CuS^-II + 4 HN^VO₃ → Cu(N^VO₃)₂ + S^IVO₂ + 2 N^IIO + 2 H₂O

This is an oxidation-reduction (redox) reaction:

S^-II - 6 e^- → S^IV (oxidation)

2 N^V + 6 e^- → 2 N^II (reduction)

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