GEOLOGIC MAP of the LINE POINT QUADRANGLE, BOUNDARY COUNTY, IDAHO, and Tion by Cominco (Hamilton and Others, 2000)

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white graded or nongraded argillite tops. Conspicuous bar code-like REFERENCES patterns in the middle, formed by alternating dark and light siltite, persist regionally (Huebschman, 1973) and have been used as markers for correla- GEOLOGIC MAP OF THE LINE POINT QUADRANGLE, BOUNDARY COUNTY, IDAHO, AND tion by Cominco (Hamilton and others, 2000). Siltite and argillite couplets, Anderson, H.E., and D.W. Davis, 1995, U-Pb geochronology of the Moyie sills, with dark, less commonly light tops, have even and parallel, uneven, wavy Purcell Supergroup, southeastern British Columbia: Implications for the or undulating lamination. Rusty nature of outcrop is due to weathering of Mesoproterozoic geological history of the Purcell (Belt) basin: Canadian CORRELATION OF MAP UNITS abundant sulfides, commonly pyrrhotite. Dominant lamination style and Journal of Earth Sciences, v. 32, no. 8, p. 1180-1193. LINCOLN COUNTY, MONTANA concentration of sulfides vary between members. Quartzite in 2-20 dm beds Anderson, H.E., and W.D. Goodfellow, 2000, Geochemistry and isotope chem- Alluvial and Colluvium and Glacial and Related Deposits is light weathering, averages about 60 percent quartz, 20 percent plagio- istry of the Moyie sills: Implications for the early tectonic setting of the Lacustrine Deposits Mass Wasting Deposits clase, with the rest mostly white micas and 5 percent biotite (Cressman, Mesoproterozoic Purcell basin, in J.W. Lydon, Trygve Höy, J.F. Slack, and 1989). Previous mapping in this area and to the east by Cressman and Harri- M.E. Knapp, eds., The Geological Environment of the Sullivan Deposit, Qlm Qt Holocene Qcg son (1986) subdivided only the top of the Prichard. Here, we follow alpha- British Columbia: Geological Association of Canada, Mineral Deposits 1 1 1 1 2 Quaternary betic member assignments following usage of Cressman (1989). Presence Division, Special Publication No. 1, p. 302-321. Russell F. Burmester , Roy M. Breckenridge , Mark D. McFaddan , Reed S. Lewis , and Jeffrey D. Lonn Qgo Qg Qgt Qgk Pleistocene versus lack of sedimentary structures reflecting strong currents or soft Bishop, D.T., 1973, Petrology and geochemistry of the Purcell sills in Boundary sediment deformation are lithologic criteria used to distinguish adjacent County, Idaho, in Belt Symposium, v. 2: Idaho Bureau of Mines and 2012 members, but assigning quartzite packages with similar characteristics to Geology Special Publication, p. 16-66. Intrusive Rocks different members was facilitated by release of mapping by Cominco with Bishop, D.T., 1976, The petrology and geochemistry of the Purcell sills, Bound- control based on “markers” (Michael Zientek, written commun., 2003). ary County Idaho and adjacent areas: University of Idaho Ph.D. disserta- These markers served for the upper units down through Ype. Locations of tion, 147 p. some of these markers north of the international border (Glombick and Breckenridge, R.M., and W.M. Phillips, 2010, New cosmogenic 10Be surface Neoproterozoic Ymi 5 others, 2010) aided matching contacts to the north. Cominco did not map exposure ages for the Purcell Trench lobe of the Cordilleran Ice Sheet in Idaho: 55 Ymi Ypf Ypf Qgt below Ype, so our attempt to identify lower units is based partly on correla- Geological Society of America Abstracts with Programs, v. 42, no. 5, p. 309. 65 40 Ypac Belt-Purcell ZYmi Yph Qgt tion of the lower-middle Aldridge contact with the top of a concentration of Brown, D.A., J.A. Bradford, D.M. Melville, A.S. Legun and D. Anderson, 1994, Qcg Supergroup Ypf 55 sills just north of the border (Glombick and others, 2010), or the Ypb-Ypc Geology and mineral deposits of Purcell Supergroup in Yahk map area, Ymi contact (Michael Zientek, written commun., 2003) and on the subdivisions Ysh southeastern British Columbia (82F/1), in B. Grant and J.M. Newell, eds, Ypf 1 of Finch and Baldwin (1984). However, we were unable to locate the base Geological Fieldwork 1993: A Summary of Field Activities and Current Ypt Qgt Ysn Ypg 20 of Ypc on this map and therefore lumped it with lower units as Ypac. Research Geological Fieldwork 1993: British Columbia Ministry of Energy, 65 Qg 45 Yw Mines and Petroleum Resources Paper 1994-1, p. 129-151. Ypf 50 Prichard Formation, transition member (Mesoproterozoic)—Gray to Ype Ypt Burmester, R.F., 1985, Preliminary geologic map of the Eastport area, Idaho and Ypf Yhw greenish gray to white siltite, dark gray or black argillite, and white quartz- Qgo 65 Ype 40 Montana: U.S. Geological Survey Open-File Report 85-517, 10 p., scale 1:48,000. Ymi Ypac Ysr ite. Tops of siltite and argillite couplets typically have discontinuous cracks Ypf Burmester, R.F., 1986, Preliminary geologic map of the Leonia area, Idaho and 65 that appear spindle shaped in plan view and ptygma-like in section. Yr Mesoproterozoic Montana: U.S. Geological Survey Open File Report 86-554, 13 p., scale 1:48,000. Ymi 35 Argillite also occurs as 10-50 cm thick massive beds. Siltite beds 3- 10 cm 70 Yb Burmester, R.F., R.M. Breckenridge, R.S. Lewis, and M.D. McFaddan, 2004, 2 thick are cross laminated or have internal grading from light to dark gray Geologic Map of the Clark Fork quadrangle, Bonner county, Idaho: Idaho Yb1 70 Yb1 where internal structure is visible; parting more commonly platy than Ymi Geological Survey Digital Web Map 25, scale 1:24,000. Qgt Ypt slabby. Brown-weathering carbonate as 1 cm layers and pods are low in the 85 Burmester, R.F., R.M. Breckenridge, M.D. McFaddan and R.S. Lewis, 2006, Qcg Qcg Qgt section. Siltite beds increase upward in relative abundance and become Yph Geologic Map of the Derr Point quadrangle, Bonner and Shoshone counties, olive drab where weathered. Quartzite is fine grained and characterized by Ypf Ypg Idaho: Idaho Geological Survey Digital Web Map 59, scale 1:24,000. 