I tested it.
Mineral fields and vespene geysers do not get removed or killed by "Remove all buildings" or "Kill all buildings".
They do get removed and killed by "Remove all any unit" and "Kill all any unit".
If you kill a refinery using triggers, the geyser will remain, even if you kill all 'any unit'. I suspect that the same sort of thing is happening when a nuke kills a bunker but not any unit inside it - the geyser is probably a 'hidden' unit.
Mineral fields simply disappear when killed. Vespene geysers give an orange explosion when killed!
So I think that it's best not to think of mineral fields and vespene geysers as buildings.
A better word may be 'resources'.
