Cenozoic Magmatism and Epithermal Gold-Silver ...

Cenozoic Magmatism and Epithermal Gold-Silver Deposits of the Southern Ancestral Cascade Arc, Western Nevada and Eastern California David A. John* U.S. Geological Survey, Menlo Park, Calif.

Edward A. du Bray U.S. Geological Survey, Denver, Colo.

Christopher D. Henry Nevada Bureau of Mines and Geology, Reno, Nev.

Peter G. Vikre U.S. Geological Survey, Reno, Nev.

ABSTRACT Many epithermal gold-silver deposits are temporally and spatially associated with late Oligocene to Pliocene magmatism of the southern ancestral Cascade arc in western Nevada and eastern California. These deposits, which include both quartzDGXODULD ORZ DQG LQWHUPHGLDWHVXO¿GDWLRQ &RPVWRFN /RGH7RQRSDK %RGLH DQG TXDUW]DOXQLWHKLJKVXO¿GDWLRQ*ROG¿HOG3DUDGLVH3HDN W\SHVZHUHPDMRUSURGXFers of gold and silver. Ancestral Cascade arc magmatism preceded that of the modern High Cascades DUFDQGUHÀHFWVVXEGXFWLRQRIWKH)DUDOORQSODWHEHQHDWK1RUWK$PHULFD$QFHVWUDO arc magmatism began about 45 Ma, continued until about 3 Ma, and extended from near the Canada-United States border in Washington southward to about 250 km southeast of Reno, Nevada. The ancestral arc was split into northern and southern segments across an inferred tear in the subducting slab between Mount Shasta and /DVVHQ3HDNLQQRUWKHUQ&DOLIRUQLD7KHVRXWKHUQVHJPHQWH[WHQGVEHWZHHQ1LQ QRUWKHUQ&DOLIRUQLDDQG1LQZHVWHUQ1HYDGDDQGZDVDFWLYHIURPDERXWWR Ma. It is bounded on the east by the northeast edge of the Walker Lane. Ancestral arc volcanism represents an abrupt change in composition and style of magmatism relative to that in central Nevada. Large volume, caldera-forming, silicic ignimbrites DVVRFLDWHGZLWKWKHWR0DLJQLPEULWHÀDUHXSDUHGRPLQDQWLQFHQWUDO1HYDGD whereas volcanic centers of the ancestral arc in western Nevada consist of andesitic stratovolcanoes and dacitic to rhyolitic lava domes that mostly formed between 25 DQG0D%RWKDQFHVWUDODUFDQGLJQLPEULWHÀDUHXSPDJPDWLVPUHVXOWHGIURPUROOback of the shallowly dipping slab that began about 45 Ma in northeast Nevada and migrated south-southwest with time. Most southern segment ancestral arc rocks have oxidized, high potassium, calc-alkaline compositions with silica contents ranging continuously from about 55 to 77 wt%. Most lavas are porphyritic and contain coarse plagioclase ± hornblende, biotite, and pyroxene phenocrysts. Seven epithermal gold-silver deposits with > 1 Moz gold production, several large elemental sulfur deposits, and many large areas (10s to > 100 km2) of hydrothermally altered rocks are present in the southern ancestral arc, especially south RIODWLWXGH17KHVHGHSRVLWVDUHSULQFLSDOO\KRVWHGE\LQWHUPHGLDWHWRVLOLFLFODYD GRPHFRPSOH[HVRQO\DIHZGHSRVLWVDUHDVVRFLDWHGZLWKPD¿FWRLQWHUPHGLDWHFRPposition stratovolcanoes. Large deposits are most abundant and well developed in *E-mail: [email protected]

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David A. John, Edward A. du Bray, Christopher D. Henry, and Peter G. Vikre YROFDQLF¿HOGVZKRVHHYROXWLRQVSDQQHGPLOOLRQVRI\HDUV0RVWGHSRVLWVDUHKXQGUHGV of thousands to several million years younger than their host rocks, although some quartz-alunite deposits are essentially coeval with their host rocks. Variable composition and thickness of crustal basement is the primary control on mineralization along the length of the southern ancestral arc; most deposits and large alteration zones are localized in basement rock terranes with a strong continenWDODI¿QLW\HLWKHUDORQJWKHHGJHRIWKH1RUWK$PHULFDQFUDWRQ*ROG¿HOG7RQRSDK RULQDQDFFUHWHGWHUUDQHZLWKFRQWLQHQWDODI¿QLWLHV:DONHU/DNHWHUUDQH$XURUD Bodie, Comstock Lode, Paradise Peak). Epithermal deposits and quartz-alunite alteration zones are scarce to absent in the northern part of the ancestral arc above an accreted island arc (Black Rock terrane) or unknown basement rocks (Modoc Plateau). Walker Lane structures and areas that underwent large magnitude extension during the Late Cenozoic (areas with Oligocene-early Miocene volcanic rocks dipping ! GRQRWSURYLGHUHJLRQDOFRQWURORQPLQHUDOL]DWLRQ,QVWHDGWKHVHIHDWXUHVPD\ KDYHVHUYHGDVORFDOVFDOHFRQGXLWVIRUPLQHUDOL]LQJÀXLGV Key Words: epithermal gold-silver, ancestral Cascade arc, Great Basin magmatism, Walker Lane

INTRODUCTION Numerous Miocene to early Pliocene epithermal gold-silver deposits, including major deposits in the Comstock Lode, *ROG¿HOGDQG7RQRSDKGLVWULFWVDUHJHQHWLFDOO\UHODWHGWRDQcestral Cascade arc magmatism in western Nevada and eastern California. These Oligocene to Pliocene rocks form the southern part of a subduction-related continental-margin magmatic arc that stretched southward from near the Canadian border in western Washington to about 250 km southeast of Reno that preceded magmatic activity of the active High Cascades (Figure 1). The north- to northwest-trending ancestral Cascade arc is broken into northern (Washington, Oregon, and northernmost California) and southern segments (eastern California and western Nevada) by an abrupt break and right step in northeastern California that is an inferred tear in the subducting slab (Figures 1 and 2; Cousens et al., 2008; Colgan et al., 2011; du Bray et al., 2014). Eruptive products and associated mineral deposits vary along the length of the ancestral arc (du Bray and John, 2011; du Bray et al., 2014). Southern segment ancestral arc magmatism is the westernmost manifestation of widespread Cenozoic magmatic activity in northern Nevada and eastern California and is related to rollback of the formerly shallow dipping Farallon slab. Slab rollback magmatism began about 45 Ma in northeastern Nevada and swept southwest across the Great Basin and into the Sierra Nevada. The widespread Cenozoic magmatic activity is EHVWFKDUDFWHUL]HGE\WKHWR0DLJQLPEULWHÀDUHXSGXUing which voluminous silicic ignimbrites were erupted from numerous caldera sources across west-central Nevada to western Utah, thereby forming the southern Great Basin ignimbrite province (Figure 1; Best et al., 2013; Henry and John, 2013). The mostly younger and more westerly located products of

southern segment ancestral arc magmatism formed about 30 to 3 Ma between the east margin of the Walker Lane, the eastern Sierra Nevada, and the Modoc Plateau; they represent a fundaPHQWDOFKDQJHLQHUXSWLYHPRGHWRPRVWO\HIIXVLYHODYDÀRZV and breccias primarily associated with stratovolcanoes and lava domes. Epithermal gold-silver deposits are especially common in the south half of the southern arc segment. Seven districts produced > 1 Moz (31 tonnes) gold and > 10 Moz (310 tonnes) silver. In contrast, epithermal deposits associated with the igQLPEULWHÀDUHXSURFNVDUHVSDUVHDQGUHODWLYHO\VPDOOH[FHSWIRU the giant Round Mountain deposit) and virtually absent in the northern arc segment (John, 2001; du Bray and John, 2011). In this paper, we (1) summarize the geologic setting of the southern arc segment, (2) describe the spatial, temporal, and compositional variations of ancestral arc eruptive products in western Nevada and eastern California, (3) review characteristics and distribution of epithermal gold-silver deposits in the southern arc segment, (4) compare magmatism and metallogeny of the southern and northern arc segments, and (5) discuss possible controls on regional variations in types and endowments of mineral deposits in the two arc segments. This paper summarizes and builds on recent comprehensive discussions of the geochemistry, petrology, and metallogeny of the ancestral Cascade arc by Cousens et al., 2008; du Bray and John (2011), Vikre and Henry (2011), John et al. (2012), Henry and John (2013), du Bray et al. (2014), and Vikre et al. (2015). CENOZOIC MAGMATISM IN THE NORTHWESTERN USA: SLAB ROLLBACK AND ANCESTRAL CASCADE ARC MAGMATISM Cenozoic subduction along western North America is widely recognized as a major contributor to the geologic evo-

Ancestral Cascade Arc Magmatism and Mineral Deposits

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Figure 1. Index map of the western US showing the ancestral Cascade and High Cascade arcs, the southern Great Basin ignimbrite province, and outlines of the *UHDW%DVLQDQG:DONHU/DQH&DVFDGHDUFIURPGX%UD\HWDO 2XWOLQHVRIWKHVRXWKHUQ*UHDW%DVLQLJQLPEULWHSURYLQFHDQGYROFDQLF¿HOGVIURP%HVW HWDO DQG+HQU\DQG-RKQ &DOGHUDVPRGL¿HGIURP+HQU\DQG-RKQ ,QIHUUHGPLG7HUWLDU\SDOHRGUDLQDJHGLYLGHVIURP%HVWHWDO DQG Henry and John (2013). Age contours show approximate location of the initiation of slab rollback magmatism at time indicated as inferred from locally sourced volcanic and intrusive rocks (Henry and John, 2013). East-west line labeled 15 Ma shows approximate location of the Mendocino fracture zone (southern edge of the Farallon plate, which was being subducted beneath North America) at 15 Ma (Atwater and Stock, 1998). The southern terminus of the southern segment of the ancestral Cascade arc gradually migrated north in concert with northerly migration of the Mendocino fracture zone. Accordingly, the southern limit of Farallon SODWHVXEGXFWLRQZDVGLVSODFHGQRUWKZDUGDQGVRXWKRIWKHIUDFWXUH]RQHWKH6DQ$QGUHDVIDXOW6$) WUDQVIRUPGH¿QHGWKHSODWHERXQGDU\$UURZVVKRZUHODWLYH SODWHPRWLRQV:DONHU/DQHPRGL¿HGIURP)DXOGVDQG+HQU\ +HDY\GDVKHGOLQHLQ1(&DOLIRUQLDDQGVRXWKHUQ2UHJRQVKRZVLQIHUUHGWHDULQVXEGXFWHG VODEWKDWVHSDUDWHVWKHDQFHVWUDODUFLQWRQRUWKHUQDQGVRXWKHUQVHJPHQWV&RXVHQVHWDO&ROJDQHWDO &19)FHQWUDO1HYDGDYROFDQLF¿HOG,3&9) ,QGLDQ3HDN&DOLHQWHYROFDQLF¿HOG:19)ZHVWHUQ1HYDGDYROFDQLF¿HOG/3/DVVHQ3HDN060RXQW6KDVWD

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David A. John, Edward A. du Bray, Christopher D. Henry, and Peter G. Vikre

lution of this region (e.g., Lipman et al., 1972; Christiansen and Lipman, 1972). The Cascades arc magmatism results from subduction of the oceanic Farallon and Juan de Fuca plates beneath North America (Figure 1; McBirney, 1978). Subduction and related Cascades arc magmatism were progressively extinguished at the southern end of the arc by northward migration of the Mendocino Triple Junction and formation of a transform plate margin (Figures 1 and 2; Atwater and Stock, 1998). Cenozoic volcanic rocks of the Cascades magmatic arc generally have been divided into two components: (1) those derived from Pliocene to Quaternary volcanoes of the active High Cascades arc (McBirney, 1978; Hildreth, 2007) and (2) those associated with deeply dissected Tertiary (mostly Eocene to late Mio-

cene) volcanoes of the ancestral Cascades arc. In Oregon and Washington, the ancestral Cascades arc rocks form the Western Cascades (Callaghan, 1933; Thayer, 1937; Peck et al., 1964); together with minor Oligocene and Miocene volcanic rocks exposed in northernmost California (Figures 1 and 2; Colgan et al., 2011; du Bray and John, 2011), these form the northern segment of the ancestral Cascades magmatic arc. The southern arc segment (Noble, 1972; Christiansen and Yeats, 1992; Cousens et al., 2008; du Bray et al., 2014) extends southeast, through northeastern California, along the California-Nevada border, and ends in western Nevada at ~latitude 37°N. The northern and southern arc segments are separated by an inferred northeast-trending tear in the subducting slab between Mt. Shasta

Figure 2. Map of northern California and western Nevada showing the inferred extent of ancestral (green polygons) and modern High Cascades magmatic (cross KDWFKHGSRO\JRQV DUFV6RXWKHUQDUFVHJPHQWURFNSRO\JRQVZHVWRIWKHVRXWKHUQDUFVHJPHQWERXQGDU\UHSUHVHQWGLVWDOO\GLVSHUVHGYROFDQRJHQLFRXWÀRZPDWHrial deposited in channels extending down the west slope of the Sierra Nevada. As such, these deposits, derived from eruptive centers to the east, are not included ZLWKLQWKHVRXWKHUQDUFVHJPHQWWHUUDQHDVGH¿QHGE\WKHH[WHQWRIDUFUHODWHGYROFDQLFHGL¿FHV6DPSOHORFDWLRQVRIDQFHVWUDO&DVFDGHDUFURFNVIURPJHRFKHPLFDOGDWDEDVHRIGX%UD\HWDO DUHLQGLFDWHGE\VPDOOGRWV+HDY\JUD\OLQHVVKRZWKHVRXWKHUQHGJHRIVXEGXFWLQJ)DUDOORQSODWHDWWKHWLPHVSHFL¿HG (Atwater and Stock, 1998). Red dashed line is the initial 87Sr/86Sr = 0.706 isopleth for Mesozoic plutonic rocks in California (Kistler, 1990) and Nevada (Tosdal et al., 2000). Blue dashed line is the 208Pb/204Pb = 38.8 isopleth (Tosdal et al., 2000). Outcrops of Mesozoic granitic rocks are from Ludington et al. (2005). Purple OLQHV+HQU\DQG-RKQ RXWOLQHWKH:HVWHUQ1HYDGDYROFDQLF¿HOG:19) DQG&HQWUDO1HYDGDYROFDQLF¿HOG&19) 150 percent (Yerington district-northern Wassuk Range; Proffett, 1977; Dilles and Gans, 1995). In areas that underwent large-magnitude extension (i.e., > 50%), an early period of rapid large-magnitude extension along closely spaced normal faults was followed by a younger period of small-magnitude extension on more widely spaced normal faults that formed the present basins and ranges (e.g., Proffett, 1977; Dilles and Gans, 1995; Surpless et al., 2002; Colgan et al., 2006; Colgan and Henry, 2009). The Walker Lane is a northwest-trending zone of dextral shear and transtension that connects to the Las Vegas shear zone south of the Garlock Fault and accommodates about 20% of WKHULJKWODWHUDOPRWLRQEHWZHHQWKH3DFL¿FDQG1RUWK$PHULFD plates (Figures 1 and 4; Atwater, 1970; Zoback et al., 1981; Stewart, 1988; Oldow, 1992, 2003; Dilles and Gans, 1995; Faulds and Henry, 2008). The Walker Lane has been divided into 11 domains based on distinct structural styles (Figure 4; Stewart, 1988; Faulds and Henry, 2008; Busby 2013). Structures in these domains include complex systems of kinematical-

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ly related and broadly coeval northwest-striking dextral faults and north- to north-northeast-striking normal faults (Modoc Plateau, Pyramid Lake, Walker Lake, Sierra Front, and InyoMono domains), east-northeast-striking sinistral-normal faults (Carson and Spotted Range-Mine Mountain domains and Mina GHÀHFWLRQ DQGDUHDVWKDWODFNPDMRUVWULNHVOLSIDXOWV*ROG¿HOGGRPDLQ 7KH0LQDGHÀHFWLRQLVDQHDVWZHVW]RQHDFURVV which right lateral displacement on northwest-striking faults in the Walker Lake domain is transferred west to similar faults in WKH,Q\R0RQRGRPDLQ7KH0LQDGHÀHFWLRQDOVRDSSUR[LPDWHly corresponds to the edge of the Neoproterozoic continental margin (Figures 2 and 4). Recent studies across much of the northern and western parts of the southern arc segment suggest that modern Basin and Range extension began between about 16 to 10 Ma; earlier, this area was part of the little deformed Sierra Nevada block (e.g., Dilles and Gans, 1995; Henry and Perkins, 2001; Stockli et al., 2002; Surpless et al., 2002; Colgan et al., 2006, 2011; Faulds and Henry, 2008; Colgan and Henry, 2009; Lee et al., 2009; Busby et al., 2013). Dextral shear in the central Walker Lane related to formation of the transform plate margin also began about 10 Ma (Faulds and Henry, 2008). However, the pre-mid Miocene tectonic history of much of the central part of southern arc segment is incompletely understood and controversial; some studies suggest earlier periods of “pre-Basin and Range” extension and (or) strike-slip faulting along ancestral Walker Lane faults (e.g., Proffett, 1977; Ekren et al., 1980; John et al., 1989; Seedorff, 1991; Hardyman and Oldow, 1991; Dilles and Gans, 1995). Early Miocene and older (t 20 Ma) volcanic rocks in numerous areas in the central and southeastern parts of the southern arc segment are steeply tilted (t 40°), which is uncharacteristic of modern Basin and Range extension (Figure 4). Several studies suggested that earlier period(s) of “pre-Basin and Range” extension, possibly related to southwestward migration of extension that accompanied or slightly post-dated silicic ignimbrite magmatism in areas northeast of the southern arc segment, affected much of the east-central and southeastern parts of the southern arc segment (Figures 2 and 4; Proffett, 1977; Seedorff, 1981, 1991; Shaver and McWilliams, 1987; John et al., 1989; Hardyman and Oldow, 1991; Dilles and Gans, 1995; John, 1995; Hudson et al., 2000). However, more recent studies of several of these areas indicate that extenVLRQ LV HLWKHU VLJQL¿FDQWO\ \RXQJHU WKDQ SUHYLRXVO\ HVWLPDWHG and broadly synchronous with the initiation of regional Basin and Range extension (e.g., Yerington district-northern Wassuk Range, Dilles and Gans, 1995; Surpless et al., 2002; southwest Paradise Range, Sillitoe and Lorson, 1994) or that these areas are paleovalleys, not extensional basins (e.g., Nine Hill paleovalley, Henry and Faulds, 2010, and Candelaria trough, Henry and John, 2013). Faulds and Henry (2008) concluded that dextral shear in the central and southern Walker Lane probably started about 10 Ma and has propagated northwest to the Modoc Plateau (Figure

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Figure 4. Map showing Cenozoic tectonic features and mineral deposits (summarized in Table 1) of the southern arc segment. Domains of the Walker Lane modi¿HGIURP)DXOGVDQG+HQU\ DQG%XVE\ $UHDVZKHUH2OLJRFHQHDQGHDUO\0LRFHQHYROFDQLFURFNVDUHVWHHSO\GLSSLQJ! PRGL¿HGIURP-RKQ et al. (1989) and Dilles and Gans (1995). Mineral deposits as in Figure 3.

