carboniferous.
Figure 2.1 - Simplified geological map of the Oslo Graben (After Larsen et al. 2008) This graben formation caused extensive volcanism and rifting followed by the uplift and emplacement of major batholiths before it culminated approximately 20-30Ma later.
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The rifting itself culminated with a definite termination of intrusive activity in the early Triassic, around 65Ma after the tectonic and magmatic onset of rifting in the Oslo area (Larsen et al. 2008).
Figure 2.2 – Simplified tectonic map showing an overview of Western Europe with the Variscan front, the Tornquist fault system and the Oslo Rift shown in the context of the pre rift configurations with the Caledonian structures and the boundary of the Fennoscandian Craton (After Larsen et al. 2008).
2.2: SUMMARY OF THE GEOLOGICAL EVOLUTION OF SOUTHERN NORWAY The geological evolution of southern Norway (in the context of Scandinavia’s geological evolution – See Figures 2.3 and 2.4) can be divided into the following events (Holtedahl 1960; Oftedahl 1980; Bingen et al. 2008a; Bingen et al. 2008b; Lahtinen et al. 2011): -
1. Formation of the Fennoscandian shield
2800Ma Karelian Block
1800Ma Svecofennian Block
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2. Formation of the Gothian accretionary terrane – 1200-1600Ma
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3. Formation of the Sveconorwegian accretionary terrane – 900-1700Ma
The Kongsberg terrane – 1520Ma-1640Ma (as part of the KongsbergBamble Complex)
The Telemarkian terrane – 1480-1520Ma
The Idefjorden terrane – 1660-1250Ma
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The Sveconorwegian metamorphic terrane – 900-1140Ma
Sveconorwegian plutonism – 920-980Ma – granite and/or anorthosite (AMC) – cooling ceased at approx. 850Ma
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4. Norway effectively becomes a craton – 850Ma (Oftedahl 1980)
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5. Formation of the Sparagmite Basin and the Fen Complex (in addition to earlier Neoproterozoic rocks) in the late Precambrian
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6. Formation of the Cambrian, Ordovician and Silurian sandstones, limestones and shales in the Oslo Region
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7. Onset of the Caledonian orogeny in Norway – Ordovician – widespread deformation and metamorphism. Formation of the Norwegian Caledonides.
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8. Formation of the Oslo Rift – Carboniferous-Permian – 320-240Ma
Figure 2.3 – Geological sketch map of the geology of Scandinavia in a Proterozoic context. The map shows how the Oslo Rift is related to the Proterozoic rocks that surround it (After Binden et al. 2008a).
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Figure 2.4 – Geological map (1:250,000) of the bedrock of southern Norway showing the regional geology of the study area. The key to the map is located on right hand side (After NGU 2013). The area of study is indicated by the red rectangle and is located in the western half of the LPC with its monzonites and syenites shown in pink-red and pink.
2.3: THE OSLO RIFT The Oslo Rift caused a prolonged period of volcanism and extensional faulting in northwestern Europe which lasted from the late Paleozoic through into the Mesozoic. North of the foreland of the Variscan orogeny, widespread rifting and magmatism developed during the uppermost Carboniferous and continued all through the Permian (Larsen et al. 2008). Figure 2.5 (below) shows the structural architecture of the Oslo Rift.
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Figure 2.5 – Schematic of the architecture of the Oslo Rift including the graben segments (Akershus, Vestfold and Skagerrak) and the master faults (After Larsen et al. 2008) The magmatic activity that occurred in association with the rifting caused the emplacement of intrusions ranging in composition from monzonitic to granitic as well as the eruption of basalts and rhomb porphyries (Rasmussen et al. 1988; Larsen et al. 2008). It is believed by Ebbing et al. (2007) state that there are mafic intrusions underlying the Oslo Graben up to 15km beneath the Oslo Region. This is based on petrophysical (magnetic and gravity) analysis of the Oslo Graben. According to Gill (2010), this is also the case for other rift provinces such as the Mesoproterozoic Gardar province (especially the Ilímaussaq Complex) in Southern Greenland and the East African Rift Valley.
2.3.1: Extrusive and intrusive lithologies of the Oslo Rift 2.3.1.1: Extrusive lithologies The extrusive lithologies of the Oslo Rift are made up of basalts, rhomb porphyries of latitic and trachyandesitic composition, trachytic lavas and tuffs and rhyolitic lavas and tuffs (Holtedahl 1960).
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2.3.1.2: Intrusives Figure 2.6 (below) shows Barth’s (1944) interpretation of the development of the intrusives of the Oslo Rift. McBirney (2007) states that nepheline syenite amounts to 210 known minerals (Larsen 2013). A lot of these mineral associations and textures are thought to have been generated during crystallization of different larvikite plutons and nepheline syenites; however, they may not be petrogenetically related to their respective host rocks (Dahlgren 2010). In some cases, the pegmatites of the Langesundsfjord area have peculiar compositions and may be unrelated to unknown parental compositions (Dahlgren 2010).
2.5.1: Pegmatite types of the Langesundsfjord and Larvik areas The nepheline syenite/syenite pegmatites of the LPC can be divided into the following pegmatite types (Dahlgren 2010): -
The Stålaker type
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The Stavern type
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The Tvedalen type
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The Bratthagen type
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The Langesundsfjord type
Only the Stavern, Tvedalen and Langesundsfjord pegmatite types will be described as only these will be focused upon during this dissertation.
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2.5.1.1: The Stavern type The Stavern type of pegmatites is known for their large prismatic zircon crystals and their schillerizing K-feldspars. They are syenite pegmatites that are often sheet like and can be up to 10m thick and 120m long. This type occurs in the Larvik, Tjølling, and Sandefjord and Tønsberg areas and has a mineralogy which includes K-feldspar, zircon, amphibole, and scarce occurrences of titanomagnetite, biotite, pyrochlore, and zirconolite. The amount of accessory minerals is generally limited with the Stavern type of pegmatites being related to the host larvikites (Dahlgren 2010).
2.5.1.2: The Tvedalen type Unlike the Stavern pegmatite type, the Tvedalen type has a large amount of accessory minerals. The mineralogy is dominated by microcline, nepheline, aegirine, barkevikite (local name for ferro-edenite), magnetite and biotite. Major accessory minerals include apatite, zircon, pyrochlore, wöhlerite and rare meliphanite. These nepheline syenite pegmatites are usually sheet like in form and have a primary, magmatic phase and a secondary, hydrothermal phase (Dahlgren 2010). Many secondary REE and Be minerals form in this late stage in the formation of Tvedalen type pegmatites. These rare minerals are associated with extensive zeolitization, alteration of the previously formed magmatic minerals and crystallization of low temperature hydroxides and hydrous silicates. Like the Stålaker and Stavern type pegmatites, the Tvedalen pegmatites are related to the host larvikites (Dahlgren 2010).
2.5.1.3: The Langesundsfjord type With this pegmatite type, the nepheline syenite pegmatites may be related to either the host larvikites or the Langesundsfjord nepheline syenites. The Langesundsfjord type pegmatites have also been observed to intrude basalts in addition to the more common larvikite and nepheline syenite hosts. These pegmatites intrude the larvikites directly east of the Langesundsfjord. The pegmatites of this type vary in size from centimetres to decimetres with the morphology varying between sheet like masses or smaller dykes that intrude the host rocks (Dahlgren 2010; Andersen et al. 2010; Andersen et al. 2012). These pegmatites have a variety of minerals, including alkali feldspar, nepheline, leucophanite, black amphibole, aegirine-augite, biotite, magnetite, meliphanite (Be), 28
homilite (B), molybdenite, astrophyllite, aenigmatite, thorite, wöhlerite, eudialyte (sensu stricto), ferrokentbrooksite, zirsilite-(Ce), mosandrite, rinkite, hiortdahlite, rosenbuchite, hainite, kochite, låvenite, grenmarite, catapleiite, zirconolite, parakeldyshite, lorenzite, albite, sodalite, secondary zircon, fluorite, zeolites, tritomite(Ce), pyrochlore and apophyllite (Dahlgren 2010; Andersen et al. 2010; Selbekk 2010; Andersen et al. 2012) Zirconosilicates and titanosilicates (e.g. eudialyte, mosandrite, wöhlerite and rosenbuchite) may occur as early magmatic phases that accompany the predominant minerals (alkali feldspar, nepheline, leucophanite, black amphibole and aegirineaugite), at a more evolved magmatic stage or as a function of the volatile content (e.g. catapleiite) (Larsen et al. 2005b; Dahlgren 2010; Andersen et al. 2010; Andersen et al. 2012). These pegmatites tend to be zoned (this applies to the smallest pegmatites) with zoning in the larger pegmatites being quite complex, with the bands of the Låven pegmatite being a prime example. These individual bands have different mineral textures and mineral associations. Shallow dipping pegmatites have denser minerals (e.g. magnetite, amphibole and clinopyroxene) that concentrate at the base of them (Dahlgren 2010). In the case of many pegmatites in the Langesundsfjord area (e.g. the Sagåsen pegmatite), there are selvages of nepheline syenite adjacent to the pegmatite. These observations suggest there is a close genetic relationship between the nepheline syenite pegmatites and the nepheline syenite itself (Dahlgren 2010).
2.5.2: Mineralogy of the nepheline syenite pegmatites of the Langesundsfjord area and the LPC The minerals listed in Figures 2.9 and 2.10 and in the literature (Brøgger 1890; Dahlgren 2010; Andersen et al. 2010; Andersen et al. 2012) suggests that a great number of pegmatites in the Langesundsfjord area are agpaitic nepheline syenite pegmatites and that they’re mineralogically unique. The remaining pegmatites in the area that lack this unique mineral assemblage are miaskitic (Andersen et al. 2010).
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Figure 2.9 – Some of the HFSE and REE minerals present in the nepheline syenite pegmatites of the Langesundsfjord (After Andersen et al. 2010). Based on the differing mineralogical assemblages of the different pegmatite groups, Dahlgren (2010) concluded that each pegmatite group must have evolved differently in relation to the original melt and the fluid evolution through the crystallization temperature range. Andersen et al. (2012) suggests that two types of zirconium silicate mineral assemblages from the Langesundsfjord area can be distinguished on the basis of the amount of water activity that occurred in the magma at the time. Catapleiite is in the high water activity assemblage and is accompanied by hainite, astrophyllite and mosandrite. Låvenite is in the low water activity assemblage and is accompanied by astrophyllite, aenigmatite and zirconolite. Based on this distinction, both the mineral assemblage and the magma can be referred to as wet (high water activity) or dry (low water activity) and this has petrogenetic implications (Andersen et al. 2012; Marks et al. 2011; Andersen et al. 2010). According to Andersen et al. (2010), examining zirconium silicate group mineral assemblages in cogenetic rocks such as miaskitic and agpaitic nepheline syenite pegmatites (such as those of the Langesundsfjord area) can provide information about 30
the alkalinity and volatile content of the original magma. These mineral assemblages can also determine whether the nepheline syenite pegmatites (and the magmas that formed them) are miaskitic or agpaitic. Based on the nepheline syenite pegmatites of the Langesundsfjord area being zircon bearing or lacking zircon as well as having minerals such as catapleiite, wöhlerite, hiortdahlite and låvenite (in addition to other Zr and Ti silicates), Semenov (1967) in Sørensen (1974) “defined the Langesundsfjord type as a separate class of nepheline syenite pegmatites, intermediate between the main miaskitic and truly agpaitic types with Andersen et al. (2010) deeming the pegmatites to be low agpaitic or transitional in composition.
