Cretaceous heavy-mineral placer sandstones (black sandstones)

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

Information leading to the delineation of this focus area

Basis for focus area Low grade titaniferous iron ore of sedimentary origin consisting of detrital Fe-Ti oxide minerals (magnetite and ilmenite). These deposits occur in bands recognized along the Rocky Mountain front and contain minor REE-bearing monazite. Focus area is defined by regressive late Cretaceous sands. In Montana, these include the Eagle/Virgelle, Horsethief, Judith River, and Fox Hills Formations (from 1:100,000 geologic map). In Wyoming (Hausel, 1990b; King and Harris, 2002; Sutherland and Cola, 2016), these include the lower Mesaverde Group in the Bighorn Basin (6 known deposits), Rock Springs uplift (8 deposits; Roehler, 1989), Wind River Basin (3 deposits, of which 1 is unverified), and Laramie Basin (1 deposit); Frontier Formation in southwestern Wyoming (2 deposits); Lewis Shale in the Wind River Basin (1 unverified) and Hanna Basin (1 unverified); Bacon Ridge Sandstone in northwestern Wyoming (1 deposit); basal Lance Formation in the Wind River Basin; and Fox Hills Sandstone in the Powder River Basin (1 unverified deposit, numerous suspected deposits). One occurrence is also known in the Jurassic Stump Sandstone in the northern overthrust belt.
Identified resources Identified resources for titanium (titaniferous magnetite).
Production None.
Status Unknown.
Estimated resources Montana: a suggested few hundred million tons of titaniferous magnetite in several deposits on the western flank of the Sweetgrass Arch (Burlington Northern, Inc., 1970). Wyoming: total state-wide estimate is 21,873,000 tons of titaniferous sandstone of varying grade (Dow and Batty, 1961).
Geologic maps Vuke and others (2007), scale 1:500,000; Love and Christiansen (1985), scale 1:500,000; Martin and others (2004), scale 1:500,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Paleoplacers in regressive-type littoral Upper Cretaceous sandstones. Ore beds consist of thin-bedded and massive dark-brown, dark-reddish-brown, and dark-greenish-gray magnetite-rich sandstone packages 1 to 8 feet thick. The magnetite-rich beds are well indurated and often form a prominent ledge. One deposit is 6 to 8 feet thick and continuously exposed for over a mile (Schmidt, 1978). Typical mineralogy consists of opaque iron-titanium oxides and zircon, with lesser abundances of rutile, chromite, monazite, tourmaline, garnet, staurolite, amphibole, pyroxene, sphene, apatite, allanite, niobium-bearing opaque minerals, anatase, biotite, brookite, chlorite, epidote, kyanite, pyrite, spinel, and gold (Houston and Murphy, 1977; Madsen and Reinhart, 1982). Alluvial deposits, both recent stream valleys and Tertiary high gravel deposits. Large valleys include Bear Valley, Long Valley near Cascade, Boise Basin and smaller mountain basins. Alluvial deposits in the Boise Basin are as much as 20 m thick. Multiple drainages empty into this large, fault-bounded basin. Originates from granitoid rocks of the Idaho batholith (Mackin and Schmidt, 1957).
Deposits Montana (from Burlington Northern, Inc., 1970): Freezeout Lake, Choteau, Conrad, Radar Station, Radar Station and Kennedy Coulee, Rimrock Butte, Disturbed Belt. Wyoming MRDS records: Black Butte Creek (MRDS dep_id: 10068540), Clarkson Hill (MRDS dep_id: 10068536), Cliff Creek deposit (MRDS dep_id: 10069136), Coalbank Hills (MRDS dep_id: 10068534), Cottonwood Creek (MRDS dep_id: 10068533), Cowley (MRDS dep_id: 10068529), Cumberland Gap Area (MRDS dep_id: 10093331), Dry Cottonwood Creek, Dugout Creek (MRDS dep_id: 10068531), Grass Creek, Lovell (MRDS dep_id: 10068530), Mud Creek (MRDS dep_id: 10068532), Murphy No. 1, Murphy No. 2, Poison Spider, Red Creek (MRDS dep_id: 10068539), Salt Wells Creek, Sheep Mountain, Union Pacific No. 1, Union Pacific No. 2, Waugh (MRDS dep_id: 10068541), Yenke (MRDS dep_id: 10069127), Zalenka (MRDS dep_id: 10068525). Also includes the following: Monazite Placer Districts: Bear Valley, Boise Basin, Burgdorf-Warren, Clearwater River, Dixie-Florence, Dismal Swamp, Rock Creek-Camp Creek, Salmon River, and Stanley Basin.
Evidence from mineral occurrences MRDS.
Geochemical evidence Virgelle ores were sampled by the U.S. Bureau of Mines during WWII near Choteau, Montana, and were found to contain 30.4 to 56.2% metallic Fe and 3.7 to 8.7% TiO2. Analyses by the U.S. Bureau of Mines throughout Wyoming ranged from 1.6 to 25.5% TiO2 (Dow and Batty, 1961). More recently some locations in Wyoming have been analyzed for REE. Where comprehensive geochemical data exist, heavy mineral sand deposits are sometimes enriched in Ti, Hf, Zr, Nb, V, and REE (Sutherland and Cola, 2016; Lichtner and others, 2021). Enriched samples may exhibit up to 10,200 ppm ΣREE. The Bacon Ridge and Stump sandstones in western Wyoming show no evidence of REE enrichment. REE enrichment in many locations remains unverified.
Geophysical evidence Montana: Radiometric anomalies associated with heavy-mineral sands around the Castle and Little Belt Mountains (Hart and Klosterman, 1956). Wyoming: Similar radiometric anomalies throughout the state (U.S. Atomic Energy Commission, circa 1950s, unpublished, cited in Houston and Murphy, 1962).
Evidence from other sources No data.
Comments Sahinen and Crowley (1959) suggested that the sedimentary deposits of titaniferous iron ore may be a future valuable source of both Fe and Ti. Sutherland and Cola (2016) identified Cretaceous heavy mineral sand deposits as possible sources of REE, but REE-enrichment in many locations remains unverified due to incomplete geochemical data. Stratigraphically similar Upper Cretaceous heavy mineral sand deposits are known throughout the Rocky Mountain region, including the Mesaverde Group in western Colorado, the Fox Hills Sandstone in eastern Colorado, and comparable units in southwestern Colorado, central and south-central Utah, northwestern New Mexico and northeastern Arizona.
Cover thickness and description Exposed in many locations along margins of intermontane basins.
Authors Rachel N. Toner, Benjamin J. Drenth, Derek T. Lichtner, Kaleb C. Scarberry, Jay A. Gunderson.
New data needs Sampling and reconnaissance geochemistry to estimate ore grade of identified deposits in northwestern Montana (Western Sweetgrass Arch), northern Wyoming (Bighorn Basin), and southwestern Wyoming (Rock Springs uplift). Mapping in areas where heavy mineral sands are identified, but not fully delineated (Montana: Crazy Mtn Basin, Bighorn Basin; Wyoming: Hanna Basin, Powder River Basin, Wind River Basin). Sedimentological studies and measured sections of most extensive, highest grade deposits (for example, Dugout Creek in Wyoming). Literature search of rock descriptions and measured sections to exclude areas of upper Cretaceous regressive sands without observed heavy mineral sands.
Geologic mapping and modeling needs None identified at this time.
Geophysical survey and modeling needs Rank 1 aeromagnetic and aeroradiometric data.
Digital elevation data needs Variable lidar across this large focus area; some complete, some in progress, some planned, some areas with no information.