GEOLOGIC MAP 51 IDAHO GEOLOGICAL SURVEY STEWART AND OTHERS MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG PLATE 1

GEOLOGIC MAP OF THE STIBNITE QUADRANGLE, VALLEY COUNTY, IDAHO

David E. Stewart, Eric D. Stewart, Reed S. Lewis, Kerrie N. Weppner, and Vincent H. Isakson CORRELATION OF MAP UNITS 2016 METASEDIMENTARY ROCKS Windermere Supergroup WHISKEY CREEK FAULT The Whiskey Creek fault strikes north-northwest, dips moderately to the Alluvial Deposits Lower Paleozoic strata Zmss Schist of Moores Station Formation (Neoproterozoic)—Schist and minor A’ Artificial Mass Movement Glacial east-northeast, and places the Moores Station Formation (Zms) over the D'C' Deposits Deposits Deposits calc-silicate rocks. Schist is medium to dark gray and consists of as much as 48 15 40 OC– ucs quartzite of Profile Creek (Zqp). It occurs only to the northwest of the Salt OC– mmq Td 3 HOGBACK Ocs Calc-silicate of Midnight Creek (Ordovician)—Mixed unit of calc-silicate rock, 40 percent small (<1 mm) biotite and muscovite in varying proportions and 30 Creek fault, and is presumably intruded by Cretaceous biotite granodiorite 37 m dolomitic marble, phyllite, and quartzite exposed northeast of the Stibnite 33 30 OC– mm 28 FAULT? Qal Holocene 60 percent or greater fine-grained quartz and plagioclase in various propor- OC– mm 70 32 35 50 10 Qaf (Kgd) to the southeast. The fault is roughly parallel to bedding in the quartz- 35 70 C– lq 30 10 C– lq Qls QUATERNARY pit, north of Midnight Creek. Previously undescribed, this unit appears to 15 20 tions. Locally includes thin quartzite beds, rare calc-silicate gneiss, 60 Tdq? Qg Pleistocene be stratigraphically above, and in gradational contact with, the upper ite of Profile Creek. The fault zone is characterized by foliated rock. No OC– ucs amphibolite, and biotite muscovite quartz feldspar schist in highly OC– mmq 5 60 50 C– Zqpc kinematic indicators were observed. 34 25 Tdp Tr quartzite unit. A less likely alternative is that this unit is a fault sliver of the metamorphosed pods, screens, and schlieren within Kgd south of the East 40 Zfm Qal 20 20 62 Fern marble and lower calc-silicate unit. Investigation of the contact with Fork of the South Fork of the Salmon River and north of Salt Creek. Includes 22 The Whiskey Creek fault is interpreted to record thrust motion; however, 70 70 C– lq C– lq the ridge- forming upper quartzite showed no clear evidence of a fault. Tdp rare matrix-supported quartz pebble conglomerate north of the mouth of there is uncertainty due to the ambiguity in the stratigraphic location of the 10 25 – 45 Instead, a traverse northward (down section) appears to transition from L 22 40 Clq OC– ucs 70 Intrusive Rocks Challis Volcanic Group CENOZOIC Whiskey Creek (44.9593˚ N, 115.3637˚ W). Sillimanite is common. Mineral 45 Kgd quartzite of Profile Creek (see discussion in the detrital zircon section). We 25 Qaf 40 35 dolomite to phyllite then into interbedded calc-silicate and quartzite, and lineations in the schist generally plunge shallowly (10-20 degrees) to the 2 Zfm – suspect the Whiskey Creek fault is connected with the Sugar Mountain fault 8 50 CZqpc 30 finally quartzite of the upper quartzite unit. Assuming no fault exists, the 15 Tss southeast. Thickness unknown because of internal folding and the presence at depth, ramping up to a hanging wall flat on footwall flat where the 65 likely correlative unit is the Ordovician Saturday Mountain Formation Tdq Qg of a foliation that may be transposed bedding. Lund (2004) assigned this unit current fault trace is exposed (see cross section C-C’). 20 Zfm Qal 12 Timi Trp TERTIARY OC– mm C– lq 30 Tr Tbr exposed in the Clayton area to the southeast (Hobbs and Hays, 1990). to the Plummer Point Formation, thought to be stratigraphically low in the TAMARACK Zfm 10 Eocene sequence. Tentatively mapped here as the younger Moores Station Forma- OC– ucs 18 Kgd Qaf CREEK Qal Tdqs Tdq Ouq Upper quartzite (Ordovician)—Light gray to white, fine- to coarse-grained 34 Zlcs 65 C– lq Td Tdp tion on the basis of stratigraphic position. 34 Qaf ANTICLINE quartzite and minor siltite. Quartzite contains approximately 99 percent MISSOURI RIDGE FAULT 21 Kgd 15 Tll 40 45 quartz as moderately to poorly sorted subrounded grains. Sedimentary Zmsm 30 Qaf 20 Marble of Moores Station Formation (Neoproterozoic)—Buff to light gray The Missouri Ridge fault in the far northwestern corner of the Stibnite 7.5’ 34 structures are commonly obscured by recrystallization and brecciation but C– Zqpc 20 Qg marble and lesser amounts of millimeter- to centimeter-laminated Qaf Qal 44 Qg? quadrangle strikes roughly east-west to northeast-southwest, and dips to the M 35 Zlcs local centimeter-scale bedding and planar cross-stratification is observed. ISSO Zfm Zfm CALDERA COMPLEX calc-silicate rock. Thickness 0-40 m (0-130 ft); unit pinches out locally. north. It places a package of gently folded strata stratigraphically above the URI Qg Kg Two thin intervals of siltite are present south of Cinnabar Peak and biotite Zqs OC– ucs 65 BOUNDING FAULT RID 18 C– Zqpc Klg quartzite and schist unit (Zqs) and below the middle marble (OCmm) over GE FA Qaf C– lq 80 Tdq phyllite interbedded with quartzite is present in the upper part of the Cinna- Ze Edwardsburg Formation (Neoproterozoic)—Predominantly metamorphosed, Kgd ULT 67 Kgds CRETACEOUS MESOZOIC more tightly folded rocks of the hanging wall and footwall of the Sugar 27 bar Creek drainage northwest of Monumental Summit. Thickness approxi- poorly sorted, faintly mm- to cm-scale bedded fine-grained to granule 35 55 Mountain fault. We interpret the Missouri Ridge fault to record normal 42 Tbr Kgd mately 400 m (1,310 ft). Lund (2004) correlated the upper quartzite of 20 SUGAR 50 28 sandstone with abundant hornblende, epidote, and biotite in the matrix. 37 43 20 Zfm 45 motion, bringing the hanging wall of the Whiskey Creek fault down to the Zmss MOUNTAIN 60 15 78 Smitherman (1985) with the Moores Lake Formation of Neoproterozoic age. Rounded quartzite pebbles as much as 8 mm in diameter are common in Zmsm Qaf 35 45 north and east (see cross-section A-A’), placing more gently folded Whiskey 32 Tdp Kgd FAULT Correlated here with the Ordovician Kinnikinic Quartzite in the Bayhorse some horizons, as are dark, angular, flattened/stretched clasts of 25 Metasedimentary Rocks Creek hanging wall strata in contact with the more tightly folded rocks Ze 35 area (Hobbs and Hays, 1990) on the basis of high stratigraphic position and calc-silicate as much as 6 cm in length. The deposit is matrix supported, 40 adjacent to the Sugar Mountain fault. Movement on the Missouri Ridge 28 25 detrital zircon ages largely >1800 Ma (sample J, Table 1, from south of with clasts comprising less than 40 percent of the rock. Long axes of clasts Zlcs Ocs fault must post-date thrusting associated with the Whiskey Creek and Sugar 26 Tdp 45 Cinnabar Peak) and thus similar to ages from the type Kinnikinic exposed to plunge 30-40 degrees to the north at one locality. Amphibolite is also 75 20 Mountain faults, but otherwise is poorly constrained. 33 45 Ouq the southeast near Clayton (Barr, 2009; Paul Link, written commun., 2012). present in layers as much as 1 m thick. The unit is most similar to the Kgd 16 ORDOVICIAN Zircon ages are discussed in more detail in the following section. matrix-supported diamictite and graded volcaniclastic rocks of the Wind Qal Qaf 75 58 53 Zqp 53 42 85 32 Ohm 45 River Meadow member of the Edwardsburg as described by Lund (2004) 31 36 27 Zfm 40 A 50 Ohm Hermes marble (Ordovician)—Light gray to light brown, massive dolomitic west of Big Creek Guard Station approximately 20 km (12 mi) to the north. MEADOW CREEK FAULT 20 OC– mq PALEOZOIC marble. Coarsely recrystallized, relatively pure carbonate that is not ribbon 30 30 50 Only the Wind River Meadow member of the Edwardsburg Formation is Zmss 75 The Meadow Creek fault is a major regional structure. In the southern 50 D – – laminated. Smitherman (1985) reports altered tremolite porphyroblasts. 45 Zmss C– Zqpc 40 OCmmq OCmm present on Sugar Mountain; the mafic metavolcanics of the Golden Cup Stibnite quadrangle, it strikes north-south, and dips sub-vertical. The strike 20 50 Includes thin (1 cm and less) discontinuous interbeds of gray chert or jasper- 40 75 E’ member and the clast-supported diamictites of the Placer Creek member turns northeastward near the Yellow Pine pit. The fault cuts Cretaceous 15 30 OC– ucs OC– ucs CAMBRIAN oid. Thickness is approximately 100 m (330 ft). Previously correlated with Tr C– lq Tbr are absent. Thickness is estimated to be 50 m (165 ft). The formation is granodiorite as well as displaces the Stibnite roof pendant from the Missouri 17 21 27 Kgd 30 C– lq the “gray marble” unit, thought to be of Neoproterozoic or Cambrian age 70 C– lq laterally discontinuous and truncated by faults. 