Groundhog; Perseverance; Alaska Gastineau; Alaska Juneau Mine, Juneau District, Juneau Borough, Alaska, USA
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Geology: The Groundhog mine is often considered part of the Perseverance Mine (JU168) which is in turn often considered part of the Alaska-Juneau Mine (JU165). The surface over the Groundhog Mine was placer-mined prior to 1888, and lode mining began in 1889. The mine was consolidated with the Perseverance Mine (JU168) in 1911. The total recorded production from the Groundhog mine is 900 tons of ore. Gold recovery from placer operations is not documented but several thousand dollars of gold (at $20.67 per ounce) were probably produced (Redman and others, 1989). There are 3 adits, placer workings and 8 open cuts. The Groundhog mine was explored extensively by Echo Bay Mines between 1986 and 1997 (Redman and others, 1989). The Groundhog deposit represents the upper portion of the Perseverance orebody of the Alaska-Juneau mine, and consists of a system of sulfide-bearing, auriferous, quartz-ankerite veins in the structurally lowest portion of the Perseverance Slate, an Upper Triassic unit of carbonaceous and graphitic quartz-sericite phyllite, schist, and black slate, with minor carbonaceous limestone and numerous sill-like lenses of amphibolite or metagabbro (Miller and others, 1992; Light and others, 1989). The vein system extends for more than 6 kilometers along strike, 700 meters in vertical extent, and is confined to the lowest 100 meters of the Perseverance Slate. The system comprises numerous veins, veinlets, stringers and stockworks; individual veins range from a few centimeters to over 1 meter thick. The veins are 95 percent quartz with subordinate ankerite, pyrrhotite, galena, sphalerite, electrum, arsenopyrite, pyrite, and native gold. Approximately 90 percent of the gold is free-milling (Light and others, 1989; Twenhofel, 1952). The Groundhog Mine is in the Juneau Gold Belt, which consists of more than 200 gold-quartz-vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a zone 160 km long by 5 to 8 km wide along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Workings: The surface over the Groundhog Mine was placer-mined prior to 1888, and lode mining began in 1889. The mine was consolidated with the Perseverance Mine (JU168) in 1911. There are 3 adits, placer workings, and 8 open cuts. The Groundhog Mine was explored extensively by Echo Bay Mines between 1986 and 1997.
Age: Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Alteration: Alternation consists of hydrothermal biotite, ferroan dolomite, and sericite; chlorite and albite partly replace amphibolite( Miller and others, 1992). The alteration has been traced with decreasing intensity as much as 1 kilometer from the Alaska-Juneau mine. Inward from its periphery, magnetite, then ilmenite and magnetite, are replaced by pyrrhotite (Miller and others, 1992; Newberry and Brew, 1987).
Production: The total recorded production from the Groundhog Mine is 900 tons of ore. Gold and silver recovery is not documented. Gold recovery from the placer operations is not documented but several thousand dollars in gold (at $20.67 per ounce) was probably produced.
Reserves: Assuming a sublevel caving mining model, Echo Bay Mines Ltd. calculated an indicated and inferred resource for the Alaska-Juneau Mine--including the Groundhog Mine--of 89 million tons of ore that contain 0.05 ounce of gold per ton.
Commodities (Major) - Ag, Au, Pb; (Minor) - Cu, Zn
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
14 entries listed. 12 valid minerals.
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Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Juneau quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-374, 155 p. Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300. Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190. Light, T.D., Brew, D.A., and Ashley, R.P., 1989, The Alaska-Juneau and Treadwell lode gold systems, southeastern Alaska, in DeWitt, E., Waegli, J., Light, T.D., Brew, D.A., and Ashley, R.P., eds., Gold deposits in metamorphic rocks, Part I: U.S. Geological Survey Bulletin 1857-D, p. D27-D36. Miller, L.D., Barton, C.C., Fredericksen, R.S., and Bressler, J.R., 1992, Structural evolution of the Alaska-Juneau lode gold deposit, southeastern Alaska: Canadian Journal of Earth Sciences, v. 29, p. 865-878. Miller, L.D., Goldfarb, R.J., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206. Newberry, R.J., and Brew, D.A., 1987, The Alaska-Juneau gold deposit; remobilized syngenetic versus exotic epigenetic origin, 1987, in Hamilton, T.D., and Galloway, J.P., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1986: U.S. Geological Survey Circular 998, p. 128-131. Redman, E.C., Maas, K.M., Kurtak, J.M., and Miller, L.D., 1989, Bureau of Mines Mineral Investigations in the Juneau Mining District, Alaska, 1984-1988, Volume 2--Detailed mine, prospect, and mineral occurrence descriptions, Section D, Juneau Gold Belt Subarea: U.S. Bureau of Mines Special Publication, 424 p. Spencer, A.C., 1906, The Juneau Gold Belt, Alaska: U.S. Geological Survey Bulletin 287, 161 p. Twenhofel, W.S., 1952, Geology of the Alaska-Juneau lode system, Alaska: U.S. Geological Survey Open-File Report 60, 170 p.