Chile’s Codelco, seeking to retain the title of world’s top copper supplier, made a $500 million offer to buy a stake in a mine run by Teck Resources Ltd., people with knowledge of the matter said.

The proposal to acquire a 10% stake in the Quebrada Blanca mine from fellow state firm Enami is before the latter’s board, said the people, asking not to be named commenting on a deal that’s yet to be made public. La Tercera, a Chilean newspaper, reported in July an offer was in the works.

Codelco and Enami declined to comment. 

The sale would help reduce Enami’s debt after years of losses from processing mineral for small miners in Chile, while minimizing the amount of fresh capital needed from public funds. 

For Codelco, the stake would help prop up the behemoth’s output, which last year sank to the lowest in a quarter century. That may be enough to prevent BHP Group from overtaking Codelco as the world’s biggest copper company.

Still, approval for the purchase would have to navigate opposition from mining society Sonami, which has a seat on the 10-person board at Enami. Sonami has said any sale should be done through an open and competitive process.