Potosi Creek

Mine, Inactive

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Hg
Ore minerals arsenopyrite; cinnabar; gold; pyrite; stibnite
Gangue minerals ilmenite; magnesiochromite; magnetite; quartz

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale D-2
Latitude 62.97594
Longitude -156.5117
Nearby scientific data Find additional scientific data near this location
Location and accuracy Potosi Creek, which is not named on the USGS D-2 topographic map, is a 1.6-mile-long west-flowing tributary of Ganes Creek. The mouth of Potosi Creek is about 0.8 mile north-northeast of the mouth of Six Gulch, near the mining camp of the Clark-Wiltz partnership in the SE1/4 SE 1/4, section 5, T. 33 N., R. 38 W., of the Seward Meridian. The location is accurate.

Geologic setting

Geologic description

The Potosi Creek gold placer is at least 1.6 mile long and averages about 160 feet wide. The overburden of organic silt and colluvium averages about 10 feet thick. The rocks in the area are mainly shale and sandstone of the Upper Cretaceous, Kuskokwim Group. Two dike-sill complexes occur along Potosi Creek; one is about 1,000 feet about its mouth and a second about 1 mile further. Samples of mineralized quartz in the dike rocks that outcrop in Potosi Creek contained up to 850 parts per billion (ppb) gold (T.K. Bundtzen, unpublished data, 1998).
Most of the material in the pay streak consists of rounded gravels of sandstone and siltstone and intermediate dike rocks that locally intrude the Kuskokwim Group sedimentary rocks. All the alluvium in the pay streak seems to be locally derived (Miller, Bundtzen and Gray, 2004). In addition to gold, the heavy minerals include major to minor amounts of magnesiochromite, ilmenite, pyrite, and magnetite, and traces of cinnabar, stibnite, and arsenopyrite (Bundtzen and others, 1987; T.K. Bundtzen, unpublished dat, 1998). Gold locally occurs in large nuggets; a 55 ounce gold-quartz nugget was found in 1995 near the mouth of the creek (Dan Wilz, oral communication, 1998).
Placer deposits near the mouth of Potosi Creek were mined on a small scale during the during the early to middle 20th Century. More extensive mining began in 1994, when the Clark-Wiltz partnership began mining the Potosi Creek pay streak. Mining stopped at the junction of two unnamed tributaries about 1.6 mile upstream from the mouth. Total production from 1994 to 1999 was about 7,500 ounces of placer gold (Dan Wiltz, written communication, 2002). In years past, some placer gold production credited to Potosi Creek was mined on a bench placer at French Hill, upstream and to the south (Mertie, 1936).
Geologic map unit (-156.514064043344, 62.9753075725019)
Mineral deposit model Placer Au deposit (Cox and Singer, 1986; model 39a)
Mineral deposit model number 39a
Age of mineralization Quaternary; probably Early to Middle Pleistocene, before stream capture of upper Ganes Creek (Mertie, 1936; Bundtzen, 1980 [GR 63]).
Alteration of deposit None.

Production and reserves

Workings or exploration Exploration from 1994 to 1998 consisted of a series of churn drill lines each spaced about 800 feet apart , and backhoe cuts across the valley in key areas. Exploration prior to that time was mainly near the mouth of Potosi Creek.
Indication of production Yes; medium
Reserve estimates None identified; probably some gold remains at the sides of the paystreaks that have been mined.
Production notes Placer deposits near the mouth of Potosi Creek were mined on a small scale during the during the early to middle 20th Century. More extensive mining began in 1994, when the Clark-Wiltz partnership began mining the Potosi Creek paystreak. Mining stopped at the junction of two unnamed tributaries about 1.2 miles from the mouth of the creek. The total production from 1994 to 1999 was about 7,500 ounces of placer gold (Dan Wiltz, written communication, 2002). In years past, some placer gold production credited to Potosi Creek was mined on a bench placer at French Hill, upstream and to the south (Mertie, 1936).

Additional comments

A significant late producer of placer gold in the Ganes Creek basin. The ground that has been mined on Potosi Creek has been reclaimed by the Clark-Wiltz Partnership to State of Alaska reclamation standards.

References