Geology and mineralization of the Volcano District, Elmore County, Idaho

Abstract

The gold-silver base metal-quartz veins and lodes of the Volcano district are located along the south margin of Camas Prairie in Elmore County, Idaho. The veins and lodes are fissure fillings with minor replacements intimately associated with granophyric dikes, both of an early Tertiary age, and are localized by an east-northeast shear zone in a quartz monzonite facies of the Idaho batholith. The emplacement of the dikes and mineralized veins was controlled by fractures resulting from the Laramide disturbance. The deposits have been exhumed from beneath a cover of Pliocene rhyolite and Pleistocene basalt.The vein and lode deposits consist of networks of small quartz seams and stringers with a N 60-70 degrees E trend and steep northwest dips along complex fracture zones. The lodes have been worked for gold, although all contain minor amounts of silver, copper, lead, and zinc.Wall rock alteration appears excessive for the small degree of metallic mineralization. Sericitization, silicification, albitization, and epidotization, in that order, have highly altered the monzonitic rock for distances up to 25 feet adjacent to the veins and lodes.