Thacker Pass lithium project is a world-class lithium project being developed in Humboldt County, Nevada, US.
Set to be the biggest lithium deposit in the US, Thacker Pass is being developed by Lithium Nevada, a fully-owned subsidiary of Lithium Americas (LAC). It is expected to have a mine life of 46 years.
Pre-feasibility study (PFS) of the two-phased project was completed in 2018. Lithium production from the first phase is anticipated to be started in 2022 at a rate of 30,000 tonnes per annum (tpa) for a period of 3.5 years. The second phase is expected to increase the production rate to 60,000tpa starting from 2026.
Thacker Pass project geology and mineralization
The Thacker Pass deposit is located within the extinct McDermitt Caldera supervolcano, which is associated with the Yellowstone hotspot.
The McDermitt volcanic field comprises four large rhyolitic calderas formed in the middle Miocene period. The project forms a part of McDermitt Caldera, the largest and south-eastern most caldera of the McDermitt field.
The volcanic eruption at McDermitt Caldera has resulted in the percolation of water through nearby volcanic rocks leaching lithium, following which lithium was deposited in the caldera basin as a large caldera lake and a thick sequence of associated lacustrine deposits.
Lithium-rich clays at Thacker Pass are located beneath a 5m alluvium layer, while intracaldera rhyolite tuffs are located beneath the clays. Basaltic lavas and ash layers are sporadically inserted with the lacustrine sediments.
The clay is inter-bedded with ash, with the upper clay horizons comprising smectite-type clay and the lower horizons consisting of illite-type clay with mineralization of up to 9,000 parts per million (ppm).
Lithium reserves at Thacker Pass
The Thacker Pass project is estimated to contain 179 metric tonnes (Mt) of proven and probable reserves of lithium ore grading 3,283ppm Li. It is estimated to contain 3.1Mt of lithium carbonate-equivalent (LCE).
Mining at Thacker Pass project
Conventional, continuous open-pit mining method using excavators and surface miners will be applied at the Thacker Pass project.
Ore will be mined by a surface miner, which will simultaneously load it into haul trucks. The ore will be hauled to an overland ore conveyor located near the pit limit, which will transport the material to the processing plant.
Ore processing at Thacker Pass
The processing plant is proposed to be developed in two phases, with the first phase treating an average of 2.2Mt of ore per annum during the first four years of production. Additional equipment and infrastructure will be installed as part of the second phase to increase the annual production to 60,000tpa.
The ore will be crushed, screened, and forwarded to the leaching circuit and treated with sulfuric acid to segregate lithium. The lithium-bearing solution from the leached unit will then be filtered and forwarded to neutralization process.
Neutralization will be achieved with ground limestone during start-ups and sustained with recycled alkaline solids from an upstream precipitation process during normal operation.
The lithium brine will be passed through evaporation and crystallization processes using steam and electricity from the sulfuric acid production process in order to remove magnesium sulfate and extract water.
Quicklime will be added to the lithium brine to increase the pH value and precipitate magnesium hydroxide and calcium sulfate crystals.
The resultant product will be precipitated in a lithium carbonate precipitation circuit, wherein the lithium will be reacted with saturated soda ash solution to produce lithium carbonate solids. The solids will be filtered, washed, dried, and packaged for sale.
Infrastructure facilities at the Thacker Pass project
The Thacker Pass lithium project area can be accessed from the State Route (SR) 293, approximately 30km from the Highway 95 junction.
Raw water supply to the plant will be sourced from a well or series of wells in the Quinn River Valley. Electrical submersible well pumps will be installed in the groundwater wells to bring water to a surface pump station, and pumped to the plant site using two booster pump stations and an approximately 12km-long pipeline.
Power will be sourced from a local cogeneration plant and from the existing 115kV transmission line owned by Harney Electric and running along the site.
The project will also feature a 60,000tpa ore stockpile pad and a limestone stockpile with a design capacity of 10,000t.
Advisian Americas, a part of WorleyParsons, prepared the technical report for the Thacker Pass lithium project, while Great Basin Environmental Services conducted the environmental and social studies.
Mining Plus provided the capital cost estimates with regards to mining as part of the PFS, while Chemetics, a Jacobs Engineering company, prepared the estimates for the sulfuric acid plant.