Inmachuk River

Mine, Active?

Commodities and mineralogy

Main commodities Au
Other commodities Hg
Ore minerals cinnabar; gold
Gangue minerals hematite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale BN
Quadrangle map, 1:63,360-scale D-3
Latitude 65.902
Longitude -163
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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).

Geologic setting

Geologic description

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).
Geologic map unit (-163.002698005365, 65.901307911955)
Mineral deposit model Placer Au-PGE (Cox and Singer, 1986; model 39a)
Mineral deposit model number 39a
Age of mineralization Quaternary; two or more cycles of erosion and placer development occurred in the area.

Production and reserves

Workings or exploration 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.
Indication of production Yes; medium
Production notes 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).

References