Ammonium sulfate is a bit acidic, sufficiently for dissolving small amount of copper oxide to form copper sulfate. Then some ammonia is freeing and form complex (formally with half of) copper sulfate. Since amount of ammonia is unsufficient to complex whole copper in solution we can expect other complexes with 1,2, or 3 ammonia in solution, and since contact with air - eventually some basic copper carbonate, especially after evaporation of water.