LONDON (Reuters) - Codelco's copper losses from the accident at its El Teniente mine are likely to be 45% higher than previously estimated, but Chairman Maximo Pacheco still expects the world's largest copper miner to slightly increase output this year.

Loss of output from Chile's El Teniente along with other disruptions including at Freeport-McMoRan's ( FCX ) Grasberg mine in Indonesia has tightened supplies and pushed copper prices to $11,000 a metric ton this week, close to the record hit last year.

The July accident at El Teniente, Codelco's most profitable mine, will reduce its output by 48,000 metric tons this year and cost the company around $500 million in EBITDA.

In an interview ahead of LME Week, a gathering of the global metal industry in London, Pacheco said Codelco's production from January to September was 2% above the same period of last year.

"We continue to believe that in 2025, we should have a production level that is slightly above last year's," he said.

The state-owned miner's copper output for the first nine months of the year was 938,000 tons while Codelco's guidance for 2025 is 1.34 million-1.37 million tons.

ROCK BURST

On the internal investigation into the El Teniente accident, due to be finalised by the end of the year, the most probable cause was a rock burst due to a change in the geological structure of the deposit, according to Pacheco.

"This was a process of vertical unloading due to geometric changes and cavity interaction in the northwest of the deposit...weakening the structure and facilitating downward movement of material. This means at depth, rock layers are shifting over one another," Pacheco said.

That, he added, means Codelco needs to monitor terrain structure, seismic activity and geomechanical factors throughout the entire mine, which is made up of 4,500 kilometers of tunnels.

The Andesita unit within the El Teniente complex will remain suspended until the investigation is complete.

ENVIRONMENTAL PERMITS

Codelco plans to apply for environmental permits by 2027 for the joint operation of its Andina mine and Anglo American's neighboring Los Bronces operation, Pacheco said. The companies finalised their agreement last month, saying it will produce $5 billion in savings.

Pacheco also said Codelco will contribute to discussions on the future of Teck Resources Quebrada Blanca mine in Chile, where it holds a 10% stake and has two seats on the mine's board.

Teck is aiming to combine Quebrada Blanca with the adjacent Collahuasi mine as part of a proposed merger with Anglo American.