Gina Rinehart – Australia's richest person and the largest shareholder of Fairfax Media – has taken legal action against Fairfax journalist Adele Ferguson in an apparent attempt to force her to reveal her sources.

At the request of Mrs Rinehart's private company, Hancock Prospecting, the Supreme Court of Western Australia has issued a subpoena demanding emails, text messages, notebooks and any recordings of interviews that may have been made between her eldest son John Hancock and Ms Ferguson since September 2011.

John Hancock was the only member of Mrs Rinehart's immediate family to contribute on the record to Ferguson's unauthorised biography, Gina Rinehart – The Untold Story of the Richest Woman in the World.