Mining pioneer Lang Hancock was at "breaking point" as he fought to stop daughter Gina Rinehart from "destroying" his life's work before his death, a multi-billion dollar legal stoush over iron ore riches has been told.
A lawyer for Mrs Rinehart's children says the reclusive billionaire's relationship with her famous father was "not good" in the late '80s and she was "crucially worried" about maintaining her claim over his fortune.
"One of the things she's worried about is (that her mother) Hope Margaret's shares ... would go to Rose (Porteous)," Adam Hochroth said as he summarised his clients' case in Perth's Supreme Court on Wednesday.
As the pair worked to resolve a family feud, Lang Hancock signed a document handwritten by his daughter that placed an equal number of company shares for her and her children in a trust.
"A week after this letter is signed, Lang wrote to Gina ... and notifies her that he considers that document to have been signed by him under duress and is not legal," Mr Hochroth said.
Lang Hancock also told his daughter the document that she intended to be legally binding was not enforceable because she had taken her mother's will to the US and that was holding up probate.
"So I don't actually have any shares to place in trust for you," the court was told he said at the time.
Mr Hancock reached "breaking point" as the dispute rolled on in the years after he married his housekeeper, Ms Porteous, Mr Hochroth said.
"I'm not prepared to continue any further argument - you've had me worried sick over the past three or four years and the straw that broke the camel's back was your indiscretion about company business," Mr Hancock was said to have written in reference to Mrs Rinehart's alleged complaints about her father to the family company's auditors.
Mr Hancock went on to threaten his daughter with compulsory acquisition of her shares in the company she now controls - Hancock Prospecting, and to have her removed as executor of her mother's estate.
"I'm not prepared to have you in any position whereby you can destroy my life's workings to the point where I have nothing to leave you and the children," the court was told he said.
The complex legal battle that started in July pits Mrs Rinehart's company Hancock Prospecting against the heirs of mining pioneer Peter Wright and engineer Don Rhodes over the massive Hope Downs mining complex amid allegations of decades-old contract breaches.
Mrs Rinehart's eldest children, John Hancock and Bianca Rinehart, are also involved in the case over claims their grandfather left them a hefty share in the Pilbara mining resources he discovered in the 1950s that are now mined in partnership with Rio Tinto.
About two dozen lawyers have packed the Perth courtroom for the trial, which has also featured allegations Mrs Rinehart denies that she devised an unlawful scheme to defraud her children
Mrs Rinehart inherited her father's iron ore discovery in WA's Pilbara region and forged a mining empire after he died.
She developed mines from tenements at Hope Downs, signing a deal in 2005 with Rio Tinto, which has a 50 per cent stake in the project.
The Hope Downs mining complex near Newman is now one of Australia's largest and most successful iron ore projects, comprising four open-pit mines.
Her wealth is estimated to be about $36 billion and she is executive chair of Hancock Prospecting.
