BHP Billiton Ltd. (BHP) said Tuesday an environmental assessment to continue mining at the Illawarra coking coal operation in New South Wales state for the next 30 years has passed government adequacy assessment, which will see output rise to 10.5 million metric tons from 7.5 million tons.

The Melbourne-based company has been mining in the area for the past 50 years. The environmental assessment addresses requirements for ongoing operation of the underground Bulli Seam mines, and will be open for public exhibition until Dec. 2.

A government decision is expected mid-next year. BHP didn't disclose a capital expenditure projection, but analysts estimated the cost of the project to be around US$310 million.

-By Elisabeth Behrmann, Dow Jones Newswires;

61-2-8272-4689 elisabeth.behrmann@dowjones.com