V014-0003
Lithium Budget and Isotopic Fractionation of Pre- and Post-Eruptive Rhyolites at Clayton Valley, Nevada: Melt Inclusion, Pumice Glass, and Mineral Insights on Economic Lithium Enrichment

Wednesday, 9 December 2020
Poster
Celestine Nicole Mercer1, Regina M Khoury1, Brian Monteleone2, Albert H Hofstra1 and Lisa L Stillings3, (1)U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center, Denver, CO, United States, (2)Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (3)U.S. Geological Survey, Geology, Minerals, Energy, and Geophysics Science Center, Reno, NV, United States
Abstract:
Lithium is a high-demand, energy-critical element used in lightweight rechargeable lithium-ion batteries [1, 2] that is primarily produced from pegmatites and brines in arid, closed lacustrine basins [3]. Clayton Valley, NV, is the only current U.S. producer of Li from subsurface brines and hosts Li-bearing clays that could be a potential new resource. Locally-exposed rhyolite tuffs have been proposed as a Li source for this brine and clay deposit [4, 5].

We investigate quartz-hosted melt inclusions, pumice glass, and phenocrysts from Miocene rhyolite tuff outcrops surrounding Clayton Valley. Our goal is to evaluate the petrogenesis and degassing processes of these rhyolites by comparing volatile- and Li-charged, pre-eruptive magmas with degassed, Li-poor post-eruptive magmas.

Preliminary results show that melt inclusion shrinkage bubbles contain extremely low CO2 contents that are not resolvable by Raman. FTIR analyses reveal that melt inclusions contain ~1-7 wt% H2O and ~300 ppm CO2 corresponding to vapor saturation pressures of ~330 MPa (~9.2 km depth). Melt inclusions and pumice glass are trachydacite to ferroan rhyolite with ASI ~1.0-1.3, Cl ~500-1500 ppm and F ~1000-2400 ppm. Feldspars range in composition from oligoclase to labradorite to sanidine, and biotites range from ~0.45-0.7 XMg. Halogen intercept values of biotite (IV(F/Cl) ~5.0-6.3) suggest an affinity to magmas parental to Sn-W-Be-mineralized systems rather than more highly evolved Mo-mineralized systems that are also associated with Li enrichments [4]. Magnetite-ilmenite pairs indicate equilibration at ~710-780 °C and fO2 ~ΔNNO+1.5 to +3.0.

Li isotopic analyses are currently underway using the Cameca IMS 1280 high-mass resolution, high-transmission SIMS instrument housed at the Woods Hole Oceanographic Institution. Planned LIBS-MC-ICPMS mapping and LA-ICP-MS analyses will shed light on Li abundances, isotopic fractionation, mineral-melt partitioning, and diffusion profiles to elucidate the source, concentration, and release mechanisms of Li in explosive rhyolitic eruptions leading to economic Li enrichments.

[1] Amer. Phys. Soc. (2011) 24. [2] Goonan (2012) USGS Circ. 1371,14. [3] Kesler et al. (2012) Ore Geol. Rev., 55-69. [4] Hofstra et al. (2013) Soc. Econ. Geol. 108, 1691-1701. [5] Price et al. (2000) Geo. Soc. NV, 241-248.

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