Lead metallurgical slag from the Dörschl furnace resembles magmatic rocks with respect to the mineral composition and petrographic structure. The majority of mineral phases in lead metallurgical slag are not 'stoichiometric' chemical compounds present in natural conditions. The slag studied contains Cu and Cu+Fe sulfides, i.e. cubanite, covellite, bornite and chalcopyrite. The most Cu-rich phase in the lead metallurgical slag is cubanite (16 - 20 % wt.). Cu is present also in the form of inclusions of metallic copper in silicates. Zinc is mostly present in the form of sulfides (sphalerite) and silicates (willemite). Iron occurs mainly as metallic iron of various composition, magnetite, phayalite and pyrrhotite. Magnetite forms tiny inclusions in silicates of phayalite type and in rhombic pyroxenes. Lead is mostly present in the form of Pb alloys with Ag, Cu, Zn. Arsenic present in the slag was captured by the crystallizing metallic iron and incorporated in its crystal lattice. The slag contains also a minor quantity of metallic silver and molybdenite. The knowledge of mineral phases composed of non-ferrous metals, i.e. Zn, Cu and Pb may facilitate the design of methods for their recovery. Thus a waste product that is arduous to the environment and deposited on a heap may become a valuable anthropogenic source of these metals.