The upgrades, which cost $NZ25 million and took 14 months, were completed in December last year. Solid Energy communications manager Bryn Somerville said these upgrades have given the company access to more than 3 million tonnes of coking coal, which will mean a further four years of production at the mine.

He said the upgrades have secured the future of the mine, raising both the volume and quality of coal that can be produced at the mine.

Underground, 4km of roadways were created, and several equipment upgrades were made, including new pumping stations from Weir Minerals Australia, electrical equipment brought in from Ampcontrol in Newcastle and reflux classifiers from Ludowici Australia.

At the surface, the mine's washery was upgraded, something Somerville said has significantly improved the quality of the coal being produced.

"Up until the upgrade was completed the finer end of the coal was not able to be completely washed and that ended up with it having a higher ash content than made it useful," he said.

Solid Energy, along with joint venture partner Cargill, has already started on the second phase of the five-year plan, continuing a drilling program to prove up further resources for what it believes will be a 20-year mine licence.