Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2
2CuFeS2 + O2 → Cu2S + 2FeS + SO2↑
2Cu2S + 3O2 → 2Cu2O + 2SO2↑
2FeS + 3O2 → 2FeO + 2SO2↑
Thus partial roasting of chalcopyrirte produced Cu20 and FeO