ENERGY-CRITICAL ELEMENTS
"Energy-critical elements" are resources necessary for green energy technologies that also have a high risk to domestic supply. A major component of Tom's research is to ascertain magmatic controls on enrichment of energy-critical elements in volcanic systems. As Lead Global Exploration Geologist at Lithium Americas Corporation, Tom is currently focusing his efforts on lithium resources hosted in old supervolcanoes like the large Thacker Pass sedimentary deposit in the McDermitt Caldera, Nevada. He is also working with scientists at the USGS, ETH Zurich, University of Nevada-Reno, and University of Ottowa to better understand the origins of all types of lithium resources.
Source: DOE Critical Minerals Strategy (2011)
MELT INCLUSIONS: INSIGHTS INTO MAGMA COMPOSITIONS
CL image of homogenized melt inclusions within a quartz grain.
As volcanic rocks erupt on the surface of the earth, many volatile elements are lost to the atmosphere as the lava or ignimbrite degasses. As a result, measured whole rock values for these elements (including energy-critical element Li) represent minimum magmatic concentrations. Post-eruptive weathering and alteration (common in volcanic settings) also alter the chemistry of rocks, making whole rock concentrations of trace elements even less reliable indices of magmatic compositions. Blebs of magma trapped as phenocrysts grow within magma chambers, commonly known as melt inclusions, offer opportunities to evaluate pre-eruptive magmatic compositions.
SHRIMP-RG analysis of quartz-hosted melt inclusions
Tom used the SHRIMP-RG at Stanford University to analyze over 500 homogenized quartz-hosted melt inclusions from lavas and ignimbrites within the McDermitt Volcanic Field and other alkali rhyolites around the world for their concentrations of 42 trace elements, including energy-critical elements Li, Ga, and REE. Tom has also analyzed many of these inclusions for volatile species H2O, S, Cl, and F using the Cs+ ion source. Results show that peralkaline rhyolitic magmas which did not fractionate chevkinite have the highest concentrations of Ga and REE, and are likely sources for Ga and REE enrichment in hydrothermal systems at the McDermitt Caldera. Li concentrations are highest (over 3000 ppm) in metaluminous magmas that incorporated relatively larger proportions of felsic crust.
SUPERVOLCANOES: POWERING THE NEXT CENTURY?
Demand for lithium is expected to drastically increase over the next half century as society becomes increasingly reliant on lithium-ion batteries to power smartphones and electric vehicles. The current market for Li is dominated by Australia and Chile, highlighting the strategic importance for most countries to secure additional Li resources. Tom's research on Li enrichment in intracontinental rhyolite magmas has shown that when these magmas erupt and form large calderas ("supervolcanoes"), they have the potential to host large Li deposits within caldera lake sediments. Meteoric and hydrothermal waters leach Li from intra- and extracaldera Li-enriched volcanic rocks, which is then deposited in the caldera basin. Additional Li is supplied to the caldera along the ring fracture system from the underlying degassing magma chamber. Li is incorporated in the structure of clays like illite within the caldera lake sediments, which then can be mined and processed for use in batteries. The largest Li resource in the United States, the ~6 Mt LCE (M&I) Thacker Pass deposit, occurs within caldera lake sediments of the McDermitt Caldera in northern Nevada. This work is published in Nature Communications.