Custer County Idaho Gold Production
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LOON CREEK DISTRICT
The Loon Creek district is between lat 44° 32' and 44°38' N. and long 114°45' and 114°52' W., in the Loon Creek drainage area.
The first mineral discoveries in this area were in 1869 when gold placers were found along Loon Creek near the abandoned town of Casto (Ross, 1934, p. 117). During the next 10 years the placers were worked out, having yielded between $1.5 and $2 million in gold.
Lode mining became significant in the district about 1902 when the Lost Packer gold-copper prospect was developed. Despite transportation difficulties, the mine remained operative through 1917, but was mostly inactive after that time. Ross (1934, p. 118) reported a production of $600,000 worth of ore for this mine, but he did not mention the amount of gold.
Considering the more conservative estimates of early placer production and assuming that at least half of the lode output of the Lost Packer mine was in gold, the total production of the district through 1959 was about 40,000 ounces. This, however, is a conservative estimate, and the production may have been several times that amount.
The geology in the vicinity of the Lost Packer mine was described by Ross (1934, p. 120, pi. 8). The ore body is in contorted Precambrian schist that was intruded by dikes and irregular bodies of aplite, lamprophyre, dacite porphyry, granophyre, and quartz monzonite. Elsewhere in the district, large areas are covered by flows and tuffs of the Casto Volcanics of Permian (?) age and the Challis Volcanics of Oligocene(?) age.
Chalcopyrite is the principal ore mineral in the lodes, which occupy steplike fissures in the schist. Also present are small amounts of tetrahedrite, pyrite, and pyrrhotite, and near the surface is bornite, native copper, and oxidized iron and copper minerals (Ross, 1934, p. 121-123). Gold is associated with the chalcopyrite and in some veins, with quartz.