Unnamed Occurrence (ARDF - ID063; upper South Fork; Otter Creek), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence is part of a gossan about a mile long that is developed on sulfide-bearing sandstone and siltstone of the Upper Cretaceous, Kuskokwim Group (Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). The gossan contains zones of quartz veinlets, silica-carbonate alteration in altered mafic dikes, and iron-oxide-cemented sandstone breccias. The orientation of the zone is uncertain. Grab samples contain up to 200 parts per billion (ppb) gold, 1,000 ppb silver, 1,900 parts per million (ppm) arsenic, 3,300 ppb mercury, 116 ppm antimony, and 300 ppm zinc (McGimsey and others, 1988).
Workings: Surface samples were collected by the Alaska Division of Geological and Geophysical Surveys and the U.S. Geological Survey in 1986 (McGimsey and others, 1988).
Age: Unknown; altered dikes have not been dated.
Alteration: Silica-carbonate alteration in mafic dikes.
Commodities (Major) - Ag, Au; (Minor) - As, Hg, Sb, Zn
Development Status: None
Deposit Model: Hot springs gold-silver? (Cox and Singer, 1986; deposit model 25a).
2 entries 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.