Fish Springs Mining District, Fish Springs Mountains, Juab County, Utah, USAi

Regional Level Types
Fish Springs Mining District	Mining District
Fish Springs Mountains	Mountain Range
Juab County	County
Utah	State
USA	Country

The Fish Springs mining district is in the northern Fish Springs Range of northwestern Juab County about 72 mi west of Eureka. The district was organized in 1891 and was a significant Ag-Pb producer continuing into the early 1960s. Total district metal production at modern metal prices is estimated at $60 million. The Utah and Galena Pb-Ag underground mines are by far the largest historical producers in the district. The large West Desert (Crypto) Zn-In skarn was discovered at depth by drilling in the late 1950s and early 1960s.
The district is located on the Deep Creek–Tintic mineral belt in the Basin and Range Province in west-central Utah. Mineralization at Fish Springs is associated with west-northwest-trending fracture zones and trachyte dikes near the Juab fault and a concealed, Eocene-age, equigranular to weakly porphyritic, monzonite-syenite stock dated at 38.5 ±1.0 Ma (Staargaard, 2009). Previously mined mineralization is primarily Pb-Ag vein and replacement ores in the Silurian Laketown Dolomite (USGS Model 19a). These replacement ores are strongly anomalous in As, B, Cd, Mn, Mo, V, and Zn.
Bleaching and recrystallization of the carbonate rocks along the northwestern range front in the Fish Springs district and a very strong magnetic high in the pediment led to drill testing and the discovery of a pair of unexposed stocks and a deep magnetite- sphalerite skarn (Christiansen, 1977). The common magnesian skarn consists of medium- to coarse-grained humite, magnetite- magnesioferrite, and phlogopite along with subordinate spinel, periclase, actinolite/tremolite, and forsterite (USGS Model 18c). The sulfide phases present in the deep skarn include sphalerite, chalcopyrite, molybdenite, pyrite, and lesser pyrrhotite and roquesite (Staargaard, 2009). The main ore hosts are the Ordovician Ely Springs Dolomite and Pogonip Group and deeper mineralization in the Cambrian Orr Formation. In 1993, Cyprus Minerals reported two separate subeconomic inferred resource estimates at Crypto: 3.1 million tons of 7.0% Zn as an oxide deposit and 6 million tons of 8.7% Zn in a deeper sulfide deposit (Staargaard, 2009). Reportedly, Cu grades increase near the stock which also hosts some Mo mineralization at the intrusive- skarn contact. More recent drilling at the deposit by Lithic Resources has revealed economically interesting indium associated with some of the sphalerite skarn mineralization, including 78.3 ft assaying 4.22% Zn and 184.9 ppm In in hole C-07-01 (Dyer and others, 2010).