Upper Chicken Creek Mine, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: This site on Upper Chicken Creek includes both a lode deposit and a residual placer over it. The lode deposit is a quartz stockworks in monzonite of the Chicken Mountain pluton which is 68.7-70.9 Ma (Bundtzen and others, 1992). Two sets of steeply dipping quartz veins in the stockworks strike N30-40E and N45-55W; a minor set is nearly horizontal. The orientations suggest that the veins are controlled by an orthogonal joint set in the monzonite (Bundtzen and others, 1992; Miller and Bundtzen, 1994, and Miller, Bundtzen, and Gray, 2005). The veins are associated with tourmaline and secondary biotite in the monzonite. The quartz veins in the stockworks contain native gold, stibnite, silver-bearing sulfosalts, cinnabar, and minor chalcopyrite (Bundtzen and others, 1992). The quartz stockworks is the source of a residual placer above it. When visited by Mertie (1936) in 1933, miners, who had been mining here since 1924, were working a 500-feet-wide residual placer deposit. Most of the gold occurred in a 3- to 6-foot thick zone of monzonite sand at the base of a 20- to 30-foot thick layer of decomposed monzonite. Small amounts of gold occurred in the gruss overburden. The gold was fine-grained, angular, and nearly equidimensional. The largest nugget weighed about 1/2 ounce. The fineness of the gold as reported by the miners was 862 based on assays of five samples collected in 1929. The residual placer was mined nearly concurrently with the Idaho, and Upgrade deposits at the head of Flat Creek (ID107). The heavy minerals in the placer are essentially those found in the lode (Bundtzen, Cox, and Veach, 1987). Heavy mineral concentrates from Chicken Creek locally were also radioactive, probably from concentrations of uranium and thorium in zircon (White and Killeen, 1953). Placer concentrates mined in the late 1950s contained 53.3 percent mercury, 500 parts per million (ppm) antimony, and 16.1 ppm silver (Maloney, 1962). Production from the placer in upper Chicken Creek is combined with that of lower Chicken Creek (ID112).
Workings: The lode gold deposit in upper Chicken Creek and the residual placer above it was known by 1912 (Eakin, 1914). Mining commenced soon afterward; extensive open cut mining occurred between 1915 and World War II, including a mining operation that lasted from at least 1924 until 1933 (Mertie, 1936; Cobb, 1976 [OFR 76-576]). Production from upper Chicken Creek is combined with that of lower Chicken Creek (ID112). The U.S. Bureau Mines tested the disseminated deposits in upper Chicken Creek with shallow auger holes (Kimball, 1969). Rock samples were collected by the U.S. Geological Survey and Alaska Division of Geological and Geophysical Surveys in the 1980s and released in Bull (1988) and Bundtzen and others (1992).
Age: Unknown; the Chicken Mountain pluton is 68.7 - 70.9 Ma (Bundtzen and others, 1992).
Alteration: Tourmaline and quartz are in the veins; the monzonite is altered to secondary biotite.
Production: Production from upper Chicken is combined with that of Lower Chicken Creek (ID112).
Commodities (Major) - Au; (Minor) - Ag, Bi, Cd, Cu, Hg, Pb, Sb
Development Status: Yes
Deposit Model: Porphyry Cu-Au and Au placer (Cox and Singer, 1986; models 20c and 39a).
7 entries listed. 7 valid minerals.
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Bull, K.F., 1988, Genesis of the Golden Horn and related mineralization in the Flat Creek area, Alaska: Fairbanks, University of Alaska M.Sc. thesis, 300 p. Bundtzen, T.K., Miller, M.L., Laird, G.M., and Bull, K.F., 1992, Geology and mineral resources of Iditarod mining district, Iditarod B-4 and eastern B-5 quadrangles, southwestern Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 97, 46 p., 2 sheets, scale 1:63,360. Bundtzen, T.K., Cox, B.C., and Veach, N.C., 1987, Heavy mineral provenance studies in the Iditarod and Innoko districts, western Alaska: Process Mineralogy VII, The Metallurgical Society, p. 221-246. Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction material) in the Iditarod and Ophir quadrangles, Alaska: U.S. Geological Survey Open-File Report 76-576, 101 p. Eakin, H.M., 1914, The Iditarod-Ruby region, Alaska: U.S. Geological Survey Bulletin 578, 45 p. Kimball, A.L., 1969, Reconnaissance sampling of decomposed monzonite for gold near Flat, Alaska: U.S. Bureau of Mines Open File Report 6-69, 39 p. Maloney, R.P., 1962, Investigation of mercury-antimony deposits near Flat, Yukon River region, Alaska: U.S. Bureau of Mines Report of Investigations RI 5991, 44 p. Mertie, J.B., Jr., 1936, Mineral deposits of the Ruby-Kuskokwim region, Alaska: U.S. Geological Survey Bulletin 864-C, p. 115-245. 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. White, M.G., and Killeen, P.L., 1953, Reconnaissance for radioactive deposits in the lower Yukon-Kuskokwim highlands region, Alaska, 1947: U.S. Geological Survey Circular 255, 18 p.