La Sal Mining District, San Juan County, Utah, USAi

Regional Level Types
La Sal Mining District	Mining District
San Juan County	County
Utah	State
USA	Country

From Utah Geological Survey:
The La Sal district of the Moab U mining area is located 24 mi southeast of Moab in northern San Juan County. The district was organized in 1954 and is a large U-V producer. The district is the largest V and second most productive U district in Utah. Total district metal production at modern metal prices is estimated at $368 million. The most productive area is the Energy Queen, Redd Block, Beaver-La Sal, and Pandora group of underground mines.

The La Sal district is situated in the Paradox Basin on the Colorado Plateau. The district contains several significant U-V mines along a 12-mi-long, east-trending channel in the Upper Jurassic Salt Wash Member of the Morrison Formation (USGS Model 30c). Most of the mines were discovered by drilling and orebodies lie at depths of 500 to 800 ft. Little has been written about the deposits; a short article by Kovschak and Nylund (1981) is the best available reference.

Individual Salt Wash channel sandstones average 40 to 50 ft thick and are generally separated by thin mudstones or scour zones. However, in the central part of the main La Sal trend, several channels coalesce to form thick sandstone bodies up to 120 ft thick, over a mile wide, and several miles long. These thicker sandstones host the Energy Queen, Redd Block, Beaver-La Sal, and Pandora orebodies. Kovschak and Nylund (1981) believe that the La Sal channel is a major trunk or distributary channel to the finer-grained, braided-stream deposits of the Uravan mineral belt to the east. The host sandstones in the La Sal district are similar to other Salt Wash sandstone, but are coarser grained, thicker, and more linear. The host sandstones are relatively homogeneous, reduced gray sandstones. The underlying mudstones are greenish-gray in contrast to the normal red-brown color away from ore. Most of the known U-V deposits occur along the southern margin of the channel where gray channel sandstones interfinger with red and pink sandstones and mudstones.

Nearly all of the deposits developed primary, unoxidized ores; the only important oxidized deposit is the Rattlesnake U-V open pit. Primary ore consists of uraninite, coffinite, montroseite, and vanadium clays. Ore coats detrital grains, fills void spaces, and may replace some detrital quartz and feldspar. Carbonaceous material does not appear to be important in most deposits, although Weir and Puffett (1981) reported that at the Rattlesnake mine, U was concentrated in and around plant remains and associated clay pebbles and galls. Although not noted in the literature, there appears to be a regional gradation in vanadium content with higher vanadium orebodies in the eastern part of the main trend.