How long ago did they start mining copper? When did they cease mining copper?
Right now the dates for the artifacts are better established than the dates for the mines. The oldest radiocarbon date known so far on a finely-made native copper tool is about 6700 years. This tool was found at South Fowl Lake, Minnesota. Clearly, the technique of working copper was discovered and highly developed earlier than this, because the tool is so carefully crafted. At Isle Royale, ancient pits were dated to about 4400 years ago.
