All ancient copper has impurities peculiar to the area from which it was mined. Most of the bronze ̣(copper-tin alloy) that survives from the Bronze Age is unaccounted for in the literature. The impurities in almost all of the unsourced copper in that bronze matches the copper that is found in the extensive and extensively mined copper lodes by Lake Superior which mining seems to have occurred back in the European Bronze age. A curious anomaly, that.
Yes it is!
It wouldn't be surprising if *some* of the copper mined in antiquity in upper Michigan turned up in Mediterranean contexts; I'd be a little surprised if the mining had been carried out by people *from* the Mediterranean. The 'oxhide' copper ingots found on the Ulu Burun wreck *may* match the UP copper, that's one of Gavin Menzies' claims, but I'd enjoy finding that out for sure. Much of the copper mining from the Bronze Age was carried out in Cyprus, an island that owes its name to copper, and the Ulu Burun wreck was found off the shores of Cyprus.