Legislation has passed in South Australia paving the way for mining giant BHP Billiton's proposed expansion of its Olympic Dam project, which is expected to be the world's largest open-cut operation.

Located north of Adelaide, Olympic Dam is the world's fourth-largest copper and gold deposit and the largest known uranium deposit.

The $30 billion expansion project, for an open-pit copper, uranium and gold mine, has the potential to boost production from about 180,000 tons a year to 750,000 tons a year for decades.

The expansion was approved Tuesday in the South Australian Parliament on a 19-2 vote after more than 30 hours of debate.

Greens members of Parliament voted against the legislation aimed at ratifying amendments to the original indenture between the South Australian government and BHP Billiton, which facilitated the mining operations and processing at Olympic Dam, as well as the construction and operation of infrastructure.

"People will look back and say this was the moment that South Australia took its rightful place amongst larger mining jurisdictions and this is the time we'll see a massive influx of new explorers and miners into the state," said South Australian Mineral Resources Minister Tom Koutsantonis, The Australian newspaper reports.

Koutsantonis chided the Greens for attempting to scuttle the legislation by seeking to pass 27 amendments.

BHP had warned that $525 million of initial investment was at risk if the indenture legislation didn't pass the Parliament before the end of the year.

"The passage of this bill provides the company with greater certainty for what would be a significant investment and demonstrates South Australia's support for the project," Dean Dalla Valle, BHP Billiton Uranium president, said in a statement.

"It also allows us to activate pre-commitment funding, previously approved by the board, for the purchase of long-lead items such as trucks, infrastructure development and early site works for the first phase of the expansion project."

Dalla Valle said BHP Billiton needs to complete further studies on the project before seeking board approval next year for the first stage of the expansion.

"If approved, the Olympic Dam project will be an economic driver for South Australia over the next 40 years," he said.

Speaking at the company's annual meeting Nov. 17, BHP Billiton Chief Executive Officer Marius Kloppers said the first two phases of Olympic Dam are copper and gold projects.

"In due course we need to see whether we extract uranium but that is a separate decision, separate capital decision, separate returns," he said.