Rio Tinto has reached revised financial terms for the Oyu Tolgoi copper project in Mongolia, a development that reshapes one of the world's largest underground mining operations. The $18bn project represents the single largest foreign investment in the country's history.

The agreement follows years of negotiation between Rio Tinto, the Mongolian government, and project operator Turquoise Hill Resources over cost overruns, tax disputes, and revenue sharing. Oyu Tolgoi sits on one of the planet's largest copper-gold deposits, critical for the energy transition.

The new terms aim to resolve a long-running impasse that has delayed underground expansion and strained diplomatic ties. Copper from the mine feeds Chinese smelters and global markets, making the settlement consequential for supply chains.

Investors will scrutinize whether the revised framework delivers the predictability Rio Tinto needs to justify continued capital deployment in a jurisdiction where resource nationalism remains a live risk.