Pryor Mountains-Little Mountain

Region West, Northwest; Rocky Mountains
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The focus area includes collapse breccia pipe U occurrences within the Little Mountains district in Wyoming (Gregory and others, 2010) and deposits with similar geology in the Pryor Mountains of Montana (Dahlkamp, 2010). Here hexavalent U minerals with accompanying silica fill open space in solution collapse features in the Mississippian Madison Limestone (Dahlkamp, 2010). No comprehensive genetic model has been proposed for these deposits.
Identified resources Historical production of uranium and vanadium.
Production 45,042 lbs U3O8 (with an average grade of 0.27%) and 30,187 lbs V2O5 (with an average grade of 0.29%) were produced from about 21 properties (deposits) in the Pryor Mountains area between 1956 and 1964 (Van Gosen and others, 1996). 177,078 lbs U3O8 (with an average grade of 0.39%) and 205,736 lbs V2O5 (average grade of 0.75%) were produced from properties of the Little Mountain district (Van Gosen and others, 1996). Ore from the Pryor Mountains area were reported at 0.5 to 0.8% U3O8 with a maximum of 1.27% (Elevatorski, 1976).
Status Past mining.
Estimated resources Van Gosen and others (1996) estimated a mean of 170 metric tons of U3O8 and 140 metric tons of V2O5.
Geologic maps Gregory and others (2010), scale 1:500,000; Horton and others (2017), scale 1:500,000; Pierce (1997), scale 1:250,000; Blackstone (1974), scale 1:24,000; Green and others (1999), scale 1:125,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Mississippian Madison Limestone with mineralized areas occurring along the flanks of Porcupine Creek anticline (in Wyoming).
Deposits Swamp Frog mine (MRDS dep_id; 10019872), Dandy (Pryor Mountain) mine (MRDS dep_id; 10019868), Sandra mine (MRDS dep_id; 10148982).
Evidence from mineral occurrences MRDS; International Atomic Energy Agency (2020b); U.S. Environmental Protection Agency (2006).
Geochemical evidence Only uranium minerals present in Wyoming are tyuyamunite and metatyuyamunite (Elevatorski, 1976).
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments Hand-picked, high-grade ore from the Swamp Frog mine contained 31.8% U and 9.88% V (Van Gosen and others, 1996). Several small historical mines in Wyoming, with mining occurring from 1956 until 1966 (Elevatorski, 1976).
Cover thickness and description Variable.
Authors Susan Hall, Jay A. Gunderson, Ranie M. Lynds.
New data needs Geologic mapping, geochemistry, geophysics.
Geologic mapping and modeling needs Large-scale mapping of individual deposits (1:12,000 or larger), paired with sedimentological and geochemical study.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar complete in Wyoming, no lidar in Montana.