It really depends on where those reserves are. I think the issue...

It really depends on where those reserves are. I think the issue pointed out by the company was that extending the mine life doesn't markedly improve the IRR and NPV because of the extreme discounting of those long term cash flows.

If they were to increase throughput in the earlier years that would have a much greater effect on the IRR and NPV because the cash flows aren't heavily discounted.

Mathematically IRR and NPV are really very simple measures and I think sometimes given too much weight. As with everything it comes down to assumptions. I don't see the copper price at US$3.20/lb in 20 years.