Australia's richest woman Gina Rinehart has started new litigation against her children's trust fund to prevent it from receiving millions of dollars in royalties from a Rio Tinto joint venture.

Mrs Rinehart, whose wealth was recently estimated at $6 billion, filed the fresh salvo against the trust that manages the inheritance of her four children – John Hancock, Bianca Rinehart, Hope Welker and Ginia Rinehart – late last month in the Federal Court.

Billionaire Gina Rinehart during a tour of Hancock Prospecting's Roy Hill Mine operations. Credit:Philip Gostelow

The legal action comes as Mrs Rinehart hit the headlines again this week with a bid for Australia's largest cattle station from Kidman & Co for $365 million.

It also comes as Hancock Prospecting ramps up production at the Roy Hill iron ore mine in the Pilbara.