This does kind of remove the trade off of prospecting early vs prospecting after the vein is delepleted completely so I understand if this suggestion is rejected.

Potential ways to implement:
- Option in the prospector ui, having it only prospect ores that are depleted. If it defaults to on it would change existing behaviour on placement though and you might need some visual indicator of it too.
- A global config option (off by default).
- Recipe to convert a prospector to a version that prospects only when needed.

As for the prospector mk2, perhaps it could prospect like the first prospector, then once that gets depleted it'll do the deeper prospecting.