CHILE'S state-run Codelco, the world's largest copper producer, said its union workers resumed output at two Chilean copper mines shuttered because of a strike.

El Teniente and Andina mines in central Chile are both working at 90 percent capacity, the company said in a statement on Saturday to Bloomberg News. Codelco's regular union employees had stopped going to work after striking contract workers attacked their union buses. The company had said work would resume when the unions' safety was guaranteed.

The walkout by contract workers demanding bonuses and benefits has lasted more than two weeks and caused almost US$100 million in losses, Codelco estimated. Contract workers' leaders were studying whether to accept a government proposal aimed at ending the strike, said Claudio Valenzuela, a spokesman for the Confederation of Copper Workers, which organized the walkout.

El Teniente and Andina produced 37 percent of Codelco's copper last year. The company's El Salvador mine, its smallest, is still shuttered because roadways to the mine remain blocked by protesters. El Teniente had been shut since last Tuesday, while Andina was closed when the strike began on April 16.

Francisco Pilu, a Codelco union leader at the Andina mine, denied that the mine was near full production. Miners from Andina's two largest unions still hadn't returned to work, he said.

Emilio Zarate, a leader of the Confederation, said hammering out the details of an accord with the government may last into early this week.

"It's complicated, but we think we can get through it," Zarate said.