The company will be responsible for funding its share of operating, capital and exploration expenditures on the Marathon properties.
Under a related supply agreement, Mitsubishi will also have an option to purchase up to 100% of the PGM production.
Stillwater Mining chairman and chief executive officer Frank McAllister said the company has recognised the critical need to grow and diversify its production, which at present is limited to its PGM operations along the J-M Reef in Montana.
“Mitsubishi’s participation adds greater certainty to Marathon in return for part-ownership in the project, a project which is now expected to see Stillwater‘s future PGM production increase 30% and add a portfolio-diversifying component of copper. Mitsubishi’s relationship with project-financing sources, particularly in Japan, should also greatly benefit the project economics,” said McAllister.
Stillwater Mining has invested a total of $159m in the Marathon PGM and copper project, and is expected to receive a $40m gain on the transaction.
The Marathon deposit is located about 10km north of the town of Marathon, Ontario, near the north shore of Lake Superior.
The advanced-stage PGM/copper development project, which was acquired in November 2010, is currently in the environmental assessment and permitting stage.
The mine may produce about 200,000oz of PGMs (mostly palladium), and 37 million pounds of copper annually, over a mine life of about 11.5 years.