Gold Bench

Mine, Probably inactive

Commodities and mineralogy

Main commodities Au
Other commodities Bi; Cu; Hg; Pb; REE; Sn; Th; Ti; U; W
Ore minerals bismuthinite; cassiterite; chalcopyrite; cinnabar; galena; gold; magnetite; monazite; pyrite; rutile; scheelite; uranothorianite
Gangue minerals garnet; hematite; magnetite; sphene

Geographic location

Quadrangle map, 1:250,000-scale BT
Quadrangle map, 1:63,360-scale D-2
Latitude 66.981
Longitude -150.6367
Nearby scientific data Find additional scientific data near this location
Location and accuracy Gold Bench is on a prominent bend in the South Fork Koyukuk River, about 1.2 miles upstream from the mouth of John R Creek. The mine is named on the current (1975) Bettles D-2 topographic map. The placer is about 1,000 feet wide, 2,000 feet long, and covers an area of about 60 to 100 acres. The location is accurate.

Geologic setting

Geologic description

Gold Bench was one of the richest of the bench gravels that have been mined along the South Fork of the Koyukuk River Kurtak and others, 2002). Gold was discovered in 1900 and there were several episodes of mining, notably from 1901 to 1910, and in 1945. The early mining was by ground sluicing and shoveling in and by 1937 about 100 acres had been mined. Hydraulic mining in the mid-1940s used a dragline. Production of 8,788 ounces of gold can be documented from incomplete records.
The gold-bearing gravel lies on top of a sloping bench inside a prominent bend in the South Fork of the Koyukuk River. The bench is about 1,000 feet wide and 4,000 feet long. Maddren (1913) reported that the gold was on false bedrock of reddish sand. The richest area was 150 to 200 feet wide and about 1,200 feet long. The gold is fine, flattened, and flaky. Reed (1938) reported that the gold was on false bedrock of blue clay developed from shale, overlain by 6 to 10 feet of gravel with many large boulders.
Samples of concentrates contained a variety of accessory minerals including magnetite, hematite, garnet, pyrite, chalcopyrite, cinnabar, rutile, cassiterite, scheelite, monazite, uranothorianite, galena, sphene, possibly bismuthinite and up to 0.18 percent equivalent uranium (Wedow and others, 1952; Nelson and others, 1954). The source of the gold is not known. Maddren (1913) speculated that it might have come from the Tramway Bar (WI006) area on the Middle Fork Koyukuk River or, more likely, from the hills to the south. Cobb (1973) thought that at least some of the gold was probably from reworked glacial deposits.
Kurtak and others (2002) sampled the placer for the Bureau of Land Management and estimated an 'inferred resource' of 160,000 cubic yards with an average grade of 0.005 ounce of gold per cubic yard. They also indicated that the bench gravel has mostly been mined out and the gravel in the modern channel of the river was subeconomic.
Geologic map unit (-150.639401091404, 66.980551342561)
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 Gold Bench was one of the richest of the bench gravels that have been mined along the South Fork of the Koyukuk River. Gold was discovered in 1900 and there were several episodes of mining, notably from 1901 to 1910, and in 1945. The early mining was by ground sluicing and shoveling in and by 1937 about 100 acres had been mined. The hydraulic mining in the mid-1940s used a dragline.
Indication of production Yes
Reserve estimates Kurtak and others (2002) sampled the placer for the Bureau of Land Management and estimated an 'inferred resource' of 160,000 cubic yards with an average grade of 0.005 ounce of gold per cubic yard. They also indicated that the bench gravel has mostly been mined out and the gravel in the modern channel of the river was subeconomic.
Production notes Production of 8,788 ounces of gold can be documented from incomplete records (Kurtak and others, 2002).

Additional comments

Pleistocene bones are said to have been common in the gravels of Gold Bench (Reed, 1938). See also: Ironside Bench (BT004).
MAS No. 0020390001

References