Xstrata chief executive officer Mick Davis said the Australian government's proposed tax measure is the "biggest assault" in the mining industry.

"I am troubled both at the magnitude of the tax impact on mining companies in Australia but also its retroactive nature and the total absence of consultation in the run-up to the announcement," Davis said.

Earlier this week, Xstrata has announced it had decided to suspend its exploration activities in north Queensland.

The proposed super-profits tax scheme continues to suffer backlash as mining executives and other stakeholders have expressed their opposition against it, with global mining firms reacting negatively against it.

BHP Billiton chief executive Marius Kloppers stressed that while he was not opposiing to the tax in principle, it should apply to future investment decisions and not to existing projects. Further, Kloppers expressed concern that it would be difficult to approve new projects until the tax issue has been resolved.

US coal giant Peabody Energy reduced its offer to buy Macarthur Coal by $300 million, citing possible impact of super-profits tax on Macarthur's operation. Macarthur Coal executives reacted "coolly" on the bid and advised shareholders not to make any decisions.

The planned super-profits tax, if implemented, would raise the effective corporate tax rate from July 1, 2012 to about 40 per cent, scrapping about $9 billion from the industry. Mining executives said such amount of tax will definitely affect the operations and cash flow of their companies. Federal treasurer Wayne Swan had urged mining companies to support the government plan, instead of "putting guns" on national interest.