The company is seeking modifications to the approved domains 1 and 2 mining areas and to increase the maximum extraction width for all miniwalls beyond miniwall 2.

Mining at the colliery began in 1962 using bord and pillar methods until 2011, when the miniwall method of mining was introduced for secondary extraction activities.

The miniwall method is similar to the longwall method, where single slices of coal are progressively extracted along a face of coal but involves extraction over a narrower face width – typically less than 100m.

The miniwall method is preferable to the longwall method at the colliery due to the geotechnical, safety and subsidence management considerations, primarily because the mining takes place underneath Lake Macquarie.

The Chain Valley underground coal mine, acquired from Peabody Energy by well-established contractor LDO in 2009, received NSW government approval for its domains 1 and 2 continuation projects on January 23.

The approval allows the mine to continue until the end of 2016 for production of no more than 1.2 million tonnes per annum using bord and pillar along with miniwall extraction techniques.

However, the NSW Department of Planning and Infrastructure said the project was also considered to be a precursor to a further application to continue mining at Chain Valley for 21 years in total.