Unnamed Occurrence (ARDF - ID144; southwest Granite Mountain), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence consists of a extensive zone of cassiterite-bearing, tourmaline-axinite greisen that may be a southwest extension of the similar occurrence to the northeast (ID146) (Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). Tourmaline-rich quartz porphyry and brecciated tourmaline-axinite-cemented hornfels occurs in the cupola zone of the 62.6 Ma, Granite Mountain pluton (Miller and Bundtzen, 1994). Bundtzen and Miller (1997) identified disseminated cassiterite in one sample; however, no sulfides or sulfosalts were observed. Grab samples of mineralization contained up to 300 parts per million (ppm) tin, 7,000 parts per billion (ppb) silver, 500 ppm lead, 54 ppm antimony, 100 ppm arsenic, 54 ppm bismuth, and more than 2,000 ppm boron (McGimsey and others, 1988).
Workings: Samples were collected by the U.S. Geological Survey and Alaska Division of Geological and Geophysical Surveys in 1984 (McGimsey and others, 1988).
Age: Undated; probably related to the nearby Granite Mountain pluton that has an age of 62.6 Ma (Bundtzen and Miller,1997).
Alteration: Development of tourmaline-axinite greisen.
Commodities (Major) - Ag, Sn; (Minor) - As, B, Bi, Pb, Sb
Development Status: None
Deposit Model: Sn-polymetallic deposit (Cox and Singer, 1986; model 20b).
2 entries listed. 1 valid mineral.
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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. 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.