|Quadrangle map, 1:250,000-scale||ID|
|Quadrangle map, 1:63,360-scale||A-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Donlin Bench placer is an alluvial terrace exposed along the east banks of upper Crooked Creek and Donlin Creek. It extends for 15 miles from Omega Gulch to the headwaters of Donlin Creek (Cady and others, 1955). However, only the portion between the mouth of Omega Gulch and the mouth of Quartz Gulch had sufficient gold to constitute an economic placer. The coordinates are at about the center of the portion that has been mined; the center is near the mouth of Lewis Gulch, about 0.3 miles southeast of the center of section 27, T. 23 N., R. 49 W. of the Seward Meridian. The Donlin Bench above Dome Creek is locality 22 of Cobb (1972 [MF 363]); also described in Cobb (1976 [OFR 76-576]).|
The Donlin Bench placer is in an ancestral alluvial terrace of Late Tertiary age that is on the east banks of Upper Crooked and Donlin Creeks. Paleocurrent data collected in mine cuts and aerial photographic interpretation indicate that at one time, probably in Tertiary time, Donlin and Upper Crooked Creek flowed north into the Iditarod River (Bundtzen, unpublished data, 1984). Subsequent tilting reversed the drainage which resulted in the present southerly stream course of Donlin and Crooked Creeks (Cady and others, 1955; Bundtzen and Miller, 1997). This ancestral channel which was first named the Donlin Bench by Cady and others (1955) is gold bearing for much of its length and it extends for a distance of about 15 kilometers from the mouth of Omega Gulch to the head of Donlin Creek. Only about 6 kilometers of the ancestral stream contained enough placer gold to be mined, and most of the gold was produced where side gulches crossed the alluvial terrace and further concentrated the gold in the Donlin Bench into economic placers. These mines are on Lewis Gulch (ID163), Queen Gulch (ID164), Ruby Gulch (ID165), Snow Gulch (ID166), and Quartz Gulch (ID168).
The rocks in the vicinity are mainly shale and graywacke of the Upper Cretaceous, Kuskokwim Group (Miller and Bundtzen, 1994). A prominent dike swarm swarm that is related to the Donlin Creek deposit lode (ID167) parallels the Donlin Bench for a considerable distance. In addition to gold, the principal heavy minerals in the Donlin Bench are cassiterite, scheelite, garnet, and magnetite (Cobb, 1976 [OFR 76-576]; Bundtzen, Cox, and Veach, 1987). Sulfide minerals are sparse probably because of weathering and oxidation in the relatively old gravels of the Donlin Bench.The gold production summarized here came from both the ancestral terrace gravels and more modern alluvial deposits along Crooked Creek between Lewis and Queen Gulches. Unpublished mint records indicate that the Donlin Bench above Omega Gulch produced 4,170 ounces of gold and 119 ounces of silver from 1911 to 1956.
|Geologic map unit||(-158.238630314837, 62.0490264025081)|
|Mineral deposit model||Placer Au deposit (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||The Donlin Bench is probably Late Tertiary.|
|Alteration of deposit||The bedrock is more deeply weathered on Donlin Bench than in nearby auriferous gulches.|
|Workings or exploration||Placer gold was found on Donlin Creek in 1909 and production commenced in 1910 (Maddren, 1911). From 1910 to 1914, most of the mining in the area took place on Quartz, Snow, and Ruby Gulches (which are described separately) but there was some on the Donlin Bench (Maddren (1915). Small scale mining in open cuts continued on the Donlin Bench until 1956 (Cobb, 1974; Cobb, 1976 [OFR 76-576]).|
|Indication of production||Yes|
|Production notes||Unpublished mint records indicate that the Donlin Bench above Omega Gulch produced 4,170 ounces of gold and 119 ounces of silver from 1911 to 1956.|
Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 242-286.
Cady, W.M., Wallace, R.E., Hoare, J.M., and Webber, E.J., 1955, The central Kuskokwim region, Alaska: U.S. Geological Survey Professional Paper 268, 132 p.
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.
Maddren, A.G., 1911, Gold placer mining developments in the Innoko-Iditarod region: U.S. Geological Survey Bulletin 480-I, p. 236-270.
Maddren, A.G., 1915, Gold placers of the lower Kuskokwim, with a note on copper in the Russian Mountains: U.S. Geological Survey Bulletin 622-H, p. 292-360.
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.
|Reporters||T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.), M.L. Miller (U.S. Geological Survey); and C.C. Hawley (Hawley Resource Group)|
|Last report date||5/26/2003|