Oyu Tolgoi currently produces from an open-pit mine that came into production in July 2013. Production in 2015 totaled 202,200 metric tons (mt) of copper and 653,000 ounces (oz) of gold in concentrate.

Work on a massive block cave, underground development project was suspended in August 2013 due to shareholder disagreements. Current planning for resumption of underground development assumes a five-year construction period, with first underground production around 2021. A five- to seven-year ramp up period will follow.

At full production, the underground mine will produce 95,000 mt/d of plant feed, and the Oyu Tolgoi plant will produce more than 500,000 mt/y of copper in concentrate. Underground mining will be based on the Hugo Dummett North deposit, which contains probable ore reserves of 499 million mt at an average grade of 1.66% copper—more than three times the grade of open-pit ore—and 0.35 g/mt gold.

Processing of underground ore will utilize the existing concentrator and infrastructure. Capital cost to complete the underground development program is estimated at $5.3 billion.

Rio Tinto Deputy Chief Executive Jean-Sébastien Jacques stated, “Today’s investment decision takes Oyu Tolgoi to another level and will transform it into one of the most significant copper mines globally, unlocking 80% of its value. Long-term copper fundamentals remain strong, and production from the Oyu Tolgoi underground will commence at a time when copper markets are expected to face a structural deficit.