Mining giant Rio Tinto said production of copper and iron ore fell in the first quarter of 2012 compared with the final three months of last year.
The company's shares that are traded on the Australia Stock Exchange fell 1% overnight on the news that bad weather had hit production.
Three tropical cyclones during the quarter resulted in the temporary shutdown of port operations at its Pilbara site in Western Australia.
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However, the company was keen to stress that production was up when compared with the first three months of 2011.
"We had a solid first quarter with increased production of iron ore, coal, bauxite, alumina and titanium dioxide compared with the first quarter of 2011," said Chief Executive Tom Albanese.
"This was driven by a combination of our consistently high operating performance and reduced impact from severe weather than in 2011."
Rio reported its share of iron ore production from mines it owns and those it operates through joint ventures dropped 11% to 45.6m tonnes in the quarter, compared to 51.2m tonnes in the previous quarter.
Analysts had pencilled in a drop, but only to 50m tonnes.
Mined copper output fell 13% to 119,500 tonnes against analysts' forecasts of 140,000 tonnes-plus.
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