LITHIUM CONCENTRATIONS IN CENOZOIC RHYOLITE VITROPHYRES AND QUARTZ-HOSTED MELT INCLUSIONS: IMPLICATIONS FOR LITHIUM DEPOSITS IN THE NORTHERN GREAT BASIN (U.S.A.)

Economically significant lithium (Li) deposits are focused on exploration models where Li, in brines and clays, is derived from felsic volcanic rocks. Thus, constraints on the concentrations of Li in rhyolite lavas and ash-flow tuffs sources is critical to refining these models. We analyzed vitrophyre glass from nine rhyolite lavas (~16.1 to 13 Ma Jarbidge Rhyolite, ~16.5 to 16.1 Ma lavas in the Santa Rosa-Calico volcanic field, NV, and an ~14 Ma lava from the Owyhee-Humboldt eruptive center, NV) and three ash-flow tuffs (~16.4 to ~15.5 Ma ash flows in the Santa Rosa-Calico volcanic field, NV and the ca. ~41 Ma Tuff of Coal Mine Canyon sourced from near Tuscarora, NV), as well as non-homogenized melt inclusions (MI) inside quartz via LA-ICP-MS, to document rhyolite source rock Li concentrations in the northern Great Basin (U.S.A). Vitrophyre Li concentrations for all samples range from 2.8 ppm - 282 ppm, averaging 42.6 ppm, while melt inclusions range from 1.8 ppm - 793 ppm, averaging 43.4 ppm. This overall range overlaps with, but is generally less than Li-in melt inclusion data reported by Benson et al. (2017) from rhyolites in the nearby McDermitt volcanic field associated with the Thacker Pass Li deposit (e.g., 50 ppm to 8548 ppm). Our data are generally higher than Li reported in <12 Ma Snake River Plain-Yellowstone rhyolite glasses (Ellis et al. 2021). In 6 of our 9 samples with MI, Li concentrations are lower relative to their vitrophyre equivalent. In 3 samples, two distinct groups of MI are present and may reflect different times of entrapment as the host melt evolved. The larger Li range in MI vs. vitrophyre and multiple groups of MI in samples, make MI unreliable in determining maximum Li concentrations upon emplacement. Following Ellis et al. (2021), we used the highest measured Li (in vitrophyre) to determine the Li lost post-eruption to estimate the original concentrations of Li upon emplacement in the host rhyolites. Via this method, our ranges for maximum Li are 34.7 - 282 ppm, averaging 88.4 ppm for the vitrophyre glass. Based on these corrected values, we suggest that the volcanic units we studied are not Li-rich enough to be associated with deposits like Thacker Pass. However, the cumulative volumes of these rocks and proximity to coeval extensional basinal strata, suggests they could be associated with smaller deposits.