Oyu Tolgoi Pauses Underground Operations After Seismic Event
Rio Tinto has paused underground operations at the Oyu Tolgoi copper-gold mine in Mongolia after seismic activity along a rock fault zone caused ground vibration in the underground mine at around 18:00 local time on October 29. There were no fatalities.
Oyu Tolgoi LLC said 15 workers were caught in the rockfall caused by the vibration. Two of them are receiving treatment in Ulaanbaatar, while the other 13 have been discharged from medical care. Rio Tinto's own statement said three employees sustained injuries.
The mine's emergency management and rescue teams responded immediately and accounted for all workers who were underground at the time. Oyu Tolgoi LLC said it is carrying out a phased assessment of the underground mine and is preparing to restart operations in a controlled manner once safety is assured. Rio Tinto shares fell as much as 2.9% on the Australian Securities Exchange following the announcement.
Why it matters
The underground block cave is central to Oyu Tolgoi's growth, as around 80% of the deposit's value lies underground. In the third quarter of 2026, Oyu Tolgoi produced 113,500 tonnes of copper and 123,600 ounces of gold in concentrate, and paid MNT 725 billion in taxes, fees and other payments. Rio Tinto owns 66% of the mine, and the Government of Mongolia holds the remaining 34% through Erdenes Oyu Tolgoi.
The pause adds to pressure on exports. Because of renovation work at the Gashuunsukhait-Ganqimaodu border crossing, the number of copper concentrate convoys crossing into China has been limited to four a day since mid-October, down from an average of 13 a day under normal conditions. The length of the underground pause will determine how much the incident affects Oyu Tolgoi's output this year.
