Rio Tinto Group, the world's second-largest iron ore exporter, narrowed full-year iron ore guidance as second-quarter volumes missed estimates because of rail maintenance and poor weather.

In its second quarter operations review, the mining giant lowered expectations about how much iron ore will be shipped this year, providing new iron ore shipments guidance for 2017 of "around 330 million tonnes (previously between 330 and 340 million tonnes)".

The average iron ore price has risen by 26.5 per cent with the price rising from $53.60 per dry metric tonne for 2016 to $67.80 per dry metric tonne for the first half of 2017. 

Rio Tinto chief executive Jean-Sebastian Jacques described the latest quarter as "a solid quarter for production," but added that iron ore shipments (down six per cent on the same quarter for 2016) were affected by rail maintenance work following poor weather earlier this year.

The update, released before the market opened on Tuesday morning, revealed a slight increase in Pilbara iron ore shipments compared to the first quarter of 2017 (up one per cent), an increase in Pilbara iron ore production compared to the first quarter (up three per cent), and a solid increase in bauxite production (up 14 per cent) compared to the first quarter of 2017.

But examination of the figures also revealed that both Pilbara iron ore shipments (down six per cent), and Pilbara iron ore production (down one per cent), were lower than for the second quarter of 2016.

In a statement, Jacques welcomed the results.

"This was a solid quarter for production, including record output at our bauxite operations. Iron ore production was in line with last year, although iron ore shipments were impacted by an acceleration in our rail maintenance programme following poor weather in the first quarter.

"We believe our focus on capital discipline, maximising cash flow from operations, driving productivity and portfolio shaping will continue to support the delivery of strong cash generation and shareholder returns," he said.

On bauxite, Rio said record quarterly production of 12.9 million tonnes had been achieved. This result "was seven per cent higher than the corresponding quarter of 2016, driven by strong production at Weipa and Gove. Third party shipments of 8.0 million tonnes were achieved in the second quarter."

Mined copper production recovered in the June quarter, up 48 per cent on the first quarter of the year, after production ramped up following a long-running labour strike earlier this year at the world's biggest copper mine, Escondida, in Chile.