Doug Casey has this calculator for evaluating value of rock when exploration company reports results of their assays.
The game is on now in PM sector. For those who are trading these tier 1 companies this calculator will be a help. Every time assay results are reported from drilling program the stock goes up.
One way to evaluate the worth of gm/t or ozs/t is to use this calculator.
It is self explanatory. Just insert the grade of metal/s and it will calculate in USD the worth off each hole.
It is good to know whether the grades are better or at discovery level.
I have developed a spreadsheet from this to calculate the on going expansion of metal find in the rock.