The stratiform CuâCo 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 CuâCo sulphides and authigenic quartz, whereas in type 2 examples, authigenic quartz and CuâCo sulphides precipitated prior to dolomite and are coarse-grained. The sulphur isotopic composition of the copperâcobalt sulphides in the type 1 pseudomorphs is between â10.3 and 3.1â° relative to the Vienna Canyon Diablo Troilite, indicating that the sulphide component was derived from bacterial sulphate reduction (BSR). The generation of 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 CuâCo 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 (8â18 eq. wt.% NaCl) fluid, possibly derived from evaporated seawater which migrated through the deep subsurface. 87Sr/86Sr 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 (87Sr/86Srâ=â0.7056â0.7087). This suggests intense interaction with siliciclastic sedimentary rocks and/or the granitic basement. The low carbon isotopic composition of the dolomite in the pseudomorphs (â7.02 and â9.93â° relative to the Vienna Pee Dee Belemnite, V-PDB) compared to the host rock dolomite (â4.90 and +1.31â° V-PDB) resulted from the oxidation of organic matter during BSR.