Marshall Pass

Region West, Rocky Mountains
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The focus area was drawn to include identified occurrences in the Marshall Pass uranium district (Chenoweth, 1980) and a favorable area identified during the National Uranium Resource Evaluation program (U.S. Department of Energy, 1980).
Identified resources Identified resources of uranium; historical production of uranium.
Production The Los Ochos mine produced about 1.25 million lbs U3O8 between 1976 and 1981 (Pool, 2017). Prior to 1971, the Los Ochos Group produced 448,685 tons of ore at 0.14% U3O8, producing 1,253,513 lbs U3O8 (Nelson-Moore and others, 1978). The Pitch mine produced about 3 million lbs U3O8 between 1959 and 1984 (Pool, 2017).
Status Past mining.
Estimated resources In a paper given at the American Institute of Mining Engineers Meeting, Denver 1978, reserves were reported as 2.1 million tons of ore at a grade of 0.17% U3O8. This would be equivalent to 1.74 million lbs U3O8 (Nelson-Moore and others, 1978).
Geologic maps Olson (1977, 1983), scale 1:24,000; Cappa and Wallace (2007), scale 1:100,000; Streufert and others (1999), scale 1:150,000; Tweto, Moench and Reed (1976), scale 1:250,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Structurally controlled mineralization in the Ordovician Harding Quartzite, Mississippian Leadville Limestone, and Pennsylvanian Belden Formation adjacent to Proterozoic diorite, quartz monzonite, gneiss and schist (Chenoweth, 1980).
Deposits Pitch mine (MRDS dep_id: 10012409), Erie No. 28, Little Indian No. 36, Lookout Claims, Marshall Pass Group.
Evidence from mineral occurrences MRDS; International Atomic Energy Agency (2020b); U.S. Environmental Protection Agency (2006); Nelson-Moore and others (1978).
Geochemical evidence No data.
Geophysical evidence No data.
Evidence from other sources No data.
Comments Mineralization at the Pitch mine is in the Laramide Chester Fault is hosted in the Belden Formation and Leadville Dolomite where these units are brecciated in the footwall of the fault (Olson, 1988). Shear zones within Precambrian rock are also mineralized. The deposit type and origin of mineralization is unclear, but because mineralization is structurally controlled and Olson (1988) argues that the source is Tertiary tuffs, the deposits are tentatively assigned to the Volcanic-related Structure-bound model type. Beryllium and Li inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020).
Cover thickness and description Exposed at the surface.
Authors Susan Hall, Michael K. O'Keeffe.
New data needs Geologic mapping, lidar, geophysics.
Geologic mapping and modeling needs The following 1:24,000 scale quadrangles would need to be mapped and compiled: the rest of the Pahlone Peak, Sargents, Mount Ouray, Sargents Mesa, Chester, and Bonanza. It appears that a portion of the Sargents, Chester and all of the Sargents Mesa quadrangles have been mapped at 1:50,000 scale (Lipman, 2012), but this would need additional research.
Geophysical survey and modeling needs High resolution Rank 1 aeromagnetic and aeroradiometric surveys needed.
Digital elevation data needs Lidar in progress in the southern half of the focus area; complete in the northern half.