An environmental impact study on the mine's expansion will be released on May 1 but will only be available for public consultation for two months.

The Opposition wants that extended to four months while Greens MP Mark Parnell has proposed three months and has the backing of the Conservation Council.

Opposition resources spokesman David Ridgway today said all South Australians needed adequate time to analyse the extensive detail of the Olympic Dam expansion.

"The Government has acknowledged that this study will be the largest ever produced in South Australia and as such the state Liberals believe it requires a longer period of time for public scrutiny," Mr Ridgway said.

"The breadth and size of this report will hamper the ability of many stakeholders to be able to analyse and develop detailed submissions in an eight-week period."

The Conservation Council said that if the expansion at Olympic Dam was to proceed it must encompass world's best practice, including the public consultation aspect.

"With this pitifully short period available for the community's consideration and feedback, the public are denied an opportunity to really examine and understand what is going on," said council chief executive Julie Pettett.

The planned expansion at Olympic Dam will lift annual copper production from 170,000 tonnes to about 730,000 and uranium oxide production from 4000 tonnes to 19,000.

It will also create the world's largest mining project and generate hundreds of new jobs.

Expanded production was originally expected to come on line in 2013 but industry analysts have suggested the project could be delayed by two years because of the global economic downturn.

Mr Parnell said if the delay was likely there was no reason to rush scrutiny of the project's environmental credentials.

"Giving the SA public more time to read the largest document ever printed in South Australia when it's released on May 1 will not delay the expansion project one single day," he said.

"There is absolutely no reason why the government shouldn't give the public a little longer."

The Greens have already introduced a bill to parliament's upper house to provide for a three-month consultation period.