An 18-year-old diary entry from a former Wright Prospecting executive has cast doubt over a billionaire family’s claim to the ownership and lucrative royalties flowing from one of Gina Rinehart’s Pilbara mines.

Excerpts from a 2005 diary entry by Wright Prospecting’s general manager were aired in the WA Supreme Court on Monday, showing they concluded the company was not entitled to a share of royalties from mining tenements now central to a multibillion-dollar legal dispute.