Bald Mountain paleoplacers

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

Information leading to the delineation of this focus area

Basis for focus area The Flathead Sandstone in the northern Bighorn Mountains, at Bald Mountain and Rooster Hill, is known to contain monazite-bearing conglomeratic sandstones with elevated REE (USMIN; Sutherland and Cola, 2015). Most data are from U.S. Bureau of Mines exploration of the Bald Mountain paleoplacer deposit in the 1950s. Other moderately enriched or unverified occurrences exist in the Flathead Sandstone elsewhere in the region, including in the southern Bighorn Mountains and the Rattlesnake Hills (Sutherland, Gregory and others (2013).
Identified resources Identified resources for REE (monazite).
Production Unknown.
Status Past exploration.
Estimated resources 18 million tonnes (20 million tons) that averaged 1.25 kg/tonne (2.5 lbs/ton) of monazite (McKinney and Horst, 1953a; Borrowman and Rosenbaum, 1962). A high-grade zone was estimated to contain 612,000 tonnes (675,000 tons) of conglomerate that averaged 6.6 kg/tonne (13.2 lbs/ton) of monazite (Borrowman and Rosenbaum, 1962).
Geologic maps Hallberg and others (1998), scale 1:100,000; Hallberg, Case and Noecker (2001), scale 1:100,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Monazite-bearing conglomerates and sandstones.
Deposits None.
Evidence from mineral occurrences Sutherland and Cola (2015), p. 100-104.
Geochemical evidence Wyoming State Geological Survey sampling demonstrated the presence of significant REE concentrations, particularly the LREE, associated with Th-bearing monazite investigated by the USBM and USAEC in 1952 (Sutherland, Gregory and others, 2013).
Geophysical evidence Unknown.
Evidence from other sources None.
Comments Includes Rooster Hill area and Flathead Sandstone outcrops in the northern Bighorns.
Cover thickness and description Variable.
Authors Thomas P. Frost, Pamela M. Cossette, Robert W. Gregory, Kevin Mosser, Derek T. Lichtner.
New data needs Sedimentological study with geochemistry-detailed quadrangle mapping not especially useful, geophysics not especially useful; need measured sections.
Geologic mapping and modeling needs None requested at this time.
Geophysical survey and modeling needs Not useful for this deposit type.
Digital elevation data needs Lidar complete in Wyoming.