Figure 2.10 - Some of the Zr, Nb, Ti and REE minerals present in the Larvik Plutonic Complex (After Andersen et al. 2012).
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2.6: THE WÖHLERITE GROUP The wöhlerite group (as referred to by Biagoni et al. 2012), is a group of Zr-Nb-Ti disilicates where the amount of Zr, Nb and Ti varies between each mineral in the group. The general formula for the group (and the rosenbuschite and mosandrite groups) is M8 (Si2O7)2(O, OH, F) 4 where the M site can represent a number of cations with coordination numbers ranging from 6 to 8. Cations with a high charge and a small ionic radius (such as Ti4+, Zr4+, Nb5+, REE3+, Mn2+ and Fe2+) can occur as can low charge and high ionic radius cations such as Na+ and Ca2+ in the adjacent NaCa site (Biagoni et al. 2012; Chakhmouradian et al. 2008; Bellazza et al. 2004; Merlino & Perchiazzi 1988; Mariano & Roeder 1989; Andersen et al. 2010).
2.6.1: Occurrence The wöhlerite group minerals occur in agpaitic nepheline syenites, carbonatites, silicocarbonatites, ijolite, pyroxenite, melteigite, urtite, malignite, trachyte and phonolite (Mariano & Roeder 1989; Biagoni et al. 2012). Wöhlerite and hiortdahlite appear in various shades of yellow in hand specimen; however, hiortdahlite often has a greenish hue. Låvenite appears pale yellow, dark reddish brown or dark brown (Larsen et al. 2010). Wöhlerite has a distinctive blue cathodoluminescence.
2.6.2: Locality occurrence Wöhlerite group minerals occur predominantly in nepheline syenites and phonolites (Langesundsfjord, Ilímaussaq, Mont Saint Hilaire, Khibiny, Lovozero, Poço de Caldas, Varennes and the Los Archipelago, the Eifel volcanic region, Tenerife, the Azore islands and Monchique) and carbonatites (Prairie Lake, Oka, Tchivira Mt., Muri Mountain, In Imanal, Anezrouf, Oldoinyo Lengai, Kaiserstuhl and Magnet Cove). These minerals have also been reported to occur in trachytes and phonolites from Tasmania and Victoria in Australia and at Monte Somma and Pian di Celle in Italy and as well as in urtites, melteigites, ijolites and malignites in Tchivira in Angola (Currie et al. 1986; Biagoni et al. 2012; Mariano & Roeder 1989; Wolff 1987; Sørensen 2001; Chakhmouradian et al. 2008; Bellazza et al. 2004; Bellazza et al. 2012).
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2.6.3: Crystal structure The wöhlerite group minerals are structurally characterized (according to Merlino and Perchiazzi 1988) by “the presence of walls of octahedra, four columns wide, that run parallel to [001].” Merlino and Perchiazzi continue on to state the walls of octahedra “are interconnected both directly by corner sharing and, through Si2O7 (sorosilicate) groups, each group being linked to three walls.” Most of the minerals of the wöhlerite group display triclinic as opposed to monoclinic symmetry (Merlino and Perchiazzi 1988). Larsen et al. (2010) indicates that hiortdahlite has triclinic symmetry, whilst wöhlerite and låvenite have monoclinic symmetry. Wöhlerite and hiortdahlite have 8 independent octahedral sites whilst låvenite and normandite have 4 independent octahedral sites (Biagoni et al. 2012).
Figure 2.11 – Crystal structure of wöhlerite. The left hand diagram shows the crystal structure of the wöhlerite group whilst the right hand diagram shows the octahedral walls of wöhlerite seen down [010](After Biagoni et al. 2012).
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Figure 2.12 – Members of the wöhlerite, rosenbuschite and mosandrite groups with their chemical formulae and physical properties (After Biagoni et al. 2012).
2.7: PETROLOGICAL, MINERALOGICAL AND ECONOMIC SIGNIFICANCE OF AGPAITIC NEPHELINE SYENITES Agpaitic nepheline syenites are of major significance, representing a minute proportion of the planet’s igneous rocks, yet being far superior in their mineralogical variety (Khomyakov 1995; Khomyakov estimates that there may be as many as 104-105 minerals in alkaline complexes). Examples of the magmatic concentration of HFSE and REE and their various ore minerals include the gravity and density accumulated eudialyte layers of Ilímaussaq and Lovozero and the apatite deposits of Khibina (Kogarko 1990; McBirney 2007). Elements such as Zr, Y, Nb, Ce, REE, Li, Be, Sr, Ba, B, P,
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Th, U, Ag, Tl, Cu, Zn, Sn, Pb, As, Sb, Mo, W, Co, Ni, F, S and Cl are enriched in agpaitic magmas and form their own minerals in agpaitic intrusions and their pegmatites such as Ilímaussaq, Lovozero, Khibina, Mont Saint-Hilaire and the Langesundsfjord. Therefore, agpaitic nepheline syenite intrusions (and their associated pegmatites) are considered to be of major economic importance as they host elements (such as those listed above) that are known as critical metals if found in economic concentrations (Hall 1987; Kogarko 1990; Sørensen 1992; Platt 1996; Pell 1996; Sørensen 1997; Moss et al. 2011; Chakhmouradian and Zaitsev 2012). Agpaitic nepheline syenites are thought to have formed by low partial melting of metasomatically enriched mantle, which was followed by extreme fractionation of an alkali basaltic, basanitic or nephelinitic parental melt (Platt 1996; Sørensen 1992, 1997, 2003; Chakhmouradian and Zaitsev 2012). A lot of the enriched elements are enriched enough to form their own ore minerals. It is apparent (Khomyakov 1995) that the formation of ore mineralization in agpaitic rocks illustrates its association with differentiation of an originally homogeneous agpaitic melt. Rising alkalinity in aluminosilicates melts increase the solubility of the aforementioned elements due to their transition to the anionic part of the structure of the melt. According to Khomyakov (1995), the very presence and extent of the enrichment in rare elements indicates that special physiochemical conditions of differentiation (which included fractional crystallization) of the alkaline magmas must have evolved in order for the magmas to greatly enrich rare elements and form extensive mineralization in agpaitic nepheline syenites. Finally, the multitude of cations and anions and their various combinations explains the variety of Zr, Nb, Ti and Be minerals (Khomyakov 1995). High charge elements such as Ti, Nb and Zr combine with Si to form mixed type radicals. Minerals in agpaitic intrusions often have similar or even identical elemental compositions but differ in their stoichiometry or structural features.
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CHAPTER 3: FIELDWORK AND SAMPLING 3.1: SAMPLING STRATEGY Samples were taken from three pegmatite localities: Sagåsen quarry, the AS Granit quarry and Arøyskjærene. The Arent quarry was visited but no samples were taken with many observations, photos and sketches resulting from the visit. Samples were also used from the Oslo NHM with samples being selected from Låven, Kjørtingholmen, Stokkøya, the Saga I quarry, the Vevja (Bakken) quarry, the Skutesundskjær, the Barkevikskjær and the Tjølling (Håkestad) quarry (See Figure 3.1). The wöhlerite group minerals wöhlerite and hiortdahlite were predominantly targeted during the sampling due to the focus, aims and objectives of this dissertation.
Figure 3.1 – Google Map showing the locations of the samples from the Langesundsfjord-Larvik area studied with locations being approximate. (Google Maps 2013).
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CHAPTER 4: ANALYTICAL PROCEDURES The following methods and equipment were used in order to achieve the aim and objectives set out in Chapter 1: -
SEM at CSM – JEOL JSM – 5400LV Scanning Microscope with EDS
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OM at CSM – Nikon Eclipse 6600 POL
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Photomicrograph OM at CSM – Nikon Microscope with a JVC KY-K1030 digital camera
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CL microscope at CSM– Nikon Microscope with a JVC KY-K1030 digital camera and an electrotest tuner appliance
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EPMA at UiO – Cameca SX-100 with 5 WDS detectors
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SEM at Oslo NHM – Hitachi 3600-N Scanning Microscope
The analysis work was undertaken at CSM at the UoE, Penryn (Cornwall) and at the UiO, Oslo (Norway). The work was carried out in June and July 2013 after fieldwork was carried out in the Langesundsfjord and Larvik areas of southeastern Norway in May 2013. The OM, CL, SEM and EPMA work were undertaken at CSM and UiO in June 2013. The The SEM at the Oslo NHM was used for capturing some BSE images in July 2013.
4.1: OM (AND PHOTOMICROGRAPH OM) AND CL METHODOLOGY The optical microscope work was carried out on a transmitted/reflected light Nikon microscope. The work was carried out at an x5 magnification, mostly in transmitted light but occasionally in reflected light (when opaques were being observed). The slides were examined and described in both PPL and XPL. Interesting areas were identified which were later viewed using CL and captured using an OM with an attached JVC KYK1030 digital camera. The areas were deemed interesting because of any unusual or striking textures being present (such as wöhlerite lamellar twinning, the high birefringence colours of wöhlerite, presence of veins penetrating through the wöhlerite and alteration textures). These interesting areas were later investigated using the SEM and EPMA.
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Further optical work was carried out using a CL optical microscope. The microscope used was a Nikon microscope attached with a JVC KY-K1030 digital camera and connected to an electrotest power appliance. The work was carried out an x4 magnification and CL images were taken with the JVC digital camera. The conditions at which the CL was operated were as follows (See Appendix 1 for descriptions of the polished thin sections under XPL, PPL and CL and Appendices 6 and 7 for OM photomicrograph and CL images of the slides): -
Pressure – 14mb
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Current – 300-400μA
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Voltage – 7-11kV
38
CHAPTER 5: FIELDWORK OBSERVATIONS 5.1: SAGÅSEN QUARRY The Sagåsen quarry is located to the south of Mørje in Telemark in southeastern Norway. The pegmatites described were located in the Sagåsen quarry dump from which the samples were taken. Mineralogical and textural observations were made from nepheline syenite pegmatite blocks and small boulders and pebbles. Yellow to honey yellow wöhlerite was observed alongside pink spreustein, black amphibole, black platy biotite, brown nepheline; grey twinned microcline, white albite, greyish green sodalite dark green aegirine, brown astrophyllite, brown-orange eudialyte, grey metallic molybdenite, metallic dark grey magnetite, small black pyrochlore and possible small orange-brown låvenite. The nepheline syenite pegmatites at Sagåsen are generally very coarse grained with the predominant albites and microclines being up to 1m across.
Figure 5.1 – Google Map showing the location of the Sagåsen quarry, near Mørje, Telemark County, Norway. Sample locations are shown and are approximate (Google Maps 2013).
