The Thacker Pass Project is located within an extinct 24x18 mile (40x30km) supervolcano named McDermitt Caldera, which was formed approximately 16.3 million years ago (Ma) as part of a hotspot currently underneath the Yellowstone Plateau. Following an initial eruption and concurrent collapse of the McDermitt Caldera, a large lake formed in the caldera basin. This lake water was extremely enriched in lithium and resulted in the accumulation of lithium-rich clays called smectite throughout the whole caldera.

In a process called magmatic resurgence, the central and southern part of the caldera near Thacker Pass was uplifted and a portion of the smectite-bearing lake sediments was altered to a lithium-bearing illite by a lithium-rich hydrothermal fluid. The process created the exceptional lithium deposited at Thacker Pass.

For more detailed information on the deposit genesis, please refer to a recent peer-reviewed paper published in Science Advances by Thomas R. Benson, Matthew A. Coble and John. H Dilles. Click here (opens in new window) to view the August 30, 2023 publication.

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Lithium Americas is engaged in an exploration program to expand the resource in the vicinity of the proposed pit area. Ongoing geophysical surveys and exploration drilling aims to increase the confidence of mineralization east and south of the proposed pit area and define the total extent of smectite and illite lithium mineralization throughout the McDermitt Caldera south of the Montana Mountains.


The McDermitt Caldera has been explored for several minerals since the 1970s during multiple drilling campaigns by many different companies. The ~50 years of drilling confirms that lithium mineralization in smectite clays is extensive throughout the McDermitt Caldera, from the Thacker Pass project area in the south and northward into Oregon. The caldera-wide smectitic mineralization is stratiform, resulting from primary deposition of lithium-rich magnesian smectite clays in a calm lacustrine environment.

Drilling by Lithium Americas identified a second type of lithium-rich claystone, illite, in the vicinity of Thacker Pass. These lithium-rich illites formed when hydrothermal fluids associated the resurgent uplift of the Montana Mountains rose through resurgence fractures in the underlying volcanic rock and spread laterally into the caldera lake sedimentary sequence, altering a section of the smectites to illties.

The upper clay horizons are dominated by the smectite-type clay with mineralization up to 4,000 ppm, while the deeper horizons are dominated by illite-type clay, with mineralization of up to 9,000 ppm. They are typically overlain by alluvium with an average thickness of approximately 6.5 yards (6 meters) and underlain by hard intracaldera tuff associated with the eruption of the McDermitt Caldera. Interbedded with the lithium-bearing clay are volcanic ashes and a small volume of interbedded hard basaltic beds. Basaltic rock increases in volume towards the southeast of the project area.