Underground operations at the Oyu Tolgoi copper mine in Mongolia have been suspended by Rio Tinto (NYSE: RIO) after a rockfall injured 15 workers on Thursday. The company attributed the collapse to a seismic event underground.
According to operator Oyu Tolgoi LLC, the accident struck at around 6 p.m. local time when a sudden geological event in a fractured rock zone set off tremors and a localized collapse that caught workers at the site. The operator reported no fatalities and said those hurt are being treated, with conditions described as stable overall.
An emergency response mechanism was activated immediately after the incident, with the company now carrying out a full review of what caused the collapse and whether the site is safe. Further updates would be released as the assessment continues, the operator said.
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One of the planet’s biggest copper mines and Mongolia’s largest investment project to date, Oyu Tolgoi sits in Umnugovi Province, also known as the South Gobi. Underground production began there in March 2023 to supplement the existing open pit, and the mine has since become central to Rio Tinto’s copper growth ambitions.
Third quarter output reached 113,500 tonnes of copper in concentrate, up 27% from a year earlier and representing roughly 56% of Rio’s consolidated copper output for the period. Over the first nine months of the year, copper production climbed 29% as underground tonnes rose, with the mine running at an annualized rate of about 450,000 tonnes in the third quarter. Rio is aiming for average annual production of about 500,000 tonnes from the combined open pit and underground mine between 2028 and 2036.
The company owns 66% of Oyu Tolgoi and manages the operation, while Mongolia’s government holds the remaining 34%.
The shutdown arrives at an already strained time. Chinese border restrictions at the Gashuunsukhait crossing have cut copper concentrate exports by about 70% over the past two weeks, with daily truck convoys falling to roughly four from 12 to 13.
