That is the point of feasibility studies. It will be a...

That is the point of feasibility studies. It will be a culmination of knowing mining costs (this will be based on mining technique used, strip ratio, ore movement, labour cost etc etc) + processing cost (how easy the gold is to seperate from host rock, reagents (cyanide etc) needed, recovery rates - this is all established via met work) + transport and other costs like admin, sustaining capex etc. DFS level is meant to be +/- 10% of the real world cost as a confidence interval.

Many cases where things don't play out like that, so it's always important to watch realised cost of production but that's the same for any commodity and any mine.