In Ada County, east of Boise 10 miles, near the Elmore County line, is the Black Hornet district. It had a total production of around 22,000 ounces of gold from area lode mines.
Black Hornet District
Lode mines in this district probably were developed in 1862, at the time discoveries were being made in the Boise Basin, but the earliest record of production was in 1895-96, when gold ore valued at $24,000 was shipped from the district. Small amounts of gold were produced annually through 1955, but during 1942-59 the output was only 119 ounces. Total recorded production from 1880 through 1959 was 21,431 ounces. The geology of the district, is fairly simple. The country rock consists of granite of the Idaho batholith, which is cut locally by granite porphyry dikes. The ore deposits are gold-bearing quartz veins that contain variable amounts of pyrite, arsenopyrite, sphalerite, and galena. The granite adjacent to the veins has been sericitized.
Diamonds have been found in the past in the Diamond Basin area of Ada County.