In a unanimous decision, the Court of Appeal of the Supreme Court on Monday rejected the giant miner's bid to overturn a verdict in the NSW Land and Environment Court that found expected economic gains from expanding the mine insufficient to justify the environmental impacts.

Rio Tinto, though, says it will submit a new development application with “significant changes” to overcome the objections and secure the future of 1300 mine-related jobs.

These include compensating for endangered eco-systems cleared in the Warkworth Sands Woodlands with an offset of 1800 hectares of land about 100 kilometres away, spending $4 million over five years to expand the woodlands through regeneration, and buying adjacent properties likely to be hit with increased noise and coal dust.

But John Krey, vice-president of the Bulga Milbrodale Progress Association, said locals would reject Rio's changes.

“There's nothing that we can see that improves the project that they are proposing versus what's been rejected soundly by both courts,” Mr Krey said.

The offsets would not be like-for-like and the results of any woodland regeneration would not be known for years, well after remaining stands have been wiped out, he said. The purchase of adjacent properties would also undermine the 350-strong community. “The bottom line is that we don't have a village any more so what's the point?” Mr Krey said.

Delays

Rio said delays in the approval had already cost about 1 million tonnes of lost coal output this year, worth about $100 million. That loss was "putting even more pressure on the economics and viability of the mine", said Chris Salisbury, managing director of the company's Australian coal division.

Current approvals only allow the Mount Thorley Warkworth mine to maintain current output and jobs until the end of 2015, the company said.

While the company is conducting drilling programs to determine the feasibility of underground mining - which would potentially reduce the issues of noise, coal dust and habitat destruction – it would take years of studies and significant investment before it could begin.

“This is not a realistic option in place of ongoing open-cut operations to sustain the mine and its workforce,” the spokesman said.

Mr Krey said the concern is that Rio's extension plan will yet get government approval after the government amended the State Environment Planning Policy (SEPP) last September to place economic interests of new mines above other concerns.

"All this here (on Monday) and the 14-day hearings in the Land and Environment Court really will go for nought if this SEPP amendment stays in," he said.