The new development is latest hurdle faced by the miner, following two delays in securing approvals from the government for the project.

Rio Tinto said it will remain committed to working with the government to secure project financing.

However, in view of the current uncertainty, including ongoing talks with the government on a variety of issues, all funding and work on the underground development will be delayed until these matters are closed and a new schedule has been agreed.

In the meantime, Rio Tinto is planning to focus on the continued safe, efficient and cost-effective management and boosting the open pit mine and sustained export of Oyu Tolgoi concentrate to customers.

Rio Tinto’s Turquoise Hill owns 66% of Oyu Tolgoi mine, while the remaining 34% is owned by the Government of Mongolia.

The proposed expansion is designed to ramp up production to 425,000t of copper and 460,000oz of gold per year.