Abstract
The Kings Mountain lithium mine operated from 1951 to 1991 and was recently acquired by Albemarle, a leading global lithium producer, who plans to re-open and expand the operation. The Kings Mountain deposit is a lithium-bearing pegmatite intrusion that penetrated along the Kings Mountain shear zone located within the tin-spodumene belt that sits at the boundary between the Carolina and Inner Piedmont Terranes in Appalachia. Principal rock units include intrusive pegmatites, amphibole gneiss, mica schist, and shear schist. Low sulfide levels, mostly pyrrhotite, occur mostly in the mica schist.
While the mine was inactive, a 22 hectare lake formed within the pit and water levels continue to gradually rise. Water quality in the pit is thought to be an ideal analogue of the future pit as geology remains similar with increasing depth in the deposit. The surface of the pit lake is neutral to alkaline pH and contains moderate levels of dissolved solids dominated by calcium and sulfate. Metal levels are generally low at surface. The deeper portions of the lake, though also neutral pH, contain abundant sulfide ion and elevated iron and manganese owing to strongly reducing conditions. The lake is meromictic meaning that it seldom turns over and oxygen is absent from the lower layers due to organic matter decomposition. The redox level is low enough (about -150 mv) to stimulate sulfate reduction, but no biogenesis of methane is evident.
A 2-layer model water balance, mass load and equilibrium geochemical model was developed to simulate the evolution of the historic lake. The calibrated model was then used to assess likely future water quality for the expanded lithium mine.