39
Wöhlerite is often associated with felsic minerals such as the feldspars and feldspathoids. Associated with the wöhlerite and eudialyte is fluorite, amphibole, biotite, albite, microcline, nepheline, sodalite, spreustein (composed of zeolites such as natrolite and analcime), and aegirine. Wöhlerite most often occurs at the boundary of a pegmatite blocks or at the base of the pegmatite blocks. Upon examination of the textures in the pegmatites and in samples taken from Sagåsen, it was observed that wöhlerite was one of the first minerals to crystallize alongside pyrochlore and magnetite. All other minerals crystallized afterwards. The pegmatites have a relatively fine grained margin and a very coarse albitemicrocline-nepheline core. Albite and microcline seem to grow in from the margins with amphibole, biotite, aegirine, wöhlerite, eudialyte, pyrochlore, magnetite, sodalite, molybdenite and låvenite being adjacently associated with these. Spreustein is only associated with the albite, microcline, nepheline and sodalite.
Figure 5.2 – Blocks of coarse fresh pegmatite at Sagåsen quarry showing the macroscopic textures prevalent in the pegmatites at Sagåsen near Mørje and the dominance of nepheline, albite and microcline.
40
5.2: ARENT QUARRY The Arent quarry is located near Tvedalen in western Vestfold near the VestfoldTelemark county border adjacent to the Langesundsfjord. Pink-red spreustein is an alteration product of nepheline, microcline and albite. Mafic minerals include biotite, amphibole and aegirine. Pyrochlore and magnetite also occur in addition to yellowhoney yellow wöhlerite. Microcline is altered to a blood red colour in some of the most altered pegmatites. The mineral textural observations are largely the same as Sagåsen except rare minerals such as eudialyte, wöhlerite, låvenite and sodalite are less abundant. The same types of nepheline syenite pegmatites observed at Sagåsen have been observed at Arent quarry as have very similar grain size variations amongst the minerals. The pegmatites generally have a fine grained margin, a very coarse grained margin and an intermediate zone which the feldspars encompass. The feldspars have been observed to grow from the margins. The pegmatites are more altered at Arent quarry than at Sagåsen quarry and there is far less exotic mineralogy (wöhlerite, eudialyte and låvenite etc.) at Arent than at Sagåsen.
Figure 5.3 – Map of the Arent quarry near Tvedalen, Vestfold County, Norway (Google Maps 2013)
41
The pegmatites range from near vertical to practically horizontal and from single dyke like bodies to pegmatites that splayed, anastomosed or had apophyses. The host larvikites are intruded by the nepheline syenite pegmatites which have later been intruded by basaltic dykes. The textures observed at Arent are much the same as those observed at Sagåsen except the grain sizes are slightly finer and the pegmatites are smaller. With regard to the wöhlerites, the main occurrence of this mineral was in association with mafic minerals such as amphibole, biotite and aegirine and dense minerals such as zircon and magnetite and, to a lesser extent, felsic minerals such as the feldspars and feldspathoids.
Figure 5.4 – Partially altered coarse grained pegmatite at Arent quarry with hammer for scale. The hammer is 30cm high.
5.3: BARKEVIK Barkevik is located on the eastern shores of the Langesundsfjord in Vestfold county, south eastern Norway. Yellow wöhlerite is associated with amphibole, aegirine, biotite, magnetite, albite, microcline, nepheline, sodalite, spreustein, eudialyte, astrophyllite and fluorite. The main and most important textural observation made at this locality (in 42
the context of the subject of this dissertation) is that wöhlerite occurs with amphibole and biotite at the margins of the pegmatites at Barkevik. Similar mineral textures and textural relationships were observed at Barkevik as at Sagåsen. The grain sizes are slightly finer grained. The nepheline syenite pegmatites at Barkevik are more alike to those at Sagåsen than at Arent both in terms of mineralogy and apparent agpaicity.
Figure 5.5 – Shows the textures on display at Barkevik. The two images focus on wöhlerite and its relation to biotite and microcline. The image on the right shows a zoomed out image of the left hand image.
5.4: LÅVEN Låven is an island located at the southern end of the islands of the Langesundsfjord archipelago. It is located to the south of Stokkøya and is protected by Norwegian law (Larsen 2010). Yellow wöhlerite occurs with nepheline, albite, microcline, aegirine, amphibole, biotite, eudialyte, sodalite, mosandrite, catapleiite, astrophyllite, leucophanite, låvenite, hiortdahlite, tritomite-(Ce) and fluorite. Textures observed on Låven are similar to those observed at Sagåsen, Arent and Barkevik. The pegmatite at Låven occupies most of the approx. 80m long (N-S) island and is quite coarse grained.
43
Figure 5.6 – Pegmatite textures on Låven. Left: Big crystals of aegirine with wöhlerite, nepheline and microcline. Right: Zoomed out view of part of the nearby pegmatite. Notebook and author’s hand and pencil for scale.
5.5: ARØYSKJÆRENE Arøyskjærene are located south of Lille Arøya and north of Store Arøya in the southern part of the Langesundsfjord. Hiortdahlite and wöhlerite are accompanied by rosenbuschite, eudialyte, rinkite, mosandrite, fluorite, albite, microcline, spreustein, amphibole, aegirine, magnetite and biotite. The textural relationships are practically the same as the localities visited except that more textures are on display. At this locality, there is a nepheline syenite pegmatite dyke exposed that reveals the country rock, the pegmatite margin and core. This pegmatite is largely composed of wöhlerite, hiortdahlite, amphibole, albite and microcline (See Figures 5.7 and 6.6). The contact between the country rock and pegmatite is well defined as is the main concentration of wöhlerite and hiortdahlite. The wöhlerites are up to a few centimetres in size. Occurrences of wöhlerite were observed but it appears that hiortdahlite was mistaken for wöhlerite at this locality and also at the AS Granit quarry.
44
Figure 5.7 – Pegmatites at Arøyskjærene. Left: A flat lying pegmatite intruding the larvikite country rock. Right: Multiple pegmatites cutting across larvikite in Arøyskjærene.
5.6: AS GRANIT QUARRY
Figure 5.8 – AS Granit quarry in near Tvedalen, Vestfold County, Norway (Google Maps 2013) The AS Granit quarry is located near Tvedalen. The AS Granit quarry has multiple nepheline syenite pegmatites on the 2nd level of the quarry. Yellow brown >1cm sized well formed wöhlerite crystals were observed alongside zircon, amphibole, microcline and spreustein (See Figure 5.10 below). These minerals are accompanied by melanocerite, hambergite, analcime, albite, nepheline, tritomite, leucophanite, 45
magnetite, biotite, aegirine, fluorite and fluoroapatite were observed. Secondary arsenates such löllingite and boron minerals such as tourmaline were also found. The nepheline syenite pegmatites observed are generally coarse grained but the grain sizes can be quite variable ranging from mm to cm sized crystals.
Figure 5.9 – Pegmatites cutting through the larvikite host rocks at the AS Granit quarry near Tvedalen.
Figure 5.10 – Wöhlerite crystals set in a feldspar-nepheline dominated pegmatite mass with biotite and fluorite also occurring. This was taken at the base of the pegmatite.
46
Wöhlerites at this locality are texturally associated with amphibole, microcline and
spreustein. Wöhlerite seems to be a really early stage mineral based on the textural relationships observed. See Appendix 4 for photographs of all the localities visited during the fieldwork undertaken.
47
CHAPTER 6: PETROGRAPHY Mineral
Formulae
Wøhlerite
NaCa2(Zr,Nb)(Si2O7)2(O,F)4
Hiortdahlite I
(Na,Ca)2Ca4Zr(Mn,Ti,Fe)(Si2O7)2(F,O)4
Låvenite
(Na,Ca)4(Mn,Fe2+)(Zr,Ti,Nb)(Si2O7)2(F,O)4
Eudialyte
Na15Ca6(Fe2+,Mn2+)3Zr3(Si,Nb)(Si25O73)(O,OH,H2O)3(Cl,OH)2
Rosenbuschite
Na2Ca4(Zr,Ti)(Si2O7)2(F,O)4
Hainite
Na2Ca4(Ti, Zr, Nb, REE)(Si2O7)2(F,O)4
Aegirine
NaFe3+Si2O6
Aegirine-augite
(Na,Ca)(Fe2+,Fe3+)Si2O6
Annite (Biotite)
K(Mg,Fe2+)3(Al,Fe3+)Si3O10(OH,F)2
Arfvedsonite
NaNa2(Fe2+4,Fe3+)Si8O22(OH)2
Pyrochlore
(Ca,Na)2Nb2O6F
Fluorite
CaF2
Zircon
ZrSiO4
Ferro-edenite
NaCa2Fe2+5Si7AlO22(OH)2
Ilmenite
FeTiO3
Titanite
CaTiSiO5
Magnetite
Fe3O4
Albite
NaAlSi3O8
Microcline
KAlSi3O8
Nepheline
(Na,K)AlSiO4
Sodalite
Na8Al6Si6O24Cl2
Natrolite
Na2Al2Si3O10•2H2O
Analcime
NaAlSi2O6•H2O
Fluoroapatite
Ca5(PO4)3F
Calcite
CaCO3
Apatite
Ca5(PO4)3(F,Cl,OH)
Monazite
(Ce,La,Nd,Pr)PO4
Chalcopyrite
CuFeS2
Pyrite
FeS2
Table 6.1 – This shows the minerals identified during the petrography. Mineral formulae are from Andersen et al. (2010, 2012) and Larsen et al. (2010). Hiortdahlite I was identified as opposed to hiortdahlite II (See Merlino and Perchiazzi 1985, 1987).
48
Wöhlerite seems to very often occur at the base or margins of the pegmatites observed and described (Sagåsen quarry, Arent quarry, AS Granit quarry, Barkevik, Arøyskjærene) as well as often found adjacent to mafic minerals at the base and margin areas (See Figures 6.1, 6.2, 6.6, 6.7. 6.8 and 6.9). These seem to be intriguing relationships and they shall be discussed in Chapter 8.
Figure 6.1 - Close up of the mafic minerals in contact with wöhlerite and surrounded by feldspars, feldspathoids and zeolites at Barkevik. The pegmatite is not in situ.
Figure 6.2 –Mafic minerals and wöhlerite exposed in a not in situ pegmatite at Barkevik.
49
Figure 6.3 – Coarse grained fresh pegmatite at Sagåsen quarry near Mørje with rucksack for scale. The photo shows a contact between the pegmatite and the larvikite country rock. Note: this is not an in situ outcrop; it is a block of pegmatite and larvikite that has been quarried.
Figure 6.4 – Photo of a finer grained, smaller pegmatite at Arent quarry near Tvedalen. Note the notebook for scale.
50
Figure 6.5 – Altered coarse grained pegmatite at Arent quarry with notebook for scale. Mafic and wöhlerite group minerals seem to be concentrated at the base or margins (See Figures 6.1, 6.2, 6.6, 6.7. 6.8 and 6.9) due to density and gravity processes (Gill 2010; Best 2003). Density and gravity processes (See Figures 6.1, 6.2, 6.6, 6.7. 6.8 and 6.9) also operate when pegmatites crystallize (Larsen 2010; Dahlgren 2010; London 2008) and these can explain why mafic minerals such as biotite, amphibole, aegirine, magnetite and ilmenite as well as the wöhlerite group minerals are concentrated at the base of the observed pegmatites in the LPC.
