Black Hornet District
Commodity: Gold
See also: Ada County, Idaho Gold Production
Note: the Boise, Shaw Mountain, and Highland districts identified on the 1936 Idaho Bureau of Mines and Geology map are today considered part of the Black Hornet district as described by the USGS.
The Black Hornet, Boise, and Shaw Mountain districts in northeastern Ada County and adjacent parts of Boise County, close to Boise, include most of the gold lode mines in Ada County, although some prospects exist in unorganized areas outside their limits. The total production probably does not exceed a few score thousand dollars and little has been done in any of these districts for many years.
The area is underlain by granitic rock of the Idaho batholith, with occasional dikes of granite porphyry and lamprophyre. The ore deposits are quartz veins in sericitized granitic rock, containing free gold, pyrite, arsenopyrite, sphalerite, and galena. The ore shoots range in thickness from 2 to rarely 10 feet, and in length up to about 120 feet. The ore mined in the early days contained 0.2 - 0.75 of an ounce of gold to the ton, occasionally materially more (especially in the Shaw Mountain district). Little attention has been paid to the sulphide ore in which the gold is not readily recovered by amalgamation.
In the Black Hornet district, the veins strike north to northwest and dip about 45° W.; in the other two districts, they strike east and dip 45° - 80° S.
