ENERGY Resources of Australia today slightly upgraded its annual production guidance, based on an earlier start to mining at its Ranger pit, which had been affected by heavy rainfall.

The Rio Tinto-controlled uranium miner said it expected to produce between 3200 and 3700 tonnes of uranium oxide in 2012, compared with a 3000-3700 tonne range issued previously.

In the three months to March 31, ERA produced 612 tonnes, up from 518 tonnes in the previous corresponding period, when operations were also hampered by rainfall.

"While there was significantly above-average rainfall at the Ranger mine during the March 2011 quarter, mining operations were able to continue in the upper benches of the pit," the company said.