Rio Tinto Begins Phased Restart of Mongolia's Oyu Tolgoi Mine After Seismic Rockfall

Rio Tinto said on Friday, October 30, that underground mining operations at its Oyu Tolgoi copper project in Mongolia were beginning a phased restart after safety assessments following a seismic event the previous day. The disruption affected one of the major sources of future copper supply as the company continues expanding underground production.

The seismic activity occurred along a rock fault zone at about 18:00 local time on October 29. Ground vibration and a localised rockfall prompted the suspension of underground work while the operator examined the affected area. Rio Tinto reported three injuries and no fatalities. Two workers continued receiving treatment for injuries described as not life-threatening, according to subsequent accounts of the operator's update.

The company and its local operator reported that the rockfall was confined to a temporary storage area next to the production zone, and preliminary checks found no structural damage to the underground cave or its operating infrastructure. The decision to restart work follows a staged safety assessment; it does not mean that all underground operations returned immediately to normal output.

Oyu Tolgoi is a large copper and gold operation in the Gobi Desert. Rio Tinto owns 66% of the project and Mongolia's government holds 34%. Underground production is important to Rio Tinto's longer-term copper expansion plans, while the government has an economic stake in the project's performance.

The safety-related interruption is separate from logistical problems affecting shipments of copper concentrate to China. Delays at the Ganqimaodu border crossing have reduced the number of available trucks and constrained outbound deliveries. A mine restart does not, by itself, resolve those transport restrictions.

The company has not yet provided a quantified estimate of lost underground production attributable to the temporary suspension. The eventual operational effect will depend on the pace of the restart, the results of continuing safety checks and the duration of cross-border transport delays. The distinction between the short-term underground pause and the continuing export bottleneck is important when assessing the mine's production and sales outlook.