Ancestral Cascade Arc Magmatism and Mineral Deposits 4). In contrast, several previous studies concluded that strikeslip faulting began in the central Walker Lane (i.e., northern Wassuk, Gabbs Valley, and Gillis Valley Ranges) at ca. 25 Ma (Ekren et al., 1980; Hardyman and Oldow, 1991; Oldow, 1992; Dilles and Gans, 1995). Faulds and Henry (2008), Henry and Faulds (2010), and Henry et al. (2012) suggest that many of the apparent fault relations described in these studies represent complexities arising from deposition of far travelled ignimbrites in paleovalleys, primary dips of the ignimbrites due to irregular topography of the paleovalleys, and erosion between deposition of the ignimbrites. The effects of the complex and variable Late Cenozoic tectonism on southern arc segment development are unclear. In general, during its earliest stages, the arc developed in a neutral RUZHDNO\H[WHQVLRQDOVWUHVV¿HOGWKDWFKDQJHGWRDPLOGO\H[WHQVLRQDORUWUDQVWHQVLRQDOVWUHVV¿HOGZLWKWKHRQVHWRI%DVLQ and Range extension and Walker Lane strike-slip faulting at DERXWWR0D$UHODWLYHO\XQLIRUPKRUL]RQWDOVWUHVV¿HOGLV suggested by volcanic landforms dominated by approximately HTXLGLPHQVLRQDO VWUDWRYROFDQRHV DQG FRPSRVLWH GRPH ¿HOGV EURDGO\FLUFXODUYROFDQLF¿HOGVDQGWKHVFDUFLW\RIGLNHV1DNDPXUD 7DNDGD -RKQ DV H[HPSOL¿HG E\ PLGGOHWRODWH0LRFHQHYROFDQLF¿HOGVLQQRUWKHDVWHUQ&DOLIRUnia (Grose, 2000), the Virginia City area (Hudson et al., 2009) DQGWKH%RGLH+LOOV-RKQHWDO 6WUHVV¿HOGSHUWXUEDWLRQVWKDWPD\KDYHLQÀXHQFHGDUFPDJPDWLVPLQFOXGLQJWKH VWURQJO\H[WHQVLRQDOVWUHVV¿HOGLQIHUUHGGXULQJHUXSWLRQRIWKH late Miocene K-rich Stanislaus Group near Sonora Pass in the eastern Sierra Nevada, are evident in some places (Putirka and Busby, 2007; Busby et al., 2008, 2013). Rapid, large magnitude extension in the Yerington district-Buckskin Range at about 14 Ma was accompanied by eruption of voluminous hornblende andesite (Proffett, 1977; Dilles and Gans, 1995). The long-acWLYHFDWR0D %RGLH+LOOVYROFDQLF¿HOGPD\KDYHEHHQ localized by its complex tectonic setting between the Walker Lane and the little deformed Sierra Nevada and at the northwest HQGRIWKH0LQDGHÀHFWLRQ7KH%RGLH+LOOVYROFDQLF¿HOGDOVR may be coincident with the margin of Neoproterozoic craton (John et al., 2012, 2015). Several volcanic centers along the east side of the Sierra Nevada near Sonora Pass, including the Little Walker caldera, may have been localized along releasing stepover zones (Busby, 2013; Busby et al., 2013). GEOLOGIC BACKGROUND OF THE SOUTHERN SEGMENT OF THE ANCESTRAL ARC Using geochemical and geochronologic databases (du Bray et al., 2009) and geologic maps showing interpretative volcanic assemblages (e.g., Christiansen and Yeats, 1992; Ludington et al., 1996), du Bray et al. (2014) described the temporal, spatial, and compositional evolution of the southern arc segment and its volcanogenic characteristics. They divided rocks of the southern arc segment into 4 time slices, 35–26, 25–18, 17–8, and 7–2 Ma, to facilitate comparison with the northern arc segment (du Bray and

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-RKQ 7KH\GH¿QHGGRPDLQVWKDWUHSUHVHQWJHRJUDSKLcally coherent parts of the southern arc segment, which consist of VXLWHVRIVDPSOHVIURPRQHRUVHYHUDOUHODWHGYROFDQLF¿HOGV7KLV approach is limited, however, by the scarcity of geochemical and JHRFKURQRORJLF GDWD IRU PDQ\ DUHDV LGHQWL¿HG DV EHLQJ SDUW RI the ancestral Cascade arc, as shown by relatively few chemical analyses in many areas of the southern arc (Figure 2). Temporal Evolution of Ancestral Cascades Arc Magmatism 6LJQL¿FDQW PDJPDWLF DFWLYLW\ LQ WKH VRXWKHUQ VHJPHQW RI the ancestral arc extended from about 28 to 2 Ma. Magmatism commonly was episodic within domains and individual volcaQLF¿HOGVDQGPD[LPXPPDJPDWLFDFWLYLW\ZDVEHWZHHQWR 8 Ma (du Bray et al., 2014; Figure 5). Spatial Distribution of Ancestral Cascades Arc Magmatism Through Time Cousens et al. (2008), Vikre and Henry (2011), and du Bray et al. (2014) showed that the locus of arc magmatism migrated systematically during ancestral arc magmatism (Figure 5). The small number and limited spatial distribution of samples of the 35–26 Ma interval suggest that southern arc segment magmatism was volumetrically minor and principally focused at its northern limit, especially in the Warner Range of northeast California, and at the east edge of the arc segment (Figure 5A). The distribution of 25–18 Ma volcanic rock samples indicates that magmatic activity remained strongly concentrated along the eastern edge of the ancestral arc (Figure 5B). During this period, magmatism was also largely restricted to the southern two-thirds of the ancestral arc south of Pyramid Lake. 6LJQL¿FDQWO\PRUHYROXPLQRXVPDJPDWLVPRFFXUUHGGXULQJWKH 17–8 Ma interval, which was the period of maximum magma productivity in the southern arc segment. During this interval, magmatism was strongly concentrated throughout the northern two-thirds of the arc (Figure 5C), consistent with northerly Mendocino triple junction migration, and shifted dramatically westward, to near the midline of the ancestral arc terrane. DurLQJWKH¿QDO±0DLQWHUYDORIVRXWKHUQDUFVHJPHQWPDJPDtism, erupted volumes appear to have decreased but remained greater than volumes erupted prior to 18 Ma. Magmatism in this interval was strongly focused in the central third of the southern arc segment (Figure 5D), especially from the Bodie Hills to the north side of Lake Tahoe. Also during this interval, arc magmatism migrated farther west, to its westernmost position prior to being extinguished by northward migration of the Mendocino triple junction. Volcanologic Characteristics of Ancestral Cascades Arc Eruptive Centers Volcanic rocks in the southern arc segment depict a broad

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35-26 Ma Silicic >68% SiO2 Intermediate 55-68% SiO2 Mafic 35. Primitive mantle-normalized patterns show ORZGHQVLW\FUXVWXQGHUO\LQJWKHFHQWUDO6LHUUD1HYDGD¿OWHUHG pronounced positive anomalies for K, Ba, Rb, Th, and Pb and PD¿FPDJPDV,QWKHDEVHQFHRIDVWURQJO\H[WHQVLRQDOVWUHVV negative anomalies for Ti, P, Zr, Nb, and Ta. These composi- ¿HOGFRQGXFLYHWRUDSLGDVFHQWRIGHHSO\VRXUFHGPDJPDGU\ tional characteristics are similar to calc-alkaline igneous rocks EDVDOWLFPHOWVODFNVXI¿FLHQWEXR\DQF\WRDVFHQGWRWKHVXUIDFH


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Figure 6. Total alkali-silica diagram showing compositions of southern arc segment rocks by age group from du Bray et al. (2014). Black and red dashed lines GHOLQHDWHWKHFRPSRVLWLRQ¿HOGVRIPRGHUQ+LJK&DVFDGHVDUFURFNV0& GDWDIURP*(252& DQGQRUWKHUQDUFVHJPHQW16 UHVSHFWLYHO\5RFNFRPposition boundaries from Le Bas et al. (1986).

and erupt. Magmas of this type may have stalled in the lower or middle crust where they crystallized, differentiated, and interacted with the crust to form MASH zones (Hildreth and Moorbath, 1988), capable of producing more silicic residual magma compositions characteristic of the central California ancestral arc segment. In northeastern California, crust underlying the northern Sierra Nevada and Modoc Plateau is thinner (Gilbert, 2012), and deeply sourced basalt melts ascended directly to the surface and erupted. Enhanced crustal thickness similarly may KDYHFRQWUROOHGHUXSWLELOLW\RIPD¿FPDJPDVLQWKHVRXWKHDVWern part of the ancestral arc resulting in the dominance of intermediate and silicic compositions in long-lived volcanic centers within the Great Basin and Walker Lane.

Comparison of the Compositional Evolution of the Northern and Southern Arc Segments The time-space-compositional evolution of southern arc segment magmatism is distinct from that of the northern arc segment, and geochemical data strongly suggest that the two DUF VHJPHQWV HYROYHG LQ VLJQL¿FDQWO\ GLIIHUHQW WHFWRQLF VHWtings (du Bray et al., 2014). The axis of northern arc segment magmatism migrated slowly eastward with time, whereas subducted slab rollback beneath the southern arc segment and arc magmatism migrated westward. Compositions of northern arc segment rocks vary systematically through time (du Bray and John, 2011), whereas southern arc segment rocks, with the ex-

626


ception of geographically isolated and incompletely sampled 35–26 Ma age group rocks, exhibit no systematic compositional variation through time or space suggesting that subductionrelated processes responsible for southern arc segment magmatism probably were also relatively uniform through time. Southern arc segment rocks have generally lower TiO2, FeO*, CaO, and Na2O contents, higher K2O contents, and exhibit less compositional variation through time than the northern arc segment rocks, which are also distinctly more ferroan and tholeiitic (du Bray and John, 2011; du Bray et al., 2014). The presence of hornblende phenocrysts in many southern arc segment rocks implies that the associated magmas were hydrous, whereas its scarcity in northern arc segment rocks suggests drier magmas. As discussed in du Bray et al. (2014), trace and rare earth element behavior also is different in the two arc segments. Compositional trends in the southern arc segment are consistent with magma genesis at depths > 70 km beneath relatively thick continental crust. In contrast, compositional features of most northern arc segment rocks are consistent with their genesis beneath thinner, more primitive crust of the accreted Siletzia terrane (Wells et al., 2014). Compositional variations among the northern and southern arc segment rocks primarily UHÀHFWGLIIHUHQWFUXVWDOWKLFNQHVVHVWKDWLQÀXHQFHGWKHGHSWKDW which their respective magmas were generated. In the southern segment, ascent of subduction-related magmas through relatively thick continental crust along the western edge of North America was slowed, allowing melting, assimilation, storage, and homogenization (MASH) processes (Hildreth and Moorbath, 1988; Annen et al., 2006) to yield a greater proportion of felsic magmas than is typical of the northern arc segment. In the southern arc segment region, compositional similarities between southern arc segment rocks and those of the co-spatial modern High Cascades arc rocks (Figure 6) suggest that magmatism transitioned continuously from that associated with the ancestral arc to that associated with the modern High Cascades arc.

mines, led to renewed exploration for gold-silver deposits and discovery or development of large, but relatively low-grade, epithermal deposits at Borealis, Santa Fe, Paradise Peak, Tonopah, and Rawhide and renewed mining in the Aurora, ComVWRFN/RGHDQG*ROG¿HOGGLVWULFWVLQWKHVWRHDUO\V (Figure 7). Exploration activity for epithermal deposits in the southern part of the ancestral arc continues today with sigQL¿FDQWUHVRXUFHVGH¿QHGLQWKH*ROG¿HOGGLVWULFW6KRHPDNHU et al., 2013), at Hasbrouck Mountain in the Tonopah district (Wilson, 2014), and elsewhere. Total production for epithermal gold-silver deposits in the southern arc segment through 2012 exceeded 23 Moz gold (715 tonnes) and 455 Moz silver (14,000 tonnes) (Table 1). Epithermal gold-silver deposits, including seven districts that produced > 1 Moz gold, are the characteristic style of mineralization in the southern arc segment (Table 1; e.g., John, 2001; Vikre and Henry, 2011), whereas known epithermal gold-silver deposits in the northern arc segment are sparse and small (du Bray and John, 2011). However, most known epithermal deposits and alteration zones in the southern arc segment are south of latitude 40°N (Figures 3, 4, 7). In contrast, plutonic rocks and genetically-related porphyry copper and other intrusion-related breccia and vein deposits are abundant in the northern arc segment, whereas plutonic rocks are rarely exposed and porphyry copper and intrusion-related deposits are unknown in the southern arc segment. Other types of mineral deposits hosted by southern arc segment rocks include stratiform sulfur, hot spring mercury, and polymetallic vein deposits (Figure 3, Table 1). Characteristics of Hydrothermal Alteration and Mineral Deposits in the Southern Arc Segment: Types, Distribution, Age, and Relationship to Magmatism

Areas of hydrothermally-altered rock and epithermal goldsilver deposits are especially abundant in (1) the Walker Lane in the western Great Basin south of latitude 40°N and (2) in adjacent areas in the eastern Sierra Nevada south of Lake DaEPITHERMAL GOLD-SILVER DEPOSITS OF THE vis (Figures 3 and 7). Some parts of the ancestral arc, notably SOUTHERN ARC SEGMENT around the Comstock Lode in the Virginia Range in western Nevada and in the Markleeville area (Monitor district) in eastern Epithermal gold-silver deposits and large areas of hydro- California, include areas of propylitically-altered rock larger thermally altered rocks are abundant in late Oligocene to early than 100 km2 (Coats, 1940; Wilshire, 1957; Whitebread, 1976; Pliocene rocks of the southern arc segment, especially in the Vikre, 1989; John, 2001; Hudson et al., 2009). Other types of western Great Basin (Walker Lane) south of latitude 40°N (Fig- hydrothermal alteration commonly are localized within more ures 3, 4, and 7; John, 2001; Vikre and Henry, 2011; du Bray et widely developed propylitic alteration. Alteration of this sort al., 2014). Rich gold-silver vein deposits of the Comstock Lode includes more than 40 quartz-alunite alteration cells, which are at Virginia City were discovered in 1859 and in the following areas of intense hydrolytic alteration that range in size from year at Aurora, leading to a major gold rush in western Nevada < 0.1 km2 to > 100 km2. Intense hydrolytic alteration results and eastern California that lasted through the 1870s (Tingley from convective circulation of low pH magmatic-hydrothermal et al., 1993). A second gold rush, touched off by discovery of ÀXLGVGHVWUXFWLRQRISULPDU\LJQHRXVPLQHUDOVDQGIRUPDWLRQ VLOYHUDQGJROGULFKGHSRVLWVDW7RQRSDK DQG*ROG¿HOG RI TXDUW] DOXQLWH S\ULWH DQG RWKHU ]RQHG PLQHUDO DVVHP(1902), lasted through the 1920s. In the 1970s, rise of gold and blages (Figure 7; Vikre and Henry, 2011). silver prices due to deregulation and changes in recovery techNumerous epithermal gold-silver deposits and prospects niques for low-grade ores that could be produced from open pit occur within areas of hydrothermally altered rock in the south-


627

Figure 7. Map of the southern ancestral arc segment showing epithermal deposits (labeled) and quartz-alunite alteration zones (Vikre and Henry, 2011). Walker /DQHGRPDLQVPRGL¿HGIURP)DXOGVDQG+HQU\ DQG%XVE\ &&DUVRQ**ROG¿HOG,0,Q\R0RQR/9/DV9HJDV0'0LQDGHÀHFWLRQ03 Modoc Plateau; PL, Pyramid Lake; SF, Sierra Front; SR, Spotted Range–Mine Mountain; WL, Walker Lake.

