The oldest copper artifacts we have are from the old copper complex around Lake Superior, and more recent metalworking traditions were present throughout much of the Americas.
Archaeological evidence has not revealed metal smelting or alloying of metals by pre-Columbian native peoples north of the Rio Grande; however, they did use native copper extensively.[32]
Which then further cites: George Rapp Jr, Guy Gibbon & Kenneth Ames (1998). Archaeology of Prehistoric Native America: an Encyclopedia. New York: Taylor & Francis. p. 26.
I do not own this book, so I apologize I cannot verify the citation.
I didn’t realize how easy native copper smelting was until I watched some of those primitive YouTube channels where they make a water filtration system and smelt some copper using a hand made smelter. Linked below if anyone is interested.
It's not exactly easy - requires good quality coal, and fine tuning to get the right airflow to coal ratio to create a sufficiently hot furnace without becoming oxidizing. Those guys describe having to try multiple times before working out a successful process to produce copper, documenting a couple of their experiments in videos. They've nicely fully documented their final configuration in this video - some high quality experimental archeology work: https://www.youtube.com/watch?v=KYaJuab5riE
Keep in mind that you have to be wary of poisonous fumes - hopefully the elements giving their copper alloy a brassy appearance don't include lead, or worse, arsenic.
Native copper working is considered metallurgy in archaeology. If you disagree, feel free to take it up with the archaeometallurgists.
Moreover, purification from ores was done. The so-called copper bells of the southwest were mainly produced from ores rather than native copper and were often alloyed with arsenic or silver to modify the color. The main center of production was paquimé (~180mi west of the Rio Grande), but the cultural area extends well over the border into AZ, NM, and CO.
For an amateur but no less correct source, wikipedia provides a good quip for us:
https://en.wikipedia.org/wiki/Metallurgy_in_pre-Columbian_Am...
Archaeological evidence has not revealed metal smelting or alloying of metals by pre-Columbian native peoples north of the Rio Grande; however, they did use native copper extensively.[32]
Which then further cites: George Rapp Jr, Guy Gibbon & Kenneth Ames (1998). Archaeology of Prehistoric Native America: an Encyclopedia. New York: Taylor & Francis. p. 26.
I do not own this book, so I apologize I cannot verify the citation.