Hectorp- I would check on your assertions regarding the price, as if you look at the Feasability Study and the cashflow figures the only explanation is that GFM were expecting to recieve about 68.3% of the LME price of the zinc metal contained within the concentrate...
In other words (using the $2300 figure assuming the gate premium) a tonne of concentrate will now be fetching around $879
(0.536t of zinc, and 185g of silver) x 68.3%
I'm happy to be PROVED wrong, as that would be good for my Griffin holding...