Li-rich Claystone in the McDermitt Caldera, Nevada: Characteristics and Possible Origin

The Lithium Nevada Corp. Thacker Pass Project has a measured resource of 242M tonnes at 0.29% Li (~0.7M tonnes Li). The deposit is the southernmost of five known lenses hosted within intracaldera tuffaceous sediments along the west side of the McDermitt caldera, which formed by eruption of 16.4 Ma peralkaline-metaluminous tuff. Analyses of 9880 core samples (~1.5-m thick) give a mean of ~ 2500 ppm Li, with some >8800 ppm. Entire sedimentary sections in the southern and western parts of the caldera basin have high Li (1500+ ppm). Pre-caldera rocks, the McDermitt Tuff, late caldera volcanics, and unaltered tuffaceous sediments have relatively low Li (5 -140 ppm). Sediment deposition was mainly subaqueous in the closed caldera basin. Li-rich fill may have been deposited from airborne sources. Claystone comprises most of the Thacker Pass deposit and dominates Li-rich intervals. The rest is mostly feldspar-rich ash. X-ray diffraction (XRD) data from six core holes across the deposit show consistent lateral min...