District/ Number Deposit Name Latitude Longitude Deposit type

Production/ resources

High Grade

41.950

–120.210 Quartz-adularia ca. 4,400 oz Au Au-Ag

2

Hayden Hill

40.995

3

Leadville

41.099

4

Pyramid

39.860

5

Guanomi

39.844

–119.455

6

Golden Dome

39.643

–120.293

Quartz-alunite 1.5 Mt @ 0.1 oz Au-Ag Au/t and 1.2 oz Ag/t

7

Peavine

39.600

–119.900

Quartz-alunite Au-Ag

8

Wedekind

39.570

–119.750


Host rocks

Rhyolite domes and andesite lava ÀRZV –120.875 Quartz-adularia 421,171 oz Au; ca. 8 Late Miocene Au-Ag 909,403 oz Ag dacite breccias and tuffs DQGÀXYLDO lacustrine sedimentary rocks –119.0404 Quartz-adu- small production undated Eocene(?) laria Au-Ag or Ag-Pb-Zn andesite polymetallic vein –119.610 Quartz-alunite minor Au, Ag 22.6 23.2 Ma Au-Ag or dacite ignimpolymetallic brite, andesite vein dikes Porphyry Cu-Mo?

none

14.5

ca. 24

7.0 to 7.2

Volcanic setting

Basement rocks

Rhyolite domes intrudLQJPD¿FODYD ÀRZV Dacite domes separated by shallow basins

Unknown

Unknown

Unknown

Unknown

Unknown

Mesozoic granitic and metavolcanic rocks Andesite dikes Unknown, intruding tuff probably Me¿OOLQJVPDOO sozoic granitic caldera(?) rocks

Early Miocene Porphyry Cretaceous quartz monzo- stock intrud- granite, Mesonite porphyry ing distally- zoic metasedistock sourced ash mentary and ÀRZWXIIV metavolcanic rocks Mesozoic gra- Dacite dome Mesozoic nitic rocks, ca. ¿HOG granitic rocks 9 Ma dacite

1,747 oz Au, ca. 16 to Miocene 199,750 oz Ag 15 andesite lava ÀRZVDQG plugs, Jurassic metavolcanic rocks included in ca. 16 to Miocene Peavine 15 andesite lava ÀRZVDQG plugs, Jurassic metavolcanic rocks

Subvolcanic Cretaceous intermediate granite, Mesocomposition zoic metasediintrusions mentary and metavolcanic rocks Subvolcanic Cretaceous intermediate granite, Mesocomposition zoic metasediintrusions mentary and metavolcanic rocks

Terrane/ Controlling Assemblage structures

Black Rock(?)

Unknown

Sand Springs

Unknown

Jurassic felsic volcanic rocks


References

Fractures Keats, 1985; and faults Feinstein, along dome 2011; du Bray margins et al., 2014 NW-striking Detra and strike-slip Burnett, 1994 and NE-striking normal faults

Bonham and Papke, 1969; du Bray et al., 2014 Wallace, 1975; Garside et al., 2003; Vikre and Henry, 2011 Prochnau, 1973; John et al., 1993

North-strikYoung and ing highCleur, 1992; angle faults Canby, 1992; and breccia Vikre and zones Henry, 2011 North-strik- Hudson, 1977 ing highangle faults and breccia zones North-strik- Hudson, 1977 ing highangle faults and breccia zones (continued)


1

Age (Ma)

628

Table 1. CHARACTERISTICS OF MINERAL DEPOSITS ASSOCIATED WITH SOUTHERN OF SEGMENT OF ANCESTRAL CASCADES ARC. ENTRIES IN ITALICS, IN PRODUCTION/RESOURCES COLUMN INDICATE RESOURCES.

Table 1 (continued). CHARACTERISTICS OF MINERAL DEPOSITS ASSOCIATED WITH SOUTHERN OF SEGMENT OF ANCESTRAL CASCADES ARC. ENTRIES IN ITALICS, IN PRODUCTION/RESOURCES COLUMN INDICATE RESOURCES. District/ Number Deposit Name Latitude Longitude Deposit type


Age (Ma)

Host rocks

Basement rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite and Jurassic metasedimentary rocks

9

Olinghouse

39.670

–119.408 Quartz-adularia 74,272 oz Au, Au-Ag 48,632 oz Ag

10.5

Miocene baVDOWODYDÀRZ and dikes, dacite dikes

Dacite dike swarm

10

Gooseberry

39.480

–119.460 Quartz-adularia 84,866 oz Au, Au-Ag 3.57 Moz Ag

10.3

Miocene andesite-dacite ODYDÀRZV breccias and domes

Flow dome complex

11

RamseyComstock

39.470

–119.380

ca. 9.3

Flow dome complex

12

Talapoosa

38.450

–119.270 Quartz-adularia 7,549 oz Au; Au-Ag 102,596 oz Ag

Miocene andesite lava ÀRZVDQG interbedded epiclastic rocks Miocene andesite-dacite ODYDÀRZV breccias and domes

13

Comstock Lode

39.300

–119.650 Quartz-adularia 8.4 Moz Au; 193 14.2 to Au-Ag Moz Ag; minor 14.0 Cu and Pb

18.3 to 17.4 Andesite Ma, 15.8 to GRPH¿HOG 15.2 Ma, and built on earlier 14.9 to 14.2 andesite straandesites tovolcano

–119.590 Quartz-adularia 130,072 oz Au; Au-Ag >305,055 oz Ag

13.4

Cretaceous Andesite granite, 15.8 GRPH¿HOG to 15.2 M, and built on earlier 14.9 to 14.2 andesite straandesites tovolcano

–119.480 Quartz-adularia Au-Ag

7.0 to 6.6

14

15

Flowery 39.320 (Golden Eagle)

Como

39.170


18,650 oz Au

small Au-Ag production

10.1

Flow dome complex

Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks


References


Northeast- Wilson et al., striking 1999; John strike-slip et al., 1999; faults and Garside and parallel dikes Bonham, 2006 Walker Lake, W- to WNWSprecher, Pine Nut asstriking 1985 semblage left-lateral oblique-slip fault Walker Lake, NortheastPine Nut asstriking norsemblage mal faults

Vikre and Henry, 2011; Clark, 1992

Walker Lake, West-striking Van NieuwenPine Nut as- normal and huyse, 1991; semblage intersecCarpenter, tions with 1992 NW-striking strike-slip faults Walker Lake, North-north- Vikre et al., Pine Nut as- east-striking 1988; Vikre, semblage normal faults 1989; Hudson, 2003; Berger et al., 2003; Hudson et al., 2009; Becker, 1882 Walker Lake, Northeast- Castor et al., Pine Nut asstriking nor2005 semblage mal faults

(continued)

629

Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Late Miocene Andesite straMesozoic Walker Lake, East-northVikre and andesite lavas tovolcano(?) metasediPine Nut as- east- and McKee, 1994 and intrusions mentary and semblage north-striking metavolcanic high-angle rocks faults


Volcanic setting

630



Age (Ma)

Host rocks

Volcanic setting

Dan TuckerSummit King

39.274

–118.353 Quartz-adularia 20,895 oz Au, Au-Ag 1.26 Moz Ag

17

Rawhide

39.030


1.56 Moz Au, 12.7 Moz Ag

18

Monitor/Leviathan

38.712

–119.658

0.466 Mt S0

19

Monitor/Zaca

38.666

–119.706 Quartz-adularia 79,000 oz Au; Au-Ag 1.82 Moz Ag

20

Patterson/ Silverado

38.451

–119.240 Quartz-adularia 3,000 oz Au; 3 ca. 5.5? Late Miocene Rhyolite dome Au-Ag Moz Ag. 35,000 rhyolite complex lb Cu

21

Masonic

38.367

–119.117 Quartz-adularia 55,791 oz Au, Au-Ag 38,749 oz Ag, minor Cu

Stratiform sulfur

ca. 19

Miocene rhyo- Rhyolite dikes lite dikes and andesite lava ÀRZV2OLJRcene rhyolite ignimbrites, Mesozoic metavolcanic rocks ca. 15.5 Mostly andesRhyoliteLWHODYDÀRZV basalt volcanic center; mostly intermediate composition lava dome ¿HOG ca. 9 Volcaniclastic Edge of sedimentary andesite strarocks tovolcano

4.9

~5 Ma rhyolite Rhyolite dome domes in older trachyandesite stratovolcano

13.4 and 15 to 14 Ma Andesite stra13.0 trachyandestovolcano LWHODYDÀRZV and volcaniclastic rocks


References


Sand Springs

East-north- Willden and east-striking Speed, 1974; veins along Garside et al., dikes and 1981 faults


Sand Springs

North- and northeaststriking oblique-slip faults

Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks Cretaceous granite, Mesozoic metasedimentary and metavolcanic rocks

Black et al., 1991; Gray, 1996

Walker Lake, Replacement Clark and Pine Nut as- of volcanicla- Evans, 1977; semblage stic rocks Vikre and Henry, 2011

Walker Lake, Pine Nut assemblage

Brecciated margin of lava dome

Clark and Evans, 1977; Prenn and Merrick, 1991; John and Armin, 1984 Walker Lake, NorthBrem et al., Pine Nut as- northeast- to 1983; du Bray semblage northwestet al., 2014 striking highangle faults Walker Lake, Pine Nut assemblage

North- and northeaststriking oblique-slip faults

Henry and Vikre, 2011; Vikre et al., 2015

(continued)


16

Basement rocks



Age (Ma)

Host rocks

Borealis

38.380

–118.760 Quartz-adularia 653,000 oz Au; ca. 16? Miocene Au-Ag >114,000 oz Ag andesites and volcaniclastic rocks

23

Bodie

38.223

–118.982 Quartz-adularia 1.456 Moz Au; Au-Ag 7.28 Moz Ag

24

Aurora

38.290


25

Cinnabar Canyon/ Calmono

38.190

–119.160

26

Paradise Peak

38.750


19 to 18

27

Santa FeIsabella-Pearl

38.590

–118.117 Quartz-adularia 356,700 oz Au, Au-Ag 721,523 oz Ag

ca. 19

Stratiform sulfur

8.5 to 8.1

9.1 to 8.9 dacite domes and breccias

Uncertain

Dacite dome ¿HOG

10.5 to 13 Ma trachy- Rhyolite dome 10.2 andesite; 11.2 ¿HOGRQHGJH Ma rhyolite of trachyandesite stratovolcano 0W# 8.8 to Volcaniclastic Trachyandes8.7 sedimentary LWHGRPH¿HOG 60 rocks

22 to 18 Ma Probably anandesite-da- desite-dacite FLWHODYDÀRZV GRPH¿HOG and breccias and ca. 25 Ma rhyolite tuffs Mesozoic Uncertain; carbonates, sparse rhyolite Cretaceous dikes granite, Oligocene ignimbrites

Basement rocks


References

Mesozoic Walker Lake, Northeastgranite and Pine Nut asstriking metavolcanic semblage normal or rocks oblique-slip faults

Eng, 1991; Steininger and Ranta, 2005; Vikre and Henry, 2011 Uncertain, Walker Lake, North- to Chesterman possibly Pamlico-Lodi northeastet al., 1986; Paleozoic assemblage striking nor- John et al., siliciclastic mal faults 2012; Vikre et metasedimenal., 2015 tary rocks Mesozoic Walker Lake, NortheastJohn et al., granite and Pamlico-Lodi striking 2012; Vikre et metavolcanic assemblage oblique-slip al., 2015; Osrocks faults borne, 1991; Twain, 1873 Cretaceous Walker Lake, Replacement Ward, 1992; granite, Meso- Pamlico-Lodi of volcanicla- Vikre and zoic metavol- assemblage stic rocks Henry, 2011; canic rocks, John et al., Paleozoic 2012; Vikre et metasedimenal., 2015 tary rocks Cretaceous Sand West-north- John et al., granite, Meso- Springs(?) west- and 1989, 1991; zoic metavol- (boundary northeastSillitoe and canic rocks, with Walker striking nor- Lorson, 1994 Paleozoic Lake) mal faults metasedimentary rocks Cretaceous Walker Lake, Santa Fe: Fiannaca, granite, Meso- Pamlico-Lodi northwest- to 1987; Albino zoic metavol- assemblage west-northand Boyer, canic rocks, west striking 1992, Vikre Paleozoic fault zone; and Henry, metasedimenIsabella2011 tary rocks Pearl: northwest- to west-northwest-striking normal faults

631

(continued)


22

Volcanic setting

632

Table 1 (continued). CHARACTERISTICS OF MINERAL DEPOSITS ASSOCIATED WITH SOUTHERN OF SEGMENT OF ANCESTRAL CASCADES ARC. ENTRIES IN ITALICS, IN PRODUCTION/RESOURCES COLUMN INDICATE RESOURCES. Production/ resources

Age (Ma)

28

Tonopah

38.070


1.86 Moz Ag, 174 Moz Ag

ca. 20

29

Divide/ Tonopah Divide

37.990

–117.240 Quartz-adularia 39,759 oz Au; Au-Ag 4.135 Moz Ag

ca. 16

30

Divide/ Hasbrouck

37.990


31

*ROG¿HOG

37.710

–117.210

32

Bruner

39.062

–117.767


small Ag production

4.19 Moz Au; 1.45 Moz Ag; 3835 t Cu

Host rocks Early Miocene andesite and rhyolite lavas, breccias, intrusions, and ignimbrites

Volcanic setting

Basement rocks


References

Uncertain; Mesozoic Nolan belt East- and Spurr, 1905; may lie inside granitic rocks, domain over- north-striking Nolan, 1935; caldera overly- Paleozoic lying North shallow dip- Bonham and ing andesite/ metasedimenAmerica ping faults Garside, dacite dome tary rocks craton 1979; Ashley, complex 1990; this study Rhyolite Paleozoic Nolan belt Northwest- Erdman and GRPH¿HOG sedimentary domain overstriking Barabas, along edge of rocks lying North normal fault 1996 sedimentary America basin craton

ca. 19 Ma rhyolite tuff; 17-16 Ma rhyolite domes, mid-Miocene volcaniclastic sediments ca. 16 Mid-Miocene Rhyolite Paleozoic Nolan belt volcaniclastic GRPH¿HOG sedimentary domain oversediments along edge of rocks lying North sedimentary America basin craton 20 to 19 22-21 Ma Andesite Jurassic gran- Nolan belt andesite and GRPH¿HOG ite; Paleozoic domain overrhyolite argillite lying North America craton

East-west Graney, 1987 normal faults

Northwesttrending strike-slip(?) and north- to northeaststriking normal faults

Vikre and Henry, 2011; Blakely et al., 2007; Berger et al., 2005; Ashley, 1974; Ransome, 1909 Quartz-alunite ~61,000 oz Au, ca. 16.3 20 and 16.6 Rhyolite dome Mesozoic Walker Lake, NorthBaldwin et al., Au-Ag 230,000 oz Ag Ma rhyolite ¿HOG granite, Meso- Pamlico-Lodi striking faults 2014 domes and zoic metasedi- assemblage and rhyolite 0DPD¿F mentary rocks DQGPD¿F dikes dikes


District/ Number Deposit Name Latitude Longitude Deposit type

Ancestral Cascade Arc Magmatism and Mineral Deposits HUQ DUF VHJPHQW %RWK TXDUW]DOXQLWH KLJKVXO¿GDWLRQ DQG TXDUW]DGXODULDORZDQGLQWHUPHGLDWHVXO¿GDWLRQRUDGXODULD sericite) types of deposits (Heald et al., 1987; Hedenquist et al., 2000) are well represented in the southern arc segment (Figure 7; Table 1). Aurora, Bodie, the Comstock Lode, Rawhide, and Tonopah are quartz-adularia deposits that had large production (t 1 Moz gold (tWRQQHV VLPLODUO\*ROG¿HOGDQG3DUadise Peak are quartz-alunite deposits that produced > 1 Moz JROG7KHVHYHQGLVWULFWVWKDWSURGXFHG!0R]JROGDUHEULHÀ\ summarized herein focusing on the nature of basement rocks, magmatic and tectonic settings, type and age of host rocks, and structures controlling mineralization. These features are then used to discuss possible regional controls on epithermal goldsilver mineralization in the southern arc segment. Additional details about these deposits and other epithermal deposits in the southern arc segment are tabulated in Table 1.

633

are altered to quartz, adularia, sericite, illite, montmorillonite, and pyrite, and alteration minerals in host rocks distal to veins include montmorillonite, sericite, quartz, calcite, chlorite, albite, and pyrite (Osborne, 1991).

