Sheeprock or Columbia-East Erickson

Region West, Southwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Outline after Foley and others (2012), Foley, Jaskula, Piatak and Schulte (2017), and Krahulec (2018b). Focus area approximately follows the Sheeprock granite and its immediate surroundings. The Sheeprock granite is a fluorine-rich topaz-bearing granite that hosts beryl rosettes, W-Sn greisen occurrences, and is cut by veins and fissures of base metal sulfides and Cu-U-F assemblages.
Identified resources Historical production of copper, lead, and zinc. Tungsten ore was reportedly stockpiled, but never shipped (Ekker prospect).
Production Unknown.
Status Past mining. Prospected intermittently since the 1950s for lithophile elements.
Estimated resources Unknown.
Geologic maps Pampeyan (1989), scale 1:100,000.
Geophysical data Inadequate Rank 4 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures The 7.8 mi2, red, oxidized Sheeprock granite has a 1.4 mi2 highly differentiated “white facies” core containing smoky quartz and blue beryl (Christiansen and others, 1991; Richardson, 2004). The granite has ilmenite, magnetite, muscovite, zircon, apatite, monazite, thorite, uraninite, fluorite, samarskite, and topaz as accessory minerals. There are also small pegmatites and aplite dikes. The “white facies” is known to be enriched in Be, Th, and HREE (Richardson, 2004). Beryl occurs as (1) disseminated grains, (2) rosettes of radiating crystals as much as 2 ft in diameter, (3) in tiny, but massive seams/veins, and (4) in small aplite dikes and quartz veins (Krahulec, 2018b). Greisen-hosted cassiterite observed in granite and also in stream sediment nearby. Fissure and vein-hosted Pb-Zn mineralization occurs near granite-metasedimentary rock contacts.
Deposits Copper Jack mine (MRDS dep_id: 10055150), Flying Dutchman, Sultana mine (MRDS dep_id: 10055178), Tintic Delaware.
Evidence from mineral occurrences MRDS; Krahulec (2018b); UMOS (Utah Geological Survey, 2021).
Geochemical evidence Seven U.S. Geological Survey National Geochemical Database samples near the Sheeprock Granite assay over 100 ppm Sn. Greisen hosted cassiterite and wolframite. Sulfides reported in Pb-Zn fissures and also as chalcopyrite in Cu-U-F-Mn veins and fissures.
Geophysical evidence Aeromagnetic anomalies associated with the Deep Creek-Tintic Belt of plutons.
Evidence from other sources See Krahulec (2018b).
Comments Numerous critical commodities are inferred to be enriched based on the mineral system and deposit types for this focus area. The following critical mineral commodities have uncertain abundances in this focus area: Sb, As, Bi, Ga, Ge, and In, inferred from the mineral system/deposit types table (Hofstra and Kreiner, 2020).
Cover thickness and description Mostly surficial.
Authors David A. Ponce, Nora K. Foley, Joshua M. Rosera.
New data needs Aeromagnetic and aeroradiometric surveys; detailed intrusive mapping.
Geologic mapping and modeling needs Detailed geologic mapping of the Sheeprock granite to determine orientation and depth of emplacement to determine mineral potential.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and radiometric surveys.
Digital elevation data needs Lidar in progress.