RE: cpht & economic thresholdI don't know any opex costs for comparable N Am mines - feel free to add I know more in Africa and Europe.
It is easy to talk about grades and often the only thing early in project life but until it is converted to rock value it doesn't mean alot and that was the point I was trying to make. Which is better 0.2cpht @ $1000/ct = $20 rock or 25cpht @ $80/ct = $20 rock? Just presenting grades doesn't tell the full story
I was adding some upwards adjustment to the opex costs Shore have previously talked about. If the rock is sub $12/t forget it, above $20/t should be mineable between $12-20 high risk would need great cost control and would still be worth investigation to improve knowledge - variable carat value, mining costs et cetera.
I haven't done any converstion of Shore's grades and carat values to rock values.