Evolution of Cu–Co mineralizing fluids at Nkana Mine, Central African Copperbelt, Zambia Ph. Muchez a, * , D. Brems a , E. Clara a , A. De Cleyn a , L. Lammens a , A. Boyce b , D. De Muynck c,d , W. Mukumba e , O. Sikazwe f a Geodynamics and Geofluids Research Group, Department of Earth and Environmental Sciences, K.U. Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium b Scottish Universities Environmental Research Centre, Rankin Avenue, Scottish Enterprise Technology Park, East Kilbride G75 0QF Scotland, UK c Center for Archaeological Sciences, Department of Earth and Environmental Sciences, K.U. Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium d Department of Analytical Chemistry, Ghent University, Krijgslaan 281-S12, B-9000 Ghent, Belgium e Mopani Copper Mines Plc., Nkana Mine Site, P.O. Box 22000, Kitwe, Zambia f University of Zambia, School of Mines, Geology Department, P.O. Box 32379, Lusaka, Zambia article info Article history: Received 7 October 2009 Received in revised form 4 May 2010 Accepted 10 May 2010 Available online 19 May 2010 Keywords: Nkana Zambian Copperbelt Sediment-hosted Cu–Co deposits Fluid inclusions Stable isotopes Sr isotopes abstract The Central African Copperbelt hosts numerous world class stratiform Cu–Co deposits in the Neoprote- rozoic Katanga Supergroup (<880 to ± 500 Ma). These high grade deposits resulted from multiple miner- alization and remobilization stages. The Nkana Cu–Co deposit in the Zambian part of the Copperbelt is such a stratiform deposit but the location of the rich ore bodies is structurally controlled, i.e. occurring in the hinge zones of tight to isoclinal folds. Late stage mineralization and/or remobilization caused this enrichment. Three major mineralization/remobilization stages have taken place during the Lufilian orog- eny. They are characterized by folded layer parallel veins, highly irregular veins crosscutting the folds, and finally unfolded massive veins. An evolution in the oxygen, carbon and sulphur isotopic composition is present from the layer parallel and irregular to the massive veins. The more negative d 18 O values in the carbonates from the massive veins most likely reflect a decrease in the oxygen isotopic composition of the ambient, metamorphic flu- ids. The d 13 C values range between 25‰ and 5‰ V-PDB with a trend towards less negative values in the massive veins, possibly reflecting an ongoing oxidation of organic matter in a relatively closed sys- tem. Early framboidal and massive pyrites disseminated in the host rock have distinctly negative d 34 S val- ues, i.e. between 16‰ and 9.7‰ V-CDT. The sulphur isotopic composition increases from these early diagenetic pyrites to sulphides in the successive vein generations. The d 34 S values of the massive veins are positive and cluster between 1.3‰ and 2.0‰ V-CDT. This enrichment in heavy sulphur is interpreted as a result of the mixing of S remobilized from early sulphides, with S derived from the thermochemical reduction of sulphate. With time, the sulphur derived from TSR became more important. The Sr isotopic composition of the carbonates in all three vein generations shows a wide range between 0.71672 and 0.75407. All values are significantly more radiogenic than the strontium isotopic composition of Neopro- terozoic marine carbonates (0.7056–0.7087). The radiogenic values indicate interaction of the mineraliz- ing fluid with the basement or the siliciclastic sediments derived from it. All fluid inclusions measured in the different vein generations have a dominant H 2 O–NaCl/KCl–MgCl 2 composition with the presence of a gaseous component in some inclusions. Fluid inclusions in the layer parallel veins suggest entrapment around 450 °C at a depth of 8.4 km (2100 bars), i.e. during the main period of metamorphism. Secondary fluid inclusions of unknown origin in the layer parallel, irregular and massive veins have a high salinity (18.1 to >23.2 eq. wt.% NaCl) and homogenization temperatures between 100 and 250 °C. These fluids were trapped after formation of the veins, likely during retrograde metamorphism. The study of the veins, which formed between 580 and 520 Ma, nicely demonstrate the complexity of the metallogenesis of the Cu–Co ore deposits in the Copperbelt. Therefore, geochemical, microthermo- metric and geochronological analyses need to be carried out on individual generations to fully under- stand the evolution of ore formation through time. Ó 2010 Elsevier Ltd. All rights reserved. 1464-343X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2010.05.003 * Corresponding author. Tel.: +32 16 327584; fax: +32 16 327981. E-mail address: philippe.muchez@ees.kuleuven.be (Ph. Muchez). Journal of African Earth Sciences 58 (2010) 457–474 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci