The depth argument.Many moons ago I worked underground at Brunswick Mines, another deep Lead Zinc mine owned by Noranda. The shaft does not have to go to the bottom....I believe at the time there was development work going on at 5200 feet and the shaft was down to about 3750. That was 20 years ago so presumeably they are deeper now. The access was via ramps, which may add to the cost of ore extraction but if the economics are there...then they will mine it. The upfront cost of driving a shaft and ramps that deep MAY be prohibitive but with a potential payoff of 20,000,000,000 that cost becomes miniscule. They may choose to drift in from the old sullivan mine as well which ultimately may be alot cheaper.
However, this is still a spec play and discussing whether they will develop it or not is entirely too premature.
Anyway, here's to 60 metres of sulphides......