I don't claim to know a lot about the philosophy of gold mining...

I don't claim to know a lot about the philosophy of gold mining strategy in response to changing gold prices, but as I read the highlights section (haven't got past that yet) it appears to me the strategy NST are adopting is to mine the lowest grade that they can profitably.  This is a long term strategy to ensure maximum mine life and continued commercial viability.  If you have low grade ore that can be mined at a profit, why not take advantage of that while you can?  If the POG drops then those ounces in the ground become worthless, because it costs more to get them out than you can sell them for.

Put it another way, if you get all the 'cheap' ounces out first, what do you do when the POG drops below your AISC?