You'll need to conjecture a mine plan (schedule) and use the...

You'll need to conjecture a mine plan (schedule) and use the present value formula to calculate the value of the royalty >1Moz from now (ie the first five years or whatever are zero).

Let's say another 3 years Resource development, licensing, mine planning and mill construction before production. Then, assuming production at 100kozpa for the first three years before expanding to 200kozpa, gives around 12 years before the 1Moz is reached.

You then find the present value of the remainder of the Resource/Reserve at a production rate of 200kozpa. What's the remainder? Well, you'll have to conjecture that.

All this is highly conjectural, so you'll need to use a discount rate of (say) 15%. So the number ain't very big at this point, because of the conjectural assumptions.

You could get even more speculative and come up with a cash flow model that contemplates a 2Mtpa mill ($120M), mine establishment ($15M), operating cost of (say) $50/t ore, head grade three times the marginal cutoff grade (1.0g/t) and work that way.