Mining is boring. Create a demolitions skill. They can use dynamite to blow up rocks, then the players collect the chunks from all over the zone. Guano is already in the game.... = D
+1
If you are close to the explosion you lose energy and mood, maybe proportionaly to how close you are.
ETA: It's not that mining is boring. It's just a nice addition. Maybe dynamite should be expensive to produce, more a toy than economically productive.