The sheer scale of Australia means that they're not about to get exhausted anytime soon though. Only something on the order of 1% of the continent has even been prospected yet.
That document lists 51GT of 'accessible economically demonstrated' iron ore, with an production rate of 0.81GT per annum, and 86GT of inferred resources (ie. yet-to-be-prospected).
So there's at least half a century of ore left, even if production ramps-up steadily. 1% prospected doesn't seem supportable though; it's more in the range of 50% based on the ratio of the inferred to known figures above.
Australia will always have whatever resource is in demand next. Three lithium mines are coming online every year for the next few years starting this year.
Australia will become the largest natural gas exporter - it will overtake iron ore in value in the next couple of years.
Then you have tourism, education and becoming the food bowl for China's growing middle class
Everyone likes to complain about being resource-export dependent but it has never been more than ~10% of GDP and is quiet an enviable position to be in
