Nugget Sandstone Copper

Region West, Northwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The focus area includes known Cu-Ag-Zn occurrences in the Lake Alice district and other similar occurrences hosted in the Nugget Sandstone in the Wyoming overthrust belt. Copper-Ag-Zn mineralization is found in the uppermost 25 feet of the Nugget Sandstone, along the contact with the overlying Gypsum Spring member of the Twin Creek Formation. The mineralized sandstone is bleached or altered, while the Gypsum Spring member is often petroliferous in these areas and also has elevated concentrations of Cu-Ag-Zn. Extensive regional faulting and fracturing (Love and Antweiler, 1973). No comprehensive genetic model has been investigated for these deposits. Polygon has been modified to reflect Nugget Sandstone and Gypsum Spring Formation at 1:500,000-scale in Wyoming.
Identified resources Historical production of copper, gold, and silver.
Production Estimated 12,000 tons of ore removed during early workings at Griggs Mine; total production at Griggs and Ferney Gulch mines is unknown. Reported ore grades in 1920 were 0.175 oz Au, 79.60 oz Ag, 33.60% Cu (Love and Antweiler, 1973).
Status Past mining.
Estimated resources None.
Geologic maps Oriel and Platt (1980), scale 1:250,500; Rubey and others (1976, 1980), scale 1:62,500; Schultz (1914), scale 1:125,000.
Geophysical data Inadequate Rank 3 to 4 aeromagnetic and Rank 4 aeroradiometric coverage.
Favorable rocks and structures Uppermost Nugget sandstone; basal breccias of Gypsum Spring member of the Twin Creek Formation.
Deposits Griggs mine (MRDS dep_id; 10080977), Ferney Gulch mine (MRDS dep_id; 10096578), Coantag prospect (MRDS dep_id; 10096577), Spring Lake Creek prospect (MRDS dep_id; 10080975), Landslide Dam prospect (MRDS dep_id; 10080838).
Evidence from mineral occurrences MRDS.
Geochemical evidence From Love and Antweiler (1973): documented Cu-Ag-Zn mineralization at 7 locations in Lake Alice district and additional location 51 miles north in Hoback Range; analyses show enriched Zn, Cu, and Ag all sites with elevated to enriched As, Ba, Co, Ce, Ni, Pb, Mo, and trace Cr. Maximum ore values are 67,000 ppm Cu; 1,200 ppm Ag; 32,000 ppm Zn; 7,000 ppm As; 5,000 ppm Ba; 700 ppm Co; 150 ppm Mo; 5,000 ppm Pb.
Geophysical evidence No data.
Evidence from other sources None.
Comments Two small historical mines and several prospects and occurrences in Wyoming, with most mining occurring from 1985-1920 (Love and Antweiler, 1973).
Cover thickness and description Well exposed bedrock at surface.
Authors Jane M. Hammarstrom, Patricia M. Webber.
New data needs Geophysics, reconnaissance geochemistry.
Geologic mapping and modeling needs None identified at this time. 1:62,500 scale bedrock mapping coverage.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage would be useful, as would gravity and electromagnetic data.
Digital elevation data needs Lidar complete in Wyoming.