Prime Minister Julia Gillard is standing by Labor's mining tax even though it's raised only about six per cent of its full-year target and the opposition says it proves the treasurer is incompetent.

Treasurer Wayne Swan on Friday released the first details of the revenue raised by the minerals resource rent tax (MRRT), which the coalition and crossbench MPS have been seeking since late last year.

The 30 per cent impost on the super-profits of iron ore and coal miners generated just $126 million in its first six months - well down on the forecast $2 billion for the 2012/13 financial year.

The figure was released after the Australian Taxation Office finally satisfied itself that disclosing the revenue would not breach taxpayer confidentiality.

Mr Swan said the revenue of $126 million reflected the impact of global economic instability, the high Australian dollar and commodity price volatility.

"Revenues across the board are down very substantially - the MRRT is a profits-based tax that raises more revenue when profits are higher and less when they are lower," he told reporters in Brisbane.

Asked if the government would reach its $2 billion MRRT revenue forecast for the year, Mr Swan said there had been a partial recovery in commodity prices.

"We will have to see what happens in the next six months," he said.

Shadow treasurer Joe Hockey said Mr Swan was the "most incompetent treasurer in Australia's history".

"If Wayne Swan had any self-respect he would resign," he told reporters in Sydney.

As the Greens and independents demanded the government change the design of the tax to generate more revenue, Ms Gillard said she stood by its settings.

"The tax works as a profits-based tax and that is the appropriate design," she told reporters in New Zealand.

Ms Gillard said the resources sector was heading towards the peak of the investment phase before moving into a "production boom", which would lead to higher revenues.

However, Mr Hockey's attack was marred by a gaffe when he said that when the coalition axes the tax it will also scrap a related rise in the superannuation guarantee from nine to 12 per cent.

He said paying for such measures would create a "massive hole in the budget".

Mr Hockey later issued a statement saying the coalition was in fact committed to the increase in compulsory superannuation, but not other measures funded by MRRT.

Greens deputy leader Adam Bandt will introduce a bill in the lower house in Monday to stop state royalties being credited to miners who pay the MRRT.

"It's now clear that Labor's mining tax is a dud," he told reporters in Canberra.

His bill will be supported by independent MP Rob Oakeshott.

"If they (the government) are serious about the rhetoric of spreading the benefits of the boom, well, there is not much spreading going on in the current figures," he said.

The opposition also criticised a government-approved 5.6 per cent average rise in private health insurance premiums, which Mr Hockey said showed Labor was not addressing cost-of-living pressures.

Meanwhile, retiring minister Chris Evans hit out at colleagues who have been criticising the government.

"Just shut up," Senator Evans said in an ABC TV interview.