I do the same thing Peck_ed. That is of course if I let them empty in the first place. Changing the subject a little Lamorally, I admit I let copper mine's run empty, the resources they return are almost worthless to me. Letting coal/iron run dry is a little expensive, might I suggest from now on you do knock them down as they return a percentage of the building costs if done correctly the resources you get back are worth more than the ore they return. It is of course down to timing.