INTEGRATING GEOLOGIC MAPPING, GEOCHEMISTRY, AND GEOCHRONOLOGY TO INVESTIGATE CRITICAL MINERAL POTENTIAL OF THE LARAMIE MOUNTAINS, SOUTHEAST WYOMING

The Laramie Mountains of southeastern Wyoming comprise a geologically complex region with an extensive history of mineral exploration and mining. The range, which is bisected by the Paleoproterozoic Cheyenne belt—the suture zone between the Archean Wyoming Craton and the Proterozoic Colorado Province—has a number of documented but relatively understudied mineral systems. Host lithologies include multiple anorthosite complexes and associated granitic, syenitic, and monzonitic plutons; metasedimentary and metavolcanic belts; and a mafic dike swarm. The critical mineral potential and lack of exploration-quality, publically available data and maps from key areas of the region prompted a targeted, detailed study of the area through the U.S. Geological Survey’s Earth Mapping Resources Initiative. A two-phased approach was used to identify, investigate, and map the least-studied and highest-priority mineral systems. New geologic mapping and geochemical and geochronological analyses targeted poorly defined polymetallic deposits associated with the Paleoproterozoic Horse Creek complex and Mesoproterozoic Sherman batholith, with the goal of determining the relationships between the mineralization and host rocks, timing, chemistry and mineralogy, and implications of these for the mineral system. Initial results indicate that the polymetallic mineralization shares similar characteristics with deposits in the Silver Crown mining district on the southeastern margin of the Sherman batholith. The deposits are structurally controlled, copper-, gold-, and tungsten-bearing, were likely emplaced between ca. 1,435–1,441 Ma, and are hosted in granodiorites of the Sherman batholith. A broad geochemical survey was conducted across the remainder of the study area, focused on graphite, iron-titanium oxides, rare earth element-enriched syenites, and various metavolcanic lithologies, which will serve as a preliminary foundation for continued critical minerals research in the region.