Silver Island Mining District, Tooele County, Utah, USAi

Regional Level Types
Silver Island Mining District	Mining District
Tooele County	County
Utah	State
USA	Country

The Silver Island (Silver Islet) mining district lies about 15 mi northeast of Wendover in northwestern Tooele County. The Silver Island district is a small Ag-Pb vein and replacement district covering the Silver Island Mountains. The district was organized in 1872 and its most productive period was between 1908 and 1913 (Tripp and others, 1989). Total district metal production at modern metal prices is estimated at $2.5 million. The southwest end of the district, near the Jensen prospect had a series of short, unsuccessful exploration programs in the 1980s, 1990s, and 2010s for Au. The Lomato Ag-Pb mine and the Haphazard Group Ag-Cu-Zn-Pb mine were the two largest producers.
The Silver Island Mountains are part of the Basin and Range Province. The northeast-trending mountains are geologically complex but show an overall pattern of gently to moderately northwest-dipping Paleozoic sedimentary rocks, so that the oldest sedimentary strata lie on the southeast flank of the range and the youngest rocks, including Tertiary volcanic rocks, lie on the northwest (Schaeffer, 1960).
Lower Paleozoic limestone and dolomites host mineralization and the mountain range is folded into a number of north-trending and plunging anticlines and synclines. Most of the mine workings are associated with the Campbell Peak and Tetzlaff Peak anticlines. Igneous rocks in the area include a Jurassic granodiorite (~160 Ma) stock, and Eocene andesitic and Miocene rhyolitic volcanic rocks. The Jurassic granodiorite plug is surrounded by a large area of recrystallization and bleaching. Diorite dikes of uncertain age are associated with the lenticular polymetallic quartz vein deposits (Schaeffer, 1960). The most important Ag-Pb-Cu-Zn ±Au ±Sb mine workings are clustered south and west of Lamus Peak in Cambrian carbonate rocks. A small body of massive barite ±As ±Sb occurs at one prospect (Bryan Group) on eastern Silver Island Mountain at the Devonian carbonate- Mississippian shale contact (USGS Model 27e).
As in the Crater Island district to the north, very weak sedimentary rock-hosted precious metal-style mineralization is associated with stratiform jasperoids at the base of the Mississippian Pilot Shale, Joana Limestone, and Chainman Shale, mostly south of Silver Island Pass (USGS Model 19c). Weakly anomalous Au-As-Sb-Hg-Ba is associated with small northerly and northeasterly trending jasperoids, structures, and faults in the Mississippian and Pennsylvanian strata.