Bismuth is an example of a byproduct metal that doesn't follow the relationship very well; the 3% lead reserves in the western U.S. would have only 100 ppm bismuth, clearly too low-grade for a bismuth reserve. The world recoverable resource potential is 2,120 million tonnes for copper, 2,590 million tonnes for nickel, 3,400 million tonnes for zinc, 3,519 BILLION tonnes for aluminum, and 2,035 BILLION tonnes for iron.[19]