Geology of the Ravens Nest Quadrangle, Nevada

Home , Candona

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/330924789

Preliminary Geologic Map of the Ravens Nest Quadrangle, Elko and Eureka Counties, Nevada

Research · February 2019

CITATIONS READS 0 165

2 authors, including:

Michael W. Ressel University of Nevada, Reno

41 PUBLICATIONS 387 CITATIONS

SEE PROFILE

Some of the authors of this publication are also working on these related projects:

Eocene metallogeny of the Great Basin View project

All content following this page was uploaded by Michael W. Ressel on 07 February 2019.

The user has requested enhancement of the downloaded file. Text and references accompanying Nevada Bureau of Mines and Geology Open-File Report 18-5

Preliminary Geologic Map of the Ravens Nest Quadrangle, Elko and Eureka Counties, Nevada

by Michael W. Ressel and Seth Dee

Nevada Bureau of Mines and Geology, University of Nevada, Reno, NV

2018

Disclaimer: NBMG open-file reports are preliminary. They have not been thoroughly edited or peer reviewed. This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G17AC00212, 2018

SUMMARY GEOLOGY

The Ravens Nest 7.5-minute quadrangle is located in Antler Orogeny the northern Piñon Range south of the town of Carlin in north-central Nevada. Mapping at Ravens Nest was The Ravens Nest quadrangle contains an unusually undertaken to address several components of the complex complete section across the Early Mississippian Antler geology of north-central Nevada, including the nature of orogen that includes highly deformed Devonian rocks of sedimentation and deformation associated with the leading the leading edge of its east-vergent allochthon, a partly edge of the Early Mississippian Antler allochthon, the deformed foreland basin consisting of fine- to coarse- effects of post-Antler contractional deformation, grained siliciclastic sedimentary rocks, and a coarse overlap development of the Eocene Elko basin and slightly younger sequence, in addition to pre- and post-Antler passive margin Robinson Mountain volcanic field, and deformation carbonate-dominant strata derived from easterly sources. associated with Cenozoic extension in the hanging wall of Thrusting associated with the Antler orogeny variably the Ruby Mountains-East Humboldt Range metamorphic affected Mississippian and older rocks at Ravens Nest. A core complex. Importantly, the northern Piñon Range lies major east-vergent thrust juxtaposes deformed Devonian to within the southern segment of the Carlin trend gold belt, Mississippian fine- to medium-grained siliciclastic rocks, which is one of the premier gold mining jurisdictions in the chert, and rare carbonate rocks over weakly to non-deformed world. Gold produced from disseminated, sedimentary rock- Mississippian to earliest Devonian medium- to coarse- hosted deposits, or Carlin-type deposits, in Nevada grained sandstone and a thick sequence of Late Devonian comprised about 90.5% of Nevada’s production and about and older carbonate rocks of the Paleozoic passive margin. 73.6% of U.S. production in 2016 (Muntean et al., 2017). A few important Early Mississippian units considered syn- The southern Carlin trend in the vicinity of the Ravens Nest orogenic (e.g., Poole, 1974; Smith and Ketner, 1975; 1978; quadrangle has seen several new Carlin-type gold Silberling et al., 1997; Mathewson, 2001; Trexler et al., discoveries since 2010 in non-traditional Paleozoic host 2003; 2004; Longo et al., 2002; Essman, 2011) likely strata. The Piñon Range and flanking Pine and Huntington straddle the orogenic front. These include the earliest valleys are also important areas for conventional and Mississippian Tripon Pass Limestone, which had an eastern unconventional hydrocarbon resources. The Blackburn and passive margin source but appears to have been deposited Tomera Ranch oil fields produce from Cenozoic and not only upon Devonian passive margin carbonate, but on Paleozoic rocks widely distributed in the Ravens Nest Devonian and Early Mississippian foreland basin rocks quadrangle, and the Elko basin has seen assessment of its largely derived from westerly sources in the allochthon. oil-bearing shale by the U.S. Bureau of Mines in the 1970s Conversely, the Early Mississippian Webb Formation was and since 2012 by energy companies. derived from Roberts Mountains allochthon sources, but its deposition extended far enough eastward such that it was also deposited conformably upon the Early Mississippian

Tripon Pass Limestone and older units of the Devonian Bullion stock and swarms of dikes of varying composition passive margin. Later south-vergent thrusting and reverse indicate multiple intrusions at depth (Hollingsworth et al., faulting and folding affect Early to Middle Mississippian 2017; Henry et al., 2015; Ressel and Henry, 2006). rocks of the Chainman Formation and Melandco formation. Widespread Carlin-type gold mineralization occurred in a The contrast in vergence with earlier Antler deformation shallow Eocene setting at or near the paleosurface, and therefore in proximity to Eocene lakes and shallow suggests that this deformation may entirely postdate Antler intrusions. Constraints on mineralization age and depth are deformation (e.g., Long et al., 2014; Rhys et al., 2015) or summarized in table 3 of the Appendix (from Hollingsworth alternatively, represent protracted Antler deformation that et al., 2017). changed vergence (Trexler et al., 2003; 2004). New biostratigraphic ages on units are provided in table 1 of the Miocene and Younger Basins and Appendix. Extension

Eocene Basins, Magmatism, Extension, Miocene through Pleistocene basin deposits in the map and Carlin-type Gold Deposits area record ongoing extension and deposition into a hydrologically closed Pine Valley. Subsequent integration The Eocene geologic record in northern Nevada and of Pine Valley into the Humboldt River watershed in the specifically, Ravens Nest, is extensive. Following middle Pleistocene resulted in widespread dissection of the contractional deformation associated with the Late deposits and numerous large landslide complexes. Fault Cretaceous Sevier orogeny, the region is widely considered scarps in middle Pleistocene fan deposits demonstrate to have been a high elevation orogenic plateau with major ongoing extension of the area and the potential for drainage both east and west from a northerly axis near the earthquake hazards. Piñon Range (Henry, 2008). Lacustrine deposition from ~47 to 38 Ma (Smith et al., 2017; Mulch et al., 2015; Horner, 2015; Haynes, 2003; Solomon et al., 1979) was widespread DESCRIPTION OF MAP UNITS near the Eocene drainage divide and probably consisted of several moderate-sized lake basins developed in a half- Quaternary and Other Late Cenozoic graben setting in the hanging wall of the incipient Ruby Deposits Mountains-East Humboldt Range metamorphic core complex (Horner, 2015; Henry, 2008). The Elko bas in , Qmd Mine disturbance (Anthropocene) Excavations, which includes rocks in the eastern part of the Ravens Nest mine dumps, heap leach, and tailings of the Rain Mine. quadrangle, was sufficiently long-lived to produce an abundance of organic-rich sediments that would later Qg wd Groundwater discharge deposits (Holocene) develop into hydrocarbon resources (Horner, 2015). Deposits of eolian and alluvial, sand and silt with organic Lacustrine deposition waned by ~38.5–38 Ma as volcanic clay, in areas surrounding intermittently discharging rocks of the 38.5–34 Ma Robinson Mountain volcanic field springs. Exposed thickness of the unit is typically 1–4 m. (RMVF) inundated the Elko basin at Ravens Nest and surrounding areas. Magmatism in the RMVF was most Qfy Young alluvial-fan deposits (Holocene) Coarse-to concentrated in a ~1 m.y. span from ~38.5 to 37.5 Ma (tables fine-grained alluvial deposits in intermittently active alluvial 2 and 3 of Appendix); magmatism was characterized by the fans and perennial tributary channels; locally sandy, pebble- emplacement of numerous rhyolite and dacite flow domes to cobble-sized gravel with silt and boulders, or sandy silt and associated small-volume ash-flow tuff. The domes are with coarse-grained material in discontinuous horizons. spatially associated with numerous intrusions (stocks, dikes, Clasts are subrounded to subangular. Fan surfaces and sills) of rhyolite, dacite, granite porphyry, and commonly have distributary flow patterns with morphology granodiorite that were emplaced into Paleozoic rocks and ranging from subdued bar-and-channel forms to slightly strongly recrystallized them to hornfels and marble over an smoothed surfaces. Map unit includes young alluvial exposed area at least 43 km2. Intrusions are spatially and deposits in incised channels along axial drainages. In Pine temporally related to numerous historically mined skarn and Valley, Qfy deposits are present in drainages that are incised polymetallic carbonate replacement deposits of the Railroa d >100 m below Qfo surfaces. The large magnitude of incision mining district, which contained copper, gold, silver, lead, is the result of base level change associated with the and zinc (Ketner and Smith, 1963; Koehler et al., 2015; integration of Pine Valley into the Humboldt River basin in Jackson et al., 2015). Peripherally distributed around the the middle Pleistocene. Qfy fans typically have weak to no largest intrusion, the Bullion composite stock, are many soil development. If present, soil development is sedimentary rock-hosted gold deposits, or Carlin-type characterized by Stage I, CaCO3 coatings on bottoms of deposits (e.g., Cline et al., 2005), which extend as far as 10 clasts. Exposed thickness of the unit is typically 1–3 m km (Hollingsworth et al., 2017; Ressel et al., 2015; Longo et al., 2002; Mathewson, 2001). However, a large magnetic Qfi Intermediate-age d alluvial-fan depos its (late anomaly underlies an area much larger than the exposed Pleistocene) Coarse-grained alluvial deposits in mostly 2

