Lithium and strontium isotopic systematics in playas in Nevada, USA: constraints on the origin of lithium
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Lithium-rich brine in playas is a major raw material for lithium production. Recently, lithium isotopic ratios (δ7Li) have been identified as a tool for investigating water–rock interactions. Thus, to constrain the origin of lithium in playas by the use of its isotopes, we conducted leaching experiments on various lacustrine sediment and evaporite deposit samples collected from playas in Nevada, USA. We determined lithium and strontium isotopic ratios and contents and trace element contents of the leachate, estimated the initial δ7Li values in the water flowing into the playas, and examined the origin of lithium in playas by comparison with δ7Li values of the possible sources. In samples from the playas, δ7Li values show some variation, reflecting differences both in isotopic fractionation during mineral formation and in initial δ7Li value in water flowing into each playa. However, all δ7Li values in this study are much lower than those in river water and groundwater samples from around the world, but they are close to those of volcanic rocks. Considering the temperature dependence of lithium isotopic fractionation between solid and fluid, these results indicate that the lithium concentrated in playas in Nevada was supplied mainly through high-temperature water–rock interaction associated with local hydrothermal activity and not directly by low-temperature weathering of surface materials. This study, which is the first to report lithium isotopic compositions in playas, demonstrates that δ7Li may be a useful tracer for determining the origin of lithium and evaluating its accumulation processes in playas.
KeywordsLithium isotope Playa Evaporite Lithium resources Nevada
We thank Atsushi Suzuki and Kyoko Yamaoka of National Institute of Advanced Industrial Science and Technology (AIST) and Toshihiro Yoshimura and Masakazu Fujii of The University of Tokyo for valuable discussion and helpful comments. Assistance in the laboratory was provided by Mihoko Hoshino of AIST and Junko Shimizu, Masaharu Tanimizu, Tsuyoshi Ishikawa, Kazuya Nagaishi, and Jun Matsuoka of Kochi Core Center, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We also appreciate the review by an anonymous reviewer and editorial handling by Rolf L. Romer and Bernd Lehmann. This study was supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for a JSPS fellow (11J06232) to Daisuke Araoka and for Scientific Research (22224009, 16740309, 22109511) to Hodaka Kawahata and Yoshiro Nishio.
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