Open-pit lithium mine
The Thacker Pass lithium project is an open-pit mine proposed to be developed in Humboldt County, Nevada, US, by Lithium Americas, a Canada-based lithium development company. It is claimed to be the largest known lithium resource in the US.
A pre-feasibility study (PFS) for the project was completed in August 2018. It confirmed a two-phase development with a mine life of 46 years. The production capacity in the first phase was estimated at up to 30,000 tonnes per annum (tpa) of battery-grade lithium carbonate, which was proposed to be increased to 60,000tpa in the second phase.
A feasibility study to expand phase one lithium carbonate production capacity to 40,000tpa is currently underway. It will also consider a potential expansion to target a total production capacity of 80,000tpa in the second phase.
The final environmental impact statement (EIS) for the lithium project was filed in December 2020 while a record of decision (ROD) from the US Bureau of Land Management was received in January 2021.
The project is estimated to involve a capital investment of $1.06bn. The early construction works are expected to commence in the first half of 2022.
The Thacker Pass lithium project is located approximately 100km north-northwest of Winnemucca and about 33km west-northwest of Orovada, Nevada.
Spanning 3,367ha, the mine is located within the extinct, 30km x 45km McDermitt Caldera supervolcano. The volcanic eruption resulted in water percolating through nearby volcanic rocks leaching lithium in the process.
A large lithium-bearing caldera lake and a series of associated lacustrine deposits were formed as a result of the eruption.
Alluvium with an average thickness of approximately 5m caps the lithium-rich clays within the deposit. The underlying sedimentation is an intra-caldera rhyolite tuff, while basaltic lavas and ash layers are intercalated with the lacustrine sediments at irregular intervals.
The mineralisation at the upper clay horizons is majorly composed of smectite-type clay while illite-type clay dominates the deeper horizons.
The Thacker Pass project is estimated to contain proven and probable mineral reserves of approximately 3.13 million tonnes (Mt) of lithium carbonate equivalent (LCE) grading 3,283 parts per million (ppm) of lithium, as of August 2018.
Announced in October 2021, an updated mineral resource estimate indicated a measured and indicated mineral resource of 13.7Mt of LCE at 2,231ppm of lithium.
The Thacker Pass operations will employ open-pit mining using a modified panel mining method with excavators and surface miners.
The pit design features a shallow pit with a maximum pit depth of 120m, which will be mined in blocks with 5m-long benches at a strip ratio of 1.6:1. Mining will be implemented in a sequential manner with one block mined at a time, while the previously mined area will be backfilled.
The project is planned to involve two 12-hour shifts a day for round-the-clock mining operations.
The run-of-mine (ROM) ore will be transferred to a toothed roll crusher and mixed with filter wash solution in attrition scrubbers to remove clay. The ore slurry will be transferred to the leaching circuit where stirred reactors will leach the slurry to produce a lithium brine by filtration.
The processing plant will separate lithium from the remaining salts such as magnesium, potassium, and sodium in the brine. The lithium brine will undergo crystallisation of magnesium sulphate, followed by the removal of residual magnesium by adding quicklime.
Lithium from the brine will be precipitated as a carbonate solid with the addition of soda ash. Magnesium sulphate is removed from the lithium brine by a magnesium sulphate evaporator and crystalliser.
The purified lithium brine will be transferred to a lithium carbonate precipitation circuit to produce lithium carbonate solids, which will be filtered and washed with water. The resulting purified lithium carbonate will be dried before it is packaged for shipment to customers.
The Thacker Pass lithium project is connected to State Route (SR) 293 highway via an asphalt paved access road.
The raw water supply will be from a series of wells in the Quinn River Valley using electrical submersible well pumps to pump water to a surface pump station. Two booster pump stations will pump the water to the processing facility through a 12km-long pipeline. The raw water will be also be treated to produce potable water that will be stored on site.
The power supply required for the operations is envisaged to be supplied from the Harney Electric grid using a 115kV transmission line that runs directly through the site.
The PFS was prepared by Advisian Americas, a division of Australian engineering company Worley. Advisian provided the design of the mine, processing plant, and project infrastructure.
Market expert Global Lithium was selected to conduct a market study and price projection for lithium carbonate for the project. Chemetics provided the design of the sulphuric acid plant and the associated infrastructure. Other contractors that supported the PFS include Great Basin Environmental Services and Mining-Plus.
Sawtooth Mining, a subsidiary of mining and natural resources company The North American Coal, was appointed as contract miner for the Thacker Pass project in September 2019. The company is responsible for mine engineering, construction, operation, and reclamation services as well as the supply of certain equipment.
US-based construction services firm TIC (The Industrial Company) was awarded the design and build contract. It is responsible for the overall cost estimate in the definitive feasibility study, as well as the engineering design of the plant, water supply and electrical infrastructure, and general site works.
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