Rio Tinto Alcan's aluminium production was nine per cent lower in 2012 compared with the previous year, and fourth quarter production was two per cent down, largely due to the impact of industrial action at one of its Canadian smelters, the company said.
Rio Tinto Alcan, the majority owner of the Tiwai Point aluminium smelter, said in its quarterly operations review that the ramp up of production at its Alma plant, in Quebec, was continuing after an agreement was reached with unions last July after a six-month dispute.
About 800 workers had been locked out of the plant since January 2012.
The Alma plant in Quebec's Saguenay region, about 225 km north of Quebec City, is one of Rio Tinto Alcan's most important aluminium smelters in North America, producing 438,000 tonnes annually. The lockout resulted in a one-third cut in production at the smelter.
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New Zealand Aluminium Smelters Limited (NZAS), which operates the Tiwai Point aluminium smelter near Bluff, is 79.36 per cent owned by Rio Tinto Alcan and 20.64 per cent owned by Japan's Sumitomo Chemical Co.
Rio Tinto Alcan is in the process of bundling Tiwai with 12 other smelter assets for sale under the new name, Pacific Aluminium.
The parent company Rio Tinto, one of the world's biggest miners, said 2012 was a strong year across the group.
"We achieved record annual iron ore production and shipments as our expansion programme continues on schedule, delivering industry leading returns for our shareholders," Rio Tinto chief executive Tom Albanese said in the review.
Rio Tinto's copper, bauxite, alumina, thermal coal and titanium dioxide businesses all delivered substantial production increases on 2011 levels, Albanese said. The company is listed on the London and Australian stock exchanges.