Thermodynamic mathematical model, describing the behavior of silver and gold during reducing smelting of roasted copper concentrates, obtaining slag and blister copper was developed. It is based on thermodynamic (literature) and experimental data, and can be useful for operative analysis of impact of different technological factors on metals distribution. Model takes into account some parameters, such as: initial materials and final slag composition, process temperature and oxidizing potential (Р_O2). Total losses of metals with final slag are divided into two parts: chemical (dissolution, determined by temperature and oxidizing potential) and mechanical (emulsion of fine drops of bottom phase in the slag, determined by temperature and slag composition), and each part is described separately.