Unnamed Occurrence (ARDF - MH091; west of lower Eureka Glacier), Valdez Creek District, Southeast Fairbanks Borough, Alaska, USA
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Geology: This occurrence is approximately on a major east-west fault that separates granitic rocks of Jurassic or Cretaceous age (on the north) from Paleozoic metasedimentary rocks or Nikolai Greenstone of Late Triassic age (Nokleberg and others, 1991). A steep northwest cross fault was mapped at about this locality by Rose (1966 [ADMM GR 20, figure 3). Rose also mapped lenticular masses of dunite and gabbro farther north, within dioritic rocks of the granitic complex. The U.S. Bureau of Mines traversed along the gulch that exposes the occurrence between about 4,500 and 5,500 feet elevation and found inclusions or dikes of serpentinized dunite in a granitic host that they called quartz monzonite (Kurtak and others, 1992, locality A 8). The serpentinized dunite contained 0.21 to 0.24 percent nickel and 0.13 to 0.15 percent chromium. The mineral host(s) of the nickel and chromium is unknown. Silicified quartz monzonite in a fault zone contained 12 parts per billion palladium and 5 parts per million platinum. Platinum and palladium were also detected in creek gravel and dunite float (Kurtak and others, 1992, table A8).
Workings: U.S. Bureau of Mines geologists traversed the deep gulch that crosses the intrusive rock-metasedimentary rock contact (Kurtak and others, 1992). Their samples of serpentinized dunite contained as much as 0.24 percent nickel and 0.15 percent chromium; an altered quartz monzonite contained 12 parts per billion palladium. The occurrence is on active MAN Resources claims (W.T. Ellis, written communication, 2001).
Age: Mesozoic (?), possibly the age of the ultramafic host rocks.
Alteration: Silicification of quartz monzonite; serpentinization of dunite (Kurtak and others, 1992).
Commodities (Major) - Cr, Ni; (Minor) - Pd, Pt
Development Status: None
Deposit Model: Ultramafic related.
1 entry listed. 1 valid mineral.
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Kurtak, J.M., Southworth, D.D., Balen, M.D., and Clautice, K.H., 1992, Mineral investigations in the Valdez Creek mining district, south-central Alaska: U.S. Bureau of Mines Open-File Report 1-92, 659 p., 2 plates, scale 1:250,000. Nokleberg, W.J., Lange, I.M., Roback, R.C., Yeend, Warren, and Silva, S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, mineral deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000. Rose, A.W., 1966, Geological and geochemical investigations in the Eureka Creek and Rainy Creek areas, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 20, 41 p., 3 maps [figures], scale 1:40,000.