Elk Ridge Mining District, San Juan County, Utah, USAi

Regional Level Types
Elk Ridge Mining District	Mining District
San Juan County	County
Utah	State
USA	Country

The Elk Ridge district is the easternmost district in the White Canyon U mining area on the Monument Upwarp in central San Juan County, 20 mi west of Monticello. Copper prospecting began in the White Canyon area in the 1880s but lead to little development. Uranium exploration and development began in the late 1940s with production from 1951 to 1970. Elk Ridge has been a significant U ±Cu producing district. Total district metal production at modern metal prices is estimated at $68 million. The largest producers are the Betty, Abe, Avalanche Group, King Edward, and Payday underground mines (Chenoweth, 1993).
Geologically, the Elk Ridge district is dominated by the north-trending Comb Ridge monocline on the east, which dips up to 30° east and defines the eastern margin of the Monument Uplift of the Colorado Plateau. The rocks of the Monument Uplift, west of Comb Ridge, generally dip gently west at about 5° (Chenoweth, 1993). The main host stratum in the Elk Ridge district is the Upper Triassic Shinarump Conglomerate Member of the Chinle Formation. In the northern part of the district, some small orebodies occur in the overlying Moss Back Member. The Shinarump Conglomerate is rarely more than 40 ft thick with an erosional unconformity at the base. The westerly flowing Shinarump stream channels are up to 250 ft wide and may scour up to 15 ft into the underlying Moenkopi. Shinarump-hosted mineralization is typically in contact with the underlying Moenkopi Formation mudstones (USGS Model 30c). Deposits occur in the basal sandstone and are tabular to lenticular, associated with asphaltite and carbonaceous trash, and contain on average from 5000 tons to 10,000 tons of ore (Doelling, 1969). The deposits are only up to about 5 ft thick but can be followed for several hundred feet along the channel.
The primary host to uranium mineralization in the Elk Ridge district is the lower section of the Triassic Chinle Formation with lesser ore produced from the Moenkopi Formation (Doelling, 1969). The ore is fine grained, occupies the interstices between sand grains, and is associated with carbonaceous matter and mudstone of the Moenkopi. The primary uranium mineral is uraninite, locally associated with chalcopyrite, bornite, tennantite, domeykite, and pyrite with traces of galena and sphalerite; however, vanadium is uncommon (Doelling, 1969).
Issues associated with the district include the lack of a V byproduct, the high Cu-content can cause metallurgical problems, its relatively remote location, and its location on National Forest System land.