With the stroke of a pen, the wealth of Gina Rinehart jumped by about $10 billion, propelling Australia's richest person closer to the title of the world's richest woman.

Ms Rinehart's Hancock Prospecting last week agreed to sell 15 per cent of the Pilbara-based Roy Hill project to South Korean steel giant Posco.

Gina Rinehart may be on course to course to become the world's first individual worth 12 figures in US dollar terms.

The Posco investment values the stake in the project at more than $1.6 billion, in turn pushing Ms Rinehart's combined wealth up from $10.3 billion, as estimated last year, to nearly $20 billion, based on the increased value of her holding in the mine.