Freeport-McMoRan Inc. has agreed to sell 13 percent of its stake in an Arizona copper mine to Sumitomo Metal Mining Co. Ltd. for $1 billion.

The deal accelerates Freeport-McMoRan’s efforts to reduce its debt, said Richard C. Adkerson, president and chief executive officer.

Freeport expects a gain of $550 million on the sale. The company is the world’s largest publicly traded copper producer, and like other commodities firms has been hit hard by the collapse in prices.

Freeport-McMoRan now owns 85 percent of the open-pit mine, known as the Morenci unincorporated joint venture. The company’s share of the mine’s 2015 production was around 900 million pounds of copper and $2.2 billion in revenue. Sumitomo Metal Mining Arizona Inc. owns 15 percent of the mine, which has estimated recoverable reserves of 12 billion pounds of copper.

The sale will leave Freeport, which moved from New Orleans to Phoenix following a 2007 merger, with 72 percent of the mine. An affiliate of Sumitomo Metal Mining Co., which has not been named yet, will own the 13 percent Freeport is selling.