Simply put, a spell that when cast causes unmined ore veins to become highlighted, even through obscuring objects.
The spell Detect Ore would be similar to the spell Detect Life or the shout Aura Whisper, in that it applies a glowing particle effect to the appropriate objects that can be seen through any walls or barriers that may be in the way. Preferably it would have a casting time and a duration of effect similar to Aura Whisper, rather than having to be concentrated on like Detect Life. The objects affected would be ore veins that have ore remaining in them. Only veins in loaded cells that are within a certain radius of the casting location would show up.
This spell would make it easier to get all the ore mined from within a dungeon, and make outdoor mining expeditions feasible. One cast in one spot is bound to highlight a vein or two somewhere outdoors, and you can venture towards its location. After mining it, you cast again and locate another one.
I'd really like to see such a mod, so please post here if you make it!