I was recently told that copper from North America (especially the current Upper Peninsula of Michigan) was important in the bronze of the early Bronze Age of east Asia. I have been unable to google such a theory. Is there any suggestion that this could have been the case? Is there any history of trade between the two areas at all?

Edit: I have found one source (a guy called Graham Hancock) who claims that this is the case, I am unable to find anything that substantiates this, nor is my chemical specialty near enough to metallurgy to validate anything that I see about the similarity of the metals to support such a conclusion.