The company constructing a controversial new lithium mine to supply GM’s electric vehicles knows where it wants to drill next based on new research it published today.

Lithium Americas broke ground on its mine at Thacker Pass in Nevada after facing fierce opposition from Native American tribes, environmental advocates, and local ranchers. But that mine is just one slice of the McDermitt Caldera, the remnants of a supervolcano that’s now believed to hold one of the biggest lithium deposits in the world.

There’s lithium spread across the caldera’s 600 square miles — split between Nevada and Oregon. Thacker Pass is near the southern rim, where especially high-grade materials have been found. What Lithium Americas is after is a clay mineral called illite, which has double the concentration of lithium as the smectite that’s more commonly found throughout the caldera. How that illite got there is a big mystery that, if solved, could help figure out where the world’s best lithium reserves might be hidden.

Lithium Americas says it has the answer, which it published in a paper in the journal Science Advances today. Not everyone is convinced it has the evidence to back that claim, but it could guide the company’s decisions on where to look for lithium, the so-called “white gold” used in rechargeable batteries that has triggered a new mining rush.

Global demand for lithium batteries is forecast to grow fivefold by 2030. Most of the silvery-white metal comes from Australia and Chile. But the Biden administration has made big plans to build up a domestic supply chain in the US to meet clean energy goals.

“The importance of understanding the origin of a mineral deposit is it determines where you look for them,” says Chris Henry, a research geologist emeritus at the Nevada Bureau of Mines and Geology. “The question becomes: what’s special about McDermitt?”

The volcano at McDermitt erupted and collapsed around 16 million years ago, leaving behind a crater filled with lithium-rich smectite clay. Previous research suggests that lithium initially leached out of volcanic glass and accumulated in the caldera.

But that alone doesn’t explain how illite formed with surprisingly high concentrations of lithium, according to the lead author of the new paper, Thomas Benson, who is vice president of global exploration at Lithium Americas and an adjunct associate research scientist at Columbia University. His research team analyzed the chemical compounds in three drill core samples taken from the southern part of the Caldera to try to trace their origins.

Benson posits that after the volcano’s collapse, a second phenomenon took place called hydrothermal enrichment. Magma moving underneath the surface pushed the center of the caldera up, creating what are now the Montana Mountains. That movement also created faults and fractures. Fluid from the magma chamber escaped through those fractures, carrying more lithium up to the surface and transforming smectite into illite along the southern rim of the basin.

“What’s really special about this deposit is you already had a big lithium inventory to begin with, and then you have this massive influx of all this lithium-rich fluid that caused hyper lithium enrichment on a giant scale,” Benson said in a call with The Verge that he took from Burning Man this week.

Henry, the geologist, cautions that there still isn’t enough evidence to say for sure whether this phenomenon actually took place millions of years ago and is responsible for the high-grade ore within McDermitt. “Some of the evidence cited for it are really pretty weak,” he says. For instance, the movement that shaped the Montana Mountains also left faults in the northern part of the caldera. So if Benson’s hypothesis holds true, there should have been illite there, too.

But according to Benson, Lithium Americas needs to focus on mining areas known to have illite in the south. “We’re not going to drill in the northern part of the caldera because we know that this hydrothermal event didn’t happen up there,” Benson tells The Verge. “Now we know that we want to drill in the south … we can really target our drilling and target the high grade material.”

So far, the Canadian mining company only has one mine site in the US at Thacker Pass. Construction started this year after lengthy legal battles, and the mine is expected to start producing lithium by 2026. In January, GM announced a $650 million equity investment in Lithium Americas, giving it exclusive access to lithium from Thacker Pass during the first phase of mining. The location holds both smectite and illite, and the company plans to extract lithium from both materials.

“Mining is inherently unsustainable, right? You take it out of the earth and don’t put it back,” Benson says. To minimize the damage, he argues, it makes sense to target illite in the future. “You want to minimize the amount of material removed from the Earth. And to do that you want to find the most concentrated rocks.”

Lithium Americas has staked claims in other parts of the caldera. Competitors are also trying to develop more mines in the area, including an Australian company exploring a deposit in the northern part of the caldera in Oregon.

“We’re very concerned that the caldera could become a mining district,” says John Hadder, executive director of the nonprofit Great Basin Resource Watch. He says the construction at Thacker Pass has already kicked up dust that creates air quality risks for nearby people, wildlife, and livestock.

Great Basin Resource Watch and other environmental groups, the Reno-Sparks Indian Colony, Summit Lake Paiute Tribe, Burns Paiute Tribe, and a local rancher have all filed suits to try to stop mining at Thacker Pass. They say the mine threatens their local water source, sensitive wildlife, and sacred sites including the location where US soldiers massacred Paiute tribal members in 1865. But in July, a federal court denied their appeal to overturn the project’s approval.

“The global search for lithium has become a form of ‘green’ colonialism,” People of Red Mountain, an Indigenous-led organization created to protect the sacred site, said in an August 7th statement. “The Caldera holds many first foods, medicines, and hunting grounds for tribal people both past and present.” The organization is now trying to stop another proposed mine on the Oregon side of the caldera.

Hadder is skeptical Lithium Americas will only target locations with high-grade illite, especially if it doesn’t withdraw its other mining claims. “If they can make money on it, they’ll probably dig it up,” he says.