Sulphurdale Mining District, Millard County, Utah, USAi

Regional Level Types
Sulphurdale Mining District	Mining District
Millard County	County
Utah	State
USA	Country

The Sulphurdale (Gordon, Cove Fort) mining district is located 24 mi north of Beaver on the west side of the southern Pahvant Range and the adjoining northwest flank of the Tushar Mountains on the Millard–Beaver County line. The district was discovered in 1869 and became a small producer of native sulfur and minor fluorite. Grades of production and possible resources range from about 14% to 30% S (Rodriguez, 1960). Total district metal production at modern metal prices is estimated at $953,000. The Sulphurdale open-pit mine in Beaver County is the largest S producer in Utah.
The Pavant Range and Tushar Mountains are part of the transition zone from the Basin and Range Province to the Colorado Plateau. The Sulphurdale district is an active geothermal system probably associated with a cooling Pleistocene intrusive at shallow depth. The deposits are fumarolic sulfur hot spring deposits (USGS Model 25m) developed along northerly trending normal faults primarily in Oligocene-Miocene volcanics and Pliocene-Pleistocene tuffs and sediments (Rowley and others, 2013). The prospects and acid leach zones are near or adjacent to major north- and northeast-trending faults, but, in several of the pits, the strongest alteration and more visually apparent native sulfur mineralization are more closely associated with smaller, generally subparallel, subsidiary faults rather than the major mapped structure. The host rocks are all white, strongly altered rocks consisting of porous aggregates of opaline silica, gypsum, anhydrite, and remnant quartz or cristobalite. Rodriguez (1960) developed a composite vertical mineralogical zoning for the deposits having gypsum at the surface grading down to gypsum-sulfur, sulfur, sulfur-pyrite-marcasite, pyrite-marcasite, to pyrite at depth. No sinters were recognized in any of the sulfur-bearing prospects. The native sulfur occurs as fine-grained disseminations and cavity fillings (Rodriguez, 1960).
Some of the deposits on the north end of the Sulphurdale district in Millard County occur in upper Paleozoic carbonates and have minor associated fluorite. Fluorite is present here, with native sulfur deposits, as open-space fillings and partial replacements of limestone breccia along major range-bounding normal faults (Rodriguez, 1960). The main fluorite occurrence is the Rain Bow (Forminco) mine. The fluorite may or may not be related to the Holocene geothermal activity that formed the native sulfur deposits.