Mexico’s president has signed a decree creating a massive lithium reserve in neighboring Sonora.

Over the weekend in the remote mountain town of Bacadehuachi, President Andrés Manuel López Obrador was joined by other top state and federal officials for the signing ceremony. The community is near what authorities say is one of the largest lithium deposits in the world, and the decree created a reserve of nearly 600,000 acres in eight Sonoran municipalities.

López Obrador said the measure, coupled with a reform last year that nationalized the mining of lithium, will prevent foreign firms from exploiting the material critical for battery production. He specifically cited Russia, the United States and China.

The mining concessions near Bacadehuachi are currently owned by the Chinese firm Ganfeng, though López Obrador has recently expressed interest in negotiating a deal in which those concessions would be turned over to Mexico.