35 dark planar laminations, as well as common ripple and larger low-angle Burmester, R.F., R.S. Lewis, M.D. McFaddan, R.M. Breckenridge, D.M. Miller and Ypg Ymi 35 YPd Ypf cross laminations, hummocky cross lamination, small “dish” structures, Yph Ymic F.K. Miller, 2007, Geologic Map of the Cocolalla quadrangle, Bonner county, 70 Ype Ype and scattered load structures 5-15 cm in depth. Dark specs within siltite Qgk Ymi Idaho: Idaho Geological Survey Digital Web Map 91, scale 1:24,000. Ype appear to be biotite low in unit but magnetite toward the top. Argillite 60 Ypd Burtis, E.W., J.W. Sears, and K.R. Chamberlain, 2003, Windermere sill and dike 80 Qcg parting surfaces have 2-5 mm long rectangular voids where chloritoid (?) complex in northwestern Montana: implications for Belt-Purcell Basin: Ymi Qg Ypac Ypm weathered out. Upper contact placed above highest recognized dark gray Northwest Geology, v. 32, p. 186-189. 50 35 argillite tops, where lighter greenish-gray argillites of Yb dominate. Best Ymic? 1 Chugg, J.C., and M.A. Fosberg, 1980, Soil survey of Boundary County, Idaho: exposed on FS Road 2540 north-northwest of Deer Ridge Lookout. Thick- Ymi United States Department of Agriculture Soil Conservation Service and 60 ness 600 m (2,000 ft). Mapped here and immediately to the east (Cressman Ypf United States Department of the Interior Bureau of Indian Affairs in coop- and Harrison, 1986) as “transition zone” into overlying Burke Formation 80 60 eration with University of Idaho College of Agriculture Idaho Agricultural 80 Qcg whereas elsewhere included in Burke (e.g., Cressman, 1985) or Creston Qgt Experiment Station, 75 p. Ypg 55 Formation (Brown and others, 1994). 80 Ypf Cressman, E.R., 1985, The Prichard Formation of the lower part of the Belt 20 Supergroup, Proterozoic Y, near Plains, Sanders County, Montana: U.S. 85 75 Qgt INTRODUCTION Yph Prichard Formation, member h (Mesoproterozoic)—Laminated gray siltite Ype Geological Survey Bulletin 1553, 64 p. Ymi and black argillite couplets to microlaminated black argillite with white Ymi Ypf Qt siltite “lines,” and minor brownish siltite and light-weathering quartzite. Cressman, E.R., 1989, Reconnaissance stratigraphy of the Prichard Formation Yb1 Ypf 30 Ymi 55 Quaternary deposits on the Line Point quadrangle were mapped in 2010 as found near Wallace, Idaho, by carbonate-free strata (Ysn). Subdivision Laminae and microlaminae characteristically very even, planar and (Mesoproterozoic) and the early development of the Belt basin, Washington, Qgt 65 and 2011 by R.M. Breckenridge. Bedrock was mapped in 2009 and 2011 follows Lemoine and Winston (1986) and Burmester (1985), but only the continuous. Parting commonly 2 mm to 5 cm. Weathers with a distinct Idaho, and Montana: U.S. Geological Survey Professional Paper 1490, 80 p. 65 85 by R.F. Burmester, M.D. McFaddan, and R.S. Lewis and in 2011 by J.D. lower unit is exposed in this quadrangle. rusty veneer. Siltite beds are 3-10 cm thick with slabby parting; quartzite Cressman, E.R., and J.E. Harrison, 1986, Geologic map of the Yaak River area, Yb 75 65 Ypg 40 Ymic 2 70 Ype Ymi Lonn to modify previous mapping (Burmester, 1985) for consistency with beds are 3-5 dm in middle of unit and 2 dm about 30 m (100 ft ) above Lincoln County, northwest Montana: U.S. Geological Survey Miscella- Ypac Ysh Shepard Formation, member 1 (Mesoproterozoic)—Tan- and brown- Qg Ype unit definitions and contact placements used in more recent mapping. 1 base. Rare centimeter-scale calcareous silty laminae weather recessively. neous Field Studies Map MF-1881, scale 1:48:000. Ymi 15 weathering uneven couplets of green siltite and carbonate-bearing light Typically forms very platy talus, but where parting is poorly developed, Evans, K.V., J.N. Aleinikoff, J.D. Obradovich, and C.M. Fanning, 2000, SHRIMP Yph Ypf 35 The oldest and most abundant rocks in the quadrangle are low metamor- green argillite. Includes intervals of unevenly laminated dark green siltite U-Pb geochronology of volcanic rocks, Belt Supergroup, western Montana; Ymi Qt A' forms bare, rounded outcrops and large boulders. Upper contact placed at YPd phic grade metasedimentary rocks of the Mesoproterozoic Belt-Purcell and light green argillite, and white quartzite. Nonresistant horizontal lowest occurrence of white quartzite and pinch-and-swell siltite and evidence for rapid deposition of sedimentary strata: Canadian Journal of Qcg Ypt 68 Qcg Supergroup. The lowest strata host penecontemporaneous mafic and differ- limestone pods usually weathered out. Contorted chip layers, soft sediment argillite