Interesting. I'd never heard this before, so I went digging myself.
It appears that Michigan's prehistory of copper working really fired some people's imaginations. If you look there are even fanciful stories about Phonecians crossing the Atlantic to get at Great Lakes copper!
There's a great paper online by what appears to be a very frustrated Archeologist (Susan R. Martin) called The State of our Knowlege about Ancient Copper Mining in Michigan, where she rails against the hookum pseudo-science writers have been perpetuating on this topic, and tries to set the record straight from an actual archeological standpoint.
MYTH: The second misstatement has to do with the duration of the
prehistoric mining era, which is quoted to last from 3000 B.C. to 900
A.D. (Sodders 1990:12).
FACT: The duration of prehistoric mining is
really much longer than this rough estimate. The dates and ranges of
time for prehistoric copper use are really from about seven thousand
years ago to protohistoric times. Suites of dates from the Upper
Peninsula and nearby areas make it clear that the age of the use of
copper lasts longer and extends farther than Sodders suggests. It does
NOT extend as far as Phoenicia or the European Bronze Age, however!
What little I can read online of The Metal Industry of the Aztecs, by George Brinton Phillips appears to be saying that the indigenous Mexicans had access to copper, but not enough to make everyday use of. However, when the Spaniards came, they found enough tin deposits around to start making their own bronze (for cannons), so it's not like the supplies weren't there for those who knew how to use them.
In South America the Moche actually did use some bronze, but not for common tools or weaponry. The Inca later started to adapt bronze to such mundane uses, but it was still an expensive material for them. Perhaps they would have soon developed their own proper bronze age, had Pizarro not intervened.