PETROGENESIS AND CLASSIFICATION OF PEGMATITES IN THE CAROLINA TIN-SPODUMENE BELT, USA

Lithium is an essential element for a reduced carbon future, and Li-rich pegmatites are an important source of lithium. The Carolina Tin-Spodumene Belt (CTSB), stretching over 60 km from near Gaffney, South Carolina, to Lincolnton, North Carolina, was originally mined for tin in cassiterite (SnO₂), but lithium in spodumene (LiAlSi₂O₆) proved much more economically important. Lithium mining in the CTSB occurred at the Kings Mountain Mine and the Hallman-Beam Mine from the 1950s to 1990s, and the recent increase in lithium demand has generated new exploration across the region. The CTSB consists of spodumene-bearing and spodumene-free granitic pegmatites of Mississippian age trending along foliation of the host amphibolite. The CTSB is coincident with the Kings Mountain Shear Zone, a northeast-southwest trending, 0.5-3 km-wide structure forming the boundary between the Inner Piedmont Terrane and the Carolina Terrane. Major-phase mineralogy is similar for spodumene-bearing and spodumene-free pegmatites and consists of K-feldspar, albite, quartz, and muscovite. The main differences are the occurrence of oligoclase instead of albite in some spodumene-free pegmatites and minor or absent muscovite in spodumene-bearing pegmatites. Accessory minerals include beryl, garnet, titanite, cassiterite, zircon, Mn-bearing fluorapatite, triphylite, columbite-group minerals, and newly documented corundum. Spatial proximity, geochronology, and O and Sr isotopic compositions suggest a similar petrogenesis of crustal anatexis for the two-mica, peraluminous Cherryville granite and CTSB pegmatites, and it is unclear if the pegmatites formed via fractional crystallization of the granite. Understanding the petrogenesis of these spodumene-bearing pegmatites is essential for lithium resource exploration. We present new petrography and whole-rock and mineral geochemistry of samples collected in the northern part of the CTSB in Gaston County, North Carolina, to understand the petrogenesis of spodumene-bearing pegmatites and assess the utility of a new pegmatite classification scheme. Our results, including the previously undocumented presence of corundum and the low-REE nature of these pegmatites, agree with an anatectic pegmatite origin and highlight the complexity of belt-wide pegmatite fields.