These can only form under the ocean, but these days, when we mine for zinc, copper, or silver on land, we're often mining massive sulfide deposits that originally formed on the ocean floor millions of years ago.

它们只能在海底形成，但如今，当我们在陆地上开采锌、铜或银时，我们开采的经常是数百万年前最初在海底形成的块状硫化物矿床。