Economic grade comparison, page-4

Not sure where you obtained your figures from but the $75m to $100m does not seem to be much capital expenditure. CAI is spending $120m to develop a gold mine to produce 90koz pa at a grade a bit over 1gm/t which includes underground as well as open Pitt. They have a very good return at current ZpIG.

BGL cap ex is $255m (underground) to produce 150k oz pa with a grade of 8gn/t while GOR (open pit) spent nearly $600m to produce 300koz pa at a grade a bit about 1gm/t.

Capital expenditure and the economics of a mine depend on more than just grade - eg metal being mined, size of mine, annual production, type of rock, recovery %. underground vs open cut, etc.

Sorry to say but both these posts seem to be too simplistic.