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

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.

The boost to Ms Rinehart's fortunes has put her on course to overtake the world's richest woman, the American Wal-Mart heiress Christy Walton, who is worth $US24.5 billion.

Last year, Forbes ranked Ms Rinehart the 19th most powerful woman in the world with a fortune of $US9 billion.

Ms Rinehart is the daughter of Lang Hancock, who helped transform Western Australia into an iron ore exporting powerhouse.

Her fortune rocketed her to the top of the BRW Rich List last year as rising demand for iron ore and coal in Asia helped double her estimated wealth in one year from $4.75 billion in 2010.

Ms Rinehart, who has waged legal battles with her children for control of the empire, is known for a keeping a low public profile.

However, she campaigned in public against the proposed minerals resource rent tax in 2010, which sought a 30 per cent levy on the ''super profits'' of the resources sector.

Her massive holding in rich iron ore and coal deposits may yet make her the richest person in the world, Citigroup estimated in a report widely circulated last year.

It predicted she might overhaul even Carlos Slim, the Mexican magnate then worth about $US75 billion and Microsoft-founder Bill Gates, who was worth in the order of $56 billion.

Other reports have used profits generated by Rio Tinto from shared assets to extend the projection further, suggesting her wealth may eventually balloon to more than $US100 billion.

If such wealth is realised, Ms Rinehart may well become the first person in history to be worth 12 figures in US dollar terms.