couplets of overlying Ypt. Best exposed across ridge between Keno Earth Sciences, v. 37, no. 9, p. 1287-1300. Ypf 10 entiated sills. All are exposed on the west flank of the Sylvanite anticline deformation, and centimeter-scale loads and flames are typical. Siltite and and Skin Creeks but most accessible on FS Road 2540 north of Deer Ridge Finch, J.C., and D.O. Baldwin, 1984, Stratigraphy of the Prichard Formation, Ypg 72 east of the Moyie fault (Fig. 1). During Pleistocene glaciations, the Cordille- quartzite are commonly cross-laminated or occur as starved ripples that Lookout. Thickness about 500 m (1,600 ft). Nicknamed the “lined unit” of Belt Supergroup, in S.W. Hobbs, ed., The Belt: Abstracts with Summaries, Ype Ymi form lenticular bedding. Top not on map; thickness to the south probably 45 ran Ice Sheet repeatedly advanced southward across the quadrangle from the Prichard Formation; equivalent to the Upper Aldridge Formation in Belt Symposium II, 1983: Montana Bureau Mines and Geology Special 10 Ymi Ymi 10 Canada. Cosmogenic Be surface exposure ages (mean weighted) less than 500 m (1,500 ft). Canada. Publication 90, p. 5-7. Qgt constrain the glacial maximum ice limit near the Clark Fork ice dam at 14.1 Glombick, P., D.A. Brown, and R.F. MacLeod (compilers), 2010, Geology, Yahk, Qgo Ymi Yb 50 Snowslip Formation (Mesoproterozoic)—Divided into three members where 1 Ypf ± 0.6 ka (Breckenridge and Phillips, 2010). Kame deposits near the United Ypg Prichard Formation, member g (Mesoproterozoic)—Green-gray siltite, British Columbia: Geological Survey of Canada, Open File 6153, scale 1:50,000. 65 10 mapped to the south as argillite of Howe Mountain (Burmester and others, Ypf States-Canada border constrain the ice recession ( Be range) from 13.3 to dark gray argillite and gray to white feldspathic quartzite. Platy, even Gorton, M.P., E.S. Schandl, and Trygve Höy, 2000, Mineralogy and geochemistry 7.7 ka (William Phillips, written commun., 2011). Locally, tributary valley 2006); undivided where mapped as lower part of upper Wallace Formation parallel siltite and dark gray argillite, which also occurs as graded tops of of the Middle Proterozoic Moyie sills in southeastern British Columbia, in J.W. 70 glaciers of the Purcell Mountains contributed to the ice stream. Sections of farther south (Lewis and others, 1999, 2000). Total thickness there about quartzite and siltite beds. Fine- to very fine-grained quartzite forms 1-5 dm, Lydon, Trygve Höy, J.F. Slack, and M.E. Knapp, eds., The Geological Environ- Qg Ymi 900 m (3,000 ft). Discontinuous exposure and faulting preclude accurate Qgk 65 glacial till, outwash, and lacustrine deposits filled the valleys. After retreat rarely thicker, beds. Some quartzite beds have ripple cross lamination, ment of the Sullivan Deposit, British Columbia: Geological Association of Yph of the continental ice, mountain valley glaciers persisted in the higher determination of thickness or subdivision within this map. rippled tops, and rare argillite clasts 1 by 10 cm with rounded corners. Canada, Mineral Deposits Division, Special Publication no. 1, p. 322-335. Qgk Ypf cirques of the Purcell Mountains. Hamilton, J.M., R.G. McEachern, and O.E. Owens, 2000, A history of geologi- Ysn Snowslip Formation (Mesoproterozoic)—Dark green siltite and light green Upper contact placed below thick interval of flat laminated dark siltite and 85 60 cal investigations at the Sullivan deposit, in J.W. Lydon, Trygve Höy, J.F. Ypf Qgt argillite graded and nongraded couplets, green siltite and dark gray argillite argillite. Thickness about 500 m (1,600 ft). Poorly exposed everywhere. Slack, and M.E. Knapp, eds., The Geological Environment of the Sullivan Ypt Ype couplets, purple siltite and argillite couplets, and green to gray siltite. Lower Ypf Prichard Formation, member f (Mesoproterozoic)—Cream- to rusty- Deposit, British Columbia: Geological Association of Canada, Mineral Qg Qgt SYMBOLS part is dominately green couplets with a purple zone near its middle. All 78 weathering, dark and light gray siltite, dark gray argillite, and minor lighter Deposits Division, Special Publication No. 1, p. 4-11. 60 characteristically have mud and dewatering cracks. Middle part is planar Qgk quartzite. Siltite is commonly in 1-20 cm tabular, structureless, or even- Harrison, J.E., and D.A. Jobin, 1963, Geology of the Clark Fork quadrangle, Ypf 55 Ymi Contact: dashed where approximately located. laminated couplets and microlaminae of greenish gray- to white- Ypg parallel laminated beds with slabby to platy parting. Tops of these beds are Idaho-Montana: U.S. Geological Survey Bulletin 1141-K, p. 1-38. weathering siltite and dark gray to black argillite with millimeter-scale 87 Ypf 60 unevenly laminated gray siltite or graded to dark argillite. Quartzite is very Harrison, J.E., E.R. Cressman, and J.W. Whipple, 1992, Geologic and structural 60 50 Normal fault: ball and bar on downthrown side; dashed where bumps on bedding surfaces. Similar plane parallel lamination is Ypf 55 fine to fine grained, poorly sorted, and biotitic in tabular beds 6-20 cm thick maps of the Kalispell 1˚ x 2˚ quadrangle, Montana, and Alberta and British 55 approximately located; dotted where concealed. widespread in middle of unit elsewhere (Burmester, 1986; Burmester and Ypf with tops graded to siltite or dark argillite. Quartzite is more abundant Columbia: U.S. Geological Survey Miscellaneous Investigations Series Map Yb 70 Ypf others, 2006; Lewis and others, 1999). Upper part is dominantly green with 1 Ymi 10 Strike and dip of bedding. toward base; some beds have carbonate concretions 5-20 cm in diameter I-2267, scale 1:250,000. Ymi minor carbonate. Upper contact placed below concentration of that weather recessively into punky brown masses. Quartzite forms Qgo Hartlaub, R.P., 2009, Sediment-hosted stratabound copper-silver-cobalt poten- 85 20 Strike and dip of bedding; ball indicates bedding known to be upright. carbonate-bearing lenticular couplets or thick white quartzite of Ysh1. Parts 60 resistant ribs where beds are concentrated over 10-20 m thick intervals. tial of the Creston Formation, Purcell Supergroup, southeastern British 50 55 Qgt exposed along Deer Creek Road (FS Road 435) in the southwest corner of 70 Bases of many siltite and quartzite beds are slightly uneven, with 1-2 cm Columbia (parts of NTS 082G/03, /04, /05, /06, /12), in Geoscience BC 60 Strike and dip of overturned bedding. the map. Thickness possibly 550 m (1,800 ft). 60 Ypf loads into subjacent argillite common. Upper part is mostly dark argillite Summary of Activities 2008: Geoscience BC, Report 2009-1, p. 123–132. Yph 80 and siltite with marker-bed-like color layering common, and abundant Hayes, T.S., 1983, Geologic studies on the genesis of the Spar Lake strata- Qgk Strike and dip of, strike variable. 20 pyrrhotite, commonly flattened in bedding planes. Hosts highest concentra- bound copper-silver deposit, Lincoln County, Montana: Stanford University Yb2 Ymi Ymi Piegan Group Qg Strike and dip of cleavage. tion of mafic sills in area. Upper contact placed below quartzite and Ph.D. dissertation, 340 p. Qgk 60 55 50 35 50 current feature-rich base of Ypg. Best exposed on north side of Keno Creek. Ysr Yr The Piegan Group was resurrected by Winston (2007) to provide group- Hayes, T.S., and M.T. Einaudi, 1986, Genesis of the Spar Lake strata-bound 75 Ice flow direction. Thickness possibly 900 m (3,000 ft); uncertainty due to fault truncation and 60 53 level correlation across the Belt basin. It includes only the Helena and copper-silver deposit, Montana: Part I, Controls inherited from sedimenta- Ypt 65 Qgt folding of upper part. Previously subdivided following Finch and Baldwin tion and preore diagenesis: Economic Geology, v. 81, p. 1899-1931. Yb Col. Wallace formations. Excluded from the Wallace are upper members 1 55 35 (1984) into lower part with more quartzite and upper argillite member Ypg mapped to the south in the past (e.g., Harrison and Jobin, 1963; Lemoine Höy, Trygve, D. Anderson, R.J.W. Turner, and C.H.B. Leitch, 2000, Tectonic, Yr Terrace escarpment. (Burmester, 1985, Cressman and Harrison, 1986). magmatic and metallogenic history of the early synrift phase of the Purcell 60 Ypf 50 and Winston, 1986; Lewis and others, 1999, 2000, 2002). Since the strata 67 below the Wallace in most of Idaho are appreciably different from those in basin, southeastern British Columbia, in J.W. Lydon, Trygve Höy, J.F. Slack, Ype Prichard Formation, member e (Mesoproterozoic)—Light gray- to white- 55 55 Cirque headwall: ticks on glaciated side. and M.E. Knapp, eds., The Geological Environment of the Sullivan Deposit, Qgk 55 Ymi the Helena’s new reference section in Glacier National Park, we distinguish weathering siltite and quartzite, and darker argillite. Rustier-weathering gray 70 British Columbia: Geological Association of Canada, Mineral Deposits Yb2 Moraine crest or kame ridge. these strata as the western facies of the Helena. siltite found as 1-5 dm tabular beds. Lighter siltite occurs as graded tops of Ysr Ypac Division, Special Publication No. 1, p. 33-60. Yr 50 quartzite beds, less commonly as their inversely graded bases. Most quartz- Ypf Yw Wallace Formation (Mesoproterozoic)—Carbonate-bearing light gray to white Huebschman, R.P., 1973, Correlation of fine carbonaceous bands across a Precam- 60 50 Ype ite is light gray, poorly sorted, fine grained and feldspathic in 2 dm to 2 m siltite and quartzite, and dark gray to black argillite. Siltite and quartzite brian stagnant basin: Journal of Sedimentary Petrology, v. 43, p. 688-699. 45 thick beds, some of which contain carbonate concretions or biotite-rich 65 commonly as bases of pinch-and-swell couplets and couples graded to Kleinkopf, M.D., 1977, Geophysical interpretations of the Libby Thrust Belt, 80 Ypf 35 zones 1-10 cm across. Exceptions are coarser grained and less feldspathic YPd DESCRIPTION OF MAP UNITS dark argillite tops. Argillite caps commonly contain ptygmatically folded northwestern Montana: U.S. Geological Survey Professional Paper 1546, 30 and have rounded medium quartz grains dispersed or concentrated at bed 55 siltite- or quartzite-filled cracks that taper downward. On bedding plane 22 p., 2 plates. Yr 55 bases. Bases commonly convolute or loaded into subjacent laminated 65 surfaces, cracks are generally discontinuous and sinuous, occurring as Lane, E.W., 1947, Report of the subcommittee on sediment terminology: Trans- 80 Qgk 60 intervals. Some beds are parallel laminated with laminated