Thermodynamic data in the literature relating to phase relationships in the Cu-Fe-O-S-SiO2 system have been reviewed critically. These phase relationships in the range of 1100 to 1350[degree]C for the binary, ternary and quaternary systems that are components of the quinary system are described with the use of T-X, potential-composition and P-1/T phase diagrams and stability diagrams. Conditions leading to the immiscibility of the liquid oxysylfide phase which results in the formation of the slag and matte phases are pointed out. Information on the quinary system is very limited.