Reaching 11 million tonnes in the three months to the end of June, exports of iron ore by Fortescue Metals Group (ASX:FMG) climbed 36 per cent from the equivalent period last year.

According to the Western Australian miner, it shipped 11.04 million tonnes of ore in the June quarter of 2010, while the volume of ore mined climbed to 11.4 million tonnes, 28 per cent higher than in the corresponding period a year earlier.

"Fortescue shipments hit a run rate of around 43 million tonnes per annum (Mtpa),'' the company told the stock exchange.

The miner said port infrastructure showed capacity of just below 51 Mtpa for June, and the Christmas Creek expansion was on schedule.

Its cash had reached $US1.24 billion ($A1.4 billion) at the end of June.

Fortescue had outperformed its operating capacity projection of 40 million tonnes, thanks to higher iron ore prices, no maintenance activities and a determined management team, according to the company.

The miner, however, warned two major maintenance shutdowns were set in the September quarter.

"Mining will continue at Cloudbreak and Christmas Creek during these shutdowns.''

"Management is targeting a quarterly result of between nine to 10 million tonnes, however, all efforts will be made to bring actual production in at the higher end of this range,'' the company said.

Fortescue had taken several strategies as a result of high prices in the June quarter to maximise tonnes produced and exported, leading to costs of about $US32.25 per tonne, up from previous guidance of $US30 per tonne.

There was strong demand for its iron ore, with an average price of about $US130 ($A146.99) per dry tonne delivered to China, according to the company.

"This substantial increase in selling price over the quarter has bolstered revenues,'' Fortescue said.

Studies for growth from 55Mtpa to 95Mtpa have well progressed with confirmation of the miner plan now the primary focus.

Fortescue shares were trading down eight cents, or 1.83 per cent, at $4.30, at 12.24pm today.