T257 The Geology and Environmental Impacts of Lithium Resources in North America and other Globally Significant Deposits II

Wednesday, 12 October 2022
1:30 PM - 5:30 PM
603

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

Paper number: T257-7
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

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.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-381197

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