* Oct 2016 deadline would align with federal approval expiry
* No guarantee a revised plan will be ready by 2016
MELBOURNE, Sept 26 (Reuters) - BHP Billiton has asked the South Australian state government to extend a December deadline to October 2016 for the company to approve an expansion of its Olympic Dam copper and uranium mine.
The top global miner scrapped a $20 billion-plus plan to expand the mine in August, saying its proposal to dig an open pit was too expensive and it was going to start from scratch to find a cheaper way to extract copper.
"Very careful consideration will now be given to the company's request and the reasons given for seeking an extension," Tom Koutsantonis, South Australian minister for mineral resources and energy, said in a statement.
BHP's decision last month was a blow to the state, which had been counting on the massive expansion to jumpstart the economy, and state leaders said they would play hardball in setting conditions for BHP if it did seek an extension.
The state imposed the December 2012 deadline for the company to approve the expansion last year, when the two sides signed a final agreement clearing the way for the project.
BHP said the extension was needed for it to complete studies on new processing technology and a less capital-intensive design for the open-pit expansion.
The new deadline would align the state's deadline with the October 2016 expiry of the federal government's environmental approval for the project.
The company gave no guarantee that a revised project plan would be completed within that timeframe, and has given no timeframe for deciding whether to go ahead with an expansion.
"We will continue to have discussions with the government in coming weeks," BHP said in an emailed statement.