China Molybdenum Co, the country's largest producer of the chemical element, has agreed to buy a copper mine in the Democratic Republic of Congo from Phoenix-based Freeport-McMoRan Inc for $2.65 billion, as the US firm reduces debt racked up in the commodities boom.

The deal involves taking over Freeport's indirect 56 percent stake in the Tenke Fungurume mine, which also produces cobalt, via a 70 percent interest in TF Holdings Ltd, Freeport said in statement on Monday.

The two companies have also agreed to negotiate the sale of its interests in other cobalt assets.

Freeport, which plunged 71 percent last year as commodity prices collapsed, has been seeking to offload assets and reduce a debt load that stood at $20 billion at the end of 2015.

Chief Executive Officer Richard Adkerson said last month he expected to sell more mines and the Tenke deal brings the total to more than $4 billion this year.

"This transaction is another significant step to strengthen our balance sheet and enhance value for shareholders," Adkerson said in the statement.

Tenke is one of Freeport's five so-called core mines, which also include Cerro Verde and Morenci, as well as El Abra in Chile and Grasberg in Indonesia.

Canada's Lundin Mining Corp owns 24 percent of Tenke, while Gecamines, the DRC's state-owned copper producer, holds 20 percent.

Lundin has yet to receive a notice from Freeport about the sale, Chief Executive Officer Paul Conibear said in response to questions.

It has the right to match any offer for Freeport's stake, and has 90 days after receiving notification to make the decision, he said.

As part of the Tenke sale, Freeport may get a further $120 million based on copper and cobalt prices. It has also agreed to negotiate exclusively with China Molybdenum on the sale of its interests in Freeport Cobalt, including the Kokkola Cobalt Refinery in Finland for $100 million and the Kisanfu Exploration project in the DRC for $50 million.

China Molybdenum last month agreed to pay $1.5 billion in cash for Anglo American Plc's niobium and phosphate unit in Brazil.