MARL GEOCHEMISTRY OF THE LOVELL WASH MEMBER OF THE HORSE SPRING FORMATION: INSIGHTS INTO A LITHIUM PROSPECTIVE BASIN

The Lovell Wash Member of the Miocene lacustrine and fluvial Horse Spring Formation, known for its lithium enrichment since first documented by the USGS in the late 1970’s, has become a prospective target for claystone-type lithium resources. The formation is dominated by shallow lake sediments that experienced different degrees of clastic input due to tectonics, climate, and volcanic events. In this study, we focus on outcrops of the Lovell Wash Member in the White Basin on land managed by the Bureau of Land Management. Here, the Lovell Wash Member alternates between evaporites, authigenic and microbial carbonates, tuffs, and clastics. We sampled seven marls in stratigraphic order for X-ray diffraction (XRD), scanning electron microscope (SEM), and handheld X-ray fluorescence (XRF) assays. Samples were also analyzed using inductively coupled plasma optical emission spectrometry (ICPOES) to determine lithium concentrations. Most samples were friable with extensively weathered surfaces with some indurated carbonate layers. XRD of all samples showed minerals that are common in evaporitic lake deposits, such as calcite, gypsum, celestine, and strontianite. XRD also confirmed volcanic input in the form of sanidine, consistent with the abundant tephra observed in the section. SEM confirmed chemistry on evaporitic minerals and identified montmorillonite. Whole-rock lithium concentrations in the Lovell Wash Member in White Basin average ~350 ppm Li (ICPOES), with the highest concentrations of Li (up to 1,200 ppm) and other trace metals (Fe, Ti, Zr) in the darker claystone layers in middle of this section around 75 to 120 meters. While the whole-rock concentrations of these Li-rich layers are considerably higher than average sedimentary rock (> 50 ppm), they are lower than most known claystone-type resources in the Basin and Range province (e.g., Thacker Pass, Clayton Valley).