Bodie Quartz-adularia gold-silver vein deposits in the Bodie disWULFWDUHKRVWHGE\a±0DODYDÀRZVVKDOORZLQWUXVLRQV and volcaniclastic rocks of the dacite of Silver Hill. The district is near the northwest corner of this large composite dome ¿HOGZKLFKLVDOVRSDUWRIWKHWR0D%RGLH+LOOVYROFDQLF ¿HOG-RKQHWDO 7KHQHDUHVWEDVHPHQWURFNVH[posed ~12 km northeast of the district, are Mesozoic (Jurassic?) metavolcanic rocks assigned to the Pamlico-Lodi assemblage of Walker Lake terrane (Crafford, 2007) and Late Cretaceous porphyritic granite. In the Bodie district, ~1.46 Moz (45.4 tonnes) of gold and Aurora 7.28 Moz (226 tonnes) of silver were produced during the periQuartz-adularia gold-silver vein deposits in the Aurora dis- od 1877–1913 mostly from steeply dipping veins; early-mined trict produced approximately 1.8 Moz (56 tonnes) of gold and veins (1877–1881) contained >1 to many ounces of gold per 20.6 Moz (640 tonnes) of silver during the period 1860–1998; WRQ0LQHUDOL]HGTXDUW]YHLQV¿OO1WR1(VWULNLQJQRUPDO ore mined during the initial years of production (1860–1864) faults that have variable shallow to steep dips (John et al., 2012; reportedly contained > 1 oz per ton (34 g/t, in tonnes) gold. The Vikre et al., 2015). The district includes three series of minerdeposits are contained in hundreds of quartz veins and vein seg- alized veins, distinguishable by diagnostic vein characteristics ments that mostly trend within a ~7.5 by 1 km corridor (Vikre and adularia 40Ar/39Ar dates (Vikre et al., 2015). Early, ~8.9–8.5 et al., 2015). Ma Silver Hill series veins, which replace fault breccia clasts The ~10.5 Ma veins (adularia 40Ar/39Ar dates) are hosted DQG¿OORSHQVSDFHEHWZHHQFODVWVDUHVLOYHUDQGEDVHPHWDO by the ~13.1 to 12.6 Ma trachyandesite of Aurora and the ~11.2 rich with high metallic mineral contents and relatively low Au/ Ma rhyolite of Aurora Creek, both parts of the 15 to 6 Ma Bodie Ag. These veins consist of quartz, lesser adularia, barite, illite, +LOOV YROFDQLF ¿HOG -RKQ HW DO QHDUO\ DOO SURGXFWLRQ and calcite, and often t 10 volume percent metallic minerals, including electrum, tetrahedrite, pyrargyrite, acanthite, sphalerwas from veins in trachyandesite. The Aurora district is near the north edge of the small Au- ite, galena, chalcopyrite, pyrite, hessite, sylvanite, and bornite. URUDVWUDWRYROFDQRZKLFKFRQVLVWVRIODYDÀRZVDQGEUHFFLDVRI Dacite in breccia fragments and adjacent to veins is altered to the trachyandesite of Aurora, and the south margin of the rhyo- quartz, illite, kaolinite, montmorillonite and pyrite. The ~8.5– OLWHRI$XURUD&UHHNGRPH¿HOGZKHUHLWRYHUOLHVWKHGLVVHFW- 8.4 Ma Burgess series and ~8.3–8.1 Ma Incline series veins ed Aurora stratovolcano (John et al., 2012, 2015). Basement DUHEDQGHGTXDUW]DGXODULDFDUERQDWHYHLQVZLWKORZVXO¿GH rocks exposed in the southeast part of the district are Meso- mineral contents and high Au/Ag. Metallic minerals in Burgess zoic (Jurassic?) metavolcanic rocks assigned to the Pamlico- series veins that occur in layers and small aggregates include Lodi assemblage of the Walker Lake terrane (Crafford, 2007) electrum, acanthite, and minor amounts of sphalerite, galena, and Late Cretaceous porphyritic granite. The veins formed in a and other Ag-Cu-As-Sb-S-Se minerals. Dacitic wall rocks and conjugate set of steeply dipping, northeast-striking, left-lateral, internal septa in veins are altered to quartz, adularia, illite, and oblique-slip faults and steeply dipping, north-striking, right- pyrite. Ore minerals in Incline series veins are electrum and lateral oblique-slip faults (John et al., 2012; Vikre et al., 2015). acanthite. Wall rocks are proximally altered to quartz, adularia, Most of the productive veins are in northeast faults. Displace- and lesser illite and pyrite, and distally to illite, chlorite, montment along both sets of faults appears relatively minor, and no morillonite, and calcite. Most production came from the Incline WKURXJKJRLQJ VWULNHVOLS IDXOWV KDYH EHHQ LGHQWL¿HG -RKQ HW series veins on Bodie Bluff at the north end of the district. al., 2012, 2015). Most veins consist of several to hundreds of millimeter- Comstock Lode Mined quartz-adularia vein deposits in the Comstock Lode WKLFN OD\HUV RI ¿QHJUDLQHG TXDUW] OHVVHU DGXODULD PHWDOOLF PLQHUDOV VHULFLWH DQG FDOFLWH DQG JHQHUDOO\ KDYH ORZ VXO¿GH district comprise the largest gold-silver production in the southmineral contents (Vikre et al., 2015). Metallic minerals include ern arc segment (Table 1). Most gold and silver occurred in pyrite, electrum, acanthite, naumannite, sphalerite, galena, “bonanza” deposits, which were high-grade (0.4 to 1.8 opt, in chalcopyrite, arsenopyrite, tetrahedrite, and polybasite. Trachy- short tons (14 to 60 g/t, in tonnes)) gold, and ~11 to 29 opt, in andesitic wall rocks and septa contained in veins and vein zones short tons silver (375 to 985 g/t, in tonnes), large tonnage (~0.1

634


to 1.4 Mt) vein segments in the north-trending and east-dipping Comstock Lode normal fault (Vikre 1989b). Lesser production was derived from mostly north ±40°-striking Silver City veins, contiguous with the Comstock Lode to the south, and from the north- and northeast-striking Occidental Lode and Flowery district veins, ~2.4–3.5 km east of Comstock Lode mines. The unprecedented width of Comstock Lode bonanzas (often tens of meters) resulted from repeated displacements along the Comstock Lode fault, replacement of breccia fragments and PDWULFHV DQG LQ¿OOLQJ RI PDWUL[ YRLGV DQG VWRFN ZRUN IUDFtures by multiple generations of quartz, adularia, sericite, elecWUXPVLOYHUDQGRWKHUVXO¿GHPLQHUDOVDQGFDOFLWH%RQDQ]DV were mined by square sets, a novel, timber-consumptive mining method that enabled complete extraction of ore from wide stopes. The ~14–13 Ma vein deposits of the Comstock Lode and nearby veins and districts occur primarily in ~18–13 Ma MioFHQHDQGHVLWHDQGGDFLWHÀRZVDQGVXEYROFDQLFLQWUXVLRQVWKDW FRPSULVHSDUWRID0LRFHQHYROFDQLF¿HOGWKDWPDNHVXSPRVWRI the Virginia Range (Thompson, 1956; Rose, 1969; Vikre et al., 1988; Hudson et al., 2009). Miocene rocks overlie and intrude Mesozoic granitic rocks of the Sierra Nevada batholith, and older metaigneous rocks of the Pine Nut assemblage of the Walker Lake terrane (Crafford, 2007). Basement rocks are exposed at the south end and west of the district, and in the footwall of the northern part of the Comstock Lode fault. Miocene volcanic rocks are locally to pervasively altered to quartz-alunitedominant mineral assemblages, which both pre- and post-date gold-silver vein deposits (Vikre et al., 1988; Vikre, 1998), and to chlorite, calcite, epidote, albite, quartz, pyrite, and zeolite minerals (propylitic and zeolitic alteration; Richthofen, 1866; Becker, 1882; Coats, 1940; Hudson, 2003), which pre-date or are contemporaneous with vein deposits. Wall rocks adjacent to vein deposits, and wall rock septa and fragments in veins and breccias, are altered to quartz, sericite, chlorite, montmorillonite, pyrite (or iron oxides after pyrite), and at higher elevations, kaolinite (Vikre 1989a).

a±NPQRUWKDQGQRUWKHDVWRI*ROG¿HOG9LNUHE although only a small proportion of hundreds of ledges in the ~70 km2 area of strongly altered rocks are mineralized. Copper, which averaged ~0.2 weight percent in gold ore and increased in abundance with depth, and silver (average grade ~0.2 opt, in short tons; ~7 g/t, in tonnes) were by-products. High-grade, multi-opt gold ore consists of several generations of mostly nested breccias (Vikre and Henry, 2011). The earliest stages of brecciation are represented by quartz-alunitepyrite-altered clasts of volcanic and pre-Tertiary rocks that are ORFDOO\HQFUXVWHGE\PPWRVXEPPWKLFNOD\HUVRI¿QHJUDLQHG quartz±alunite. Later breccias consist of clasts of earlier brecFLDVHQFUXVWHGE\DVPDQ\DVHLJKWOD\HUVRI¿QHJUDLQHGTXDUW] pyrite, enargite, luzonite, famatinite, tennantite, gold, bismuthinite, numerous Pb-Bi-Cu-Ag-Au-Hg sulfosalt, selenide and telluride minerals, and, occasionally, alunite. Clasts of Mesozoic rocks in some mineralized breccias have been displaced upward tens to hundreds of meters, based on stratigraphy exposed in nearby mines and drill holes, and locally milled and sorted. These displacements and textures are consistent with episodic ÀRZ RI KLJK YHORFLW\ ÀXLGV LQ DW OHDVW VRPH PLQHUDOL]HG ¿Vsures. Miocene and pre-Tertiary granitic rocks in and adjacent WR ERWK PLQHUDOL]HG DQG XQPLQHUDOL]HG ¿VVXUHV DUH DOWHUHG WR proximal assemblages of quartz, alunite, pyrite, and lesser pyrophyllite. These erosionally resistant proximal assemblages DUH ÀDQNHG E\ UHFHVVLYHO\ ZHDWKHUHG PHGLDO DVVHPEODJHV dominantly sericite, illite, montmorillonite, and pyrite, and by distal assemblages characterized by chlorite, calcite, and pyULWH7KH ZLGH GLVWULEXWLRQ DQG FORVH VSDFLQJ RI ¿VVXUHV KDYH caused alteration mineral assemblages to coalesce, producing a vast landscape of discolored, beige to red-brown volcanic and granitic rocks punctuated by linear gray to red-brown ridges.

Paradise Peak Quartz-alunite gold-silver deposits at Paradise Peak were discovered in 1983, and district production from 1985 to 1994 totaled about 1.61 Moz (57.8 tonnes) gold and 40.3 Moz (1255 *ROG¿HOG tonnes) silver, mostly from the main Paradise Peak pit. ParaQuartz-alunite gold-silver-copper deposits in the Gold- dise Peak is near the northeast edge of a large ~22 to 15 Ma ¿HOGGLVWULFWRFFXULQa±0D0LRFHQHDQGHVLWHGDFLWHDQG DQGHVLWHGDFLWHODYDGRPH¿HOGDORQJWKHQRUWKHDVWPDUJLQRI latite, Mesozoic granitic rocks, and Paleozoic metasedimentary the Walker Lane (John et al., 1991; John, 1992). Miocene volrocks that were pervasively altered to quartz, alunite, kaolinite, canic rocks north and west of the deposit include several zones other aluminosilicate and aluminosulfate minerals, and pyrite at of quartz-alunite and residual quartz alteration, more extensive ~21–19.5 Ma (Ransome, 1909; Ashley, 1974; Ashley and Sil- argillic alteration, and a zone of quartz-sericite-pyrite alteration berman, 1976; Vikre et al., 2005; Vikre and Henry, 2011). Base- that Sillitoe and Lorson (1994) suggest is the upper part of a ment metasedimentary rocks represent the “Nolan belt domain” porphyry gold system. The nature of basement rocks at Paradise of Crafford (2007, 2008). Peak is uncertain; the deposit lies along the boundary between Ore, which averaged > 1 opt, in short tons (34 g/t, in tonnes) metamorphosed volcanogenic rocks of the Sand Springs tergold during the most productive period of mining (1906–1918; rane and carbonate rocks of the Pamlico-Lodi assemblage of Albers and Stewart, 1972), was mostly recovered from an en the Walker Lake terrane. Both groups of rocks are intruded by HFKHORQVHULHVRIVLOLFL¿HGVXEOLQHDUWHQVLRQDO¿VVXUHVRUOHGJ- Mesozoic granitic plutons. es, in Miocene rocks immediately east and northeast of the town Gold-silver mineralization at Paradise Peak is mostly stratRI*ROG¿HOG/HVVHUDPRXQWVRIRUHZHUHSURGXFHGIURPPLQHV abound in a local sequence of silicic welded tuff and volcani-

Ancestral Cascade Arc Magmatism and Mineral Deposits FODVWLF VHGLPHQWDU\ URFNV WKDW SUREDEO\ ¿OOHG D VPDOO JUDEHQ ZLWKLQWKHGRPH¿HOG6LOOLWRHDQG/RUVRQ (DUO\RSDO marcasite altered rock containing relatively low gold and silver grades is crosscut by two generations of hydrothermal breccia, DQG³EODFNPDWUL[´EUHFFLDVVLJQL¿FDQWO\LQFUHDVHGRUHJUDGHV locally to > 1 opt, in short tons (> 34 g/t, in tonnes) gold (John et al., 1991; Sillitoe and Lorson, 1994). Most ore is oxidized and FRQVLVWVRIVLOYHUKDOLGHVDFDQWKLWHDQGQDWLYHJROGLQD¿QH grained quartz matrix. Other metallic minerals include stibnite, bismuthanite, plumbojarosite, and minor covellite. Late stage barite and cinnabar are common. Hypogene alunite alteration IULQJHG ]RQHV RI VLOLFL¿FDWLRQ 6LOOWRH DQG /RUVRQ DQG was faulted against and underlain by montmorillonite-pyrite alteration (John et al., 1991). Alunite K-Ar dates indicate that the Paradise Peak deposit formed about 19-18 Ma, although other samples from within the district yielded alunite dates as old as 22 Ma (John et al., 1989). Most hydrothermal alteration and mineralization were localized by NW- to WNW-striking high-angle normal faults, although steeply dipping northeast-striking normal faults also localized ore to a limited extent. The main Paradise Peak deposit was structurally dismembered into at least three blocks that were displaced unknown distances from their original location by low-angle normal (detachment) faults (Sillitoe and Lorson, 1994). Detachment faulting occurred between 18 and 10 Ma, possibly during weathering and supergene oxidation of much of the deposit at ~10 Ma (jarosite K-Ar date; Sillitoe and Lorson, 1994).

635

part of the Rawhide volcanic center is undated, but Ekren and Byers (1986) suggest that these rocks overlie the ~22 to 15 Ma rocks of Mt. Ferguson. A post-alteration rhyolite dike is known to be about 15 Ma (Silberman et al., 1975). Ore is primarily hosted by fractured andesite that hosts rhyolite intrusions; mineralized rock consists of sheeted to stockwork quartz-adularia-pyrite veins. Ore is characterized by quartz-adularia-illite-pyrite alteration with more distal argillic alteration. The deposits are oxidized to depths of 215 m. ElecWUXPVLOYHUVXO¿GHVVHOHQLGHVDQGVXOIRVDOWVDUHSUHVHQWLQK\pogene ores and silver halides in oxide ores. Adularia and sericite K-Ar dates indicate that gold-silver mineralization formed about 15.5 Ma (Silberman et al., 1975; Black et al., 1991). Mineralized veins are along north- to northeast-striking high-angle faults with dominantly normal displacement (Black et al., 1991). Gray (1996) suggests that north-striking faults have a right-lateral oblique–slip component, whereas northeaststriking faults are normal faults. He also suggests that the two fault sets are kinematically linked and are related to northweststriking right-lateral faults coincident with the northeast edge of the Rawhide volcanic center and an abrupt change in depth to Mesozoic basement rocks across the inferred structure.

Tonopah Rich silver-gold veins in the Tonopah district were discovered in 1900, and about 174 Moz (5400 tonnes) silver and 1.86 Moz (58 tonnes) gold were produced from underground mines mostly from 1910 to 1930. The geologic setting of silver-gold veins in the Tonopah district is complex and incompletely unRawhide derstood. Basement rocks exposed about 10 km north and 15 km Quartz-adularia gold-silver deposits at Rawhide are along south of the district include Mesozoic granitic rocks intrusive the northeast margin of the Walker Lane and the northeast edge into Lower Paleozoic siliciclastic metasedimentary rocks of of the Miocene Rawhide volcanic center (Ekren and Byers, the “Nolan belt domain” (Crafford, 2007, 2008); the metasedi1986; Black et al., 1991). Gold was discovered at Rawhide mentary rocks were deposited on Neoprotoerozoic siliciclastic in 1906, and early production from 1907 to 1920 was about rocks derived from the North American craton. Mineralized 50,000 oz (1.5 tonnes) gold and 750,000 oz (23 tonnes) silver. YHLQV DUH KRVWHG SULPDULO\ E\ DQGHVLWH DQG GDFLWH ODYD ÀRZV Beginning in late 1960s, Rawhide was explored as bulk ton- and breccias of the Mizpah Formation near the south end of a nage deposit. Open pit mining started in 1990 and has produced dome(?) complex (Nolan, 1935; Bonham and Garside, 1979; more than 1.5 Moz (46 tonnes) gold and 13 Moz (400 tonnes) this study). New 40Ar/39Ar dates suggest that the Mizpah Forsilver. Basement rocks consist of lower Mesozoic volcanogenic mation is about 21.4 to 21.2 Ma (M.A. Cosca, written comm., rocks and limestone of the Sand Springs terrane that crop out a 2015). Multiple cooling units of the Fraction Tuff overlie the few hundred meters northeast of the deposits. Gold-silver min- Mizpah Formation. The Fraction Tuff in the Tonopah district eralization in the Rawhide district is hosted by the ~80 km2 LVHLWKHU SUR[LPDORXWÀRZWXIIHUXSWHGIURPDFDOGHUDZKRVH Rawhide volcanic center, which ranges in composition from QRUWKHUQPDUJLQLVDERXWNPVRXWKRI7RQRSDKRU ¿OOVWKH basalt to rhyolite, although a series of coalescing intermediate outer of two nested calderas whose northern margin is about 10 FRPSRVLWLRQODYDÀRZVDQGODYDGRPHFRPSOH[HVDUHLWVSULQFL- km north of Tonopah (Bonham and Garside, 1979; this study). pal constituents. A basal series of rhyolite tuffs and volcaniclas- New 40Ar/39Ar dates and existing K-Ar dates for the Fraction WLFURFNVDUHRYHUODLQE\DQGHVLWHODYDÀRZVZKLFKWKHPVHOYHV 7XII DUH LQFRQVLVWHQW ZLWK ¿HOG UHODWLRQV EXW VXJJHVW WKDW WKH are overlain by a sequence of tuffaceous sedimentary rocks and lower cooling unit of the King Tonopah member, the middle intercalated volcanic breccias (Black et al., 1991). The upper SDUWRIWKH¿HOGEDVHG)UDFWLRQ7XIIVWUDWLJUDSK\LVDERXW sedimentary sequence includes pyritic siltstones thought to Ma (Bonham and Garside, 1979; M.A. Cosca, written comm., KDYH SUHFLSLWDWHG IURP K\GURWKHUPDO ÀXLGV WKDW YHQWHG LQWR D 2015). In the area around Tonopah, the overlying Siebert Forlacustrine environment (Black et al., 1991). A biotite rhyolite mation may consist in part of voluminous, thick ash-fall decomplex intrudes the entire stratigraphic sequence. The older posits that accumulated in the intracaldera environment during

