Not quite sure what you are suggesting, but in regards to timelines, no mining analysts consider income past 10 years. The reason for this is in the way presest worth of discounted cash flow gets smaller as one adds years. Therefore, the present value of 20 years of discounted cash flow is only a fraction higher than the value of 10 years - not double. In otherwords, major miners may pay a premius to ensure very long term supplies, but not all that much.

Besides modern mining techniques ensure that a Bisbee-scale discovery will be mined out in a few decades or less, not a hundred years.

In matters of valuation, then, it's more about how much wealth can be produced in 10 years, than is about how much wealth can be produced in the life of a mine. This is why high grades in the early years of production are more important that what are average grades encountered across the whole of a deposit.

VP