Mineral resources of Du Noir Addition, Washakie Wilderness area, Fremont County, Wyoming

Abstract

The Du Noir Addition to the Washakie Wilderness area consists of 34,200 acres (13,840 hectares) of scenic mountainous terrain that adjoins the Teton Wilderness and Washakie Wilderness areas. The area was studied in 1973 by the U.S. Geological Survey and U.S. Bureau of Mines to evaluate its mineral, fuel, and geothermal energy potential. This evaluation is based on a search of the geologic literature, claim and production records, and fieldwork including mapping, inspection of claims and prospects, interpretation of aeromagnetic maps, and analyses of bedrock and stream-sediment samples. Flat-lying Eocene volcaniclastic rocks of the Absaroka volcanic field are exposed in about two-thirds of the Du Noir Addition. These volcanics unconformably overlie the deeply eroded, northwest-trending Du Noir anticline in which Paleozoic marine strata of Devonian through Permian age are exposed. Of lesser importance are small deposits of Eocene non-volcanic conglomerate, and basaltic intrusive and extrusive rocks of late Pliocene and possibly younger age. The results of this study indicate that the mineral, fuel, and geothermal potential of the Du Noir Addition are minimal. Low-grade copper-molybdenum mineralization occurs outside the addition, associated with intrusive rocks, but no indications of alteration or mineralization were found within the study area. Anomalous, but not economically important, concentrations of molybdenum and uranium were found in Permian and Eocene carbonaceous shales. Phosphate rock in the Phosphoria Formation occurs in beds too thin to constitute a resource. Large amounts of very pure limestone are present in the Madison Limestone, but equally pure limestone, much closer to transportation facilities, is found throughout this part of Wyoming. That part of the Du Noir anticline in the addition is too deeply eroded to be a likely reservoir of oil and gas. Present data indicates a low potential for geothermal energy in or near the addition.