Unnamed Occurrence (ARDF - ID093; north of hill 2170), Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This occurrence is a pyrite-quartz-bearing shear zone about 65 feet thick that occurs at the contact of a small granite porphyry intrusion with biotite hornfels (Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). The rocks in the vicinity are mainly fine grained intrusive rocks and a large hornfels aureole; this suggests a large underlying intrusive body (Miller and Bundtzen, 1994). The mineralized shear zone can be traced for about a mile to the northeast. Grab samples collected along the zone contain 1,000 parts per million (ppm) mercury (D. Obolewicz, written communication, 1981). Other samples contain up to 500 parts ppm arsenic but no gold (McGimsey and others, 1988).
Workings: The mineralized shear zone was sampled by Anaconda Minerals in 1981 (D. Obolewicz, written communication, 1981 and the U.S. Geological Survey in 1986 (McGimsey and others, 1988).
Age: Unknown; the nearby intrusion is undated (Miller and Bundtzen, 1994).
Commodities (Major) - Hg; (Minor) - As
Development Status: None
Deposit Model: Polymetallic vein? (Cox and Singer, 1986; model 22c).
2 entries listed. 2 valid minerals.
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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.