Ok. I don't really see avg. mine grades in the 0.5-0.7 oz/tonne over the entire mine life. They are more likely to mix in some of the 'lower grade' ore from the exisiting mines (though 0.2-0.3 oz/tonne is hardly 'low grade'), since it absolutely worth extracting. Couple that with inevitable development shafts, etc., and I doubt they could average those kinds of grades over 25 y, though it would be really nice if they did.

That said...

Gold = US$780. CD1$=$1USD, 259M shares fully diluted (as per SGR web site), 25 year mine life

0.529 oz/tonne avg. grade:

$5.74 10% DR

$7.18 7% DR

$8.52 5% DR

This would require a high-grade resource of 7.3M oz.

0.705 oz/tonne avg. grade:

$8.87 10% DR

$11.05 7% DR

$13.06 5% DR

This would require an ultra high-grade resource of ~10M oz.