The problem I have with different takes on the idea that the Great Lakes copper fueled the Mediterranean bronze age (most recently, Gavin Menzies in his book on the Minoans) are the navigational barriers, such as Niagara Falls. Until the construction of the 18th- and 19th-century canals (to some extent), the Soo Locks, and the 20th century St Lawrence seaway, moving literally millions of tons of copper out of Lake Superior and into world trade routes, by water, appears to have been (ahem) impractical.
If it can found that there was an ancient PreColumbian canal system leading from Huron to Ontario for example, I’d probably be all on board, despite the major drop from Superior to Huron.
Another thing I’d regard as hard evidence would be an ancient, Med-style wreck (or ancient American wreck) loaded with copper and just setting where it sank, at the bottom of Lakes Superior, Huron, Erie, or Ontario, or as Menzies would have it, Lake Michigan.
I am of a similar opinion. The 'missing' copper cannot be found in the Americas is a good argument for it being some where else though, lol.
A matching of the isotopes in Med/Michigan copper would convince me.
The mined copper went somewhere as American Indians used very little mainly for ornaments. I don’t think its too much of a stretch to think it moved mainly through the Mississippi river system.
We should be able to agree a lot of copper was mined over perhaps a thousand years in upper Michigan. Where do you suggest the bulk of it went?