As a thought experiment, let's just think for a minute about mining the Moon. Let's assume for a moment that the mineral you're interested in is just lay about on the surface. Great big lumps of gold or diamonds just scattered all over, and all you've got to do is stuff it into bags and return to Earth. How much would this exercise cost? I'm betting a lot more than the value of the minerals you're bringing back. If we then add up the cost if we do have to actually dig for the stuff, it just doesn't make sense to mine the Moon.