Rio Tinto is racing to seal a new Mongolian copper deal as part of urgent efforts to avoid a slump in copper grades and volumes from its giant Oyu Tolgoi mine, forecast to be one of the world’s top-five copper producing mines by 2030.

Rio is in three-way talks with Toronto-listed Entree Resources and the Mongolian government over a deal that would bolster Oyu Tolgoi by adding to the project some copper-rich tenements that are partly controlled by Entree.