The extraordinary run experienced by Australia's iron ore miners this year is quickly coming to an end, according to Deloitte, which says a sharp sell-off in recent months is a "sobering reminder" of how quickly things can change in the volatile commodities market.

Delivering a bumper profit season for BHP, Rio Tinto, Andrew Forrest's Fortescue Metals and Gina Rinehart's Hancock Prospecting, iron ore has been comfortably the best performing commodity of 2019 in a market reeling from trade conflict and uncertainty, said Deloitte mining lead partner Ian Sanders.

The steelmaking commodity iron ore mined in Western Australia's Pilbara is the nation's biggest export. Credit:Tony McDonough

On the back of strong demand from China's steel mills and a global supply shortage following a dam collapse at a major Brazilian mine, the benchmark price of iron ore hit about $US120 a tonne.

The boom also delivered a significant and timely boost to national GDP growth and the Morrison government's federal budget, as iron ore is Australia's biggest export.