At first I thought this was a pretty good idea, but after thinking about it I'm a lot more skeptical with this approach and it comes down to the idea of what NPV is and stands for.
NPV relies on two things - the time value of money and the risk of the future (discount rate). You can't "reset the view for 2035" because you're putting down the money today (i.e. buying those properties now, opposed to putting them on layaway to buy at that point) for "phase 2" not putting it down in 2035. The value isn't accurate for the NPV you come up with for that as you're not taking into account what they could do with that money as an alternative (i.e. buy another property/put money into one of their properties that's already mothballed that they can generate revenue on the today (or in a 5 years) till 20 years, and then utilize all that income to buy the property they didn't buy then).
The second thing is discount rates. The future is uncertain. 20 years is a long time especially with how fast paced things are now a days. Currency may be valueless at the rate nations are devaluing and printing money or perhaps mining won't be needed because we have a nuclear world war that wipes out half the population - and obviously metal demand won't be that high then. Or maybe even something optimistic where we create new technology that allows us to create metals for a cheaper price and less environmental damage than mining (i.e. alchemy essentially). We could also just have more realistic scenarios where you don't know and can't forecast the price of any of the metals that 20 years in the future let alone 40 years. How many forecasters said gold would be where it is today 10 years ago? Sure there was a few that said "higher" but out of how many? And how many of those got the exact number right - even within a range? How many believed that guy?
I don't think we can utilize NPV for our properties that won't be mined till decades out and get value for ourselves (though it'll be something that the buyer would recognize and acknowledge). We just won't get anywhere near any real value for them unless our new BFS incorporates setting up multiple mines and mills at the same time and we process stuff a lot faster - or we try to sell the lands separately to different buyers and let them do that on their own, however management has stated they'd rather sell it all at once. At the end of the day - we'll be giving a lot of stuff away "for free" to make sure we get the price we want for today (which will still be something of substantial value).
