Lewis Gulch

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Hg
Ore minerals arsenopyrite; cinnabar; gold; ilmenite; monazite; stibnite
Gangue minerals garnet

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale A-5
Latitude 62.04942
Longitude -158.22431
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Lewis Gulch placer extends for about 0.6 mile above its mouth on Crooked Creek. The center of the placer is about 0.3 mile above its mouth and about 0.6 mile southeast of the center of section 27, T. 23 N., R. 49 W., of the Seward Meridian. The location is accurate. Lewis Gulch is locality 17 of Cobb (1972 [MF 363]); also described in Cobb (1976 [OFR 76-576]).

Geologic setting

Geologic description

The Lewis Gulch mine is a placer deposit near the intersection of Lewis Gulch and the ancestral 'Donlin Creek' alluvial terrace that developed on the southeast flank of modern Donlin and Crooked Creeks. According to Cady and others (1955) and Bundtzen and Miller (1997), Donlin Creek originally flowed northeast into the Iditarod River. After regional tilting, the drainage reversed direction and Donlin and Crooked Creeks subsequently flowed into the Kuskokwim River. In Lewis Gulch, low grade auriferous gravel deposits in the ancestral channel were reworked to form locally rich placer gold deposits. This ancestral bench is probably Late Tertiary in age.
The gold-bearing fluvial gravels in Lewis Creek extend for about 0.6 mile. The gravel is from 15 to 65 feet thick. The gold was distributed irregularly; some gravel was rich and some was almost barren. The principal heavy minerals identified in concentrates are cinnabar, stibnite, arsenopyrite, garnet, ilmenite, and monazite (Bundtzen, Cox, and Veach, 1987). The source of the placer gold is probably the Donlin Creek lode prospect (ID167), which is at the head of Lewis Gulch (Miller and Bundtzen, 1994; Bundtzen and Miller, 1997). Unpublished U.S. Mint data indicate that Lewis Gulch produced 6,039 ounces gold from 1918 to 1939 (Miller, Bundtzen, and Gray, 2005).
Geologic map unit (-158.226720034226, 62.048726426422)
Mineral deposit model Placer Au deposit (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization The alluvium in modern Lewis Gulch is probably Quaternary; the ancestral terrace is probably Late Tertiary.

Production and reserves

Workings or exploration Gold was first found on Lewis Gulch in 1910 (Maddren, 1911). Most mining since has been from small scale open cuts (Cobb, 1972 [MF 363]; Cobb, 1973; Cobb, 1976 [OFR 76-576]).
Indication of production Yes
Production notes Production began on Lewis Gulch in 1911, and continued intermittently on a small scale at least through the early 1950s (Brooks, 1912; Cady and others, 1955). Unpublished Mint data indicate that Lewis Gulch produced 6,039 ounces of gold from 1918 to 1939 (Bundtzen, Cox, and Veach, 1987; Miller, Bundtzen, and Gray, 2005).

References

MRDS Number A015061

References

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.
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.
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