inactive alluvial fans; sandy pebble- to cobble-sized gravel, QThr Hay Ranch Formation (middle Pleistocene to and local boulders. Clasts are subrounded to subangular. Pliocene) Basin fill deposit comprised of tuffaceous Surface morphology is generally planar with rounded mudstones, siltstones, sandstones, fanglomerates and beach margins. Soils consist of stage II–III CaCO3 horizons (Bk) gravel conglomerates. The coarse fanglomerates are more up to 1 m thick. Exposed thickness of the unit rarely exceeds common adjacent to Pine Mountain and interfinger with and 4 m. Qfi is only present on the eastern edge of the map area grade basinward into fluvio-lacustrine sandstone and adjacent to drainages flowing eastward towards Dixie siltstone, and lacustrine mudstone. The fanglomerate Creek. Exposed thickness of the unit is typically 1–10 m. deposits contain mostly subangular to subrounded clasts up to 2 m in diameter, with clast imbrication suggesting Qfo Older alluvial-fan depos its (middle Pleistocene) westward flow directions. All lithologies are locally Coarse-grained alluvial deposits in inactive alluvial fans; tuffaceous, and a 1m thick tephra is exposed along the north typically sandy pebble- to cobble-sized gravel with side of Mill Creek. Regnier (1960) used vertebrate fossils to boulders. Locally mantled by an eolian cap. Surfaces are establish a middle Pleistocene to Pliocene age for the highly dissected with active channels incised over 100 m formation. Reheis, et al. (2002) describe deposits of the Lava deep. Upper soil horizons erosionally stripped, Stage III–IV Creek B ash bed (660 Ka) near the top of the lacustrine CaCO3 horizons up to 1.5 m thick form a semi-continuous sediments. The Hay Ranch Formation was deposited when carbonate rich layer with local development of laminar Pine Valley was a closed basin, prior to subsequent carbonate structure. Qfo includes alluvial-fan deposits integration with the Humboldt River basin via Pine Creek preserved on the planar interfluves and piedmont slopes that (Smith and Ketner, 1976; Gordon and Heller, 1993, and flank Pine Valley. The unit gradationally overlies QThr and Reheis, et al., 2002). Most of the sediments exposed in the the basal contact is not distinct. The Qfo geomorphic surface map area were deposited into a basin marginal, alluvial plane was the depositional base level elevation in Pine Valle y setting with periodic pluvial lake transgressions immediately prior to integration with the Humboldt River demonstrated by beds of lacustrine siltstone and mudstone basin. Reheis, et al. (2002) suggest that Pine Valley began up to 3 m thick. Reheis (1999) shows the extent of middle draining into the Humboldt River, via Pine Creek, shortly Pleistocene Pine Lake as reaching a maximum elevation of after the deposition of the Lava Creek B ash bed (660 Ka). approximately 1800 m. Our mapping found that the 1800 m Integration of Pine Valley into the Humboldt River drainage contour enclosed the thickest fluvio-lacustrine basin fill caused a major reduction in local base elevation triggering sediments, as well as the majority of post-lake dissection of rapid dissection of unlithified basin deposits and the landscape; corroborating the ~1800 m maximu m abandonment of the Qfo surface. Because the basal contact elevation of lacustrine inundation. Reheis, et al. (2002) of Qfo is gradational with QThr, the unit thickness has not suggest that Pine Valley began draining into the Humboldt been estimated. River shortly after the deposition of the Lava Creek B ash bed (660 Ka). The maximum exposed thickness in the map Qls Lands lide depos it (Holocene to middle Pleistocene) area is approximately 700 m. Slope failure deposits sourced from over-steepened slopes in Tertiary sediments adjacent to creeks. Landslide deposits Rocks of the Middle Miocene Humboldt are sourced from fine-grained Humboldt Formation Basin sediments in Cole Creek, and from fine through coarse- grained Hay Ranch Formation sediments in Ferdelford Th Humbol dt Formation (Miocene) Tan, brown or light Creek. Typically form uneven, hummocky surfaces. Head gray, generally weakly consolidated, tuffaceous sandstone, scarps vary from sharp and fresh to rounded and indistinct. siltstone and conglomerate. Very poorly exposed with one The larger landslides deposits in the map area are likely the lithified outcrop identified near Red Springs where steeply result of repeated episodes of slope movement. Fresh tension east dipping tuffaceous siltstone is pervasively silica cracks and very sharp head scarps suggest portions of these cemented adjacent to a west-dipping normal fault. Local landslide complexes remain active. The over steepening of conglomeratic beds identified from float containing rounded hillslopes and subsequent slope failure is the result of rapid gravel clasts. The indistinct Th/QThr contact was mapped at dissection of the landscape following integration of Pine the increase in clastic sediments associated with the Hay Valley into the Humboldt River basin in the middle Ranch Formation. Th exposed in the map area is likely Pleistocene. correlative with the upper epiclastic member (Thu), and the ash-rich member of the Humboldt Formation described by QTls Lands lide depos it (middle Pleistocene? to Wallace, et al. (2008) in the Huntsman Ranch 7.5' Pliocene?) Megabreccia landslide deposit of unknown age quadrangle to the north, with an age range of 16 Ma to 14.8 exposed in a prominent mound on the north side of Pine Ma. Mountain. Contains displaced Nevada Formation quartzite and dolomite blocks up to 15 m in diameter sourced fro m adjacent Pine Mountain

Rocks of the Eocene Robinson Volcanic Mountain, immediately north of the headwaters of Webb Field Creek. Tfpd are widespread but are especially abundant in the southeast quarter of the Ravens Nest quadrangle near Tiw Indian Well Formation, undivi de d rhyolite and Tiw and Tiwr domes for which they are probably related. dacite lavas and lesser tuffs (late Eocene) Finely Tfpd are correlative with the Early dacite (Td and Tdq) dikes porphyritic light brownish gray to maroon rhyolite and of Henry et al. (2015). U/Pb zircon and 40Ar/39Ar dacite lavas and domes and associated small-volume, non- hornblende, plagioclase, biotite, and whole-rock ages range welded, white weathering silicic ash-flow tuff and light from ~38.4 to 38.9 Ma (Henry et al., 2015; Ressel and brown-weathering tephra; locally contains minor amounts of Henry, 2006). tuffaceous sandstone and conglomerate, especially near its base. All volcanic units contain ubiquitous phenocrysts of Tpr Coarsely porphyritic rhyolite dikes and sills (late plagioclase (5–15%, 1–2 mm) and biotite (2–6%, 1–3 mm) , Eocene) Abundant white weathering, porcelaineous with or without quartz (0–5%, 1–2 mm), hornblende (0–3%, coarsely quartz-phyric rhyolite dikes, sills, and stocks. Tpr 1–2 mm), and sanidine (0–1%, 1–2 mm). Lavas and tuffs are intrusions are generally pervasively altered and bleached to variably glassy, and lavas commonly contain flow bands of an assemblage containing albite and/or K-bearing white alternating devitrified and glassy layers. Flow breccia is phyllosilicate after plagioclase phenocrysts and secondary associated with the bases of some lavas. The Indian Well quartz in the groundmass. Quartz phenocrysts (5–10%) to 5 Formation covers >600 km2 along the east flank of the Piñon mm diameter, are particularly prominent and commonly and Sulfur Springs ranges, the north end of Diamond Valley, have euhedral bipyramidal forms. Other phenocrysts include and the low hills extending northward from the north end of sanidine (<3%; 3–5 mm) are commonly fresh despite the Diamond Mountains (Smith and Ketner, 1976; Lund alteration, whereas biotite (<5%; 2–4 mm) is everywhere Snee et al., 2016). The age of the Indian Well Formation is altered to sericite. Tpr rhyolite dikes and sills commonly broadly constrained to ~37.5 to 38.5 Ma based on numerous occur in swarms in and around the Bullion composite pluton isotopic ages (e.g., Smith and Ketner, 1976; Solomon et al., and in a prominent WNE-trending swarm >4 km long by 1.5 1979; Henry et al., 2015; Lund Snee et al., 2016; Mulch et km wide along the north ridge of Webb Creek. Widths of al., 2015; and Smith et al., 2017), although in the immediate dikes and sills range up to 30 m, and a discrete ~0.3 km2 Tpr vicinity of Ravens Nest is more tightly constrained to ~37.55 stock containing sheeted and stockwork quartz veining to 38.0 Ma based on sanidine 40Ar/39Ar ages (Henry et al., within the eastern part of the Bullion composite pluton. The 2015; table 2 in Appendix A). Rocks of the Indian Well age of Tpr (unit Trc of Henry et al., 2015) based on sanidine Formation rest unconformably upon lacustrine and fluvial and hornblende 40Ar/39Ar dating is ~37.6 to 38.1 Ma (Henry deposits of the Eocene Elko Formation, and in turn, are et al., 2015). unconformably overlain by gravel, and tuffaceous siltstone and sandstone of Miocene to Quaternary age. Ts pd Sparsely porphyritic dacite dikes (late Eocene) Generally fresh to weakly chlorite altered, grayish green Ti wr Indian Well Formation rhyolite lavas and tuffs weathering dikes of sparsely but coarsely porphyritic dacite. (late Eocene) Lavas and domes dominated by rhyolite, with Tspd dikes cut the highly altered and quartz veined granite lesser amounts of dacite. Small-volume ash-flow tuff and porphyry intrusion (Tqbg) and coarsely porphyritic rhyolite tephra are associated with the bases and peripheries of some intrusion (Tpr), both part of the Bullion composite pluton. dome lava. Descriptions are otherwise similar to Tiw. Ages Euhedral phenocrysts of alkali feldspar are prominent (8– of rhyolite ash-flow tuff and rhyolite porphyry from the 10%; up to 12 mm), with smaller phenocrysts of quartz (1– domes east of the historical Bullion town site yield 40Ar/39Ar 2%; 2–4 mm), biotite (2–3%; 2–3 mm), and lesser ages of ~37.55 to 38.0 Ma (Henry et al., 2015; table 2 in hornblende (1%; 2 mm) set in a fine-grained groundmass Appendix A). containing alkali feldspar, quartz, and biotite. Tspd is undated, but Tspd dikes cut Tpr coarsely porphyritic rhyolite 40 39 Tfpd Finely porphyritic dacite dikes (late Eocene) dated at 37.63 +/- 0.09 Ma using Ar/ Ar on sanidine Dikes and sills of hydrothermally altered, finely porphyritic (Henry et al., 2015). dacite and lesser quartz-poor rhyolite; phenocrysts comprise 10–25% and consist of, in order of abundance, plagioclase, Tpm Rhyolite dikes of Pine Mountain (late Eocene) biotite, hornblende +/- quartz and sanidine. Intrusions are Bleached white to yellow weathering, pervasively altered, bleached white and buff due to moderate to strong clay nearly aphyric high-silica rhyolite containing sparse alteration, which accompanies varying degrees of phenocrysts of partly sericitized euhedral sanidine (1%, 2 silicification. Pervasive clay alteration, mostly illite or mm) quartz (1%, <1 mm), which is commonly bipyramidal kaolinite, affects the granular feldspathic groundmass as and variably smoky, and biotite (<2%, <1 mm), which is well as 1–2 mm plagioclase, biotite, and hornblende pervasively altered to sericite. The groundmass of the Tpm phenocrysts; 1–2 mm resorbed quartz phenocrysts are rare rhyolite is spherulitic, with radiating intergrowths of K- and unaltered. Intrusions are commonly 1–3 m wide but feldspar and quartz, the feldspar dusty with partial sericitic Tfpd dikes and sills as much as 12 m wide occur on the alteration. Spherulitic texture suggests the dikes were southeast flank of the broad peak informally named Bald originally glassy. Dikes are of variable width but commonly 4