Figure 6.6 – Photograph of the base/margin of a pegmatite at Arøyskjærene showing mafic minerals (such as amphibole, biotite, magnetite, ilmenite and aegirine), wöhlerite, rosenbuschite and hiortdahlite. The pegmatite is not in situ but would have been horizontal with the way up being in the opposite direction to where the pencil (for scale) is pointing. 51
Figure 6.7 – Coarse grained fresh pegmatite at Arent quarry which shows the textural relationships in the pegmatite and the accumulation of mafic minerals at the base and margins of the pegmatite. The plant is about 50cm high.
Figure 6.8 – Close up of the mafic minerals and wöhlerite accumulated at the base of one of the splays of the pegmatites at Arent quarry. The photo is about 50cm across.
52
Figure 6.9 – Crystals of wöhlerite (or of one the wöhlerite group minerals) located towards the bottom of the pegmatite. It is interesting that hiortdahlite crystals from AS Granit quarry have been found as this is a new occurrence of hiortdahlite in the Langesundsfjord area based on Larsen (2010) and Larsen et al. (2010). It is also interesting that a Ca-Na-Ti zirconosilicate has been found in sample Arøy-N1 from Arøyskjærene. This mineral is deemed to be part of the rosenbuschite group and appears to be hainite, which is of intermediate composition between Zr rich rosenbuschite and Ti rich götzenite (Christiansen et al. 2003) and has more Ti than Zr. This would also appear to be the first occurrence of this mineral at Arøyskjærene and first occurrence outside of Teineholmen and Låven in the Barkevik area, which are the only known localities of this mineral in the Langesundsfjord (Larsen et al. 2010).Through observing and describing the samples in both hand specimen and under OM, CL, SEM and EPMA, it was possible to come up with the following paragenesis. Magnetite is the first mineral to crystallize followed by pyrochlore. Zircon follows these two minerals with apatite following. The wöhlerite group minerals wöhlerite, hiortdahlite and låvenite crystallized next with evidence of feldspar and calcite crystallizing around wöhlerite and both biotite and aegirine growing into wöhlerite. Rosenbuschite and hainite crystallized next and also crystallizes after biotite (See Figure 8.2). Aegirine crystallizes after wöhlerite as evidenced by the textures of Sku-N3. 53
Figure 6.10– Diagram showing a mineral paragenesis of the studied nepheline syenite pegmatite localities. The placement of the lines is only an estimate based on optical petrography and hand specimen petrography work. This paragenesis broadly agrees with observations by Larsen et al. (2010).
54
Figure 6.11– Sku-N3. SEM-BSE image of rosenbuschite crystals that have grown into the biotite space with aegirine formed in between the rosenbuschite crystals. The biotite crystallized after the rosenbuschite based on the textures observed. Biotite, amphibole and aegirine crystallized at roughly the same time, however, aegirine crystallized at a later stage. Aegirine first crystallized as acicular, well formed crystals in feldspar, nepheline and spreustein and then as secondary generation felty masses in feldspar. Microcline, albite, nepheline and cancrinite crystallized afterwards with eudialyte crystallizing before or contemporaneously with these minerals. Fluorapatite and ilmenite followed with titanite crystallizing contemporaneously with these minerals. Sodalite followed in the crystallization sequence with second generation aegirine and monazite crystallizing near contemporaneously afterwards. Fluorapatite and fluorite crystallized slightly later with secondary titanite crystallizing slightly later than these. Secondary pyrochlore, zircon and ilmenite followed by secondary sodalite and late stage pyrite, chalcopyrite, natrolite and calcite. Secondary pyrochlore, zircon and late stage fluorite and zeolites (analcime, natrolite) are associated with some of the rims of the wöhlerite and hiortdahlite as well as the more altered parts of these crystals (such as in Håke-N1). Another interesting texture to be found (in Sagå-N5) is a 1mm microveinlet of calcite which intrudes through the large 55
wöhlerite crystal in the slide. The calcite has secondary zircon entrained within it as well as minor fluorite. At the edge of the wöhlerite crystal is a mass of late stage calcite (which encloses some wöhlerite), primary apatite, secondary pyrochlore and late stage fluorite accompanied by minor late stage monazite. Apatite and primary zircon crystallized after magnetite and primary pyrochlore, with titanite crystallizing after the wöhlerite and rosenbuschite group minerals but before the feldspars, feldspathoids and mafic minerals. Monazite crystallized as a late stage mineral and occurs associated with apatite in Bakk-N1 and Østok-N1. Calcite is the latest mineral to crystallize and occurs in Sagå-N5 and is associated with pyrochlore, apatite and fluorite in a mass near the contact between wöhlerite and microcline (See Figure 8.15 below). It also occurs as a pyrochlore and zircon bearing veinlet that propagates through a crystal of wöhlerite which suggests that the calcite fluid must have penetrated through the crystal altering the wöhlerite to fluorite, zircon and pyrochlore in the process. The presence of fluorite, zircon and pyrochlore adjacent to the vein margin suggests alteration of the wöhlerite crystal by the late stage vein. The zircon and pyrochlore crystals that are hosted by the vein are either from the alteration zone or from elsewhere in the pegmatite (See Figure 6.13 below).
Figure 6.12 –SEM-BSE image showing the apatite-fluorite-pyrochlore-zircon mass in at the contact between the wöhlerite and the microcline in Sagå-N5. It appears as though the wöhlerite has been altered to zircon, fluorite and pyrochlore. Pyrochlore and zircon are the brighter minerals. The scale bar represents 100μm.
56
Figure 6.13 – Sagå-N5. Top left: SEM-BSE image of calcitezircon-fluorite-pyrochlore vein through a crystal of wöhlerite (grey). Top right: Close up of part of the calcite vein. Bottom: Another part of the calcite (dark) vein with more zircon and pyrochlore (bright).
The alteration assemblage of fluorite, secondary zircon and pyrochlore see in Figure 6.13 was caused by the intrusion of a calcite veinlet through the wöhlerite crystal in Sagå-N5. There is a rim alteration assemblage of fluorite, secondary zircon and pyrochlore surrounding wöhlerite crystals from Sku-N1 which has a different texture to the alteration seen in Sagå-N5 (See Figure 6.14).
Figure 6.14- SEM-BSE image of Sku-N1 with microcline, albite, wöhlerite, fluorite and zircon. The fluorite and zircon forms as a result of alteration that occurs around the rim of the wöhlerite. 57
Own Sample ID
Locality (Pegmatite
Rare metal and
Felsic and rock
type)
accessory
forming minerals
Level of agpaicity
minerals SKU-N1
Skutesundskjær
Wöhlerite and
Microcline, albite,
Miaskitic to low
(Langesundsfjord)
fluorite
nepheline, biotite,
agpaitic
aegirine SKU-N3
SKU-N4 SAGA-N3
Skutesundskjær
Eudialyte,
Biotite, aegirine,
(Langesundsfjord)
hiortdahlite,
arfvedsonite,
zircon,
microcline, albite,
wöhlerite and
nepheline, sodalite,
fluorite
cancrinite, magnetite
Skutesundskjær
Wöhlerite and
Biotite, microcline and
Miaskitic to low
(Langesundsfjord)
hiortdahlite
aegirine
agpaitic
Saga 1 quarry
Wöhlerite
Biotite, albite,
Low agpaitic
(Langesundsfjord)
Medium agpaitic
nepheline, microcline, aegirine, amphibole, magnetite, natrolite
SAGA-N4
Saga 1 quarry
Wöhlerite and
Aegirine, biotite,
(Langesundsfjord)
fluorite
magnetite, albite,
Low agpaitic
nepheline, microcline, pyrite, ilmenite LÅV-N4 (1)
Låven
Hiortdahlite,
Natrolite, nepheline,
(Langesundsfjord)
titanite,
albite and microcline
Low agpaitic
pyrochlore, rosenbuschite and fluorite LÅV-N4 (2)
Låven
Hiortdahlite,
Magnetite, microcline,
(Langesundsfjord)
rosenbuschite
natrolite, cancrinite,
and fluorite
albite, nepheline,
Low agpaitic
biotite, aegirine, pyrite, chalcopyrite ARØY-N1
Arøyskjærene
Hiortdahlite,
Amphibole, microcline,
Miaskitic to low
(Langesundsfjord)
rosenbuschite
biotite, aegirine, albite,
agpaitic
and fluorite
nepheline
58
ØSTOK-N1
Øst Stokkøya
Wöhlerite,
Biotite, albite, apatite,
(Langesundsfjord)
hiortdahlite,
natrolite, analcime and
låvenite,
microcline
Low agpaitic
monazite and fluorite BARK-N1
Barkevik
Wöhlerite
(Langesundsfjord) GRAN-N1
Biotite, nepheline,
Miaskitic to low
microcline
agpaitic Low agpaitic
AS Granit quarry
Hiortdahlite,
Biotite, magnetite,
(Tvedalen)
zircon,
microcline, albite,
monazite, and
nepheline, apatite
fluorite SAGÅ-N5
Sagåsen quarry
Wöhlerite,
Microcline, natrolite,
Miaskitic to low
(Langesundsfjord)
pyrochlore,
nepheline, calcite,
agpaitic
zircon,
sodalite and fluorite
monazite BAKK-N1
Bakken (Vevja) quarry
Monazite
(Tvedalen)
Amphibole, aegirine,
Miaskitic to low
apatite, ilmenite,
agpaitic
magnetite, nepheline, microcline SAGÅSEN 4
Sagåsen quarry
Wöhlerite and
Amphibole, nepheline,
(Langesundsfjord)
hiortdahlite
biotite, albite and
Low agpaitic
zeolites HÅKE-N1
Håkestad (Tjølling)
Wöhlerite,
quarry
zircon and
(Stavern)
pyrochlore
Fluorite and zeolites
Miaskitic
Table 6.2 – Determination of the agpaicity of the Langesundsfjord nepheline syenite pegmatites studied based on mineral identification, Based on Mitchell (1996) and Khomyakov (1995). Table 6.2 shows how the mineralogy of the nepheline syenite pegmatites studied has been interpreted in terms of miaskitic, low or mildly agpaitic mineral assemblages. The classifications presented here are only approximate and based only on the samples selected.
59
Figure 6.15 – Wöhlerite under XPL from Saga-N3 and Bark-N1. The top left and top right images are of twinned wöhlerites from Saga-N3. The bottom left image is of twinned and non twinned wöhlerites from Bark-N1. The top images show wöhlerite with microperthite and aegirine (r) and microperthite (l). The scale bar length equates to 500μm. Figure 6.15, 616, 6.17 and 6.18 show the varying textures of the wöhlerites found in the pegmatites sampled. Figure 6.15 shows a variety of wöhlerite lamellar twinning textures that are present in Saga-N3 and Bark-N1. Figure 6.16 shows wöhlerite lamellar twinning, fractures and veins and highlights wöhlerite’s very interesting optical properties. Figure 6.17 shows a veinlet of calcite intruding through a Sagå-N5 wöhlerite crystal (see Figure 6.13 for SEM-BSE images of this vein). Figure 6.18 shows fractures in wöhlerites from Sagå-N5.
