The Warren-Marshall (Resort) district is in southern Idaho County between Tps. 20 and 24 N., and Rs. 4 and 8 E.
Rich placers were discovered in Warren Meadows in 1862 shortly after the discoveries at Florence; rich lode deposits were found as early as 1866 (Lindgren, 1900, p. 238-239). Before 1900 an estimated $15 million in gold was mined from the district; most of it, from placers. After the initial boom period which lasted through the 1860's, activity continued on a much-reduced scale, especially from 1902 to 1932 (Reed, 1937, p. 25). Bucket dredges were introduced in 1932, and large-scale placer production recreated on a lesser scale the booming days of the 1860's. Production from placers gradually diminished through the 1950's.
Detailed production data for the district from 1902 through 1936 were listed by Reed (1937, p. 25). From 1902 through 1928, the combined output of lodes and placers was 21,581 ounces of gold. From 1929 through 1935, lode mines yielded $37,992 (about 1,765 ounces) and placers $1,593,062 (about 56,640 ounces). From 1936 through 1959 the district produced 98,519 ounces. Total gold production, including Lindgren's estimate of early production, was about 906,500 ounces.
The oldest rocks in the Warren-Marshall district are quartzite, gneiss, and schist of the Belt Series of Precambrian age. These rocks are intruded by quartz monzonite of the Idaho batholith, the predominant bedrock in the district (Reed, 1937, p. 8) ; over most of the district, the quartz monzonite is deeply weathered. Locally, lamprophyre dikes of middle Miocene age also intrude the older rocks.
The gold lodes are known collectively as the Warren vein system, consisting of quartz veins in a strong set of northeast-trending joints in the quartz monzonite. Mineralization probably occurred in Late Cretaceous time before the intrusion of the lamprophyre dikes. The primary vein minerals are gold, galena, sphalerite, tetrahedrite, stibnite, and pyrite in a gangue composed mainly of quartz and locally abundant calcite and muscovite. Arsenopyrite, ruby silver, chalcopyrite, and scheelite may be found at some localities, and silver is rare (Reed, 1937, p. 35-37).
The most productive placers in the district occur in unconsolidated deposits called younger gravels by Reed (1937, p. 13-15) and in Recent alluvium. These are distinguished from older gravels which are believed to be middle Miocene to Wisconsin in age (Reed, 1937, p. 12). The younger gravels include bench gravels and high meadow deposits; the Recent alluvium consists of broad sand and gravel deposits along present streams. The older gravels have been mined locally but have sustained no large production.
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