Production has been hit at the massive Grasberg mine in Indonesia's Papua province as more than 9,000 workers stage an extended strike.
The mine's owner, Freeport McMoRan, also says a "large number" of the absentee workers are deemed to have resigned.
Meanwhile, the striking miners, angry at the American company's decision to lay off thousands of workers, have agreed to extend their industrial action for a second month.
Freeport deems the strike illegal, and had followed through on a threat to take disciplinary action against absenteeism, considering staff who are absent for more than five days to have resigned.
A Freeport spokesperson told Reuters it was trying to mitigate the strike's effect on mining and milling rates, which it did not quantify, by re-allocating resources and training additional workers.
The strike was a further disruption for Freeport, which had lost hundreds of millions of dollars in a protracted dispute with the Indonesian government over new mining laws.
Copper concentrate exports had only resumed late last month, when the strike began.