查看配图A view of the Oyu Tolgoi site. Credit: Rio Tinto.
Rio Tinto (ASX, LSE, NYSE: RIO) said it’s progressively restarting underground operations at Mongolia’s Oyu Tolgoi mine a day after a seismic event triggered a rockfall, stopping production at a cornerstone asset of the company’s copper growth strategy.
Three employees were injured and two continue to receive treatment for non-life-threatening injuries, the company said Friday. Thursday’s rockfall was confined to a temporary storage zone beside the production area, and safety reviews have been completed.
The incident caused “no structural impact to the cave or its operating infrastructure,” Rio said in Friday’s statement.
Rio didn’t quantify lost production or provide a timetable for completing the restart.
Shares in Rio Tinto dropped 1.8% to $81.76 in New York trading Friday morning, cutting the company’s market value to about $143.3 billion (C$201 billion). The stock has traded between $67.74 and $112.58 in the past year.
Key role
The disruption comes as Oyu Tolgoi delivers some of Rio’s strongest operating growth even as it encounters border restrictions that recently curtailed copper concentrate exports by 70%. Copper production rose 27% in the third quarter from a year earlier and 29% over the first nine months.
The operation was running at an annualized rate of about 450,000 tonnes during the quarter, CEO Simon Trott said in Rio’s Oct. 14 production update.
That expansion makes uninterrupted underground mining increasingly important to the group. While Oyu Tolgoi’s output climbed sharply, Rio’s third-quarter consolidated copper production was little changed at 205,000 tonnes. Group copper output rose just 1% over the first nine months, highlighting the Mongolian operation’s key role.
Before the incident, Rio reaffirmed its target for Oyu Tolgoi’s combined underground and open-pit operations to average about 500,000 tonnes of recoverable copper annually from 2028 through 2036. Rio expects the operation to become the world’s fourth-largest copper mine by 2030.
Located in Mongolia’s South Gobi region, Oyu Tolgoi is managed by Rio, which owns 66%, while the Mongolian government holds 34%. Open-pit mining began in 2011, followed by concentrate production in 2013. Sustainable underground production started in March 2023, opening access to the deposit’s most valuable mineralization.
Underground value
More than 80% of the deposit’s total value lies underground, according to Rio. Its development underpins the company’s long-term investment in the operation and its ambition to expand copper supply for electrification and other uses.
The underground mine uses block caving, a method in which miners remove rock beneath an orebody, allowing it to fracture and collapse under its own weight. Broken ore is collected through draw points and transported for crushing and delivery to the surface.
Rio consolidated its ownership in December 2022 by acquiring the remaining minority interests in Turquoise Hill Resources, simplifying the ownership structure ahead of underground production. The transaction increased Rio’s interest in Oyu Tolgoi from about 34% to 66%.