CuS-II + 4 HNVO3 Cu(NVO3)2 + S0 + 2 NIVO2 + 2 H2O

This is an oxidation-reduction (redox) reaction:

S-II - 2 e- S0 (oxidation)

2 NV + 2 e- 2 NIV (reduction)

CuS is a reducing agent, HNO3 is an oxidizing agent.