Rio Tinto has reiterated full-year shipment guidance of 330 million tonnes from its Pilbara iron ore operations after lifting production by 6 per cent in the third quarter.
That was also more than the 84.6 million tonnes that UBS had forecast.
Quarterly bauxite production was 12.9 million tonnes for a second consecutive quarter, four per cent higher than the third quarter of 2016, driven by strong performances at Gove and Weipa.
The company said it continues to expect production of refined copper for the year to be between 185,000 and 225,000 tons, although that was subject to the outcome of an investigation into a fatal accident at Kennecott in early May.
But rail disruption and bad weather ensure the miner had a weak start to the year, and Rio was forced to downgrade that guidance to "around 330 million tonnes".
In a rare occurrence after years of production and export growth, Rio has mined less iron ore in the first nine months of 2017 than in the first nine months of 2016, and exports are only marginally higher.
The remainder was sold either on current quarter average, current month average or on the spot market.
It is the second time this year that Rio has downgraded copper guidance, and the new target is well below original forecasts that the company could produce as much as 665,000 tonnes of the red metal this year.
The bulk commodity was fetching $US62.94 per tonne on Tuesday morning.
The Anglo-Australian giant blamed lower copper head grades at the Rio Tinto Kennecott mine in the U.S. and its Oyu Tolgoi copper-gold operation in Mongolia for the miss.
Rio's initial guidance was 500,000-550,000 tonnes of copper for the full year.
Those forecasts were made before a seven week strike at the Escondida copper mine in Chile.
Rio produced 120,600 tonnes of copper in the September quarter, which is lower than expected and just as copper prices hit three-year highs. Bauxite production guidance is revised to between 50 and 51 million tonnes (previously 48 to 50 million tonnes).
Rio shares were up 26¢, or 0.37 per cent, at $70.81 at 7.55am.
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