Miner Rio Tinto (LON:RIO) reported a dip in copper output and reduced guidance for the industrial metal, confounding hopes that demand was picking up.
RIo said mined copper production in the third quarter fell 24% to 115,000 tonnes against the same period a year ago.
This year, Rio expects its share of mined copper production to total about 510 thousand tonnes, versus between 500 and 535 thousand tonnes previously.
But global iron ore production lifted 12% to 86.1 million tonnes in the quarter against a year earlier.
The rise in ore production came despite calls for Rio to further reduce output to help boost ore prices.
Commentators said the miner's move in July to cut its 2015 export forecast by 10mln metric tonnes was unlikely to make much of a dent in a current supply glut.
The miner has faced criticism that it is using its market muscle to keep turning out ore at relatively low prices, hitting competitors.
Accendo Markets analyst Mike van Dulken said a cut to copper production guidance towards the lower end of the prior range would help limit supply and keep the price of the red metal off six-year lows.
But he added that given the Chinese economic slowdown, only major production cuts or a big pick-up in global economic growth were likely to help copper prices break above September highs and push Rio shares above July and August resistance levels of around 2600p.
Brokers were upbeat on Rio's figures despite the news about copper, voicing satisfaction that they were in line with expectations.
Numis Securities said the production figures met expectations. It said in a note: "In all a solid performance from Rio with all divisions on track to make guidance."
Deutsche Bank said : "Rio remains our top sector pick on valuation, growth, cash flow and strong balance sheet."
Shares in Rio increased 11p to 2524p