37 Ridge-Sugar Mountain roof pendant. Parts of the fault zone are mineralized. Qaf Zmsm 33 60 Tbr OZmu (Lund, 2004). Correlated here with the Ordovician Ella Dolomite in the Tr 33 OC– mm 20 30 30 Timi – Bayhorse area (Hobbs and Hays, 1990) on the basis of stratigraphic position. OZmu Metasedimentary rocks, undivided (Ordovician to Neoproterozoic)—Schist, 70 CZqpc The Meadow Creek fault has components of both right-lateral and west-side Qaf 22 33 43 Tr T quartzite, and calc-silicate rocks present as small roof pendants and screens 11 20 16 25 Zfm OCmq up movement. It is uncertain if the fault has been rotated, and whether the B 12 Middle quartzite (Cambrian to Ordovician)—Light gray, medium- to within intrusive rocks. Many contain igneous-like components, including Ze45 west-side up motion represents original reverse or normal slip. The age of 20 15 FAUL Zfm Zlcs Zqs fine-grained quartzite. Contains approximately 99 percent quartz and 1 Zqp 45 60 Zlcs mafic-rich quartz-feldspar rock with abundant sphene and (or) hornblende. movement is poorly constrained, but must post-date both the emplacement Kgd 47 10 percent potassium feldspar. Moderately to poorly sorted and moderately Stratigraphic position is uncertain. In the southwestern part of the quad- 65 46 C– Zqpc Timi of the Cretaceous granodiorite (Kgd) as well as the development of the 80 Zqs rounded. Bedding locally is centimeter scale, although sedimentary rangle, south and east of Meadow Creek, several relatively large bodies of 65 Zmsm Tdq Garnet Creek and Tamarack Creek folds. It also has at least some 28 65 NEOPROTEROZOIC PRECAMBRIAN features are largely obscured by recrystallization and brecciation. Thickness CREEK calc-silicate rock crop out. These are included in OZmu because they do 27 30 60 Kgd post-mineralization movement (Chris Dail; oral commun., 2012). 21 30 approximately 80 m (260 ft). Previously included in the “gray marble” unit, 70 Zqp not exhibit distinctive characteristics that would allow them to be assigned Qls 36 thought to be of Neoproterozoic or Cambrian age (Lund, 2004). The quartz- 32 16 Qls 40 32 Tdp to or excluded from the Zlcs or OCucs. SALT E ite contains four 500 Ma detrital zircons (sample I, Table 1, from south of 55 C– lq Kgd 45 CALDERA COMPLEX Zmsm Zmss Cinnabar Peak) indicating a likely Cambrian or Ordovician age. Not shown WEST END FAULT Qls Tdp Qls Kgd BOUNDING FAULT 40 Zmss SUGAR in Figure 1 because of discordance >10%. See zircon age discussion in WHISKE M Ze The West End fault is subsidiary to the Meadow Creek fault. It strikes north- 37 OUNTAIN DISCUSSION OF 45 following section. 30 FAULT OC– mmq east and dips to the southeast. Movement on the West End fault included 30 35 36 DETRITAL ZIRCON DATA Y 32 both normal and right-lateral components, as shown by drill hole data (Chris 28 25 OCmm Middle marble (Cambrian to Ordovician)—Medium gray, mostly massive 40 Trp marble with faint millimeter-scale laminations. Top 10 m consists of millime- Dail, oral commun., 2012). Drill core also demonstrates that, at the West 35 End pit, the West End fault dips steeply (65 degrees) to the east while miner- 30 56 ter- to centimeter-scale interbeds of marble and resistant silica-rich laminae Quartzite samples for detrital zircon dating were collected from nine localities 40 35 C alized zones dip shallowly to the east (Chris Dail, oral commun., 2012). R (ribbon laminated). Medium to coarsely recrystallized. Includes a thin within the quadrangle and one locality along Profile Creek two miles west of E Zmss 35 INTRODUCTION E K Kgd interval of sillimanite-biotite schist in northwest part of map. Locally the quadrangle (Table 1). Individual U-Pb zircon ages were obtained by Vince Qaf 25 Qls Kgd contains gray anthophyllite as 1cm long “sticks” with square cross section, Isakson and Darin Schwartz using laser-ablation ICP-MS methods at Washing- 40 FA Qls 45 OTHER FAULTS U Qaf Tdq The Stibnite quadrangle is underlain by metamorphosed sediments of along with phlogopite, biotite, graphite, and diopside. Thickness is approxi- ton State University and Boise State University. LT Kgd – 38 OCmm 10 Tbr Neoproterozoic and Paleozoic age within the Stibnite and Missouri Ridge- mately 160 m (525 ft) in the Stibnite roof pendant, but may be greater in the Zqp Kgd OC– mmq Qg A series of northeast-striking normal faults cut the roof pendant, Cretaceous Kgd Sugar Mountain roof pendants. They have undergone lower amphibolite Missouri Ridge-Sugar Mountain roof pendant. Previously included in the The Profile Creek sample (unit Zqp) has major populations at 1000-1200 Qls 25 Zqs C– lq Zqs Tr INTRUSIVE ROCKS intrusive rocks, and in places the Challis volcanics. The Salt Creek fault, 34 Zlcs Qaf facies metamorphism of probable Cretatceous age. These strata have been “gray marble” unit, thought to be of Neoproterozoic or Cambrian age, and and 1400-1500 Ma (Fig.1). A single grain at about 685 Ma is the youngest. 40 striking northeast and dipping steeply to the northwest, is one of the more Qaf Zfm Tr The quartz pebble conglomerate (CZqpc), collected near the Stibnite pit (G, 25 extensively intruded by several pulses of Cretaceous magma, and are Rhyolite dikes (Eocene)—Light to medium gray rhyolite with less than 15 Missouri Ridge Formation, thought to be Neoproterozoic (Lund, 2004). On 32 Qaf Qls important northeast-striking structures. It shows both normal and left-lateral Zmss complexly folded with apparent reverse, normal, and (or) strike-slip fault percent phenocrysts of quartz (as much as 2 mm in length and typically the basis of stratigraphic position we consider its age to be Cambrian or, less Table 1), yielded similar results with major populations at 1000-1250, Zmss Qal motion, but doesn’t displace the Challis volcanic caldera boundary in the Tr movement. Some of the structures were extensively mineralized and have partially resorbed), potassium feldspar (as much as 2 mm in length), plagio- likely, Ordovician. 1350-1500, and 2550 Ma; three grains are between 620 and 700 Ma. Also 25 Zmss upper reaches of Tamarack Creek. Another significant northeast-striking Zmss C– lq been exploited to produce gold, tungsten, antimony, and mercury. Most of the clase, and minor biotite. Phenocrysts are set in an aphanitic matrix of similar is sample K from the quartzite and schist unit (Zqs) northeast of 40 25 normal fault is the the Fern fault in the southeastern portion of the map area. Trp quartz and feldspar. Locally aphyric. OCmmq Quartzite within middle marble (Cambrian to Ordovician)—Light gray, Cinnabar Peak. Aside from the youngest ages, these results are similar to 75 Qaf Tdp metasedimentary rocks are nearly vertical to overturned and young to the medium- to coarse grained quartzite present locally within the middle marble detrital zircon results from the lower part of the Neoproterozoic to It dips steeply to the northwest, and cuts metasediments of the Stibnite roof Kgd Trp Zqs Qaf southwest. All of these factors add to the difficulty of correlating units between unit. Locally contains approximately 5 percent potassium feldspar and about Cambrian Camelback Formation in southeast Idaho (Yonkee and others, pendant folded by the Garnet Creek syncline. This fault displays a “scissors” Td areas separated by intrusive rock. Volumetrically minor Eocene dikes, sills, Tr p Rhyolite porphyry dikes (Eocene)—Light gray to light pink, highly porphyritic Zlcs 55 Qls 3 percent plagioclase. Thickness is approximately 25 m (80 ft). The quartzite 2014) and consistent with a Neoproterozoic to Cambrian age for these type offset with the northwest side down in the south and the southeast side Qaf C– Zqpc and small intrusions are also present. In the eastern part of the quadrangle rhyolite containing as much as 70 percent phenocrysts of quartz (typically contains abundant 500 Ma detrital zircons (samples E and L, Table 1, from rocks. Although few in number, the youngest zircons are likely sourced down in the north. It is interpreted to have had both normal and left-lateral Timi 50 down-faulted Eocene volcanic rocks fill a caldera collapse structure. Quater- partially resorbed), potassium feldspar, plagioclase, and minor biotite. south of Sugar Mountain and Missouri Ridge) consistent with a Cambrian or movement. 24 Zmss 18 Kgd CINNABAR Kgd nary surficial deposits occur in stream beds and glaciated areas. from the Edwardsburg Formation, which contains volcanic rocks of about WEST END Phenocrysts are as much as 20 mm in size, set in an aphanitic groundmass PEAK 45 Ordovician age (see zircon age discussion in following section). 685 Ma and is exposed 20 km (12 miles) to the north (Lund and others, Zmss FAULT 85 FAULT of quartz and feldspar. Kgd Geologic mapping was conducted during the summers of 2012, 2013, 2003) and in the map area. In contrast, three samples of the overlying lower Zmss 60 OCucs Upper calc-silicate (Cambrian to Ordovician)—Light to medium gray-green, Zqs 2014, and 2015. The work of Smitherman (1985) on the Stibnite roof quartzite (Clq from Cinnabar Peak, north highwall of the West End pit, and Qls Qal orange calc-silicate, marble, and silicic layers, which are interbedded on a 35 49 Ouq Zfm pendant was used extensively by the present authors and many of his unit Td Dacite dikes (Eocene)—Medium gray to dark green-gray, fine-grained to aphanitic 27 Qaf Qls Sugar Mountain; D, F, and H in Table 1) contain mostly 1740-1840 Ma names are utilized in this study. Virginia Gillerman of the Idaho Geological dacite with sparse phenocrysts of plagioclase, biotite, and hornblende. millimeter to centimeter scale to produce a distinctive “ribbon-laminated” grains and lack the young Grenville-age and 685 Ma grains. These results C 27 appearance. Minerals include quartz, calcite, biotite, plagioclase, scapo- 60 Qls Survey conducted parallel research on the ore deposits in the quadrangle. are similar to detrital zircon signatures of Cambrian quartzite from other Kgd Tdp Dacite porphyry dikes (Eocene)—Dark gray to dark green-gray dacite with lite, wollastonite, diopside, tremolite, muscovite, and magnetite. Serpen- 40 40 Zqs Preliminary results are presented in Gillerman and others (2014). Previous localities in the region such as the Addy Quartzite in northeastern Washing- 60 30 40 Kgd 65 conspicuous white phenocrysts of plagioclase as long as 10 mm in a Qg? studies that focused on the mineralization in the area include Schrader and tine and chlorite (after olivine?) are present in some of the marble. Thick- ton (Linde and others, 