several meters wide and have strike lengths of up to 1 km or Elko Formation in the Piñon Range from >43.5+/-0.02 Ma more. Flow bands are particularly abundant. Tpm dikes form to about 37.5+/-0.1 Ma. The Elko Formation is highly a swarm (5 km long by 1 km wide) of north-northwest variable in thickness in the Piñon Range; maximu m striking dikes that intruded intensely hornfels-altered thickness estimates to the east of the Rain Mine in the siliciclastic rocks of the Chainman and Webb Formations Bullion quadrangle are between ~700 and 1300 m (Haynes, along the east flank of Pine Mountain and extending to the 2003; Horner, 2015). south-southeast into the Papoose Canyon quadrangle. The age of Tpm rhyolite is uncertain but it is younger than its Teb Matrix-suppor te d basal breccia of the Elko enclosing biotite hornfels dated by Henry et al. (2015) at Formation (Eocene) Composed of angular clasts of dark 38.02 +/- 0.06 Ma. Unit Tpm is correlative to unit Tpr of gray siliceous mudstone and tan- to light-gray silicifie d Henry et al. (2015). siltstone and/or limestone set in a white- to light-gray, very fine-grained quartz-rich groundmass containing abundant (5 Tqbg Quartz-biotite granite porphyr y (late Eocene) –10%; 1–3 mm) monocrystalline, clear quartz conchoidally White to light gray porphyritic granite containing fractured fragments. Breccia overlies brecciated Woodruff phenocrysts of quartz (10%, 2–3 mm) and biotite (10%, 2–4 Formation siliceous and phosphatic mudstone and probably mm) in a fine-grained, graphic groundmass of intergrown Webb Formation siliceous siltstone on the east flank of the quartz and alkali feldspar. The Tqbg unit forms a discrete prominent hill immediately southeast of the Rain mine in the plug-like intrusion in the center of the Bullion polyphase northeast corner of the quadrangle. Breccia is pervasively stock and is cut by numerous dikes of sparsely and coarsely silicified. porphyritic dacite (Tspd) up to 10 m wide. The Tspd dikes also cut Tpr rhyolite dated at 37.63 +/- 0.09 Ma (Henry et Rocks of the Permian Strathearn Basin al., 2015). Pds Fossiliferous limy sandstone, siltstone, Tbg d Biotite granodiorite (late Eocene) Equigranular to conglomerate, dolomite, and pebbly limestone, and weakly biotite-phyric, fine to medium grained plagioclase- limestone (early Permian) Partly age equivalent to the biotite-alkali feldspar-quartz granodiorite stock and uppermost Strathearn Formation but may also include rocks associated dikes that form the outer and oldest part of the younger than early Wolfcampian (Smith and Ketner, 1975). Bullion composite pluton. The unit is commonly fresh or has The Pds unit is exposed along a 2-km-wide, 5-km-long mafic minerals that are variably altered to chlorite. The north-south corridor from north of Cole Creek to south of biotite granodiorite represents the volumetrically largest Red Springs. Rocks of Pds weather distinctly red, reddish- phase of the Bullion composite intrusion. orange, yellow, and tan; beds vary in lithology and in thickness from thin to thick along strike; some massive beds Rocks of the Elko Basin form ledges 10 m thick or more. Macrofossils are locally abundant in gray limestone and yellow limy siltstone and Te Lacustrine and fluvial sedimentary rocks of the include bryozoans, brachiopods, gastropods, pelecypods, Elko Formation (Eocene) The Elko Formation herein crinoids, fusulinids, sponge spicules, clasts in conglomerate comprises all Eocene sedimentary strata that directly are rounded to subangular quartzite, white quartz, chert, underlie Eocene Indian Well Formation volcanic rocks shale, and gray to white limestone. Clasts range up to (Tiw, Tiwr) and age-equivalent sedimentary units not cobbles (4-cm across). Rocks of the Pds unit were deposited overlain by Indian Well Formation volcanic rocks. The unit conformably on Early Permian limestone (Pl). comprises diverse lithologies that include in order of abundance: limy to tuffaceous siltstone, shale, freshwater Pl Gray limestone, tan silty limestone and yellow limy algal limestone and marl, pebble and cobble conglomerate, siltstone with lesser pebbly cross-bedded s ands ton e and sandstone. Limestone commonly weathers light gray to (early Permian) partly age equivalent to the Wolfcampian pale yellow, has distinct anastomosing microbial mat upper Strathearn Formation (Smith and Ketner, 1975). Beds layering, and contains abundant lenses of pale brown to tan range from thin to thick bedded, although float of fissile silty chert; 2–3 mm diameter Candona ostracods and other limestone and siltstone crop out poorly and are macrofossils are common. Shale weathers white and is volumetrically greater than thick-bedded gray limestone. distinctly fissile forming “paper” shale; where unoxidized, Unit rests mainly on Pennsylvanian–Mississippian Tonka shale is black and commonly petroliferous. The base of the conglomerate and is in fault contact with mudstone of the Elko Formation is commonly marked by pebble to boulder Devonian Woodruff Formation. conglomerate that contains round to subangular clasts of quartzite, chert, and sandstone, and less common limestone, Rocks of Pennsylvanian–Mississippian mudstone, conglomerate, and silicic to intermediate igneous Antler Overlap Affinity clasts. Dating of interbedded tephra and detrital zircons (Smith and Ketner, 1976; Solomon et al., 1979; Haynes, Mt Tonka Formation conglomerate (Ear l y 2003; Lund Snee et al., 2016; Horner, 2015; Smith et al., Pennsylvanian to Late Mississippian) Pebble to boulder 2017; Hollingsworth et al., 2017) constrain the age of the 5 conglomerate, pebbly sandstone, limy siltstone, and rare Antler Foreland Basin Rocks Involved in limestone of the Mississippian Tonka Formation but also Antler Hanging Wall Deformation containing conglomeratic rocks as young as Pennsylvanian. Unit weathers brown to red-brown except for siltstone, Mc Chainman Shale (Late to Early Mississippian) The which weathers white, tan, or yellow. Bedding varies in main lithology is a homogeneous dark olive green fissile thickness and lithology over short distances; in Ferdelford shale with much less intercalated red-brown sandstone and Creek canyon, highly irregular conglomerate channel-fill pebble to boulder conglomerate, and rare greenish gray deposits in excess of 200 m thickness are resistant and form limestone. A weak penetrative cleavage in shale resulted in prominent cliffs. Clasts in conglomerate consist of well- its breakage into small rectangular chips a few mm in rounded quartzite and subround to subangular chert to less diameter. Shale rarely crops out in incised drainages and abundant or absent white siliceous mudstone, chert-quartz under sandstone ledges; an exception is within the hornfels sandstone, limestone, and rare basalt. Also in Ferdelford aureole of the Bullion intrusive complex where the unit has Creek canyon, a sequence of limy siltstone, pebbly been recrystallized, largely to biotite, quartz, and less sandstone, and lesser conglomerate contains an Early commonly, calc-silicate minerals. A specimen possibly of Mississippian marine macrofossil faunal assemblage that Lonsdelia tabulate coral from the northeast flank of Pine includes bryozoans, rugose corals, brachiopods, crinoids, Mountain constrains the age of the Chainman Shale at and gastropods (Smith and Ketner, 1975). Ravens Nest to Meremecian (C. Sandberg and C. Thorman, personal communications, 2018). Other fossils Ms t Basal siltstone of the Tonka Formation (Late or collected include a branch of Lepidodendron. The Middle Mississippian) Distinctive white weathering Chainman Shale in the Ravens Nest quadrangle rests siltstone and chert pebble siltstone and mudstone that occurs on foliated units of Mississippian Webb and Devonian at or near the base of the Tonka Formation in the northeast Woodruff, the three units comprising the allochthon part of the quadrangle. The basal siltstone rests on brown emplaced upon Mississippian Melandco sandstone. The weathering, planar-bedded Mississippian Melandco Chainman Shale is depositionally overlain by sandstone and on Devonian Woodruff siliceous siltstone and conglomerate of the Tonka Formation, the contact mudstone. Unit is hydrothermally altered to white clay with defined as the C2 unconformity of Trexler et al. variable amounts of hematite stain where exposed near the (2004). Rain Mine. Mcc Chainman Shale, conglomerate and Rocks of the Antler Foreland Basin coarse sandstone facies (Late to Early Mississippian) Conglomerate and coarse sandstone Mm Melandco sandstone (Late to Early Mississippian) facies. Consists of medium brown, massively Medium yellow brown weathering, homogeneous, planar- bedded pebble to boulder conglomerate containing bedded sandstone and pebble conglomerate with lesser round to subangular clasts of quartzite, chert, amounts of cobble conglomerate and siltstone. The color of sandstone, mudstone, limestone, and rare mafic and the sandstone reflects a large component of variably colored intermediate igneous rocks. Less abundant shale and fine chert grains in addition to variable amounts of clean quartz sandstone are present as interbeds. grains. In places, the sandstone also contains variable amounts of angular white siliceous mudstone clasts that are Mw Webb Formation (Early Mississippian) Where less significantly larger than the sand grains and which impart a oxidized, the Webb Formation consists of medium gray spotted character to the sandstone. Throughout the to black, homogenous siliceous siltstone and mudstone quadrangle, the Melandco sandstone is in thrust contact with that generally is poorly exposed but forms subcropping the overlying highly deformed Devonian Woodruff siliceous slopes underlain by platy rectangular to hackly fractured mudstone. The Melandco is possibly equivalent to the fragments up to 5 or 6 cm long commonly stained Osagean to Meremecian Mississippian Chainman Shale, olive green to yellowish green from iron oxides. which is present in the western half of the quadrangle and Where hydrothermally altered, the Webb Formation is comprises the uppermost exposed unit in the allochthon that commonly brecciated and distinctly mottled brick red overrides the Melandco in the quadrangle. In the area north and light gray, with abundant hematite with or without of the headwaters of Webb Creek, the Melandco is barite. The Webb Formation in the western half of the pervasively altered to white and tan hornfels and its very quadrangle is foliated and allochthonous and rests fine-grained character indicates a greater amount of siltstone structurally on contorted chert, cherty mudstone, and in the protolith than elsewhere. The Melandco sandstone is siliceous siltstone of the Woodruff Formation. The overlain by conglomerate of the Tonka Formation, the allochthonous Webb Formation is as much as 300 m thick. contact between the two a slight angular unconformity or a In the eastern half of the quadrangle, the non-foliated disconformity that represents the C2 unconformity of Webb Formation rests unconformably on earliest Trexler et al. (2004). Mississippian Tripon Pass Limestone, late Devonian Pilot Shale, and/or Guilmette Limestone where it is much thinner, ~50 m or less. Similarly, the tectonized 6 Webb is overlain by weakly cleaved Chainman Shale in the western half of the Ravens Nest quadrangle, and by planar-bedded brown sandstone of

