Unfortunately sevo the discount factor used in an NPV is more...

Unfortunately sevo the discount factor used in an NPV is more important factor than life of the asset.

AMN's Argonaut report assumes a 10% discount factor.

If we use that, then 95% of any company's NPV is accounted for by year 30.
That means only an additional 5% NPV accretion occurs between years 31 to 100

So what's the benefit of having a resource that large?

I think it justifies the capex spend.

For instance, why spend US$300m capex on a project that will have a 20yr life...
when you can spend Us$300m capex on a project that has say a 100yr+ life.