9/7/2020 · For rare earths, some 20 to 160 tons of ore are mined per ton of element.[] For cobalt, roughly 1,500 tons of ore are mined to get to one ton of the element. In the calculus of economic and environmental costs, one must also include the so-called overburden—the tons of rocks and dirt that are first removed to get access to often deeply buried mineral-bearing ore.