Willow Springs Mining District, Tooele County, Utah, USAi

Regional Level Types
Willow Springs Mining District	Mining District
Tooele County	County
Utah	State
USA	Country

The Willow Springs mining district lies in the Deep Creek Range about 50 mi south of Wendover in southwesternmost Tooele County and adjoining portions of Juab County. The district encompasses a large area of the central Deep Creek Range. The Willow Springs district was organized in 1891, it was intermittently productive from then until 1982, and was a significant Au-Pb producer. Total district metal production at modern metal prices is estimated at $16 million. The Oro del Rey Au-Ag-Pb mine was the largest producer in the district and the workings include eight adits and one shaft scattered over 1200 ft of strike (Thompson, 1973).
The Deep Creek Range is a significant mountain chain in the Basin and Range Province of western Utah. The rocks in the Willow Springs district generally dip homoclinally west, and the east side of the range has a precipitous slope. Host rocks for mineralization range from Proterozoic metasedimentary rocks on the east to Devonian carbonate rocks on the west (Thompson, 1973). The district’s most significant mines were the Eagles Nest, Oro del Rey, Devils pit, and Evelyn (from north to south) which all developed a narrow Au-Pb-Ag quartz-sulfide vein set cutting the Lower Cambrian Prospect Mountain Formation. The vein set generally trends north-northeast but is somewhat sinuous and is offset by numerous cross faults with mostly modest displacement. The Au-Ag-Pb vein typically dips nearly perpendicular to the west-dipping bedding in the quartzite, or typically about 75° east except for the Eagles Nest mine in the north where the vein dips about 45° west. The vein can have a wide selvage of bleached, silicified, and quartz-sulfide veinlets, which can make the precise vein margins indistinct. The Au- Ag-Pb veins have been traced intermittently for about 10,000 ft. The vein reportedly horsetails to the north. The vein ranges from a few inches wide up to 5 ft but only averages about 1.5 ft. The immediate margins of the vein are typically Fe-stained for a few inches to several feet and generally carries Au. The Au-Ag-Pb vein is not continuously mineralized but is thought to have discrete north-plunging ore shoots. The vein is locally parallel to a propylitized rhyolite dike of unknown age. The primary sulfides, where seen, generally make up less than 10% of the vein and are predominantly auriferous fine-grained pyrite, argentiferous galena, and lesser chalcopyrite and sphalerite. The Au generally occurs as fine-grained (<1 mm) native gold. The gauge minerals are quartz, barren crystalline pyrite, and minor specularite. In addition to Au, Ag, and Pb, the vein is weakly to moderately anomalous in As, Cu, Mo, and Sb. The average grade of shipments in 1945 was 60 ppm Au, 86 ppm Ag, 3.5% Pb, and 0.85% Cu. However, short individual channel samples of the vein run up to 207 ppm Au, 686 ppm Ag, 46.5% Pb, and 14.4% Cu (Thompson, 1973; Hannigan, 1990).
Elsewhere in the Willow Springs district, the Cougar Hill mine on the west side of the district produced minor Hg and the Roy Ag-Pb and Dewey Ag-Cu mines to the north had nominal production (Thompson, 1973; Hannigan, 1990).