RE: RE: DCF analysis? That is the link, however if you just google 'income_approach.pdf aggregate mines' the doc will be openable from the link (weird..).
For the calculators just google 'dcf calculator' and you can see a number of them out there.
Then start plugging in the numbers provided by HBK, that would be 1,500,000 tons per year for a cash flow of 33 million per year for 20 years etc & so forth.
YMMV - That's all I did, as I'm not a financial whizz in these matters.
Also see: https://en.wikipedia.org/wiki/Discounted_cash_flow
At this point I expect our resident experts to chime in and inform us why this method is total BS, but hey maybe we'll learn something.