Crater Island Mining District, Crater Island, Box Elder County, Utah, USAi

Regional Level Types
Crater Island Mining District	Mining District
Crater Island	Mountain
Box Elder County	County
Utah	State
USA	Country

The Crater Island mining district is in the northernmost Silver Island Mountains of southwestern Box Elder County, about 25 mi northeast of Wendover. The district has had a limited production of Au-Cu mostly from 1934 to 1948. Total district metal production at modern metal prices is estimated at $180,000. The Copper Blossom mine is the only recognized producer. The northern portion of Crater Island was explored for W in the 1970s, but there is no record of any production (Doelling, 1980). In the 1990s, the southern part of the district was explored by Franco Nevada Mining Corp. and Kennecott Exploration Co.
Crater Island consists of northerly trending Paleozoic sedimentary rocks cut by a series of north-trending normal faults and has Jurassic plutons (about 152 Ma) on both the north end (Sheepwagon porphyritic biotite granodiorite) and southern end (Crater Island quartz monzonite) of the range. The southern Crater Island stock has an extensive aeromagnetic high (especially in the pediment to the west of Donner-Reed Pass), while the magnetic expression of the northern Sheepwagon stock is much more subdued. These two plutons and associated dikes have produced broad zones of bleaching and recrystallization up to a half mile wide with narrow zones of calc-silicate development. Typical mineralization is associated with narrow, anhydrous, prograde, garnet-epidote ±diopside skarns adjacent to the Jurassic plutons (Miller and others, 1990). Skarn mineralization consists of either Cu-Au-Ag near the Crater Island stock (USGS Model 18b) or weak W-Mo adjoining the Sheepwagon stock (USGS Model 14a). Chalcopyrite and bornite are the primary Cu minerals in the Copper Blossom mine which averages about 0.5% Cu, 12 ppm Ag, and 0.3 ppm Au over a couple of feet. Doelling (1980) reports scheelite, powellite, molybdenite, and chalcopyrite in the northern skarns and grades of 0.13% to 0.34% WO3 over 3 to 4 ft. One sample of ore from the Copper Blossom mine reported 0.61% Cu, 20.6 ppm Ag, and 686 ppb Au.
Argillization, silicification, and disseminated pyrite occur locally with granodiorite dikes along the northerly trending Sheepwagon fault zone (east-central Crater Island). Small jasperoids in this zone host weak Au-Ag-As-Bi-Sb-Te mineralization in the Mississippian Joana Limestone and Chainman Shale (Doelling, 1980; Miller and others, 1990).