| 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. |