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the waning stages of caldera formation (Bonham and Garside, 1979; this study). New adularia 40Ar/39Ar dates on quartz-adularia veins in altered Mizpah Formation rocks range from ~20.6 to 19.9 Ma (M.A. Cosca, written comm., 2015), which suggests nearly simultaneous eruption of the Fraction Tuff, caldera formation(?), and vein mineralization. Mineralized veins are along shallowly dipping, east- and north-striking normal faults and high-angle north-striking normal faults (Nolan, 1935). HowHYHU WKH GLVWULFW PD\ KDYH VLJQL¿FDQW SRVWPLQHUDO WLOWLQJ DV suggested by moderate to steep dips (up to 60°) in the Fraction Tuff and older units and shallower dips in parts of the overlying Siebert Formation and younger units (Bonham and Garside, 1979; this study). These relations suggest that a period of sigQL¿FDQWH[WHQVLRQPD\KDYHDIIHFWHGWKHGLVWULFWEHWZHHQDERXW 20 to 17 Ma (also see Shaver and McWilliams, 1987). In addition, the Tonopah district may be coincident with an accommodation zone within which regional dips in the Fraction Tuff and overlying Siebert Formation generally change from east to west (Bonham and Garside, 1979). 2UHRFFXUVDVVXO¿GHEHDULQJTXDUW]YHLQVZLWKOHVVDEXQGDQWDGXODULDDQGVHULFLWHDQGDVTXDUW]DGXODULDVHULFLWHVXO¿GH replacement of wall rocks. The main silver-bearing minerals are acanthite, polybasite, and pyrargyrite. Gold occurs as electrum. Sphalerite, galena and chalcopyrite are present locally in minor quantities. Major gangue minerals are quartz, adularia, and sericite, with minor rhodochrosite and late barite and calcite. Oxidized ores mined early in the district’s history contained silver halides and native gold (Burgess, 1911). Alteration is zoned around mineralized veins over a distance of tens of meters from DQLQQHUSRWDVVLFDVVHPEODJHRITXDUW]DGXODULDVHULFLWH pyrite, that grades outward to intermediate argillic assemblages RINDROLQLWHTXDUW]VHULFLWHS\ULWHIROORZHGE\PRQWPRULOORQLWHTXDUW]NDROLQLWHVHULFLWHS\ULWHDQG¿QDOO\LQWR several types of propylitic alteration (Bonham and Garside, 1979).

Comstock Lode, Aurora), but hydrothermal events that altered and mineralized these stratovolcanoes are as much as several m.y. younger than all eruptive rocks (Table 1; Vikre et al., 1988; Hudson et al., 2009; Vikre and Henry, 2011; John et al., 2012, 2015; Vikre et al, 2015). 9ROFDQLFODVWLFURFNVLQFOXGLQJGHEULVÀRZDQGS\URFODVWLF deposits related to stratovolcanoes and lava domes, are strongly hydrothermally altered in many places but generally are poor host rocks for economic mineral deposits. These rocks have high primary permeability, which, although conducive to conYHFWLYHFLUFXODWLRQRIK\GURWKHUPDOÀXLGVSURGXFHODUJHDUHDV of intensely altered, but unmineralized or weakly mineralized rock (e.g., the 20–30 km2 Red Wash and Paramount-Bald Peak alteration zones in the Bodie Hills; Vikre et al., 2015). Notable exceptions include the large Leviathan and Calmono stratiform sulfur deposits, which are hosted in sequences of volcaniclastic URFNVDQGODYDÀRZVSUREDEO\UHODWHGWRVWUDWRYROFDQRHVDQGDUH WKHRQO\RWKHUVLJQL¿FDQWPLQHUDOGHSRVLWVNQRZQWREHDVVRFLated with the southern arc segment (see below; Vikre, 2000a; Vikre and Henry, 2011; Vikre et al., 2015). Ages of mineral deposits in the southern arc segment range from about 22 to 5 Ma (Table 1). Although ages generally decrease from southeast to northwest and from east to west, and mimic the age of nearby magmatic activity, the oldest deposits are small polymetallic veins in the Pyramid district (about 22 Ma) and in the Leadville district (undated, probably d 30 Ma) in the northern part of the southern arc segment. In addition, PLQHUDOGHSRVLWDJHVYDU\ZLGHO\ZLWKLQVRPHYROFDQLF¿HOGV such as in the Bodie Hills, where epithermal deposits range from about 13.4 to 8.1 Ma (Vikre et al., 2015). Volcanic host rocks for well-dated epithermal deposits commonly are hundreds of thousands to several million years older than the ages of contained deposits. Large age differences between mineralization and associated host-rocks are especially notable among quartz-adularia deposits (Table 1). For example, rocks of the 18.3 to 17.4 Silver City and 15.8 to 15.3 Regional Controls on Epithermal Gold-Silver Mineral Ma Virginia City magmatic suites host much of the 14.2–14.0 Deposits in the Southern Arc Segment Ma Comstock Lode veins (Hudson et al., 2009), and the 13.1 to 12.6 Ma trachyandesite of Aurora hosts most of the ~10.5 As described above, most of the large gold-silver epither- Ma veins in the Aurora district (John et al., 2012; Vikre et al., mal deposits are associated with eruptive centers or volcanic 2015). In contrast, ages of quartz-alunite deposits and related ¿HOGVWKDWZHUHHSLVRGLFDOO\DFWLYHIRUH[WHQGHGSHULRGVFRP- quartz-alunite alteration cells are often similar to those of their monly several million years (Table 1; John, 2001; du Bray et host rocks. For example, in the Masonic district, two episodes al., 2014). For example, (1) the Comstock Lode formed at about of alunite alteration and associated gold-silver-copper mineral14 Ma, following discontinuous magmatism that began about ization, 13.4 and 13.0 Ma, are approximately the same age as 18 Ma and persisted until about 14.2 Ma (Vikre et al., 1988; two sets of proximal trachyandesite domes (Vikre et al., 2015). Hudson et al., 2009) and (2) deposits in the Aurora and Bodie Epithermal gold-silver deposits associated with the southdistricts formed at about 10.5 and 8.9 to 8.1 Ma, respectively, ern arc segment formed both north and south of the NeoproLQWKH%RGLH+LOOVYROFDQLF¿HOGZKLFKZDVHSLVRGLFDOO\DFWLYH terozoic continental margin, but nearly all deposits north of the between about 15 to 6 Ma (John et al., 2012; Vikre et al., 2015). continental margin are underlain by basement rocks with conMost of the large epithermal deposits are temporally relat- WLQHQWDO DI¿QLWLHV PRVWO\ LQ WKH :DONHU /DNH WHUUDQH )LJXUH ed to intermediate to silicic composition lava dome complexes, 3). Numerous quartz-alunite alteration zones, both mineralized QRWWRPRUHPD¿FVKLHOGRUVWUDWRYROFDQRHV6RPHDUFUHODWHG and unmineralized, also are coincident with this part of the anVWUDWRYROFDQRHV KRVW VLJQL¿FDQW PLQHUDO GHSRVLWV HJ WKH cestral arc (Figure 7; Vikre and Henry, 2011). However, epith-

Ancestral Cascade Arc Magmatism and Mineral Deposits ermal gold-silver deposits and quartz-alunite alteration zones are scarce to absent in the northern part of the southern arc segment, both in the western Great Basin part of the arc, which is underlain by an accreted island arc (Black Rock terrane), and in the southern Cascade Mountains (Modoc Plateau), for which basement rock characteristics are unknown (Figure 3). Epithermal deposits at Hayden Hill and in the High Grade district are WKHRQO\VLJQL¿FDQWNQRZQGHSRVLWVLQWKLVSDUWRIWKHVRXWKHUQ arc segment (Figure 7, Table 1). Both deposits formed in silicic dome complexes that are uncommon elsewhere in the northern part of the southern arc segment and the part of the southern arc segment north of the inferred edge of the Sierra Nevada batholith (Figures 2 and 3). Most known epithermal deposits in the southern arc segment are in a northwest-trending belt approximately coincident with the Walker Lane, although large known deposits are limited to the outer margins of this belt (Figures 4 and 7). Most quartz-alunite alteration cells (Vikre and Henry, 2011) also are within the Walker Lane (Figure 7). However, several large GHSRVLWVQRWDEO\*ROG¿HOG7RQRSDKDQG3DUDGLVH3HDN DQG many alteration zones in the central Walker Lane formed millions of years prior to initiation of dextral shear characteristic of the central Walker Lane at about 10 Ma (Faulds and Henry, 2008). These relations suggest that Walker Lane tectonics miniPDOO\LQÀXHQFHGIRUPDWLRQRIPRVWHSLWKHUPDOPLQHUDOGHSRVLWV in the southern arc segment, although faulting since ~10 Ma dismembered and partially concealed deposits in some districts HJ VRPH 7RQRSDK GLVWULFW YHLQV DQG WKH *HP¿HOG GHSRVLW LQ WKH *ROG¿HOG GLVWULFW +RZHYHU WKH WUDQVWHQVLRQDO VWUHVV regime characteristic of the Walker Lane (Pluhar et al., 2009; Busby et al., 2013) may have provided structural conduits that KHOSHG IRFXV PLQHUDOL]LQJ ÀXLGV UHVSRQVLEOH IRU JHQHVLV RI some of these systems (e.g., Bodie and Aurora). Large epithermal gold-silver deposits (> 1 Moz Au production) in the southern arc segment range in age from about 20 to 8 Ma (Table 1) and are both older and younger than Basin and Range extension, which began between about 16 to 10 Ma throughout much of the southern arc segment (Faulds and Henry, 2008). Although some deposits are inferred to have formed along pre-Basin and Range extensional faults that were active contemporaneously with mineralization, (e.g., John et al., 1989) or by reactivation of transverse structures in basement rocks (Berger et al., 2005), these inferred structures merely seem to localize mineralization and do not fundamentally control the overall distribution of mineral deposits in the southern arc segment. The scarcity of epithermal gold-silver deposits in the QRUWKHUQSDUWRIWKHVRXWKHUQDUFVHJPHQWPD\UHÀHFWVHYHUDO factors. These include (1) the dearth of intermediate to silicic composition (andesite-rhyolite) dome complexes, the dominant magmatic systems with which epithermal gold-silver deposits are associated; (2) the lack of suitable basement rocks, including the North American continental margin and terranes that contain continentally-derived sedimentary and volcanic rocks,

637

which, especially Neoproterozoic siliciclastic sedimentary rocks (Vikre et al., 2011; Vikre and Henry, 2011), are possible sources of metals and other hydrothermal mineral components; and/or (3) the prevalence of relatively thin and/or low density crust, such as the Sierra Nevada batholith, which allowed direct DVFHQWDQGHUXSWLRQRIPDQWOHGHULYHGPD¿FPDJPDV5HJLRQV in which magmas quickly passed through the crust may have inhibited formation of the intermediate to silicic magma reservoirs that are characteristic of the mineralized systems associated with the southern arc segment. Lacking these shallowly emplaced magma reservoirs, the shallow magmatic-hydrothermal systems required to form epithermal deposits did not develop. Other Mineral Deposit Types in the Southern Arc Segment Stratiform elemental sulfur deposits are the only other sigQL¿FDQWW\SHRIPLQHUDOGHSRVLWSUHVHQWO\NQRZQLQWKHVRXWKHUQ arc segment. Two large stratiform sulfur deposits, the Leviathan and Calmono deposits, are hosted in sequences of volcaQLFODVWLFGHSRVLWVDQGODYDÀRZVSUREDEO\UHODWHGWRDQGHVLWLF stratovolcanoes in the western part of the ancestral arc (Figure 7, Table 1; Vikre and Henry, 2011; Vikre et al., 2015). Sulfur isotope data indicate that both deposits formed from magmaticK\GURWKHUPDOÀXLGV9LNUH9LNUHDQG+HQU\ 7KH Calmono sulfur deposit is within the coeval trachyandesite of :LOORZ6SULQJVGRPH¿HOGZKLFKFRQWDLQVWKHODUJH&LQQDEDU Canyon-US 395 quartz-alunite alteration zone (Vikre et al., 2015). Small hot-spring mercury deposits are scattered across the southern arc segment. Several notable occurrences include the Nody prospect, which was superimposed on the upper parts of the Paradise Peak quartz-alunite deposit (John et al., 1991; Sillitoe and Lorson, 1994), the Paramount mine in the Bodie Hills (Vikre et al., 2015), and the Calmono (Old Timer) Hg deposit that was directly adjacent to and above the Calmono sulfur deposit (Vikre et al., 2015). Most of the southern arc segment is not deeply eroded and plutonic rocks are rarely exposed. Consequently, most epithermal gold-silver, mercury, and sulfur deposits that formed at shallow depths (0 to 1500 m) are largely preserved. Small polymetallic (Ag-Pb-Zn-Cu-Au) vein deposits, possibly formed at somewhat greater depths, are present in early arc-related volcanic rocks in the Pyramid district and at Leadville (Figure 3). Near the Guanomi mine on the southwest side of Pyramid Lake, distally-sourced Oligocene ignimbrites are intruded by a small quartz monzonite porphyry stock that contains low-grade Cu-Mo mineralization in ca. 24 Ma stockwork quartz-pyritemolybdenite veins associated with sericitic alteration (Figure 3; Bonham and Papke, 1969; Prochnau, 1973). However, drilling WKHVHDOWHUHGURFNVGLGQRWUHVXOWLQLGHQWL¿FDWLRQRISRUSK\U\ Cu-Mo resources (Prochnau, 1973). Although no known porphyry copper or genetically-related skarn, polymetallic vein, or polymetallic replacement deposits are exposed in the southern arc segment, some studies have

638


suggested that porphyry copper deposits may underlie areas of advanced argillic alteration and (or) epithermal gold-silver deposits, notably in the Pyramid district west of Pyramid Lake (Wallace, 1979), in the Peavine and Wedekind districts near Reno (Wallace, 1979; Hudson, 1977, 1983) and at the south end of the Bodie district (Hollister and Silberman, 1995). Others have suggested that porphyry molybdenum systems may underlie altered late Miocene rhyolite dome complexes at Washington Hill just east of Reno (Margolis, 1991; Albino, 1992) and along the crest of the Sweetwater Range (Brem et al., 1983). However, limited drilling in these areas has not revealed porphyry-style mineralization.

