Quarmm

"Popping an asteroid doesn't affect regeneration. When you mine an asteroid down, whether it be to a pebble or nothing at all, its ore gets respawned elsewhere in the EVE world. It will regenerate in your own system when it's depleted elsewhere, though due to the mechanics of the regeneration (which I can't go into) it may take a while for the asteroid to resume its former size. There's no rhyme or reason to how quickly it'll respawn; it depends completely on how much ore of that type is mined elsewhere, and where in the respawn order your belt happens to land."

- [GM]Abraxas