Tinkler’s stake in the miner, which owns the 610 million tonne Maules Creek open cut coal resource in New South Wales, is now believed to be reduced to $450 million.

Meanwhile, Gloucester Coal has reported that its institutional book build at $9.25 per share, which was announced as part of an acquisition of a share of the Queensland Middlemount project from the Noble Group, came in oversubscribed and raised $434 million.

Aston is believed to be selling its shares for $5.96 each, down from $8.20, and planning to sell 67.1 million shares compared with 48.8 million previously, to raise $400 million.

Noble Group is believed to be taking up a $58.8 million stake in the company while Itochu Corp’s Australian subsidiary will be investing $33 million.

A third cornerstone investor – believed to be European trader Glencore – is in negotiations to take another stake, but Tinkler is believed to want the company to remain independent.

Located about 18 kilometres northeast of the town of Boggabri, the Maules Creek project is targeting 13Mtpa of raw coal for at least 21 years of open cut mining, with development scheduled to start in the December quarter of 2011.

The coal reserves total about 240Mt while total resources are estimated to be 610Mt of thermal and semi-soft coking coal.

Aston will mine the reserves using excavators and shovels along with a fleet of haul trucks, dozers and graders.

The operation workforce is estimated to be 400 permanent employees.

To get the coal out, Aston is seeking government approval for the construction of a rail spur, rail loop and associated load-out facility to link up with the Werris Creek to Mungindi railway line.

Aston purchased the Maules Creek project from Rio Tinto subsidiary Coal & Allied for $480 million cash in November.