You don't have to worry about the spinning ball question. Moving ore from the ground is not going to have an impact. In fact if you want to see how we know this then take the earth about 10,000 years ago and you would see a gigantic layer of ice that covered most of North America over a mile thick. This weighed down the land so much that when it melted there was actually a rebound of the ground to what we have today. The amount of minerals that are mined would pale in comparison to the weight of that glacier that once sat on North America. Moving minerals from one place to the other is not going to affect the earth's spin. However taking toxic minerals below ground water levels and moving them into our ground water will affect us adversely.