No North American natives cast copper. Beating to form a piece from raw copper nuggets was the method used.
Although high temperatures are needed to melt copper, annealing the native copper to make it softer and more inclined to bend or flatten only requires a heat of 700 to 1200 degrees F. Generally around 800 degrees Fahrenheit is all you need to anneal copper, that's a dull red glow and easily obtainable with a wood fire.
As you form the copper with blows it hardens again rather quickly. Beating the copper after it work hardens leads to cracks and brittle metal and will ruin your piece. For that reason it's necessary to anneal the piece several times before you get to the final form. All that is very doable with a few rocks and a wood fire but it does require knowledge and experience to be successful.
Native coppersmiths were few and far between due to the lack of raw material and the experience needed to successfully complete a piece. For the most part it can be demonstrated that hand copper work before the arrival of Europeans was restricted to an area around the Great Lakes copper deposits where native copper is fairly common in a relatively pure form.
Copper is pretty easy to buy in a pure form today. You aren't going to risk much by buying some copper at the hardware store and practicing with a hammer and anvil. Anneal with a cheap propane torch and a bucket of water. Get a few dozen pieces under your belt and you might be ready to tackle making something from your copper nugget.
Heavy Pan
