The fate of the biggest coal mine expansion project in Australia lies in the hands of the NSW Independent Planning Commission, after state planners declined to recommend approval.

Global coal giants Glencore and Yancoal are seeking approval for the massive expansion of the Hunter Valley open pit coal mining operations near Singleton in the NSW Hunter Valley and want to extract an extra 429 million tonnes of thermal coal, resulting in more than 800 million tonnes of Co2 emissions once burned.

The mines had been due to close, but were granted an 18-month extension to December this year while their application was considered.

The developers have refined their plans, reducing the proposed amount of coal to be mined by more than 200 million tonnes, and will now avoid high gas areas.

These revised plans still attracted 83 opposing submissions – forcing the project to be automatically referred to the IPC under state rules (any project with more than 50 opponents) – although 1,097 submissions were filed in support, many from employees, contractors and local businesses that benefit from the existing mining operations.