Mountain Groves should sometimes have surface mineshafts

I think it would make a lot of sense, lore-wise, for there to be mineshafts in the mountains, especially with the new emerald ore generation and especially because that's where a lot of mining operations are done in real life. Plus, it would offer a nice reward for climbers! To specify, I don't think these mineshafts should be as common as those in the Mesa, and it could also be interesting for them to be made out of spruce rather than oak.