siltite and Intrusive rocks are classified according to IUGS nomenclature using isolated parallel or three-pointed stars, with concave up argillite between. actions of the American Geophysical Union, v. 28, no. 6, p. 936-938. Qgo Qgk argillite caps, but more exhibit features of current traction such as trough 85 Yph normalized values of modal quartz (Q), alkali feldspar (A) and plagioclase Less diagnostic components are dark bluish gray silty dolomite in beds 1-5 Lemoine, S.R., and Don Winston, 1986, Correlation of the Snowslip and cross bedding, ripple cross lamination, rip-up clasts, and rippled tops. (P) on a ternary diagram (Streckeisen, 1976). Mineral modifiers are listed in dm thick with molar tooth calcite ribbons, uneven graded couplets of pale Shepard formations of the Cabinet Mountains with upper Wallace rocks of 60 Clasts, typically near tops of beds, are composed of white argillite, quartzite, 65 Qgt order of increasing abundance for igneous rocks. Grain size classification green siltite and calcitic argillite, and white, pyritiferous, very fine-grained the Coeur d’Alene Mountains, western Montana, in S.M. Roberts, ed., Belt Yhw Qgo and siltite, and are 2-20 cm long, variously rounded, distorted or stretched. Qlm 40 of unconsolidated and consolidated sediment is based on the Wentworth calcitic quartzite in 1-5 dm beds, some with hummocky cross stratification. Supergroup: A Guide to Proterozoic Rocks of Western Montana and 60 50 Soft-sediment deformation features common; ball-and-pillow structures Yhw Yb1 scale (Lane, 1947). Bedding thicknesses and lamination type are after Upper contact not exposed, but elsewhere placed at the top of pinch-and- Adjacent Areas: Montana Bureau of Mines and Geology Special Publica- A Yr 60 45 locally abundant. Quartzite-rich sections include amalgamated beds and Ypt Ymi McKee and Weir (1963), and Winston (1986). Grain sizes and bedding swell couplets with black argillite caps. Best exposures are near mouth of tion 94, p. 161-168. Ypg Ypf commonly form clear ribs and talus slopes. Very dark argillite found as rare 50 thicknesses are given in abbreviation of metric units (e.g., dm=decimeter). Solomon Creek and section 6-5 line near south edge of map. Minimum Lewis, R.S., R.F. Burmester, M.D. McFaddan, P.D. Derkey, and J.R. Oblad, layers 2-10 cm thick. Upper contact placed above highest zone of quartzite 60 Unit thickness and distances are listed in both meteric and English units. thickness 220 m (700 ft), much less than to the south (790 m, 2,600 ft; 1999, Digital geologic map of the Wallace 1:100,000 quadrangle, Idaho: with abundant current features and below thick section of uniformly Yb Multiple lithologies within a rock unit description are listed in order of Burmester and others, 2004). Zircons from a tuff near the contact with U.S. Geological Survey Open-File Report 99-390, scale 1:100,000. 2 55 parallel-laminated rusty-weathering siltite. Best exposed on Keno Mountain decreasing abundance. Soil descriptions for Quaternary units are after Snowslip Formation about 170 km (105 mi) east yielded a U-Pb date of Lewis, R.S., R.F. Burmester, R.M. Breckenridge, M.D. McFaddan, and J.D. Kauff- 50 and the ridge to the south. Thickness approximately 1,200 m (3,600 ft). Chugg and Fosberg (1980) and Weisel (2005). 1.454 Ga (Evans and others, 2000). man, 2002, Geologic map of the Coeur d’Alene 30 x 60 minute quad- Yr 40 Ymi Prichard Formation, member d (Mesoproterozoic)—Dark to light gray rangle, Idaho: Idaho Geological Survey Geologic Map 33, scale 1:100,000. Qg ALLUVIAL AND LACUSTRINE DEPOSITS Yhw Helena Formation, western facies (Mesoproterozoic)—Pale green carbonate- Ypd Ype siltite and darker gray argillite. Lamination is typically even and parallel in McKee, E.D., and G.W. Weir, 1963, Terminology for stratification and cross- ZYmi bearing siltite and argillite. Carbonate-bearing uneven green siltite and stratification in sedimentary rocks: Geological Society of America Bulletin, Qlm Lacustrine and mud deposits (Holocene)—Organic muck, mud, and peat bogs siltite and argillite couplets and in microlaminae. Rusty weathering is 55 Qgt argillite laminae and couplets are concentrated near base. Dolomite is v. 64, p. 381-390. Yr in poorly drained paleoglacial outwash channels, kettles, and scoured common. Less common are intervals a few meters in thickness of white, typically disseminated in tabular beds of tan-weathering greenish siltite and Poage, M.A., D.W. Hyndman, and J.W. Sears, 2000, Petrology, geochemistry, Yw bedrock depressions. Interbedded with thin layers of fine sand, silt, and very fine- to fine-grained quartzite in rarely amalgamated beds, or rusty- 65 Yb Ypt less so in argillite; calcite is concentrated in nonresistant horizontal 2 45 weathering 1-5 dm white siltite. A zone of contorted beds near end of thin and diabase-granophyre relations of a thick basaltic sill emplaced into wet clay. Soils of the Pywell series. Thickness 1-5 m (3-16 ft). centimeter-scale pods and vertical ribbons (molar tooth structure). Contains sill, above a larger one, is atypical. Exposure generally poor and discon- sediments, western Montana: Canadian Journal of Earth Sciences, v. 37, Yph Ypf 1-2 mm pyrite cubes. Includes zones of carbonate-free laminated to 35 85 tinuous, with