Whitehaven Coal (WHC) has cut its full-year production guidance to between 9.8 million tonnes and 10 million tonnes of saleable coal, compared with an earlier forecast of 10.7 million tonnes, after an operational issue at its Narrabri mine.
The miner also blamed previously disclosed geotechnical challenges at its Rocglen mine for the reduction.
Whitehaven said the costs of its recovery plan to fix the issue at Narrabri are not expected to be material and controls have been implemented to stop the event happening again.
Mining in the third longwall panel at Narrabri started in March with a different configuration to the first two longwall panels.
Two extra roof supports were added to the tailgate end of the longwall to improve safety and reduce costs, Whitehaven said.
But the floor horizon control at the tailgate end of the longwall face-line was lost, resulting in a difference between floor levels in the mine and causing management to stop production, the miner said.
Whitehaven implemented a recovery plan that at the time was not expected to affect production forecasts but changing conditions have led to a revision of the recovery plan timetable, which the company said would affect output.