It was 20 years ago that the mining magnate Lang Hancock's widow, Rose, summoned journalists to the gate of her flamboyant mansion, and dispensed copies of her recently departed husband's will.

It was 1992, the year both Hancock's daughter, Gina Rinehart, and Rose first appeared on the BRW Rich List. Lang Hancock's $150 million fortune had been divied up, each woman listed with a fortune of $75 million, in recognition of the will's 50:50 split.

There were decade-long legal battles, the bankrupting of the estate and paying down debts for business follies. But importantly the iron ore royalty ''rivers of gold'' paid by Hamersley Iron (now Rio Tinto) to Hancock Prospecting were preserved in corporate structures for Mrs Rinehart and her children. The deal struck in 1962 involves a continuing royalty valued at 2.5 per cent of ore mined from many of Rio's West Australian mines.

Given today's iron ore price, that royalty stream now accounts for about $100 million a year.

In 20 years, Mrs Rinehart has taken her $75 million inheritance to her fortune as Australia's richest citizen. The Forbes Asia rich list named her this week as the wealthiest woman in Asia, worth $16.88 billion. Other calculations, based on iron ore prices of US$140 a tonne last week, value her at $20 billion.