Sheep Creek; Gossan Peak Prospect, Bonnifield District, Denali Borough, Alaska, USA
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Geology: The Sheep Creek deposit is in the Totatlanika Schist near its contact with the Keevy Peak Formation (Nokleberg and others, 1994). The Totatlanika Schist ranges in age from Early Mississipian to Middle Devonian and consists mostly of felsic and mafic metavolcanic and metavolcaniclastic rocks (Wilson and others, 1998). The deposit is 200 feet thick and 2,000 feet long, and consists of isoclinally folded, stratabound lenses of massive sulfides in tuffaceous chlorite schist and chert (O'Connor and others, 1989). The sulfides are fine-grained sphalerite, galena, and pyrite. This deposit has high values of Sn, reported as either cassiterite or stannite. Channel sampling and grab samples contain up to 11% combined lead and zinc, and 10 grams of silver per ton. Zones up to 1 meter wide contain 1% tin (Nokleberg and others, 1994).
Workings: At least three drill holes to a maximum depth of 470 feet were completed in the 1970's (O'Connor and others, 1989). Channel sampling and grab samples contain up to 11% combined lead and zinc, and 10 grams of silver per ton. Zones up to 1 meter wide contain 1% tin (Nokleberg and others, 1994).
Age: Mineralization is syngenetic with the Paleozoic host rocks.
Alteration: Alteration consists of sericitized schist in both the hanging and footwall of the deposit.
Reserves: Based on limited data a tentative resource of 5.5 million pounds of tin has been identified (O'Connor and others, 1989). There are no estimates of base metal reserves.
Commodities (Major) - Pb, Zn; (Minor) - Ag, Sn
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model 28a)
Mineral List
7 entries listed. 6 valid minerals.
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References
Bundtzen, T.K., Eakins, G.R., Clough, J.G., Lueck, L.L., Green, C.B., Robinson, M.S., and Coleman, D.A., 1984, Alaska's mineral industry, 1983: Alaska Division of Geological and Geophysical Surveys Special Report 33, 56 p. Cox, D.P., Light, T.D., Csejtey, Bela, Jr., and Campbell, D.L., 1989, Mineral resource assessment map of the Healy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map, MF-2058-A, 1 sheet, scale 1:250,000. Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D.J., Robinson, M.S., Smith, T.E., and Yeend, W., 1987, Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p., 2 plates, scale 1:5,000,000. Nokleberg, W.J., and (seven) others, 1994, Metallogeny and major mineral deposits of Alaska and Metallogenic map of significant metalliferous lode deposits and placer districts of Alaska, in Plafker, G. and Berg, H.C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol.. G1, p. 855-904, Plate 11, scale 1:2,500,000. O'Connor, W.K., Dahlin, D.C., and Warner, J.D., 1989, Characterization of the Sheep Creek Pb-Zn-Ag-Sn prospect, north-central Alaska Range: U.S. Bureau of Mines Report of Investigations 9256, 15 p. Wahrhaftig, Clyde, 1970, Geologic map of the Healy D-3 quadrangle: U.S. Geological Survey Geologic Quadrangle Map GQ-805, scale 1:63,360. Wilson, F.H., Dover, J.H., Bradley, D.C., Weber, F.R., Bundtzen, T.K., and Haeussler, P.J., 1998, Geologic map of central (interior) Alaska: U.S. Geological Survey Open-File Report 98-133, 76 p., 3 sheets, scale 1:500,000.