Rio Tinto has suspended underground mining at its Oyu Tolgoi copper project in Mongolia after seismic activity along a rock fault zone triggered ground vibration in the underground mine, injuring three employees.

The company confirmed that the event occurred at approximately 18:00 local time on 29 October 2026. “There have been no fatalities,” Rio Tinto said in a statement on 30 October. “Three employees sustained injuries. Underground operations are currently paused in line with procedure, subject to completion of a safety review”.

The disruption comes as Rio Tinto has been ramping up underground production at Oyu Tolgoi, one of the world’s largest known copper and gold deposits and a central pillar of the company’s copper growth strategy.

Earlier in October, the miner reported a 29% year-to-date increase in Oyu Tolgoi copper production and said it expects the operation to become the fourth-largest copper mine in the world by 2030.

Rio Tinto owns 66% of Oyu Tolgoi and manages the operation, while the Mongolian government holds 34%. Open-pit mining at the site began in 2011, but the most valuable copper resources lie deeper underground, where the company has been investing heavily to expand output.

The pause adds a fresh supply-side concern to a copper market already facing interruptions and tight inventories. U.S. copper futures were up 17% so far this year amid worries about availability. The duration of the suspension will depend on the outcome of the safety review, which Rio Tinto has not yet put a timeline on.