[UnderseaLcpl]

I can only answer the last question with any degree of certainty, and the answer is "Much more than any rock in this solar system has, Mars included". There would have to be a remarkable advance in spacecraft propulsion to make it profitable to mine gold on Mars, let alone the worthless rock that it is primarily composed of. I think the day will come when it is economically feasible to exploit extraterrestrial resources, but we're a long way from it at present.