Central Laramie Range

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 Focus area is based on the outline of the Laramie Anorthosite Complex as shown on the state geologic map compilation (Horton and others, 2017). Syenite and monzonite bodies associated with the Laramie Anorthosite Complex, namely the Red Mountain and Sybille plutons, have elevated REE due to abundance of allanite, zircon, and apatite (Anderson and others, 2003; Scoates and others, 1996).
Identified resources Identified resources of REE.
Production Unknown.
Status Current exploration for REE.
Estimated resources Unknown.
Geologic maps Ver Ploeg and Boyd (2007), scale 1:100,00; Ver Ploeg and McLaughlin (2009, 2010), scale 1:24,000; Ver Ploeg (2009), scale 1:24,000; Carnes and others (2013), scale 1:24,000; Ver Ploeg and others (2012), scale 1:24,000; Newhouse and Hagner (1957), scale 1:63,360; Ramarathnam (1962), no scale; Kolker (1989), scale 1:24,000; Snyder (1984), scale 1:24,000; Snyder and others (1995), scale 1:24,000; Snyder, Peterman and others (1997), scale 1:24,000; Snyder, Siems and others (1997), scale 1:24,000; Snyder and others (1998), scale 1:24,000; Segerstrom and others (1977), scale 1:48,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Sybille and Red Mountain plutons are REE-enriched (Anderson and others, 2003).
Deposits Halleck Creek Rare Earth Project.
Evidence from mineral occurrences American Rare Earths LTD (2021).
Geochemical evidence Coarse-grained allanite in clinopyroxene syenite and quartz monzonite is being explored as a REE deposit by American Rare Earths (specifically Nd, Pr, and Dy); total rare-earth oxide is estimated to be up to 0.60% or 5,756 ppm. (American Rare Earths LTD, 2021). At Halleck Creek, TREO is 3,187 ppm (Pr+Nd averages 7.02 ppm).
Geophysical evidence No data.
Evidence from other sources Lanthanum values in samples from Red Mountain pluton are 160-3800 greater than chondrite values due to the presence of allanite, zircon, and apatite, which are generally LREE enriched (Anderson and others, 2003); monzosyenite in the western part of the Sybille intrusion have high total REE concentrations (Scoates and others, 1996). Allanite nodules reported in pegmatites that cut the Sherman Granite, in southern portion of the focus area (Sutherland and Cola, 2016).
Cover thickness and description Most of the region has exposed bedrock, or bedrock with shallow (<100 m) burial depth; however, Precambrian mapping would be greatly enhanced with geophysics; very high density of sill and dikes with complex outcrop patterns.
Authors Robert W. Gregory, Jane M. Hammarstrom, Patricia M. Webber, Joshua M. Rosera.
New data needs 1:24,000 scale mapping, geochemical survey, geophysics.
Geologic mapping and modeling needs Geologic mapping of the igneous stratigraphy with precise ground control is essential. Requires outcrop-level mapping. Mapping with extensive geochemistry and with the help of geophysics.
Geophysical survey and modeling needs Rank 1 aeromagnetics and aeroradiometrics, also additional gravity stations; Elmer's Rock greenstone belt might be a good place for airborne gravity gradient survey (i.e., small area, rugged terrain that may preclude ground gravity).
Digital elevation data needs Lidar in progress with small areas complete.