Nippon Mining Holdings Inc., Japan's biggest copper producer, plans to raise as much as 75.6 billion yen ($650 million) for capital spending by selling new shares.

Nippon Mining plans to sell 70 million new shares to the public and 10 million new shares to Nikko Citigroup Ltd., it said in a statement filed today with the Tokyo Stock Exchange. The sale would increase the Tokyo-based company's shares outstanding by 9.4 percent, it said.

Proceeds from the sale will pay for the upgrade of an oil refinery and expansion of the company's smelting operations. Nippon Mining will invest 11 billion yen at its copper refining plant in Oita, southern Japan, and 14 billion yen at its refinery in Mizushima, central Japan.

Nippon Mining's oil refining unit, Japan Energy Corp., generates about 80 percent of its revenue.