Melandco in the western half (Mathewson, 2001; Smith and DMpt Undivi de d Webb Formation-Tri pon Pass Ketner, 1975). The Webb is recrystallized to quartz and Limes tone-Pilot Shale (Early Mississippian to Latest biotite hornfels in the south half of the quadrangle. Table 1 Devonian) Exposures of strongly recrystallized mudstone, in Appendix A provides new biostratigraphic ages for rocks siltstone, and limestone protoliths to green and red-brown of the Webb Formation. Mapped Webb Formation may garnet-pyroxene skarnoid, brown and black siliceous and include some rocks of the Devonian Woodruff Formation, biotite hornfels, chocolate brown jasperoid, and white particularly in areas of strong recrystallization to hornfels. marble in and near the Bullion pluton. Units that stratigraphically underlie marble correlated with the Tripon Dw Woodruff Formation (Late to Ear l y De vonian) Pass Limestone are interpreted to be earliest Mississippian Laminated, black carbonaceous mudstone, and thin-bedded, or Late Devonian, and, therefore, not Webb Formation light to medium gray cherty mudstone, chert, and limestone, siltstone. and white siliceous siltstone. Rocks of the Woodruff Formation are poorly exposed except where silicified, DMp Pilot Shale (Early Mississippian to Late hornfels recrystallized, or recently incised by streams or Devonian) Laminated to medium-bedded mudstone and roadcuts. Float is distinctive as small (<10 mm dia.) rhomb- siltstone that rests on the Guilmette Limestone and is shaped white mudstone chips and/or as blocky fragments of overlain by the Tripon Pass Limestone throughout the light gray cherty mudstone. Conspicuous white siliceous Ravens Nest quadrangle. In the Railroad mining district, the lenses and elongate nodules in gray cherty mudstone occur Pilot Shale has been strongly recrystallized to biotite in much of the Woodruff; nodules are typically 0.5–1.5 cm hornfels. diameter and as much as 5 cm long and are phosphatic (Smith and Ketner, 1975). Near thrusts and tight folds, the Dg Guilmette Limestone (Late Devonian) Thick- to nodules are stretched, forming boudinage. The Woodruff is medium-bedded, light- to medium-gray fossiliferous generally highly deformed, possessing penetrative limestone that forms prominent outcrops, ledges, and cliff foliations, tight folds, and thrust and reverse faults. It forms exposures. Macrofossils are locally abundant and include the lowermost allochthonous unit emplaced over the amphipora and syringopora corals, brachiopods, Melandco sandstone. The Woodruff is altered to dense dark stromatopora, and crinoids. The Guilmette Limestone and gray hornfels where exposed over much of the south half of other carbonate units are coarsely recrystallized to white or the Ravens Nest quadrangle. The mapped Dw may include mottled or striped (i.e., zebra-textured) gray and white some Early Mississippian siliceous siltstone and mudstone marble in the Railroad mining district; in areas of historical of the Webb Formation. Table 1 in Appendix A provides mines, the Guilmette Limestone has in part been new biostratigraphic ages on the Woodruff. metasomatically altered to garnet-bearing and magnetite skarns containing copper oxide and sulfide minerals. The mapped Dw includes siliceous mudstone as young as earliest Mississippian based on microfossil ages (table 1) Dn Nevada Formation, undivided (Middle to Ear l y and therefore is age correlative with the Webb and Tripon Devonian) Chiefly dark- to medium-gray, medium- to Pass Limestone Formations. thick-bedded dolomite or coarsely recrystallized, white, tan, and/or dark gray dolomitic marble with much less light- to Rocks of the Early and Middle Paleozoic medium-gray limestone or white marble. Usage of the term Passive Margin Nevada Formation, although largely discontinued, is useful to describe intensely recrystallized dolomitic rocks at Mtp Tripon Pass Limestone (Earliest Mississippian) Ravens Nest, wherein precise subdivision is generally not Light gray weathering, thin- to medium-bedded micritic possible. The unit is exposed in the southeast quarter of the limestone that is carbonaceous and dark gray on fresh Ravens Nest quadrangle where it is invariable contact surfaces. Contains distinct horseshoe-shaped macrofossils metamorphosed and locally garnet or magnetite skarn or burrows. The unit is generally 5 to 20 m thick. Similar to altered. The Nevada Formation is divided into four member s the Webb siltstone, the Tripon Pass Limestone is both from oldest to youngest: allochthonous and autochthonous. Its western exposures are characterized by moderate to strong tectonic cleavage, and Dnu Upper Nevada Formation dolomite Thick the unit rests on fine-grained clastic strata of the Devonian interval of thick bedded, dark gray and white dolomitic Woodruff Formation. To the east, the Tripon Pass Limestone marble exposed in the Railroad mining district as well as is undeformed and overlain Webb siltstone and Melandco on the west flank of Pine Mountain; unit contains sandstone. On the west side of the Railroad mining district, abundant tremolite on Pine Mountain. Includes the Bay the Tripon Pass Limestone unit is strongly recrystallized to State Dolomite. white marble, calcic garnet skarn, and less common Dno Oxyoke Member, Nevada Formati on magnetite skarn. The early Mississippian age of limestone sandstone The middle member of medium- to thick- correlated with the Tripon Pass Limestone are indicated in bedded, clean white quartzite and lesser dolomitic table 1 in Appendix A. marble exposed on the east flank of Pine Mountain, and correlative with the Oxyoke Canyon Sandstone Member. 7

Dnb Beacon Peak Member, Nevada Formati on Dean Heitt, P.J. Shumway, and Franck Valli at Newmont dolomite Mostly dark-gray, thick-bedded dolomite Mining Corporation, Elizabeth Hollingsworth and the late containing lenses of light gray sandy dolomite; Jim Trexler at the University of Nevada, Reno, and Dave recrystallized to coarse, granular, mottled white and gray Mathewson of US Gold Corp. Research supported by the marble and sandy marble where exposed in the Railroad U.S. Geological Survey National Cooperative Geologic mining district and on Pine Mountain. Mapping Program, under USGS award number Dnbl Beacon Peak Dolomite Member, Nevada G17AC00212. The views and conclusions contained in this Formation 20-m thick, thick bedded, continuous gray document are those of the authors and should not be limestone, now coarse white marble, intercalated within interpreted as necessarily representing the official policies, Dnb dolomite. either expressed or implied, of the U.S. Government.

