Granite Mining District, Beaver County, Utah, USAi

Regional Level Types
Granite Mining District	Mining District
Beaver County	County
Utah	State
USA	Country

The Granite (North Granite) mining district is situated on the southeast flank of the Mineral Mountains 9 miles northwest of Beaver in east-central Beaver County. The district was organized in 1863 and became a small Zn-Cu-Pb-W producer, but the most productive period was from 1911 to 1932. Total district metal production at modern metal prices is estimated at $263,000. The largest producer was probably the Beaver Tungsten Mines, including the Garnet and Contact mines.

The Granite district is on the Wah Wah-Tushar mineral belt in the Basin and Range Province of southwestern Utah. The Mineral Mountains expose a large, mostly gray, alkalic, high-silica, composite Oligocene-Miocene (25 to 18 Ma) granite, monzonite, and syenite batholith (78 sq mi), the largest exposed batholith in Utah. The main granitic phase of the Mineral Mountains batholith has an interpreted age of about 18 to 17 Ma. The batholith has been strongly rotated to the east (40°–85°), so that the east side of the mountain is near the paleo-top of the batholith. The Granite district covers an 8-mi-long by 1-mi-wide contact on the east side (paleo-top) of the Mineral Mountains granite.

The district shows a broad, but poorly defined zonation from Pb-Zn-rich ores on the north and south to W, Sn, and Mo in the center, near the Garnet and Contact mines. Mineralization is developed in prograde, anhydrous, tabular garnet-vesuvianite-epidote ±diopside ±tremolite ±wollastonite W skarns (USGS Model 14a) formed near the contact of the quartz monzonite porphyry and the Mississippian Deseret Limestone (?). The porphyry is finer grained at this contact and there are numerous minor pegmatitic phases and quartz veins associated with the border facies. The carbonate rocks are broadly conformable with the porphyry contact and are skarnified within a couple hundred yards of the batholith and marbleized or bleached for a few hundred yards more (Sibbett and Nielson, 1980).

Weakly mineralized skarn may be up to 800 feet long, 30 feet wide, and 100 feet deep, although the ore mined to date occurs in much smaller, higher-grade, structurally controlled, brecciated pods unevenly distributed within these broader, low-grade zones (Everett, 1961). The skarns range from dark brown, massive garnet lenses near the granite to pale yellow-green banded epidote-zoisite marble beds in the outer contact zone. The ore minerals are scheelite, galena, sphalerite, argentite, molybdenite, chalcopyrite, and bismuthinite, typically found with pyrite, fluorite, and barite. Nearly all of the scheelite fluoresces cream-yellow instead of the normal blue-white, which indicates isomorphous substitution of Mo for W. Everett (1961) reports a W ore sample from the district as running 0.53% WO3 and 0.15% Mo. Some U.S. Geological Survey National Geochemical Database rock samples from the Granite district also run up to 450 ppm Sn and 70 ppm Mo.