Unnamed Occurrence (ARDF - ID141; southwest of Granite Mountain), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence is a mineralized zone of uncertain size and orientation in iron-oxide-bearing hornfels derived from sandstone of the Upper Cretaceous, Kuskokwim Group; the hornfels is associated with a swarm of monzonite dikes (Miller and Bundtzen, 1994; Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005). One grab sample of mineralization contained 2,000 parts per billion (ppb) silver, 500 parts per million (ppm) copper, 600 ppm arsenic, 50 ppm antimony, 150 ppm lead, 3.0 ppm bismuth, 20.00 percent iron, and more than 2,000 ppm boron (McGimsey and others, 1988). The iron oxides are probably an oxidization product of sulfides; the high boron content suggests that tourmaline or axinite may be present in the altered sandstone.
Workings: Samples were collected by the U.S. Geological Survey and Alaska Division of Geological and Geophysical Surveys in the 1980s (McGimsey and others, 1988).
Alteration: Iron oxide alteration.
Commodities (Major) - Ag, Cu; (Minor) - As, B, Bi, Fe, Sb
Development Status: None
Deposit Model: Polymetallic vein (Cox and Singer, 1986; model 22c).
1 entry listed.
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Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 242-286. Bundtzen, T.K., Miller, M.L., and Laird, G.M., 1986, Prospect examination of the Wyrick placer/lode system, Granite Creek, Iditarod-George mining district, Iditarod B-2 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File Report 86-29, 10 p., 1 sheet, scale 1:200. 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. Szumigala, D.J., 1993, Gold mineralization related to Cretaceous-Tertiary magmatism in the Kuskokwim Mountains of west-central and southwestern Alaska: Los Angeles, University of California Ph.D. dissertation, 300 p.