The southern miniwall panel, MW9, will be 93m wide and 1500m long.
“The miniwall section would leave a wide pillar of coal in place to reduce subsidence impacts on Bowmans Creek and its alluvium,” Ashton Coal Operations said in its assessment report.
Longwall panel 9 starts up a further 50m north of the creek’s alluvial boundary and will be 141m wide and 1250m long.
The combined longwall and miniwall extraction is estimated to yield 1.25 million tonnes of raw coal from the Pikes Gully seam.
ACO also successfully applied to boost its total approved production to 5.45Mt per annum.
To ensure approval for its new panels, the change point from miniwall to longwall mining was moved 50m north.
Vertical subsidence on Bowmans Creek is expected to be about 0.2m.
The company said this level of subsidence was considered unlikely to cause connective cracking of the alluvium, thus avoiding an impact on the water source.
The maximum vertical subsidence of up to 1.2m is expected to occur in LW9, affecting land owned by Macquarie Generation, including its access road, sedimentation ponds and Brunkers Lane.
With Xstrata planning to use Brunkers Lane for a proposed relocation of Lemington Road in respect to proposals for its Ravensworth mine, ACO will make agreements with the two parties for mitigation measures.
But with Xstrata, the company only intends to accept responsibility for the lane as it exists and not if it is upgraded for an expanded purpose.
As part of the approval requirements, ACO will prepare subsidence management plans before kicking off the new panels, which include a minimum of two years of baseline data.
Main headings to access the new panels will be developed as an extension of the approved headings for the nearby LW1 and MW8 panels.
ACO is a subsidiary of Felix Resources, which was formally acquired by Yanzhou Coal Mining in January.
The operation is seeking separate federal government clearance to kick off another open cut and to lift the complex’s peak production to 8.6Mtpa of run-of-mine coal.
The open cut and longwall thermal coal mine produces more than 5Mtpa of ROM coal, with Ashton’s underground operations reaching 2.81Mt in 2009.