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.
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