Phase equilibria of the Cu-O-MgO system was experimentally investigated in air over the temperature range of 1200-1500 degrees C employing a static high-temperature equilibration and quenching method. The resulting phase compositions were analysed with EPMA. A small solubility of MgO into the liquid oxide phase and considerable solid solubility of CuOx into the solid MgO phase were observed. (C) 2015 Elsevier B.V. All rights reserved.