60
Figure 6.16 – OM photomicrograph image of the textures present in a wöhlerite from Sagå-N5 in XPL. The textures seen include wöhlerite lamellar twinning, fractures and veins. The scale bar length equates to 500μm.
Figure 6.17 – OM photomicrograph image of calcite veinlet present in a wöhlerite from Sagå-N5 in XPL. Alteration has taken place adjacent to the veinlet with secondary zircon and pyrochlore present in addition to fluorite. The scale bar length equates to 500μm.
Figure 6.18 – OM photomicrograph image of the microfractures present in a wöhlerite crystal from Sagå-N5 in XPL. The scale bar length equates to 500μm.
61
CHAPTER 7: SEMI QUANTITATIVE AND QUANTITATIVE MICROBREAM RESULTS In addition to the use of polished thin sections for SEM and EPMA analytical work and BSE imaging, epoxy mounts (or polished mounts) were also used for the EPMA work. CSM ID 1 2
Own ID
Oslo NHM ID
Locality
County
Sample type
SKU-N1
No ID – Draw
Skutesundskjær,
Vestfold
Polished section
35
Langesundsfjord
No ID – Draw 9
Skutesundskjær,
Vestfold
Polished section
Vestfold
Polished section
Saga I quarry, Mørje
Telemark
Polished section
Saga I quarry, Mørje
Telemark
Polished section
No ID – Draw
Låven,
Vestfold
Polished section
24
Langesundsfjord
No ID – Draw
Låven,
Vestfold
Polished section
24
Langesundsfjord
N/A
Arøyskjærene,
Vestfold
Polished section
Vestfold
Polished section
Vestfold
Polished section
Vestfold
Polished section
SKU-N3
Langesundsfjord 3
SKU-N4
KNR 30087
Skutesundskjær, Langesundsfjord
4
SAGA-N3
No ID – Draw 29
5
SAGA-N4
No ID – Draw 29
6 7 8
LÅV-N4 LÅV-N4 ARØY-N1
Langesundsfjord 9
ØSTOK-N1
KNR 30140
Øst Stokkøya, Langesundsfjord
10
BARK-N1
KNR 30087
Barkevikskjær, Langesundsfjord
11
GRAN-N1
N/A
AS Granit quarry, Tvedalen
12
SAGÅ-N5
N/A
Sagåsen quarry, Mørje
Telemark
Polished section
13
BAKK-N1
No ID – Draw
Barkevikskjær,
Vestfold
Polished section
53
Langesundsfjord
Table 7.1 – Table with information on the samples taken, the localities sampled, their locations and the type of sample
62
CSM ID
Own sample
Oslo NHM ID
Location
Fylke
Minerals present
KNR 30148
Kjørtingholmen,
Vestfold
Wöhlerite
ID 1
KJØR-N1
Langesundsfjord 2
HÅKE-N1
KNR 14448
Håkestad, Tjølling
Vestfold
Wöhlerite
3
LÅV-N1
KNR 70146
Låven, Langesundsfjord
Vestfold
Wöhlerite
4
SAGÅSEN 4
N/A
Sagåsen quarry, Mørje
Telemark
Wöhlerite and hiortdahlite
5
SAGÅSEN
N/A
Sagåsen quarry, Mørje
Telemark
Wöhlerite
6
SAGÅ-N1
N/A
Sagåsen quarry, Mørje
Telemark
Wöhlerite
7
SAGA-N1
N/A
Saga 1 quarry, Mørje
Telemark
Wöhlerite
8
SAGA-N1
N/A
Saga 1 quarry, Mørje
Telemark
Wöhlerite and hiortdahlite
9
SAGA-N1
N/A
Saga 1 quarry, Mørje
Telemark
Hiortdahlite
10
SAGA-N1
N/A
Saga 1 quarry, Mørje
Telemark
Wöhlerite, hiortdahlite and magnetite
11
SAGA-N2
Draw 29 (B)
Saga 1 quarry, Mørje
Telemark
Wöhlerite
Table 7.2 – Provides information about the epoxy mount samples, their IDs, their localities and the type of analysis/microscope sample. Due to time constraints, only the Sagåsen 4 and Håke-N1 epoxy samples were analysed.
7.1: SEM AND EPMA METHODOLOGY 7.1.1: SEM Two different SEMs were used for the qualitative-semi quantitative phase of the analysis of the polished sections. A JEOL JSM – 5400LV SEM was used at the UoE’s analytical labs in June 2013 whilst a Hitachi S3600-N SEM was used at the Oslo NHM. In both cases the beam width was approximately 2μm whilst the accelerating voltage was set at 15 kV in both instances. The beam current for the SEM at the UiO was 71nA. The SEM at the UoE was used for obtaining spectra and images whilst the SEM at the Oslo NHM was used for just obtaining images. The spectra analyses were obtained at the UoE’s SEM due to it having an EDS (Energy Dispersive Spectra) detector.
63
7.1.2: EPMA Two hundred and eighty nine chemical analyses were obtained by using a Cameca SX100 EPMA at the University of Oslo’s Blindern campus in June 2013. This EPMA has 5 WDS (Wave Dispersive Spectra) detectors. The accelerating voltage was set at 15kV whilst the beam current was 15nA with a focussed beam being used. The counting time for each analysis was approximately 240s. The EPMA was calibrated with a program being set up that would analyse for the following elements and X-ray lines: Si Kα, Ca Kα, Al Kα, Ti Kα, Mn Kα, Fe Kα, Mg Kα, K Kα, Na Kα, F Kα, Zr Lα, Hf Mα, Nb Lα, Y Lα. Ce Lα, La Lα, Pr Lβ and Nd Lβ. The following calibration standards were used: Wollastonite (Si Kα, Ca Kα), Al2O3 (Al Kα), pyrophanite (Ti Kα, Mn Kα), Fe metal (Fe Kα), MgO (Mg Kα), orthoclase (K Kα), albite (Na Kα), fluorite (F Kα), Monastery mine zircon (Zr Lα), Hf metal (Hf Mα), Nb metal (Nb Lα) and synthetic orthophosphates for the REE and Y (Y Lα. Ce Lα, La Lα, Pr Lβ, Nd Lβ). It should be noted that the matrix corrections were made according to the PAP program of Pouchou and Pichoir (1984) which was developed for Cameca, with the atomic number (Z), absorption (A) and fluorescence (F) corrected for.
7.2: SEM OBSERVATIONS The SEM work seemed to confirm most OM observations and also provide some additional information to aid in the interpretation of the nepheline syenite pegmatites sampled. The original mineral identifications were confirmed whilst some additional minerals were identified such as pyrite, chalcopyrite, monazite, ilmenite, analcime, natrolite and apatite. See Appendix 8 for EPMA images of the slides.
7.3: EPMA DATA RESULTS AND OBSERVATIONS The main function of using the EPMA at the UiO in Oslo was to obtain a data set of chemical analysis of the wöhlerite group minerals (wöhlerite, hiortdahlite and låvenite) and rosenbuschite group minerals (rosenbuschite) as well as to take EPMA-BSE images and identify any unknown minerals. Calcite, fluorapatite and titanite were identified using the EPMA EDS spectra whilst the analyses were made using WDS spectra. The
apfu compositions of each of the mineral analyses were calculated based upon the procedure outlined in Appendix 5. See Appendix 8 for SEM and EPMA images of the slides. 64
Table 7.3 - Representative individual analyses and apfu compositions of wöhlerites from Saga-N3, Sku-N4, Sagå-N5, Bark-N1, Østok-N1 and Sku-N1 Wöhlerite Saga-N3 HfO2 Nd2O3 Pr2O3 Ce2O3 La2O3 Nb2O5 ZrO2 Y2O3 FeO MnO TiO2 CaO K2O SiO2 Al2O3 MgO Na2O F Total
Sku-N4
Sagå-N5
Bark-N1
Østok-N1
Sku-N1
0.45 b.d.l. b.d.l. 0.11 0.08 13.11 14.42 0.40 1.47 1.12 0.94 26.53 0.03 29.92 b.d.l. 0.23 7.35 4.52
0.47 0.09 0.01 0.34 0.15 13.34 14.69 0.36 0.74 1.54 1.41 25.67 0.01 29.88 b.d.l. 0.05 7.72 3.91
0.44 b.d.l. 0.03 0.38 0.17 13.00 14.84 0.38 0.57 1.51 1.39 25.49 0.01 29.88 b.d.l. 0.08 7.88 3.82
0.43 0.14 b.d.l. 0.38 0.17 13.27 14.76 0.30 0.93 1.38 1.50 25.63 0.01 29.89 0.01 0.04 7.75 3.72
0.46 0.14 0.04 0.14 0.08 12.16 14.53 0.32 2.04 1.04 1.36 26.68 0.02 29.77 0.01 0.21 6.90 3.83
0.40 b.d.l. 0.01 0.15 0.03 13.19 14.45 0.45 1.46 1.02 0.68 26.79 b.d.l. 29.81 b.d.l. 0.29 6.93 3.43
0.40 0.04 0.16 0.17 0.07 11.73 14.66 0.30 1.52 1.02 1.47 27.70 0.03 30.08 b.d.l. 0.18 7.33 4.69
0.47 0.02 0.01 0.19 0.03 12.15 14.63 0.23 1.23 1.40 1.18 26.99 b.d.l. 29.98 0.02 0.15 7.50 4.05
0.36 0.07 b.d.l. 0.19 0.06 12.80 14.16 0.38 1.67 1.09 1.23 26.60 0.01 30.16 0.01 0.19 7.44 4.22
100.67
100.37
99.88
100.31
99.74
99.08
101.54
100.22
100.66
-O = F
1.90
1.65
1.61
1.57
1.61
1.45
1.97
1.70
1.78
R total
98.76
98.73
98.27
98.74
98.13 97.64 Wöhlerite
99.56
98.52
98.89
Saga-N3
NaCa site Na Ca Fe Mn
M site Ti
Zr Nb REE Hf Z site Si O
X site O F
5.935 1.886 3.761 0.162 0.125 1.859 0.093 0.931 0.784 0.034 0.017 17.960 3.960 14.000 4.000 2.107 1.893
5.906 1.991 3.659 0.082 0.174 1.965 0.141 0.953 0.802 0.051 0.018 17.975 3.975 14.000 4.000 2.355 1.645
5.926 2.042 3.649 0.063 0.171 1.961 0.140 0.966 0.785 0.053 0.017 17.991 3.991 14.000 4.000 2.385 1.615
Sku-N4 5.918 2.002 3.657 0.103 0.156 1.978 0.150 0.959 0.799 0.052 0.018 17.981 3.981 14.000 4.000 2.432 1.568
5.962 1.790 3.827 0.228 0.117 1.880 0.137 0.948 0.736 0.040 0.018 17.985 3.985 14.000 4.000 2.379 1.621
Sagå-N5 5.956 1.809 3.866 0.164 0.117 1.874 0.069 0.949 0.803 0.038 0.015 18.014 4.014 14.000 4.000 2.538 1.462
Bark-N1 6.037 1.864 3.894 0.167 0.113 1.833 0.145 0.937 0.696 0.040 0.015 17.946 3.946 14.000 4.000 2.054 1.946
Østok-N1 6.074 1.935 3.846 0.136 0.157 1.841 0.118 0.948 0.731 0.026 0.018 17.987 3.987 14.000 4.000 2.298 1.702
Sku-N1 5.983 1.907 3.768 0.185 0.123 1.854 0.123 0.913 0.765 0.039 0.014 17.988 3.988 14.000 4.000 2.234 1.766
*The number of analyses averaged in a slide is signalled by the number above the analyses **Total Fe = FeO *** b.d.l. = below detection limit ****The number of oxygens that the calculations were based on was 18 for wöhlerite *****REE = Nd, Pr, Ce, La and Y
65
Table 7.4 - Representative individual analyses and apfu compositions of wöhlerites, rosenbuschites and hiortdahlites from Arøy-N1, Låv-N4(2), Låv-N4(1), Sku-N1, Sagåsen 4, Gran-N1 and Håke-N1 Wöhlerite Sku-N1 HfO2 Nd2O3 Pr2O3 Ce2O3 La2O3 Nb2O5 ZrO2 Y2O3 FeO MnO TiO2 CaO K2O SiO2 Al2O3 MgO Na2O F Total -O = F R total
NaCa site Na Ca Fe Mn
