Unnamed Occurrence (ARDF - ID128; north of Beaver Creek), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence is an extensive pyrolusite-bearing bed or layer in sandstone, shale and volcaniclastic conglomerate of the Upper Cretaceous, Kuskokwim Group (Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). The blue-gray zone of semi-massive pyrolusite is about 3 feet thick and can be traced for about 1,000 feet along strike. Grab samples of the sandstone with pyrolusite contained more than 0.5 percent manganese, 240 parts per billion (ppb) mercury, and 10.0 parts per million (ppm) molybdenum (McGimsey and others, 1988).
Workings: Samples were collected by the U.S. Geological Survey and the Alaska Division of Geological and Geophysical Surveys in 1984 (McGimsey and others, 1988).
Age: Late Cretaceous?
Commodities (Major) - Mn; (Minor) - Hg, Mo
Development Status: None
Deposit Model: Probably sedimentary Mn (Cox and Singer, 1986; model 34b).
1 entry listed. 1 valid mineral.
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McGimsey, R.G., Miller, M.L., and Arbogast, B.F., 1988, Paper version of analytical results, and sample locality map for rock samples from the Iditarod quadrangle, Alaska: U.S. Geological Survey Open-File Report 88-421-A, 110 p., 1 sheet, scale 1:250,000. Miller, M.L., and Bundtzen, T.K., 1994, Generalized geologic map of the Iditarod quadrangle, Alaska showing potassium-argon, major oxide, trace element, fossil, paleocurrent, and archeological sample localities: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-A, 48 pages; 1 sheet, scale 1:250,000. Miller, M.L., Bundtzen, T.K., and Gray, J.E., 2005, Mineral resource assessment of the Iditarod quadrangle, west-central Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-B, scale 1:250,000, pamphlet.