Being your from the upper midwest you must mean Crandon area? Or the Copper Country of the UP of Michigan? I know that some of the masses found up there reached the 20 ton range and over. Divers have told me that while diving in the big lake, they have seen entire ledges of pure copper under the water.
The Crandon copper mine my brothers did his masters in mining engineering on that ore deposit.
It was a huge money maker at 35 cents a pound.
At todays prices wow.