2014), the Gold Creek quartzite in northern Idaho Qal Ohm fine-grained to aphanitic groundmass. Phenocrysts that comprise as much ness is approximately 125 m (410 ft). Previously assigned to the “gray 10 50 Zlcs Ross (1925), Currier (1935), White (1940), Cooper (1951), and Cookro and (Lewis and others, 2010), the Clayton Mine Quartzite of central Idaho (Paul 18 Zlcs as 50 percent of the rock consist of plagioclase, potassium feldspar, marble” unit, of Neoproterozoic or Cambrian age (Lund, 2004). On the 75 Kgd others (1988). Foliation measurements in intrusive rocks are in part from Link, written commun., 2012), and the Gibbson Jack Formation of south- Zfm 85 hornblende, biotite, and minor quartz. basis of stratigraphic position we consider its age to be Cambrian or, less 57 55 unpublished mapping by B.F. Leonard (U.S. Geological Survey Field eastern Idaho (Yonkee and others, 2014). Quartzite within the middle Kgd Ouq Qg Records Library). likely, Ordovician. m C– Zqpc Timi Intermediate and mafic intrusive rocks (Eocene)—Dark green-gray to black, marble southeast of Sugar Mountain (OCmmq; E, Table1) yielded numerous 30 Qg Kgds grains with ages about 500 Ma. That sample contained a second population Kgd OC– ucs weakly porphyritic dacite to basaltic andesite. Phenocrysts that comprise Clq Lower quartzite (Cambrian)—Light gray, medium- to very coarse grained 40 65 Zqs Qaf Tbr 58 Kgd at about 1680-1800 Ma, and a number of Archean grains. Similarly, sample REFERENCES 35 Zfm K 60 72 <10 percent of the rock consist of white plagioclase as much as 4 mm in quartzite and minor schist or phyllite. Moderately to poorly sorted, locally Qls F 67 62 Tdp C– lq SYMBOLS length, minor hornblende, and, locally, biotite or pyroxene. No visible bi-modally sorted with coarse grains “floating” in a medium-grained L from the same unit on Missouri Ridge contained numerous 500 Ma Zqs 65 grains. A stratigraphically higher sample from the middle quartzite (OCmq) 40 56 quartz. Two whole-rock geochemical samples are dacite in composition 25 Zlcs matrix. Most exposures contain little or no feldspar, but a sample of quartz- Barr, E.E., 2009, Determining the regional-scale detrital zircon provenance of 75 (Table 2, Plate 2). Fisher and others (1992) show the exposure north of ite from Sugar Mountain contains about 5 percent potassium feldspar and southwest of Cinnabar Peak (I, Table 1) yielded a primary peak of about Zfm C– lq Kgds Ohm OC– mm H Contact: dashed where approximately located. 1680-1800 Ma, a few Grenville (1060-1140 Ma) ages, and four grains with the Middle-Late Ordovician Kinnikinic (Eureka) Quartzite, east-central OZmu 63 OC– ucs Monumental Summit as Tertiary latite lavas. We found no vesicles, trace amount of plagioclase feldspar. Moderately rounded grains. Overall Zlcs? R Idaho, U.S.: Washington State University M.S. thesis, 134 p. Qg? C 60 71 Zqs autoclastic breccia, or other indications of volcanic origin. Instead we coarser grained and less well sorted than upper quartzite (Ouq). ages about 500 Ma (but with discordance >10%). The abundance of 500 83 Normal fault: ball and bar on downthrown side; dashed where approxi- Cooper, J.R., 1951, Geology of the tungsten, antimony, and gold deposits near 45 Ocs Kgd 80 Ma grains in the former is similar to that reported for the Worm Creek Kgd Kgd 45 G mately located; dotted where concealed. interpret this unit as entirely intrusive. It occurs as composite dikes, sills, Decimeter-scale bedding with diffuse bedding traces that locally display Stibnite, Idaho: U.S. Geological Survey Bulletin 969-F, 197 p. Zfm 75 81 70 Member of the St. Charles Formation in southeastern Idaho (Todt and Tbr and small stocks with multiple internal contacts and heterogeneous compo- abundant planar cross laminae and, less commonly, trough cross laminae, 45 others, 2014), which contains only 500 Ma grains and is known to be Cookro, T.M., M.L. Silberman, and B.R. Berger, 1988, Gold-tungsten-bearing Kgd Kgd 80 Zlcs 74 Thrust fault: teeth on upper plate; dashed where approximately located; sition and texture. In places intrusion was along the ring fracture/caldera ripple marks, and diffuse heavy mineral laminae. Thin (<3 cm) discontinu- 80 Timi Upper Cambrian on the basis of fossils and local stratigraphy. The 500 Ma hydrothermal deposits in the Yellow Pine mining district, Idaho: in Schafer, 60 76 m Qaf bounding fault zone of the Thunder Mountain caldera complex following ous beds of granule- to pebble-sized material fill scours and are more abun- 15 54 OC– mq 75 40 dotted where concealed. R.W., Cooper, J.J., and Vikre, P.G., eds., Bulk mineable precious metal 40 71 C– lq grains are likely sourced from Late Cambrian and Early Ordovician plutons 50 42 I post-eruption collapse of the caldera floor. Two dikes north of Sugar Creek dant lower in the unit. The granule beds are locally graded. Thickness is 15 36 65 Ouq deposits of the western United States, Symposium Proceedings, the 50 Qg Overturned thrust fault: teeth in direction of dip; dashed where approxi- near the center of section 25 contain dark, dense very fine-grained rock that approximately 180 m (590 ft). Previously assigned to the Umbrella Butte described by Lund and others (2009) that are exposed to the north and east 18 C– Zqpc Qls of the quadrangle. Quartzite sampled south of Cinnabar Peak (unit Ouq; J, Geological Society of Nevada, Reno, Nevada, p. 577-624. 60 54 Zqs mately located; dotted where concealed. displays a conspicuous thick weathering rind and may be Miocene(?) basalt Qg OC– ucs 80 Formation of Neoproterozoic to Cambrian age (Lund, 2004). Detrital zircon Currier, L.W., 1935, A preliminary report on the geology and ore deposits of the Zfm 46 Kgd or basaltic andesite. samples from Cinnabar Peak (F, Table 1), from west of West End Creek (H, Table 1) contained an abundance of 1800-1950 Ma zircons that is most 20 J Right-lateral strike-slip fault: dashed where approximately located; dotted eastern part of the Yellow Pine district, Idaho: Idaho Bureau of Mines and Zqs Zlcs Table 1), and from Sugar Mountain (D, Table 1), all contain abundant similar to ages reported from the Ordovician Kinnikinic Quartzite (Barr, 75 70 where concealed. Klg Leucocratic granite (symbol only) (Cretaceous)—White to light gray, generally 2009; Paul Link, written commun., 2012). Overall, the detrital zircon Geology Pamphlet no. 43, 27 p. Qaf 25 C– lq 63 Ohm 1740-1840 Ma grains similar to Cambrian strata in the region. Zircon ages Qg? 70 results support the idea that the majority of the metasedimentary rocks in Fisher, F.S., D.H. McIntyre, and K.M. Johnson, 1992, Geologic map of the – 36 30 67 fine- to locally medium-grained biotite-muscovite granite. Unit is shown as are discussed in more detail in following section. OZmu 24 OCucs C– lq Reactivated(?) right-lateral strike-slip fault: bar and ball on downthrown Zlcs Ouq 71 point data on map and does not show on cross sections. Equigranular with the Stibnite and Missouri Ridge-Sugar Mountain roof pendants are Paleo- Challis 1° x 2° quadrangle, Idaho: U.S. Geological Survey Miscellaneous OZmu 85 Zqs 65 reactivated segments; dashed where approximately located; dotted Investigations Series Map I-1819, scale 1:250,000. m 18 OC– mm 80 subequal amounts of quartz, plagioclase, and potassium feldspar. Musco- zoic in age. This finding supports early stratigraphic assignment of these 27 30 where concealed. Gillerman, V.S., V.H. Isakson, M.D. Schmitz, J. Benowitz, and P.W. Layer, 2014, Qaf Kgd 23 vite occurs as disseminated flakes as much as 2 mm in size, comprising a rocks to the Paleozoic (Schrader and Ross, 1925; Shenon and Ross, 1936) 70 Lower Paleozoic or Neoproterozoic strata Geochronology of intrusive rocks and hydrothermal alteration at the 38 20 Zlcs 60 maximum of 5 percent of the rock. Biotite is rare. Termed “alaskite” by based on lithologic features. Kgd 55 Trp Tbr Reactivated(?) left-lateral strike-slip fault: bar and ball on downthrown structurally controlled Stibnite Au-Sb-W deposit, Idaho: Geological Society 37 Kgd 55 58 previous workers. Occurs primarily as dikes cutting both country rock and CZqpc 63 38 Ouq reactivated segments; dashed where approximately located; dotted Quartz pebble conglomerate (Cambrian to Neoproterozoic)—Light to medium 60 Qg 43 of America Abstracts with Programs, v. 46, no. 6, p. 165. OZmu 38 70 55 Tdqs Kgd, but also as small stocks. Two phases of leucocratic granite intrusion gray, medium- to coarse-grained quartzite, matrix-supported conglomerate, Qaf where concealed. Hobbs, S.W., and W.H. Hays, 1990, Ordovician and older rocks in the Bayhorse Zfm 60 are noted; pre- and post-Kgd. Many ore bodies in the Stibnite area are schistose quartzite, and muscovite-biotite schist. Individual conglomerate STRUCTURE Qaf area, Custer County, Idaho: U.S. Geological Survey Bulletin 1891, 40 p. Qg OC– ucs Anticline axial trace: dashed where approximately located; dotted where localized at the intersections of leucocratic granite dikes and faults or beds are as thick as 1 m and make up approximately 15-20 percent of the OZmu 30 60 70 CINNABAR Lane, E.W., 1947, Report of the subcommittee on sediment terminology; Trans- Kg 35 concealed. Arrow indicates plunge. favorable host sediments (Chris Dail, oral commun., 2012). Post-Kgd unit, with the major part being sand to granule size. As noted by Smither- T PEAK actions of the American Geophysical Union, v. 28, no. 6, p. 936-938. Kg GARNET intrusion emplaced the greater volume of leucocratic granite and appears man (1985), pebbles in the central and southeast part of the map are well The deformational history of the metamorphosed sediments of the Stibnite FAULT S Tdq Le Maitre, R.W., 1984, A