IRR/Payback invariably looks good on restarts as most of the...

IRR/Payback invariably looks good on restarts as most of the CAPEX that was needed has already been sunk previously .
What under pins the pay back and longer term the NPV (although NPV is less relevant from a lenders perspective nowadays ) is the profit margin per unit , so a reliance is needed that the cost estimates are correct ,
I lack the geological knowledge to be confident to estimate the costs on such a complex main ore body with remnant ore to be mined , the upper main lode looks compelling but it is only a small proportion of the initial MRE .