Mining giant BHP Billiton on Thursday asked South Australia state for a 46-month extension to the approval of its Olympic Dam project expansion, which was shelved last month on cost concerns. BHP, the world's largest miner, put its multibillion-dollar plans to expand the copper and uranium mine on the backburner after reporting a 35 percent slump in annual profit because of plunging commodity prices. The resources giant's approval from South Australia's government for the expansion expires in December and a BHP spokeswoman said it had written to Resources Minister Tom Koutsantonis about extending the deadline. "BHP Billiton has today formally applied for a 46-month extension to the indenture agreement negotiated with the state government for the Olympic Dam expansion and passed by the South Australian parliament last year," the spokeswoman said. When it shelved the project last month to pursue a less cost-intensive design BHP Billiton said it would take a "couple of years" at least to get the revamped Olympic Dam off the ground. BHP's existing underground mine at Olympic Dam is already Australia's largest and national Resources Minister Martin Ferguson has said the site had the potential to become one of the world's largest mines, if not the largest. The spokeswoman said the extension would give BHP time to complete the required feasibility studies and bring the SA permit in line with the approval period from the national government. Koutsantonis said "very careful consideration" would be given to the application -- including independent assessment of the new proposals. "I think a lot of South Australians were shaken to the core when BHP decided not to approve the expansion of the mine," he told ABC radio. "Ultimately now it's a conversation with BHP. I've received an initial letter, I'm going to require some more information. Obviously I'll be taking a lot of crown law advice." BHP reported a 35 percent plunge in annual profit to US$15.42 billion last month owing to falling commodity prices caused by a slowdown in key market China and the debt crisis in Europe. It is among a number of major miners that have scaled back, cancelled or closed projects in Australia because of the commodity downturn.