Billiton PLC recently purchased another 56% stake in the Worsley, Australia, alumina refinery from U.S.-based majority owner Alcoa Inc. for $1.49 billion. Billiton said the purchase lifted its stake in the alumina refinery—one of the world’s most efficient—to 86%. It also announced a $750 million share offer to raise funds for the deal.

Alcoa is selling its controlling stake in Worsley as a result of its merger with Reynolds Metals Co. The deal came a week after Billiton, whose stock had risen sharply in August, agreed to buy the Canadian copper miner Rio Algom Ltd. for $1.15 billion.

Billiton said it gave its Japanese partners in Worsley an option to increase their stake while still leaving Billiton in control. Under the arrangement, Kobe Steel, Nissho Iwai and Itochu may increase their total holdings to 32% from 14% by buying part of Billiton’s stake at the same price Billiton paid Alcoa. Billiton’s finance director, Mick Davis, said the price it paid for Alcoa’s stake was equal to about $850 for each ton of production, well below the $1,000-a-ton it would cost to build an alumina refinery from scratch.