Swiss mining giant Glencore has failed to lodge an appeal over the Independent Planning Commission's rejection of its proposed Glendell extension project.

The IPC ruled in late October that the project would have "significant, irreversible and unjustified impacts on the historic heritage values of the Ravensworth Homestead complex"

The homestead, which is made up of colonial buildings and gardens in the middle of the proposed mine site, has cultural and historic significance dating back to 1825.

Colonial records show a series of attacks and counter-attacks between Aboriginal people and settlers at the homestead and the adjoining Lethbridge Estate.

Tensions between the groups culminated in late 1826 when, with the endorsement of Governor Darling who sought revenge for the murder of two settlers and destruction of crops, a posse of mounted police and settlers hunted down and massacred a group 18 Aboriginal people.

Historians are divided on the exact location of the massacre. Glencore disputes that a massacre occurred on the site of the proposed mine extension.

The influential Heritage Council, which acts as a government advisory body, opposed a proposal by Glencore to relocate the homestead to a nearby farm.

The IPC agreed saying that moving the house "would constitute a significant loss to future generations" - arguing the site "is not suitable for development" and "is not in the public interest".

The Glendell project would have extended the mine's life until approximately 2044 and resulted in the extraction of an additional 140 million tonnes of coal. It is estimated the project would support more than 1000 jobs and inject $229 million into the Hunter economy.

The 90-day window for an appeal to be lodged closed last week.

Glencore has not confirmed or commented about why it didn't challenge the decision.

The Environmental Defenders Office, which represented Wonnarua Traditional Owners Scott Franks and Robert Lester, said it was satisfied the matter was now finalised.

"We welcome the news that Glencore is not appealing the Independent Planning Commission's decision to refuse Glencore's Glendell coal mine expansion," EDO Managing Lawyer Rana Koroglu said.

"This result is testament to our clients' tireless advocacy on the profound significance of the project area, including its strong associations with the Frontier Wars in the Hunter Valley."

Mr Franks said he was delighted the area's cultural significance would be preserved.

"The outcome has clearly been a win for the environment and the silent voice that nobody ever hears from has got a bit of a reprieve," he said.

"One thing that this process has really brought to the forefront is the inadequacies of the department (of Planning and Environment)."

Mr Franks said he planned to take legal action to stop the expansion of the Hunter Valley Operations project, a joint venture between Glencore and Yancoal.

"The footprint of that mine comes into the section 10 area (a Commonwealth legal protection applied when an area of Aboriginal significance is under threat of injury or desecration).

"A lot of people don't seem to understand the actual zone is 80 square kilometres. It's effectively from the backdoor of Ashton Coal Mine all the way to the Muswellbrook side of Liddell power station."

Greens Senator David Shoebridge, who applied in 2018 to have the area protected, under sections 9 and 10 of the Aboriginal and Torres Strait Islander Heritage Protection Act, 1984, said Glencore's failure to appeal the IPC ruling was a win for the Plain Clans of the Wonnarua People, "a win for the Hunter and a win for the climate."

"Finally, after years of truth-telling about the cultural and environmental devastation this proposed open cut mine would create, we have an end to this disastrous project," he said.

"Glencore proved themselves to be a discreditable opponent in this fight, willing to use public bullying, back-channel arm-twisting and endless corporate resources to force an approval and thankfully these tactics backfired.

"Today I want to acknowledge the hard work of First Nations activists, environmental defenders and those committed locals who stayed with them in the hope that decency would prevail."

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