Rocky Mining District, Rocky Range, Beaver County, Utah, USAi

Regional Level Types
Rocky Mining District	Mining District
Rocky Range	Mountain Range
Beaver County	County
Utah	State
USA	Country

The Rocky mining district lies in the Rocky Range immediately south of the Beaver Lake district in central Beaver County 6 mi northwest of Milford. The Rocky district was organized in 1872 and has a long history of sporadic Cu, Fe, and W production up to the present day. The history of the district changed with the discovery of the Bawana, Hidden Treasure, and Maria Cu skarns by Cerro Verde Mining Company in 1956–58. This was followed by small-scale open pit mining and the discovery of several other small Cu skarn deposits and the larger Valley deposit at depth in the pediment on the southwest flank of the range by Anaconda in 1961 (Wray, 2006). These discoveries resulted in several generally unsuccessful attempts at Cu production from the small, open pit skarns. Most of the mining problems with the Rocky Cu skarn deposits were their relatively small size and partial oxidation resulting in small pits with steep walls, high stripping ratios, and poor metallurgical recoveries due to the mixed oxide-sulfide nature of the ores. District Cu production restarted in 1962 and continued until 1974. A new mill was completed in 2008 and intermittent production continued through 2018. The total historical district production is estimated at about 3,400,000 tons averaging nearly 2% Cu with minor Ag, Au, and locally W and/or Mo (Wray, 2006). Approximately another 2,600,000 tons of somewhat lower grade Cu ore has been mined in the last decade. Total district metal production at modern metal prices is estimated at $138 million. The Bawana, Maria, and Hidden Treasure mines are the largest producers. The Cu skarns remain in sporadic production and the Copper Ranch Cu deposit is currently in production (April 2018).
The Rocky Range is a small range situated on the Wah Wah–Tushar mineral belt in the eastern Basin and Range Province. Geologically the district is composed of a series of Cu skarns adjacent to a quartz monzonite stock (~30 Ma) (Best and others, 1989). The stock also intrudes and possibly domes the east-dipping Horn Silver Andesite on the east flank of the range. These mineralized Permian-Triassic limestone xenoliths or roof pendants lie in a large (6-sq-mi) quartz monzonite composite stock. This stock, or possibly a series of thick dikes and sills, appears to have been passively injected, stoping its way upward. The skarn deposits are typically metamorphosed to anhydrous, prograde, garnet-diopside-epidote skarns containing magnetite- chalcopyrite-bornite ±scheelite mineralization having a low pyrite content (USGS model 18b). The grades range from just under 1% to just over 2% Cu and probably average about 1.4% Cu. The largest remaining resource is the covered Valley Cu skarn deposit with a subeconomic inferred resource of about 26 million tons at 1.4% Cu. The Valley Cu skarn deposit lies beneath 230 to 1300 ft of alluvium in the pediment west of the smaller, open pit skarn deposits in the range.