Alabama pegmatite zone

Region East, Southeast
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area McAllister deposit, a tin-tantalum pegmatite deposit located in Coosa County, Alabama; hosted in graphitic schist. Nearest similar deposit is Kings Mountain, North Carolina.
Identified resources Identified resources with historical production of tin and a minor amount of historical production of tantalum.
Production An unknown quantity of Ta was produced between 1989 and 1992 (White and Dean, 1991, 1992, 1993, 1994). Past Sn exploration and prospecting with minor production between 1880 and 1945 (for example, Hunter, 1944; Rheams, 1984). Historical production numbers are incomplete, but it is estimated that about 10 short tons of concentrate containing almost 6 short tons of Sn were produced from the Alabama pegmatite zone (Reed, 1950, p. 5). Coosa cassiterite produced 5 metric tons of cassiterite concentrate in 1942.
Status Past mining.
Estimated resources Historical estimates indicate that the Alabama pegmatite zone contains Indicated reserves of around 103,000 metric tons of ore containing an average grade of 0.12% Sn (Cook and others, 1987, p. 212). McAllister mine: Proven reserves at the 91 metric tons of ore at 0.08% SnO2 and 90 tons at 0.07% Ta2O5 (Foord and Cook, 1989).
Geologic maps Hicks (1981), scale 1:12,000; Osborne and others (1989), scale 1:500,000; Neathery (1977), scale 1:126,720; Allison (2020), scale 1:24,000; Allison and Durden (2002), scale 1:24,000; Allison and Hay (2006), scale 1:24,000.
Geophysical data Inadequate Rank 4 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures Two-mica, peraluminous, ilmenite-series tin- and tantalum-bearing granite (for example, the Rockford Granite) that is relatively leucocratic, medium grained, infoliated, and potassic, with greisen-like pipes that intrude into Neoproterozoic to Lower Paleozoic Hatchet Creek and Wedowee Groups (Cook and others, 1987; Dean and Cook, 1987; Drummond, 1987a, b; Drummond and Allison, 1987); weathered bedrock makes mining open-pit mining suitable.
Deposits McAllister Sn-Ta deposit (USMIN Site_ID: AL00008); No. 1 mine (MRDS dep_id: 10097451), No. 2 mine (MRDS dep_id: 10079476), Alabama tin belt (see Hunter, 1944).
Evidence from mineral occurrences MRDS; USMIN; Geological Survey of Alabama's FY19 NGGDPP-Priority 3 critical minerals database.
Geochemical evidence Data suggests ~ 65.5 ppm Li in parts of the pluton. Muscovite has up to 0.13% Li2O, greisen in the range 300 ppm Li. Analyses of spodumene-rich 1.5 m drill-core intervals indicate maximum content of > 1% Li. Reported heavy mineral concentrates from the focus area indicate: 2,532 to 650,000 ppm Ta, 7,870 to 70,000 ppm Nb, >70,000 ppm Sn, 15 and 500 ppm Be, 10 to 84 ppm Cr, 17 to 5,000 ppm Mn, and up to 356 ppm W (for example, Dean and Cook, 1987, p. 205). See Cook and others (1987) for Ta and Sn data and Dean and Cook (1987) for Sn and Au data.
Geophysical evidence Inadequate aeromagnetic/radiometric data (aeromagnetic data rank 4; radiometric rank 5).
Evidence from other sources Unknown.
Comments Past producers in areas that might be mined again (for example, Burgert, 1998). Geophysical data are likely to be helpful in determining the extent of source rocks. Detailed surficial and bedrock geologic mapping needed and geochemical analyses likely to be very helpful.
Cover thickness and description Exposed bedrock to thin cover.
Authors Arthur J. Merschat, Nora K. Foley, Bernard E. Hubbard, Dane S. VanDervoort, John P. Whitmore.
New data needs Geophysical data, geologic mapping, and geochemical analyses.
Geologic mapping and modeling needs Geologic mapping to determine the extent and distribution of cassiterite- and tin-bearing pegmatitic quartz veins and geochemical analyses to assess the resource quality/grade.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage. Aeromagnetic data expected to image mafic rocks and associated structures, radiometric data can help with geologic mapping in vegetated terrane; alteration may be imaged. Electromagnetic methods may help image sulfides.
Digital elevation data needs Lidar complete.