Gibbonsville Mining District, Lemhi County, Idaho, USAi

Regional Level Types
Gibbonsville Mining District	Mining District
Lemhi County	County
Idaho	State
USA	Country

The Gibbonsville District covers a loosely defined area generally accepted to include the north half of the North Fork Salmon River drainage. It contains the historic Hughes Creek and Dahlonega Creek Mining districts.

The first mining activity in the district occurred during 1867 when gold placer was found in Hughes Creek. Placer mining soon expanded to include the North Fork Salmon River, Dahlonega Creek, and Anderson Creek. The first lode claims were staked on gold-bearing quartz veins in 1877 near the confluence of Anderson Creek with Dahlonega Creek. The deposit, later known as the AD&M mine (American Development and Reduction Mining Company) eventually became the largest producer in the district. Other gold-bearing quartz veins were soon discovered; the most notable were at the Twin Brothers mine and the Clara Morris mine (Mayerle and Close, 1993, p. 19).

In 1895, the AD&M Company built a 30-stamp mill that treated the ore by amalgamation followed by chlorination (MacDonald, 1896, p. 319-320). According to Umpleby (1913, p. 133), the mill was destroyed by fire during 1907. A new 20-stamp mill and 20-ton cyanidation plant was built the following year (Kiilsgaard and others, 1989, p. B40). A mill was built in 1935 at the Twin Brothers mine to process its ore and ore from smaller mines. Several other smaller mills were built in the district in addition to those near Gibbonsville.

Production from the Gibbonsville District has been about 100,000 ounces of gold. The AD&M mine is credited with 48,000 ounces, the Twin Brothers with 14,500 ounces, and the Clara Morris with 12,000 ounces. The remaining production came from smaller lode mines and placer deposits (Wark, 1984, p. 10).

Mineralization generally consists of gold-, silver-, and copper-bearing quartz veins trending eastwest in phyllite and micaceous quartzite. The deposits appear to be zoned around the AD&M where gold and silver are the major constituents. As one moves away from the AD&M, copper concentrations increase and eventually lead concentrations increase.

Recently, significant resources have been identified at the Humbug deposit located along Ditch Creek. Drilling programs conducted by FMC Corporation and American Gold Resources delineated minable concentrations of gold in quartz veins and silica rich zones in dark grey siltite and argillite of the Apple Creek Formation. Proven and probable reserves are 16.5 million tons grading 0.037 ounce gold per ton. The deposit contains a geological resource of 1,056,000 ounces of gold (International Gold Resources Corporation press release, 1995).