Rio Tinto suspended underground operations at the Oyu Tolgoi copper mine in Mongolia after seismic activity along a rock fault zone at about 6 p.m. local time on Thursday caused ground vibration and a rockfall. The company said three employees were injured and there were no fatalities, and that underground work was paused in line with procedure pending a safety review. Surface milling and open pit mining continued, according to Jefferies analysts cited by Bloomberg.
By Friday the picture had narrowed. Oyu Tolgoi LLC said a preliminary inspection found the rockfall localised and confined, with no structural impact to the cave or its operating infrastructure, and that it was preparing a safe and controlled restart following a systematic staged assessment. Two employees were receiving treatment in Ulaanbaatar for non life threatening injuries, and 13 others were discharged locally after assessment.
Oyu Tolgoi is one of the world’s largest copper and gold deposits, with about 80 percent of its value underground. Rio Tinto owns 66 percent and manages the operation, with the Mongolian government holding 34 percent. The mine has been running at an annualised output rate of about 450,000 tonnes of copper, according to its latest operational update.
Jefferies judged the incident unlikely to have long term impacts on production expectations, which is the right frame if the restart proceeds as described. The pause also arrived in the same week the company flagged delays at the Ganqimaodu border crossing with China that have cut concentrate trucking, covered on this site on October 29, so Oyu Tolgoi’s near term constraint is logistics and safety sequencing rather than geology. Rio Tinto shares fell 3.12 percent in the market tables updated this morning.