by An underground lithium deposit along the Nevada-Oregon border could meet growing demand for the metal, according to a new analysis.
It is estimated that 20 to 40 million tons of lithium metal lie in the volcano that was formed about 16 million years ago. This is significantly larger than the lithium deposit found under the salt flats of Bolivia, which was once considered the largest deposit in the world.
‘If you believe their back-of-the-envelope estimates, this is a very important lithium deposit,’ says Anouk Borst, a geologist at KU Leuven University and the Royal Museum of Central Africa in Tervuren, Belgium. ‘It could change the dynamics of lithium globally, in terms of price, security of supply and geopolitics.’
A new in situ analysis shows that the unusual clay rock, made of the mineral illite, contains 1.3% to 2.4% of lithium in the volcanic crater. This is almost twice the lithium present in the lithium-bearing clay mineral, magnesium smectite, which is more common than not.
Some unusual conditions have created what could be a particularly rich volcanic deposit. The crater – McDermitt caldera – was formed 16.4 million years ago when it is about 1000km.3 of magma erupted out. The caldera was filled with explosive products of alkaline magma rich in sodium and potassium, as well as lithium, chlorine and boron. This cooled rapidly to form a brilliantly polished volcanic rock, gnimbrite, which cooled to produce lithium-rich particles.
The lake then formed in the crater, progressing for hundreds of thousands of years, and the covered volcano and surrounding materials formed a clayey sediment at its bottom. The new analysis suggested that, after the lake had dried up, another source of the volcano exposed sediments in a hot, alkaline, saline environment rich in lithium and potassium.
‘Previous research assumes that the uneducated person was everywhere deep in the caldera,’ says Thomas Benson, a geologist at the Lithium Americas Corporation, and was made when high temperatures and pressures turned out to be uneducated.
Benson’s team suggested that an illite layer about 40m thick was formed in the lake sediments by this hot brine. The liquid moved up along the fissures created as the volcano resumed its activity, turning the smectite into an illite at the bottom of the crater, Thacker Pass. The result was a clay rock rich in lithium.
‘This would be the transformation of lithium-bearing smectite to illite, where hydrothermal fluids enrich the clay in potassium, lithium and fluorine,’ says Borst. ‘They seem to have hit a sweet spot where the clay is kept close to the surface, so they won’t have to remove a lot of rock, but it’s not over yet.’
The material is best described as looking ‘a bit like brown potter’s clay’, says Christopher Henry, an emeritus professor of geology at the University of Nevada, Reno. ‘It’s not very interesting, unless it has a lot of lithium in it.’
‘There is a lot more research to be done [lithium] deposits,’ Henry added. ‘The United States has one small lithium production facility in Nevada.’
Henry does not fully agree with the new proposed history of the crater, because isotopic dating showed that the lake existed until 15.7 million years ago, but the volcanic process ended in 16.1 million years. The new timeline would require volcanic activity longer than the evidence suggests, he explains.
Benson says his company expects to begin mining in 2026. It will remove the clay with water and then separate the small grains of lithium from the larger minerals by centrifuging. The clay will then be placed in vats of sulfuric acid to extract the lithium.
‘If they can extract lithium in a very low-energy way, or in a process that doesn’t consume a lot of acid, this could be very important economically,’ says Borst. ‘The US will have its own lithium and businesses will have less to fear about supply shortages.’
Benson considers the lithium-rich claystone at Thacker Pass to be ‘unique’ among volcanic sediment deposits. ‘Smectite clay is very abundant,’ he says. The study of more deposits of lithium following the eruption should focus on calderas and lake sediments that have been hydrothermally changed in lakes without coming out, he adds.
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