while the 2.3 gram cut off is way too high, i don't know that a 0.5 gram cut off would apply becuase this will be an underground mine. i have seen some resource estimates with a cut off as low as 0.3 - skygold's spanish mountain and silver standard's snowfield project come to mind. but those are expected to be open pit mines, and they are different animals.

at $910 gold, 0.5 grams is worth about $15, and it is hard to see an underground operation making a profit on that. maybe those resources could be used to extend mine life after years of operation on the higher-grade mineralization.

i'm not an expert on mining and i'd like to be proven wrong if the lower grade rock at the south end of fdn can be mined profitably, but i think it will take much higher gold prices for 0.5 grams to become economic.