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 ° 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/SO 2(g)-O 2 (g) with X Zn ≥ 0,5 (this is, X Fe = 0,125 X Pb = 0,015) between 300 to 900 o C, confirms the strong presence of Zn SO 4, Fe 2(SO 4) 3, PbSO 4 and ZnFe 2O 4 under reactor operating conditions of roasting, validating this analysis with experimental observations.