CALGARY -- TransAlta Corp. says it will end mining operations at its Highvale coal mine by the end of 2021 and will stop using coal to power its generators in Canada effective Jan. 1, 2022.

The company says its Keephills Unit 1 and Sundance Unit 4 will stop using coal and will only operate on gas.

TransAlta chief executive Dawn Farrell says the closing will come four years ahead of its original off-coal schedule for the mine.

The announcement came as TransAlta reported a loss attributable to common shareholders of $136 million or 50 cents per diluted share for the quarter ended Sept. 30 compared with a profit of $51 million or 18 cents per diluted share in the same quarter a year earlier.

Revenue for the quarter totalled $514 million, down from $593 million in the same quarter last year.

TransAlta has electrical power generation assets in Canada, the United States and Australia.