A mining company that plans to drill for gas under one of Australia’s oldest Indigenous heritage sites is facing a revolt from traditional landholders.

Djungan clan leaders said they were not told of the environmental risks of coal seam gas (CSG) when Mantle Mining – appealing directly to the community’s desire for economic opportunities – won access to land around Ngarrabullgan, or Mount Mulligan, west of Cairns.

The leaders said the community’s early assent to a land use agreement with Mantle – at a meeting in 2012 at which people were paid $100 “transport money” to attend – has been replaced by near-universal opposition.

Their plan to fight the CSG project has the unlikely joint backing of politicians from the Greens and Katter’s Australian party.

One clan leader, Judulu Neal, said: “I’m going to say that 95% of the Djungan people oppose this.”

Judulu said there was no “informed consent” because the impacts – including potential damage to waterways around a sacred site linked to the Djungan people for more than 35,000 years – were never explained.

“If this site is destroyed, it’s like spiritual genocide for the Djungan people,” he said. “The state should be protecting it, not giving licences out to mine it.”

That the industry’s first attempted foothold in north Queensland lies beneath a sacred mountain has not been lost on anti-CSG activists. They see in Ngarrabullgan a potent symbol of the fight to beat back an industry they say has ridden roughshod over the Darling Downs further south, leaving the worst of the long-term environmental impacts unknown.

Their foe is an industry minnow whose shares, amid sinking oil prices, are at an all-time low of just over a cent.

Ngarrabullgan was formerly mined for coal and was the site of one of Australia’s worst mining disasters in 1921 when an explosion killed 75 miners.

Mantle can explore for coal but is still seeking a licence from the state government to drill for CSG, seven years after it bought the Mount Mulligan mining lease.

In 2011, Mantle stunned a rural community in Victoria by abandoning in the face of opposition its plans to explore for brown coal in the unspoiled Otway ranges.

“If a raise of hands shows me that you’re against it, I will walk away,” Mantle’s managing director, Ian Kraemer, told a town hall meeting at the time.

Kraemer did not respond to repeated calls and messages from Guardian Australia.

The Djungan’s agreement with Mantle was signed at the tail-end of a 15-year quest for native title, and led to a schism within the group that led the claim.

Another clan leader, Paul Neal, said Mantle’s proposal came without prior information and after a series of land use agreements the Djungan had been obliged to sign with utilities in order to press their native title claim.

A north Queensland land council lawyer told the crowd of just over 100 people at the 2012 meeting that Mantle’s $50,000 offer for “authorisation” was the best deal they could get for such an agreement, Neal said.

“There were some of us knew that Mantle Mining shouldn’t be there so we put our hands up,” he said. “Those were the people that were informed. All of the others were frustrated, a lot of them didn’t know what was going on.

“We didn’t talk over the pros and cons of it, like where do we put the poisoned water? [Kraemer] was telling us they can put it into bladders. No one told us this bladder needs to hold a million litres.”

Neal said that after the Djungan later received firsthand accounts of CSG impacts on the Darling Downs, many at the meeting now wanted their signatures off the agreement.

He said Mantle milked the economic appeal of its operations to the Djungan. The majority live in relative disadvantage in the mission town of Yarrabah, where many, including his father, were forcibly relocated last century.

“Mantle Mining knew that as a people, we were frustrated,” Neal said. “We have all these things we wanted to grasp for our kids. We wanted a mango farm. Our kids get fuck all. We can’t even get a job at a McDonald’s.

“We wanted all these things that Mantle Mining was promising once they get this mine going.

“So people were looking at it and thinking: ‘I’m sick of my kids dying, I’m sick of people hanging themselves, always people in jail, incarcerated.’

“You can imagine why some of those people who have been living this shit for so long thought: ‘I’ll take my chance.’ That was a total con and total confusion.”

Judulu said he thought no one at the meeting knew that it was a sign-off for the mine.

He said Mantle must know the level of resistance now to their project among Djungan people.

“I think this is the hardest fight that any mining company is going to come up against,” he said. “Even in those times [when Ngarrabullgan was first mined for coal], when Indigenous people were shot for even talking up, the Djungan people fronted up.

“That’s the strength of our people and that shows you the significance of this place to the Djungan people and our neighbours around us.”