Energy Resources of Australia Ltd. (ERA.AU) on Wednesday downgraded its annual uranium oxide production guidance for the second time this year and said the shortfall means it will have to cover some supply requirements with purchases.

The uranium miner said the fall in production volumes, caused by lower-than-expected ore grades, will adversely impact its 2010 full year earnings.

Output for the three months to Sept. 30 was 911 metric tons, down 35% from a year earlier but up 10% from the June quarter. "Mill head grade has improved compared with the June 2010 quarter but remains significantly below 2009 levels," ERA said in a statement.

ERA, 68%-owned by Rio Tinto Ltd. (RIO.AU), cut its annual production forecast to 3,900 tons, from previous guidance of 4,300-4,700 tons, meaning it will fall well short of supply requirements of 5,000 tons.

Selling purchased product is expected to adversely impact ERA's earnings because the small margin earned from selling purchased material is more than offset by operation costs, the company said.

-By Ross Kelly, Dow Jones Newswires; 61-2-8272-4692; Ross.Kelly@dowjones.com