RIO Tinto's local uranium subsidiary, Energy Resources of Australia, has narrowed its full-year production guidance and given some certainty by confirming an expected full-year loss would be limited to between $135 million and $155m.

In presentation slides filed with the Australian Securities Exchange yesterday, ERA said it expected to produce between 3500 and 3700 tonnes of uranium oxide this year, up from 2641 last year and slightly improved from previous guidance of 3400 to 3700 tonnes.

ERA's net loss after tax, which was $59m in the first half, was forecast to be between $135m and $155m, which was close to market expectations.

Credit Suisse was, before ERA's announcement yesterday, forecasting a $142m loss this year, followed by losses of $131m next year and $173m in 2014.

Despite the looming losses, ERA's shares ended 5c or 4.2 per cent higher at $1.25.

The company said mining of its Pit 3 at the Ranger uranium mine in Kakadu National Park would finish next month, with backfilling of 30 million tonnes of earth to start in December in the mine's rehabilitation process.

"ERA will be a stockpile miner in 2013, as the transition from open-pit mining to planning for an underground mine continues," the company said.

The backfilling will decrease Ranger's mineral resources, ERA said, adding that work to quantify the impact was in train.

ERA has 1.4 million tonnes of stockpiled ore containing 2300 tonnes of uranium waiting to go into its plant before the middle of next year. After that, it will use other stockpiled ore.

A long-awaited mining agreement with the Mirrar people, the traditional owners of Ranger, to mine the Ranger 3 Deeps underground mine was "close to finalisation", ERA said.

The miner, which is 68 per cent owned by Rio, expects production to slip to between 500 and 1500 tonnes in 2016, after which production would be dependent on Ranger 3 Deeps, economic conditions and studies on processing low-grade ore.

ERA is about to start a $120m tunnel designed to access 34,000 tonnes of uranium beneath the Ranger 3 open-cut. A $57m pre-feasibility study into the development of the project Ranger 3 Deeps is due to next year.