Just to clarify - the IRR should not change if you change the...

Just to clarify - the IRR should not change if you change the discount rate - the IRR IS the discount rate at which NPV = 0.

The question I like to ask - which is along the lines of ur AISC comment - is what makes this project better than the others out there (of which there are plenty)... be it grade, proximity to infrastructure and/or customer, metallurgy, capital requirements, opex requirements (power costs, strip ratios, flow sheet / met - cost to remove impurities)... if it’s at the top of the batting order it will be developed and it will give you a return (provided the market needs product / is not saturated)..