DSlm Lone Mountain Dolomite (Early Devonian to REFERENCES Late Silurian) Consists of massively bedded, dark- to medium-gray to medium-brown weathering dolomite and Armstrong, R.L., 1970a, Geochronology of Tertiary igneous rocks, coarsely recrystallized dolomitic marble. The Lone eastern Basin and Range province, western Utah, eastern Mountain Dolomite occurs in a thin belt of Lower Paleozoic Nevada, and vicinity, U.S.A.: Geochimica et Cosmochimica strata exposed on the east side of the Railroad mining Acta, v. 34, p. 203–232. district. Cline, J.S., Hofstra, A.H., Muntean, J.L., Tosdal, R.M., and Hickey, K.A., 2005, Carlin-type gold deposits in Nevada— Ohc Hanson Creek Formation (Late Ordovic i an) critical geologic characteristics and viable models, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., and Chiefly composed of thin- to thick-bedded, dark brown, Richards, J.P., editors, Economic geology—one hundredth brownish-gray, and dark gray dolomite with rare gray anniversary volume 1905–2005: Littleton Colorado, Society limestone beds. The uppermost Hanson Creek Formation of Economic Geologists, p. 451–484. contains a 5- to 7-m-thick yellow or tan weathering limy or Essman, J.E., 2011, Rain revisited—new structural and dolomitic siltstone. In the Ravens Nest quadrangle, the stratigraphic insights and their implication for Carlin-type Hanson Creek is exposed only east of the high ridge deposits, in Pennell, W.M., and Garside, L.J., editors, containing Bunker Hill and Ravens Nest peaks. Steininger, R., and Pennell, B., editors, Great Basin evolution and metallogeny , Geological Society of Nevada Symposium Oe Eureka Quartzite (Middle Ordovician) White to tan, Proceedings, p. 511–535. Gordon, I., and Heller, P., 1993, Evaluating major controls on nearly pure medium- to coarse-grained, mature quartzite. basinal stratigraphy, Pine Valley, Nevada—implications for Occurs as relatively thin slivers of nearly continuous syntectonic deposition: Geological Society of America quartzite separating Pogonip Group and Hanson Creek units. Bulletin. 105(1), p. 47–55. The Eureka is only exposed east of the high ridge containing Haynes, S.R., 2003, Development of the Eocene Elko basin, Bunker Hill and Ravens Nest peaks; the unit is typically northeastern Nevada—implications for paleogeography and brecciated and attenuated. regional tectonism: University of British Columbia, M.S. thesis, 156 p. Op Pog onip Group (Middle Ordovician) Only the Henry, C.D., 2008, Ash-flow tuffs and paleovalleys in northeastern uppermost part of the Pogonip Group is exposed in southeast Nevada—implications for Eocene paleogeography and extension in the Sevier hinterland, northern Great Basin: corner of the Ravens Nest quadrangle. The unit consists of Geosphere, 1–35. thin- to medium-bedded, medium- to dark-gray, Henry, C.D., Jackson, M.R., Mathewson, D.C., and Koehler, S.R., recrystallized dolomite and less common limestone. The 2015, Eocene igneous geology and relation to Pogonip is the oldest recognized unit exposed in the Ravens mineralization—Railroad district, southern Carlin trend, Nest quadrangle. Nevada: in Pennell, W.M., and Garside, L.J., editors., New concepts and discoveries 2015, Geological Society of Nevada Symposium Proceedings, p. 939–965. ACKNOWLEDGMENTS Hollingsworth, E.R., Ressel, M.W., and Henry, C.D., 2017, Age and depth of Carlin-type gold deposits in the southern Carlin The current mapping draws significantly from previous trend—Eocene mountain lakes, big volcanoes, and mapping of the Ravens Nest quadrangle during 1997–1998 widespread, shallow hydrothermal circulation in Bedell, R. by Richard M. Tosdal that was supported by the U.S. and M.W. Ressel, M.W., editors., Shallow expressions of Geological Survey Western Minerals Branch. The original Carlin-type systems, Alligator Ridge and Emigrant mines, mapping of the Piñon Range by Keith Ketner and Fred Smith Nevada, Geological Society of Nevada special publication 64, field trip guidebook, p. 149–173. established the stratigraphic and structural framework for all Horner, W.H., 2015, Tertiary lake sedimentation in the Elko subsequent work. The map and cross sections were greatly Formation, Nevada—the evolution of a small lake sy s t em in enhanced by data and geologic input provided by Mac an extensional setting: Colorado State University, Fort Jackson, Mike Harp, Steve Koehler, and Steve Moore at Collins, M.S. thesis, 93 p. Gold Standard Ventures Inc., Chris Henry of the Nevada Jackson, M.R., Mathewson, D.C., Koehler, S.R., Harp, M.T., Edie, Bureau of Mines and Geology, Jim Essman, Gerry Greisel, R.J., Whitmer, N.E., and Norby, J.W., 2015, Geology of the North Bullion gold deposit—Eocene extension, intrusion and 8

Carlin-style mineralization, the Railroad district, Carlin Ressel, M.W., Dendas, M., Lujan, R., Essman, J., and Shumway, Trend, Nevada, in Pennell, W.M. and Garside, L.J., editors., P.J., 2015, Shallow expressions of Carlin-type hydrothermal New concepts and discoveries 2015, Geological Society of systems—an example from the Emigrant mine, Carlin trend, Nevada Symposium Proceedings, p. 313–331. Nevada, in Pennell, W.M., and Garside, L.J., editors, New Ketner, K.B., and Smith, J.F., Jr., 1963, Geology of the Railroad concepts and discoveries 2015, Geological Society of Nevada mining district, Elko County, Nevada: U.S. Geological Survey Symposium Proceedings, p. 501–524. Bulletin 1162-B, p. B1–B27. Rhys, D., Valli, F., Burgess, R., and Heitt, D., 2015, Controls of Koehler, S.R., Jackson, M.R., Harp, M.T., Edie, R.J., Whitmer, fault and fold geometry on the distribution of gold N.E., Mathewson, D.C., and Norby, J.W., and Henry, C., mineralization on the Carlin trend, in Pennell, W.M., and 2015, Precious and base metal mineralization within a large Garside, L.J., editors, New concepts and discoveries 2015, Eocene, magmato-thermal system, Railroad district, Carlin Geological Society of Nevada Symposium Proceedings, p. trend, Nevada, in Pennell, W.M., and Garside, L.J., editors., 333–389. New concepts and discoveries 2015, Geological Society of Silberling, N.J., Nichols, K.M., Trexler, J.H., Jr., Jewell, P.W., and Nevada Symposium Proceedings, p. 1229–1242. Crosbie, R.A., 1997, Overview of Mississippian depositional Long, S.P., Henry, C.D., Muntean, J.L., Edmondo, G.P. and Cassel, and paleotectonic history of the Antler Foreland, Nevada and E.J., 2014, Early Cretaceous construction of a structural western Utah, in Link, P.E., and Kowallis, B.J., editors, culmination, Eureka, Nevada, U.S.A.—implications for out- Proterozoic to recent stratigraphy, tectonics, and volcanology, of-sequence deformation in the Sevier hinterland: Geosphere, Utah, Nevada, southern Idaho and central Mexico: Bringham v. 10, no. 3, p. 564–584. Young University Geology Studies, v. 42, Part I, p. 161–196. Longo, A.A., Thompson, T.B., and Harlan, J.B., 2002, Geologic Smith Jr., J.F., and Ketner, K.B., 1975, Stratigraphy of Paleozoic overview of the Rain subdistrict, in Thompson, T.B., Teal, L., rocks in the Carlin-Piñon Range area, Nevada: U.S. and Meeuwig, R.O., editors, Gold deposits of the Carlin trend: Geological Survey Professional Paper 867-A, 48 p. Nevada Bureau of Mines and Geology, Bulletin 111, p. 168– Smith Jr., J.F., and Ketner, K.B, 1976, Stratigraphy of post- 189. Paleozoic rocks and summary of resources in the Carlin-Piñon Lund Snee, J.E., Miller, E.L., Grove, M., Hourigan, J.K., and Range area, Nevada: U.S. Geological Survey Professional Konstantinou, A, 2016, Cenozoic paleogeographic evolution Paper 867–B, pages B1–B48. of the Elko basin and surrounding region, northeast Nevada: Smith, J.F., Jr., and Ketner, K.B., 1978, Geologic map of the Carlin Geosphere, v. 12, doi: 10.1130/GES01198.1. Piñon Range area, Elko and Eureka counties, Nevada: U.S. Mathewson, D.C., 2001, Tectono-stratigraphic setting for the Rain Geological Survey Miscellaneous Investigations Map 1-1028, district gold deposits, Carlin trend, Nevada: Geological scale 1:62,500. Society of Nevada Special Publication no. 33, p. 90–109. Smith, M.E., Cassel, E.J., Jicha, B.R., Singer, B.S., and Canada, McKee, E.H., Silberman, M.L., Marvin, R.F., and Obradovich, A.S., 2017, Hinterland drainage closure and lake formation in J.D., 1971, A summary of radiometric ages of Tertiary response to middle Eocene Farallon slab removal, Nevada, volcanic rocks in Nevada and eastern California— Part I, U.S.A.: Earth and Planetary Science Letter, 479, p. 156–169. central Nevada: Isochron/West, no. 2, p. 21–42. Solomon, B.J., McKee, E.H., and Andersen, D.W., 1979, Mulch, A., Chamberlain, C.P., Cosca, M.A., Teyssier, C., Methner, Stratigraphy and depositional environments of Paleogene K., Hren, M.T., Graham, S.A., 2015, Rapid change in high- rocks near Elko, Nevada, in Pacific Coast Paleogeography elevation precipitation patterns of western North America Symposium 3: Cenozoic Paleogeography of the western during the middle Eocene climatic optimum (M ECO): United States, p. 75–88, Pacific Section, SEPM (Society for American Journal of Science, v. 315, p. 317–336. Sedimentary Geology). Muntean, J.L., Davis, D.A., and Ayling, B., 2017, The Nevada Steiger, R.H., and Jäger, E., 1997, Subcommission on Mineral Industry 2016: Nevada Bureau of Mines and Geology geochronology—convention on the use of decay constants in Special Publication M I-2016, 187 p. geo- and cosmochronology: Earth and Planetary Science Poole, F.G., 1974, Flysch deposits of the Antler foreland basin, Letters, v. 36, p. 359–362. western United States, in Dickinson, W.R., editor, Tectonics Trexler, J.H., Jr, Cashman, P.H., Cole, J.C., Snyder, W.S., Tosdal, and sedimentation: Society of Economic Paleontologists and R.M., and Davydov, V.I., 2003, Widespread effects of mid- Mineralogists, Special Publication 22, p. 58–82. Mississippian deformation in Nevada: Geological Society of Regnier, J., 1960, Cenozoic geology in the vicinity of Carlin, America Bulletin, v. 115, p. 1278–1288. Nevada: Geological Society of America Bulletin, v. 71, p. Trexler, J.H., Jr, Cashman, P.H., Snyder, W.S., and Davydov, V.I., 1189–1210. 2004, Late Paleozoic tectonism in Nevada—timing, Reheis, M.C., 1999, Extent of Pleistocene lakes in the western kinematics, and tectonic significance: Geological Society of Great Basin: U.S. Geological Survey Miscellaneous Field America Bulletin, v. 116, p. 525–538. Studies MF-2323, scale 1:800,000. Wallace, A.R., Perkins, M.E., and Fleck, R.J., 2008, Geologic map Reheis, M.C., Sarna-Wojcicki, A.M., Reynolds, R.L., Repenning, of the Huntsman Ranch quadrangle, Elko County, Nevada: C.A., Mifflin, M.D., 2002, Pliocene to middle Pleistocene Nevada Bureau of Mines and Geology Map 163, scale lakes in the western Great Basin—ages and connections, in 1:24,000, 22 p. Hershler, R., Madsen, D.B., Currey, D.R., editors, Great Basin Suggested citation: aquatic systems history, Smithsonian Institution Press, Ressel, M.W., and Dee, S., 2018, Preliminary geologic map of the Washington, D.C., p. 53–108. Ravens Nest quadrangle, Elko and Eureka counties, Nevada: Ressel, M .W., and Henry, C.D., 2006, Igneous geology of the Nevada Bureau of Mines and Geology Open-File Report 18- Carlin trend, Nevada—development of the Eocene plutonic 5, scale 1:24,000, 20 p. complex and significance for Carlin-type gold deposits:

