Medicine Bow Mountains

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 Mafic and ultramafic intrusions and plutons (associated with the Geon 17 Cheyenne Belt-Medicine Bow orogeny), metasedimentary, and metavolcanic rocks exist in the greater Cheyenne Belt corridor with documented and theorized mineralization. The region in part conforms to the "Wyoming Platinum-Palladium-Nickel Province" of Hausel (2000), who considers it underexplored relative to its apparent potential. The Mullen Creek and Lake Owen layered mafic intrusions have documented PGE potential and strong theoretical potential for undiscovered Cr deposits (Hausel, 1987). Multiple PGE past-producing mines and occurrences in the New Rambler and Centennial Ridge districts (MRDS; McCallum and Orback, 1968). Elevated concentrations (5 times crustal abundance) of Cr and Mg exist in shear zones near the Mullen Creek complex (Sutherland and others, 2018).
Identified resources Identified resources of copper gold, PGE, silver, and vanadium. Historical production of copper, gold, PGE (from shear-hosted veins), and silver.
Production McCallum and Orback (1968) report Pt and Pd recovered from "hydrothermally altered metapyroxenite and metagabbro in shear zone tectonites and mylonitic gneiss" near the Mullen Creek Complex from the New Rambler mine between 1900 and 1918. From Hausel (2000): "Total metal production was reported at 1,753,924 lbs Cu, 171.35 oz Au, 7346 oz Ag, 170.16 oz Pt, and 451.4 oz of Pd (Needham, 1942). Silver Lake Resources (1985) estimated platinum-group metal production was more on the order of 16,870 oz Pd and 910 oz Pt.
Status Past exploration occurred for PGE, Cu, Au, and Ag in the mafic intrusions, shear zones, and associated metamorphic and hydrothermally altered stratigraphy. Status of current exploration is unknown-one of the last companies exploring the Lake Owen Complex was Trend Mining, but exploration was hampered by surficial cover and inadequate geophysics.
Estimated resources From Hausel (2000): Lake Owen complex: four stratigraphic horizons with PGE + Au grades > 1 ppm, two other units with 1.2–6 miles of ppm-level PGE, Au, and Ag mineralization (Loucks, 1991; Hausel, 2000), and 1.4 billion tons mineable surface vanadium oxide cumulates (Loucks and Glasscock, 1989); Mullen Creek complex New Rambler mine: "After the fire, the mine manager estimated probable reserves at 7,000 tons of 7 to 8% Cu and 0.25 opt Pt, with some gold and silver (Needham, 1942).
Geologic maps Blackstone (1970, 1973a, b), scale 1:24,000; Houston (1977a, b), scale 1:24,000; Houston and Childers (1977), scale 1:24,000; Houston and Karlstrom (1992), scale 1:50,000; Houston and Orback (1976), scale 1:24,000; Houston and others (1977), scale 1:24,000; Houston, McCallum and others (1978) scale 1:63,360; Hyden and others (1967), scale 1:24,000; Hyden and others (1968), scale 1:24,000; Karlstrom and Houston (1979), scale 1:48,000; McCallum and Kluender (1983), scale 1:24,000; Sutherland and Hausel (2004), scale 1:100,000; Sutherland and Hausel (2005b), scale 1:24,000; Sutherland and Kragh (2018), scale 1:24,000; Sutherland and Worman (2013), scale 1:24,000; Toner and others (2019), scale 1:24,000; Ver Ploeg and Boyd (2007), scale 1:100,000.
Geophysical data Inadequate aeromagnetic coverage, partly (~50%) adequate aeroradiometric coverage, poor ground gravity coverage.
Favorable rocks and structures Layered mafic intrusive complexes with associated felsic intrusives and vein systems-in particular, the Lake Owen Complex, which lies outside wilderness area boundaries (the Mullen Creek complex is partially within wilderness); Vanadium oxide cumulates in the Lake Owen complex; The layered mafic intrusions are found along the Mullen Creek-Nash Fork shear zone (Cheyenne Belt) and associated shear zones, which adds to the focus area's favorability for critical mineral potential.
