Iron ore production at Fortescue Metals Group's Pilbara mines was off 15 per cent on the previous quarter because of delays and stoppages associated with cyclones in the region.
Fortescue mined 9.68 million tonnes of ore in the three months to March 31.
That was up 41 per cent from the previous corresponding period, but down 14 per cent from the three months to December 31, 2011.
The amount of ore shipped by Fortescue in the three months to March was 8.37 million tonnes, up 44 per cent on the previous corresponding period, and down 16 per cent on the December 2011 quarter.
Cyclones resulted in two separate closures of Port Hedland port in the period, delaying ship loading for about eight days, Fortescue said.
Mining operations were also impacted by heavy rain, which hampered production at Fortescue's main Cloudbreak mine for around two weeks.
The company said it expects to catch up on the delayed shipments, as it expects a ramp-up of its second shiploader and other port infrastructure in the coming months.
The extreme weather also caused a rise in production costs in the three months to March, but Fortescue said the increase in volumes in the current quarter would bring costs back into into its previous guidance range.
Fortescue shares were up 2.5 cents, or 0.4 per cent, at $5.595 at 8.50am.