The melting point of pure copper is 1083 degree C, but to remove stone and slag a temperature of 1200 is needed. Chemically bound copper is also found in ores. It is green or black and doesn't look like a metal. To make copper it should me heated to a temperature of 700-800 C mixed with wood or charcoal. The chemical process is called reduction and the production method smelting .
Many hypothesis exist.
It is possible that the discovery of changing properties of copper with heating, higher and higher temperatures are tried. An other plausible theory starts with lead as the first metal to be melted and with silver as next intermediate step. Lead has a melting point of only 327 degree Celsius. Native lead is not found in nature. All findings of pure lead thus indicate the process of melting.