Marysvale Mining District, Piute County, Utah, USAi

Regional Level Types
Marysvale Mining District	Mining District
Piute County	County
Utah	State
USA	Country

The Marysvale mining district is about 28 mi northeast of Beaver along the Piute–Sevier County line. The district is a modest U producer and was not discovered until 1947. The bulk of the production (1,330,797 lbs U3O8) came from underground mines (Chenoweth, 2007). Total district metal production at modern metal prices is estimated at $40 million. The largest operations in the district are the Freedom, Prospector, and Farmer John (Chenoweth, 2007).
The Marysvale district lies on the east flank of the Marysvale Oligocene-Miocene volcanic field in the transition zone between the Basin and Range Province to the west and the Colorado Plateau on the east. The most important production came from the Central Mining Area (CMA), all in an area of less than 0.5 sq mi. The CMA is underlain by a series of subvolcanic plugs ranging in age from about 23 to 18 Ma (Cunningham and others, 1998). Mineralization (19–18 Ma) at Marysvale consists of an anastomosing set of steeply dipping, northeast-trending, quartz-fluorite-pyrite veins (each vein up to 20 inches wide) and subsidiary sub-horizontal, open-space breccia veins generally cutting the monzonitic Central Intrusion (23 Ma). The primary U ore occurs as pitchblende and jordisite containing geochemically anomalous As, Mo, Sb, Tl, and W in steeply pitching shoots within the veins and as breccia pipes and stockworks (USGS Model 25f). At depth, the vein quartz, pyrite, and jordisite content increases and the veins have 2-inch-wide sericitic selvages. Mineralization appears to be related to glassy rhyolite dikes containing trace molybdenite (Cunningham and others, 1998).
Cunningham and others (1998) postulate the CMA mineralization is related to an unexposed 18 Ma rhyolite plug at depth, coeval with the rhyolite porphyry dikes, and the hypothetical plug may host porphyry Mo mineralization.