Freeport-McMoRan Copper & Gold Inc said supervisory staff and volunteers are operating its Cerro Verde mine in Peru and production has not been hurt by a strike.

Production of copper and molybdenum concentrates have not been materially affected by the strike that began on Sept. 29, spokesman Eric Kinneberg told Reuters in an e-mail.

We will continue negotiating a new labor contract to replace the one that expired on Aug. 31, 2011, he said.

Talks last Friday failed to end a strike at the giant pit, which churns out 2 percent of the global copper supply.

Kinneberg said Cerro Verde is operating with supervisory and personnel that volunteered to work under strike conditions.

In what appeared to be a bid to pressure the U.S. company to reach a pact to raise pay for workers, Peru's government upheld a ruling that declared the strike legal. That gives the union the right to formally ask the government to establish a wage settlement that would end the walkout.