APPENDIX A

Table 1 . Microfossils from the Ravens Nest quadrangle and surrounding areas, northeastern Nevada.

Zone Sample No. Easting Northing Latitude Longitude Formation Age (Ma) Reference1 11T Early WGS Webb M ississippian 90FP-33F 580105 4491762 40°34'22" 116°03'13" 1 84 Formation (late Kinderhookian) Ferdelford Early M ississippian WGS fossil beds (late 91FP-378F 577180 4490205 40°33'31' 116°05'19" 1 84 (Tonka Kinderhookian - Fm.) Osagean) Early WGS Webb 94FP-54F 580548 4490010 40°33'25" 116°02'55" M ississippian 1 84 Formation (Kinderhookian) 93-FP- WGS Woodruff Early Devonian 574252 4496215 40°36'48.5" 116°07'20' 1 412F 84 Formation (Lochovian) Early M iddle WGS Woodruff 93FP-267F 574299 4496269 40°36'50" 116°07'18" Devonian (early 1 84 Formation Eifelian) Early WGS Tripon Pass M ississippian 90FP-21F 580510 4499263 40°38'25" 116°02'52.5" 1 84 Limestone (late Kinderhookian) Early WGS Tripon Pass M ississippian 90FP-23F 581089 4498768 40°38'09" 116°02'28" 1 84 Limestone (late Kinderhookian) Early WGS Tripon Pass M ississippian 90FP-25F 582940 448351 40°29'12.5" 116°01'12.5" 1 84 Limestone (late Kinderhookian) Early WGS Tripon Pass M ississippian 91FP-311F 582938 4482261 40°29'48" 116°01'17" 1 84 Limestone (late Kinderhookian) Early WGS Tripon Pass M ississippian 91FP-315F 84 586885 4496063 40°37'29.5" 115°59'03" Limestone (late 1 Kinderhookian) Early Late WGS basal Tonka M ississippian 93FP-297F 585919 4497611 40°36'39" 115°58'22.5" 1 84 Formation (early M eramecian) Early WGS Webb M ississippian NEP-49 580947 4492234 40°34'37" 116°02'37" 2 84 Formation (late Kinderhookian) Radiolaria Early NAD Webb M ississippian NEP-112 581655 4491996 40°34'29" 116°02'07" 3 83 Formation (early Kinderhookian) NAD Woodruff Devonian Unknown 580296 4490017 40°33'25" 116°03'06" 3 83 Formation (Famennian) 1References: 1Forrest G. Poole, 1999, written communication; 2Anita G. Harris, 1999, written communication; 3 Paula J. Noble, 2000-2001, written communication, 2000-2001; samples with “NEP” prefix were collected by Richard M. Tosdal, 1997-1999.

Table 2 . New and Previously published 40Ar/39Ar, K-Ar, and U-Pb isotopic ages from the Ravens Nest quadrangle and immediately surrounding areas, northeastern Nevada.

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age this report; data 40 39 from Ar/ Ar Humboldt R.J. NEP -4 Air fall tuff Pine Valley 573025 4490269 Sanidine laser Igneous 15.08 0.06 Formation Fleck fusion and R.M. T osdal, 1999 this report; data 40 39 from Rhyolite Palisade Ar/ Ar R.J. NEP -7 vitrophyre Pine Valley Canyon 569955 4497511 Sanidine laser Igneous 15.16 0.08 Fleck flow Rhyolite fusion and R.M. T osdal, 1999 R.J. Fleck/R. White 40Ar/39Ar M. biotite-rich Cissilini 584107.24 4491434.7 Biotite step Igneous 37.47 0.11 T osdal NEP -14 tuff; canyon area heating in rhyodacite Haynes, 2003 R.J. Fleck/R. White 40 39 Ar/ Ar M. biotite-rich Cissilini NEP -14 584107.24 4491434.7 Hornblende step Igneous 38 0.3 T osdal tuff; canyon area heating in rhyodacite Haynes, 2003

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age this report; data 40 39 from Biotite Ar/ Ar Railroad R.J. NEP -16 monzogranit Bullion Stock 582742 4486533 Biotite laser Igneous 36.66 0.09 district Fleck e fusion and R.M. T osdal, 1999 R.J. Fleck/R. M. Biotite 40Ar/39Ar T osdal quart z- Bullion rhyolite Bunker Hill 583998.69 4484737.2 Sanidine single Igneous 37.38 0.16 in NEP -44 feldspar stock xtal Ressel intrusion and Henry, 2006 Armstro Biotite Cissilini 109 Bullion stock? 582709.95 4485871.2 Whole rock K-Ar Igneous 35.3 1.4 ng, adamellite canyon area 1970 Biotite Armstro quartz latite Cissilini Tuffs of 585530.1 4486211.4 Biotite K-Ar Igneous 36.2 1.4 ng, 111 crystal vitric canyon area Cissilini canyon 1970 t uff Armstro Rhyolite Cissilini Tuffs of 110 582709.95 4485871.2 Whole rock K-Ar Igneous 36 2.8 ng, porphyry canyon area Cissilini canyon 1970 40 39 Ressel Basaltic Rain Saddle Ar/ Ar Core hole; and RCR-62- andesite Carlin-type 581175.74 4499238.1 Matrix step Igneous 37.8 2.4 alt ered dike Henry, 2151' dike deposit heating 2006 40 39 Ressel Rain Saddle Ar/ Ar Porphyritic Core hole; and RCR-61- Carlin-type 418824.26 4499238.1 Biotite step Igneous 39.13 0.36 diorite dike altered dike Henry, 2092' deposit heating 2006 Ressel Monzonite Emigrant RCR-9- U/Pb and porphyry Carlin-type Core hole; dike 586700.56 4496858 Zircon Igneous 37.5 1.6 676' Sh r im p Henry, dike deposit 2006 McKee Emigrant Indian Well 73 T uff 584989.28 4492372.9 Biotite K-Ar Igneous 38.6 1.6 et al., Spring Formation? 1971

