Lemhi County Idaho Gold Production
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The Blackbird district, about 35 miles southwest of Salmon, was discovered in 1893. Ores were first worked for gold, with discouraging results, but copper was found in 1896 and cobalt in 1901 (Umpleby, 1913b, p. 160). Before 1957 the district produced only 1,205 ounces of gold. However, increased activity at the Calera cobalt-copper mine yielded 3,683 ounces of gold in 1957, a total of 9,506 ounces in 1958, arid an undisclosed amount in 1957; all production was a byproduct of cobalt-copper ore.
Rocks of the Blackbird district are metamorphosed sedimentary rocks of the Belt Series of Precambrian age, intruded by granitic rocks of the Idaho batholith (Vhay, 1948, p. 2). At the Calera mine, the only significant producer in the district, quartz-biotite and garnet-chloritoid schists are the favorable host rocks for copper-cobalt deposits. These rocks are contained in a structural unit, the Blackbird block, which is 5 miles long, 2 miles wide, and is elongate northward. Copper-cobalt mineralization is controlled by north-trending shear zones and north-plunging folds; deposits are in veins and lenses formed by replacement. The ore minerals are chalcopyrite, cobaltite, safflorite, and gold; the gold is present in trace amounts to a few hundredths of an ounce per ton.
CARMEN CREEK-ELJDORADO-PRATT CREEK-SANDY CREEK DISTRICT
Carmen Creek, Eldorado, Pratt Creek, and Sandy Creek are contiguous small camps in the northeastern part of Lemhi County along the flanks of the Beaverhead Mountains. The Kirtley Creek camp is also in this area but it will be considered separately.
Mining first began in the 1870's in the Eldorado area, where Chinese were mining the gravels on Bohannon Bar. From 1895 through 1911, the placers produced $350,000 in gold (Umpleby, 1913b, p. 123-124). Lode mines were also developed but were not very successful.
In the Carmen Creek camp, only small amounts of bullion were produced (Umpleby, 1913b, p. 125). The only property of significance was the Oro Cache mine, opened about 1897. At Pratt Creek, gold lodes were found in the early 1890's at the Goldstone mine. According to Ross (1941, p. 68), total production from all camps was about $1 million, including $500,000 in gold credited to the Kirtley Creek camp (Anderson, 1956, p. 64). Considering that about $350,000 came from the Eldorado camp, the Pratt Creek, Carmen Creek, and Sandy Creek camps produced about $150,000 in gold. In the 1930's and 1940's this area was active, but only small amounts of gold were mined. Total gold production through 1959 was about 24,500 ounces.
The rocks underlying this district are quartzites, quartzitic slates, and schists of the Precambrian Belt Series which are covered in the valleys by Miocene lake beds. The Precambrian rocks are cut locally by diorite dikes and granitic intrusions (Umpleby, 1913b, p. 121-127; Ross, 1941, p. 68). Most of the lode deposits are found in the metasedimentary rocks and are fissure fillings of quartz with variable amounts of pyrite, chalcopyrite, galena, and sphalerite. Gold occurs with the sulfides.