subsequent arc magmatism, may be critical to porphyry copper deposit formation in highly productive arcs, such as the Andes; Muntean et al. (2011) suggested that metal-enriched subcontinental mantle lithosphere may have been similarly important to formation of late Eocene Carlin-type gold deposits in the northern Great Basin. Relatively steep subduction may have precluded preservation of metasomatically metal enriched subcontinental mantle lithosphere beneath the northern part of the northern arc segment. In contrast, limited isotopic data suggest that the setting RIVRXWKHUQDUFVHJPHQWPDJPDWLVPPLJKWKDYHEHHQVLJQL¿FDQWO\GLIIHUHQW3XWLUNDHWDO VXJJHVWWKDWPD¿FURFNV containing > 8 wt % MgO with initial 87Sr/86Sr > 0.705 and 143Nd/144Nd < 0.5127 are associated with subcontinental mantle Comparison of the Metallogeny of the Northern and Southern Segments of the Ancestral Cascades Arc and lithosphere, but not asthenospheric mantle. The most primitive Controls on Mineralization 0J2!ZW %RGLH+LOOVYROFDQLF¿HOGURFNVKDYHLVRWRSLF compositions (B.L. Cousens, written comm., 2014) compatible Occurrences related to porphyry copper systems, including with this model, which suggests that subcontinental mantle lithporphyry copper deposits and prospects, copper-rich breccia osphere was involved in the genesis of the Bodie Hills magmas. pipes, and polymetallic veins, dominate known mineral depos- Consequently, magma systems represented by rocks included in its and prospects in the northern arc segment in Oregon and WKH%RGLH+LOOVYROFDQLF¿HOGVHHPLQJO\PHHW5LFKDUGV¶ Washington. These deposits and prospects are widely exposed requirement for the presence of subcontinental mantle lithoin southern Washington and northernmost Oregon and mostly sphere, and these systems appear to have been fertile with reformed between about 23 to 16 Ma (du Bray and John, 2011). gard to enhanced mineralizing potential. However, most rocks Epithermal gold-silver deposits are notably scarce; the approxi- in the southern arc segment with less primitive compositions mately 32,000 oz (1 tonne) of gold and 40,500 oz (1.3 tonnes) (< 8 wt % MgO) have radiogenic isotope signatures suggesting of silver produced from several small mines in the Bohemia DVLJQL¿FDQWFUXVWDOFRPSRQHQW%/&RXVHQVZULWWHQFRPP district in west-central Oregon represent most of the recorded 2014, Vikre and others, 2013). gold-silver production in the northern arc segment (du Bray The near absence of phaneritic plutonic rocks in the southand John, 2011). In contrast, in the southern arc segment, epi- ern arc segment suggests a prevailing level of erosion that is thermal gold-silver deposits are numerous (Figure 7), some are generally less than that in the northern part of the northern arc large (> 1 Moz Au (> 31 tonnes), > 10 Moz Ag (> 310 tonnes)); segment and that the lack of exposed porphyry copper systems Table 1), and porphyry copper systems appear to be absent. The LQWKHVRXWKHUQDQFHVWUDODUFPD\EHGXHWRLQVXI¿FLHQWHURVLRQ variation in the types and metal contents of mineral deposits Abundant quartz-alunite epithermal deposits and quartz-alunite in the two arc segments, and within different parts of the two alteration, which may constitute lithocaps, such as those that VHJPHQWVOLNHO\UHÀHFWPXOWLSOHIDFWRUVSRVVLEO\LQFOXGLQJ commonly overlie porphyry copper systems (Sillitoe, 2010), thickness and composition of the crust, (2) regional stress en- also indicate the potential for unexposed porphyry copper sysvironment during magma genesis and emplacement, (3) angle tems in the southern arc segment. However, the generally neuof subduction and metasomatism of the subcontinental mantle tral to moderately extensional or transtensional regional stress lithosphere, and (4) depth of erosion. regime inferred for the southern arc segment (John, 2001; Pludu Bray and John (2011) suggested that the distribution of har et al., 2009; John et al., 2012; Busby et al., 2013) contrasts SRUSK\U\ FRSSHU V\VWHPV LQ WKH QRUWKHUQ DUF VHJPHQW UHÀHFWV with the compressional or transpressional stress environment variations in the regional stress regime during arc magmatism inferred during formation of porphyry copper systems in the and/or the nature of the underlying crust. They inferred that northern arc segment (du Bray and John, 2011). Consequently, porphyry copper systems are limited to parts of the arc un- the prevailing regional stress regime in the southern arc segdergoing transpression to mild compression and underlain by ment may not have been favorable for porphyry copper deposit thicker, lower density crust along the western edge of the North formation (Tosdal and Richards, 2001; Richards, 2003). American plate. In contrast, the southern part of the northern The scarcity of epithermal gold-silver deposits in the arc segment, underlain by young accreted oceanic platform ba- QRUWKHUQSDUWRIWKHVRXWKHUQDUFVHJPHQWPD\UHÀHFWWKHW\SH salts (Siletzia terrane; Wells et al., 2014), is not favorable for of crust underlying the arc, level of erosion, and the scarcity of magmatic systems that host porphyry copper deposits (du Bray silicic dome complexes (du Bray and John, 2011). In addition, and John, 2011). the relatively neutral to weakly extensional to transtensional Richards (2009) suggested that metasomatized metal-en- UHJLRQDOVWUHVV¿HOGFKDUDFWHULVWLFRIWKHVRXWKHUQDUFVHJPHQW riched subcontinental mantle lithosphere, remobilized during (John, 2001; Pluhar et al., 2009; John et al., 2012; Busby et


639

al., 2013) may have been more conducive to development of crysts, they apparently were derived from relatively water-poor shallow hydrothermal systems necessary for formation of epi- magmas. WKHUPDOGHSRVLWVWKDQWKHPRVWO\FRPSUHVVLRQDOVWUHVV¿HOGWKDW Close spatial, temporal, and geochemical associations beprevailed in the northern arc segment (du Bray and John, 2011). WZHHQ HSLWKHUPDO GHSRVLWV DQG YROFDQLF ¿HOGV LQ WKH VRXWKHUQ arc segment imply a genetic relationship between the two. In SUMMARY AND CONCLUSIONS contrast, only sparse, small epithermal deposits are known in the northern arc segment. Plutonic rocks, and genetically reEocene to Pliocene (approx. 45 to 2 Ma) magmatism in lated subeconomic porphyry copper and related deposits, are the ancestral Cascades arc was a major element in the geologic widespread in the northern arc segment, whereas plutonic rocks evolution of western North America that preceded initiation are rare and porphyry copper and skarn deposits are unknown of modern High Cascades arc volcanism. The associated sub- in the southern arc segment. Distinctive mineralizing processes duction-related continental margin arc extended from near the DQGWKHUHVXOWLQJPLQHUDOGHSRVLWVUHÀHFWWKHWZRGLIIHUHQWDQG Canada-USA border in Washington southward to near Gold- characteristically distinct tectonic and magmatic regimes with¿HOG 1HYDGD DQG LQFOXGHG QRUWKHUQ DQG VRXWKHUQ VHJPHQWV in which the two arc segments evolved. separated by a proposed tear in the subducting slab between Large epithermal gold-silver deposits (> 1 Moz gold proMount Shasta and Lassen Peak in northeast California. Ances- duction) of both quartz-adularia and quartz-alunite types, and tral arc magmatism was related to subduction of the Farallon their associated large areas of hydrothermally altered rock, plate beneath North America. The northern segment resulted are abundant in early Miocene to early Pliocene rocks of the from reestablishment of steeply dipping subduction after shal- southern arc segment, especially south of latitude 40°N in the low-dipping subduction from the Late Cretaceous through early western Great Basin. These deposits are principally hosted by Eocene led to dispersed magmatism far to the east of the mod- intermediate to silicic lava dome complexes; fewer deposits are ern arc. In contrast, the southern arc segment was related to KRVWHGE\PRUHPD¿FVWUDWRYROFDQRHVDOWKRXJKODUJHDUHDVRI progressive rollback of the formerly shallow dipping slab and hydrothermally altered volcaniclastic rocks are common. Minrenewed magmatism behind the sinking slab that began about HUDO GHSRVLWV DUH PRVW DEXQGDQW DQG ODUJHU LQ YROFDQLF ¿HOGV 45 Ma in northeastern Nevada and progressively migrated that erupted and evolved for millions of years. Many deposits southwest to the Sierra Nevada. are hundreds of thousands to several million years younger than The southern arc segment extended between about latitudes their host rocks, although some quartz-alunite epithermal de42°N in northern California and 37°N in western Nevada and posits are essentially coeval with their host rocks. was active from ca. 30 to 3 Ma; erupted volumes were largest Variable composition and thickness of crustal basement between 17 and 8 Ma. The southern arc segment approximately DSSHDU WR KDYH VWURQJO\ LQÀXHQFHG PLQHUDOL]LQJ SURFHVVHV coincided with the present Walker Lane and marked a sharp along the length of the southern arc segment. Most deposits transition from magmatism dominated by explosive eruptions are localized in basement rock terranes having with a strong of caldera-forming silicic ignimbrites of the southern Great FRQWLQHQWDODI¿QLW\W\SLFDOO\3URWHUR]RLFFRQWLQHQWDOFUXVWRU Basin ignimbrite province on the east to effusive eruptions overlying accreted terranes with continentally-derived volcaof intermediate to silicic magmas that primarily formed lava nic and sedimentary rocks. In areas south of about latitude domes and stratovolcanoes in the ancestral arc. Most southern 40°N, it appears that relatively thick and/or lower density arc segment rocks have ages between 25 and 4 Ma. In contrast continental crust promoted development of crustal magma to the northern arc segment, the compositions of southern arc reservoirs that stalled and fractionated to yield intermediate segment rocks mostly remain constant with time, which sug- and silicic magma compositions and magmatic-hydrothermal gests that subduction and associated magma genesis processes ÀXLGVFRQGXFLYHWRHSLWKHUPDOGHSRVLWIRUPDWLRQ,QDUHDVIDUwere fundamentally uniform during the development of the WKHUQRUWKWKLQQHUDQGRUGHQVHUFUXVWDOORZHGK\GURXVPD¿F southern arc segment This consistency also implies that mag- magmas to ascend directly to the surface and erupt, precludmas associated with the formation of epithermal gold-silver ing development of shallow crustal magma reservoirs that dedeposits were compositionally indistinguishable from magmas velop epithermal systems. that were not associated with precious metal deposition. Rocks Although most large epithermal deposits lie within the of the southern arc segment are dominantly potassic and calc- Cenozoic Walker Lane, this major tectonic feature is younger alkaline with silica content that ranges continuously from ~55 than many deposits and alteration zones in the southern arc segto 77 wt.% SiO2. Mineralogical and major, trace and rare-earth ment, including most major deposits; only deposits at Bodie element trends indicate these rocks were derived from oxidized, and Aurora may have formed along “Walker Lane” structures. hydrous magmas, which suggests magma genesis at depths Therefore, structures related to the Walker Lane do not appear > 70 km beneath relatively thick continental crust. In contrast, to have exerted strong regional control on deposit localization. the compositions of most rocks in the northern arc segment are Similarly, strong correlations between “pre-Basin and Range consistent with their genesis beneath thinner, primitive crust, extension” and formation of epithermal deposits in the southern and because most of these rocks lack hydrous mineral pheno- arc segment are absent.

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ACKNOWLEDGMENTS The USGS Mineral Resources Program provided funding for this study. Jeff Mauk, Bill Pennell, and an anonymous Geological Society of Nevada reviewer provided helpful comments on an earlier version of this manuscript. REFERENCES CITED Albers, J.P., and Stewart, J.H., 1972, Geology and mineral deposits of Esmeralda County, Nevada: Nevada Bureau of Mines and Geology, Bulletin 78, 80 p. Albino, G.V., 1992, Washington Hill prospect: Reno, Geological Society of Nevada Special Publication 15, p. 193–198. Albino, G.V., and Boyer, Clyde, 1992, Lithologic and structural control of gold deposits of the Santa Fe district, Mineral County, Nevada, in Craig, S.D., ed., Structure, tectonics and mineralization of the Walker Lane, a short symposium, April 24, 1992, Proceedings Volume: Reno, Geological Society of Nevada, p. 187–211. Annen, C., Blundy, J.D., and Sparks, R.S.J., 2006, The genesis of intermediate and silicic magmas in deep crustal hot zones: Journal of Petrology, v. 47, p. 505–539. $VKOH\ 53 *ROG¿HOG PLQLQJ GLVWULFW 1HYDGD %XUHDX RI 0LQHV DQG Geology Report 19, p. 49–66. Ashley, R.P., 1990, The Tonopah precious-metal district, Esmeralda and Nye Counties, Nevada: U.S. Geological Survey Bulletin 1857-H, p. H8–H13. Ashley, R.P., and Silberman, M.L., 1976, Direct dating of mineralization at *ROG¿HOG1HYDGDE\SRWDVVLXPDUJRQDQG¿VVLRQWUDFNPHWKRGV(FRnomic Geology, v. 71, p. 904–924. Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America: Geological Society of America Bulletin, v. 81, p. 3513–3535. $WZDWHU7DQG6WRFN-3DFL¿F±1RUWK$PHULFDSODWHWHFWRQLFVRIWKH Neogene southwestern United States—An update: International Geology Review, v. 40, p. 375–402. Baldwin, Dylan, Arehart, G.B., and Muntean, J.L., 2014, Evidence for rapid epithermal mineralization and coeval bimodal volcanism, Bruner Goldsilver property, NV USA: Reno, University of Nevada, MS thesis, 45 p. Barton, M.D., Battles, D.A., Debout, C.E., Capo, R.C., Christensen, J.N., Davis, S.R., Hanson, R.B., Michelson, C.J., and Trim, H.G., 1988, Mesozoic contact metamorphism in the western United States, in Ernst, W.G., ed., Metamorphism and crustal evolution of the western United States: Rubey Volume 7: Englewood Cliffs, New Jersey, Prentice Hall, p. 110–178. Becker, G.F., 1882, Geology of the Comstock Lode and the Washoe district: U.S. Geological Survey Monograph 3, 422 p. Berger, B.R., Anderson, R.E., Phillips, J.D., and Tingley, J.V., 2005, Plateboundary transverse deformation zones and their structural roles in loFDOL]LQJPLQHUDOL]DWLRQLQWKH9LUJLQLD&LW\*ROG¿HOGDQG6LOYHU6WDU mining districts, Nevada, in Rhoden, H.N., Steininger, R.C., and Vikre, P.G., eds., Geological Society of Nevada Symposium 2005: Window to the World, Reno, Nevada, May 2005, p. 269–281. Berger, B.R., Tingley, J.V., and Drew, L.J., 2003, Structural localization and RULJLQRIFRPSDUWPHQWDOL]HGÀXLGÀRZ&RPVWRFN/RGH9LUJLQLD&LW\ Nevada: Economic Geology, v. 98, p. 387–408. Best, M.G., Barr, D.L., Christiansen, E.H., Gromme, Sherman, Deino, A.L., and Tingey, D.G., 2009, The Great Basin Altiplano during the middle &HQR]RLFLJQLPEULWHÀDUHXSLQVLJKWVIURPYROFDQLFURFNV,QWHUQDWLRQDO Geology Review, v. 51, p. 589–633.

Best, M.G., Christiansen, E.H., and Gromme, S., 2013, Introduction: The 36-18 0DVRXWKHUQJUHDWEDVLQ86$LJQLPEULWHSURYLQFHDQGÀDUHXS6ZDUPV of subduction-related supervolcanoes: Geosphere, v. 9, p. 260–274. Black, J.E., Mancuso, T.K., and Gant, J.L., 1991, Geology and mineralization at the Rawhide Gold-silver deposit, Mineral County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, Symposium Proceedings: Geological Society of Nevada, p. 1123–1144. Blakely, R.J., John, D.A., Box, S.E., Berger, B.R., Fleck, R.J., Ashley, R.P., Newport, G.R., and Heinemeyer, G.R., 2007, Crustal controls on magmatic-hydrothermal systems: A geophysical comparison of White 5LYHU:DVKLQJWRQZLWK*ROG¿HOG1HYDGD*HRVSKHUHYS± Bonham, H.F., Jr., and Garside, L.J., 1979, Geology of the Tonopah, Lone Mountain, Klondike, and northern Mud Lake quadrangles, Nevada: Nevada Bureau of Mines and Geology Bulletin 92, 142 p. Bonham, H.F., Jr., and Papke, K.G., 1969, Geology and mineral deposits of Washoe and Storey Counties, Nevada: Nevada Bureau of Mines and Geology Bulletin 70, 140 p. Brem, G.F., Chaffee, M.A., Plouff, Donald, Lambeth, R.H., Campbell, R.W., Scott, D.F., and Spear, J.M., 1983, Mineral resource potential of the Sweetwater Roadless Area, Mono County, California and Lyon and Douglas Counties, Nevada: U.S. Geological Survey Miscellaneous Field Studies Map MF-1535-A, scale 1:62,500, 26 p. Burgess, J.A., 1911, The halogen salts of silver and associated minerals at Tonopah, Nevada: Economic Geology, v. 6, p. 13–21. Busby, C.J., 2013, Birth of a plate boundary at ca. 12 Ma in the Ancestral Cascades arc, Walker Lane belt of California and Nevada: Geosphere, v. 9, p. 1147–1160. Busby, C.J., Hagan, J.C., Putirka, Keith, Pluhar, C.J., Gans, P.B., Wagner, D.L., Rood, Dylan, DeOreo, S.B., Skilling, Ian, and Wagner, D.L., 2008, The ancestral Cascades arc—Cenozoic evolution of the central Sierra Nevada (California) and the birth of the new plate boundary in Wright, J.E., and Shervais, J.W., eds., Ophiolites, arcs, and batholiths—A tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 331–378. Busby, C.J. Hagan, J.C., and Renne, Paul, 2013, Initiation of Sierra Nevada range front-Walker Lane faulting ca.12 Ma in the ancestral Cascades arc: Geosphere: v. 9, p. 1125–1146. Callaghan, Eugene, 1933, Some features of the volcanic sequence in the Cascade Range in Oregon: Eos, Transactions of the American Geophysical Union, v. 14, p. 243–249. Canby, V.M., 1992, Porphyry-type gold mineralization of late Neogene age at the Zule volcanic center, Sierra County, California: Reno, University of Nevada, M.S. Thesis, 108 p. Carmichael, I.S.E., Lange, R.A., Hall, C.M., and Renne, P.R., 2006, Faulted and tilted Pliocene olivine-tholeiite lavas near Alturas, NE California, and their bearing on the uplift of the Warner Range: Geological Society of America Bulletin, v. 118, p. 1196–1211. Carpenter, A.S., 1992, Geology and mineralization of the Talapoosa mining district, Lyon County, Nevada, in Craig, Steve, ed., Walker Lane SympoVLXPVSULQJ¿HOGWULSJXLGHERRN5HQRDUHDQRUWKHUQ:DONHU Lane mineralization and structure: Reno, Geological Society of Nevada Special Publication 15, p. 63–70. Castor, S.B., Garside, L.J., Henry, C.D., Hudson, D.M., and McIntosh, W.C., 2005, Epithermal mineralization and intermediate volcanism in the Virginia City area, Nevada, in Rhoden, H.N., Steininger, R.C., and Vikre, P.G., eds., Geological Society of Nevada Symposium 2005: Window to the World, Reno, Nevada, May 2005, p. 125–134. Chesterman, C.W., Chapman, R.H., and Gray, C.H., Jr., 1986, Geology and ore deposits of the Bodie mining district, Mono County, California: California Division of Mines and Geology Report 206, 36 p. Christiansen, E.H., and McCurry, M., 2008, Contrasting origins of Cenozoic

