It was just after this scene, T'Challa grabbed Bucky's arm and his ring was close to it, camera focused on it for a while.
In terms of what that thing was, the wikipedia page for Vibranium has info on antarctic Vibranium:
Don't think Bucky's arm's Vibranium because it'd be difficult to blast his arm off if it were. T'Challa's ring evidently has some sort of magnetic/metal-disrupting thing going on....native to the Savage Land. This variation produces vibrations of a specific wavelength that break down the molecular bonds in other metals...