Smith Lake Prospect, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Smith Lake prospect is located about 150 meters west of the outlet of Smith Lake and 120 meters upstream of the confluence of a small unnamed tributary and the Smith Lake fork of Sheep Creek. It is at an elevation of 3,000 feet (915 m) in the SW1/4 sec. 21, T. 26 N., R. 24 W., of the Seward Meridian. The reporter investigated the prospect in 1981.
Geology: The Smith Lake prospect consists of a high angle, sulfide-rich shear zone in mid-Silurian clastics of the Terra Cotta Sandstone, a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). The shear (fault) zone trends N45E, dips steeply to vertically, and ranges from 0.5 to one meter wide. An adit has been driven into the mineralized zone and explored about 8 meters of the sulfide-vein along strike. Principle sulfides include abundant pyrrhotite, which comprises up to 75 percent of the total sulfides, and minor amounts of pyrite, chalcopyrite, galena and sphalerite. The gangue material contains significant secondary siderite and highly deformed clinopyroxene. Selected chip-channel samples reported by Bundtzen, Kline, and Clough (1982) and Smith and Albanese (1985) contained up to 1.05 percent copper, 1.74 percent lead, 5.22 percent zinc, 42.0 grams/tonne silver, 100 ppm cobalt, and 100 ppm bismuth. A 0.3 meter channel sample collected by Brewer and others (1992) contained 14.8 percent lead, 10.6 percent zinc, 0.6 percent copper, and 90.2 grams/tonne silver.
Workings: Some time prior to 1980, an 8 meter long adit was driven into the sulfide-rich shear zone. Selected chip-channel samples reported by Bundtzen, Kline, and Clough (1982) and Smith and Albanese (1985) contained up to 1.05 percent copper, 1.74 percent lead, 5.22 percent zinc, 42.0 grams/tonne silver, 100 ppm cobalt, and 100 ppm bismuth. A 0.3 meter channel sample collected by Brewer and others (1992) contained 14.8 percent lead, 10.6 percent zinc, 0.6 percent copper, and 90.2 grams/tonne silver.
Alteration: Siderite alteration.
Commodities (Major) - Ag, Cu, Pb, Zn; (Minor) - Bi, Co
Development Status: No
Deposit Model: Polymetallic veins (Cox and Singer, 1986; model 22c).
Mineral List
7 entries listed. 6 valid minerals.
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References
Brewer, N.H., Puchner, C.C., and Gemuts, I., 1992, Farewell district, southwest Alaska Range: North Pacific Mining Company prospectus report, 21 p. Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000. Bundtzen, T.K., Kline, J.T., and Clough, J.G., 1982, Preliminary geologiy of the McGrath B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File report 149, 22 p., 1 sheet, scale 1:40,000. Smith, T.E., and Albanese, M.D., 1985, Preliminary prospect examinations in the McGrath A-2, A-3, and B-2 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 85-54, 19 p.
