Clough Occurrence, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: The Clough occurrence is in a saddle that separates two northwest-trending ridgelines about 2.0 kilometers west of the north end of Smith Lake at an elevation of 4,500 feet (1,372 m) in the SW1/4 sec. 20, T. 26 N., R. 24 W., of the Seward Meridian. The reporter visited the site with Jim Clough in 1981. Note that the occurrence as shown in Bundtzen, Harris, and Gilbert (1997; map no. 10) is mislocated.
Geology: The Clough occurrence is a small but rich massive sulfide skarn zone adjacent to an altered, east-west-trending felsic (?) dike. The host rock for the skarn is argillaceous limestone of the mid-Silurian Terra Cotta Mountains Sandstone, a unit of the Dillinger subterrane (Bundtzen, Harris, and Gilbert, 1997). Principle sulfide minerals include massive pyrite and sphalerite veins up to 8 centimeters thick, and a trace of chalcopyrite in an epidote-quartz skarn. One grab sample of high grade mineralization contained 13.0 percent zinc, 0.11 percent lead, 0.50 percent copper, 26 grams/tonne silver, and 300 ppm cobalt. (Bundtzen, Kline, and Clough, 1982; Bundtzen, Harris, and Gilbert, 1997).
Workings: The Clough occurrence was found by Jim Clough of Alaska Division of Geological and Geophysical Surveys during a geologic mapping program in 1981 (Bundtzen, Kline, and Clough, 1982). One grab sample of high grade mineralization contained 13.0 percent zinc, 0.11 percent lead, 0.50 percent copper, 26 grams/tonne silver, and 300 ppm cobalt.
Alteration: None.
Reserves: None.
Commodities (Major) - Ag, Cu, Pb, Zn; (Minor) - Co
Development Status: No
Deposit Model: Low temperature lead-zinc skarn (Cox and Singer, 1986; model 18c).
Mineral List
5 entries listed. 5 valid minerals.
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References
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.
