Fourth of July Creek Mine, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: The Fourth of July Creek placer deposit extends for about 2.5 miles along the creek from an elevation of from 1,250 and 1,450 feet in elevation. At the upper end of the auriferous zone, the pay gravel overlies altered dacite of the Beaver Mountains volcanic field (Bundtzen, Laird, and Lockwood, 1988; Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). The lower end of the paystreak overlies shale and sandstone of the Upper Cretaceous, Kuskokwim Group (Bundtzen, Laird, and Lockwood, 1988). The auriferous gravel ranges from about 6 to 25 feet thick and it is overlain by about 10 feet of overburden. The gold varies from 853 to 899 fine (Bundtzen, Cox, and Veach, 1987). The heavy minerals identified in concentrates include native mercury, cinnabar, scheelite, native silver, tetrahedrite, polybasite, magnetite, and chromite. One sample of heavy-mineral concentrate contained 24.8 percent chromite. During 1982 and 1983, 45 ounces of gold were recovered in mine tests by Magnuson Mining Company (Bundtzen, Laird, and Lockwood, 1988). Water was a problem during test mining in 1982 and the bedrock and the stream gradient may play key roles in future exploration and mining. The placer contains a significant amounts of chromite; concentrates were tested by the U.S. Bureau of Mines for platinum minerals but they were found to only contain about 60 ppb palladium (Bundtzen, Cox, and Veach, 1987).
Workings: The Fourth of July Creek placer deposit was churn drilled in 1937 by the USSR&M Company (Smith, 1939 [B 910-A]). It was trenched by Magnuson Mining Company in 1982 and 1983 (Bundtzen and others, 1988). Surface samples were also collected by the U.S. Geological Survey in 1985 (McGimsey and others, 1988).
Age: Probably Quaternary.
Production: Placer gold in Fourth of July Creek was first noted in 1911 (Brooks, 1912), but the only production that has been documented is from 1982 and 1983 when 45 ounces gold were recovered during mine tests by Magnuson Mining Company (Bundtzen, Laird, and Lockwood, 1988). Water was a problem during test mining in 1982 and the bedrock and the stream gradient may play key roles in future exploration and mining.
Reserves: None documented, but gold resources are likely (Miller, Bundtzen, and Gray, 2005).
Commodities (Major) - Au; (Minor) - Ag, Cr, Hg, W
Development Status: Yes; small
Deposit Model: Placer Au deposit (Cox and Singer, 1986; model 39a).
9 entries listed. 9 valid minerals.
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Brooks, A.H., 1912, The mining industry in 1911, in Brooks, A.H., and others, Mineral resources of Alaska, report on progress of investigations in 1911: U.S. Geological Survey Bulletin 520-A, p. 17-44. 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. Bundtzen, T.K., Laird, G.M., and Lockwood, M.S., 1988, Geologic map of the Iditarod C-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 96, 13 p., 1 sheet, scale 1:63,360. Cobb, E.H., 1972, Metallic mineral resources map of the Iditarod quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-363, 1 sheet, scale 1:250,000. 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. 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. Smith, P.S., 1939, Mineral industry of Alaska in 1937: U.S. Geological Survey Bulletin 910-A, p. 1-113.