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Dumps in the Central German Mansfeld mining district have been investigated by a multi-disciplinary research team to develop a holistic concept for the recovery of base and trace metals from low-grade Kupferschiefer ore. Geochemical and mineralogical data from representative sampling indicate that the low-grade Kupferschiefer dumps contain significant amounts of Cu (0.6 %) and Ag (up to 800 ppm), besides exploitable grades of Pb and Zn. Additionally to flotation and hydrometallurgy, first shake flask bioleaching experiments on otherwise untreated Kupferschiefer ore yield Cu recovery rates of up to 95 %. A total of 900 t Cu and 5 t Ag contained in black copper can thus be produced from the pilot dump of 100 000 m 3 low-grade Kupferschiefer ore. Additionally, large volumes of limestone waste, separated from the dumps by sensor-based sorting, can be utilized as aggregate in the construction industry.Figure 6. Mass balance of Cu in different solvents with varying pretreatment of the material.

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In this study, two black shale copper ores from different Mid-European Kupferschiefer-type deposits and their flotation concentrates were used for bioleaching tests. All samples were subjected to stirred tank bioleaching using an acidophilic, moderately thermophilic microbial consortium. The distribution of sulfides and gangue minerals in the ores, copper concentrates and residues of both, bioleaching and sterile chemical control tests were investigated using EDX-based particle analysis. The black shale ores and the extracted copper concentrates varied in their mineralogical composition with respect to the distribution of sulfides and gangue. While the copper-bearing sulfides in the Sangerhausen black shale and concentrate were dominated by bornite and chalcopyrite, the Rudna black shale and its flotation concentrate were rich in chalcocite and bornite. Differences in the portion of gangue minerals were detected in particular for carbonates that represented the dominant mineral group in the Rudna black shale and its copper concentrate. Distinct Cu dissolution kinetics and recovery rates of Co and other associated metals were observed for the various materials processed by bioleaching. Copper sulfides were completely dissolved also in both black shale ores. However, the sulfide distribution in the bioleaching residues of the Sangerhausen concentrate revealed that a significant portion of chalcopyrite was not leached. Even higher recovery rates for copper and other metals were determined for the bioleaching tests on the Rudna concentrate, in which copper sulfides were nearly completely dissolved. Alteration of copper sulfides and the formation of calcium sulfate were in particular observed in the sterile control residue of the Rudna concentrate, due to excessively use of sulfuric acid for pH stabilization. Lead sulfate precipitates increasingly occurred in the bioleaching residues, but represented also a common secondary phase in the sterile leaching residues.