Here is a good read on the changing economics of mining...

Here is a good read on the changing economics of mining coal:

"TER: Is it becoming more difficult to get coal out of the ground because we've taken so much already?"

"SG: The answer is definitely yes and this goes for both met and thermal. What it comes down to is you always want to mine the easiest coal that you can deliver first. About 100 years ago, they were mining easier seams than those we are mining today. In fact, in Appalachia, the seams continue to get thinner and thinner and that continues to hinder productivity. If you think about it from a fixed-cost-absorption perspective, it increases your costs over time. Because met coal is relatively scarce right now, people are going to areas they might not have chosen to mine 20 years ago. But at current prices, it suddenly makes sense to mine those reserves."

http://oakshirefinancial.com/2011/03/24/shneur-gershuni-from-ubs-thinks-coal-stocks-are-fired-up/