2 Cu2S + 2 CaCO3 + 5 O2 → 2 CaSO4 + 4 CuO + 2 CO2
This is an oxidation-reduction (redox) reaction:
4 CuI - 4 e- → 4 CuII (oxidation)
2 S-II - 16 e- → 2 SVI (oxidation)
10 O0 + 20 e- → 10 O-II (reduction)
Cu2S is a reducing agent, Cu2S is a reducing agent, O2 is an oxidizing agent.