quartzite commonly over-represented in float. Upper no. 8, p. 1109–1119. Yb1 Ypg thin-bedded green siltite and lighter green argillite and rare graded Ysr Qg contact placed at lowest occurrence of current-laminated siltite and Sears, J.W., K.R. Chamberlain, and S.N. Buckley, 1998, Structural and U-Pb COLLUVIAL AND MASS WASTING DEPOSITS couplets. Some parting surfaces are rippled; lenticular nonparallel bedding Qt 50 quartzite of Ype. Best exposure in map is east of ridge northeast of Keno geochronological evidence for 1.47 Ga rifting in the Belt basin, western Qgt is attributed to ripple and starved ripple lamination. Siliciclastic to carbon- 60 42 Qt Talus (Holocene)—Blocky and tabular, poorly sorted angular clasts of Mountain. Thickness 200-500 m (600-1,600 ft); range uncertainty due to Montana: Canadian Journal of Earth Sciences, v. 35, p. 467-475. Qgo Ypf ate cycles typical of Helena were not recognized, perhaps due to discon- Belt-Purcell Supergroup rocks form talus deposits below cirque headwalls poor exposure of contacts. Streckeisen, A.L., 1976, To each plutonic rock its proper name: Earth-Science Yhw 45 Ypf tinuous exposure. Upper contact, placed at lowest occurrence of black Reviews, v. 12, p. 1-33. 60 50 Ypf and cliffs oversteepened by glaciation. Generally no soil development. 80 60 Yb2 45 argillite-capped pinch-and-swell couplets, may be too high in places where Thickness varies, usually 3-9 m (10-30 ft). Ypac Prichard Formation, members a, b, and c (Mesoproterozoic)—Light Weisel, C.J., 2005, Soil survey of Boundary County, Idaho: United States Qt Ymi solution of calcitic black caps of Yw hinders identification of pinch-and- weathering quartzite, darker siltite, and rusty-weathering unevenly Department of Agriculture, Natural Resources Soil Conservation Service in Qgo Yr 52 Qcg Colluvial deposits derived from glacial materials (Holocene and swell couplets. Best exposed along Deer Creek Road near mouth of laminated, dark gray siltite and argillite couplets. Fine-grained to rarely cooperation with United States Department of the Interior, Bureau of Land 80 Ymi Yhw Ype Pleistocene)—Silt, sand, and gravel colluvium. Forms debris fans and collu- Solomon Creek. Thickness on the order of 150-240 m (500-800 ft). Unit medium-grained quartzite, similar to that of Ype but in thinner packages, is Management, University of Idaho College of Agriculture; and Idaho Soil 75 corresponds to the Helena and Empire formations to the east (Harrison and Ypt Ypg vial aprons along steep valleys and gullies mostly derived of glacial depos- characteristic of the upper part. Some beds have ripples and cross lamina- Conservation Commission, Idaho Agricultural Experiment Station, Part I, 75 Ypf its. Includes small unmappable mass movements. Thickness varies, others, 1992). tion; other beds 1-3 m thick, appear structureless. Circular brown spots 3-6 144 p. Part II, 452 p. Ymi typically 5 m (15 ft). cm in diameter with alteration “halos” probably formed from concentra- Winston, Don, 1986, Stratigraphic correlation and nomenclature of the Meso- Ysn 55 Qt tions of manganiferous carbonate. Top placed above set of quartzite beds proterozoic Belt Supergroup, Montana, Idaho and Washington, in S.M. Qgt 47 ZYmi Yph Ravalli Group and below interval of more evenly laminated, rustier weathering siltite and Roberts, ed., Belt Supergroup: A Guide to Proterozoic Rocks of Western Qgo Qgk Ypf Qgt GLACIAL DEPOSITS argillite. Lower part not exposed in map, but a stratigraphically lower Montana and Adjacent Areas: Montana Bureau of Mines and Geology, Yw Qt The swath of Ravalli Group strata across the map is only slightly thicker Qt 60 massive unit is exposed in the Canuck Peak quadrangle to the north and the Special Publication 94, p. 69-84. Yhw than documented to the southeast (Cressman and Harrison, 1986) and Yhw Qgk Qgo Outwash deposits, undivided (Holocene and Pleistocene)—Bouldery and Mount Baldy quadrangle to the east (Cressman and Harrison, 1986). Winston, Don, 2007, Revised stratigraphy and depositional history of the 80 55 Ypg south-southwest (Burmester and others, 2007). Although cosets of thick sets Qcg sandy gravels. Moderately sorted and rounded pebbles and cobbles. Gravity modeling (Kleinkopf, 1977) suggests that there is a minimum of Helena and Wallace formations, mid-Proterozoic Piegan Group, Belt 65 Ypt of quartzite used to define the Revett elsewhere (Hayes, 1983; Hayes and 70 Qg Ymi Ymi Includes small unmappable deposits of alluvium. Soils are sandy loams and 3,000 m (10,000 ft) of sedimentary strata between the massive unit and Supergroup, Montana and Idaho, U.S.A., in P.K. Link and R.S. Lewis, eds., 70 55 Einaudi, 1986) are rarely observed, Revett is mapped on the east side of the 70 loamy sands of the Selle-Elmira Association. Maximum thickness about 20 basement. Best exposed northeast of Buckhorn Ridge, north edge of map. Proterozoic Geology of Western North America and Siberia: SEPM Special Yb Sylvanite anticline, Fig. 1, (Cressman and Harrison, 1986) and correlated 1 m (60 ft). Publication 86, p. 65-100. 