The Australia-listed Rio Tinto subsidiary said the completion of the transaction remained subject to customary closing conditions, including regulatory approvals.
Coal & Allied is expecting the deal to be completed in early 2010 and to notch up $340 million in after-tax profit.
Maules Creek has total coal resources of 398 million tonnes, but Coal & Allied managing director Bill Champion said it was never part of the company’s short or medium-term development plans.
Aston is the mining investment arm of the privately owned Tinkler Group, which is headed by Nathan Tinkler, a former Macarthur Coal investor and last year’s BRW young rich list frontrunner.
The project is 20km northeast of Boggabri.
Coal & Allied is 76% owned by Rio.
Shares in Coal & Allied were trading up almost 2% this morning at $77.