Ancestral Cascade Arc Magmatism and Mineral Deposits silicic volcanic rocks from the western Cordillera of the United States: Bulletin of Volcanology, v. 70, p. 251–267. Christiansen, R.L., and Lipman, P.W., 1972, Cenozoic volcanism and plate tectonic evolution of the western United States. II. Late Cenozoic: Philosophical Transactions of the Royal Society of London, Series A, v. 271, p. 249–284. Christiansen, R.L., and Yeats, R.S., 1992, Post-Laramide geology of the U.S. Cordillera region, in %XUFK¿HO%&/LSPDQ3:DQG=REDFN0/ eds., The Cordilleran Orogen—Conterminous U.S.: Boulder, Colo., Geological Society of America, The Geology of North America, v. G-3, p. 261–406. Clark, S.H., 1992, Mineralization, alteration, trace-element geochemistry and SUHOLPLQDU\ÀXLGLQFOXVLRQDQDO\VLVRIWKH5DPVH\GLVWULFW/\RQ&RXQty, Nevada: Moscow, University of Idaho, M.S. thesis, 193 p. Clark, W.B., and Evans, J.R., 1977, Mines and mineral resources of Alpine County, California: California Division of Mines and Geology, County Report 8, 48 p. Coats, R.R., 1940, Propylitization and related types of alteration on the Comstock Lode: Economic Geology, v. 35, p. 1–16. Colgan, J.P., Dumitru, T.A., Reiners, P.W., Wooden, J.L., and Miller, E.L., 2006, Cenozoic tectonic evolution of the Basin and Range province in northwestern Nevada: American Journal of Science, v. 306, p. 616–654. Colgan, J.P., Egger, A.E., John, D.A., Cousens, B., Fleck, R.J., and Henry, C.D., 2011, Oligocene and Miocene arc volcanism in northeastern California—Evidence for post-Eocene segmentation of the subducting Farallon plate: Geosphere, v. 7, p. 733–755. Colgan, J.P., and Henry, C.D., 2009, Rapid middle Miocene collapse of the Mesozoic orogenic plateau in north-central Nevada: International Geology Review, v. 51, p. 920–961. Coney, P.J., and Harms, T.A., 1984, Cordilleran metamorphic core complexes: Cenozoic extensional relics of Mesozoic compression: Geology, v. 12, p. 550–554. Coney, P.J., and Reynolds, S.J., 1977, Cordilleran Benioff zones: Nature, v. 270, p. 403–406. Cousens, B.L., Prytulak, J., Henry, C.D., Alcazar, A., and Brownrigg, T., 2008, Geology, geochronology, and geochemistry of the Miocene-Pliocene ancestral Cascades arc, northern Sierra Nevada, California and Nevada—The roles of the upper mantle, subducting slab, and the Sierra Nevada lithosphere: Geosphere, v. 4, p. 814–828. Crafford, A.E.J., 2007, Geologic map of Nevada: U.S. Geological Survey Data Series 249, CD-ROM. http://pubs.usgs.gov/ds/2007/249/ Crafford, A.E J., 2008, Paleozoic tectonic domains of Nevada: An interpretive discussion to accompany the geologic map of Nevada: Geosphere, v. 4, p. 260–291. Detra, E.H., and Burnett, J.L., 1994, Geology of Hayden Hill, a new mine revitalizing an old mining district: California Geology, v. 47, p. 134–138. Decelles, P.G., 2004, Late Jurassic to Eocene evolution of the Cordilleran thrust belt and foreland basin system, western U.S.A: American Journal of Science, v. 304, p. 105–168, doi:10.2475/ajs.304.2.105. Dickinson, W.R., 2006, Geotectonic evolution of the Great Basin: Geosphere, v. 2, p. 353–368. Dilles, J.H., and Gans, P.B., 1995, The chronology of Cenozoic volcanism and deformation in the Yerington area, western Basin and Range and Walker Lane: Geological Society of America Bulletin, v. 107, p. 474–486. du Bray, E.A., and John, D.A., 2011, Petrologic, tectonic, and metallogenic evolution of the ancestral Cascades magmatic arc, Washington, Oregon, and northern California: Geosphere, v. 7, p. 1102–1133. du Bray, E.A., John, D.A., and Cousens, B.L., 2014, Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada: Geosphere, v. 10, p. 1–39; doi:10.1130/GES00944.1

641

du Bray, E.A., John, D.A., Putirka, K., and Cousens, B.L., 2009, Geochemical database for igneous rocks of the ancestral Cascades arc—Southern segment, California and Nevada: U.S: Geological Survey Data Series 439, 1 CD-ROM. 'XI¿HOG:$DQG0F.HH(+*HRFKURQRORJ\VWUXFWXUHDQGEDVLQ range tectonism of the Warner Range, northeastern California: Geological Society of America Bulletin, v. 97, p. 142–146. Ekren, E.B., and Byers, F.M., Jr., 1986, Geologic map of the Murphy’s Well, Pilot Cone, Copper Mountain, and Poinsettia Spring quadrangles, Mineral County, Nevada: U.S. Geological Survey Miscellaneous Investigations Series Map I-1576, scale 1:48,000. Ekren, E.B., Byers, F.M., Jr., Hardyman, R.F., Marvin, R.F., and Silberman, M.L., 1980, Stratigraphy, preliminary petrology, and some structural features of Tertiary volcanic rocks in the Gabbs Valley and Gillis Ranges, Mineral County, Nevada: U. S. Geological Survey Bulletin 1464, 54 p. Eng, Tony, 1991, Geology and mineralization of the Freedom Flats gold deposit, Borealis mine, Mineral County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, Symposium proceedings: Reno, Geological Society of Nevada, p. 995–1019. Erdman, C.P., and Barabas, A.H., 1996, Precious metal mineralization at Gold Mountain, Tonopah Divide district, Esmeralda County, Nevada, in Coyner, A.R, and Fahey, P.L., eds., Geology and Ore Deposits of the American Cordillera Symposium Proceedings: Reno, Geological Society of Nevada, p. 329–351. )DXOGV-(DQG+HQU\&'7HFWRQLFLQÀXHQFHVRQWKHVSDWLDODQGWHPporal evolution of the Walker Lane: An incipient transform fault along WKHHYROYLQJ3DFL¿F1RUWK$PHULFDQSODWHERXQGDU\ in Spencer, J.E., DQG 7LWOH\ 65 HGV 2UHV DQG RURJHQHVLV &LUFXP3DFL¿F WHFWRQLFV geologic evolution, and ore deposits: Arizona Geological Society Digest 22, p. 437–470. Fiannaca, M., 1987, Geology of the Santa Fe gold-silver deposit, Mineral County, Nevada, in Johnson, J.L., ed., Bulk mineable precious metal GHSRVLWVRIWKHZHVWHUQ8QLWHG6WDWHVJXLGHERRNIRU¿HOGWULSV5HQR Geological Society of Nevada, p. 233–239. Feinstein, M.H., 2011, A proposed epithermal model for the High Grade district, California: El Paso, University of Texas at El Paso, Ph.D. dissertation, 286 p. Garside, L.J., and Bonham, H.F., 2006, Geologic map of the Olinghouse quadrangle, Washoe County, Nevada: Nevada Bureau of Mines and Geology Map 157, scale 1:24,000. Garside, L.J., Bonham, H.F., Jr., Ashley, R.P., Silberman, M.L., and McKee, E.H., 1981, Radiometric ages of volcanic and plutonic rocks and hydrothermal mineralization in Nevada: Determinations run under the USGSNBMG Cooperative Program: Isochron/West, no. 30, p. 11–19. Garside, L.J., Castor, S.B., dePolo, C.M., Davis, D.A., and Widmer, M.C., 2003, Geology of the Fraser Flat quadrangle and the west half of the Moses Rock quadrangle: Nevada Bureau of Mines and Geology, Map 146. GEOROC, 2010, Geochemistry of rocks of the oceans and continents: Max Plank Institut für Chemie, http://georoc.mpch-mainz.gwdg.de/georoc/. Gilbert, Hersh, 2012, Crustal structure and signatures of recent tectonism as LQÀXHQFHGE\DQFLHQWWHUUDQHVLQWKHZHVWHUQ8QLWHG6WDWHV*HRVSKHUH v. 8, p. 141–157. Graney, J.R., 1987, Hasbrouck Mountain, Nevada. Precious-metal mineralization in a fossil hot springs environment, in Johnson, J.L., ed., Bulk mineable precious metal deposits of the western United States, Guidebook for Field Trips: Reno, Geological Society of Nevada, p. 120–125. Gray, D.S., 1996, Structural controls of precious metal mineralization at the Denton-Rawhide mine, Rawhide, Nevada, in Coyner, A.R., and Fahey, P.L., eds., Geology and Ore Deposits of the American Cordillera: Geo-

642


logical Society of Nevada Symposium Proceedings, Reno/Sparks, Nevada, April 1995, p. 263–281. Grose, T.L., 2000, Volcanoes in the Susanville region, Lassen, Modoc, and Plumas Counties, northeastern California: California Geology, v. 53, p. 4–23. Hardyman, R.F., and Oldow, J.S., 1991, Tertiary tectonic framework and Cenozoic history of the central Walker Lane, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, Symposium proceedings: Reno, Geological Society of Nevada, p. 279–302. Heald, P., Foley, N.K., and Hayba, D.O., 1987, Comparative anatomy of volcanic-hosted epithermal deposits: Acid sulfate and adularia-sericite types: Economic Geology, v. 82, p. 1–26. Hedenquist, J.W., Arribas, Antonio, Jr., and Gonzalez-Urien, Eliseo, 2000, Exploration for epithermal gold deposits, in Hagemann, S.G., and Brown, P.E., eds., Gold in 2000: Reviews in Economic Geology, v. 13, p. 245– 277. +HQU\&'DQG)DXOGV-($VKÀRZWXIIVLQWKH1LQH+LOO1HYDGD paleovalleys and implications for tectonism and volcanism of the western Great Basin, U.S.A.: Geosphere, v. 6, p. 339–369. Henry, C.D., Hinz, N.H., Faulds, J.E., Colgan, J.P., John, D.A. Brooks, E.R., Cassel, E.J., Garside, L.J., Davis, D.A., and Castor, S.B., 2012, Eocene–Early Miocene paleotopography of the Sierra Nevada–Great BaVLQ±1HYDGDSODQREDVHGRQZLGHVSUHDGDVKÀRZWXIIVDQGSDOHRYDOOH\V Geosphere, v. 8, p. 1–27. doi:10.1130/GES00727.1 +HQU\&'DQG-RKQ'$0DJPDWLVPDVKÀRZWXIIVDQGFDOGHUDVRI WKHLJQLPEULWHÀDUHXSLQWKHZHVWHUQ1HYDGDYROFDQLF¿HOG*UHDW%DVLQ USA: Geosphere, v. 9, p. 951–1008. Henry, C.D., and Perkins, M.E., 2001, Sierra Nevada-Basin and Range transition near Reno, Nevada; two-stage development at 12 and 3 Ma: Geology. v. 29, p. 719–722. Hildreth, W., 2007, Quaternary magmatism in the Cascades; geologic perspectives: U.S. Geological Survey Professional Paper 1744, 125 p. Hildreth, W., and Moorbath, S., 1988, Crustal contributions to arc magmatism in the Andes of central Chile: Contributions to Mineralogy and Petrology, v. 98, p. 455–489. Hollister, V.F., and Silberman, M.L., 1995, Silver-gold and polymetallic quartz veins in the Bodie mining district, east-central California–are they related to a porphyry Cu-Mo system at depth?, in Pierce, F.W., and Bolm, J.G., eds., Porphyry Copper Deposits of the American Cordillera: Arizona Geological Society Digest 20, p. 297–305. Hudson, D.M., 1977, Geology and alteration of the Wedekind and part of the Peavine districts, Washoe County, Nevada: Reno, University of Nevada, M.S. thesis, 102 p. Hudson, D.M., 1983, Alteration and geochemical characteristics of the upper parts of selected porphyry systems, Western Nevada: Reno, University of Nevada, Ph.D. dissertation, 229 p. Hudson, D.M., 2003, Epithermal alteration and mineralization in the Comstock District, Nevada: Economic Geology, v. 98, p. 367–385. Hudson, D.M., Castor, S.B., Garside, L.J., and Henry, C.D., 2009, Geologic map of the Virginia City quadrangle, Washoe, Storey, Lyon Counties, and Carson City, Nevada: Nevada Bureau of Mines and Geology Map 165, scale 1:24,000. Hudson, M.R., John, D.A., Conrad, J.E., and McKee, E.H., 2000, Style and age of late Oligocene-early Miocene deformation in the southern Stillwater 5DQJHZHVWFHQWUDO1HYDGD3DOHRPDJQHWLVPJHRFKURQRORJ\DQG¿HOG relations: Journal of Geophysical Research, v. 105, p. 929–954. Humphreys, E.D., 1995, Post-Laramide removal of the Farallon slab, western United States: Geology, v. 23, p. 987–990. John, D.A., 1992, Stratigraphy, regional distribution, and reconnaissance geochemistry of Oligocene and Miocene volcanic rocks in the Paradise

Range and northern Pactolus Hills, Nye County, Nevada: U.S. Geological Survey Bulletin 1974, 67 p. -RKQ'$7LOWHGPLGGOH7HUWLDU\DVKÀRZFDOGHUDVDQGVXEMDFHQWJUDnitic plutons, southern Stillwater Range, Nevada: Cross-sections of an Oligocene igneous center: Geological Society of America Bulletin, v. 107, p. 180–200. John, D.A., 2001, Miocene and early Pliocene epithermal gold-silver deposits in the northern Great Basin, Western United States—Characteristics, distribution, and relationship to magmatism: Economic Geology, v. 96, p. 1827–1853. John, D.A., and Armin, R.A., 1984, Geology of the Monitor district, Alpine County, California: unpublished Society of Economic Geologists Field Trip Guidebook, p. 1–15. John, D.A., du Bray, E.A., Blakely, R.J., Fleck, R.J., Vikre, P.G., Box, S.E., and Moring, B.C., 2012, Miocene magmatism in the Bodie Hills volcanic ¿HOG&DOLIRUQLDDQG1HYDGD²$ORQJOLYHGHUXSWLYHFHQWHULQWKHVRXWKern segment of the ancestral Cascades arc: Geosphere, v. 8, p. 44–97. John, D.A., du Bray, E.A., Box, S.E., Vikre, P.G., Rytuba, J.J., Fleck, R.J., and Moring, B.C., 2015, Geologic map of the Bodie Hills, California and 1HYDGD 86 *HRORJLFDO 6XUYH\ 6FLHQWL¿F ,QYHVWLJDWLRQV 0DS 3318, scale 1:50,000, 64 p. John, D.A., Garside, L.J., and Wallace, A.R., 1999, Magmatic and tectonic setting of late Cenozoic epithermal gold-silver deposits in northern Nevada, with an emphasis on the Pah Rah and Virginia Ranges and the northern Nevada rift, in .L]LV -$ -U HG /RZVXO¿GDWLRQ JROG GHposits in northern Nevada: Reno, Geological Society of Nevada, 1999 Spring Field Trip Guidebook, Special Publication No. 29, p. 64–158. John, D.A., Nash, J.T., Clark, C.W., and Wulftange, W., 1991, Geology, hydrothermal alteration, and mineralization at the Paradise Peak gold-silvermercury deposit, Nye County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, Symposium proceedings: Reno, Geological Society of Nevada, p. 1020–1050. John, D.A., Stewart, J.H., Kilburn, J.E., Silberling, N.J., and Rowan, L.C., 1993, Geology and mineral resources of the Reno 1° by 2° quadrangle, Nevada and California: U.S. Geological Survey Bulletin 2019, 65 p. John, D.A., Thomason, R.E., and McKee, E.H., 1989, Geology and K-Ar geochronology of the Paradise Peak mine and the relationship of pre–Basin and Range extension to early Miocene precious metal mineralization in west-central Nevada: Economic Geology, v. 84, p. 631–649. Keats, D.G., 1985, Geology and mineralization of the High Grade district, Modoc County, California: Corvallis, Oregon State University, M.S. thesis, 139 p. Kistler, R.W., 1990, Two different lithosphere types in the Sierra Nevada, California, in Anderson, J.L., ed., The nature and origin of Cordilleran metamorphism: Geological Society of America Memoir 174, p. 271–281. Le Bas, M.J., Le Maitre, R.W., Streckeisen, Albert, and Zanettin, Bruno, 1986, $FKHPLFDOFODVVL¿FDWLRQRIYROFDQLFURFNVXVLQJWKHWRWDODONDOL±VLOLFD diagram: Journal of Petrology, v. 27, p. 745–750. Lee, J., Stockli, D.F., Owen, L.A., Finkel, R.C., and Kislitsyn, R., 2009, Exhumation of the Inyo Mountains, California: Implications for the timing of extension along the western boundary of the Basin and Range Province and distribution of dextral fault slip rates across the eastern California shear zone: Tectonics, v. 28, doi:10.1029/2008TC002295, 20 p. Lerch, D.W., Klemperer, S.L., Glen, J.M.G., Ponce, D.A., and Miller, E.L., 2007, Crustal structure of the northwestern Basin and Range province and its transition to unextended volcanic plateaus: Geochemistry, Geophysics, Geosystems, v. 8, 21 p., doi:10.1029/2006GC001429. Lipman, P.W., Protska, H.J., and Christiansen, R.L., 1972, Cenozoic volcanism and plate tectonic evolution of the western United States, I. Early and middle Cenozoic: Philosophical Transactions of the Royal Society of London, Series A, v. 271, p. 217–248.

