Depletion

Iron ore reserves at present seem quite vast, but some are starting to suggest that the maths of continual exponential increase in consumption can even make this resource seem quite finite. For instance, Lester Brown of the Worldwatch Institute has suggested iron ore could run out within 64 years based on an extremely conservative extrapolation of 2% growth per year.[10]
Pilbara depletion

Geoscience Australia calculates that the country's "economic demonstrated resources" of iron currently amount to 24 gigatonnes, or 24 billion tonnes. It is being used up at a current rate of 324 million tonnes a year. In the 1960s it was reportedly called "one of the most massive ore bodies in the world" by Thomas Price, then vice president of US-based steel company Kaiser Steel.

According to the Australian Bureau of Agricultural and Resource Economics, that resource is being used up at a rate of 324 million tonnes a year, with rates expected to increase over coming years. Experts Dr Gavin Mudd (Monash University) and Jonathon Law (CSIRO) expect it to be gone within 30 to 50 years (Mudd) and 56 years (Law).[11]