Unnamed Occurrence (ARDF - MG017; near Cheeneetnuk River), McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This unnamed occurrence is a pyrite-rich gossan developed in Upper Paleozoic argillite of the Mystic subterrane near a thrusted contact with an overlying, Late Devonian shallow water limestone (Gilbert, 1981; Wilson and others, 1998). The pyritic gossan parallels the thrust contact and may mark a subsidiary thrust fault zone. The argillite host appears to be thermally upgraded to hornfels by a buried intrusive system; a Tertiary granite is exposed about 5 kilometers NE of the occurrence area. Platey axinite and quartz were found in two localities in the argillite. The extent of the site is unknown. One grab sample of the pyritic material contained 290 ppm copper, 150 ppm zinc, and 7 ppm molydenum (Gilbert, 1981).
Workings: W.G. Gilbert sampled the mineralized zone during geologic mapping for the Alaska Division of Geological and Geophysical Surveys in 1977 (Gilbert, 1981). One grab sample of the pyritic material yielded 290 ppm copper, 150 ppm zinc, and 7 ppm molybdenum.
Reserves: None.
Commodities (Major) - Cu; (Minor) - Mo, Zn
Development Status: No
Deposit Model: Polymetallic replacement (?) (Cox and Singer, 1986; model 19a).
Mineral List
3 entries listed. 2 valid minerals.
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References
Gilbert, W.G., 1981, Preliminary geologic map and geochemical data, Cheeneetnuk River area, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File Report 153, 12 p., 2 sheets, 1:63,360 scale. 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.
