Trace Element Geochemistry of Li-Rich Pegmatites in the Carolina Tin-Spodumene Belt, North Carolina, USA: Implications for Petrogenesis and Exploration
Adam Curry, Michael A. Wise, Russell S. Harmon
Abstract
Abstract The Carolina tin-spodumene belt, North Carolina, hosts one of the largest economic deposits of Li pegmatite ore in the United States, yet the petrogenesis of Carolina tin-spodumene belt pegmatites remains poorly understood. We use whole-rock and mineral trace element geochemistry to (1) evaluate the petrogenesis of Carolina tin-spodumene belt pegmatites, (2) compare their geochemistry to other Li-rich pegmatites worldwide, and (3) propose mineral chemistry indices for Li mineralization. Trace element modeling demonstrates that spodumene-bearing pegmatites are not related to the nearby Cherryville Granite through fractional crystallization, and rare earth element contents in plagioclase, garnet, and apatite indicate that spodumene-bearing pegmatites are also not derived from spodumene-free pegmatites. We prefer a petrogenesis in which both types of pegmatites and the Cherryville Granite are derived through similar, but individual, crustal anatectic events. Muscovite and K-feldspar K/Rb-Li systematics indicate that Carolina tin-spodumene belt pegmatites do not attain fractionation levels as high as those reached in the Oxford County pegmatite field in Maine or the Custer and Keystone pegmatite fields in South Dakota. Quartz and garnet Li abundances in Carolina tin-spodumene belt pegmatites are some of the highest in the world, and garnet rare earth element concentrations are the lowest. Contents of Ga, Mn, Ge, and Ti in spodumene allow for discrimination of pegmatites from the Carolina tin-spodumene belt, Maine, South Dakota, Canada, and Portugal. Based on this extensive trace element study, plagioclase, K-feldspar, quartz, muscovite, garnet, and apatite chemistry offer a comprehensive methodology to distinguish pegmatites with and without spodumene in the Carolina tin-spodumene belt, which may be useful in exploration for Li pegmatite ore worldwide.