Rio Tinto Restarts Oyu Tolgoi Underground Operations After Rockfall

Rio Tinto (RIO ) said in an update datelined London at 1100 GMT on 30 October 2026 that underground operations at the Oyu Tolgoi copper mine in Mongolia are being progressively restarted following completion of safety reviews, after a seismic event on 29 October 2026 triggered a localised rockfall and a procedural pause in underground mining.

The company said the rockfall was confined to a temporary storage zone adjacent to the production area, with no structural impact to the cave or its operating infrastructure. Two employees continue to receive treatment for non-life-threatening injuries, Rio Tinto said, adding that Oyu Tolgoi is working closely with the relevant authorities and continues to support its employees and contractors.

Oyu Tolgoi LLC, the mine’s operator, said in its own update on 30 October 2026 that the two employees are receiving treatment in Ulaanbaatar and that 13 other employees were discharged locally after being assessed. The operator said a preliminary inspection identified that the localised rockfall is confined, with no structural impact to the cave or its operating infrastructure, and that following a systematic and staged assessment it is now preparing to commence a “safe and controlled restart” of operations. Further updates will be communicated as additional information becomes available, it said.

The 29 October Seismic Event

Rio Tinto’s initial statement on the event, datelined London at 1900 GMT, confirmed that at approximately 18:00 local time on 29 October 2026, seismic activity occurred along a rock fault zone at Oyu Tolgoi, resulting in ground vibration in the underground mine. The company said there had been no fatalities, that three employees sustained injuries, and that underground operations were paused in line with procedure, subject to completion of a safety review.

Oyu Tolgoi LLC said in a situation update published on 29 October 2026 that fifteen employees were affected by a rockfall triggered by the seismic event and sustained injuries, and were receiving medical care and undergoing assessment. The operator said the mine’s Incident Management Team and Mine Rescue Teams responded immediately and accounted for all personnel working underground at the time, and that the situation was still being evaluated.

Mine Profile, Production and Ownership

Oyu Tolgoi, in the Umnugovi province in Mongolia’s South Gobi, is one of the largest known copper and gold deposits in the world, according to Rio Tinto’s profile of the operation. Open pit mining began in 2011, and the copper concentrator, which Rio Tinto describes as the largest industrial complex ever built in Mongolia, began processing mined ore in 2013. March 2023 marked the start of sustainable production from the underground mine. The complex uses block-caving, a method in which a void is created under the ore body so that the ore collapses gradually under its own weight and passes through funnels in the rock known as draw points before being hauled for crushing and transported to the surface. Rio Tinto says the underground mine will have approximately 200 kilometres of tunnels and five shafts, the deepest reaching 1.3 kilometres, with ore carried to the surface by shaft or a 13.2-kilometre conveyor belt. At peak, the underground and open pit mines are targeted to produce an average of around 500,000 tonnes per annum of copper, stated as recoverable metal, from 2028 to 2036, and Rio Tinto expects Oyu Tolgoi to be the fourth-largest copper mine in the world by 2030.

Oyu Tolgoi LLC is owned 66% by Rio Tinto and 34% by the Government of Mongolia through Erdenes Oyu Tolgoi, with Rio Tinto managing the operation on behalf of the owners. The operation employs around 17,000 people, 97.8% of whom are Mongolian, and Rio Tinto describes Oyu Tolgoi as the largest-ever foreign direct investment made in Mongolia.

Oyu Tolgoi LLC reported in its third-quarter 2026 performance results production of 113.5 thousand tonnes of copper and 123.6 thousand ounces of gold in concentrate, with copper production 10% above plan, driven by increased underground mine production and strong metal recovery performance at the concentrator. Panel 0 maintained stable production during the quarter while mining preparation and development activities advanced at Panel 2 North. The operator reported an injury frequency rate of 0.27 per 200,000 person-hours worked in the quarter, meeting its annual performance target. It also reported paying US$202 million in taxes, fees and other payments in the quarter and spending US$389.5 million on domestic procurement and suppliers, and said it has paid US$6.6 billion in taxes, fees and other payments since 2010, a total that includes VAT paid to Mongolian suppliers and a disputed US$880 million tax payment pending an international arbitration decision.

Rio Tinto reported on 14 October 2026 that Oyu Tolgoi’s copper production increased 27% year on year in the third quarter and 29% year to date; Chief Executive Simon Trott said the operation ran at an annualised rate of approximately 450 kt in the quarter. Rio Tinto’s consolidated copper production was 205 kt in the third quarter and 646 kt for the first nine months of 2026, with full-year copper guidance of 800 to 870 kt unchanged.

Earlier in 2026, Rio Tinto and the Government of Mongolia reached agreement on 30 June 2026 to adjust the shareholder loan interest rate for the Oyu Tolgoi project. Rio Tinto Copper Chief Executive Katie Jackson said at the time that the agreement, along with an agreement in principle on management fees reached in May, demonstrated Rio Tinto’s ongoing commitment to the long-term success of Oyu Tolgoi and its partnership with the Government of Mongolia. On 11 September 2026, the chief executive officers of Erdenes Oyu Tolgoi and Oyu Tolgoi signed an agreement amending the 2011 Oyu Tolgoi Shareholders’ Agreement to reduce shareholder loan interest rates and management fees, with loan interest rates to be renegotiated and reviewed every three years instead of every seven, according to Oyu Tolgoi LLC’s scorecard. The shareholders also agreed that Oyu Tolgoi will distribute dividends from 2027, and a working group has been established to determine the terms and conditions of distribution.