Willow Creek Mine, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA
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Geology: The Willow Creek Mine is developed on an auriferous paystreak in the valley of modern Willow Creek. It could be the extension of the Happy Creek placer (ID103), although the lower Happy Creek placer is lower grade and the the two deposits may not be continuous (John Fullerton, oral communication, 1986). The bedrock under most of the Willow Creek placer is shale and sandstone of the Upper Cretaceous. Kuskokwim Group. Willow Creek is aligned along a northeast trending lineament that is interpreted to be a high angle fault. A dike swarm nearly parallel to the fault lends credence to this interpretation (Bundtzen and others, 1988; Bundtzen and others, 1992; Miller and Bundtzen, 1994; Miller, Bundtzen, and Gray, 2005). The paystreak in Willow Creek starts at the mouth of Happy Creek. The overburden increases from about 12 feet thick at that point to about 25 feet thick at the southwest end of the paystreak (Mertie, 1936; John Fullerton, oral communication, 1986). The principal heavy minerals in concentrates are abundant zircon, cinnabar, magnetite, ilmenite, and chromite (Cobb, 1976 [OFR 76-576]; Bundtzen Cox, and Veach, 1987; Bundtzen and others, 1992). The gold averages 874 fine, the same as the gold on the Willow bench (ID105). The pay zones in Lower Willow Creek were lower grade than either Happy Creek or the Willow bench. The placer deposits on lower Willow Creek are largely mined out. However, the paystreak deepens downstream, suggesting that the cutoff is economic rather than abrupt. Mineralized gold-bearing stockwork quartz veins in intrusive rocks on Chicken Mountain could be the lode source for the gold and heavy minerals on Willow Creek (Bundtzen and others, 1992). However, there are few monzonite cobbles in the Lower Willow Creek paystreak; this may, however, reflect the considerable distance from distance from Chicken Mountain that would tend to break down the granitic material (Mertie, 1936). The dike swarm exposed at the head of the creek also may be a source of the placer gold in Willow Creek. Based on examination of published and unpublished records, Bundtzen and others (1992) estimated that Willow Creek and the Willow bench (ID105) produced at least 41,948 ounces of gold and 5,033 ounces of silver, mainly from 1910 to 1986.
Workings: Gold was discovered on Willow Creek early in the 20th Century, and part of the creek was explored by test pits and drifts in 1910 (Maddren, 1911). An early claimant was Frank G. Manley who also developed placer claims in Flat Creek. A steam-powered dragline began to operate in 1915, the first to be used in the district (Brooks, 1916). Manley worked the claims at intervals into the 1920s. In about 1933, Manley leased the claims to the Iditarod Mining Company of W. E. Dunkle and Pardners Mines of New York who erected a large dragline in 1935, after the creek was redrilled under the supervision of Ben Bromberg. It was necessary to construct a long bedrock drain and to bring water to the field (Hawley, 2003). The project failed in 1936 or 1937 partly because of low-grade gold values and frozen ground. However, the development led to the successful mining of Willow Creek by the Fullerton brothers from the 1960s to the 1980s.
Age: The Willow Creek placer is probably Quaternary.
Production: Based on examination of published and unpublished records, Bundtzen and others (1992) estimated that Willow Creek and the Willow bench (ID105) produced at least 41,948 ounces of gold and 5,033 ounces of silver, mainly from 1910 to 1986.
Reserves: The placer deposits on lower Willow Creek are largely mined out. However, the paystreak deepens downstream, suggesting that the cutoff is probably economic rather than abrupt.
Commodities (Major) - Ag, Au; (Minor) - Cr, Hg, Sn, U, W, Zr
Development Status: Yes
Deposit Model: Au placer deposit (Cox and Singer, 1986; model 39a).
6 entries listed. 6 valid minerals.
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Brooks, A.H., 1916, Antimony deposits of Alaska: U.S. Geological Survey Bulletin 649, 67 p. Bundtzen, T.K., Green, C.B., Deagen, J.R., and Daniels, C.L., 1987, Alaska's mineral industry, 1986: Alaska Division of Geological and Geophysical Surveys Special Report 40, 68 p. Bundtzen, T.K., Miller, M.L., Bull, K.F., and Laird, G.M., 1988, Geology and mineral resources of Iditarod mining district, Iditarod B-4 and eastern B-5 quadrangles, west-central Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File Report 88-19, 45 p., 1 sheet, scale 1:63,360 scale (largely superseded by DGGS Geologic Report 97, Bundtzen and others, 1992). 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. 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. Hawley, Charles C., 2003, Wesley Earl Dunkle, Alaska's Flying Miner: University of Alaska Press, 380 p. Maddren, A.G., 1911, Gold placer mining developments in the Innoko-Iditarod region: U.S. Geological Survey Bulletin 480-I, p. 236-270. 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.