Worsley billions my biggest error: BHP chief Marius Kloppers DEPARTING BHP Billiton chief executive Marius Kloppers says the worst mistake of his 5 1/2-year tenure was not to do with acquisitions but a decision to pour billions of dollars into the Worsley alumina plant south of Perth. "We spotted a technological change in aluminium and we made a great decision to not continue to invest in aluminium," Mr Kloppers told ABC's Inside Business program.