Blaine County Idaho Gold Production
The Warm Springs district, between lat 43°35' and 43°50' N. and long 114°10' and 114°30' W., near Ketchum, is predominantly a silver-lead district; gold is produced as a byproduct.
Though the initial discoveries were made in 1864, the district was not developed until 1880. Production was high from 1880 to 1887, when many of the richer ore bodies were exhausted. Depletion of ore and a decrease in the price of silver forced closure of many of the mines. Activity in the district gradually decreased through the 1900's, although the Triumph mine, which was reopened in 1927 and which became the largest producer of base-metal ore in the district, continued to be productive until 1957, when the ore bodies were mined out and the mine was abandoned
Value of gold produced before 1902 is not known, although Ross (1941, p. 15) credited the district with more than $3 million worth of combined metals from 1880 to 1902. From 1902 through 1926, the district produced 6,069 ounces of gold (Umpleby and Ross, in Umpleby and others, 1930, p. 84). From 1932 through 1959, a total of 70,570 ounces was produced; almost all production was from the Triumph mine. Total recorded gold production was 76,639 ounces, a byproduct of the silver-lead ores.
Metasediments composing the Hyndman and East Fork Formations of Algonkian (?) age are the oldest rocks in the district and are exposed in the mountainous areas in the eastern part. Overlying these is a thick series of Paleozoic sedimentary rocks consisting of the Phi Kappa Formation of Ordovician age, the Trail Creek Formation of Silurian age, the Milligen Formation of Devonian (?) and Mississippian age, and the Wood River Formation of Pennsylvanian age (Westgate and Ross, in Umpleby and others, 1930, p. 9-34).
Numerous masses of plutonic rocks ranging in composition from granite through quartz monzonite to granodiorite cut the Paleozoic rocks. Tertiary and Quaternary andesite, basalt, and rhyolite lavas interbedded locally with tuffs cover large parts of the district (Westgate and Ross, in Umpleby and others, 1930, p. 43-61). Pre-Tertiary rocks are complexly folded and faulted, and some of the faults offset Tertiary rocks.
The important ore deposits are in Mississippian and Pennsylvanian sedimentary rocks, according to Umpleby and Ross (in Umpleby and others, 1930, p. 88-112), and are of two general types: lodes in shear zones in sedimentary and granitic rocks, and contact metamorphic deposits in calcareous beds adjacent to intrusive bodies. The shear-zone deposits, from which most of the production came, contain argentiferous galena, sphalerite, tetrahedrite, pyrite, and variable amounts of gold in a gangue of crushed and altered country rock, siderite, and quartz.
The contact metamorphic ore deposits are a skarn of garnet, epidote, diopside, augite, actinolite, and wollastonite through which is disseminated variable amounts of argentiferous galena, sphalerite, chalcopyrite, pyrrhotite, magnetite, and pyrite.