At least one of said materials is sulphide bearing, and which contain one or more impurities forming the group arsenic, antimony, bismuth, mercury, tin, chlorine and other halogens. The invention is characterized by adjusting the halogen content of the mix so that it is substantially at least stoichiometric in relation to remaining impurities in the group, whereafter the mix is charged to a furnace in which melting can take place and in which the mix is heated to at least 500 deg.C, but beneath the melting points of respective ingredients of the mix, while maintaining good contact with hot gas therewith to expel substantially all of the aforementioned impurities present. The mix is then heated to completely smelt the ingredients present, to form a slag and a copper matte, which latter contains the valuable metal content, whereafter this valuable metal content is recovered with the aid of a suitable, conventional method. |