Aspen Mountain

Region West, Rocky Mountains
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Elevated Sb and other critical mineral values are noted at Aspen Mountain along the trend of a northeast-striking fault, which is crudely subparallel to the trend of the Rock Springs anticline (that is, the Rock Springs uplift). The elevated Sb values correspond with a prominent zone of silicified Upper Cretaceous strata, thought to be epithermal in origin. Also elevated Hg, As, and Th. The zone includes various degrees of silicification over an area of about 30-50 square km, and includes secondary kaolinite and alunite (Kehoe and others, 2020).
Identified resources None.
Production None.
Status No known past/current mining or exploration.
Estimated resources No data.
Geologic maps Kehoe and others (2020), scale 1:24,000; Schultz (1920), scale 1:250,000; Sears (1926), scale 1:62,500; Hale (1950), scale 1:253,440.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Mineralization and areas with enriched/elevated critical minerals typically occurs in the Blair Formation along structural boundaries and depositional contacts. Silicification is common along faulted zones and mineralization has been observed between the contacts of the underlying Baxter Shale and the lower sands of the Blair Formation. (Kehoe and others, 2020). Kaolinite and alunite present in Bishop Formation (Love and Blackmon, 1962).
Deposits Aspen Mountain occurrence (MRDS dep_id: 10090647).
Evidence from mineral occurrences MRDS.
Geochemical evidence White claystone from Bishop Formation contains 60-90% alunite (Love and Blackmon, 1962); additional alunite-bearing samples indicate 32.0% and 29.5% Al2O3 and 6.8% and 5.8% K2O, respectively (Osterwald and others, 1966).
Geophysical evidence No data.
Evidence from other sources Wyoming State Geological Survey data show elevated Sb, Ba, Fe, Sn, U, V, As, Bi, Te, Mo, Zn, Pb, Ag, Tl, Se (> 5 times crustal abundances); Cs and Hg above background levels.
Comments At the Aspen Mountain occurrence alunite in a white alunite tuffaceous sandstone was discovered in shallow drill cuttings during oil and gas exploration. Area is poorly understood: geophysics, especially magnetics and radiometrics, could be important for seeing the bigger 3D picture; electromagnetics also perhaps important for potential metallic resource.
Cover thickness and description Partially exposed; alunite and kaolinite bodies largely covered, minimum 18 feet depth.
Authors Rachel N. Toner, Ranie M. Lynds, Benjamin J. Drenth, Patricia Webber.
New data needs Rank 1 aeromagnetic and radiometric data; additional geochemical analyses (particularly for covered bodies that have been found previously by trenching).
Geologic mapping and modeling needs 1:24,000 scale geologic mapping recently completed (Kehoe and others, 2020, also selected surrounding quadrangles in Rock Springs uplift).
Geophysical survey and modeling needs Rank 1 aeromagnetic and aeroradiometric data.
Digital elevation data needs Lidar complete in Wyoming.