By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Most of the gold-producing districts in Elmore County are clustered in its northeastern part, in an area underlain by granitic rocks of the Idaho batho-lith. Shear zones that trend nearly east contain lode deposits of gold and silver, which have yielded most of the gold produced in Elmore County, although placers were important in the Featherville and Rocky Bar districts, especially before 1900.
Gold lodes were discovered in 1862 in the Rocky Bar district and soon afterward at Atlanta. The 1870's and 1880's were years of intense lode-mining activity, but by the early 1900's many of the mines closed. Gold mining in Elmore County, with the exception of that in the Atlanta district, continued to decline, although by 1956 the Atlanta district also ceased significant production. Gold production for the county from 1889 through 1942 was 381,396 ounces (Staley, 1946, p. 19) and from 1943 through 1959 it was 60,300 ounces. A total of 441,696 ounces was produced through 1959.
The Atlanta (Hardscrabble, Middle Boise, Yuba) district is in T. 5 N., Rs. 11 and 12 E., in rugged, mountainous country 65 to 70 miles east of Boise.
Gold was first discovered in the district in 1864, in veins on Atlanta Hill, but extreme inaccessibility of the area hindered its development for almost 10 years (Ballard, 1928, p. 7-8). The greatest activity was in the 1870's and 1880's. Ballard (1928, p. 10) reported that the Monarch Mining Co. shipped ore valued at $700,000 in the period 1876-78. Mining declined after the 1880's but was rejuvenated in 1929 (Ross, 1941, p. 51) and increased steadily until 1956.
The total gold production of the Atlanta district is difficult to ascertain because figures for both gold and silver were combined in the early reporting. According to Ross (1941, p. 51), total metal production to 1936 was valued at $6 million, but the amount of this in gold was not stated. From 1932 through 1959 the district produced 243,175 ounces of gold. If at least half of the early production worth $6 million was in gold, most of which was from lode deposits, total district gold production may have been 385,000 ounces. Placers were worked in the district, but their yield was not great (Ballard, 1928, p. 9).
The country rock in the district is granite of the Idaho batholith which was fractured and intruded by aplite and porphyry dikes. These fractures and dikes are arranged in a zone about 1.5 miles wide that trends northeastward. The ore deposits are in veins filling the fissures (Ballard, 1928, p. 13-18). The chief vein is the Atlanta on which most of the workings of the district are located. Stephanite and pyrargyrite are silver minerals characteristic of the ores that were mined in the early days. Ore mined more recently contains auriferous pyrite (Ross, 1941, p.51).
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