The miner, Fortescue Metals Group, has admitted to the destruction of Aboriginal sites at its Solomon Hub project in Western Australia's Pilbara.
In November last year, Indigenous people said sites had been damaged but FMG dismissed the claims as offensive and untrue.
Now, the Yindjibarndi Aboriginal Corporation has documents, obtained under the Freedom of Information act, showing that two heritage sites were destroyed and a third was damaged by earth-moving equipment.
The two sites that have been destroyed were identified as possible hearths, or camp sites, with scattered artefacts.
One consultancy found heritage sites while another found nothing significant.
The Yindjibarndi Aboriginal Corporation's CEO Michael Woodley says the documents prove their point.
"What they prove all along is that FMG were in fact destroying and damaging sites," he said.
The company says it was given permits on the basis of mistaken information but Mr Woodley says FMG should be held to account.
"At the end of the day, FMG is responsible for the requirements that the department gives them under these permits," he said.
"These sites actually establish the connection to Yindjibarndi people to their country.
"All sites on Yindjibarndi country have high significant value, they are all important to the Yindjibarndi people, and these sites have no exception.
"What makes them sacred is that they are part of the traditional ceremonies that we do when we put our young people through initiation." Expert opinions In a statement, FMG says the sites were "declassified" by an "independent expert archaeological firm." That firm was Alpha Archaeology but the consultant who did the report is no longer with the company.
Acknowledging and registering sites is a complex business.
The Department of Indigenous Affairs found that Alpha's reporting was at times more accurate than an earlier report by Eureka.
FMG says it has since taken steps to minimise the risk in the future.
Yindjibarndi people are bitterly divided over the deal that FMG has offered for access to Solomon Hub.
Fortescue is putting forward $4 million a year plus housing, training and employment worth millions more but Mr Woodley's group is seeking half a per cent of all future royalties.
"Our position is quite simple, it's industry standards," he said.
"It's what industry people, the Rios of the world, the BHPs of the world [offer].
"That's our position and we're not going to settle for anything less.
"At the end of the day, 0.5 per cent is based on the iron ore price obviously so if it's $180 a tonne then it's 0.5 of $180 a tonne.
"If it's $90 a tonne, which it is now, then it's $90 a tonne so it loses and grows with the current iron ore price." The Indigenous Affairs department says it investigated the case but decided on the advice of the state solicitor that it was not in the public interest to prosecute FMG.
In a statement, the department said its decision was based on the fact that FMG had had conflicting opinions from the heritage consultants.
It concluded there was not enough evidence to mount a successful prosecution.