Grasberg, which had been slated to sell 1.4 million tonnes of copper contained in copper this year -- making it the world's number two mine -- ships much of its material to smelters in Asia and Europe where it is transformed into usable form.

"If this goes on, you will see the screws tightened again on spot concentrate terms," said analyst Rob Nachum of Australia-based Minalysis.

U.S.-Based Freeport McMoran Copper and Gold Inc which runs Grasberg through its P.T. Freeport Indonesia subsidiary has invoked a force majeure legal clause on deliveries from the mine, but continues to meet concentrate sales commitments from existing stockpiles, a company spokesman said on Thursday.

Industry estimates put thestockpile at between 160,000 and 190,000 tonnes.

Anglo-Australian miner Rio Tinto plc Ltd has a 12 percent stake in the Indonesian company.

Metals dealers said refined copper prices in terminal markets had failed to react to the strike due to high inventory levels in the U.S.

"People are still wary because there is a surplus of metal around," a dealer in Sydney said.

"There's plenty of copper in U.S. LME (London Metal Exchange) warehouses," the dealer noted.

In light midday trading in Australia, three-month copper was being quoted at $1,621-$1,626 a tonne versus a late kerb close of $1,628 on Thursday.

Freeport shuttered the mine after employees covered by a Freeport contract walked off the job over wages.