Desert Mountain Mining District, Juab County, Utah, USAi

Regional Level Types
Desert Mountain Mining District	Mining District
Juab County	County
Utah	State
USA	Country

The Desert Mountain mining district is located 27 mi west-southwest of Eureka in central Juab County. The district has two parts, Desert Mountain itself and the Coyote Knoll and Allison Knolls area to the northeast. The district is a minor Ag-Cu producer. Total district metal production at modern metal prices is estimated at $15,000. The largest producers are the Rockwell Ag-Cu underground mine and Coyote Knoll Ag-Au open pit.
The Desert Mountain district lies on the Deep Creek–Tintic mineral belt of the Basin and Range Province. Desert Mountain proper is underlain by an exposed 14 sq mi, Oligocene granodiorite and granite intrusive complex, but aeromagnetic surveys suggest it is at least 30 sq mi. The early granodiorite is dark, fine-grained, with abundant plagioclase, biotite, and magnetite. The younger granite is light-colored, fine-grained, porphyritic, with abundant K-spar and quartz. The eastern margin of the Desert Mountain intrusive complex is cut by an arcuate caldera margin with down-dropped volcanic rocks to the east (Krahulec, 1996).
Ore deposits in the Desert Mountain district are generally small and mineralization is sporadic with little production. Minor production has come from the narrow Rockwell Ag-Cu vein on the west flank of Desert Mountain where a north-striking, moderately west-dipping vein is associated with a dike in granitic country rock. The Rockwell mine produced some 200 short tons of ore around 1905 and the best grade of ore contained approximately 5% Cu, 275 ppm Ag, and 0.17% U3O8. The ore/ sulfide minerals include pyrite, chalcopyrite, barite, and possibly tetrahedrite and fluorite (USGS Model 22c). These ores are also anomalous in Au, Bi, Pb, and Zn. There are also some small, but intense areas of pervasive, greisen-like, quartz-muscovite- pyrite alteration in the intrusive complex, but no mineralization has been identified with these peculiar, texturally destructive alteration zones (Rees and others, 1973).
The Allison Knolls area to the northeast of Desert Mountain has had significant exploration drilling and limited development at the Coyote Knoll Ag-Au prospect. This prospect produced a few thousand tons of high-grade, low-sulfidation, Ag-Au quartz vein or strongly silicified pebble dike ore (USGS Model 25c) in and/or near the caldera margin fault from a small open cut. The vein averages about 10 ft thick, strikes east-northeast, and dips moderately to the north. Alteration is primarily silicification transitioning outward to argillic alteration of the host volcanics. Ore minerals include native silver, horn silver, native gold, and covellite. The ore is estimated to average about 330 ppm Ag and 1.9 ppm Au and is only weakly anomalous in Sb, Cu, Pb, As, and Zn.