M site Ti
Zr Nb REE Hf Z site Si O
X site O F
Hiortdahlite
Sagåsen 4 0.48 0.08 0.27 0.17 b.d.l. 12.58 14.44 0.39 1.46 1.53 0.92 26.11 0.01 29.75 0.02 0.18 7.31 3.58 99.28 1.51
HåkeN1 0.44 b.d.l 0.03 0.38 0.17 13.00 14.84 0.38 0.57 1.51 1.39 25.49 0.01 29.88 b.d.l. 0.08 7.88 3.82 99.88 1.61
Sku-N4
99.82
97.78 Wöhlerite
98.27
Sku-N1
Sagåsen 4
HåkeN1
5.938 1.897 3.777 0.159 0.105 1.899 0.115 0.937 0.787 0.043 0.017 17.959 3.959 14.000 4.000 2.229 1.771
6.019 1.910 3.770 0.165 0.175 1.878 0.093 0.949 0.767 0.051 0.019 18.009 4.009 14.000 4.000 2.475 1.525
5.904 1.747 3.836 0.083 0.238 1.851 0.127 0.908 0.753 0.041 0.023 17.933 3.933 14.000 4.000 2.076 1.924
0.45 0.07 b.d.l. 0.23 0.05 13.26 14.63 0.42 1.45 0.95 1.17 26.85 0.01 30.15 b.d.l. 0.19 7.45 4.26 101.61 1.80
0.41 0.13 0.04 0.32 0.09 2.25 16.42 1.07 1.43 0.92 0.87 31.41 0.01 30.42 b.d.l. 0.03 7.11 8.17 101.11 3.44
GranN1 0.51 0.09 b.d.l. 0.70 0.17 3.11 17.46 1.15 1.37 1.68 0.45 28.22 0.02 30.57 b.d.l. 0.06 7.67 8.06 101.29 3.39
LåvN4(2) 0.40 0.14 b.d.l. 0.26 0.09 2.45 16.25 1.25 1.12 1.19 1.02 31.69 b.d.l 30.74 b.d.l. 0.09 7.19 8.06 101.93 3.39
97.67
97.90
98.54 Hiortdahlite
Sku-N4
6.468 1.805 4.405 0.157 0.102 1.376 0.086 1.048 0.133 0.093 0.016 17.982 3.982 14.000 4.000 0.618 3.382
GranN1
LåvN4(2)
6.260 1.952 3.970 0.150 0.187 1.483 0.045 1.118 0.184 0.117 0.019 18.014 4.014 14.000 4.000 0.653 3.347
6.468 1.810 4.405 0.122 0.131 1.385 0.099 1.028 0.144 0.099 0.015 17.988 3.988 14.000 4.000 0.695 3.305
Rosenbuschite LåvN4(1) 0.46 0.12 b.d.l. 0.43 0.17 2.78 15.82 0.87 1.04 1.09 1.02 32.20 0.01 30.76 b.d.l. 0.04 7.15 8.57 102.52 3.61
Sagåsen 4 0.42 0.14 b.d.l. 0.35 0.13 2.87 16.38 1.13 1.47 1.32 0.69 30.72 0.05 30.20 b.d.l. 0.09 7.11 7.61 100.67 3.21
98.92
97.47
LåvN4(1) 6.460 1.785 4.444 0.112 0.119 1.358 0.099 0.994 0.162 0.087 0.017 17.963 3.963 14.000 4.000 0.508 3.492
Sagåsen 4 6.472 1.819 4.343 0.162 0.148 1.410 0.068 1.054 0.171 0.100 0.016 17.986 3.986 14.000 4.000 0.822 3.178
ArøyN1 0.27 0.02 b.d.l. 0.27 0.07 1.07 13.28 0.59 0.41 0.69 8.11 29.54 0.02 31.66 0.04 0.02 8.43 7.18 101.67 3.02
98.65 97.95 Rosenbuschite ArøyN1
LåvN4(2)
6.173 2.063 3.994 0.043 0.074 1.709 0.770 0.817 0.061 0.051 0.010 17.994 3.994 14.000 4.000 1.135 2.865
5.922 2.327 3.428 0.037 0.131 1.900 0.597 1.126 0.065 0.099 0.012 18.011 4.011 14.000 4.000 1.129 2.871
*The number of analyses averaged in a slide is signalled by the number above the analyses **Total Fe = FeO *** b.d.l. = below detection limit ****The number of oxygens that the calculations were based on was 18 for hiortdahlite, wöhlerite and rosenbuschite *****REE = Nd, Pr, Ce, La and Y 66
LåvN4(2) 0.33 0.01 b.d.l. 0.26 0.08 1.12 17.89 1.37 0.34 1.19 6.15 24.78 b.d.l. 31.06 b.d.l. b.d.l. 9.29 7.03 100.91 2.96
The formulae and analyses of the wöhlerites, hiortdahlites, rosenbuschites, pyrochlore, titanite and låvenite seem to generally agree with standard compositions for these although there is definite variation in the wöhlerites, hiortdahlites and rosenbuschites between the localities and within the localities. The variations in the wöhlerites and hiortdahlites are quite distinguishable and these variations seem to occur elsewhere (Chakhmouradian et al. 2008; Mariano & Roeder 1989; Biagoni et al. 2012; Andersen et al. 2010, 2012). The chemistry of the wöhlerites and hiortdahlites generally appears to fall within the variations of these minerals; however, there are some interesting anomalies in the chemistry of these minerals. There are two analyses which show wöhlerites that have more Nb than Zr which corresponds to apfu values of Nb 0.880/Zr 0.916 (Sku-N1) and Nb 0.931/Zr 0.941 (Sagåsen 4). Sample ID
Mineral
Structural formula
Saga-N3
Wöhlerite
Na2.0(Ca3.7Mn0.2,Fe0.1)4.0Zr0.9Nb0.8Ti0.1REE0.1(Si4.0O14)(O2.3,F1.7)
Sku-N4
Hiortdahlite
Na1.8(Ca4.4,Fe0.2,Mn0.1)4.7Zr1.1Nb0.1Ti0.1REE0.1(Si4.0O14)(F3.3,O0.7)
Sku-N4
Wöhlerite
Na1.8 (Ca3.9,Fe0.2,Mn0.1)4.2Zr1.0Nb0.7Ti0.1REE0.1(Si4.0O14)(O2.3,F1.7)
Sagå-N5
Wöhlerite
Na1.8 (Ca3.9,Fe0.1,Mn0.1)4.1Zr0.9Nb0.8Ti0.1REE0.1(Si4.0O14)(O2.4,F1.6)
Bark-N1
Wöhlerite
Na1.9 (Ca3.9,Fe0.2,Mn0.1)4.2Zr0.9Nb0.7Ti0.1REE0.1(Si4.0O14)(O2.2,F1.8)
Gran-N1
Hiortdahlite
Na2.0 (Ca4.0,Mn0.2, Fe 0.1)4.3Zr1.1Nb0.2TiNb, however, in the carbonatites it is the other way round. The ZrO2 and Nb2O5 contents in the Langesundsfjord (Brevik), Guyana and Angola nepheline syenite hosted wöhlerites range from 13.66% to 16.11% and 10.50% to14.20% respectively; these compositions are quite similar to the wöhlerites analysed from the pegmatites studied. On the otherhand, the ZrO2 and Nb2O5 contents in the Mali, Oka and Prairie Lake carbonatite hosted wöhlerites range from 13.64% to 14.98% and 14.50% to 16.07% respectively, which is noticeably different. This distinction is interesting when compared to the analyses in this dissertation, not only because these analyses are similar to those in Mariano and Roeder (which is not a surprise given the similarity of the rock types) but also because in two analyses of wöhlerites from Sku-N1 (core) and Sagåsen 4 (rim) there is Nb>Zr which resembles the carbonatite wöhlerite analyses. The compositions of these Sku-N1 and Sagåsen 4 rim analyses resemble that of marianoite or an intermediate composition between wöhlerite and marianoite, which has never been reported in literature on wöhlerites from any nepheline syenite locality. This suggests that the Zr4+ + F- ↔ Nb5+ + O2- and Ti4+ + F- ↔ Nb5+ + O2- (own work; Mariano and Roeder 1989; Mellini and Merlino 1979) coupled substitution mechanisms (which were mentioned in the section above) must have acted preferentially over any Ti and Zr concentrating processes. This may be due to predominance of Nb rich minerals in the case of localized areas of the Sku-N1 and Sagåsen 4 pegmatites and the carbonatites of Oka, Prairie Lake and Mali. Chemical substitution mechanisms can be governed by the coexisting mineral assemblages, which could mean that additional Nb was sourced from adjacent minerals and transferred by mobility processes in the melt. Mariano and Roeder (1989) state Nb bearing minerals such as pyrochlore, betafite, latrappite, Nb perovskite and Nb zirconolite occur in carbonatites and associated alkaline rocks. The majority of these minerals occur only in carbonatites, whilst only pyrochlore and zirconolite are known to occur in alkaline rocks such as nepheline syenites. Therefore, only these minerals could have provided the additional Nb in the
112
Langesundsfjord with only pyrochlore occurring in Sku-N1 and Sagåsen 4 adjacent to wöhlerite. It is interesting to note that, according to Mariano and Roeder (1989), the other Nb bearing minerals (such as pyrochlore, betafite, Nb perovskite and Nb zirconolite) in the Prairie Lake carbonatite complex normally occur away from the wöhlerites. This may suggest that either the Nb concentration processes are not as dependent upon the coexisting mineral assemblage as with the Langesundsfjord nepheline syenite pegmatites or that Nb was already sufficiently concentrated in the carbonatitic melt (which is often the case in carbonatites). The substitution mechanisms outlined above and in Mariano and Roeder are validated by the inverse relationship between Nb and F, which is observed in that paper as well as in the chemical data generated by this project and in Mellini and Merlino (1979). Mariano and Roeder have also suggested that divalent elements such as Ca2+, Mn2+, Fe2+ and Mg2+ can substitute for Nb5+, with the Mn2++ 2Na+ O2-↔ Nb5+ + 2Ca2+ + F- coupled substitution mechanism outlined in the section above therefore being possible. Perchiazzi et al. (2000) endorse a substitution mechanism where REE can substitute for Ca in cuspidine group minerals (an alternative name for the wöhlerite group) through the following mechanism Ca2+ → REE3+ + Na+. This mechanism seems reasonable, however, it doesn’t accord to substitution mechanisms put forward in this dissertation or to those put forward by other works on the wöhlerite or rosenbuschite groups. REE could substitute for Nb by the following simple substitution mechanism Nb3+ → REE3+ due to the occurrence of Nb in its unstable 3+ oxidation state (Dayah 1997). This 3+ oxidation state based simple substitution mechanism could also be applied to Fe3+ and Mn3+, however, this has not been endorsed in the literature on the wöhlerite or rosenbuschite group minerals. Another substitution mechanism that could be put forward is Zr4++ Na+ → REE3+ + Ca2+ based upon the inverse proportion relationships between Zr and REE and Na and Ca. This could be applied to REE substituting for Ti or Hf, with Mn2+ or Fe2+ being able to substitute for Na+. These are based upon chemical correlation relationships between these elements and can be put forward to explain any variations in the REE contents of the wöhlerites, hiortdahlites or rosenbuschites analysed, however, these have not been suggested by any of the works referred to in this dissertation.
