CLIMATE VS. HYDROTHERMAL CONTROLS ON LITHIUM ENRICHMENT IN LACUSTRINE CLAYS: A CASE STUDY FROM CLAYTON VALLEY, NEVADA

Access to lithium resources is critical for building and sustaining a green energy infrastructure. Li-rich clay deposits are soon to be mined directly, and the existence of these clay deposits in terminal basins contributes to the genesis of Li brine deposits, such as in Clayton Valley, NV (CV). Thus, understanding the process by which Li clay deposits form may assist future exploration efforts in securing this resource. Here we use carbonate and clay oxygen stable isotopes along with bulk Li concentrations from lacustrine sediments to investigate the potential processes responsible for clay Li enrichment. Our previous work revealed a positive correlation between bulk lithium concentrations, ranging from 20 to 2000 ppm, and carbonate ẟ¹⁸O ranging from 16 to 35‰ (VSMOW), suggesting that Li was incorporated during authigenic clay precipitation in equilibrium with evaporatively enriched lake water. This finding suggests that the long-term basin water balance has a large role in concentrating Li in clays as opposed to post depositional hydrothermal alteration in the subsurface. In this work, we further investigate this hypothesis by measuring the clay fraction ẟ¹⁸O and Δ¹⁷O. We combine the clay and carbonate measurements to infer formation temperature and test the assumption that carbonate and clay fractions formed from the same lake water at near surface temperatures. Our results show samples with bulk lithium concentrations <1000 ppm likely formed in equilibrium with the lake water as previously suspected. The clay ẟ¹⁸O, ranging from 17 to 30 ‰, on these <1000 ppm Li samples is also positively correlated with bulk lithium measurements and carbonate ẟ¹⁸O. Samples with lithium concentrations >1000 ppm may not have formed in equilibrium with the lake water. The samples with higher lithium concentrations could have been further enriched with Li after deposition from hydrothermal fluids circulating in the subsurface. Our work suggests that while climate may play a role in concentrating Li into authigenic clays, the incorporation of hydrothermal fluids may be necessary to achieve bulk concentrations of Li >1000ppm in CV. Future clay mineralogy analyses, and the application of carbonate clumped isotope and clay ẟ¹⁸O-ẟD thermometry, will clarify the role of climatic versus hydrothermal processes in this system.