John Hancock told his sister Hope Rinehart in a 2006 email that he had consented to a secret Supreme Court hearing to protect a deal with mining giant Rio Tinto, DFD Rhodes lawyer Jeremy Stoljar told a complex legal case over mining tenements in Western Australia's northwest on Tuesday.
"(This) is to ensure there is no publicity that might jeopardise the banks or Rio in dealings with Hope Downs," Mr Stoljar said Mr Hancock wrote.
"Our case is based purely on the very straightforward legal principle that a trustee of a trust cannot do a deal with trust assets that result in a benefit to herself or one of her companies," the email continued.
"My case is simply that any benefit that flows from the Rio deal must flow to the trust."
Mr Hancock went on to say there was no doubt that their mining pioneer grandfather, Lang Hancock, wanted Hancock Prospecting to give financial assistance to the trust to develop Hope Downs.
He said there was no reason to take Hope Downs out of the trust for the company to develop it.
In a further email to Hope Rinehart, Mr Hancock calls her "Hopstar" and warns her to be careful about what documents she signs.
Mr Stoljar also read two emails sent from Hope Rinehart to Mr Hancock expressing concerns that if he won the case over the trust it could cause the joint venture deal with Rio Tinto to fail.
"(Hope Downs) will be screwed," she said in one.
"Glad to hear of your plan for financing and Rio (Tinto). Just hope it is solid so it doesn't mess up Hope Downs' dollars," she said in another.
Hope Rinehart forwarded the email to her sister Bianca Rinehart several days later, who then sent it to her mother, Gina Rinehart, according to Mr Stoljar.
"That's all that was there. I'll have to wait for idiot John to reply to her before I can see if she sent anything else," Bianca Rinehart wrote.
The family company of deceased prospector Don Rhodes wants 1.25 per cent royalty share of Hope Downs' production, over an alleged deal with Lang Hancock and his business partner, Peter Wright, that saw it hand over tenements in the 1960s.
But the high-stakes stoush in the WA Supreme Court centres around Mr Wright's heirs, who are fighting through their company, Wright Prospecting, for a series of Hope Downs tenements and royalties.
Gina Rinehart's company Hancock Prospecting is also represented, as are John Hancock and Bianca Rinehart, with about two dozen lawyers packing the Perth courtroom for the case that is expected to run until November.
The pair assert they are entitled to a hefty share in the Pilbara operation, amid a fraud allegation against their mother, which they say defeats the Wrights' claim.
Hancock Prospecting is defending against the prospectors' claims and maintains it undertook all the work at Hope Downs and bore the financial risk involved in the development, and is the legitimate owner of the assets.