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age Silicic Sm it h intrusive Railroad and 3 Bullion stock 582711.22 4485980.2 Biotite K-Ar Igneous 36.8 1 rocks district Ketner, (stock) 1976 Silicic Sm it h intrusive Railroad and Bullion stock 582711.22 4485980.2 Sanidine K-Ar Igneous 35.4 1.1 3 rocks district Ketner, (stock) 1976 Sm it h Indian Well Northern Indian Well and Formation 570640.31 4493683.3 Biotite K-Ar Igneous 37.6 1.3 2 Pine Valley Formation? Ketner, volcanics 1976 40Ar/39Ar Granodiorit SE o f Bald Granodiorite SE Henry et 583436.69 4486803.6 Biotite step Igneous 37.98 0.03 H12-110 e Mountain of Bald Mt n al., 2015 heating 40Ar/39Ar Granodiorit SE o f Bald Granodiorite SE Henry et 583436.69 4486803.6 Hornblende step Igneous 41.04 0.83 H12-110 e Mountain of Bald Mt n al., 2015 heating 40Ar/39Ar Granodiorit SE o f Bald Granodiorite SE Henry et H12-110 583436.69 4486803.6 Hornblende step Igneous 39.11 0.32 e Mountain of Bald Mt n al., 2015 heating Granodiorit SE o f Bald Granodiorite SE U/Pb LA- Henry et 583561.13 4485600.4 Zircon Igneous 38.27 0.16 H12-110 e Mountain of Bald Mt n ICP/MS al., 2015 U/Pb Granodiorit SE o f Bald Granodiorite SE Henry et 582804.7 4486349.2 Zircon Shrimp Igneous 38.91 0.38 H12-110 e Mountain of Bald Mt n al., 2015 RG 40Ar/39Ar Qtz-phyric near Webb Henry et Dacite dike 580827.69 4488672.1 Biotite step Igneous 38.46 0.03 H12-105 dacite dike Creek al., 2015 heating 40Ar/39Ar Qtz-phyric Mendota Henry et H12-149 Dacite dike 584037.73 4485862.1 Hornblende step Igneous 38.68 0.34 dacite dike Mine area al., 2015 heating Ridge west 40Ar/39Ar Qtz-phyric Altered dacite Henry et H12-122 of Pine 582029.97 4486388.3 Adularia step Alteration 37.83 0.03 dacite dike dike al., 2015 Mountain heating Ridge west 40Ar/39Ar Porphyryitic Altered rhyolite Henry et of Pine 580373.33 4486745.5 Sericite step Alteration 38.02 0.02 H12-117 rhyolite dike dike al., 2015 Mountain heating WNW of 40Ar/39Ar Biotite Hornfelsed Henry et St anding 581202.89 4485585.5 Biotite step Alteration 38.02 0.06 Maq hornfels siltstone al., 2015 Elk Mine heating near 40Ar/39Ar Calc-silicate Henry et RRB12- Sylvania Calc-silicate 583561.13 4485600.4 Muscovite step Alteration 38.15 0.11 03-1450' limestone al., 2015 Mine heating

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age Core hole; Granodiorit SE o f Bald U/Pb Henry et RRB12- altered 583527.14 4485608.9 Zircon Igneous 38.21 0.43 03-526' e Mountain Sh r im p al., 2015 granodiorite Qtz-phyric Pod Carlin- U/Pb LA- Henry et Dacite dike 584247.25 4487491 Zircon Igneous 38.55 0.37 H12-142 dacite dike type deposit ICP/MS al., 2015 North RR12- Bullion U/Pb LA- Henry et Dacite sill Dacite sill 584879 4488764.3 Zircon Igneous 38.4 0.63 10-400' Carlin-type ICP/MS al., 2015 deposit North Bullion U/Pb Henry et RR11- Dacite sill Dacite sill 585121.8 4489227 Zircon Igneous 38.9 0.4 09-1225' Carlin-type Sh r im p al., 2015 deposit North Bullion U/Pb LA- Henry et RR12- Dacite sill Dacite sill 585062 4488727.3 Zircon Igneous 38.22 0.44 05-746' Carlin-type ICP/MS al., 2015 deposit North RR12- Bullion U/Pb LA- Henry et Dacite sill Dacite sill 585062.3 4488726.9 Zircon Igneous 38.28 0.64 05-1425' Carlin-type ICP/MS al., 2015 deposit Coarse Q- 40Ar/39Ar Kf rhyolite Railroad Granodiorite Henry et 582824.35 4486078.2 K-feldspar step Igneous 38.4 0.25 H12-114 adjacent district porphyry al., 2015 heating granit e Rhyolite 40 39 Ar/ Ar ash-flo w Indian Well Henry et H12-94 585422.81 4484987 Sanidine single Igneous 37.83 0.02 tuff, Xtl- rhyolite tuff al., 2015 xtal rich, fine Upper, 40 39 Railroad, Ar/ Ar rhyolite ash- Indian Well Henry et H12-93 Indian Well 585756.7 4484483.9 Sanidine single Igneous 37.821 0.021 flow tuff, rhyolite tuff al., 2015 Fm. xtal vitrophyre Porphyritic Railroad 40 39 Ar/ Ar rhyolite district, Indian Well Henry et H12-91 585072.45 4483848.7 Sanidine single Igneous 37.947 0.016 dike, north Indian Well rhyolite dike al., 2015 xtal end Fm. Rhyolite, Railroad 40 39 unoxidized, Ar/ Ar district, Henry et H12-158 H12-98 Late rhyolite 584068.76 4485387.1 Sanidine step Igneous 37.63 0.09 St anding al., 2015 with high Y, heating Elk Mine HREE

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age Gran it e-qt z- SE Railroad 40Ar/39Ar feldspar Granodiorite Henry et H12-143 district, big 583273.39 4485984 K-feldspar step Igneous 37.44 0.15 rhyolite; porphyry al., 2015 cut area heating fine matrix Railroad Rhyolite 40Ar/39Ar district, Indian Well Henry et ash-flo w 585338.7 4485597.2 Sanidine single Igneous 37.797 0.014 H12-88 Indian Well rhyolite tuff al., 2015 t uff xtal Fm. Quartz Railroad 40 39 porphyry Ar/ Ar district, Indian Well Henry et H12-87 rhyolite 585317.48 4485505 Sanidine single Igneous 37.781 0.016 Indian Well quartz porphyry al., 2015 intrusion or xtal Fm. lava dome Rhyolite, Railroad 40 39 Ar/ Ar qt z-san- district, Henry et H12-98 Late rhyolite 584068.76 4485387.1 Sanidine single Igneous 37.63 0.09 plag-bio; St anding al., 2015 xtal unoxidized Elk Mine Gran it e-QF 40 39 SE Railroad Ar/ Ar rhyolite, Granodiorite Henry et H12-145 district, big 583215.68 4485996.8 Hornblende step Igneous 38.2 moderate Y, porphyry al., 2015 cut area heating Qtz veined Coarse Railroad dacite, Qtz-phyric U/Pb LA- Henry et H12-154 district, NW 582882.32 4486360 Zircon Igneous 38.45 silicified, dacite ICP/MS al., 2015 of big cut high Y 40Ar/39Ar Piñon Horner, Horner1 T uff Upper Elko Fm. 585256 4492650.3 Biotite step Igneous 43.5 0.02 Range 2015 heating Coal Mine Canyon, U/Pb LA- Horner, T uff Basal Elko Fm. 614103 4553304.4 Zircon Igneous 48.2 0.02 Horner2 Adobe ICP/MS 2015 Range 0.3 km 40 39 Ar/ Ar Mulch south of Indian Well Fm. NV-IW- Biotite tuff 595711.49 4484578.4 Biotite step Igneous 38 0.4 et al., USBM oil biotite tuff 21-07 heating 2015 shale trench 40Ar/39Ar Mulch NV-IW- Indian Well Fm. Biotite tuff “ 595711.49 4484578.4 Biotite step Igneous 38.4 0.3 et al., 21-07 2 biotite tuff heating 2015 40Ar/39Ar Mulch Indian Well Fm. NV-IW- Biotite tuff “ 595716.35 4484419.3 Biotite step Igneous 37.6 0.5 et al., biotite tuff 03-07 heating 2015 40Ar/39Ar Mulch Indian Well Fm. NV-IW- Biotite tuff “ 595716.35 4484419.3 Biotite step Igneous 38 0.4 et al., biotite tuff 03-07 2 heating 2015 15

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585497.78 4492440.4 Biotite step Igneous 40.7 0.3 et al., 027-07 t uff heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585497.78 4492440.4 Biotite step Igneous 39.9 0.3 et al., t uff 027-07 2 heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585497.78 4492440.4 Biotite step Igneous 40.6 0.3 et al., t uff 027-07 3 heating 2015 40Ar/39Ar Mulch NV-EF- Elko Fm. biotite Biotite tuff “ 585451.04 4492456.5 Biotite step Igneous 38.2 0.5 et al., 25-07 t uff heating 2015 40Ar/39Ar Mulch NV-EF- Elko Fm. biotite Biotite tuff “ 585451.04 4492456.5 Biotite step Igneous 38.9 0.9 et al., 25-07 2 t uff heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585451.04 4492456.5 Biotite step Igneous 40.9 0.6 et al., t uff 25-07 3 heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585453.73 4492467.6 Biotite step Igneous 39.6 0.3 et al., t uff 028-07 heating 2015 0.3 km 40 39 Ar/ Ar Mulch south of Elko Fm. biotite NV-EF- Biotite tuff 585453.73 4492467.6 Biotite step Igneous 39.1 0.4 et al., USBM oil t uff 028-07 2 heating 2015 shale trench 40Ar/39Ar Mulch NV-EF- Elko Fm. biotite Biotite tuff “ 585451.04 4492456.5 Biotite step Igneous 40.2 0.3 et al., 029-07 t uff heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585418.44 4492469.1 Biotite step Igneous 41.6 0.4 et al., t uff 031-07 heating 2015 40Ar/39Ar Mulch Elko Fm. biotite NV-EF- Biotite tuff “ 585398.67 4492470.7 Biotite step Igneous 41.6 0.4 et al., t uff 32-07 heating 2015 0.3 km 40 39 NV12- Ar/ Ar south of Elko Fm. biotite Smith et 099ES Biotite tuff 585515.0 4492536.8 Biotite step Igneous 41.6 0.4 USBM oil t uff al., 2017 heating shale trench 40Ar/39Ar NV12- Elko Fm. biotite Smith et Biotite tuff “ 585506.4 4492547.8 Biotite step Igneous 41.6 0.4 139SR t uff al., 2017 heating NV12- 40Ar/39Ar Elko Fm. biotite Smith et 129SR Biotite tuff “ 585421.3 4492591.2 Biotite step Igneous 41.6 0.4 t uff al., 2017 heating

40Ar/ Stratigraphic UTME- UTMN- Type of U-Pb Age Sample Lithology Location Mineral Method 39Ar 2ϭ 2ϭ Description NAD83 NAD83 Analysis age Ref age 40Ar/39Ar Elko Fm. biotite Smith et NV12- Biotite tuff “ 585378.7 4492612.9 Biotite step Igneous 41.6 0.4 121SR t uff al., 2017 heating NV12- 40Ar/39Ar Elko Fm. biotite Smith et 113SR Biotite tuff “ 585361.5 4492634.9 Biotite step Igneous 41.6 0.4 t uff al., 2017 heating 40Ar/39Ar Elko Fm. biotite Smith et NV-EF- Biotite tuff “ 585140.7 4492699.0 Biotite step Igneous 41.6 0.4 t uff al., 2017 32-07 heating 40Ar/39Ar ANV14- Elko Fm. biotite Smith et Biotite tuff “ 585344.3 4492656.9 Biotite step Igneous 41.6 0.4 010PR t uff al., 2017 heating 40Ar/39Ar NV12- Elko Fm. biotite Smith et Biotite tuff “ 585515.0 4492536.8 Biotite step Igneous 41.6 0.4 110SR t uff al., 2017 heating *decay constants from Steiger and Jäger, 1977; ages published before 1977 are recalculated to Steiger and Jäger, 1977.

