Sierra Madre

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 Remnant volcanic seafloor deposits hosting massive sulfide deposits exist within the focus area Archean Silver Lake Metavolcanics of the Phantom Lake Metamorphic Suite, the Green Mountain Formation, and the Pearl mining district of northern Colorado and southern Wyoming (Hausel, 1986; Houston and others, 1992).
Identified resources Identified resources for zinc. Historical production of copper, gold, and silver.
Production From Hausel (1986): "The amount of copper mined from the Encampment district is unknown; however, from 1899 to 1908, 24 million pounds of copper were produced in Wyoming, nearly all from the Encampment district.
Status Past exploration and mining for copper, gold and silver throughout Encampment district.
Estimated resources From Hausel (1997), the Broadway mine "was estimated that the ore in sight over a surface area of 150 feet by 8 feet to a depth of 100 feet, totaled 12,000 tons of 10% Zn. This represented only a very small portion of the ore deposit.
Geologic maps Houston and Graff (1995), scale 1:50,000; Sutherland and Hausel (2004), scale 1:100,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage, poor ground gravity coverage.
Favorable rocks and structures Stratiform volcanogenic sulfide deposits (iron-formation, metachert, metarhyolite, meta-andesite, exhalite) within Proterozoic gneisses and amphibolites.
Deposits Meta mine (MRDS dep_id: 10157139), Doane-Rambler mine (including Rex mine) (MRDS dep_id: 10303046), Bridger mine (MRDS dep_id: 10254793), Colorado Belle Group (MRDS dep_id: 10132498), Itmay mine (MRDS dep_id: 10229976).
Evidence from mineral occurrences MRDS.
Geochemical evidence Hausel (1982b, 1992a, 1997) documented volcanogenic massive sulfide mineralization at the Itmay mine in Fletcher-Huston Park and at the Broadway mine. From Hausel (1997), the Broadway mine had multiple assays with "Anomalous amounts of lead and zinc..." , a drillhole "encountered 20.5 feet of 8% Zn", and a geochemical survey identified "a 2200-foot-long, 100- to 1000-foot-wide zinc soil anomaly; and a 1500-foot-long lead anomaly." Sutherland and others (2018) report elevated concentrations (at least 5 times crustal abundance) Mn at Broadway mine.
Geophysical evidence No data.
Evidence from other sources No data.
Cover thickness and description Variable, mix of good exposure to abundant surficial cover and heavily forested areas.
Authors Rachel N. Toner, Patricia M. Webber, Benjamin J. Drenth, Michael L. Zientek, Robert W. Gregory, Kevin Mosser.
New data needs 1:24,000 scale geologic mapping supported by high-quality geophysics and lidar, especially along trace of Cheyenne Belt; new reconnaissance geochemistry.
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 major ground gravity campaign.
Digital elevation data needs Lidar in progress with small areas complete.