Question

why carbonate and sulphide Ores are usually converted into oxides during the process of extraction

Answer 1

Because we can't take the suphide.ore and carbonate ore directly
sulphide ore we do roasting
and carbonate ore we do calcination

Answer 2

It is easier to obtain a pure metal from the element's oxide rather than it's sulphide or carbonate.
Calcination is the process of burning a carbonate pre into oxide ore by burning it in the prescence of limited supply of air &
Roasting is the process of burning a sulphide ore into oxide ore by burning it in the prescence of excess of air.