Opposition leader Tony Abbott sought on behalf of BHP Billiton (ASX: BHP) from Prime Minister Julia Gillard a written assurance that the mining tax would never be imposed on copper, gold and uranium.

These three commodities are vital to the planned Olympic Dam expansion which is currently under review because of economic uncertainty, low commodity prices and high cost of doing business in Australia. Mr Abbott promised to make the success of the Olympic Dam expansion a priority if the Coalition wins in the 2013 election.

The permanent exemption of the three commodities from the Minerals Resource Rent Tax is a prelude to the vow of Mr Abbott to scrap the mining and carbon taxes which the Gillard government is slated to collect beginning July 1.

He explained that going ahead with the Olympic Dam expansion would create thousands of jobs and add up to $7 billion a year to the gross domestic product of Southern Australia.

"I want to do everything I humanly can to help this expansion to go ahead by not having a carbon tax, not having a mining tax, and trying to ensure that we don't have bloated construction costs because of union militancy through the restoration of the Australian Building and Construction Commission," The Advertiser quoted Mr Abbott.

He attributed the hesitancy on the part of BHP to go ahead with the Olympic Dam project to worries about sovereign risk in which there is future danger of profit erosion due to expanded taxes or more new taxes. Mr Abbott warned that a re-elected Labor government will not limit the mining tax to just coal and iron.

"The only way to persuade the mining industry the tax will not be extended to other minerals is to abolish the bloody thing and that's what we'll do," Mr Abbott said.

He quoted BHP top officials that the expansion of the project is still hanging in the air. He cited a statement from BHP Chief Executive Marius Kloppers that due to several factors, including the carbon tax, it has become very costly to do business in Australia, and Chairman Jac Nasser who said the giant miner would no longer push through with $80 billion worth of investments in the Olympic Dam project.

However, BHP could face opposition from green groups over the Olympic Dam expansion project because of its impact on fish catch in the area. Whyalla News quoted an independent study commissioned by BHP which found a decline in local cuttlefish population by 78 per cent in the past decade.

In 2011, a record-low catch of 38,000 cuttlefish was made, significantly down from the 75,295 logged in 2008. While reasons for the decline are still unclear, there are concerns that the construction of a desalination plant as part of the Olympic Dam project would worsen the situation. The venture includes a desalination facility north of Whyalla to pump hypersaline brine into Spencer Gulf.

The state and federal governments required the dilution of waste water in sea water prior to discharge to be hiked beyond the 50 times increase proposed by BHP as part of the conditions for the desalination plant's approval in October 2011.

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