Injury to 3 Employees Halts Underground Operations at Oyu Tolgoi Mine
Key Facts
Rio Tinto suspended underground operations at the Oyu Tolgoi mine in Mongolia after seismic activity at about 18:00 local time on October 29 injured 3 employees, according to a company statement. The company said the activity occurred along a rock fault zone and caused ground shaking inside the mine. No fatalities were reported, the statement said. The company added that operations were suspended under its procedures pending completion of a safety review. It did not say when the review would be completed or mining would resume. The suspension puts a project that has recorded strong copper production growth in 2026 under a safety review before underground work can resume.
Rio Tinto said copper production at Oyu Tolgoi rose 27% year on year in the third quarter of 2026 and 29% in the first nine months of the year. Copper production in concentrates was 113.5 thousand tonnes in the third quarter, compared with 89.2 thousand tonnes in the same period of 2025. In the first nine months, output was 312 thousand tonnes, versus 241.3 thousand tonnes in the corresponding period last year. The company said the mine operated at an annualized rate of about 450 thousand tonnes in the third quarter. The figures show the mine’s output before the October 29 incident, while the incident statement did not specify the suspension’s impact on production.
Oyu Tolgoi’s growth came as Rio Tinto’s consolidated copper production was 205 thousand tonnes in the third quarter, down 4% from the second quarter, according to the company’s operating results. The company attributed the mine’s production growth to higher copper output there, against a decline in its consolidated output compared with the previous quarter. Chief Executive Simon Trott said the company sees opportunities to improve safety, productivity and reliability by applying its operating system. This comes as underground operations at the mine undergo a safety review following the ground shaking and injuries to the 3 employees. The company’s incident statement did not say whether the suspension would change its production outlook or operating plans.
Rio Tinto owns 66% of Oyu Tolgoi and operates the mine, while the Mongolian government owns 34%, according to Dow Jones coverage. The mine is a major copper project in the country, and Rio Tinto says it is expected to become the world’s fourth-largest copper mine by 2030. The project plan targets average production of about 500 thousand tonnes of copper a year between 2028 and 2036 from the open-pit and underground mines. That long-term target puts the mine’s operation in context, while the next step remains tied to the ongoing safety review. The company has not announced a timeline for resumption or an estimate of the suspension’s impact on project targets.
The incident coincided with a slowdown in copper concentrate shipments to China; the Associated Press said exports had fallen by about 70% in the two weeks before its report, citing the mine operator. The number of daily truck convoys crossing into China also fell from the usual rate of 12 to 13 convoys to about 4 convoys. Mongolian border authorities attributed the slowdown to infrastructure and technology upgrades on the Chinese side, including the installation and maintenance of a system to recognize truck drivers’ faces inside vehicles. This slowdown is a separate development from the suspension of underground mining announced by Rio Tinto after the seismic activity. In June 2026, the company and the Mongolian government agreed to amend the interest rate on the project’s shareholder loan and said they would work to resolve issues involving the Entrée mine concession areas.
About 17 thousand people work at Oyu Tolgoi, 97.8% of them from Mongolia, according to Rio Tinto data released in June 2026. The size of the local workforce adds an operational dimension to the safety review that followed injuries to 3 employees. The company said resumption of underground operations is conditional on completing that review. It has not announced when it will be completed or set a date for work to resume. The company’s findings from the review remain the next announced development concerning the mine.