The other thing to note about NPV is that it values money up front over the long term. I've seen people here throw numbers between 25K-50K tons of production per year. Everything else being equal, a higher ton per year project will have a higher NPV value because the money in the earlier years will be discounted less. Even if we can make educated guesses at avg revenue per ton, cost of production per ton + Corporate overlays, etc, a major driver of value will be how large of a mine they choose to construct for annual production.