The Thacker Pass Project is located within an extinct 40x30 km 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. Late volcanic activity uplifted the caldera, draining the lake and bringing the lithium-rich moat sediments to the surface resulting in the near-surface lithium deposit which is the subject of the Project.

Lithium enrichment (>1,000 ppm Li) in the Thacker Pass Deposit and deposits of the Montana Mountains occur throughout the caldera lake sedimentary sequence above the intra-caldera Tuff of Long Ridge. The deeper illite-rich portion of the sedimentary sequence contains higher lithium than the shallower, smectite-rich portion. The uplift of the Montana Mountains during both caldera resurgence and Basin and Range faulting led to increased rates of weathering and erosion of a large volume of caldera lake sediments. As a result, much of the sediments in the Montana Mountains have eroded away.

South of the Montana Mountains in the Thacker Pass Deposit, caldera lake sediments dip slightly away from the center of resurgence. Because of the lower elevations in Thacker Pass, a smaller volume of the original caldera ........

The shallow and massive nature of the deposit makes it amenable to open-pit mining methods. The mining method assumes hydraulic excavators loading a fleet of end dump trucks. This truck/excavator fleet will develop several offset benches to maintain geotechnically stable highwall slopes. These benches will also enable the mine to have multiple grades of ore exposed at any given time, allowing flexibility to deliver and blend ore as needed.

The annual production rate for the 40-year mine is based on varying plant feed leach ore rates caused by the availability of sulfuric acid for the leaching process. Phase I (years 1-3) has an annual feed rate of 1.7 million dry tonnes of ore to leach and Phase 2 (years 4-40) has 4.0 million dry tonnes of ore to leach.

Pit Design
The geotechnical analysis indicates that the geology is generally uniform across the Project site. The competence of the in-situ material in conjunction with the use of the proposed highwall angles meets or exceeds the minimum recommended factor-of-safety values for intermediate and overall slope configurations.

A bench width of 50 m and a height of 5 m was chosen. This face height is amenable to efficient loading operations while still shallow enough to allow for the removal of thicker barren horizons within the cut to minimize dilution. Double benching and increasing the bench height to 10 m before implementing offsets, will be used to increase mining depths while maintaini ........

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