Table 3 . Constraints on mineralization age and depth, from Hollingsworth et al., 2017.

Deposit/Sample Dating Specific Anomalous Mineralization Depth Age Mineral Age Type Alteration Ref1 Type Method Method Geochemistry Age Constraint

Rain Whole- Relict fresh Basaltic andesite 38.21 ± 40 39 Pre-mineral Adjacent Ar/ Ar Wt d avg rock rock; otherwise <38.2 Ma > 1.1km (Rain) 3 dike 0.20 igneous QSP devitrified mineralized Relict fresh 39.06 ± 40 39 Pre-mineral Adjacent Diorite dike Ar/ Ar Wt d avg Biotite rock; otherwise <38.2 Ma > 1.1km (Rain) 3 0.20 igneous QSP mineralized Emigrant Tertiary Basal 44.5 ± LA-ICP- Pre-mineral <37.5 Ma and U/Pb Zircon Silicified As 733 ppm ~400-500m 1 Conglomerate 0.64 Ma MS sedimentary >10.8 Ma Weakly Quartz Monzonite 37.5 ± 0.8 Pre-mineral <37.5 Ma and U/Pb SHRI MP Zircon Argillic mineralized(?); ~400-500m 4 Porphyry Dike Ma igneous >10.8 Ma in deposit Supergene Alunite 10.8 ± 0.8 40 39 Supergene in Alunitic- Au in SEM <37.5 Ma and (Rhombic Alunite Ar/ Ar Plateau Alunite ~400-500m 1 Ma deposit argillic analysis >10.8 Ma Massive ) North Bullion 38.22 Weakly Porphyritic Dacite LA-ICP- Pre-mineral <38.2 Ma and +0.44/- U/Pb Zircon QSP mineralized; in ~600 m 2 Sill MS igneous >37.8 Ma 0.22 Ma deposit 38.40 Weakly Porphyritic Dacite LA-ICP- Zircon Pre-mineral <38.2 Ma and +0.63/- U/Pb QSP mineralized; in ~600 m 2 Sill MS igneous >37.8 Ma 0.55 Ma deposit 38.77 Weakly Porphyritic Dacite Pre-mineral <38.2 Ma and +1.22/- U/Pb SHRI MP Zircon QSP mineralized; in ~600 m 2 Sill igneous >37.8 Ma 0.85 Ma deposit 38.28 Weakly Porphyritic Dacite Pre-mineral <38.2 Ma and +0.64/0.20 U/Pb SHRI MP Zircon QSP mineralized; in ~600 m 2 Sill igneous >37.8 Ma Ma deposit Au 0.026, Sb Porphyritic Dacite Eocene*, Carlin-type <38.2 Ma and 40Ar/39Ar - Illite QSP 45, As >250, ~600 m 1 Sill but too old mineralization >37.8 Ma Tl 6.7 (ppm) Indian Well Fm. 37.82 ± 40 39 Single Post-mineral <38.2 Ma and Rhyolite Ash-flo w Ar/ Ar Sanidine Fresh ~600 m 2 0.02 Ma xtal igneous >37.8 Ma T uff Indian Well Fm. 37.80 ± 40 39 Single Post-mineral <38.2 Ma and Rhyolite Ash-flo w Ar/ Ar Sanidine Fresh ~600 m 2 0.01 Ma xtal igneous >37.8 Ma T uff

Deposit/Sample Dating Specific Anomalous Mineralization Depth Age Mineral Age Type Alteration Ref1 Type Method Method Geochemistry Age Constraint Indian Well Fm. 37.78 ± 40 39 Single Post-mineral <38.2 Ma and Rhyolite Ash-flo w Ar/ Ar Sanidine Fresh ~600 m 2 0.02 Ma xtal igneous >37.8 Ma T uff Indian Well Fm. 37.83 ± 40 39 Single Post-mineral <38.2 Ma and Rhyolite Dome Ar/ Ar Sanidine Fresh ~600 m 2 0.02 Ma xtal igneous >37.8 Ma Lava

Indian Well Fm. 37.95 ± 40 39 Single Post-mineral <38.2 Ma and Ar/ Ar Sanidine Fresh ~600 m 2 Rhyolite Dike 0.02 Ma xtal igneous >37.8 Ma Indian Well Fm. 40 39 Post-mineral <38.2 Ma and 40.2 Ar/ Ar - Sanidine Fresh ~600 m 1 Ash-flow Tuff igneous >37.8 Ma Pinion Au 0.487, Sb Porphyritic Dacite 38.3 ± LA-ICP- Pre-mineral <38.3 Ma; other U/Pb Zircon QSP 26.9, As 614, ~500 m 1 Sill 0.62 Ma MS igneous ages pending Tl 2.7 (ppm)

Porphyritic Dacite Eocene*, 40 39 Carlin-type <38.3 Ma; other Ar/ Ar - Illite QSP no assay ~500 m 1 Sill Illite but too old mineralization ages pending Au 0.066, Ag Calcite, Illite Vein 34.99 ± Carlin-type <38.3 Ma; other 40Ar/39Ar - Illite QSP 5.65, Sb 20.9, ~500 m 1 Fill 0.08 Ma mineralization ages pending As 25 (ppm) Supergene Alunite Supergene in <38.3 Ma; other (Porcelaineous ~9.7 Ma 40Ar/39Ar - Alunite QSP No assay ~500 m 1 deposit ages pending Vein ) Whole- 40 39 Post-mineral Weak to <38.3 Ma; other Mafic Dike 38.3 ± 0.3 Ar/ Ar - rock Ba 0.4% ~500 m 1 igneous nil ages pending devitrified Dark Star Tertiary Basal 45.2 ± LA-ICP- Pre-mineral < ~43.7 and Conglomerate U/Pb Zircon Silicified No assay ~200-300 m 1 0.82 Ma MS sedimentary >14.5 Ma (Clasts Only) Au 0.392, Sb Tertiary Basal 43.67 ± LA-ICP- Pre-mineral < ~43.7 and U/Pb Zircon Silicified 60.3, As 426, ~200-300 m 1 Conglomerate 0.27 Ma MS sedimentary >14.5 Ma Tl 3.55 (ppm) Supergene Alunite 14.47 ± Supergene in Alunitic- < ~43.7 and (Porcelaineous 40Ar/39Ar Plateau Alunite No assay ~200-300 m 1 0.03 Ma deposit argillic >14.5 Ma Vein ) Dixie Creek Au 0.029, Sb Tertiary Basal 44.4 ±1.0 LA-ICP- Pre-mineral U/Pb Zircon Silicified 27, As 124, Tl < ~39.9 Ma ~100 m 1 Conglomerate Ma MS sedimentary 0.62 (ppm) Au 0.026, Sb Tertiary Basal 45.3 ± 0.7 LA-ICP- Pre-mineral U/Pb Zircon Argillic 53, As 464 < ~39.9 Ma ~100 m 1 Conglomerate Ma MS sedimentary (ppm)

Deposit/Sample Dating Specific Anomalous Mineralization Depth Age Mineral Age Type Alteration Ref1 Type Method Method Geochemistry Age Constraint Au 0.419, Sb Porphyritic 39.9 ± LA-ICP- Pre-mineral U/Pb Zircon Argillic 154, As 911, Tl < ~39.9 Ma ~100 m 1 Rhyolite Lava 0.78 Ma MS igneous 1.72 (ppm) Pony Creek Au 0.047, Sb Rhyolite Porphyry 45.92 ± 40 39 Carlin-type ~45.9 Ma, 46.1 Ar/ Ar Plateau Illite Sericitic 3.45, As 14.9, ~300-400 m 1 Body 0.48 Ma mineralization Ma Tl 3.92 (ppm)

Rhyolite Porphyry 46.08 ± 40 39 Carlin-type ~45.9 Ma, 46.1 Ar/ Ar Plateau Illite Sericitic No assay ~300-400 m 1 Body 0.11 Ma mineralization Ma Supergene Alunite 9.54 ± Supergene in Alunitic- ~45.9 Ma, 46.1 (Porcelaineous 40Ar/39Ar Plateau Alunite No assay ~300-400 m 1 0.046 deposit argillic Ma Vein )

* 40Ar/39Ar alteration ages give Eocene ages that are older than the emplacement age due likely to excess 40Ar and/or 39Ar recoil effects (see Age column). 1 References: 1 Hollingsworth et al., 2017; 2 Henry et al., 2015; 3 Ressel and Henry, 2006, 4 Longo et al., 2002

View publication stats