I'm not sure I get what you're saying, so please tell me if this is it. There are different mines (e.g. Gold mines, Coal mines...etc.), and there are drilling/resource gathering equipment. the quality of the building depends on what you're mining, i.e. resources; so if you're mining Gold it's obviously going to be better than Coal, and it also depends on the equipment you're using to gather those resources. Say you're using bad equipment you get a resource called "Cracked Gold", normal equipment you get "Gold", and good equipment you get "Pure Gold".