By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Prospectors, drawn to central Idaho by the rich gold strikes in the Boise Basin in 1862, went from there into what is now Blaine County. Silver-lead deposits were found in the Wood River region in 1864, but these were ignored for a few years, because the chief interest was in gold (Umpleby and Ross, in Umpleby and others, 1930, p. 81).
Gold deposits in the Camas district southwest of Hailey were developed in 1879. By 1880 the Wood River silver-lead deposits were worked, and gold was yielded as a byproduct. A decline in mining in the county began in the early 1900's and, except for a few brief revivals, continued until the early 1940's, when a period of high productivity of base-metal ores with gold as a byproduct commenced. Mining in the county slowly declined from the late 1940's through 1959.
Production of gold from 1874 through 1942 was 176,262 ounces (Staley, 1946, p. 13) ; total production from 1874 through 1959 was 212,638 ounces.
The Camas (Hailey, Mineral Hill) district is in west-central Blaine County, 5 to 15 miles southwest of Hailey in T. 1 N., Rs. 16 and 17 E.
Gold was first discovered in this district in 1865 at the site of the Camas 2 mine, but there was no production until 1879 (Anderson and Wagner, 1946, p. 9). Other discoveries were made in 1880, and the period from 1880 to the early 1900's was one of great prosperity in the district. The chief mine, the Camas 2, produced ore valued at $1 1/4 million before it was closed in 1898 (Anderson and Wagner, 1946, p. 9). Most of the mines in the district remained closed, but the Camas 2 and the Hattie were reopened for short periods in the 1930's, 1940's, and 1950's.
Production records are not complete, especially for the years of peak activity before 1900. Of the 175,770 ounces of gold produced in Blaine County from 1874 to 1900, Anderson and Wagner (1946, p. 9-10) estimated that more than half of it came from the Camas district. Umpleby and Ross (in Umpleby and others, 1930, p. 84) listed a total of 7,019 ounces produced from the Mineral Hill camp between 1902 and 1926; 7,161 ounces were produced from 1932 through 1959.
Total gold production, including the estimate of Anderson and Wagner (1946, p. 9), was about 102,000 ounces. Much silver, lead, and zinc was mined also.
The district is underlain by granodiorite and quartz monzonite of the Idaho batholith of middle Cretaceous age, which is cut by many aplite and pegmatite dikes and a few lamprophyre dikes (Anderson and Wagner, 1946, p. 4-9). Remnants of a once-extensive cover of Tertiary basalt that buried an erosion surface carved into the granitic rock are found at a few places. The gold occurs in quartz veins along gently dipping faults in the batholith.
The veins are generally rich in silver and carry two to four times as much silver by weight as gold. Some contain moderately large amounts of sulfides (Anderson and Wagner, 1946, p. 10).
In the northeastern part of the district, near Hailey, the country rock consists of tightly folded Paleozoic sedimentary rocks - the Milligen (Missis-sippian and Devonian) and the Wood River (Pennsylvanian) Formations. These have been faulted and intruded by several stocks, which are probably related to the Idaho batholith (Ross, 1941, p. 13). Most of the deposits are in shear zones in the Mis-sissippian sedimentary rocks, which largely are thin-bedded carbonaceous argillites.
The ore minerals are argentiferous galena, sphalerite, and tetrahedrite, with minor pyrite in a gangue of altered and crushed country rock, siderite, and a little quartz (Ross, 1941, p. 13).
WARM SPRINGS DISTRICT
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.
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