"I was asked why i haven't invested in MYL I gave an honest...

"I was asked why i haven't invested in MYL I gave an honest answer and explained the reasoning. Opportunity Cost and Utility of other investments, including copper miners"

I will give you that , there is an opportunity cost in using capital if one chooses a Cu miner over a Zn miner all things being equal , but there is no substitution between the 2 metals and from memory comparative advantage was one of Adam Smiths ideas involving nations , ie one nation A is better at producing both wagons and oil , than another nation B which produces Oil at 70% the cost of B and wagons at 50 % of B .
Even though A produces both oil and wagons cheaper than B It is still worth nation A selling to nation B wagons , in exchange for oil as overall both nations aggregated GDP will improve with the trades .
Maybe there is a place for comparative advantage between a zinc miner and Cu miner but I just can not see it .
Sorry for getting angry with you . I would say Adam Smiths comparative advantage ideas still apply even if Trump seems to think China is screwing him on trade

I would say the reason for the sp fall yesterday was people got stunned at the high CAPEX for the project , and are concerned at getting the finance for it , maybe there is an "opportunity "to start the mine off with a smaller plant initially ?