Deposits Chromium: Cuprite mine (MRDS dep_id: 10080871); Cobalt: Keystone Mining District (MRDS dep_id: 10400529); Nickel: New Rambler mine (MRDS dep_id: 10103638); PGE: 30 records around layered mafic intrusions and Centennial Ridge; occurrences, prospects and past producers include the Queen mine (MRDS dep_id: 10038162), Utopia mine (MRDS dep_id: 10038156), Free Gold Claim (MRDS dep_id: 10038161); Titanium: two occurrence (MRDS dep_ids 10080940, 10008229); Vanadium: Lake Owen Complex (MRDS dep_id: 10008229); Zinc: unnamed prospect (MRDS dep_id: 10048495).
Evidence from mineral occurrences MRDS.
Geochemical evidence Mike Zientek (USGS) collected a suite of samples from one of the Lake Owen complex mineralized outcrops in 1988, in which the highest value Pt was 190 ppb. From Hausel (2000): Mullen Creek complex, New Rambler mine: "Production records of the last ore shipped from the mine following the 1918 fire showed values to range from 3.24% to 61.37% Cu, 0.0007 to 1.4 opt Au, 1.01 to 7.5 opt Ag, 0.047 to 3.2 opt Pt, and 0.33 to 12.3 opt Pd (Anonymous, 1942)."; "According to Knight (1902) a composite sample of dump material from the mine yielded 0.06 opt Pt, 0.04 opt Ir, 0.04 opt Pd, 0.10 opt Ag, and a trace Au.", and "Two assays reported by Knight (1902) included: (1) an assay of copper minerals which yielded 0.10 to 0.70 opt Pt, and (2) seven carloads of covellite ore which contained 0.40 to 1.4 opt Pt."; Blanche shaft estimates from dump samples "assayed 6 and 17 ppm Pt, 30 and 20 ppm Pd, and 20 and 17% Cu (Loucks, 1976)."; Henry Lode estimates from vein assays "yielded 1.94% Cu, 0.16 opt Au, 0.22 opt Ag, and 0.0054 opt Pt." and another vein assayed at "0.54 opt Au, 0.70 opt Ag, and trace Cu." From Osterwald and others (1966): Rambler mine: assays "averaged 3 oz. of platinum and palladium per ton; Independence mine near Keystone: "An analysis of 'mine-run' ore showed 0.27 oz. of platinum per ton..."; Queen shaft: "The gouge material assayed 0.03 oz. per short ton in platinum..."; Wyoming Gold and Platinum Mining Co. at Centennial: "U.S. Bureau of Mines assays show 11 oz. of palladium per ton...", McCallum and Kluender (1983) reported up to 0.015 ppm Pd, 10,000 ppm Sb, 5,000 V, and 10,000 ppm As in association with Ag, Cu, Pb, Zn, Cd, and Mo from veins associated with small granitic intrusives intercalated with the Mullen Creek layered mafic complex. From Sutherland and others (2018): elevated concentrations (at least 5 times crustal abundance) of Cr and Mg within the focus area.
Geophysical evidence Prominent magnetic anomalies associated with Lake Owen and eastern part of Mullen Creek.
Evidence from other sources Exploration by Chevron in the 1980s and 1990s found four separate zones of anomalous platinum group metals mineralization and at least two zones of magnetite mineralization.
Comments Chevron spent approximately US$570,000 on past exploration of the Lake Owen Project, which included, between 1983 and 1992, the drilling of 14 diamond core holes totaling 5,214 feet (1,590 meters). Significant results included 3.0 meters grading 1.338 g/t Au and 0.605 g/t PGM (1.94 g/t PGM and Au combined) and 1.0 meter grading 3.97 g/t Au and 0.255 g/t PGM (4.22 g/t PGM and Au combined). (Trend Mining Company Fact Sheet).
Cover thickness and description Variable, mix of good exposure to abundant surficial cover and heavily forested areas, which has hampered previous exploration efforts.
Authors Rachel N. Toner, Patricia M. Webber, Robert W. Gregory, Benjamin J. Drenth.
New data needs 1:24,000 scale geologic mapping supported by high-quality geophysics and lidar.
Geologic mapping and modeling needs 1:24,000 scale geologic mapping of the igneous and metamorphic stratigraphy, structural and deformation features (especially along Cheyenne Belt), and mineralization trends with precise ground control is essential. Requires outcrop-level mapping.
Geophysical survey and modeling needs Rank 1 aeromagnetics and radiometrics, also a significant ground gravity campaign.
Digital elevation data needs Lidar in progress with small areas complete.