////there WAS no serious 'culture' doing real 'mining'.////

The copper pits number in the thousands and the mining operation went on for centuries. Look it up. My guess is that Indian tribes used slave labor--i.e. others captured in war--to do the mining and did not allow them to leave anything of their old identities behind. I can't believe any overseas power had a colony here for that long. Had to be a native culture that did it.