Tracing lithium enrichment in the McDermitt caldera system by melt/fluid inclusions and in situ oxygen isotopes

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

This project aims to study how lithium concentrates during supergiant volcanic eruptions, eventually forming lithium ore deposits. Lithium is a critical element that is essential to support the rapid development of rechargeable batteries used by electric vehicles and to mitigate the impacts of climate change. Understanding the mechanisms of lithium transfer in the Earth’s crust is therefore of great importance to address the global demand for lithium. This research project will study the McDermitt volcanic caldera (Nevada/Oregon) which hosts one of the most important lithium deposits in the United States. By studying microscopic inclusions of solidified silicate melts trapped in volcanic rocks (“melt inclusions”), Drs. Harlaux and Ruprecht will determine the chemical composition of the magmas that generated a catastrophic eruption at McDermitt about 16 million years ago. This research work will help to better understand how magmas become enriched in lithium and can produce high-temperature lithium-rich vapors during magma outgassing, eventually forming lithium deposits after collapse of the caldera floor. A doctoral student at the University of Nevada, Reno, will conduct the research project with students from underrepresented demographic groups in STEM specifically encouraged to apply. Results will also be shared through public outreach activities with a broader audience. This project will benefit directly to Nevada’s economy and to society in general for investigating the mineralization potential for lithium in other volcanic calderas in the western United States. The geochemical cycle of lithium (Li) in the Earth’s crust yielding the formation of Li-bearing clay deposits hosted in volcanic calderas is at the center of this project. Enrichment of Li in caldera-forming systems is thought to result from either magma fractionation followed by degassing of Li-rich magmatic fluids possibly mixing with meteoric groundwaters, or remobilization of Li during post-magmatic leaching of volcanic glasses by meteoric fluids without hydrothermal contribution. Considering that most volcanic calderas are not mineralized with Li, the question arises whether leaching of volcanic rocks by meteoric water alone is sufficient, or Li-rich hydrothermal fluids are required to provide sufficient Li for the subsequent formation of intracaldera Li clay deposits. This research project will focus on the McDermitt volcanic caldera (Nevada/Oregon) that produced voluminous evolved peralkaline and peraluminous magmas and Li-bearing clays that formed after the caldera collapse. By studying melt and fluid inclusions hosted in igneous phenocrysts from diverse Miocene volcanic rocks (ca. 16.7-16.0 Ma) exposed in the McDermitt caldera, Drs. Harlaux and Ruprecht will determine how Li is progressively enriched in the silicate magmas and partitioned into the magmatic volatile phase during magma outgassing and cooling of the magmatic system. The in-situ chemical and isotopic composition of melt inclusions and the host quartz phenocrysts will be analyzed by EPMA and LA-ICP-MS for major and trace elements, respectively, and SIMS for oxygen isotopes. This analytical work will allow to investigate Li enrichment during the long-lived (ca. 1 Ma) lifetime of the McDermitt magmatic system and the remobilization of Li by hydrothermal fluids released through the caldera floor and along its margins during magma degassing immediately after collapse. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.