I wouldn't think about going inside the mines,but I bet all around the entrance you might find stuff,also think about their camps,where the lived and ate.
You will find a lot of interesting tools and other items related to the mining industry. We had one very small mining town here, but I've found enough relics to set up a display of the stuff. Check along any old RR grade too. Quite often you will find items within yards of the tracks. Seems like they didn't want to waste energy by tossing them very far from the tracks