BILLINGS, Mont. (AP) â¿¿ Mitsubishi Corp. of Japan will pay $95 million for a 25 percent interest in a Montana company's proposed copper and platinum mine in Canada. Stillwater Mining Co. of Billings says the partnership with Mitsubishi will help finance an open-pit mine near Marathon, Ontario. Mine development costs are estimated at $550 million to $650 million. The company projects initial annual production of about 200,000 ounces of platinum and palladium and 37 million pounds of copper. Mitsubishi has an option to purchase 100 percent of the mine's platinum metals. Stillwater operates the only platinum and palladium mines in the U.S. in south-central Montana. The metals are used in vehicle catalytic converters and for jewelry. Stillwater shares fell 4 percent to $12.25 in Thursday morning trading on the New York Stock Exchange.