That was a lot of copper to just disappear.
To be sure. If we go back to the era from say 3000 to 1000 BC, we have thousands of tons too much copper in the Old World, and at the same time thousands of tons too much in the New (it WAS mined, but there were only very few and scattered populations in the New World anywhere, with no evidence they used copper to any extent).
It is now being whispered at last that it may have been shipped from the New World to the Old. If I live to be a 100, they may yet get to where I was when I was 15.