In the fourth round of metal auctions this year, the administration will sell off 30,000 tonnes of copper, 50,000 tonnes of zinc and 70,000 tonnes of aluminum.

Unifor, which represents about 900 workers at the miner's aluminum smelting plant in Kitimat and power generating facility in Kemano, had started a strike action in July.

China is in the grip of a power crunch as a shortage of coal supplies, toughening emissions standards and strong demand from manufacturers and industry have pushed coal prices to record highs.

After six years of lying idle, the Alumar aluminum smelter in Brazil is about to restart operations.

Alumar, fully curtailed since 2015, is set to produce its first molten metal in the second quarter of next year.

This year, curbs on smelter output and electricity usage in several regions have sharply cut domestic aluminum supply in China.

The coup exacerbated concerns about supply constraints that have pushed aluminum prices to the highest level in 13 years.