4 CuFeIIS2-II + 13 O20 2 Fe2IIIO3-II + 4 CuO-II + 8 SIVO2-II

This is an oxidation-reduction (redox) reaction:

8 S-II - 48 e- 8 SIV (oxidation)

4 FeII - 4 e- 4 FeIII (oxidation)

26 O0 + 52 e- 26 O-II (reduction)

CuFeS2 is a reducing agent, CuFeS2 is a reducing agent, O2 is an oxidizing agent.