The announcement, made Wednesday, was made prior to environmental regulations that would have forced the facility to close next year.
About 276,000 tonnes of aluminum capacity had been scheduled to be removed when it was slated to close facilities in Shawinigan and Arvida, Que., by the end of 2014. That will be offset by the addition of 60,000 tonnes with the impending opening of a facility using AP60 technology.
It said that it will immediately be cutting 50,000 tonnes of aluminium production, with another 50,000 tonnes at the end of November.
Rio Tinto and rival Alcoa have been looking to curtail the rising cost of aluminum production as it adjusts to low metal prices.
Rio Tinto Alcan suspended two lines of production at its 100,000-tonne Shawinigan smelter after a major power outage at the end of 2011 forced the closure of two of the plant's four production lines. The process of gradually restarting the 280 cells that were shut down was completed in the second quarter of 2012.
Commissioned in 1941, the smelter uses Soderberg technology, which is to be phased out of all Quebec primary aluminium smelters by Dec. 31, 2014