113
Figure 8.4 - Compositional variation plot of the wöhlerite and rosenbuschite group minerals from across the Larvik Plutonic Complex with data being plotted using the Triplot program. (Ca+Mg+Mn+Fe) is equal to VI (R2+). The data in this dissertation was plotted in a triangular compositional variation plot (See Figure 8.4) in order to compare the wöhlerite, hiortdahlite and låvenite compositions to the wöhlerite group minerals plotted in Chakhmouradian et al. (2008). Marianoite, which is the main focus of the paper and was first described in the paper, is hosted in silicocarbonatites of the Prairie Lake intrusive complex and has similar compositions to the carbonatite hosted wöhlerites discussed in Mariano and Roeder (1989). If Figures 8.4 and 8.5 are compared (with the bottom half of Figure 8.5 not being involved in the comparison), it appears there is some overlap in the compositions of the wöhlerites, låvenites and hiortdahlites analysed in samples from the Langesundsfjord and the marianoites and other wöhlerite group minerals plotted in Chakhmouradian et al. (2008).
114
Figure 8.5 Compositional variation of cuspidine-group minerals expressed in atomic percentage of the major occupants of octahedrally coordinated cation sites, including Ti, Zr + Hf, Nb + Ta and divalent cations (VIR2+ = VI Ca + Mn + Fe + Mg). (After Chakhmouradian et al.. 2008).
As in Figure 8.4, the Langesundsfjord wöhlerites and hiortdahlites plot in the bottom left part of the triangle plot and are concentrated close to the edge of the plot. The sole låvenite (from Østok-N1) plotted overlaps with the låvenites plotted in Figure 8.5. As in Figure 8.5, there are variations in the chemistry of the wöhlerites and hiortdahlites analysed. Table 2 of Chakhmouradian et al. (2008) shows the compositional variations in the wöhlerite group minerals. Analyses 1-4 are Zr rich wöhlerites from nepheline syenites in Siberia, Mont Saint-Hilaire, Tchivira and Brevik, whilst analyses 5-6 are Nb rich wöhlerites from clinopyroxenite in the Prairie Lake intrusive complex. The marianoites (Analyses 7-8) are from carbonatites in Kaiserstuhl, Okorusu and Prairie Lake has compositions that resemble the Nb rich wöhlerites from Prairie Lake and the Nb rich wöhlerite analyses from Sku-N1 and Sagåsen 4. The nepheline syenite wöhlerite analyses from Chakhmouradian et al. (2008) have ZrO2 compositions that range from 13.66% to 16.35%, which overlap with those from the Langesundsfjord, whilst the Nb2O5 compositions range from 8.35% to 12.83%. These Nb2O5 compositions 115
broadly overlap with those from the Langesundsfjord, which range from 11.00% to 15.30%. The ZrO2 is more enriched whilst the Nb2O5 is more depleted. None of the substitution mechanisms referred to in this dissertation or in the wöhlerite literature that has been discussed has been discussed in Chakhmouradian et al. (2008). However, the substitution mechanisms implicated above can be used to explain the chemical variations in the wöhlerite group minerals analysed as well as differences between the compositions of the wöhlerites studied and those in that paper.
Figure 8.6 – Triangular composition variation plot showing the distribution of Ti and Zr across the 10 localities sampled by Andersen et al. (2010). The data used was provided by Andersen et al. (2010).
116
Figure 8.6 was compiled using data from Andersen et al. (2010) and confirms the compositional variations in rosenbuschites, hiortdahlites and wöhlerites from the LPC. It also shows the compositional trends and variations in låvenites and catapleiites across the LPC. The interesting aspect about the localities sampled from in Andersen et al. (2010) is that the samples were taken predominantly from the islands of the Langesundsfjord archipelago whilst more samples for this dissertation were taken from mainland pegmatite localities. It is interesting that there are both similarities and differences in the compositional variations of the rosenbuschites, hiortdahlites and wöhlerites analysed. The wöhlerites analysed by Andersen et al. (2010) are all sourced from islands in the Langesundsfjord archipelago and from different localities to the wöhlerites sampled for this dissertation. The wöhlerites analysed by Andersen et al. have a possible Ti enrichment trend from south to north in the archipelago and become increasing Zr rich. They’re more Zr and Ti rich than the wöhlerites analysed from the mainland and the archipelago. The hiortdahlite compositional trend overlaps with the studied wöhlerite and hiortdahlite analyses. The hiortdahlites are noticeably enriched in Zr and depleted in Ti compared to the wöhlerites in Figures 7.11, 7.13, 8.4 and 8.6. The composition of rosenbuschites analysed by Andersen et al. show some overlap with those sampled for this dissertation. The studied rosenbuschites came from Arøyskjærene and Låven whilst the rosenbuschites analysed by Andersen et al. came from Arøyskjærene, Vesle Arøya, Skutesundskjær, Risøya and Trompetholmen. There appears to be a convex curve trend in the rosenbuschites analysed for this dissertation and those analysed by Andersen et al. The analyses at the top of curve are most likely hainite (which has only been found at Trompetholmen and Låven before; Andersen et al. 2012, Larsen et al. 2010, Christiansen et al. 2003). The analyses at the bottom are rosenbuschite and the intermediate analyses resemble an intermediate composition (Zr>Ti, higher Ca than typical kochite compositions) between kochite and rosenbuschite. One of the most Ti rich members of the rosenbuschite group minerals is hainite which has been found at Arøyskjærene in the case of the samples collected for this dissertation. The most Zr rich rosenbuschites (sensu stricto) are from Skutesundskjær according to Figure 8.6. The variations in the ideal compositions of wöhlerite, hiortdahlite, låvenite and rosenbuschite can be explained by the element substitution mechanisms alluded to 117
above. Andersen et al. (2010) explains the variation in the composition of rosenbuschites by a coupled Na2M4+Ca-3 substitution (where M = Ti or Zr) or a simple (Zr, Hf) Ti-1 substitution. A high volatile content in a nepheline syenite melt allows for Zr and Nb, which are normally incompatible in most melts, as well as Ti, to become more soluble in the melt until they become concentrated enough to form major components of minerals such as wöhlerite, hiortdahlite, låvenite, eudialyte, rinkite, mosandrite and rosenbuschite. The element substitution mechanisms outlined above are thought to be the micro scale consequences of fractionation processes which are in turn influenced by the conditions of the evolving magma at the time of crystallization. Andersen et al. (2010, 2012) offers no substitution mechanisms to explain the compositional variations in wöhlerite, hiortdahlite and låvenite. According to Andersen et al. (2012), “the members of the wöhlerite and rosenbuschite mineral groups show little internal compositional variation, due to their rigid structure types in which a small chemical change would induce a new configuration of coordination polyhedra and thereby stabilize another mineral species. The simple identification of minerals such as wöhlerite, hiortdahlite or låvenite can therefore give important information on the crystallization conditions even without chemical analysis of the individual phases.” This dissertation has found distinguishable chemical variations in these minerals (wöhlerite, hiortdahlite and rosenbuschite) between the localities, within single localities and within single crystals of these minerals.
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Figure 8.7 – Shows the most important Zr and Ti mineral assemblages present in the different pegmatite types of the LPC (After Andersen et al. 2012). Figure 8.7 demonstrates the coexisting minerals that occur with the wöhlerite group and rosenbuschite group minerals. These assemblages govern the substitution mechanisms that have been outlined in this chapter because the minerals that coexist with the wöhlerite group and rosenbuschite group minerals (and the wöhlerite group and rosenbuschite group minerals themselves) govern the presence and concentration of the elements of interest. These mineral assemblages are, by extension, governed by the conditions of the magma. Figure 8.8 displays the conditions at which the wöhlerite group and rosenbuschite group minerals are stable at as well as other associated Zr, Ti, Nb minerals. These associated minerals governed the availability of Nb, Zr, Ti, Ca, Na, F, Mn and Fe in the crystallizing magma, which in turn governs the substitution mechanisms that can take place which then affects the composition of the minerals of interest. 119
Figure 8.8 - Shows the stability conditions of the minerals of interest as well as minerals such as zirconolite, catapleiite, lorenzite, astrophyllite, rinkite, mosandrite, eudialyte, zircon and titanite in 2D (top) and 3D (bottom). The αHF, αNds and αH2O affect the stability of all of these minerals and are a function of the alkali and volatile activities of the magma and by extension the peralkalinity of the magma.
