The IPC determination allowed AusPac to proceed with an underground mine at Dartbrook using bord-and-pillar methods for three years.

"The determination … has taken many months and while the main elements of mining and transport were approved, it is disappointing the IPC did not approve the additional five years of mine life," Robinson said.

"The application was subject to significant support and scrutiny from the local community and we will endeavour to work closely with all stakeholders as we embark on the next phase for Dartbrook."

Robinson said the company would carefully review and consider the reasons for the decision and evaluate all available options.

The Dartbrook application came under heavy criticism by nearby landowners that included high profile horse stud owners.

Commissioners Zada Lipman, Ross Carter and Peter Cochrane were appointed to determine the application.

They met with AQC Dartbrook Management, the department, Muswellbrook and Upper Hunter Shire Councils, and toured the site and surrounding areas.

The panel also held a public meeting in Muswellbrook to hear community's concerns.

Those concerns included air, noise, visual and water impacts; greenhouse gas emissions and climate change; rehabilitation requirements; impacts on the local equine industry; and the cost benefit and viability of the project.