Located in the Southern Highlands and under continuous production since 1926, the mine is a bord and pillar operation with capacity to produce up to 500,000tpa.

But the mine has been producing around 220,000tpa ROM, according to the preliminary environmental assessment lodged by consultancy EMGA Mitchell McLennan last year.

“Current production rates are below economic scale and an increase is required to improve the commercial viability of the colliery,” the consultancy said.

By slightly more than doubling production, the mine will continue supplying the long-associated Berrima cement works and other domestic customers, but could also lift its exports through Port Kembla.

The consultancy said supply to external customers would vary but was unlikely to exceed 240,000tpa.

After extracting the panels in its current mining area, extraction is expected to take place in panels located off main roadways to the northeast.

The mine employs around 38 people and is operated by contractor Delta Mining.

Mining at the site first started in 1872 when it was known as the Rockroof Colliery.

The village of Medway was developed in 1926 to service the mine, which was acquired by cement maker and construction materials producer Boral in 1988.

The exhibition period ends next month.

NSW mining projects have faced more assessment uncertainties since the O’Farrell government announced it would scrap Part 3A of the state’s planning laws.