Fox Hills Sandstone heavy mineral placers

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 Colorado: Previous subsurface drilling investigations, general area of geophysical anomalies based on proprietary survey. Beds of coal are in the Fox Hills Formation.
Identified resources Identified resources of REE (allanite/monazite/xenotime), titanium (ilmenite/rutile), garnet, and zircon. Historical production of coal from coal interbeds in the Fox Hills Formation.
Production Unknown.
Status Colorado: Past exploration by Rocky Mountain Energy (mostly associated with coal), DuPont, Riverbend, and Radar Acquisitions.
Estimated resources Colorado: Along a portion of one trend in the Fox Hills Formation (3.5 miles/5.6 km): 14.2 million short tons at 2.5% ilmenite/rutile (Measured and Indicated resource); 3.3 million short tons at 2.4% ilmenite/rutile, 0.5% zircon and 3.1% garnet also reported. Other trends may extend 23 km, with one identified for 11 km by drilling.
Geologic maps Sharps (1980), scale 1:250,000; Moore and others (2001), scale 1:250,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Upper Cretaceous Fox Hills Formation.
Deposits Colorado: Titanium Ridge, Riverbend.
Evidence from mineral occurrences O'Keeffe and others (2019).
Geochemical evidence Recent investigations by Colorado Geological Survey (O'Keeffe and others, 2019) indicate total REE concentrations along other trends ranging between 3,302 and 4,909 ppm and averaged 4,187 ppm associated with allanite/monazite and xenotime.
Geophysical evidence Proprietary data only.
Evidence from other sources AEC airborne radiometric anomalies (Malan, 1965).
Comments Colorado: Several companies have drilled this property for either heavy minerals (DuPont, Radar Acq.) or coal/uranium (Rocky Mountain Energy).One area of the deposit has been marketed as a combined heavy mineral and coal (mostly lignite in the overlying Laramie Formation) target. The paleo-coastlines in the Fox Hills contain beach placer deposits that are generally subparallel and strike to the northwest. These deposits occur in the subsurface with minimal to over 100 feet of cover in some areas.
Cover thickness and description Colorado: Near surface deposits and subsurface in areas up to 150 feet deep. Cover includes Laramie Formation and other Paleogene deposits to the west (for example, Denver Formation).
Authors Michael K. O’Keefe, Matthew L. Morgan.
New data needs 1:62,500 scale geologic mapping, geochemical analysis of additional samples for REE.
Geologic mapping and modeling needs New 1:62.500 scale geologic mapping is recommended in ten quadrangles in Colorado: Matheson, Matheson NE, Beuck Draw, River Bend, Agate, Barking Dog Spring, Noonen Reservoir SW, Cottonwood Valley South,, Noonen Reservoir, and Cottonwood Valley North.
Geophysical survey and modeling needs Need aeromagnetic/aeroradiometric data. AEC aeroradiometric survey identified surficial deposits. Proprietary aeromagnetics survey identified targets at depth. Aeromagnetics may be appropriate as indicated by past surveys.
Digital elevation data needs Lidar complete.