Greens leader Bob Brown warned today that any agreement on the RSPT reached behind closed doors could be amended in the Senate.

Senator Brown expected a "cave-in" by the Gillard government to the mining industry as he commented to news that Rio Tinto boss Sam Walsh has demanded an unbreakable guarantee from Julia Gillard that any deal struck will remain intact after the federal elections.

"There's a small thing called democracy here, and a big thing called the Australian parliament," Senator Brown said.

"Unless Labor gets control of both houses, and that's not going to happen, the agreement will be subject to parliamentary scrutiny."

He said the ability of the Greens to enhance such a package had been "established" in talks over the government's economic stimulus package last year.

"We saved the country from recession in the process," he said.
Senator Brown, who wants part of the approximated $12 billion gain from the tax paid into an infrastructure fund, said the focus of the Greens "is to see the Australian public gets a dividend out of this, not just the mining barons".

"We've got an eye on the key factor, which is the $12 billion in the forward estimates that's going to come from this tax," he said.

"We don't want to see that $12 billion reduced. Each billion that goes back to the mining industry, and will in substantial part flow overseas, is a billion that has to be made up for in some other way, against the public interest."

Senator Brown criticized the secrecy with which negotiations over the RSPT are being conducted.

"Which other sector of the Australian community expects to have such a monumentally important tax item negotiated so rigidly behind closed doors?" he said.

According to the Green leader, the future shape of the tax, and the Coalition's stated intention to reject it, made it crucial for the Greens to maintain the balance of power in the senate after the election.

"If we get a Gillard government and an Abbott-controlled senate, we get gridlock," he said.

"But the Coalition's 'no' under any circumstances will melt if the mining industry is happy with the outcome. That gives the mining industry, through the Coalition, the balance of power in the senate."