Third Term Mining District, Stansbury Mountains, Tooele County, Utah, USAi

Regional Level Types
Third Term Mining District	Mining District
Stansbury Mountains	Mountain Range
Tooele County	County
Utah	State
USA	Country

The Third Term (Grantsville) mining district is in the central Stansbury Mountains 17 mi west of Tooele in east-central Tooele County. The district was organized in 1875 and had small, intermittent Pb-Ag production from 1880 to 1917 and again briefly in 1939. Total production is estimated to be about 400 tons of ore (Sorensen and Kness, 1982). Total district metal production at modern metal prices is estimated at $131,000. The most productive mines were probably the Metal Queen and Third Term in the Willow Canyon section of the district.
The Third Term district is geologically situated on the west end of the Bingham–Park City mineral belt of the Basin and Range Province. The geology of the Stansbury Mountains is dominated by the north-south-trending Deseret anticline which is cored by Tintic Quartzite and the fold axis lies near the crest of the range. Moderately outward-dipping Paleozoic sedimentary rocks flank its quartzite core. Eocene (about 40 Ma) volcanic rocks lie on the east flank of the range near Willow Canyon (Sorensen and Kness, 1982). These volcanic and volcaniclastic rocks dip from 10° to 25° east, suggesting some post-Eocene eastward rotation of the range similar to the Oquirrh Mountains to the east. A pair of long, north-south-trending quartz monzonite dikes intrude the Paleozoic strata between North Willow Canyon and the Mining Fork of South Willow Canyon (Sorensen and Kness, 1982).
The main ore control in the Third Term district is often an unconformable contact between Cambrian and Devonian-Mississippian strata and much of the ore is hosted in the overlying Fitchville Formation and Gardison Limestone. Small replacement orebodies occur in these rocks near this unconformable contact, particularly near the dikes in the Willow Canyon area (Sorensen and Kness, 1982; Tripp and others, 1989; Stein and others, 1989).
Most of the Third Term district is in part of the Wasatch National Forest and the central third, covering the crest of the Stansbury Mountains, is in the Deseret Peak Wilderness Area.