Ann: RWD 2016 Annual Report, page-18

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.