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Rio Tinto says it has begun a progressive restart of underground operations at Mongolia’s Oyu Tolgoi mine, one 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 the rockfall caused no structural damage to the mine’s cave or operating infrastructure. The company has not disclosed lost output or a timeline 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 caused a rockfall that halted production and injured three employees. The company said two workers remained under treatment for non-life-threatening injuries and that inspections found no structural impact to the mine’s cave or operating infrastructure.
Rio said the rockfall was confined to a temporary storage zone beside the production area. The company reported that safety reviews had been completed before the restart began. Its statement did not specify which parts of the underground operation were restarting, how quickly activity would return, or when the mine would be back at full production.
The company also did not disclose how much copper output was lost during the interruption. The Northern Miner reported that Rio’s shares were down 1.8% to $81.76 in New York trading Friday morning, putting the company’s market value at about $143.3 billion at that point in the session. The share move was reported during trading and does not establish the market’s overall response to the incident.
Oyu Tolgoi’s underground operation is a major contributor to Rio’s copper growth plans. The mine’s output increased as the rockfall disrupted activity: Rio reported 27% year-on-year copper production growth at Oyu Tolgoi in the third quarter and a 29% rise over the first nine months. Chief Executive Simon Trott said the operation was running at an annualized rate of about 450,000 tonnes during the quarter, according to the company’s October 14 production update.
Oyu Tolgoi’s Role in Rio’s Copper Plans
The incident put a short-term interruption at a mine central to Rio’s planned expansion of copper supply. Although the company has started a restart and reported no structural impact, the amount and duration of lost production have not been disclosed. Those figures will help show how much the event affects output in the current reporting period.
The mine’s importance is visible in Rio’s production figures. While Oyu Tolgoi’s copper output rose sharply, Rio’s consolidated third-quarter copper production was 205,000 tonnes and little changed, and group output for the first nine months was up only 1%. The gap underlines how much the company’s copper growth depends on the Mongolian operation continuing to expand.
Oyu Tolgoi is also operating amid restrictions that have recently curtailed copper concentrate exports by 70%, according to the source report. The rockfall and export constraints are distinct disruptions: the first affected underground production, while the second limited exports. Together, they leave open questions about how much of the mine’s output can be produced and shipped, though Rio has not said the rockfall will change its longer-term plans.
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The Mine’s Underground Expansion
Oyu Tolgoi is in Mongolia’s South Gobi region. Rio Tinto manages the operation and holds a 66% interest; the Mongolian government owns the remaining 34%. Open-pit mining began in 2011, and concentrate production followed in 2013. Sustainable underground production started in March 2023, opening access to higher-value mineralization beneath the open pit.
Rio says more than 80% of the deposit’s total value lies underground. The mine uses block caving: rock is removed beneath an orebody so that it fractures and collapses under its own weight. Broken ore is gathered through draw points and transported for crushing and delivery to the surface. The event’s location in a temporary storage zone beside the production area is relevant, but Rio has not released further technical details about the seismic event or the rockfall.
Rio has said it expects the combined underground and open-pit operation to average about 500,000 tonnes of recoverable copper annually from 2028 through 2036. The company has also forecast that Oyu Tolgoi could become the world’s fourth-largest copper mine by 2030. Those are company targets and expectations, not outcomes established by the restart announcement.
“No structural impact to the cave or its operating infrastructure.”
— Rio Tinto, in its Friday statement
Production Losses and Restart Pace
Rio has not provided a restart completion timetable or a figure for copper production lost during the stoppage. It is not clear how long the progressive restart will take, whether all underground areas were affected, or when production will return to the rate recorded before the incident.
The company has said three employees were injured and that two continued to receive treatment for non-life-threatening injuries. It has not released further information about their identities or the circumstances of their injuries. Rio’s description of the rockfall as confined to a storage zone, and its statement that no structural impact occurred, are the company’s account; the supplied report provides no independent engineering assessment.
The cause and scale of Thursday’s seismic event have not been detailed. It also remains unclear whether the interruption will change Rio’s production forecasts or its longer-term Oyu Tolgoi targets. No such change was announced in the restart update.
Monitoring the Return to Production
The immediate next step is the progressive restart of underground operations following Rio’s safety reviews. The company has not announced specific milestones, so the pace of the restart and the date for a return to normal production remain unknown.
Further updates from Rio are expected to clarify operating status, any continuing workforce impacts, and the production effect of the stoppage. Investors and customers will also be watching for revised output information and updates on the separate export restrictions affecting copper concentrate shipments. Until the company provides those details, the full operational and financial impact of the rockfall cannot be determined.
Key Questions
What happened at Oyu Tolgoi?
A seismic event on Thursday caused a rockfall in a temporary storage zone beside the underground production area and stopped production. Rio Tinto said it began progressively restarting underground operations the following day.
Were workers injured?
Rio said three employees were injured. Two were still receiving treatment for injuries the company described as non-life-threatening.
Did the rockfall damage the mine?
Rio said the rockfall caused no structural impact to the cave or its operating infrastructure. The source report does not provide an independent engineering assessment.
When will production return to normal?
Rio has not provided a date. It said the restart is progressive but did not publish a timeline for completion or a figure for lost production.
Why is Oyu Tolgoi important to Rio Tinto?
The mine is a central part of Rio’s copper growth plans. Oyu Tolgoi’s output grew faster than the company’s overall copper production in the reported period, and Rio has set targets for higher output from its combined underground and open-pit operations.
Source: northernminer.com
