If approved, the Ravensworth "consolidation" project would create about 500 construction jobs over three years and secure employment for at least 550 mineworkers for another 29 years.

With Hunter coal selling for about $100 a tonne, the 20 million tonnes a year of coal the combined Ravensworth complex is predicted to produce would be worth about $2 billion.

It would help cement Xstrata's role as the Hunter's biggest coal producer, accounting for 29 per cent of Newcastle's coal exports, well ahead of Coal & Allied's 20 per cent.

In an environmental assessment on display with the NSW Department of Planning until March 29, Xstrata said "there are extensive socio-economic benefits at a regional, state and national level", including capital expenditure of $900 million.

The number of 7300-tonne trains leaving the Ravensworth complex is expected to rise from 20 a day to 26 a day, an increase of 30 per cent.

The assessment notes that the Ravensworth project would have "a substantial impact" environmentally, with more than 2840 hectares of vegetation, including 870 hectares of native forest, to be removed.

Using "biodiversity offsets", Xstrata proposes to balance the loss of 559 hectare of native vegetation with 722 hectares of "vegetation community offset".

One of the offset areas, "Hillcrest", north of Lake Liddell, includes 144 hectares of vulnerable dry gully rainforest.

Greenhouse gas emissions from the mine, including those from the combustion of the coal, would equal 0.046 per cent of global emissions.

With Newcastle's third coal loader starting operations this year, the coal export capacity could increase by nearly one-third, leading various coal companies to lodge expansion plans with the Government.

Some of these plans, including Xstrata's, involve amalgamating previously separate mines under a single, all-encompassing approval.

Some Ravensworth approvals expire next year and the 29-year approval would cover operations at the Ravensworth, Cumnock, Narama and Newpac mine sites.

As much as 16 million tonnes of coal a year would come from the combined Ravensworth open-cut and underground mine, with an expanded Ravensworth washery to handle another four million tonnes a year from Xstrata's Muswellbrook mine.