Because someone posted earlier that you need a certain grade to do "economical" mining, let me give you an example of the largest, low-cost open-pit mine in Mexico:
Goldcorp´s Penasquito mine:
http://www.goldcorp.com/_resources/project_pdfs/Penq-dec-08-reserves.pdf
They have really large tonnage (1 million tonnes)
with an average grade of 0.456 gpt
for 17.369 M oz. gold !
So grade is NOT the only variable to determine ECONOMICAL mining.
Tonnage, open-pit or by-products can help.
And we are going for: tonnage, tonnage, tonnage.
FANTOMAS