Wyoming Metasedimentary and Metavolcanic Belts

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 Precambrian mafic/ultramafic metasedimentary and metavolcanic belts, associated dike, sill, vein, and pegmatite complexes, and derived placers – all with similar depositional and metamorphic histories not included within other focus areas. This deposit type includes ophiolite/komatiitic greenstone belt units suites and associated Cr-schists at South Pass and in the Deer Creek district and Casper Mountain supracrustals, as well as Ti-bearing BIFs at South Pass and the Hartville Uplift. With the exception of the somewhat better-understood South Pass greenstone belt, these metasedimentary and metavolcanic rocks have generally poorly constrained mineral potential.
Identified resources Identified resources of chromite; historical production of chromite, gold, and iron.
Production 2,294 tons of ore containing 35–45% Cr2O3 were mined from the Deer Creek mine (Hausel, 1987).
Status Past mining.
Estimated resources From Hausel (1987): Casper Mountain: "Trenching and drilling by the U.S. Bureau of Mines delineated Inferred reserves of 575,000 tons of chromite averaging 8.7% Cr2O3, and a total low-grade resource of 4,160,000 tons of 2.5% Cr2O3 (Julihn and Moon, 1945). These resources are calculated to a depth of 95 feet, and drilling indicates mineralization occurs to depths of at least 480 feet (Daellenback, 1985)."; Deer Creek: "...estimated at least 2,500 tons of 40% Cr2O3 ore remained exposed on the surface.
Geologic maps Harris and others (1985), scale 1:500,000; Love and Christiansen (1985), scale 1:500,000; Mineral system-specific maps include: Casper Mountain: Gable and others (1988), scale 1:20,000; Wind Rivers/South Pass: Hausel (1991), scale 1:48,000; Scott and Sutherland (2009), scale 1:100,000; Sutherland and Hausel (2006), scale 1:100,000); Hartville Uplift: Day and others (1999), scale 1;24,000; McLaughlin and Harris (2005), scale 1:100,000; McLaughlin and others (2011), scale 1:100,000; Sims and Day (1999), scale 1;48:000; Sims and others (1997), scale 1:24,000; Deer Creek: McLaughlin and Ver Ploeg (2008), scale 1:100,000; Hunter and others (2005), scale 1:100,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Ultramafic schists; serpentinites; mafic/ultramafic intrusions, flows, sills, and dikes; komatiites; pillow lavas; metagraywackes; veins/pegmatites within previously-listed rock types.
Deposits Casper Mountain mine (MRDS dep_id: 10254356), Deer Creek Canyon chromite (MRDS dep_id: 10132903).
Evidence from mineral occurrences MRDS.
Geochemical evidence From Hausel (1987): "Metakomatiites (serpentinites and talc-actinolite schists) in the South Pass, Seminoe Mountains...greenstone belts of Wyoming contain Cr2O3 concentrations commonly greater than 0.1% but less than 1.0%. But in the Casper Mountain and Deer Creek regions, relatively high-grade chromite is found in talc-actinolite schist."; "Assays of the [Deer Creek] ore yielded 35 to 45% Cr2O3..."; "Values as high as 0.87% chromium and 0.17% nickel were obtained from serpentinites and talc-actinolite schists in the Lewiston Lakes area" (South Pass greenstone belt); A Casper Mountain chromite-bearing schist "...averages about 2% chromium oxide (Cr2O3), but contains bands that run 5 to 25% Cr2O3.". From Hausel (1990a, 1994): several samples from Seminoe Mountains (Bradley Peak area, serpentinites, and schists) show elevated (greater than 5 times crustal abundance) Cr. From Hausel (1991): "South Pass MgO-rich serpentinites and cumulate-textured serpentinites yielded MgO concentrations of 36.3 to 38.1% and nickel concentration..."; "Chromium contents as high as 10,100 ppm (1.01%) were detected in some South Pass serpentinites...". From Sutherland and others (2018): elevated Cr and Ti concentrations in the Miner's Delight Formation, Goldman Meadows Formation (BIF), veins, and metagraywackes at South Pass.
Geophysical evidence No data.
Evidence from other sources No data.
Cover thickness and description Variable, mix of good exposure to thick surficial cover and heavily forested areas.
Authors Rachel N. Toner, Patricia M. Webber, Benjamin J. Drenth.
New data needs New Rank 1 geophysics-supported and modern geochronology-supported mapping could be a game-changer. Could use new reconnaissance geochemistry.
Geologic mapping and modeling needs Variable, but new, modern 1:24,000 scale mapping generally needed, supported by Rank 1 geophysics and modern geochronology.
Geophysical survey and modeling needs Rank 1 aeromagnetics and aeroradiometrics.
Digital elevation data needs Lidar coverage variable with some completed and some areas in progress.