McCullough Butte

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

Information leading to the delineation of this focus area

Basis for focus area MRDS past Be producers; Foley, Jaskula, Piatak and Schulte (2017).
Identified resources Identified beryllium and fluorite resources; historical production of beryllium (beryl) and fluorite.
Production Unknown.
Status Past mining. Episodic exploration 1960s-1980s(?); semi-active exploration by Tertiary Minerals plc since ~2013 (~40 drill holes).
Estimated resources Beryllium: Resource of 175 million metric tons, contained 47,000 metric tons of BeO, grade of 0.27% BeO, and grade of 0.01% Be (Foley, Jaskula, Piatak and Schulte (2017)). Fluorite: 2015: 6,700,000 tons, 10.8% CaF2 (Indicated mineral resource, 9% CaF2 cut-off); 88,500,000 tons, 0.7% CaF2 (Inferred mineral resource, 9% CaF2 cut-off) [JORC compliant] (Davis and Muntean, 2018). Asarco estimated resources of 110 million tonnes grading 10% CaF2 and Wardell Armstrong International Ltd estimated 85-105 million tonnes grading 9-11% fluorspar at 8% cut-off grade CaF2. The target is part of a larger mineral system estimated by Tertiary Minerals plc at 395 to 615 million tonnes grading 5-7% fluorspar at 2% cut-off grade (Hayes and others, 2017).
Geologic maps Roberts and others (1967), scale 1:250,000; Long and others (2014), scale 1:48,000; Stewart and Carlson (1978), scale 1:500,000.
Geophysical data Adequate Rank 1 aeromagnetic and aeroradiometric coverage; See Ponce and Drenth (2020).
Favorable rocks and structures Mineralization occurs as a skarn-type replacement of flat-lying limestone beneath a quartzite cap. Beryllium is in carbonate rocks and fluorite associated with dikes. Porphyritic felsite dikes (ca. 84 Ma) and aplite in Paleozoic limestone, dolomite, and quartzite, altered to dolomite, greisen/quartz veins, tremolite, phlogopite, and calcite; 6 vein types containing quartz, feldspar, garnet, epidote, feldspar, fluorite, pyrite, muscovite, sphalerite, molybdenite, zoisite, beryl, barite, and Sb sulfosalts.
Deposits McCullough Butte, Reese and Berry mine (MRDS dep_id: 10044701).
Evidence from mineral occurrences MRDS; Foley, Jaskula, Piatak and Schulte (2017).
Geochemical evidence Reportedly elevated W, Sn, Mo, Zn concentrations in a relatively large fluorite deposit (>80 Mt at ~10% CaF2).
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments Tin and W reported by Barton (1987). Bismuth and Sc enrichment is inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020).
Cover thickness and description Unknown.
Authors David A. Ponce, Peter G. Vikre.
New data needs Geophysics, lidar.
Geologic mapping and modeling needs Would need access to drill hole data for 3D molding. Drill holes may not be deep enough to make it worthwhile.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage.
Digital elevation data needs Lidar inadequate.