Twentymile River

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale AN
Quadrangle map, 1:63,360-scale A-5
Latitude 61
Longitude -148.9
Nearby scientific data Find additional scientific data near this location
Location and accuracy Includes upper portions of Twentymile River. Twentymile River also flows in the Anchorage A-6 map and southerly into the Seward Quadrangle. Accurate to within 3 miles. This is locality P-42 of Hoekzema and Fechner (1986).

Geologic setting

Geologic description

Placer gold is disseminated in poorly- to moderately-washed glacial fluvial gravels along the upper portions of Twentymile Creek. Five alluvium samples from the upper portions of Twentymile River contained from a trace to 0.0073 oz Au/cubic yard (Jansons and others, 1984). Numerous large boulders are present (Hoekzema and Fechner, 1986). The bedrock in the region is Late Cretaceous metasedimentary rocks of the Valdez Group.
Geologic map unit (-148.902175067696, 60.9994324454851)
Mineral deposit model Placer Au (Cox and Singer, 1986; model 39a)
Mineral deposit model number 39a
Age of mineralization Quaternary.

Production and reserves

Workings or exploration Five alluvium samples from the upper portions of Twentymile River contained from a trace to 0.0073 oz Au/cubic yard (Jansons and others, 1984).
Indication of production None
Production notes No recorded production, however Hoekzema and Fechner (1986) state the mineral development potential is moderate for small mining operation. Pockets of higher grade material may occur within and adjacent to the river channel (Jansons and others, 1984).

References

MRDS Number A106179

References

Reporters D.P. Bickerstaff (USGS contractor); S.W. Huss (USGS)
Last report date 7/30/1998