CHARACTERIZING LITHIUM BEARING CLAYS IN THE WESTERN US USING DETAILED SAMPLING, GEOCHEMICAL ANALYSIS, AND MACHINE LEARNING STATISTICAL ANALYSIS

The lithium used in battery technology is currently sourced primarily from high-altitude saline brines and spodumene-bearing pegmatites. In the coming years, lithium-bearing lacustrine deposits are expected to become an increasingly important source of lithium, with several lacustrine lithium deposits under development throughout the Basin and Range. Chief among these is the Lithium Americas Thacker Pass Project hosted in caldera lake sediments of the ~16.3 Ma McDermitt Caldera, Nevada. Because this type of deposit is critical to obtaining a secure domestic supply of lithium in the United States, we initiated a study to ascertain the occurrences and formation of sedimentary lithium deposits and their key characteristics. Over the past three years, we traveled to >500 sedimentary basins in 14 states across the western U.S., carrying out observational field work, detailed sampling, and geochemical analyses from stratigraphic sections in the various basins. We also performed automated statistical and machine learning analysis for interpretation of the variation in the data. Through this work we created a database of over 1600 samples from sedimentary basins in the western US. In combination with machine learning analysis, this data allows us to characterize the features of each basin (i.e., chemistry, grain size, sedimentary history) and correlate those features to the amount of lithium trapped in the sediment. While sediments of the McDermitt Caldera contain anomalously high amounts of lithium, few other sedimentary basins in the U.S. contain economic levels of lithium (>1000 ppm). Basins that do contain >1000 ppm lithium are predominantly characterized by Miocene-aged small lake deposits formed in closed systems containing a high proportion of fine-grained clay material. Sedimentary samples from the various basins were primarily defined by high variation in Ca and Mg, while Li was most highly correlated with the behavior of Mg, K, V and Al. The physical property that most strongly correlates with Li concentration is grain size, with coarser material holding considerably less Li across the various systems. We interpret these preliminary analyses and observations to be indicative of high volcanic and/or hydrothermal input into the lacustrine systems that contain economic concentrations of Li.