Anhydrite pseudomorphs and the origin of stratiform Cu-Co ores in the Katangan Copperbelt (Democratic Republic of Congo)

The stratiform Cu–Co ore mineralisation in the Katangan Copperbelt consists of dispersed sulphides and sulphides in nodules and lenses, which are often pseudomorphs after evaporites. Two types of pseudomorphs can be distinguished in the nodules and lenses. In type 1 examples, dolomite precipitated first and was subsequently replaced by Cu–Co sulphides and authigenic quartz, whereas in type 2 examples, authigenic quartz and Cu–Co sulphides precipitated prior to dolomite and are coarse-grained. The sulphur isotopic composition of the copper–cobalt sulphides in the type 1 pseudomorphs is between −10.3 and 3.1‰ relative to the Vienna Canyon Diablo Troilite, indicating that the sulphide component was derived from bacterial sulphate reduction (BSR). The generation of HCO<sub>3</sub>during this process caused the precipitation and replacement of anhydrite by dolomite. A second product of BSR is the generation of H2S, resulting in the precipitation of Cu–Co sulphides from the mineralising fluids. Initial sulphide precipitation occurred along the rim of the pseudomorphs and continued towards the core. Precipitation of authigenic quartz was most likely induced by a pH decrease during sulphide precipitation. Fluid inclusion data from quartz indicate the presence of a high-salinity (8–18 eq. wt.% NaCl) fluid, possibly derived from evaporated seawater which migrated through the deep subsurface. <sup>87</sup>Sr/<sup>86</sup>Sr ratios of dolomite in type 1 nodules range between 0.71012 and 0.73576, significantly more radiogenic than the strontium isotopic composition of Neoproterozoic marine carbonates (<sup>87</sup>Sr/<sup>86</sup>Sr  = 0.7056–0.7087). This suggests intense interaction with siliciclastic sedimentary rocks and/or the granitic basement. The low carbon isotopic composition of the dolomite in the pseudomorphs (−7.02 and −9.93‰ relative to the Vienna Pee Dee Belemnite, V-PDB) compared to the host rock dolomite (−4.90 and +1.31‰ V-PDB) resulted from the oxidation of organic matter during BSR

Overview of the Neoproterozoic sedimentary series exposed along margins of the Congo Basin

The Congo Shield is a central African large landmass with several Archean nuclei welded during the Eburnean orogeny approx. 2.1-1.8 Ga and subsequently stabilized as a coherent unit throughout late Paleoproterozoic to Meso-Neoproterozoic times. The early Neoproterozoic was marked by rifting along the margins of the Congo Shield related to the break-up of Rodinia at about 1.0 Ga, and opening of the Adamastor Ocean, followed by passive margin-type sedimentation and, finally, foreland basin deposition during the amalgamation of Gondwanaland initiated at approximately 600 Ma. We summarize the present knowledge of the lithostratigraphy of the Neoproterozoic basins exposed along margins of the Congo Basin in an attempt to establish chronostratigraphic correlations between these isolated basins in the Democratic Republic of Congo and neighboring countries.SCOPUS: ch.binfo:eu-repo/semantics/publishe