RE: interestingNice find and good inference, lucci. I will add a couple of comments for color.
1) August 2008 had much higher overall energy prices than we have right now, although the beginning of the steep collapse was right around that time. Either way, the valuation of that mine was surely inflated relative to today. (This point means your NAG estimate is undervalued)
2) There is a difference between going concern value and liquidation value. No one would conceivably pay $210m for a mine for which the present value of the extraction and sale of its contained coal was $210m. Thus, the value of the mine to a mine operator such as NAG would be higher than $210m. (This point also means your NAG estimate is undervalued)
3) Are mines #4, #5, #6 really going to produce 25,000 tons/month? I submit that we'd be getting ahead of ourselves by including them - and they represent 75% of your 18m ton estimate. I think that giving NAG credit for running a 100,000 ton/month operation when they have thus far struggled to get 10,000/month is too much for me to accept right now.
Moreover, their mine life estimates have thus far proven to be too optimistic. Mine #1 was gone in the blink of an eye. Mine #2 claims are that it will last a year - does anyone here believe that? I definitely do not. It would probably be more prudent to suggest 10 years of mine life for mine #3 than 15 years. Just saying - take all management "estimates" with very large grain of salt.