Miyaoka West Prospect, Bonnifield District, Southeast Fairbanks Borough, Alaska, USA
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Geology: Rocks at the Miyaoka West prospect consist of complexly deformed greenstone, chlorite schist, and calc-schist of Devonian age (Nokleberg and Aleinikoff, 1985; Lange and others, 1993). The deposit is generally stratabound and consists mainly of pyrrhotite and pyrite. Chalcopyrite, sphalerite, and galena locally occur in fairly sparsely distributed pods, disseminations, and vein-like zones. The pods are as much as about 3 feet across. Samples collected during a 1980's U.S. Geological Survey reconnaissance contained as much as 0.5 percent zinc, 0.43 percent copper; and 0.017 percent lead. Trace elements in the mineralized rocks include as much as 50 parts per million (ppm) tin, 0.2 ppm gold, and 500 ppm cobalt (Nokleberg and others, 1991).
Workings: Re-examination of the prospect by American Copper and Nickel Company in 1993 indicated that pyrrhotite is the main sulfide and that base metal concentrations are generally low (W.T. Ellis, unpublished data, 1993).
Age: Devonian, the age of the host strata.
Commodities (Major) - Cu, Zn; (Minor) - Ag, Au, Co, Pb, Sn
Development Status: None
Deposit Model: Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
5 entries listed. 5 valid minerals.
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Aleinikoff, J.N., and Nokleberg, W.J., 1985, Age of Devonian igneous-arc terranes in the northern Mount Hayes quadrangle, eastern Alaska Range, Alaska, in Bartsch-Winkler, Susan, ed., The United States Geological Survey in Alaska--Accomplishments during 1984: U.S. Geological Survey Circular 967, p. 44-49. Lange, I. M., Nokleberg, W.J., Newkirk, S. R., Aleinikoff, J.N., Church, S.E., and Krouse, R.H., 1993, Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana terrane, eastern Alaska Range, Alaska: Economic Geology, v. 88, p. 344-376. Nokleberg, W.J., and Aleinikoff, J.N., 1985, Summary of stratigraphy, structure, and metamorphism of Devonian igneous-arc terranes, northeastern Mount Hayes quadrangle, eastern Alaska Range, IN Bartsch-Winkler, Susan, ed., The United States Geological Survey in Alaska--Accomplishments during 1984: U.S. Geological Survey Circular 967, p. 66-71. Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000.