proposal by the IUGS Subcommission on the System- 38 75 Overturned anticline axial trace: dashed where approximately located. to be temporally associated with intrusion of Kg. Compositions of the rounded and commonly flattened and stretched. Most clasts consist of and Missouri Ridge-Sugar Mountain roof pendants is complicated, and 20 15 C– Zqpc 80 Zlcs FAUL Zqs Kgd atics of Igneous Rocks for a chemical classification of volcanic rocks based 14 Zfm leucocratic granite and Kg are similar; the latest-stage leucocratic granite quartz, some of which are bluish, but dark-gray siltite, dark chert, and includes multiple episodes of contractional folding and faulting as well as 20 75 Zfm Zfm Timi Syncline axial trace: dashed where approximately located; dotted where on the total alkali silica (TAS) diagram: Australian Journal of Earth Sciences, 60 CREEK perhaps forms dikes that radiate from Kg bodies. U-Pb age determination marble comprise as much as 5 percent of the clast population near the base extension. The roof pendants lie along the eastern margin of the Cretaceous m concealed. Arrow indicates plunge. v. 31, p. 243-255. C– lq on sample from drill core near the Meadow Creek landing field is 87.9 ± north of the Fern mine. Overall poorly sorted with pebbles supported by Idaho batholith, and along the western boundary of the Thunder Mountain 30 C– Zqpc C– Zqpc Lewis, C.F., and R.D. Lewis, 1982, Fossil evidence for Ordovician age roof Zlcs 4.9 Ma (Table 1). Age is based on seven zircon rim analyses on four zircons granule and sand-sized matrix. Exposures in the West End pit and Stibnite caldera complex. Much of the contractional deformation likely predated or Kgd C– lq Overturned syncline axial trace: dashed where approximately located. pendants previously considered as Precambrian in the Idaho batholith: 15 by laser-ablation ICP-MS methods at Washington State University (Richard pit areas are more schistose than those to the south near the Fern mine and was synchronous with the later stages of the emplacement of the early MEADOW N 40 Geological Society of America Abstracts with Programs, v. 14, p. 265. Qg Strike and dip of bedding. Gaschnig, written commun., 2011). Large error is due to a low number of clast diversity is greater in the south. Thickness is approximately 100 m (325 CREEK SYNCLINE 26 Tr metaluminous suite of the Idaho batholith (100-85 Ma, Gaschnig and OZmu Kgd Td ER Lewis, R.S., J.D. Vervoort, R.F. Burmester, and P.J. Oswald, 2010, Detrital zircon F zircons found in sample. Gillerman and others (2014) report an age on ft) but is variable, and locally the unit is not present. Previously assigned to others, 2010). Extension was likely synchronous or post-dated the eruption FAULT Zfm analysis of Mesoproterozoic and Neoproterozoic metasedimentary rocks of Strike of vertical bedding. “alaskite” as 83.6 ± 0.1 Ma collected from a drill hole north of the Yellow the Umbrella Butte Formation of Neoproterozoic age (Lund, 2004). Detrital of the Eocene Challis volcanics, and resulted in the preservation of Challis A m Qal Tbr north-central Idaho: implications for development of the Belt-Purcell basin: Qg 31 12 Pine pit. This intrusion cuts Kgd and is mineralized (Virginia Gillerman, zircon ages from the quartz pebble conglomerate (G, Table 1) as young as volcanics within and adjacent to the caldera complex in the eastern portion 20 Strike and dip of bedding where sedimentary structures show bedding to Canadian Journal of Earth Sciences, v. 47, p. 1383-1404. 22 42 C– lq 15 written commun., 2014). Leucocratic granite both cross-cuts and is 685 Ma indicate a Neoproterozoic or younger age (see zircon age discus- of the map. This extension also formed a series of northeast-striking normal be upright. Qg 65 Lewis, R.S., D.E. Stewart, and E.D. Stewart, 2012, Geologic Map of the Big 25 OZmu 45 40 deformed by the folding in the area, indicating multiple intrusive ages. sion below). Rests unconformably on the underlying Fern marble, with faults within the batholith and roof pendants. Caldera complex bounding 65 Creek quadrangle, Idaho and Valley counties, Idaho: Idaho Geological B 45 Zfm 44 channels and karst at the contact (Chris Dail, oral commun., 2012). faults are discussed in the regional structure section on Plate 2. Qls Strike and dip of bedding where sedimentary structures show bedding to be Kg Granite (Cretaceous)—Light gray, medium- to locally coarse-grained Survey Digital Web Map 143, scale 1:24,000. overturned. Qaf OZmu 30 equigranular biotite-muscovite granite consisting of subequal quartz, Linde, G.M., J.H. Trexler, Jr, P.H. Cashman, and W.R. Dickinson, 2014, The P Kg Kg 58 Kgd 45 plagioclase, and potassium feldspar. Muscovite occurs as books as much as provenance of detrital zircons from the Cambrian Addy Quartzite, northeast O Strike and dip of bedding where stratigraphic position indicates bedding is Windermere Supergroup(?) GARNET CREEK SYNCLINE Qg M Td 11 3 mm thick. Biotite is minor constituent at some localities. Locally porphy- Washington: connections between British Columbia and central Nevada?: likely overturned. Qal Qaf Kgd Tss ritic with quartz as much as 4 mm in size. The northwest-trending Garnet Creek syncline exposed within the Stibnite Geological Society of America Abstracts with Programs, v. 46, no. 5, p. 3. 65 Qaf C– Zqpc Zfm Fern marble (Neoproterozoic)—Medium to dark gray, coarsely re-crystallized 30 Strike and dip of foliation. roof pendant is doubly plunging and overturned to the southwest (see Lund, Karen, 2004, Geology of the Payette National Forest and vicinity, west- Qg Kg Q Kgds Granodiorite of the Stibnite stock (Cretaceous)—Light gray, fine- to medium- marble. Massive to ribbon laminated on a millimeter to centimeter scale. central Idaho: U.S. Geological Survey Professional Paper 1666, 2 plates, m Qg 26 cross-section B-B’). It was first described by Smitherman (1985). The 65 grained equigranular muscovite-biotite granodiorite. Plagioclase feldspar is Strike of vertical foliation. North of Monumental Summit contains thin (< 20 cm) interbeds of quartz- syncline is tentatively interpreted to fold the Cinnabar Peak fault at depth. scale 1:100,000; 89 p. OZmu the principle constituent, followed by quartz and potassium feldspar. ite. Dolomite is the principle mineral, with tremolite present locally. Thick- Lund, K., J.N. Aleinikoff, K.V. Evans, and C.M. Fanning, 2003, SHRIMP U-Pb Qaf Kgd 60 Estimated strike and dip of foliation. Contains both muscovite and biotite and overall is finer grained and more ness is approximately 40 m (130 ft). Lund (2004) assigned the Fern marble geochronology of Neoproterozoic Windermere Supergroup, central Idaho: muscovite-rich than Kgd. Like the more widespread Kgd unit, the stock has of Smitherman (1985) and underlying calc-silicate rocks to the Neoprotero- Implications for rifting of western Laurentia and synchroneity of Sturtian Qal Strike and dip of mylonitic foliation. TAMARACK CREEK ANTICLINE 40 been termed “quartz monzonite” by previous workers, but quartz content 19 N zoic Missouri Ridge Formation. Neoproterozoic age also assigned here on glacial deposits: Geological Society of America Bulletin, v. 115, p. Qg Qg is more than 20 percent. May also include some granite. U-Pb age determi- the basis of stratigraphic position. Fossil locality reported from the Fern The Tamarack Creek anticline is exposed within the Missouri Ridge-Sugar 349-372. Qaf 75 Strike and dip of flow or compaction foliation in volcanic rocks. nation on sample from the north rim of the Stibnite pit is 84.9 ± 2.0 Ma marble along ridge in sec. 12, T. 18 N., R. 9 E., north of the Fern Mine (Lewis Mountain roof pendant in the northwest part of the quadrangle. For most of Lund, K., J.N. Aleinikoff, K.V. Evans, E.A. duBray, E.H. Dewitt, and D.M. Unruh, Qls (Table 1). Age is based on 10 zircon rim analyses by laser-ablation ICP-MS and Lewis, 1982) was visited in 2014 by the authors. Fossil-like structures Qal 30 50 Bearing and plunge of lineation, type unknown. its exposed trace, the fold is overturned to the southwest. However, near 2009, SHRIMP U-Pb dating of recurrent Cryogenian and Late Cambrian– Kgd 80 Kgd methods at Washington State University (Richard Gaschnig, written there were reinterpreted as metamorphic minerals, mostly amphibole. Qls Tamarack Creek the fold becomes upright and the fold wavelength Early Ordovician alkalic magmatism in central Idaho: Implications for 15 Bearing and plunge of mineral lineation. commun., 2011). Gillerman and others (2014) report a similar but more Qg increases. Smaller northeast-trending folds northwest of the Salt Creek fault Rodinian rift tectonics: Geological Society of America Bulletin, v. 122, no. 30 Zlcs Lower calc-silicate (Neoproterozoic)—Medium to dark gray-green, orange OZmu precise age of 85.7 ± 0.1 Ma based on U-Pb TIMS analyses. re-fold the sedimentary units as well as the Tamarack Creek anticline. The 3/4, p. 430-453. Timi Bearing and plunge of crenulation lineation. calc-silicate rock and calc-silicate marble. Thin bedded and ribbon 65 Tamarack Creek anticline is interpreted to have formed at roughly the same Schrader, F.C., and C.P. Ross, 1925, Antimony and quicksilver deposits in the Kgd Granodiorite (Cretaceous)—Light gray, medium- to locally coarse-grained laminated on a millimeter to centimeter scale. Quartz, biotite, calcite, and Qg Qls T Tss 60 Bearing and plunge of small fold axis. time as the Garnet Creek syncline (Middle Cretaceous?). Yellow Pine district, Idaho: U.S. Geological Survey Bulletin 780, p. 137-164. 