|Quadrangle map, 1:250,000-scale||BT|
|Quadrangle map, 1:63,360-scale||D-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Ironside Bench is along the south side of the South Fork Koyukuk River about a mile upstream from Gold Bench (BT003). Both Ironside Bench and Gold Bench are named on the current (1975) Bettles D-2 topographic map. The mine is near the center of the south boundary of section 5, T. 25 N., R. 14 W., of the Fairbanks Meridian. The location is accurate.|
Geologic descriptionPlacer gold was discovered on the Ironside Bench of the South Fork of the Koyukuk river in 1900 (Maddren, 1913; Kurtak and others, 2002). Placer mining by hand methods and with heavy equipment continued at erratic intervals until 1941, but only 243 ounces of gold production can be documented. These were mined by ground sluicing and shoveling in 1937 and about 40 acres were said to have been mined by that time (Reed, 1938). Mining took place on a channel about 30 feet higher than the modern channel of the South Fork of the Koyukuk River. The gold was in gravel on a false bedrock (?) surface of decomposed shale. The gravel is coarse with few boulders and there was 6 to 30 feet of gravel, muck and ice over the false bedrock. The gold was distributed through gravel that assayed 0.007 to 0.016 ounce of gold per cubic yard. There was prospecting as recently as 1999 and numerous test pits, tailings piles, and mining equipment from past mining were on the property in 2000. In a 7-foot-deep test pit, Kurtak and others (2002) collected a sample of unmined gravel that contained 0.107 ounce of gold per cubic yard. Kurtak and others (2002) estimated an 'inferred resource' of 50,000 cubic yards with a grade of 0.107 ounce of gold per cubic yard.
|Geologic map unit||(-150.61300184784, 66.9865519558044)|
|Mineral deposit model||Placer Au (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Quaternary.|
|Workings or exploration||Placer gold was discovered on the Ironside Bench of the South Fork of the Koyukuk river in 1900 (Maddren, 1913; Kurtak and others, 2002). Placer mining by hand methods and with heavy equipment continued at erratic intervals until 1941, but only 243 ounces of gold production can be documented. These were mined by ground sluicing and shoveling in 1937 and about 40 acres were said to have been mined by that time (Reed, 1938). There was prospecting as recently as 1999 and numerous test pits, tailings piles, and mining equipment from past mining were on the property in 2000. Sampling by the U.S. Bureau of Land Management in the early 2000s.|
|Indication of production||Yes; small|
|Reserve estimates||Kurtak and others (2002) estimate an 'inferred resource' of 50,000 cubic yards with a grade of 0.107 ounce of gold per cubic yard.|
|Production notes||Kurtak and others (2002) document production of 243 ounces of gold but the data are incomplete.|
See also: Gold Bench (BT003).MAS No. 0020390043
|MRDS Number||A011012; A015626|
Bottge, R.G., 1986, Maps summarizing land availability for mineral exploration and development in northcentral Alaska, 1985: U.S. Bureau of Mines Open-File Report 70-86, 14 sheets.
Bundtzen, T.K., Swainbank, R.C., Wood, J.E., Clough, A.H., 1991 (1992), Alaska's Mineral Industry 1991: Alaska Division of Geological & Geophysical Surveys, Special Report 46, 89 p.
Cobb, E.H., 1972, Metallic mineral resources map of the Bettles quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-387, 1 sheet, scale 1:250,000.
Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Beaver, Bettles, and Medfra quadrangles: U.S. Geological Survey Open-File Report 78-94, 54 p.
Heiner, L.E., and Wolff, E.N., eds., 1968, Mineral resources of northern Alaska, Final report, submitted to the NORTH Commission: University of Alaska, Mineral Industry Research Laboratory Report No. 16, 306 p.
Kurtak, J.M., Klieforth, R.F., Clark, J.M., and Maclean, E.A., 2002, Mineral investigations in the Koyukuk mining district, northern Alaska, 2 vols.: Bureau of Land Management, Alaska Technical Report 50, 845 p.
Maddren, A.G., 1910, The Koyukuk-Chandalar gold region: U.S. Geological Survey Bulletin 442-G, p. 284-315.
Maddren, A.G., 1913, The Koyukuk-Chandalar region, Alaska: U.S. Geological Survey Bulletin 532, 119 p.
Mulligan, J.J., 1974, Mineral resources of the Trans-Alaska Pipeline corridor: U.S. Bureau of Mines Information Circular 8626, 24 p., 9 sheets, scale 1:250,000.
Reed, I.M., 1938, Upper Koyukuk region, Alaska: Alaska Territorial Department of Mines Miscellaneous Report 194-7, 169 p.
Schrader, F.C., 1904, A reconnaissance in northern Alaska across the Rocky Mountains, along Koyukuk, John, Anaktuvuk, and Colville rivers and the Arctic coast to Cape Lisburne, in 1901, with notes by W.J. Peters: U.S. Geological Survey Professional Paper 20, 139 p.
|Reporters||J.M. Britton (Anchorage, Alaska); D.J. Grybeck (Contractor, U.S. Geological Survey)|
|Last report date||4/18/2010|