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Inmachuk River Mine, Fairhaven District, Northwest Arctic Borough, Alaska, USA

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Location: Inmachuk River is a major drainage on northeast Seward Peninsula that flows northward to Deering on Kotzebue Sound. Its floodplain has been extensively placer mined for gold over about 8.5 miles of length starting at an elevation of about 100 feet and continuing upstream to an elevation of about 250 feet. This is locality 71 of Cobb (1972; MF 417; 1975; OFR 75-429).
Geology: A significant part of the 578,000 ounces of gold and 32,000 ounces of silver recorded as produced from the Fairhaven district came from Inmachuk River (Hudson and DeYoung, 1978) . Its floodplain has been extensively placer mined, mostly by dredging (Cobb, 1975), over about 8.5 miles of length starting at an elevation of about 100 feet and continuing upstream to an elevation of about 250 feet. These elevations suggest that nearshore processes that accompanied Quaternary sea level fluctuations could have influenced the character of these deposits. The sides of Inmachuk River valley contain terrace gravels capped by basalt flows. Some of these gravels are gold-bearing (Moffit, 1927), and some Inmachuk River gold could have been reworked from them. However, early mining reported that the gold was little worn, some with quartz, and some in hematite pebbles (Moffit, 1905). Cinnabar pebbles up to 1/2 inch across were reported to be present in dredge concentrate by Anderson (1947). Most of the bedrock in the area is a metasedimentary schist and marble sequence of Lower Paleozoic age (Till and others, 1986).
Workings: The floodplain of Inmachuk River has been extensively placer mined, mostly by dredging (Cobb, 1975), over about 8.5 miles of length starting at an elevation of about 100 feet and continuing upstream to an elevation of about 250 feet.
Age: Quaternary; two or more cycles of erosion and placer development occurred in the area.
Production: A significant part of the 578,000 ounces of gold and 32,000 ounces of silver recorded as produced from the Fairhaven district came from Inmachuk River (Hudson and De Young, 1978). The majority came from the Candle Creek area (BN074).

Commodities (Major) - Au; (Minor) - Hg
Development Status: Yes; medium
Deposit Model: Placer Au-PGE (Cox and Singer, 1986; model 39a)

Mineral List



4 entries listed. 4 valid minerals.

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References

Anderson, Eskil, 1947, Mineral occurrences other than gold deposits in northwestern Alaska: Alaska Territorial Division of Mines Pamphlet 5-R, 48 p. Cobb, E.H., 1972, Metallic mineral resources map of the Bendeleben quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-417, 1 sheet, scale 1:250,000. Cobb, E.H., 1975, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Bendeleben quadrangle, Alaska: U.S. Geological Survey Open-File Report 75-429, 123 p. Hudson, T.L., and DeYoung, J. H., Jr., 1978, Map and tables describing areas of mineral resource potential, Seward Peninsula, Alaska: U.S. Geological Suvey Open-File Report 78-1-C, 62 p., 1 sheet, scale 1:1,000,000. Moffit, F.H., 1905, The Fairhaven gold placers, Seward Peninsula, Alaska: U.S. Geological Survey Bulletin 247, 85 p. Moffit, F.H., 1927, Mineral industry in Alaska in 1925: U.S. Geological Survey Bulletin 792-A, p. 1-39. Till, A.B., Dumoulin, J.A., Gamble, B. ., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic map and fossil data, Soloman, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86-276, 10 p., 3 plates, scale 1:250,000.

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