Ancestral Cascade Arc Magmatism and Mineral Deposits Ludington, S., Cox, D.P., Leonard, K.R., and Moring, B.C., 1996, Cenozoic volcanic geology of Nevada: Nevada Bureau of Mines and Geology Open-File Report 96-2, p. 5-1 to 5-10. Ludington, S., Moring, B.C., Miller, R.J., Stone, P.A., Bookstrom, A.A., Bedford, D.R., Evans, J.G., Haxel, G.A., Nutt, C.J., Flynn, K.S., and Hopkins, M.J., 2005, Preliminary integrated geologic map databases for the United States: U.S. Geological Survey Open-File Report 2005-1305. Margolis, J., 1991, Miocene acid-sulfate epithermal mineralization related to a Mo porphyry system, Washington Hill, Nevada [abs.]: Geological Society of America Abstracts with Programs, v. 23, p. 76. McBirney, A.R., 1978, Volcanic evolution of the Cascade Range: Annual Review of Earth and Planetary Science, v. 6, p. 437–456. Muntean, J.L., Cline, J.S., Simon, A.C., and Longo, A.A., 2011, Magmatichydrothermal origin of Nevada’s Carlin-type gold deposits: Nature Geoscience, v. 4, p. 122–127. Nakamura, K., 1977, Volcanoes as possible indicators of tectonic stress orientation—principal and proposal: Journal of Volcanology and Geothermal Research, v. 2, p. 1–16. Noble, D.C., 1972, Some observations on the Cenozoic volcano-tectonic evolution of the Great Basin, western United States: Earth and Planetary Science Letters, v. 17, p. 142–150. Noble, D.C., Slemmons, D.B., Korringa, M.K., Dickinson, W.R., Al-Rawi, Y., and McKee, E.H., 1974, Eureka Valley Tuff, east-central California and adjacent Nevada: Geology, v. 2, p. 139–142. Nolan, T.B., 1935, Underground geology of the Tonopah mining district, Nevada: Nevada University Bulletin 29, no. 5, 49 p. Oldow, J.S., 1984, Evolution of a late Mesozoic back-arc fold and thrust belt, northwestern Great Basin, U.S.A.: Tectonophysics, v. 102, p. 245–274. Oldow, J.S., 1992, Late Cenozoic displacement partitioning in the northwestern Great Basin: Reno, Geological Society of Nevada, Structure, Tectonics and Mineralization of the Walker Lane Symposium, April 24, 1992, Reno, Proceedings, p. 17–52. Oldow, J.S., 2003. Active transtensional boundary zone between the western Great Basin and Sierra Nevada block, western U.S. Cordillera: Geology, v. 31, p. 103301036. 2OGRZ-66DWWHU¿HOG-,DQG6LOEHUOLQJ1--XUDVVLFWR&UHWDFHRXV transpressional deformation in the Mesozoic marine province of the northwestern Great Basin, in Lahren, M.M., Trexler, J.H. Jr., and Spinosa, C., eds., Crustal evolution of the Great Basin and Sierra Nevada: University of Nevada, Reno, Cordilleran/Rocky Mountain Section Geological Society of America Guidebook, p. 129–166. Osborne, M.A., 1991, Epithermal mineralization at Aurora, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin: Reno, Geological Society of Nevada Symposium Proceedings, p. 1097–1110. Peck, D.L., Griggs, A.B., Schlicker, H.G., Wells, F.G., and Dole, H.M., 1964, Geology of the central and northern parts of the western Cascade Range in Oregon: U.S. Geological Survey Professional Paper 449, 56 p. Pluhar, C.J., Deino, A.L., King, N.M., Busby, C., Huasback, B.P., Wright, T., and Fischer, C., 2009, Lithostratigraphy, magnetostratigraphy and radio-isotopic dating of the Stanislaus Group, CA, and the age of the Little Walker caldera: International Geology Review, v. 51, p. 873–899. Prenn, N., and Merrick, P., 1991, The Monitor-Mogul mining district, Alpine County, California: The Mineralogical Record, v. 22, p. 29–40. Priest, G.R., 1979, Geology and geochemistry of the Little Walker volcanic center, Mono County, California: Corvallis, Oregon State University Ph. D. dissertation, 253 p. Prochnau, J.F., 1973, Summary report on the 1971-72 exploration program Pyramid Lake (Guanomi) property Paiute Indian Reservation, Washoe County, Nevada, U.S.A. unpublished report for American Selco Inc., 14 p., 8 plates, available at: http://www.nbmg.unr.edu/ scans/3720/37200001.pdf

643

Proffett, J.M., Jr., 1977, Cenozoic geology of the Yerington district, Nevada and implications for the nature and origin of basin and range faulting: Geological Society of America Bulletin, v. 88, p. 247–266. Proffett, J.M., and Dilles, J.H., 2008, Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context: Geological Society of America Special Paper 438, p. 251–288. 3XWLUND.DQG%XVE\&-7KHWHFWRQLFVLJQL¿FDQFHRIKLJK.2YROcanism in the Sierra Nevada, California: Geology, v. 35, p. 923–926. Putirka, K., Jean, M., Cousens, B., Sharma, R., Torrez, G., and Carlson, C., 2012, Cenozoic volcanism in the Sierra Nevada and Walker Lane, California, and a new model for lithosphere degradation: Geosphere, v. 8, p. 265–291. 5DQVRPH)/7KHJHRORJ\DQGRUHGHSRVLWVRI*ROG¿HOG1HYDGD86 Geological Survey Professional Paper 66, 258 p. Richards, J.P., 2003, Tectono-magmatic precursors for porphyry Cu-(Mo-Au) formation: Economic Geology, v. 98, p. 1515–1533, Richards, J.P., 2009, Post-subduction porphyry Cu-Au and epithermal Au deSRVLWV²3URGXFWVRIUHPHOWLQJRIVXEGXFWLRQPRGL¿HGOLWKRVSKHUH*Hology, v. 37, p. 247–250. Richthofen, F.B., 1866, The Comstock lode: Its character, and the probable mode of its continuance in depth: San Francisco, Sutro Tunnel Company, Towne and Bacon Printers, 83 p. Rose, R.L., 1969, Geology of parts of the Wadsworth and Churchill Butte quadrangles, Nevada: Nevada Bureau of Mines and Geology Bulletin 71, 27 p. Seedorff, C.E., 1981, Geology of the Royston porphyry copper deposit, Nye County, Nevada: Stanford, Calif., Stanford University, MS thesis, 106 p. Seedorff, E., 1991, Magmatism, extension, and ore deposits of Eocene to Holocene age in the Great Basin—mutual effects and preliminary proposed genetic relationships, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, Symposium proceedings: Reno, Geological Society of Nevada, p. 133– 178. Shaver, S.A., and McWilliams, M., 1987, Cenozoic extension and tilting recorded in Upper Cretaceous and Tertiary rocks at the Hall molybdenum deposit, northern San Antonio Mountains, Nevada: Geological Society of America Bulletin, v. 99, p. 341–353. Shoemaker, Sam, Jr., Gowans, Richard, Jacobs, Christopher, and Srivastava, 508SGDWHWRIHDVLELOLW\VWXG\RQWKH*ROG¿HOGSURSHUW\1Hvada, USA: NI 43-101 technical report, 177 p., available at http://www. FKDSDUUDOJROGFRPJROG¿HOGWHFKQLFDOUHSRUW Silberling, N.J., Jones, D.L., Monger, J.W.H., and Coney, P.J., 1992, Lithotectonic terrane map of the North American Cordillera: U.S. Geological Survey Miscellaneous Investigations Map I-2175, 1:5,000,000, 2 plates. Silberman, M.L., Bonham, H.F., Jr., Garside, L.J., and Osborne, D.H., 1975, New K-Ar ages of volcanic and plutonic rocks and ore deposits in western Nevada: Isochron/West, no. 13, p. 13–21. Sillitoe, R.H., 2010, Porphyry copper systems: Economic Geology, v. 105, p. 3–41. Sillitoe, R.H., and Lorson, R.C., 1994, Epithermal gold-silver-mercury deposits at Paradise Peak, Nevada; ore controls, porphyry gold association, detachment faulting, and supergene oxidation: Economic Geology, v. 89, p. 1228–1248. Smith, J.G., 1993, Geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington: U.S. Geological Survey Miscellaneous Investigations Series Map I-2005, scale 1:500,000, 19 p. 6SUHFKHU7$:DOOURFNDOWHUDWLRQYHLQVWUXFWXUHDQGSUHOLPLQDU\ÀXLG inclusion studies, Gooseberry mine, Story County, Nevada: Reno, University of Nevada, M.S. thesis, 93 p.

644


Spurr, J.E., 1905, Geology of the Tonopah Mining District, Nevada: U.S. Geological Survey Professional Paper 42, 295 p. 6WHLQLQJHU5&DQG5DQWD'(*HRORJ\RIWKHKLJKVXO¿GDWLRQJUDben gold deposit, Borealis district, Mineral County, Nevada, in Rhoden, H.N., Steininger, R.C., and Vikre, P.G., eds., Geological Society of Nevada Symposium 2005: Window to the World, Reno, Nevada, May 2005, p. 385–398. Stewart, 1980, Geology of Nevada: Nevada Bureau of Mines and Geology Special Publication 4, 136 p. Stewart, J.H., 1988, Tectonics of the Walker Lane Belt, western Great Basin; Mesozoic and Cenozoic deformation in a zone of shear, in Ernst, W.G., ed., Metamorphism and crustal evolution of the Western United States: Englewood Cliffs, N.J., Prentice Hall, Rubey Volume VII, p. 683–713. Stockli, D.F., Surpless, B.E., Dumitru, T.A., and Farley, K.A., 2002, Thermochronological constraints on the timing and magnitude of Miocene and Pliocene extension in the central Wassuk Range, western Nevada: Tectonics, v. 21, no. 4, doi:10.1029/2001TC001295. Surpless, B.E., Stockli, D.F., Dumitru, T.A., and Miller, E.L., 2002, Two-phase westward encroachment of Basin and Range extension into the northern Sierra Nevada. Tectonics, v. 21, p. 2-1 to 2-13. 7DNDGD$7KHLQÀXHQFHRIUHJLRQDOVWUHVVDQGPDJPDWLFLQSXWRQVW\OHV of monogenetic and polygenetic volcanism: Journal of Geophysical Research, v. 99, p. 13,563–13,573. Thayer, T.P., 1937, Petrology of later Tertiary and Quaternary rocks of the north-central Cascade Mountains in Oregon, with notes on similar rocks in western Nevada: Geological Society of America Bulletin, v. 48, p. 1611–1651. Thompson, G.A., 1956, Geology of the Virginia City quadrangle, Nevada: U.S. Geological Survey Bulletin 1042C, p. 45–77. Tingley, J.V., Horton, R.C., and Lincoln, F.C., 1993, Outline of Nevada mining history: Nevada Bureau of Mines and Geology Special Publication 15, 48 p. Tosdal, R.M., and Richards, J.P., 2001, Magmatic and structural controls on the development of porphyry Cu ± Mo ± Au deposits: Reviews in Economic Geology, v. 14, p. 157–181. Tosdal, R.M., Wooden, J.L., and Kistler, R.W., 2000, Inheritance of Nevadan mineral belts from Neoproterozoic continental breakup, in Cluer, J.K., et al., eds., Geology and ore deposits 2000—The Great Basin and beyond: Geological Society of Nevada Symposium Proceedings, May 15–18, 2000, p. 451–466. Twain, M., 1873, Roughing It: Hartford, Conn., American Publishing Company, 591 p. Van Buer, N.J., Miller, E.L., and Dumitru, T.A., 2009, Early Tertiary paleogeologic map of the northern Sierra Nevada batholith and northwestern Basin and Range: Geology, v. 37, p. 371–374. Van Nieuwenhuyse, R., 1991, Geology and ore controls of gold-silver mineralization in the Talapoosa Mining District, Lyon County, Nevada, in Raines, G.L., Lisle, R.E., Schafer, R.W., and Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin, symposium proceedings, Great Basin Symposium, April 1990: Reno, Nevada, Geological Society of Nevada, p. 979–993. Vikre, P.G., 1989, Fluid-mineral relations in the Comstock Lode: Economic Geology, v. 84, p. 1574–1613. Vikre, P.G., 1998, Quartz-alunite alteration in the western part of the Virginia range, Washoe and Storey Counties, Nevada: Economic Geology, v. 93, p. 338–346. Vikre, P.G., 2000a, Elemental sulfur (S°) deposits and S° associated with precious metals, mercury, and thermal springs in the Great Basin, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F., and Morris, C.L., eds., Geology and Ore Deposits 2000: The Great Basin and Beyond:

Geological Society of Nevada Symposium Proceedings, May 15-18, 2000, p. 735–767. Vikre, P.G., 2000b, Subjacent crustal sources of sulfur and lead in eastern Great Basin metal deposits: Geological Society of America Bulletin, v. 112, p. 764–782. Vikre, P.G., Fleck, R., and Rye, R.O., 2005, Ages and geochemistry of magPDWLFK\GURWKHUPDODOXQLWHVLQWKH*ROG¿HOGGLVWULFW(VPHUDOGD&RXQW\ Nevada: U.S. Geological Survey Open-File Report 2005-1258, 1 sheet. Vikre, P.G., and Henry, C.D., 2011, Quartz-alunite alteration cells in the ancestral southern Cascade magmatic arc, in Steininger, R., and Pennell, B., eds., Great Basin evolution and metallogeny: Reno, Geological Society of Nevada, 2010 Symposium proceedings, p. 701–745. Vikre, P.G., John, D.A., du Bray, E.A., and Fleck, R.J., 2015, Gold-silver mining districts and alteration zones in the Miocene Bodie Hills volcanic ¿HOG&DOLIRUQLDDQG1HYDGD86*HRORJLFDO6XUYH\6FLHQWL¿F,QYHVWLgations Report 2015-5012 (in press). Vikre, P.G., and McKee, E.H., 1994, Geology, alteration, and geochronology of the Como district, Lyon County, Nevada: Economic Geology, v. 89, p. 639–646. Vikre, P.G., McKee, E.H., and Silberman, M.L., 1988, Chronology of Miocene hydrothermal and igneous events in the western Virginia Range, Washoe, Storey, and Lyon Counties, Nevada: Economic Geology, v. 83, p. 864–874. Vikre, P.G., Poulson, S.R., and Koenig, A.E., 2011, Derivation of S and Pb in Phanerozoic intrusion-related metal deposits from Neoproterozoic sedimentary pyrite, Great Basin, United States: Economic Geology, v. 106, p. 883–912. Vikre, P.G., Premo, W.R., Hayden, L.A., Koenig, A.E., and Pribil, M.J., 2013, Sources of host rocks and hydrothermal mineral components in the 0LRFHQH *ROG¿HOG 7RQRSDK DQG &RPVWRFN /RGH $X$J&X GLVtricts: Geological Society of America Abstracts with Programs, v. 45, p. 536. Wallace, A.B., 1975, Geology and mineral deposits of the Pyramid district, Washoe County, Nevada: Reno, University of Nevada, Ph.D. dissertation, 162 p. Wallace, A.B., 1979, Possible signatures of buried porphyry- copper deposits in middle to late Tertiary volcanic rocks of western Nevada, in Ridge, J.D., ed., 1979, Papers on mineral deposits of Western North America (papers presented at the Fifth Quadrennial Symposium of IAGOD: Nevada Bureau of Mines and Geology Report 33, p. 69–76. Ward, J.M., 1992, The Cinnabar Canyon sulfur deposit, in Wessel, G.R., and Wimberly, B.H., eds., Native sulfur developments in geology and exploration: Society for Mining, Metallurgy and Exploration, p. 159–164. Wells, R., Bukry, D., Friedman, R., Pyle, D., Duncan, R., Haeussler, P., and Wooden, J., 2014, Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot: Geosphere, v. 10, p. 692–719. Whitebread, D.H., 1976, Alteration and geochemistry of Tertiary volcanic rocks in parts of the Virginia City quadrangle, Nevada: U.S. Geological Survey Professional Paper 936, 43 p. Willden, Ronald, and Speed, R.C., 1974, Geology and mineral deposits of Churchill County, Nevada: Nevada Bureau of Mines and Geology Bulletin 83, 95 p. Wilshire, H.G., 1957, Propylitization of Tertiary volcanic rocks near Ebbetts Pass, Alpine County, California: University of California Publications in Geological Sciences, v. 32, p. 243–272. Wilson, S.E., 2014, Technical report for the Hasbrouck project, Esmeralda County, Nevada, USA West Kirkland Mining Inc.: Highlands Ranch, Colo., Metal Mining Consultants Inc., 89 p., available at http://wkmining.com/_resources/reports/2014-02-24b-Hasbrouck_ProjectTRFINAL.pdf

Ancestral Cascade Arc Magmatism and Mineral Deposits Wilson, W.R., Cox, J.W., and Jones, B.K., 1999, Geology of the Olinghouse gold mine, in .L]LV -$ -U HG /RZVXO¿GDWLRQ JROG GHSRVLWV LQ northern Nevada: Reno, Geological Society of Nevada, 1999 Spring Field Trip Guidebook, Special Publication No. 29, p. 175–180. Wyld, S.J., 2002, Structural evolution of a Mesozoic backarc fold-and-thrust belt in the U.S. Cordillera: New evidence from northern Nevada: Geological Society of America Bulletin, v. 114, p. 1452–1468. Young, T.H., and Cluer, J.K., 1992, The Antelope Valley precious metal depos-

645

its, a Tertiary acid sulfate system in Sierra County, California, in Craig, 6WHYHHG:DONHU/DQH6\PSRVLXPVSULQJ¿HOGWULSJXLGHbook, Reno area - northern Walker Lane mineralization and structure: Geological Society of Nevada Special Publication no. 15, p. 33–42. Zoback, M.L., Anderson, R.E., and Thompson, G.A., 1981, Cainozoic evolution of the state of stress and style of tectonism of the Basin and Range province: Philosophical Transactions of the Royal Society of London, v. A300, p. 407–434.