Why are sulphide ores converted to oxide form before reduction to metal ?

Explanation

Sulphide ores thermodynamically more stable than `CS_(2)` and hence cannot be converted by using coke (general and common reducing agent) as reducing agent. Moreover `CO_(2)` is more volatile and thermodynamically more stable than `CS_(2)`. Thus all means that `Delta_(f)G^(@)` of a metal sulphide is not compensated by the energy of reaction of metal sulphide with coke.
Hence, it is better to convert the sulphide ore to oxide form and then apply smelting, i.e. carbon reduction method.