Codelco chairman Maximo Pacheco has called the type of collapse that killed six miners at Chile’s El Teniente mine on 31 July “a new phenomenon”.
Speaking on a panel at the FT Live Metals and Mining Summit today (10 October), Pacheco said the rock burst that caused the death of six miners “overwhelmed” the mine fortification, “with tremendously painful consequences”.
Sharing preliminary investigation findings on the El Teniente tragedy, Pacheco said that “the most probable cause of the rock burst, as precisely stated in the preliminary investigation, was a process of vertical unloading due to geometric changes and cavity interaction in the north-west of the deposit”.
Put simply, this means that the disaster occurred due to changes in terrain that impacted how material was supported in the deposit. Codelco currently has eight mines at the deposit (seven underground and one open pit) and three more underground areas currently under construction, all interconnected by 4,500km of tunnels. Over time, cavities have developed and connected, weakening the structure and enabling the downward movement of material.
Of the earthquake that caused the collapse, Pacheco explained that there were two main epicentres. The first was in Andesita, where one worker died. The second occurred on the seventh level in Teniente (in the northern part of the mine) where five other workers were trapped and subsequently died.
Pacheco explained that the mine was designed for events up to magnitudes of 1.5, but the El Teniente earthquake measured 4.3. Attendees at the summit were told that the investigation had examined seismic records and found no observable movements of lesser magnitude ahead of the actual event. If the final investigation findings support this, Codelco will ascertain that there were no missed warnings.
The company also maintains that from the first moment of seismic activity at 5:34pm on 31 July 2025, emergency activation and management protocols were correctly handled, which allowed the safe evacuation of approximately 2,500 workers.
Pacheco told delegates that while rock bursts will always be an inherent danger for mining operations, the investigation into the disaster will make mining at the deposit safer.
“The investigative team presented preliminary actions, deeper terrain studies, new rock mass preparation techniques, improved support design and installation, mechanisation, enhanced deep monitoring, updated numerical models, experimental failure simulations and a global long-term monitoring plan,” he said.
Pacheco concluded: “Our commitment is clear. We owe it to turn this pain into improvements that protect life and strengthen underground mining in our country and the world.”
The Codelco chairman is no stranger to disasters at the El Teniente mine. He was the chief operating officer in 1990, when six miners were also killed.
“The tragedy forced us to raise standards,” he said of that incident. “We brought it to international experts, innovated with new certification and microcystic monitoring technologies and advanced our intelligent mining with remote operation.”
