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Rio Tinto says it has begun a phased restart of underground operations at Mongolia’s Oyu Tolgoi copper mine, a day after a seismic event caused a rockfall and stopped production. Three employees were injured; two were still receiving treatment for non-life-threatening injuries, and Rio said inspections found no structural impact to the cave or operating infrastructure. The company has not disclosed lost production or a timetable for completing the restart.
Rio Tinto has begun progressively restarting underground operations at Mongolia’s Oyu Tolgoi copper mine, a day after a seismic event triggered a rockfall and halted production at the company’s major copper growth asset. Three employees were injured, Rio said Friday; two remained under treatment for injuries described as non-life-threatening.
Rio said the rockfall was confined to a temporary storage zone beside the production area. The company reported that safety reviews had been completed and that the incident caused “no structural impact to the cave or its operating infrastructure.” It did not provide a detailed account of how the workers were injured or specify what work has resumed in the phased restart.
The company has not quantified production lost during the stoppage or given a date for completing the restart. The report by The Northern Miner said production at the underground operation was stopped after Thursday’s seismic event; Rio’s Friday statement indicated operations were being brought back progressively rather than all at once.
Oyu Tolgoi’s growing output has increased its importance to Rio’s copper business. Rio’s third-quarter production update put the mine’s annualized operating rate at about 450,000 tonnes during the quarter. The company had previously reaffirmed a target for combined underground and open-pit operations to average about 500,000 tonnes of recoverable copper a year from 2028 through 2036.
Restart Risks for Rio’s Copper Growth
The interruption is significant because Oyu Tolgoi has been a key source of growth as Rio seeks to expand its copper production. The mine’s copper output rose 27% in the third quarter year over year and 29% in the first nine months, according to the figures in Rio’s production update. By comparison, Rio’s consolidated copper production was little changed at 205,000 tonnes in the third quarter, while group output rose just 1% over the first nine months.
Those figures help explain why the duration of the shutdown matters to the company’s plans. A short, contained interruption would have a different production impact from a prolonged stoppage, but Rio has not reported the lost volume or said when the restart will be complete. The company’s statement that there was no structural impact is a status update on the mine’s infrastructure, not a quantified estimate of operational losses.
The mine also faces a separate constraint: The Northern Miner reported that border restrictions had recently curtailed copper concentrate exports by 70%. The rockfall and the export restrictions are distinct developments, but together they underline that mine production and the ability to move product are both relevant to Oyu Tolgoi’s contribution to Rio’s results.
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How Oyu Tolgoi Reached This Point
Oyu Tolgoi is in Mongolia’s South Gobi region and is managed by Rio Tinto, which owns 66%; the Mongolian government holds the remaining 34%. Open-pit mining began in 2011, concentrate production followed in 2013, and sustainable underground production began in March 2023.
The underground project is central to the mine’s longer-term production outlook. Rio says more than 80% of the deposit’s total value lies underground. The underground mine uses block caving: rock is removed beneath an orebody so it fractures and collapses under its own weight, after which broken ore is collected and transported for processing. That mining method makes the condition of the cave and associated infrastructure directly relevant to operations, though Rio said the rockfall did not structurally affect either.
Rio increased its stake in Oyu Tolgoi from about 34% to 66% in December 2022 by acquiring the remaining minority interests in Turquoise Hill Resources. Before the rockfall, the company’s stated plan was for the mine’s combined operations to average about 500,000 tonnes of recoverable copper annually from 2028 to 2036. Rio has said it expects Oyu Tolgoi to become the world’s fourth-largest copper mine by 2030.
““No structural impact to the cave or its operating infrastructure.””
— Rio Tinto, in a Friday statement as reported by The Northern Miner
Lost Output and Worker Updates
Rio has not said how much production was lost, how quickly underground operations can return to normal, or when the phased restart will be complete. The available account also does not specify the precise tasks or locations involved in the restart, or provide further updates on the two employees receiving treatment.
The company said its safety reviews were completed and reported no structural impact to the cave or operating infrastructure. The report does not include independent findings or further technical details about the seismic event, the rockfall’s size, or the measures being taken before each part of the mine resumes work. Those details remain unreported.
Monitoring the Phased Restart
The immediate development to watch is whether Rio can continue restoring underground operations after the safety reviews, and whether the company provides a timetable for returning to normal production. A later update on operating rates or lost output would clarify the effect of the stoppage on the mine’s contribution to Rio’s copper production.
Further information from Rio on the injured employees and any additional safety or operational findings may also clarify the incident’s consequences. For now, the company’s confirmed position is that a progressive restart has begun and that its review found no structural impact; the pace and production effects have not been disclosed.
Key Questions
What happened at Oyu Tolgoi?
A seismic event triggered a rockfall in a temporary storage zone beside the production area, stopping underground production. Rio said it began progressively restarting underground operations the following day.
Were any workers injured?
Yes. Rio reported that three employees were injured. Two continued to receive treatment for injuries the company described as non-life-threatening.
Was the mine’s infrastructure damaged?
Rio said safety reviews found no structural impact to the cave or its operating infrastructure. The company has not released further technical details about the rockfall.
How much copper production was lost?
Rio has not quantified lost production or provided a completion date for the restart. The mine’s pre-incident operating rate does not establish how much output was missed during the stoppage.
Why is Oyu Tolgoi important to Rio Tinto?
The mine has been a major source of Rio’s copper growth. Its output rose 27% year over year in the third quarter, while Rio’s consolidated copper production was little changed over that period.
Source: northernminer.com
