Medicine Bow Mountains

Region West, Rocky Mountains
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Felsic plutons found throughout the Medicine Bow Mountains, both in association with the mafic-ultramafic intrusions and as Colorado Province island-arc accretions along the Cheyenne Belt have mineralization potential. Elevated Sb has been reported in sheared and brecciated zones within the New Rambler and Keystone areas that also have elevated Zn, Pb, Cu, Ag, and Cd (McCallum and Kluender, 1983; Sutherland and others, 2018). Manganese-enriched veins are also locally present (Hausel, 1987).
Identified resources Unknown.
Production Unknown.
Status Unknown.
Estimated resources Unknown.
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 Felsic intrusives and vein systems associated with the layered mafic intrusive complexes; Locally-present manganese-enriched veins in the Lake Owen and Mullen Creek complexes and the Centennial Ridge district; Locally present Sb-enriched mineralized quartz veins hosted in felsic intrusives in the Mullen Creek complex; Felsic plutons 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 Unknown.
Evidence from mineral occurrences McCallum and Kluender (1983); Loucks (1976).
Geochemical evidence McCallum and Kluender (1983) reported up to 0.015 ppm Pd, 10,000 ppm Sb, 5,000 ppm 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 McCallum and Kluender (1983): high-grade argentiferous galena from a prospect pit contains as much as 1,600 ppm Ag, 1% As, 2% Pb, 1% Zn, 1% Sb, and as much as 7000 ppm Cu, 70 ppm Mo, 500 ppm Cd, 70 ppm Bi, 5000 ppm V, and 0.15 ppm Pd. From Sutherland and others (2018): elevated concentrations (at least 5 times crustal abundance) of Sb within the focus area.
Geophysical evidence Prominent magnetic anomalies associated with Lake Owen and eastern part of Mullen Creek.
Evidence from other sources No data.
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 inadequate, although expected to be covered by a FY20-funded 3DEP lidar survey.