STABLE ISOTOPES FOR TRACKING ORE FORMATION AT THE THACKER PASS SEDIMENT-HOSTED LITHIUM DEPOSIT, NEVADA, USA

Global demand for lithium (Li) has increased dramatically in recent years as automotive manufacturers continue to plan and produce new models of battery electric vehicles, and the combined scarcity and importance of this element to existing and emerging technologies has resulted in its prominence as a resource critical to national security. The Thacker Pass deposit in northern Nevada is a sediment-hosted Li deposit where the Li occurs within the octahedral sheet of Mg-rich clay minerals. Two types of Li-rich clays are known from Thacker Pass: a smectite-type clay similar to hectorite (Na_0.3(Mg,Li)₃(Si₄O₁₀)(OH,F)₂) and an illite-type clay analogous to tainiolite (KLiMg₂(Si₄O₁₀)F₂). A zone of mixed-layer illite-smectite occurs between the smectite and illite zones. The Li and F content of the illite is higher than that of smectite within the deposit suggesting that the conversion of smectite to illite in the presence of Li- and F-rich fluids resulted in an upgrade of the resource. This study will use O, C, and D/H isotope geochemistry to better understand how fluid input and paleoenvironmental controls contributed to Li enrichment in the clays at Thacker Pass. Initial carbonate δ¹⁸O data suggest bimodal O isotope signatures for carbonate from the smectite and mixed zones with data clustering at c. -5‰ and -16‰ for the smectite zone carbonates and -6‰ and -20‰ for the mixed zone carbonates whereas the illite carbonate data cluster at -21‰ δ¹⁸O VPDB. The available data are consistent with multiple O sources for carbonate minerals, although data from the clays will reveal if the O source (and thus, fluid source) is also responsible for changes in lithium grades within the deposit. The results of this work will yield insight into what the important factors are in producing high Li grades sediment-hosted deposits and may help refine exploration parameters for discovering new world-class Li deposits to meet rising demand.