It used to be that we got all of our copper either from the very small deposits of pure metallic copper or from the larger deposits of copper sulfides.

FORBES: Peak Copper: Worldwatch Institute Gets It Wrong Again

Then a coat is applied of yttrium, barium and copper, the metallic elements of YBCO, today's HTS recipe of choice, along with impurities just nanometres (billionths of a metre) across.

ECONOMIST: Inside story

Miners can use underwater robots to dig up deposits left from "black smokers, " which are little towers of metallic sulfides that form after magma forces fluids with copper, gold and other metals through the seafloor.

WSJ: Exhausting the Earth's Resources? Not So Fast