COMPARISON OF MINERALOGY OF LI PEGMATITES IN THE KINGS MOUNTAIN DISTRICT, NORTH CAROLINA

This study is a continuation of earlier studies on spodumene pegmatites in the Kings Mountain District of the Carolinas. A suite of samples from the Kings Mountain Mine (KMM) collected by Dr. Gilles Allard in 1966 and additional Hailman-Beam Mine ( HBM) samples were examined and analyzed. Results were compared to the previous studies on samples from the HBM (Stander et al, 2011; and Cameron et al., 2011) . Students in the Spring 2011 Earth Materials class at UGA applied newly-learned skills in the collection of data for this study. The purpose of the study is to determine how mineralogy varies between different mines in the Kings Mountain District.

Barren and ore (spodumene-bearing) pegmatites intrude amphibolite and mica schist of the Inner Piedmont. The zone of Li pegmatites is several km wide and the eastern margin corresponds to the Piedmont shear zone, a fault contact between the Inner Piedmont and the rocks of the Kings Mountain Belt. The HBM is 1-2 km west of the shear zone while KMM exposes the shear zone in the eastern wall of the mine.

Polished thin sections were examined on a petrographic microscope and analyzed on the electron microprobe at UGA. Primary mineral assemblages in the two mines are the same: spodumene (Spd) + quartz (Qtz) + plagioclase (Pl) + K-feldspar (Kfs) + muscovite (Ms) + beryl (Brl) + fluroapatite (Ap) + triphylite (Tph). Pl is a sodic oligoclase, but extensive replacement of the primary assemblage by albite + Qtz is common in both mines. Trace element compositions of the Brl and Spd are the same in both mines. Ms shows a higher range of Fe+ Mg in HBM (0.2 to 0.4 apfu) than in the KMM (0.2 to 0.3 apfu). Overall concentrations of FeO+MgO in muscovite from the HBM are higher (1.5 to 3.9 wt. %) in HBM samples than in the KMM samples (1.1 to 2.3 wt. %). Primary grains of the Mn phosphate mineral triphylite are common in HBM ore pegmatites, but were only observed in one sample from the KMM.

Mineralogy of spodumene-bearing pegmatites at the HBM and KMM are generally similar. The absence of primary Mn phosphate minerals in the KMM samples (and the abundance of secondary Mn phosphate minerals at the KMM) and lower Mg+Fe in KMM Ms may be due to more extensive alteration at KMM (Saneger and Swanson, this meeting) related to the proximity to the Piedmont shear zone.