It is to buy $180M of additional shares in the Quebec-based smelter from the Canadian government company Investissement Quebec in early 2012.
The stake increase will double Marubeni's equity holdings in terms of aluminium output in the company to 76kt/y.
Its global equity holdings in aluminum production will thus rise to 200kt/y in 2016, from the current 160kt, putting it on par with Japan's top aluminium producer Mitsubishi Corp.
Aluminerie Alouette plans to raise its output capacity by 60% to 930kt in 2016 with investment cost of CA$2bn.
The smelter is 40%-owned by Rio Tinto Alcan of Canada and 20%-owned by Norway's Norsk Hydro. Its production capacity of 575kt/y makes it the largest aluminium smelter in the Americas.