Unnamed Occurrence (ARDF - ID139; south of hill 1735), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence is a quartz breccia zone with limonite and tourmaline in hornfelsed sandstone of the Upper Cretaceous, Kuskokwim Group, adjacent to a small body of biotite quartz monzonite. The mineralized breccia covers an area about 160 by 500 feet in area that is oriented northeast The monzonite contains a stockworks of numerous small quartz-tourmaline-sericite veins. The quartz monzonite is undated, but a similar intrusive body exposed about 0.3 mile to the south has a 40K/40Ar age of 71.1 Ma (Bundtzen, Miller, and Laird, 1986; Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). Grab samples of mineralization contained up to 1,000 parts per million (ppm) tin, 1,000 parts per billion (ppb) silver, 500 ppm copper, 350 ppm zinc, 100 ppm lead, 160 ppm arsenic, 54 ppm antimony, and 1,200 ppb mercury (McGimsey and others, 1988).
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). Battle Mountain Mining Company explored the occurrence in the late 1980s and drilled one diamond-drill hole; the results are confidential (Szumigala, 1993) Placer Dome U S flew an aeromagnetic survey over the Upper Granite Creek area but that survey has not been publicly released (L.E. Wyrick, oral communication, 2003).
Age: Undated; a similar intrusive of quartz monzonite exposed about 500 meters to the south has a 40K/40Ar age of 71.1 Ma (Bundtzen, Miller, and Laird, 1986; Miller and Bundtzen, 1994).
Alteration: Development of quartz-tourmaline-sericite greisen; iron-oxide alteration.
Commodities (Major) - Ag, Sn; (Minor) - As, B, Cu, Hg, Pb, Sb, Zn
Development Status: None
Deposit Model: Sn-polymetallic deposit or Polymetallic vein (Cox and Singer, 1986; model 20b o
4 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. 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.