The Rinehart family trust fund battle may not be played out in court next month, with the billionaire mining magnate seeking to have the case referred to arbitration.
Fresh claims made by two of Ms Rinehart's children in relation to her conduct as a trustee in 2006 have shed doubt on whether the matter can proceed to trial.
Lawyers for Ms Rinehart on Wednesday sought for the proceedings to be stayed.
They said the fresh claims made by Mr Hancock and his sister Bianca Hope Rinehart fall under the terms of the family trust fund deed and should therefore be referred to arbitration.
Mr Hancock and his sister Bianca Rinehart are seeking to oust their mother as trustee of the family's multi-billion dollar trust fund.
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They claim their mother acted "deceitfully" and with "gross dishonesty" in her dealings with the trust, set up in 1988 by her father, Lang Hancock, with her children as the beneficiaries.
The pair was previously supported by their sister Hope Welker, but she withdrew from the case earlier this year.
Ms Rinehart, who is supported by her youngest daughter Ginia, has denied the claims.
Previously the case mainly turned on allegations relating to Ms Rinehart's alleged conduct in 2011, when the trust fund was due to vest.
Mr Hancock and Bianca Rinehart now claim that their mother also changed the constitution of the family company, Hancock Prospecting Pty Limited (HPPL) in 2006 in such a way as to prevent her being removed as trustee.
Christopher Withers, representing the two children, told the court the changes meant the children couldn't take their shares unless they had the financial means to pay the capital gains tax that would be incurred.
Richard McHugh SC, representing Ginia Rinehart, said it was "unarguable" that these fresh allegations must be referred to arbitration because they fall under the terms of the deed.
"The question is what does your honour do with the (current) proceedings?" Mr McHugh said.
Mr Withers urged Justice Patricia Bergin to continue with the October 1 trial date even if she did decide the 2006 claims needed to go to arbitration.
But Justice Bergin said she would have "really serious doubts" about such a scenario.
"If I were to decide that this new pleading of yours (the 2006 allegations) are covered by the deed, then I don't see how the trial can go on," she said.
The judge reserved her decision.