54 Qaf 70 Kgd equigranular biotite granodiorite. Isolated flakes of muscovite as large as 2 muscovite are common; calc-silicate minerals include epidote, tremolite, 80 60 Tr Shenon, P.J., and C.P. Ross, 1936, Geology and ore deposits near Edwardsburg 15 mm comprise as much as 2 percent of the rock locally. Plagioclase feldspar actinolite, anthophyllite, hornblende, diopside, scapolite, and vesuvianite. 66 Bearing and plunge of asymmetrical small fold showing clockwise rotation and Thunder Mountain, Idaho: Idaho Bureau of Mines and Geology OZmu is the principle constituent, followed by quartz comprising more than 20 Qal viewed down plunge. Smitherman (1985) reports microcline-rich layers and, in one sample, mats CINNABAR PEAK FAULT Pamphlet 44, 45 p. Kgd Qg percent, and potassium feldspar. Biotite is the most abundant mafic mineral of cross-cutting talc. Thickness is approximately 300 m (980 ft). Lund 60 Qal Smitherman, 1985, Geology of the Stibnite roof pendant, Valley County, Idaho: Qls OZmu Qls Location of Klg. present, occurring as small (<2 mm) well-disseminated flakes that make up (2004) assigned the lower calc-silicate and overlying Fern marble to the 43 Kgd The Cinnabar Peak fault strikes northwest and dips steeply to the northeast. M.S. thesis, University of Idaho, 62 p. OZmu less than 10 percent of the rock. Rare hornblende in mafic inclusions. Missouri Ridge Formation of Neoproterozoic age. We also assign a Neopro- Kgd The fault was originally mapped by Smitherman (1985) as a normal fault, but Stewart, D.E., R.S. Lewis, E.D. Stewart, and P.K. Link, 2013, Geologic map of B’ Tectonic breccia. Myrmekitic intergrowth of feldspar and quartz is conspicuous in thin terozoic age based on stratigraphic position. 60 he did not name the structure. The fault places overturned upper quartzite the central and lower Big Creek drainage, central Idaho: Idaho Geological Kgd section. Termed “quartz monzonite” by previous workers, but quartz Qg Kgd Qg Quartz vein. (Ouq) next to overturned quartzite and schist (Zqs). The fault appears to be Survey Digital Web Map 161, scale 1:75,000. content and feldspar ratios indicate a granodiorite composition using the Zqs Quartzite and schist (Neoproterozoic)—Interbedded light-gray quartzite and parallel or nearly parallel to bedding on both the hanging wall and footwall. Streckeisen, A.L., 1976, To each plutonic rock its proper name: Earth-Science classification of Streckeisen (1976). May also include some granite. Locally medium- to dark-gray muscovite-biotite-quartz-feldspar schist. Schist that Open pit mine headwall. The fault zone is poorly exposed, kinematic indicators were not observed, Reviews, v. 12, p. 1-33. displays a weak to strong foliation, most of which is probably magmatic. comprises approximately 80 percent of the unit consists of as much as 40 E and the interpretation of a fault was largely due to the repetition of strata. Todt, M.K., P.K Link, L.K. Beal, D. Pearson, and M. McCurry, 2014, Sedimentary D A Foliation orientations typically do not parallel mapped faults or the bound- percent small (<1 mm) biotite and muscovite in varying proportions and 60 Base Map Credit Field work conducted 2012-2015. Location and letter of samples used for age determination (See Table 1). Fault relations near the Stibnite stock are also uncertain, but the present provenance of the Upper Cambrian Worm Creek Quartzite, Idaho, using aries of the roof pendants. Locally porphyritic with euhedral potassium percent or more fine-grained quartz and plagioclase in varying proportions. MN interpretation is that the Cinnabar Peak fault is cut by the stock. If correct, the Base digitally scanned from 24,000-scale USGS film separates, This geologic map was funded in part by Q Location and letter of samples used for chemical analysis (See Table 2, At some localities, such as at the headwaters of Fern Creek, the rock is U-Pb and Lu-Hf isotopic analysis of zircon grains: Geological Society of CENTER feldspar crystals as much as 3 cm in length. U-Pb age determination on PROFILEGAP 1973. SCALE 1:24,000 MOUNTAIN Midas Gold Inc. fault would be older than the 85.7 0.1 Ma age of the intrusion. America Abstracts with Programs, v. 46, no. 5, p. 80. GN EDWARDSBURG Plate 2). sample from drill core near the Meadow Creek landing field is 91.2 ± 2.2 phyllitic siltite (or meta-siltite) rather than schist. Smitherman (1985) reports E Shaded elevation from 10 m DEM. 1 0.5 0 1 Digital cartography by Jane S. Freed at the Idaho White, D.E., 1940, Antimony deposits of a part of the Yellow Pine district, Valley 0o 35 13.69o MILE Ma (Table 1). Age is based on 13 zircon rim analyses by laser-ablation andalusite, fibrolitic sillimanite, and chlorite, along with accessory miner- We tentatively interpret the Cinnabar Peak fault to be an overturned thrust Topography by photogrammetric methods from aerial Geological Survey’s Digital Mapping Lab. County, Idaho: U.S. Geological Survey Bulletin 922-I, 279 p. FEET ICP-MS methods at Washington State University (Richard Gaschnig, written als tourmaline, zircon, sphene, apatite, graphite, magnetite, and pyrite. fault, folded by the Garnet Creek syncline (see cross-section E-E’). If correct, photographs taken 1964 and 1972. Field checked 1973. YELLOWPINE PEAK Technical review by Niki E. Wintzer, Stephen E. Box, 1000 0 1000 2000 3000 4000 5000 6000 7000 STIBNITE RAINBOW Yonkee W.A., C.D. Dehler, P.K. Link, E.A. Balgord, J.A. Keeley, D.S. Hayes, commun., 2011). Gillerman and others (2014) report a similar age of ~89 Garnet-bearing schist is reported from 610 m (2000 ft) south of the Hermes thrust motion was originally to the southwest, and represented a hanging Projection: Idaho coordinate system, west zone (Transverse Renee L. Breedlovestrout, Dennis Feeney, M.L.Wells, C.M. Fanning, and S.M. Johnston, 2014, Tectono-stratigraphic DESCRIPTION OF MAP UNITS Ma from “quartz monzonite” collected from a drill hole north of the Yellow mine (Smitherman, 1985). Quartzite is medium grained to coarsely recrys- wall flat on footwall flat. An alternative, less-favored interpretation is that Mercator). 1927 North American Datum. UTM Grid and KILOMETER Virginia S. Gillerman, and Michael E. Ratchford. framework of Neoproterozoic to Cambrian strata, west-central U.S.: 1 0.5 0 1 tallized and moderately sorted and rounded. It contains quartz and musco- 2014 Magnetic North IDAHO Editorial review by Alyson R. Kral. Pine pit (U-Pb zircon LA-ICP-MS analysis). the Cinnabar Peak fault is a late-stage normal fault that post-dates the 10,000-foot grid ticks based on Idaho coordinate system, west Declination at Center of Map Protracted rifting, glaciation, and evolution of the North American Cordille- PEAK BIG CHIEF CHILCOOT CREEK BIG BALDY vite and in one sample 3 percent plagioclase. Locally dark gray due to zone. Contour interval 80 feet Map version 2-13-2017. Garnet Creek syncline. In the following unit descriptions and later discussion of structure we use recrystallization, silicification, or intergranular graphite especially on upper ran margin: Earth-Science Reviews, v. 136, p. 59-95. 1000-meter Universal Transverse Mercator grid ticks, zone 11. PDF (Acrobat Reader) map may be viewed online at the metric system for sizes of mineral or clast constituents of rock units and Fern Creek. Thickness is approximately 130 m (425 ft), but lower contact is QUADRANGLE LOCATION ADJOINING QUADRANGLES www.idahogeology.org. CHALLIS VOLCANIC GROUP Declination from NOAA National Geophysical Data Center. also for small-scale features of outcrops. Unit thickness and distance are assimilated by intrusives. Lund (2004) variously assigned this unit to the listed in both meters and feet (m/ft). Grain size classification of unconsoli- SUGAR MOUNTAIN FAULT The IGS does not guarantee this map or digital data to be Tss Sunnyside tuff (Eocene)—Light tan to medium reddish orange-brown, crystal- Neoproterozoic Moores Station and Plummer Point formations at different dated and consolidated sediment is based on the Wentworth scale (Lane, free of errors nor assume liability for interpretations made rich, moderately to densely welded rhyolitic ash to lapilli tuff. Phenocrysts localities. We too assign a Neoproterozoic age, based on stratigraphic The Sugar Mountain fault strikes northwest and dips steeply to the north- 1947). Intrusive rocks are classified according to IUGS nomenclature using from this map or digital data, or decisions based thereon. as much as 5 mm in size of quartz (commonly partially resorbed), sanidine, position and similarity of detrital zircon ages (sample K, Table 1) to regional east, though it is locally folded. The fault separates overturned lower quartz- normalized values of modal quartz (Q), alkali feldspar (A), and plagioclase and rare biotite and hornblende that comprise from 20 percent to 40 strata of this age as discussed in the following section. ite (Clq) and upper calc-silicate (OCucs) from overturned Edwardsburg (P) on a ternary diagram (Streckeisen, 1976). Volcanic rocks are classified percent of the rock are set in a pervasively altered aphanitic groundmass. Formation (Ze) and the marble of Moores Station (Zmsm). Both the by total alkalis versus silica chemical composition according to IUGS Zqp The unit is made up of multiple cooling units. Some beds contain flattened Quartzite of Profile Creek (Neoproterozoic)—Medium gray, medium- to Edwardsburg Formation and upper calc-silicate units are discontinuous recommendations (LeMaitre, 1984). pumice as much as 15 mm in length. Lithic fragments of volcanics and coarse-grained feldspathic quartzite with feldspar content as much as 20 along the fault, though the fault appears to be roughly bedding parallel. The percent. Plagioclase feldspar is in excess of potassium feldspar and some of 3 quartzite as much as 1 cm in size are present at