Phase equilibria in the ZnO-''CuO 0.5 ''-SiO 2 system have been investigated at 1403-1948 K (1130-1675°C) for oxide liquid in equilibrium with Cu-Zn metal ([ 99% Cu) and solid oxide phases: (a) tridymite or cristobalite SiO 2 ; (b) willemite Zn 2 SiO 4 ; (c) zincite ZnO; and (d) cuprite Cu 2 O. Two-liquid immiscibility range in the high-SiO 2 slags has also been studied. High-temperature equilibration on primary phase (SiO 2 , Cu 2 O), inert metal (platinum-iridium wire), or ceramic (Al 2 O 3 for high-Cu 2 O slags) substrates, followed by quenching and direct measurement of Zn, Cu, Si and possible impurities (Al, Pt, Ir) concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with metal. All results are projected onto the ZnO-''CuO 0.5 ''-SiO 2 plane for presentation purposes.