This study has of central aim to establish the physicochemical characteristics of the accretions present in an industrial furnace of sphalerite roasting (ZnS) operating at 945 degrees C which, according to observations on plant, they are formed preferentially on surfaces at low temperature such as boiler output, cooling pipes and hoppers. The analysis by X-Ray Diffraction, Atomic Absorption, and Image Analysis showed that the main components of these deposits are zinc sulfate, lead sulfate and zinc ferrite. A thermodynamic analysis based on the construction of stability diagrams for the system Zn-Fe-Pb/SO2(g)-O-2 (g) with X-Zn >= 0,5 (this is, X-Fe = 0,125 X-Pb = 0,015) between 300 to 900 degrees C, confirms the strong presence of ZnSO4, Fe-2(SO4)(3), PbSO4 and ZnFe2O4 under reactor operating conditions of roasting, validating this analysis with experimental observations.