some intervals. The unit is fault zone is characterized by abundant breccia and fracturing, and locally ubiquitously iron stained and weathers to a coarse soil. the feldspar is interstitial or in veinlets, indicating a secondary origin. is intruded by Tertiary dikes. Iron staining is common along the fault. We SEDIMENTARY DEPOSITS Bedded on a centimeter scale with planar cross laminations and rare graded tentatively interpret the Sugar Mountain fault to be an overturned thrust Tbr Buff rhyolite (Eocene)—Light tan to gray, nearly aphyric, moderately to densely beds. Contains millimeter-scale biotite-rich interbeds and centimeter-scale m Made ground (Recent)—Mine dumps, tailings piles, and disturbed glacial and fault folded by the Tamarack Creek anticline. Like the Cinnabar Peak fault, Table 1. U-Pb zircon ages for igneous rocks and detrital zircons in the Stibnite quadrangle and Profile Creek area. 2.5 welded rhyolitic ash tuff. Rare phenocrysts are as much as 2 mm in size of granule beds. Amphibolite sills present locally. Minimum thickness is stream deposits along East Fork of the South Fork of the Salmon River, we interpret thrust motion to have originally been to the southwest, and to ACKNOWLEDGMENTS quartz (commonly partially resorbed), feldspar, and altered biotite. Pheno- approximately 500 m (1640 ft); base is not exposed. Lund (2004) assigned represent a hanging wall flat on a footwall flat. Some attenuation of the Meadow Creek, and upper Cinnabar Creek. Not shown in upland areas. crysts comprise less than 10 percent of the rock. The aphanitic groundmass this unit to the Gunsight Formation of the Mesoproterozoic age Lemhi Map Sample UTM UTM Unit Consists of cobble, pebble, boulder, sand, and silt-sized material. Many of Edwardsburg Formation and the upper calc-silicate units during folding is Letter number Sampler Latitude* Longitude* Easting** Northing** Location Unit name Lithology Analyst Results is flow banded with discontinuous dark gray flow and compaction laminae Group. A sample collected along Profile Creek, west of the map, contains required for this interpretation. The mapping presented here and the complementary ore deposit research 2 the dumps and tailings have been re-contoured. Hangar Flats; DDH MGI-10-21; 15 zircons analyzed; 13 rims gave 91.2 +/- 2.2 age; 1759 and at millimeter or finer scale and is pervasively altered. Flow laminations are an abundance of 1090-1150 Ma detrital zircons with one as young as 685 of Virginia Gillerman were funded in part by a grant from Midas Gold Inc. A 10RL889 Reed Lewis 44.9022 -115.3352 631216 4973059 Kgd Granodiorite Medium-grained biotite granodiorite Rich Gaschnig J 12DS14 171-174 ft down hole 689 Ma cores Upper commonly folded at millimeter to centimeter scale. Deposit is made up of Ma, indicating that these rocks are more likely Neoproterozoic in age. The relationship between the Sugar Mountain fault and the Cinnabar Peak The authors benefited greatly from discussions on the general geology, quartzite Qal Alluvium (Holocene)—Silt, sand, pebbles, and cobbles formed as channel or Hangar Flats; DDH MGI-10-20; Altered and mineralized fine-grained Few zircons present in sample; three rims gave 87.9 +/- 4.9 Ma B MGI-10-20 Chris Dail 44.8989 -115.3380 631150 4973052 Klg Leucocratic granite Rich Gaschnig multiple cooling units and includes rare vitrophyre as much as 8 cm thick Zircon ages are discussed in more detail in following section. fault is uncertain. These two structures, as well as the Stibnite and Missouri structure, and mineralization of the Stibnite area with Chris Dail of Midas 240-243 ft down hole leucogranite (alaskite) age; 2649, 1466, and 1440 Ma cores I 12DS16 overbank deposits. May include terrace deposits along Tamarack Creek. 1.5 Middle containing small porcelain-like spherical masses with concentric layers, Ridge-Sugar Mountain roof pendants, are offset by the Meadow Creek fault. Gold. Austin Zinsser, Daniella Anguita, and Brian Hardell, also of Midas 18 zircons analyzed; 10 rims gave 84.9 +/- 2.0 age; 1850 to 704 quartzite Clasts are rounded and locally show crude stratification and sorting. C 10RL887 Reed Lewis 44.9272 -115.3182 632646 4976227 N rim, Stibnite pit Kgds Granodiorite of the Stibnite stock Fine-grained muscovite-biotite granite Rich Gaschnig and rare, thin (<50 cm) layers of pumice or lithic-rich tuff. Dark, flattened Gold, were extremely forthcoming and very helpful in providing data and Ma cores Up-on-the-west and right-lateral motion on the Meadow Creek fault D 12DS24 David Stewart 44.9727 -115.3118 633045 4981292 Sugar Mountain Clq Lower quartzite Very coarse-grained quartzite Darin Schwartz principal mode at ca. 1760-1800 Ma Qls Landslide deposits (Holocene)—Silt- to boulder-sized debris; subangular to pumice as much as 6 mm in length is present in some layers. Weathers to indicates the Missouri Ridge-Sugar Mountain roof pendant exposes a in discussing the myriad stratigraphic and structural possibilities for the E 12DS33 Quartzite of E 12DS33 David Stewart 44.9633 -115.3056 633556 4980258 SE of Sugar Mtn OCmmq Quartzite within middle marble Medium-grained quartzite Darin Schwartz numerous 500 Ma, 1630-1800, and 2350-2800 Ma grains L 14DS12 middle marble angular and poorly sorted. Formed by slope failure and characterized by distinctive thin (2-4 mm) plates that form abundant float; forms poor soil deeper crustal section than the Stibnite roof pendant. Assuming both the Stibnite area. Niki E. Wintzer and Stephen E. Box kindly provided helpful 1 with little vegetation. technical reviews. F 10RL888 Reed Lewis 44.9306 -115.3218 632354 4976599 West End Pit Clq Lower quartzite Coarse-grained quartzite Vince Isakson principal mode at ca. 1760-1800 Ma hummocky surface and fan-shaped plan view. Sugar Mountain and Cinnabar Peak faults are overturned folded thrust Relative Probability / Height faults, the Sugar Mountain fault may simply be a separate, deeper level G QPC Austin Zinsser 44.9255 -115.3223 632323 4976033 W of Stibnite pit CZqpc Quartz pebble conglomerate Quartz pebble conglomerate Vince Isakson numerous 1000-1250 Ma, 1350-1500, and 2550 Ma grains F 10RL888 Tdq Lower Qaf Alluvial fan deposits (Holocene)—Pebbles, cobbles, sand, and silt deposited Dime and quarter tuff (Eocene)—Multiple cooling units of densely welded, thrust fault relative to the Cinnabar Peak fault. Alternatively, they could be H 12DS19 quartzite H 12DS19 David Stewart 44.9271 -115.2998 634098 4976246 NW of Fern Mine Clq Lower quartzite Very coarse grained quartzite Darin Schwartz principal mode at ca. 1720-1840 Ma D 12DS24 near the mouth of streams where the gradient decreases. Clasts are lithic lapilli to ash flow tuff of dacitic composition. Green flattened pumice considered the same fault and the Sugar Mountain fault may be linked to 0.5 clasts the size of dimes and quarters, present locally, are diagnostic. More I 12DS16 David Stewart 44.9233 -115.2992 634154 4975825 NW of Fern Mine OCmq Middle quartzite Fine-grained quartzite Darin Schwartz principal mode at ca. 1680-1800 Ma; a few 500 Ma grains Quartz pebble rounded; deposits locally stratified. the Cinnabar Peak fault by a lateral ramp, present along the dismembered conglomerate J 12DS14 David Stewart 44.9203 -115.3007 634043 4975489 NW of Fern Mine Ouq Upper quartzite Coarse-grained quartzite Darin Schwartz principal mode at ca. 1800-1840 Ma G QPC extensively exposed northeast of the map area in the Big Creek drainage stratigraphic zone north of Sugar Creek. This lateral ramp would have to Quartzite and K 14RL011a Qg schist Glacial deposits (Pleistocene)—Unsorted to poorly sorted cobbles, gravel, (Stewart and others, 2013) and to the south along Indian Creek (Fisher and K 14RL011a Reed Lewis 44.9303 -115.2947 634493 4976610 NE of Cinnabar Peak Zqs Quartzite and schist Medium-grained quartzite Vince Isakson numerous 1000-1250 Ma grains 10RL893 have been reactivated by the Meadow Creek fault, and the presence of such — Quartzite of boulders, and sand deposited as lateral, ground, and end moraines. 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 others, 1992). Pro le Creek a lateral ramp may have induced the transtensional bend in the Meadow L 14DS12 David Stewart 44.9931 -115.3708 628347 4983463 Missouri Ridge OCmmq Quartzite of middle marble Calc-silicate quartzite Vince Isakson numerous 500 Ma, and 1700-1800 Ma grains Includes outwash material in the lower elevations. Some material has been Creek fault. However, if the Cinnabar Creek and Sugar Mountain faults are – 10RL893 Reed Lewis 44.9751 -115.4197 624532 4983463 Profile Creek (W of map) Zqp Quartzite of Profile Creek Feldspathic quartzite Vince Isakson numerous 1050-1200 Ma and 1450 Ma grains re-worked by streams. Lateral moraine deposits extend as much as 125 m Tdqs Sedimentary rocks of dime and quarter tuff (Eocene)—Boulders and cobbles both normal faults (i.e. Smitherman, 1985), both may be the same structure, (410 ft) above valley floor. of dacitic volcanic rock and biotite granodiorite. Possibly a lahar deposit. *NAD 27 Age (Ma) with the Sugar Mountain fault representing the structure at a deeper level. **UTM, Zone 11, NAD 83 Figure 1. Age-probability plot of detrital zircon U-Pb analyses from the Stibnite quad- Tll Lower latite lava (Eocene)—Crystal-poor, flow-layered latite lavas and porphy- Analyses are by laser-ablation ICP-MS methods performed at Washington State University, Pullman, Washington, or at Boise State University, Boise, Idaho. rangle and Profile Creek area. ritic dacite and rhyodacite flows. Shown only in cross section and on regional geologic map (Fig. 2). Exposed south of map area in Indian Creek drainage (Fisher and others, 1992).

