Twin Peaks Mining District, Millard County, Utah, USAi

Regional Level Types
Twin Peaks Mining District	Mining District
Millard County	County
Utah	State
USA	Country

The Twin Peaks mining district is in southeastern Millard County. The district is an insignificant Fe producer. Bullock (1970) reported approximately 50 tons of ore was shipped to the Ironton Works in Provo in 1940. The Twin Peaks Fe mine is the only operation with recorded production.
The Twin Peaks district is in the southern Sevier Desert section of the Basin and Range Province. Mineralization is associated with the Pleistocene North Twin Peaks rhyolite dome. The dome is part of a bimodal basalt-rhyolite volcanic suite. The North Twin Peaks dome is estimated to be 600 ft high and a basalt flow lies just 1.5 mi to the southeast. The rhyolite is porphyritic and has phenocryts of plagioclase, sanidine, quartz, and biotite (Hintze and Davis, 2003).
Three areas of magnetite veining occur on North Twin Peak and the largest workings are a 200-foot-deep incline shaft and several small prospect pits located just northeast of North Twin Peak proper. The mineralization consists of narrow, open-space veins and veinlet zones of magnetite with subordinate hematite and martite (hematite pseudomorphs after magnetite) cutting the North Twin Peak rhyolite. The veins are narrow, from 0.5 to 3 ft wide, and traceable for less than 100 ft (Bullock, 1970). Zones of anastomosing magnetite veinlets may be up to 6 ft wide (Crawford and Buranek, 1945). The main vein was developed along an east-trending, south-dipping fault, but smaller veins apparently developed along N. 50° E. and N. 70° W. joints in the rhyolite. Seven samples collected by Bullock (1970) contained an average of 60.7% Fe and 3.8% SiO2.
The prospect has little potential as an iron mine, but it does contain nice crystals of martite, augite, and apatite (Crawford and Buranek, 1945).