Dishna River Prospect, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Location: This prospect is on a knob along a ridge overlooking the headwaters of the Dishna River. It is about 0.5 mile southwest of hill 1528, about 0.8 mile northeast of hill 1803, and about 0.5 mile west-southwest of the center of section 22, T. 29 N., R. 44 W., of the Seward Meridian. The location is accurate.
Geology: This prospect consists of brecciated, pod-shaped, quartz-sulfide veins that cut sheared shale and sandstone of the Upper Cretaceous. Kuskokwim Group (Miller and Bundtzen, 1994; Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005). The rocks are sericitized and alunite has been reported (Don Harris, oral communication, 1983). Numerous slickensides in the wall rock suggests that the prospect occurs along a major, high-angle, fault. Individual brecciated veins strike N05E to N05W and dip steeply to vertically. Mineralization consists of sulfide-bearing masses in quartz that locally contain up to 25 percent stibnite and 3-5 percent arsenopyrite (Bundtzen and Miller, 1997). At least three individual veins have been recognized over a total width of about 20 feet. Caved and overgrown prospect pits were dug before World War II. The area has long been regarded as having economic potential and the prospect is a plausible source for placer gold and cinnabar found in the Dishna River (Don Harris, oral communication, 1983). Eighteen chip-channel samples were taken at uniform intervals along the largest vein for about 460 feet. The samples average 2.46 parts per million (ppm) gold, 5,200 ppm antimony, and 4,500 ppm arsenic (Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005). The highest grade sample contained 11.0 ppm gold, more than 1.00 percent antimony, more than 1.00 percent arsenic, more than 10.0 ppm mercury, and 1.0 ppm silver. Based on the surface sampling, Bundtzen and Miller (1997) estimated a resource of abut 41,000 tons of material that averages 2.46 ppm gold and 0.52 percent antimony.
Workings: Caved and overgrown prospect pits were dug before World War II. The area was mapped and sampled by the U.S. Geological Survey and the Alaska Division of Geological and Geophysical Surveys in 1986.
Alteration: The host rocks are sericitized and alunite has been reported.
Production: Not determined; possibly small production from old pits.
Reserves: Based on the surface sampling, Bundtzen and Miller (1997) estimated a resource of about 41,000 tons of material that averages 2.46 ppm gold and 0.52 percent antimony.
Commodities (Major) - Au, Sb; (Minor) - Ag, As, Hg
Development Status: Undetermined.
Deposit Model: Simple Antimony deposit (Cox and Singer, 1986; model 27d).
4 entries listed. 4 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.