Published and sold by the Idaho Geological Survey University of Idaho, Moscow, Idaho 83844-3014 GEOLOGIC MAP 51 IDAHO GEOLOGICAL SURVEY STEWART AND OTHERS MOSCOW-BOISE-POCATELLO IDAHOGEOLOGY.ORG PLATE 2

115° 30' 115° 00' 114° 45'

45° 15' * | A A’

Ti | Ti ¡ |

| Ti Cold ¡ 8,000 8,000

| | Mountain Ys | | Ki Ys | Ti Ys Ki Whiskey

¡ ¡ OC– mm Creek fault Zmsm OC– ucs Papoose Ys 7,000 7,000

Zs FAULT Ys Peak ¬

Ti Zs ¬ Zfm

| * Zmss –

FAULT CZqpc

¬ | Zi ¡ Zfm

Ys |

¡ Zlcs | Ys | Ys Zmss C– lq

| Tdq

| ¹ 6,000 6,000

¬

| ¬ Zqp ¡ | ¹ Zs Acorn Ys Black Zqs MEADOW Ti Zs ¹ Butte Butte Zqp Zlcs Wolf Fang ¡ *

Zs ¬

¹ * Zqp FEET Peak ~ Zi Zmss Missouri Ridge ¹ Zqs

* 5,000 5,000 * Tdq ¡ fault McFadden FEET Zqp | Zmss Ki | | Zs Peak Zi ¡

| | Ys C– lq Zqp | ¬ Zmsm FAWN Zmsm Zmss

| Zi ¡ Ti 4,000 4,000 Zs

¡ EXPLANATION HOGBACK

| Horse

| Ys ¡ Zqp Mountain C– lq

| ¬ Tdq Ys | ¬ Tdq  * Ÿ ¡ Tdu Eocene dikes. 3,000 Kgd 3,000 | Ys ¬ ~ Ÿ Whiskey | PzZs Kgd

| | Edwardsburg Zs FAULT ¡ Creek ¡ | Ti Zmss ¬ Zs Zi Eocene intrusive rocks. Routson Taylor fault

| Center |

|

Ki ~ Peak Rush Creek

Mountain Ranch 2,000 2,000 | | * ¡ ¡ Peak ) Tla

* Ys Latite flows. Quaternary surficial units too thin to show.

| ¬ Zs FAULT * Zi | Ti ¬ | GRABEN No vertical exaggeration.

| Tssu Upper Sunnyside tuff. ¡ ¡ ¡ Scale 1:24,000 | ¡ CREEK ¡ ¡ Ys ¬ Ys Ys | | ¡ Tmbx Megabreccia. ¡ | ¡ ¬ | | 1. Dime and quarter CREEK | ¡ Ys Zi

¡ Cougar ¡

| Tssl | Lower Sunnyside tuff. Peak

| caldera Ys ¬

|

| ¡

| Tbr Tdq ¡

* CAVE BIG Dave Lewis |

| Tbr | Tssl Buff rhyolite.

¡ Peak Ti

| ¡ * Tbr ¬ Tdq Tssl Ti |

| ¡ Lookout | The ¡ Mountain Tdq Dime and quarter-size lapilli tuff.

| Pinnacles ¬ * Ki

¡ | * | ¬

| Mormon ¡

| Tbr CREEK Tll ¡ Tbr Lower latite lava. ¡ ¬ Tla Peak | Tbr |

¬ *

Ki ¬

| Zs | ¬

| ¡

| PzZs Tbr

¡ Te Tuff of Ellis Creek.

¡

¡ 5. Graben Tdq

ª ¡

| | ¬ ¡ ¬ Cinnabar Peak ¡ collapse Ti Fern |

Ridge GROUP VOLCANIC EOCENE CHALLIS | Two Point | ¬ ¬ Tdf Dacitic and rhyodacitic lava. fault Caldera complex

Van Meter Peak Creek Hill | Missouri ¡ COW bounding fault | *

|

ª PzZs

« * ª Te Ki Cretaceous intrusive rocks. B C– Zpqc B’ ¡ Fern

| Tla

| | Ki ¡ 9,000 9,000 « ¬

| « Tla fault

¡ ¡ ¡ East Fork of A Yellow ¬ PzZs Paleozoic and Neoproterozoic sedimentary rocks. West End

| |

| Zs ª 2. Buff ¬ South Fork of Zfm

Pine | Tbr Shellrock « fault

ª Zs Meadow Creek T | ¡ Zfm rhyolite ¬ Peak | ¡ Tdq Salmon River ¡ Whiskey Creek

| | Ki Tbr Tla * Zi fault

| ¡ Neoproterozoic intrusive rocks. 8,000 Zlcs Ocs C– lq 8,000 Zs ¡ caldera ¡

| | Tssl fault

| ª * ¬ OC– mm Zqs ª ¬ Tdq

| ª ¬ Zqs Zqs

| ¡ ¬ | Ki Thunder Te Zs Neoproterozoic sedimentary rocks (Winderemere Group). Sugar OC– ucs

FAULT Salt Creek

| Mountain ¬ Te FAULT ¡

¡ | | « ¡ Zlcs Cinnabar ¡ fault Creek C– lq

| Tbr Tla Zfm Zlcs Tss

| « 7,000 Kgd 7,000

Peak ¬ Ys Mesoproterozoic sedimentary rocks (Belt Supergroup). ~ ¬

| * Salt Zlcs Zfm Kgd

| Tdp Zqs

| | Tdq OZmu C– Zpqc

¡ ¬

CREEK « Ki Tssl Zmss

Ti ¡ ¬ Creek ¡ « –

Ki ¡ Zfm CZpqc Cinnabar Peak

| | ¬ ¬ –

¬ Tssu T Clq Zlcs T Zqs fault | ¡ SALT « – Ouq CREEK Tbr Te 6,000 Zqp CZpqc 6,000

| PzZs A Timi | ¬ A Zqs

| ¬ FEET Tdq ¡ Bear Creek Zqp Kg ~ Tssu OZmu Zqs

| Murphy ¡ Kg

¬ Point Ouq ¡ ¬

¡

Inferred caldera boundary or FEET | | Peak ¡ ¡ ¬ * ¡ ¡

| * ¡ Cinnabar Peak

¬ Ki PzZs ¬ 4. Upper ¡ graben collapse feature. Ouq

| ¡ C– Zpqc ¬ 5,000 OZmu 5,000

Johnson Creek shear zone PzZs Tssu Zmss Kgd Ohm fault Tbr

Sunnyside ¡ ¡ | | ¬ ¬ | | ¡ MEADOW Tssl Tssu Tdq Cinnabar Peak | Meadow Creek caldera Ohm Tssl ¡ | fault | Lookout * Stibnite quadrangle

| Tmbx Zmss Kgds Tdq

¡

¬ ¡ ¬ 3. Lower 0 5 Miles 4,000 4,000

| | ¬ ¡ T A

PzZs ¡ Tll T | ¡ Sunnyside Kgd ¡ A

| | PzZs ¡ T caldera Zs Kgd Kgd | Tssu | Tssl A

|

¡

Ÿ Ÿ Ÿ

Ki ¡ ¡ Grays C– lq

| 3,000 A T 3,000

| | ¡

¡ ¡ Ÿ Ÿ Tssu ¬ T

Ÿ Ÿ Peak Tssl 0 5 10 Kilometers A OZmu

| Tssl |

PzZs ¬ Ÿ * ¬ Tdq ¡

Tdq Ÿ Ÿ Ÿ Tmbx Sugar Mountain ¡ T | | ¡ A

Ÿ Ÿ Ÿ

|

PzZs ¡ fault

| Ÿ Tdq? ¡

Ÿ Ÿ 2,000 2,000

| |

Ÿ Ÿ ¡

| ŸŸ Ÿ Ti PzZs ¡ Quaternary surficial units too thin to show. Ÿ ¡

| | Ÿ Ÿ Ti ¡ Swarm | Ÿ No vertical exaggeration. | PzZs C-C’ D-D’ E-E’ PzZs Tdu Ÿ Ÿ Ÿ Ki

| Ÿ ¬ Tdq Tssu Scale: 1:200,000 Scale 1:24,000

DikeŸ PzZs Ti | | Ÿ Ÿ Ÿ ¬ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ PzZs Tdq PzZs ¡ Big Ÿ | Ÿ | Tll Creek Ÿ Baldy*

Ÿ Ÿ Ÿ Ÿ Ki Tssl ¬

| Chicoot Ÿ Ÿ Tll Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ Peak Ÿ Ÿ Ÿ Ÿ | PzZs Ÿ | Ÿ Ÿ * PistolŸ Ÿ Ÿ PzZs Ki Ÿ Ÿ Ki Tdf Ÿ Ÿ Tdu Ti PzZs Ÿ Ÿ Ÿ

| Ÿ Ÿ Ÿ ¬ Ÿ Ÿ Ÿ Ÿ Ÿ PzZs Ki Ÿ ŸŸ 44° 45' Ÿ Ÿ Ÿ Ÿ

Figure 2. Regional geology of the Stibnite and Big Creek area.

