These copper pieces are known as bronzed copper, as they do not look like copper coins, but more like bronze. If your medal is copper - bronze, skip to number 8, below. It was struck after 1904, only for collectors. These are all common, and of modest collector value. They exist in small and large sizes, both common.
Silver medals exist and are rare.
Most genuine silver Indian Peace medals, except the U.S. Grant medals, were issued holed or looped at the top for wearing by the Indians. If yours is not holed, and shows no sign of being looped, it is most likely a modern copy. Some later issue IP medals were issued in silver, unholed. Generally a hole is a good sign of your medal being genuine. If yours is in near mint condition, it is likely a modern strike.