75 45 with the middle Creston north of the border where copper-silver-cobalt Prichard Formation, massive unit (Mesoproterozoic)—Structureless, 73 Qt Qgt Ypm 45 Qg Till and kame deposits (Pleistocene)—Mapped where Qgt and Qgk, described mineralization is similar to that in the Revett to the south (Hartlaub, 2009). Ysr 55 poorly sorted quartzite and siltite shown only in cross section. Location 55 50 85 Yph below, are not separable at the map scale. Revett mapped here as the swath of quartzite-rich strata below more typical based on west-dipping exposures mapped by Cressman and Harrison 85 55 Ypt St. Regis Formation may correspond to the upper Revett mapped elsewhere, Ypf (1986) immediately east of quadrangle. Qgk 55 Qgt Till deposits (Pleistocene)—Dense silt, pebble, and cobble till with local 52 and the upper Burke (Yb2) may correspond to the lower Revett. Yw 52 boulders deposited by the Purcell Trench lobe of the Cordilleran Ice Sheet. Yr 5 Poorly stratified compact basal till includes ground moraine and some Ysr St. Regis Formation (Mesoproterozoic)—Purple and green siltite, argillite, and Yb 55 2 interbedded proglacial deposits. Deposit includes kame terraces and some quartzite. Lower strata are entirely shades of purple with lighter siltite and STRUCTURE 75 Qt 70 Qgo 60 outwash along the south margin. Soils include silt loams and gravelly silt darker argillite couplets that are uneven to lenticular and commonly mud Yhw Qgt loams of the Pend Oreille-rock outcrop and the Stien-Pend Oreille associa- cracked. Includes discrete layers of thin mudchips 1-3 cm thick. Green Qlm The major structure in the area is the Sylvanite anticline. Strata over most of Qgo tions. Thickness varies; 1-30 m (3-100 ft). lithologies are more common toward the top. These include dark green Ysr 50 the map are on the nearly homoclinal west limb, but the hinge line crosses 65 Qt siltite and lighter green argillite in wavy couplets and couples with rare 1 80 Qgk the northeast corner. Gravity modeling suggests the anticline is cored by a Qgk Kame deposits (Pleistocene)—Poorly stratified and compact silty to sandy mm thick brown dolomitic wisps, pale green tabular very fine-grained 65 boulder lodgment till; locally includes ground moraine and some interbed- quartzite beds (2-5 cm, rarely 10-20 cm) with green argillite caps, and fault slice of crystalline basement (Kleinkopf, 1977). The southwest corner Ysn 75 Ypf ded proglacial and ice contact and outwash deposits. Soils include silt green argillite 5-20 cm thick. Upper contact placed above highest cracked of the map is complicated by faults that repeat and attenuate the highest loams and gravelly silt loams of the Stien-Pend Oreille association. Thick- strata. Ysh1 Yr Qgt and mudchip-bearing purple siltite and argillite. Parts well exposed along Qlm ness varies; may exceed 50 m (160 ft). FS Road 2549 to Solomon Mountain, along top cliff west of Solomon Lake, Yph 50 and along Deer Creek near west edge of map. Thickness from map pattern 70 about 450 m (1,500 ft). Qt 40 INTRUSIVE ROCKS Qgt Qgo Yr Yw Yb Revett Formation (Mesoproterozoic)—White and greenish-gray quartzite, pale 49°45' 30 Qgo Yb2 Qcg 1 50 ZYmi Mafic intrusive rocks (Neoproterozoic or Mesoproterozoic)—Fine- to Qcg 50 purple, gray, and green siltite, and darker gray or purple argillite. Very Yb2 1 5 ° 3 0 ' Ysn Ypg 1 medium-grained diorite or gabbro. Locally contains calcite and possibly fine-grained feldspathic quartzite is commonly in 1-5 dm, rarely 1 m, 1 7 ° 0 ' Sullivan 85 1 Ypg Mine Yhw 50 actinolite, probably from greenschist facies metamorphism. Occurs as sills tabular beds that contain parallel, cross, and convolute laminations. Some 35 Yr Ypt 47 of varied thicknesses and continuity. Intrusion into units above Prichard thicker beds have large trough cross bedding and scoured bases. Tops are Ysh 75 Qlm 45 1 53 55 Formation indicate that they cannot be Moyie sills. May be coeval with the 25 rippled or capped with mudcracked argillite, or missing where beds are Purcell lava (rhyolite about 55 km (35 mi) east-northeast dated 1.443 Ga; amalgamated. Siltite is similar to quartzite and occurs as bases of couplets Evans and others, 2000), or possibly a sill complex farther east (760 Ma; 49°30' SCALE 1:24,000 graded to argillite tops. Mud cracks and chips are distributed throughout. Cranbrook Burtis and others, 2003). 1 0.5 0 1 1 Contains visible magnetite octahedra as reported to the east (Harrison and Base Map Credit MILE Idaho Geological Survey 2 others, 1992). Poor exposure in area attributed to fracturing of brittle lt FEET Montana Bureau of Mines and Geology Ymi Mafic intrusive rocks, undivided (Mesoproterozoic)—Fine- to medium- u Base digitally scanned from 24,000-scale USGS film fa quartzite into small cubes during deformation. Upper contact placed above K MN 1000 0 1000 2000 3000 4000 5000 6000 7000 separates, 1996. Field work conducted 2009-2011. grained, rarer coarse-grained hornblende gabbro and quartz diorite. oot highest thick white quartzite. Top best exposed south of Solomon Lake ie e y PEAK n Shaded elevation from 10 m DEM. EASTPORT This geologic map was funded in part by the U.S. Geological Survey Variants have laths of plagioclase, or quartz as large blue grains or in grano- o GN NORTHWEST a KILOMETER CANUCK PEAK along FS Road 2404. Thickness about 400 m (1,300 ft). i M 1 0.5 0 1 National Cooperative Geologic Mapping Program, USGS Award No. L o o phyre. Grain size, quartz, and mafic mineral content vary between a

