I'm open to Phoenicians visiting North America, but it would be quite an undertaking to have them work these mines. Plus, there are rapids and cataracts on the St. Lawrence where portages would have to be maintained. It would be an enormous effort.
An easier theory is that the Native Americans worked the mines because they heard of markets on the East Coast and Central and South America.
I mostly agree, and that’s the point I was trying to make up above — that a trade network that reaches from Lake Superior to the Yucatan across the hostile territories without any overall governance makes crossing the Atlantic look tame by comparison. :’) The Vikings (and the English after them) entered the North American interior via Hudson’s Bay — during the medieval warming Scandinavians reached the Bering Strait by sailing east, because the route was open in the summers (private communication from a descendant of traders, for those who need citations). The Phoenicians (and others, for that matter) may have been chronologically well-placed to use the Arctic Ocean in that same way.