This wasn’t too plausible decades ago, but the quite legitimate mystery on which it was based was, where did all the copper that was mined in precolumbian times wind up? The prehistoric works, tailings, etc are larger than had ever been accounted for.
At that time.
Turns out the copper went to undocumented trade routes; this has been fleshed out by more recent research, but if any records were kept (possible, but not likely; most or all of the North American tribes were preliterate) they don’t exist, so the way this has been figured out is by where the copper wound up.
UP copper (much of it worked into artifacts) wound up all over this continent, and I think it has even been found in Central America. IOW, if the Minoans (who in my view were the Carians, or at least closely related people, which is what Herodotus said, and he was able to understand the spoken languages of both groups) or Phoenicians managed to get North American, Northern Michigan copper during the Bronze Age (a good time to get copper, obviously), they would have gotten it in trade on the coasts of the Americas, not through colonization. AFAIK there’s not a shred of evidence for “Old World” cultures at the mining sites, other than modern, post-Columbian stuff.
There have been enigmatic carved/inscribed artifacts (many now lost, actually deliberately destroyed by “scholars” from various universities) found in situ in Michigan, Ohio, and all over the US and Canada. My personal favorite is Mystery Hill in NH, which was emphatically NOT built as a colonial root cellar (it was or may have been reused as a foundation for someone’s shack at one time); one of the Pennsylvania U’s did some work there in the 1990s, and *inside* the barrow part of the structure found a onetime hearth the ash from which RC-dated at 2000 BC. It’s too big a site to destroy without a LOT of effort, and is obviously related to European sites. Period.
Cyprus was *the* copper source for a long time. The oxhide ingots from Cyprus are seen in some Egyptian bas-reliefs and paintings, and the people carrying them are (by inference) referred to as the Keftiu — the people of Cyprus which in the Bible is known as Capthor. The name Caphtor is often applied to Crete, but that is erroneous; Crete was known in the Bible (and in transliterated form, in Assyrian records) as Tarshish, which we’ve all seen equated with Tartessos. If they were the same place (it’s not unlikely), there was no Tartessos in Spain. :’)
http://www.varchive.org/ce/baalbek/caphtor.htm
http://www.varchive.org/nldag/tarshish.htm
http://www.varchive.org/ce/baalbek/tarshish.htm
Copper was valuable during the Bronze Age but tin was the constraining material.