Rio Tinto Group (ASX:RIO) has signed a binding agreement with state-owned Empresa Nacional de Minería (ENAMI) to form a joint venture for the Salares Altoandinos lithium project in Chile's Atacama region, according to a media release on Thursday.

The company will acquire a 51% stake in the project and commit up to AU$425 million, including direct lithium extraction technology, to fund staged studies as the joint venture advances, the release said.

The transaction is expected to close in the first half of 2026, pending regulatory approvals and customary conditions.