Even before the culmination of its inquiry on the proposed mineral resource rent tax, the chair of the Senate Select Committee on the Scrutiny of New Taxes is convinced that the planned measure is detrimental to the Australian economy.

Liberal Senator Mathias Cormann of Western Australia said on Monday that the MRRT would negatively job and investment prospects in the mining industry especially in the Pilbara region of WA.

Senator Cormann also lamented that some committee members who are investigating the proposed MRRT were lacking in knowledge as he argued that sufficient know-how should come handy in the task of assessing the new tax measure.

The WA Senator specified that his colleagues from the eastern states need to brush up their knowledge on the MRRT as he revealed lawmakers sitting on the committee he chairs seemed split on the issue, with some members supportive of the measure while others were dismissive.

Meanwhile, Fortescue Metals Group top honcho Andrew Forrest re-echoed his opposition on the federal-sponsored mining tax as he stressed before Senator Cormann's committee that the proposed measure was simply unconstitutional.

Mr Forrest has been one the mining tax's harshest critics, voicing out his opposition on the measure even before its earlier form as the resource super profits tax, and is confident that an Australian court would reaffirm his views.

Simply put the MRRT, according to Mr Forrest, was discriminatory against iron ore and coal productions and snatch the responsibility of the mining resources from host states, rendering them less enthusiastic in encouraging the further development of their area's resources industry due largely to the lower royalty rates.

Even Fortescue Metals was forced to shelve its WA mining projects as the company cited of uncertainties due to the controversial mining tax though following the election and the establishment of a minority government, Mr Forrest steered FMG through $17 billion worth of expansion projects in the Solomon Hub and the Western Hub.

Barring any delays, the Senate Select Committee is expected to wrap up its investigation on the mining tax as well as the equally sticky carbon tax by the end of November, with its report set to be released immediately afterwards.