15 Workers Affected by Rockfall at Mongolia’s Oyu Tolgoi Underground Mine

Key Facts

Mongolia’s e-government website reported on October 29 that a seismic-like tremor occurred at the Oyu Tolgoi underground mine, followed by a rockfall that affected 15 workers. The website said the injured workers received medical care and no deaths were reported. Incident management and rescue teams accounted for all workers who were underground and checked their health. Assessment of the mine’s condition was ongoing, according to the government report. The mine is in Mongolia and includes open-pit operations and an underground mining project.

The condition of the underground section is significant to Oyu Tolgoi’s structure, with Rio Tinto saying more than 80% of the mine’s total value lies at depth. The site combines an open-pit mine and an underground mining project, according to the company’s description. Rio Tinto owns 66% of the operating company, while the Mongolian government owns 34% through Erdenes Oyu Tolgoi. This ownership structure reflects the project’s shared ownership between the company and the Mongolian government. The government report did not specify when the assessment of the mine’s condition would be completed.

The incident comes as Rio Tinto targets average Oyu Tolgoi production of about 500 thousand tons of copper annually from 2028 to 2036, from both the open-pit and underground mines. At group level, the company maintained its 2026 consolidated copper production guidance at 800 to 870 thousand tons. Consolidated production was 205 thousand tons in the third quarter, unchanged from the same period a year earlier but down 4% from the second quarter. The company said its 2026 production guidance was unchanged. Chief Executive Simon Trott also said the company still targets an annualized productivity benefit rate of $1.8 billion by the end of 2026, and that its major projects were on schedule and within budget.

The mine is also facing a slowdown in copper concentrate shipments to China because of border transit restrictions, an issue separate from the rockfall. The Associated Press quoted Oyu Tolgoi as saying the number of truck convoys crossing the border had fallen to about four a day, compared with a usual rate of between 12 and 13 convoys. The agency said concentrate exports to China had fallen about 70% in the two weeks before its October 29 report. Mongolian authorities attributed the slowdown at the crossing to infrastructure and technology upgrades on the Chinese side. The agency added that a facial recognition system for truck drivers was introduced in August, and that upgrade work could continue through the end of December.