INVESTIGATING LITHIUM ENRICHMENT MECHANISMS WITHIN THE BARSTOW FORMATION USING STABLE ISOTOPES OF LACUSTRINE CARBONATES, CLAYS, AND CHERTS

Lithium is a critical mineral resource necessary to the U.S. economy and national security. Domestic Li-clay resources in the western United States such as the Thacker Pass, Clayton Valley (CV), and Barstow deposits are crucial for fulfilling rising demand as the United States infrastructure transitions to greener technologies.

Formation mechanisms responsible for Li enrichment in Li-clay deposits vary between deposits. While high-grade deposits found at the McDermitt Caldera involve high-temperature >200℃) hydrothermal alteration of primary smectite-bearing sediments to illite (Benson et al., in press, Science Advances), evidence from CV suggests that Li enrichment occurred primarily from low temperature near-surface processes (Gagnon et al., 2023, GSA Bulletin). Here, we present on the occurrence, distribution, and potential enrichment mechanisms for the recently discovered Li-rich claystones within the Miocene Barstow Formation (BF), Mojave Desert, CA (Benson, 2023, Mojave Desert Symposium Proceedings). We analyzed the oxygen isotopic compositions of calcareous sediments, clay minerals, and chert collected from the Mud Hills to the Calico Mountains. We also present preliminary XRD results on clay separates spanning different facies and Li concentrations.

Our preliminary results show some covariation between the Li concentration of bulk sediments (24-2500 ppm) and the oxygen isotopic composition (δ¹⁸O; 17‰-35‰ VSMOW) of the carbonates, with clay rich members of the BF showing more correlation than others. This covariance also exists for δ¹³C and δ¹⁸O in the lacustrine units, suggesting the Barstow basin was a closed-basin lake environment. Temperatures calculated from samples with paired carbonate and chert δ¹⁸O measurements in the lower BF reveal diagenetic chert formation temperatures of 45-55 ℃ and carbonate clumped isotope (Δ₄₇) measurements from the upper Calico Member suggest carbonate formation temperatures between 30-40 ℃. Similar to CV, we argue that initial Li enrichment occurred within clays near the time of authigenic clay deposition in a warm Miocene lake environment. Ongoing clay δ¹⁸O and δD analyses will provide further evidence for enrichment mechanisms by elucidating thermal and source water conditions at the time of clay mineralization.