A lawyer for Mrs Rinehart's children says there is clear evidence that mining licences were unlawfully transferred to her company, Hancock Prospecting, and a subsidiary after her father Lang Hancock died in 1992.
"We don't use the word fraud lightly," lawyer Christopher Withers SC told a complex trial over mining assets and royalties in Western Australia's northwest on Monday.
Mr Withers accused Mrs Rinehart of exploiting a joint venture agreement with Hamersley Iron to move Hope Downs and East Angeles tenements.
"We say the evidence that fraud was perpetuated by Gina on her children is overwhelming," he said.
Mr Withers said the action was contrary to Lang Hancock's intentions for Mrs Rinehart's eldest children, John Hancock and Bianca Rinehart, to benefit from the assets via a trust.
"The events after Lang died constitute an egregious fraud orchestrated by Gina and carried out by people who did whatever Gina wanted without questioning," he said.
He said the actions were "covered up" with a "false narrative to her children and the public generally that (Hancock Prospecting's) and her personal success was simply a product of hard work rather than dishonesty".
Mr Withers said the false narrative was that Lang Hancock dishonestly breached his fiduciary duty and mismanaged Hancock Prospecting, which "Gina had to clean up".
"The truth is Lang discovered the mining areas in the Pilbara. He was the driving force behind the decision to start a mine, which Gina was against," he said in reference to Hope Downs mining complex that Mrs Rinehart's company and Rio Tinto operate.
Mr Withers said Mrs Rinehart's alleged fraud "increased her own shareholding at the expense of her children" and that she lied to them about it.
He also claimed that the West Australian of the Year 2023 threatened John Hancock and his lawyers when they attempted to investigate the matter.
The claims were made in a high-stakes legal stoush in the Supreme Court in Perth in which Mrs Rinehart's company and her children are defending the claims of Wright Prospecting and DFD Rhodes.
Wright Prospecting has demanded a share of some Hope Downs tenements and royalties amid a claim that it never relinquished the assets and Hancock Prospecting has breached a series of partnership agreements.
The family company of the late prospector Don Rhodes, DFD Rhodes, says it is entitled to 1.25 per cent royalty share of the Hope Downs production.
It claims a deal was struck in the 1960s with Mr Hancock and Mr Wright in which the rights to ore-rich reserves in the Pilbara were handed over.
The Hope Downs mining complex near Newman is one of Australia's largest and most successful iron ore projects, comprising four open-pit mines.
Mrs Rinehart, the executive chair of Hancock Prospecting, secured the development of the mines after signing a deal in 2005 with Rio Tinto - which has a 50 per cent stake in the project.
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