Little Clearwater Creek Occurrence, Valdez Creek District, Matanuska-Susitna Borough, Alaska, USA
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Location: The Little Clearwater Creek placer extends from an elevation of about 3,000 feet near the Denali Highway upstream to 3,700 feet in section 33, T. 20 S., R. 5 E., Fairbanks Meridian. The location for this record is at an elevation of 3,300 feet, just below where the creek leaves the mountains and enters a broad flood plain. The occurrence corresponds to placer locality A32 of Kurtak and others (1992).
Geology: The lower course of Little Clearwater Creek drains bedrock composed mainly of metabasalt of Nikolai Greenstone of Late Triassic age. In upper Little Clearwater Creek, diverse sedimentary, volcanic, and metamorphic rocks are juxtaposed by a series of low-angle thrust faults (Nokleberg and others, 1991). The thrust-faulted rocks are mineralized at several places, including at MH048, MH049, and MH056, thus furnishing potential source rocks for the placer deposit in lower Little Clearwater Creek (Clautice and others, 1989; Kurtak and others, 1992). The lode deposits in the upper course of Little Clearwater Creek are enriched in tungsten and mercury, trace elements that are found downstream in the placer deposits. Seven samples of alluvium were collected in lower Little Clearwater Creek for placer evaluation (Kurtak and others, 1992, table A42). All contained visible particulate gold. Samples at four sites contained 0.001 ounce of recoverable gold per cubic yard. Sample 3142 contained 0.015 ounce gold per cubic yard. Concentrate samples contained as much as 2.4 parts per million (ppm) silver; all were enriched in tungsten. Sample 1869 contained 3,950 ppm tungsten, 379 ppm mercury, and 325 ppm arsenic, in addition to 0.001 ounce of recoverable gold per cubic yard. The concentrate probably contained scheelite, a tungsten mineral known at upstream site MH048, and possibly cinnabar (mercury sulfide).
Workings: Tammany Mining Company staked the Little Clearwater Creek claims in 1979 and subsequently dug a number of test pits along the creek. The U.S. Bureau of Mines collected a series of placer samples along the creek that contained as much as 0.015 ounce of recoverable gold per cubic yard; concentrate samples contained as much as 3,950 parts per million (ppm) tungsten and 379 ppm mercury (Kurtak and others, 1992).
Commodities (Major) - Au; (Minor) - Ag, Hg, W
Development Status: None
Deposit Model: Placer Au (Cox and Singer, 1986; model 39a).
4 entries listed. 4 valid minerals.
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Clautice, K.H., Smith, T.E., Pessel, G.H., and Solie, D.N., 1989, Geology and mineral occurrences, upper Clearwater Creek area, Mt. Hayes A-6 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Public-data File 89-18, 14 p., 2 sheets, scale 1:24,000. 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.