from wikipedia

In 2004, the world production of iron ore exceeded a billion metric tons.[4] In comparison, a comparatively small M-type asteroid with a mean diameter of 1 km could contain more than two billion metric tons of iron-nickel ore,[5] or two to three times the annual production for 2004. The asteroid 16 Psyche is believed to contain 1.7×1019 kg of nickel-iron, which could supply the 2004 world production requirement for several million years. A small portion of the extracted material would also contain precious metals.