The complexity of expanding the refinery “has resulted in significantly lower levels of construction progress than previously anticipated, while broader inflationary pressures and the strengthening of the Australian dollar have also contributed to the cost increase,” Andrew Mackenzie, ceo of Melbourne-based BHP's non-ferrous unit, said.

The estimates include developing the Marradong mine, enlarging the refinery and connecting a multi-fuel cogeneration unit, BHP said in a statement. First production is now expected in the first three months of 2012. BHP has previously said Worsley was set for completion in H1 2011.

BHP approved the project in May 2008 at a cost of $US1.9bn to increase mining, boost refinery capacity by 31% to 4.6Mt and upgrade the port serving the site.

BHP owns 86% of Worsley, with the rest held by Japan Alumina Associates and Sojitz Alumina. The project produced 1.5Mt of alumina in the six months ended December 31.