The homogeneity boundaries of liquid two-component solutions of sulfur with copper, lead of three component Cu-Pb-S melts are determined and approximated by solving the thermodynamic equations of heterogeneous P-T-x phase equilibrium using MGA. Experimental data were used for state diagrams of boundary systems Copper-Sulfur Lead-Sulfur and the quasi-binary section Copper (I) Sulfide -Lead (II) Sulfide. For the first time, critical temperatures (Tcr) and pressure (Pcr) were determined for the immiscibility regions of sulfur-rich liquid alloys, which have high values: Pcr = 170 ÷ 510 atm and Tcr = 1520 ÷ 1880 K. Lead (II) sulfide crystallization surfaces p-type PbS1 + x and n-type conductivity Pb1 + xS, as well as the saturated vapor pressure of diatomic sulfur molecules above the liquidus surface of lead sulfide of variable composition were calculated and modeled. All functional relationships Temperature (T)-Pressure (P)-Mole fraction (X) for the phase diagram of the Cu-Pb-S system are 3D modeled and visualized using the OriginLab computer program.