If the application is successful and permissions are obtained, Solid Energy would begin developing the Mount William North block in 2015.

Mt William North is one of several future resource blocks in the east of the Stockton area.

It is positioned north of the Cypress area, which is being prepared for mining.

Mt William North is expected to share the water treatment and other infrastructure requirements being developed ahead of mining at Cypress.

“Water management and treatment systems to support the development of Stockton’s eastern resource blocks are expected to complement work in the Mangatini Stream catchment,” Solid Energy general manager for environment Mark Pizey said.

Mining the Mt William block would increase the mine’s overall output by 500,000 tonnes per annum over the course of ten years.

Solid Energy said it needed to bring forward new coal resources, such as the Mt William North block, so it could continue to meet customer demands and produce at current levels for another 20 years.

The Stockton mine, located north of Westport, is currently the largest opencast mine in New Zealand.