Other rock forming minerals such as biotite, amphibole, nepheline and the feldspars, which are associated with the wöhlerite group and rosenbuschite group minerals may also affect the type of substitution mechanisms that can take place due to their varying Fe, Mn, Mg, Na and K contents. Fractional crystallization causes the Cl and HCl activity of the magma to increase leading to the stable crystallization of eudialyte sensu lato from fluorite ± låvenite ± hiortdahlite (Andersen et al. 2010). The αHF activity is increased through fractional crystallization which leads to the stabilization of F rich assemblage of wöhlerite, låvenite, hiortdahlite and fluorite (Andersen et al. 2010) as zircon became unstable due to the increased αHF activity and is not dependent upon the αH2O and αNds activity. 120
This increase in αHF activity may cause the degree of polymerization of the magma to decrease. Rosenbuschite occurs at higher αHF, αNds and αH2O than wöhlerite, låvenite and hiortdahlite but is stable at lower αHF, αNds and αH2O than eudialyte (Andersen et al. 2010). Saturation of the magma in F leads to crystallization of F rich minerals which prevented the evolved agpaitic magma from evolving to hyperagpaitic melt compositions, despite the crystallization of highly agpaitic minerals such as eudialyte. Biagoni et al. (2012) has carried out the most recent study on the wöhlerite group minerals, this time on the Albian aged nepheline syenites of the Los Archipelago in Guinea. Låvenite, wöhlerite, hiortdahlite and normandite were analysed in this paper. Wöhlerite, låvenite and hiortdahlite I (as opposed to hiortdahlite II – see Merlino and Perchiazzi 1985, 1987 and Robles et al. 2001) were analysed with substitution mechanisms being provided. The låvenites from Los Archipelago are less Zr and Fe rich and more Nb, Ti and Mn rich than the låvenite from Østok-N1 analysed. The wöhlerites from the Langesundsfjord pegmatites analysed are more Zr, Nb and Fe rich and are poorer in Ti and Mn than those in the Los Archipelago. The hiortdahlites from Los Archipelago are poorer in Zr, Nb but are richer in Ti, Mn and Fe than those from the AS Granit quarry, Låven, Øst Stokkøya and Arøyskjærene. Biagoni et al. (2012) and Perchiazzi et al. (2000) give the following substitution mechanisms to explain the variations in låvenite-normandite, wöhlerite and hiortdahlite (signified in brackets): -
Na+ + F- → Ca2+ + O2- (låvenite-normandite)
-
Zr4+ → Ti4+ (låvenite-normandite)
-
Na+ + Zr4+ + F- → Ca2+ + Ti4+ + O2- (låvenite-normandite)
-
Mn2+ + Ti4+ → Ca2+ + Zr4+ (låvenite-normandite)
-
Mn2+ + Ca2+ + F- → Ti4+ + Na+ + O2- (låvenite-normandite)
-
Zr4+ + F- → Nb5+ + O2- (wöhlerite)
-
Nb5+ + 2Na+ O2- → Mn2+ + 2Ca2+ + F- (wöhlerite)
-
Na+ + F- → Ca2+ + O2- (hiortdahlite I)
The coupled Zr4+ + F- → Nb5+ + O2- substitution mechanism has been hypothesized by Biagoni et al. (2012) to explain the substitution of Zr4+ by Nb5+, however, no clear 121
relationship between Zr and Nb was observed in the chemical data of wöhlerites analysed by Biagoni et al. They suggested that the two elements do not occupy the same structural position in the structural formula of wöhlerite. However, based on the chemical data and the apfu chemical relationships between Zr and Nb from this dissertation, there is an inverse proportional relationship between the two elements and that the substitution mechanism stated in this dissertation and hypothesized by Biagoni et al. is correct.
8.2.2: Brief discussion of the chemical indicators of magmatic evolution in nepheline syenites A major indication of increasing agpaicity in agpaitic nepheline syenites is an increasing Mn/Fe ratio in eudialytes, amphibole and aegirine which occurs in kakortokites (arfvedsonite -eudialyte-alkali feldspar-nepheline cumulates) and lujavrites (extremely evolved nepheline syenites) from the Ilímaussaq Complex in the Gardar province of southern Greenland (Pfaff et al. 2007; Pfaff et al. 2008; Schilling et al. 2009). Mn/Fe ratios are an index of the evolutionary stage at which eudialyte minerals crystallized with decreasing Mn/Fe indicating continued fractionation (Schilling et al. 2009) with variations in the Mn/Fe ratios of eudialyte group minerals at the Tamazeght Complex in Morocco signifying that the transition from miaskitic to agpaitic conditions took place at different stages. This could be applied to the agpaitic nepheline syenite pegmatites of the Langesundsfjord based not only on the Mn/Fe ratios of the eudialytes and amphiboles but also on Na Zr-Nb-Ti silicates such as the wöhlerite and rosenbuschite group minerals. Varying Mn/Fe ratios in the amphiboles, eudialytes and other Na Zr-Nb-Ti silicates in the Langesundsfjord pegmatites may suggest multiple small batches of magma being intruded to form the region’s pegmatites. Lorch et al. (2007) suggests that alteration of feldspar to analcime suggests low SiO2 activity and increased H2O activity and therefore increased agpaicity and alkalis, indicates that the changing mineralogy of the crystallizing magma can affect its magmatic evolution.
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CHAPTER 9: CONCLUSION It has been possible to draw a number of conclusions from carrying out this investigation of some of the Langesundsfjord’s nepheline syenite pegmatites: 1. The mineral assemblages in the pegmatites indicate that the nepheline syenite pegmatites studied are transitional to medium agpaitic in composition 2. The wöhlerite group minerals are some of the first minerals to have crystallized (preceded by apatite, zircon, pyrochlore and magnetite) followed by the rosenbuschite group minerals, the feldspars/feldspathoids, the eudialyte group minerals, the mafic minerals and the late stage minerals (such as monazite, chalcopyrite, pyrite, analcime and natrolite) in the pegmatites studied 3. The feldspars and nepheline occur adjacent to the wöhlerite group minerals the most often and are the most common minerals in the pegmatites investigated 4. Wöhlerite group minerals are concentrated at the base of most pegmatites due to density and gravity processes 5. The wöhlerite group minerals either occur together or with other minerals such as rosenbuschite, amphibole, biotite, microcline, albite and eudialyte. 6. The apfu composition in wöhlerite varies from Zr 0.92. Nb 0.71 and Ti 0.09 to Zr 0.95, Nb 0.78 and Ti 0.14, the hiortdahlite apfu composition varies from Zr 1.12, Nb 0.20 and Ti 0.10 to Zr 1.03, Nb 0.14 and Ti 0.04 and the rosenbuschite apfu composition varies Zr 1.75, Nb 0.10 and Ti 1.21 to Zr 1.15, Nb 0.08 and Ti 0.94. 7. The final wöhlerite group mineral to be analysed, låvenite, has an apfu composition of Na2.6(Ca2.2Fe0.6,Mn0.4)3.1Zr1.8Nb0.1Ti0,2REE0.1 (Si4O14)(F2.2,O1.8) 8. There are distinct variations in the chemistry of the wöhlerite and rosenbuschite group minerals with variations occurring between samples as well as between different localities 9. In two wöhlerite analyses from Sku-N1(core) and Sagåsen 4 (rim), there is Nb>Zr, with the oxide and apfu compositions being intermediate between wöhlerite (Zr>Nb) and marianoite (Nb>Zr), which appears to be a world first in nepheline syenite hosted wöhlerites. 10. Element substitution mechanisms can explain both variations from ideal compositions and localized and regional variations in the chemistry of the wöhlerite and rosenbuschite group minerals
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11. These element substitution mechanisms occur due to an element’s valency and ionic radius as well as due to the varying coexisting mineral assemblage, which is a function of the magmas pressure, temperature, fO2 and the fractionation processes that took place as the nepheline syenite pegmatite magmas were evolving 12. The mobility of Zr, Nb and Ti is governed by the substitution mechanisms which are based upon their valency and ionic radii, the coexisting mineral assemblage at each locality 13. A new occurrence of hainite has been identified in a pegmatite sample from Arøyskjærene, which is only the third hainite locality found in the Langesundsfjord 14. A new occurrence of hiortdahlite in the LPC has been found at the AS Granit quarry after it was previously thought to have been wöhlerite 15. Some analyses of rosenbuschite group minerals from Arøyskjærene have a composition that is intermediate between rosenbuschite and kochite, with the Zr/Ti ratio matching kochite and the Ca content being more akin to rosenbuschite Further recommendations include obtaining mineral analyses of the other adjacent minerals to wöhlerite such as eudialyte, the feldspars, feldspathoids, amphiboles, aegirine and zircon to find out how the compositions of these minerals vary and what these compositional variations reveal about the magmatic evolution of the pegmatites. Sampling a wider range of pegmatites in the Langesundsfjord can allow for a more complete picture of mineral composition variations therefore leading to a better understanding of the magmatic evolution of the pegmatites. Performing ICP-MS and isotope analyses on samples of nepheline syenite pegmatites and their parental nepheline syenites could provide new information on the evolution of the parental magmas.
WORD COUNT: 18,963 (Excluding references, in text references, appendices, figure/table captions, table titles and tables)
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APPENDICES APPENDIX 1 Microscope qualitative and semi quantitative observations The qualitative observations made by microscope work were carried out using optical microscope (OM), cathodoluminescence (CL) microscope and scanning electron microscope (SEM) work. This work was carried during the period of June 10th to June 22nd 2013 at CSM at the UoE. The microscope work was done using polished thin sections and epoxy mounts (polished blocks). Table detailing each polished section looked at and analysed. CSM ID 1 2
Own ID
Oslo NHM ID
Locality
County
Sample type
SKU-N1
No ID – Draw
Skutesundskjær,
Vestfold
Polished section
35
Langesundsfjord
No ID – Draw 9
Skutesundskjær,
Vestfold
Polished section
Vestfold
Polished section
Saga I quarry, Mørje
Telemark
Polished section
Saga I quarry, Mørje
Telemark
Polished section
No ID – Draw
Låven,
Vestfold
Polished section
24
Langesundsfjord
No ID – Draw
Låven,
Vestfold
Polished section
24
Langesundsfjord
N/A
Arøyskjærene,
Vestfold
Polished section
Vestfold
Polished section
Vestfold
Polished section
Vestfold
Polished section
SKU-N3
Langesundsfjord 3
SKU-N4
KNR 30087
Skutesundskjær, Langesundsfjord
4
SAGA-N3
No ID – Draw 29
5
SAGA-N4
No ID – Draw 29
6 7 8
LÅV-N4 LÅV-N4 ARØY-N1
Langesundsfjord 9
ØSTOK-N1
KNR 30140
Øst Stokkøya, Langesundsfjord
10
BARK-N1
KNR 30087
Barkevikskjær, Langesundsfjord
11
GRAN-N1
N/A
AS Granit quarry, Tvedalen
12
SAGÅ-N5
N/A
Sagåsen quarry, Mørje
Telemark
Polished section
13
BAKK-N1
No ID – Draw
Barkevikskjær,
Vestfold
Polished section
53
Langesundsfjord
134
OM and CL observations SKU-N1 Slide description The bottom half of the slide is dominated texturally by a mottled texture and mineralogically by albite (identified by albite twinning), microcline and nepheline. The top half of the slide is dominated by a large mass of biotite that has been replaced by aegirine around the entire rim as well as in the interior of the biotite mass. The aegirine seems to grow from the biotite. The aegirine and biotite has been subjected to late stage penetration of blebs and veinlets of fluorite. Wöhlerite also has veinlets and blebs of fluorite associated with it. The wöhlerite is concentrated on either side of the slide and lies adjacent to fluorite, biotite, aegirine, microcline, albite and nepheline. The wöhlerite has second order birefringence in XPL and is pale yellow in PPL. It appears that the wöhlerite formed before biotite, microcline, albite, nepheline, aegirine and fluorite. The wöhlerites are up to 1cm in length. There are veinlets that penetrate through the mass of feldspars and feldspathoids that are of unknown composition. Estimated mineral percentages: -
Biotite – 35%
-
Wöhlerite – 10-15%
-
Aegirine – 10%
-
Feldspar/feldspathoids – 40-45%
-
Fluorite -
