(Reuters) - General Motors ( GM ) is eyeing further North American investments in lithium and other critical minerals used to build electric vehicles after boosting its investment in a Nevada mine to nearly $1 billion earlier this week, an executive said on Thursday.

The U.S. automaker on Wednesday said it would form a joint venture with Lithium Americas ( LAC ) to develop the Thacker Pass lithium mine, North America's largest source of the battery metal.

The move increases GM's investment in the project by an additional $325 million to $950 million after an initial investment announced last year. It also gives the automaker a partial ownership stake in the mine and doubles its access to production to at least 20 years.

While the Thacker Pass JV should supply GM with a "significant" amount of its lithium, the company is open to other critical minerals deals on the continent, Jeff Morrison, GM's senior vice president of global purchasing and supply chain, said in an interview on Thursday.

A majority of GM's deals are for minerals supply, not necessarily JVs, and the automaker likely would continue that approach, he added.

"We don't want to become a mining company," Morrison said. "Our main goal is to build out a North American based, Western-allied, reliant supply chain. To do that, we have to pick partners and assets and figure out what they need to do to industrialize and be successful."

GM also has agreements to buy cobalt from Glencore ( GLCNF ), an investment in nickel and cobalt miner Queensland Pacific Metals ( QPMLF ), and a lithium supply deal with Arcadium Lithium ( ARLTF ), among others.

The automaker in 2021 invested in Controlled Thermal Resources Hell's Kitchen geothermal brine project in California, although that project has experienced delays.

Morrison said GM is "still working with them and still staying close with them."