REGIONAL VOLCANIC STRATIGRAPHY AND STRUCTURE Sugar Mountain Caldera complex C East Fork of fault bounding fault C’ The Stibnite quadrangle is a small piece of the stratigraphically enigmatic The faults bounding the Big Creek graben extend into the Tertiary intrusive In the Stibnite quadrangle the Meadow Creek-West End fault zone, 9,000 South Fork of 9,000 and structurally cryptic area that is central Idaho. Figure 2 shows the rocks (Ti) to the northeast and into Cretaceous batholith rocks to the south- predominantly a right-lateral strike-slip structure, offsets the trace of the Salmon River surrounding area where regional structures and trends illuminate what we west (Ki). Southwest of the upper Sunnyside (Tssu) caldera the graben has Cinnabar Ridge fault and the Sugar Mountain fault by some 3.5 km (2.2 mi). Tamarack Kgd find at Stibnite, while at the same time findings from detailed work at been down-dropped less and exposes a deeper crustal section containing This is assuming that the Cinnabar Ridge and Sugar Mountain are the same Creek 8,000 Zmss 8,000 Stibnite encourage speculation as to possible connections with what is dime and quarter tuff (Tdq) and equivalent Tertiary intermediate intrusive fault (see Structure section on Plate 1). In the Big Creek quadrangle 20 km Zmsm Zqs found outside the confines of the quadrangle. The following discussion is rocks in which are exposed tabular, north-northeast striking intrusive bodies (12 mi) to the north the Hogback fault, also a right-lateral strike-slip fault, Whiskey Creek Zmss based on work by Stewart and others (2013), Lewis and others (2012), that comprise the Pistol Creek dike swarm (Tdu). This indicates that the Zlcs displaces Neoproterozoic metasedimentary rocks there by approximately 4 fault Fisher and others (1992), Lund (2004), and our reconnaissance efforts. Pistol Creek dike swarm either post-dates the dime and quarter tuff and km (2.5 mi) (Lewis and others, 2012). This raises the possibility that these 7,000 Zmss 7,000 Zmss Zlcs Zfm pre-dates the upper Sunnyside tuff, or, less likely, that the intrusive event is two faults are the same. The Hogback fault has been traced with confidence Zmss C– lq OC– ucs younger than the upper Sunnyside tuff but the dikes died at depth and did by the authors southward to the northern edge of the dime and quarter C– Zqpc C– lq THUNDER MOUNTAIN CALDERA COMPLEX not penetrate the younger, higher level volcanics. caldera (Fig. 2). Recent mapping by the authors suggests that it may 6,000 Tdq? 6,000 – FEET continue into the Eocene volcanic deposits as far as the ridge west of Zfm CZqpc FEET Zqp While the Thunder Mountain area east of the Stibnite quadrangle clearly Zqp Kgd Cougar Peak in the central part of the dime and quarter caldera and on to FEET contains collapse features such as normal faults and megabreccia, the The faults that bound the caldera complex are not uniform in nature, near the confluence of Tamarack and Bum Creeks after which it may trend 5,000 Zqp 5,000 Eocene volcanic field shown in Figure 2 is extremely large, too large to be reflecting the compositionally heterogeneous and structurally compro- south-southeast and then southward, defining the southern edge of the a single caldera. It is perhaps for this reason that Fisher and others (1992) mised crustal block in which the magma chambers that fed the Tertiary Thunder Mountain caldera complex as far as the saddle east of Sugar Moun- Zmss referred to the area as the “Thunder Mountain cauldron.” In this study we pyroclastic eruptions developed. Some segments of the caldera-bounding tain (Plate 1). Expression of the fault zone within the volcanics does not term the area a “caldera complex” and propose a possible sequence of fault system are characterized by large (10 m) blocks of collapse debris such demonstrate post-Challis strike-slip movement but is indicated by abundant 4,000 Zmss Tll 4,000 events to produce the extensive and dominantly fault-bounded volcanic as those found in the Stibnite quadrangle north of Sugar Creek. Portions of iron staining, brecciation, and by kilometers-long dikes that cut the volca- Kgd Zmsm field that we see at present. the faults bounding the caldera complex have been intruded by mafic nics and which are up to 50 m in width. Ze Eocene bodies north of Cane Creek (Plate 1), or are marked by abundant 3,000 C– lq Kgd Kgd 3,000 breccias and iron staining as is found west of Murphy Peak and south of the The northward extension of the Meadow Creek fault is not directly aligned Sugar Mountain Ze Previous mapping by Fisher and others (1992) has established that at least Pinnacles (Fig. 2). Local exposures of sediments rest unconformably on Tdq with the most southward known extension of the Hogback fault. North of its fault Zmsm Timi four of the ash-flow deposits associated with the Thunder Mountain vents and contain internal angular unconformities, indicating that subsidence intersection with the fault that bounds the caldera complex there is no were produced by large-volume eruptive events. They also assigned expression of the Meadow Creek fault within the volcanics. Presumably the 2,000 2,000 was a protracted process, at least during formation of the Tdq caldera. On Quaternary surficial units too thin to show. informal names to these four units. The oldest is the dime and quarter tuff fault trace turns northwesterly and provided the zone of weakness along the east edge of the Stibnite map a block of biotite granodiorite (Ki on Fig. No vertical exaggeration. B-B’ D-D’ sequence (Tdq), followed by the buff rhyolite (Tbr), the lower Sunnyside tuff 2) 1 km across lies entirely surrounded by volcanics, with faults on its which the segment of the caldera complex bounding fault southeast of Scale 1:24,000 (Tssl), and finally the upper Sunnyside tuff (Tssu). While it is difficult to western and eastern margins; observations did not establish whether the Sugar Mountain activated following eruption of the buff rhyolite (Tbr). establish with precision where the collapse boundaries following the four block is rooted or if it is an extremely large slide block. Alternatively, if the Meadow Creek fault and the Hogback fault are not eruptive events might have been, this regional map presents a first attempt directly connected they may be en echelon right-lateral strike-slip faults. at postulating outlines for the linked calderas that may have produced the Regardless of their exact relationship, the Meadow Creek fault and the present caldera complex. These outlines are based primarily on where each POSSIBLE EXTENSIONS OF Hogback fault are segments of a deep-seated north-trending system of faults ash-flow deposit is preserved and, in the case of the upper Sunnyside tuff, STIBNITE QUADRANGLE FAULTS that accommodated largely right-lateral strike-slip motion. The short the presence of collapse-associated megabreccia (Tmbx). Following the eastward jog that the Meadow Creek fault takes along the caldera complex four eruptions, each forming its respective caldera, there was a fifth The Salt Creek fault was traced by the authors southwest up Salt Creek and bounding fault may be due to strain refraction as the stress generated by the collapse event, the Big Creek graben collapse. This may have taken place off the quadrangle, where it offsets batholithic rocks. The Salt Creek fault deep, north-south fault zone intersected and interacted with the northwest- soon after the latest caldera collapse, or over an extended period after also likely continues to the northeast into the dime and quarter caldera near striking folded strata of the roof pendant. volcanic activity ended. the confluence of Bum Creek with Tamarack Creek, based on linear north- northeast striking creeks and alignment of saddles. It does not appear to significantly displace the caldera-bounding fault, suggesting that post-Challis slip was insignificant. Sugar Mountain fault

Caldera complex bounding fault D OC– mm D’ 9,000 East Fork of 9,000 South Fork of Zmsm Meadow Fiddle Salmon River Zmss Tamarack 8,000 Creek Creek Zmss 8,000 Sugar Zmss Creek Yellow Pine Zlcs Creek OC– ucs Qg pit Zmss Ze Qg C– lq Qal 7,000 7,000 OC– ucs Zfm OZmu Qg OZmu C– lq Qal Zqs Zfm Qg Tdq? OZmu Table 2. Major oxide and trace element chemistry of samples collected in the Stibnite quadrangle. 6,000 6,000 OZmu Zqp? FEET C– Zqpc Major elements in weight percent Trace elements in parts per million FEET C– Zqpc Tdq? OZmu Map Sample Map 5,000 5,000 † †† Meadow Creek letter number Latitude* Longitude* Lithology Unit name unit SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 Sum LOI Ni Cr Sc V Ba Rb Sr Zr Y Nb Ga Cu Zn Pb La Ce Th Nd U Co fault Zmss M 12DS42 44.8955 -115.3080 hb diorite Granodiorite pod in Kgd 59.13 1.127 17.45 5.55 0.103 3.67 5.43 3.39 2.25 0.222 98.31 9 11 13 146 897 66 815 353 17 23.5 20 4 81 5 22 46 6 23 2 Kgd N 12RL154b 44.8890 -115.2894 bt granodiorite Granodiorite Kgd 69.33 0.47 15.78 2.81 0.060 0.71 2.50 4.00 3.67 0.360 99.69 0.52 8 11 3 37 1012 149.2 527 268 22.3 51.6 27.2 13 52 16 55 121 28.6 4.7 1 4,000 Kgd Zqs Tll 4,000 O 12DS43 44.8957 -115.3128 2-mica granite Granite Kg 73.05 0.040 14.58 0.91 0.366 0.06 0.86 3.82 4.65 0.095 98.42 0 3 4 6 402 144 200 124 65 41.1 16 1 3 17 20 34 12 15 10 OZmu P 12DS44 44.8967 -115.3169 2-mica granite Granite Kg 72.19 0.176 14.32 1.48 0.060 0.29 1.18 3.87 4.13 0.081 97.80 0 5 3 13 640 141 277 126 27 39.9 18 0 30 17 43 79 19 28 4

Q 12ES016 44.8933 -115.2713 2-mica granite Granite Kg 73.91 0.123 14.83 0.59 0.073 0.12 0.43 3.20 4.78 0.136 98.20 0 5 5 8 524 144 187 83 27 47.2 20 1 1 16 26 42 11 16 3 3,000 Zmss Timi 3,000 R 14RL015 44.9272 -115.3198 mu-bt granodiorite Stibnite stock Kgds 71.66 0.15 16.34 1.37 0.060 0.41 1.73 4.46 3.11 0.210 99.50 0.95 12 28 1 14 655 133.4 538 150 11.5 28.9 29.7 8 33 2 32 59 6.6 0.5 <1 Kgd S 12DS46 44.9088 -115.2628 dacite Int. and mafic intrusives Timi 63.07 0.715 15.43 4.72 0.063 2.11 4.25 3.16 3.30 0.229 97.04 7 68 14 96 1086 105 476 219 27 16.5 22 14 71 17 58 91 16 47 3 Kgd

T 12ES014 44.8824 -115.2573 dacite Int. and mafic intrusives Timi 62.58 0.682 17.24 3.89 0.052 1.70 2.68 4.10 2.92 0.220 96.06 11 59 10 68 1259 89 708 205 17 14.8 23 6 69 18 40 73 12 33 3 2,000 2,000 Some Quaternary surficial units too thin to show. *NAD 27 No vertical exaggeration. B-B’ C-C’ All analyses by X-ray fluorescence methods. Samples 12RL154b and 14RL015 analyzed by Stanley Mertzman at Franklin and Marshall X-Ray Laboratory, Lancaster, Pennsylvania; remainder of samples Scale 1:24,000 analyzed by Washington State University (WSU) GeoAnalytical Laboratory, Pullman, Washington. † Franklin and Marshall reports total iron as Fe2O3. ††WSU reports total iron as FeO.

E Caldera complex E’ 9,000 East Fork of bounding fault 9,000 South Fork of Salmon River Sugar 8,000 Creek 8,000 C– lq Zqs Kgd OC– mm Zfm Kgd Zlcs Qg Tbr OZmu C– lq OC– ucs 7,000 Qg C– Zqpc 7,000 OZmu OC– ucs Ouq

Kg FEET OZmu OZmu 6,000 Zlcs 6,000

FEET Kg fault Tdq OZmu Zqs OZmu Cinnabar Peak 5,000 Ouq C– lq 5,000 Meadow Creek OC– mm Kgd fault Timi Kgd Ohm Kgd Tll 4,000 OC– mq 4,000 Kgd Kg T A OZmu 3,000 3,000 Some Quaternary surficial units too thin to show. No vertical exaggeration. B-B’ Scale 1:24,000

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