From Vibranium Wiki:
One such instance was when the oil conglomerate Roxxon discovered that a small island in the South Atlantic had a foundation composed of vibranium. Due to this, Roxxon found it necessary to destroy the island and blew it up with bombs. Unable to absorb the force of the explosions, the vibranium was destroyed
Why exactly would a corporation find it necessary, never mind desirable, to destroy an enormous quantity of extremely rare, uber-useful, and, presumably, super expensive mineral (instead of, say, mining it ala Wakandians and selling to governments/other companies/arms dealers)?