Warnings by Goldman Sachs, UBS and others iron ore would tumble as low as $70 a tonne in the third quarter proved unfounded. In fact, it ended the quarter 12 percent higher.
Driving up prices is China, which buys most of Australia's ore and where steel demand is growing by 8 percent a year.
(Read more: Fortescue CEO refutes $70 call on iron ore)
Fortescue, despite dabbling in copper and gold and looking at shale oil, remains entirely dependent on iron ore.
"If the iron ore price goes, so goes most, if not all their profits," said Eagle Mining analyst Keith Goode.
BHP and Rio Tinto also risk alienating investors traditionally buying their stock for exposure to a diversified portfolio.
Even buffered by its oil and gas business, BHP would have seen its last full-year earnings before interest and tax drop to $10 billion from the $21.1 billion it reported without iron ore.
(Read more: Iron ore may gain as cyclone 'rusty' menaces Australia)
Rio Tinto, the world's biggest aluminium producer and a top five miner of copper and producer of a dozen other commodities, last year derived all but a fraction of earnings from iron ore.
Citigroup estimates miners have cut capital spending budgets by $19 billion, or 5 percent, after some disastrous investments in struggling metals like copper and aluminium.
"Iron ore is covering a multitude of sins committed by these companies," said Morning star analyst Mark Taylor.