Topography compiled 1963. Planimetry derived from 0 42 18 t k l G11AC20207 (IGS) and Award No. G11AC20257 (MBMG). e aerial photographs taken 1992. intrusions and commonly within single bodies, both along and across 49°15' u

Contour interval 40 feet Burke Formation (Mesoproterozoic)—Siltite, argillite, and quartzite. Subdi- a f

Digital cartography by Jane S. Freed at the strike. Occur as Moyie sills in Ypf and lower units, locally concordant, but k MOUNT Projection: Idaho coordinate system, west zone Supplementary contour interal 20 feet MEADOWCREEK BALDY vided into two members on this map based on bedding characteristics and LINE POINT Idaho Geological Survey’s Digital Mapping Lab. e

(Transverse Mercator). 1927 North American Datum. some laterally pinch and swell, include rafts of country rock, branch into e

sediment structures. r

UTM Grid and Reviewed by John D. Kauffman, C multiple sills, end abruptly, or gradually pinch out (Bishop, 1976). Although

10,000-foot grid ticks based on Idaho coordinate l

1996 Magnetic North l

0 ' Susan M. Vuke, and Catherine McDonald. o 0 '

system, west zone and Montana coordinate system, Yb Burke Formation, member 2 (Mesoproterozoic)—Green to gray-green r Yahk Declination at Center of Map sills lower and higher in the Aldridge Formation (Prichard correlative in 2 0

0 MOYIE r CURLEY NEWTON

CREEK a

IDAHO SPRINGS 6 ° north zone. MOUNTAIN Map version 11-16-2012. Creston 7 °

Canada) are similar in chemistry (Anderson and Goodfellow, 2000), they siltite, purple and green argillite and siltite, and purple laminated quarzite. 1 C 1 1 1000-meter Universal Transverse Mercator grid ticks, PDF (Acrobat Reader) map may be viewed online at seem to have intruded in at least two separate events. Early intrusions were Lower part is dominantly 10-20 cm thick siltite beds, typically with macro- 1 BRITISH COLUMBIA CANADA 49°00' zone 16. QUADRANGLE LOCATION ADJOINING QUADRANGLES www.idahogeology.org. at shallow levels closely following sedimentation of the Lower Aldridge scopic magnetite octahedra. Slabby partings are commonly along Eastport MONTANA

x (Höy and others, 2000; Gorton and others, 2000; Cressman, 1989; Sears mm-thick skins of dark green and some lighter green argillite. Sedimentary M e - o

and others, 1998; Poage and others, 2000). Age of these sills is probably features include cross lamination, ball and pillow structures, rare convolute y i

tns e

M L close to U-Pb dates on zircons from near Kimberley, British Columbia, lamination, and rare thin mud chips. Purple colors, mudcracks, mudchips, compl t

r l i

k b

r e u f i a b

and quartzite increase upward. Quartzite is very fine grained with planar a about 100 km (60 mi) north (1.468 Ga; Anderson and Davis, 1995), and k S

f u y

l l

h v t Riv t

from Plains, Montana, about 190 km (120 mi) south-southeast (1.47 Ga; and rarer cross laminae enhanced by purple hematite concentrations. Sel a t c

n h es n i r i t

r u

Sears and others, 1998). Higher intrusions sport chilled margins and Purple-banded or zebra-striped quartzite in beds 10-30 cm thick present e e r

P s T

Ymi contact aureoles, evidence that they invaded consolidated rock at a later near top. Upper contact placed at base of lowest thick white quartzite. Best l l

e l

A’ e c

exposed on rib north of Skin Creek, southwest part of map. Thickness u ant time. Best observed near Keno Mountain. l

Qgt YPd r Bonners t

6,000 a

u f O N

icl

approximately 550 m (1,800 ft). P

Ferry

i G

Ymic Mafic intrusive rocks, Crossport C sill (Mesoproterozoic)—Fine- to coarse- t n r

Keno Qgt e N

Ymi I o

H Yb Burke Formation, member 1 (Mesoproterozoic)—Green to gray-green siltite p

Creek grained hornblende gabbro to quartz diorite. Correlated with the middle or 1 w

Ypd A S 5,000 “C” sill of (Bishop, 1973, 1976) defined in the Moyie Springs quadrangle to and argillite, and gray to white quartzite. Lower part is dominantly slabby e

W N

Ypac

the southwest based on occurrence low in Ype across Buckhorn Ridge, and platy parting 10-20 cm thick tabular beds of tan- to olive-drab-

Ypf 48°30' t

northeast corner of map. Thickness about 60 m (100 ft). weathering, greenish-gray siltite, commonly with flat laminations. Magnetite s Bonners Ferry 30' x 60' map

A N

Ymi O a Troy

A Qg Ypm A

O H

octahedra are as large as 1 mm. Minor carbonate near base occurs as very A Libby N 4,000 Ymic 4,000 D

Ymi I

H A D

Qgk thin beds and scattered nodules less than 1 cm in length. Light gray, very I O ZYmi M Ymi BELT-PURCELL SUPERGROUP fine-grained quartzite increases upward, most commonly as bases of undu-

Qgo FEET lating couplets and couples that grade up through gray siltite with rare 0 10 20 30 40 50 kilometers 3,000 3,000 Yph Ymi Ypf Missoula Group argillite skins. Upper contact placed at lowest occurrence of purple Scale Ype Yb1 Ypf mudcracked argillite and quartzite. Best exposed on FS Road 2540 and spurs Yb The Missoula Group includes all Belt units above the Piegan Group as northwest of Deer Ridge Lookout. Thickness approximately 550 m (1,800 ft). Ysr 2 Ypg Figure 1. Location of Line Point 7.5' quadrangle (red box) with respect to 2,000 Ypt Ypac 2,000 recently redefined by Winston (2007). It is similar to the Ravalli Group in FEET Yw major structural and physiographic features. Ypf Ype that it is characterized as a clastic wedge consisting of quartzite, siltite, and Yr Ymi argillite. Only the lowest two formations are mapped here. Lower Belt Yhw 1,000 1,000 Shepard Formation (Mesoproterozoic)—Occupies same stratigraphic level as The Prichard Formation consists of the lowest strata of the Belt-Purcell the upper two units of the Wallace Formation mapped to the south of quad- Supergroup. It is equivalent to the Aldridge Formation in Canada. rangle (Harrison and Jobin, 1963; Lewis and others, 1999, 2000, 2002). 0 0 Named Shepard Formation here because it is not markedly different from Prichard Formation (Mesoproterozoic)—Dark to light gray siltite, black, gray, the Shepard Formation at its type locality and is separated from the and white argillite, gray to white feldspathic quartzite, and white quartzite. carbonate-bearing pinch-and-swell strata typical of the Wallace Formation Siltite is typically rusty weathering and planar laminated with black or rarely

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