Rio Tinto has paused underground operations at its Oyu Tolgoi copper-gold mine in Mongolia after seismic activity along a rock fault zone injured workers. No fatalities were reported. The seismic event occurred at about 18:00 local time on Thursday, October 29 (10:00 London time), causing ground vibration in the underground mine.
According to Rio Tinto, underground operations are “paused in line with procedure, subject to completion of a safety review.” Accounts of the injuries differ. Rio Tinto said three employees were hurt, while operator Oyu Tolgoi LLC initially said 15 workers were injured in a rockfall triggered by the tremor. By Friday, Oyu Tolgoi LLC said two employees remained in hospital in Ulaanbaatar with non-life-threatening injuries and 13 had been discharged.
Oyu Tolgoi LLC said a preliminary inspection found the rockfall “is confined, with no structural impact to the cave or its operating infrastructure,” and that it is preparing a “safe and controlled restart.” This is a preliminary assessment by the operator and does not replace the safety review that Rio Tinto says is still in progress. Neither Rio Tinto nor the operator has said when the restart will begin. Oyu Tolgoi is a central part of Rio Tinto’s copper growth.
According to calculations by The Oregon Group, based on International Copper Study Group (ICSG) market forecasts and Rio Tinto production results, the mine produced 345,000 tonnes of copper in 2025, about 1.5% of world mine output of 23.2 million tonnes estimated by the ICSG. Rio Tinto reported that the mine produced 113,500 tonnes of copper in concentrates in the third quarter of 2026, up 27% from a year earlier. Rio Tinto’s total copper output was 204,500 tonnes in the quarter, so Oyu Tolgoi accounted for more than half of it, or 56% by The Oregon Group’s calculations.
Rio Tinto attributed the higher output to the underground ramp-up, higher grades and better recoveries, and targets average annual output of about 500,000 tonnes of copper from 2028 to 2036. Rio Tinto has kept its 2026 group copper guidance of 800,000 to 870,000 tonnes but has not commented on guidance since the seismic event. The copper price showed little reaction.
Business Recorder reported that three-month copper on the London Metal Exchange was down 0.25% at US$14,320.50 a tonne at 03:10 London time on Friday. The border may pose a more immediate constraint than the underground damage. Rio Tinto flagged delays affecting all vehicles at the Ganqimaodu crossing into China, which have reduced the trucks available to carry copper concentrate, according to Mining.com.
The Associated Press reported that Oyu Tolgoi LLC said its concentrate exports fell about 70% in two weeks, since mid-October, as daily truck convoys dropped from 12–13 to about four. Mongolian officials link the slowdown to China’s installation of face-recognition checks for drivers, a process expected to run until the end of December, according to the Mongolian government portal egov.mn. Because Oyu Tolgoi has no smelter, its concentrate feeds smelters in northern China, which Shanghai Metals Market (SMM) says face near-term delivery risk.
The pause adds Oyu Tolgoi to a list of large underground copper mines disrupted since 2025. Freeport’s Grasberg block cave in Indonesia was hit by a September 2025 mud rush that killed seven workers, and its mill ran at 67% of capacity in the third quarter of 2026, according to Freeport. Codelco’s El Teniente in Chile suffered a seismic event in July 2025 that killed six workers, according to Codelco.
Ivanhoe’s Kamoa-Kakula in the Democratic Republic of Congo was partly flooded after seismic activity in May 2025, and Ivanhoe cut its 2025 copper guidance to 370,000–420,000 tonnes from 520,000–580,000 tonnes, according to Moneyweb. The Oregon Group notes that Oyu Tolgoi, El Teniente and Grasberg are all block caves. The supply backdrop is already tight.
The ICSG has cut its 2026 mine supply growth forecast to 1.3%, with output at Grasberg and Kamoa-Kakula still constrained. The World Bank expects copper to average a record US$13,200 a tonne in 2026, according to The Oregon Group. Some analysts see limited long-term impact.
Jefferies analyst Christopher LaFemina described the event as “unlikely to have long-term impacts on production expectations,” noting that surface operations, including open-pit mining and milling, are still running, according to Moneyweb. Analysts polled by Reuters raised their 2026 global copper surplus estimate to 125,000 tonnes, according to Business Recorder, which suggests the refined market is not currently short of metal. Still, a mine producing more than half of Rio Tinto’s copper now faces two bottlenecks: underground ground conditions and truck capacity at the Chinese border.
Source: theoregongroup.com