Sulphide Re-Os geochronology links orogenesis, salt and Cu-Co ores in the Central African Copperbelt

N. J. Saintilan, D. Selby, R. A. Creaser, S. Dewaele
2018 Scientific Reports  
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more » ... . Please consult the full DRO policy for further details. The origin of giant, sedimentary rock-hosted copper-cobalt (Cu-Co) provinces remains contentious, in part due to the lack of precise and reliable ages for mineralisation. As such, no consensus has been reached on the genetic model for ore formation, and the relationships between tectonism, palaeo-fluid circulation and mineralisation. Here, we link the timing of Cu-Co mineralisation in the Central African Copperbelt to compressional tectonics during the Lufilian Orogeny by using new ca. 609-473 Ma ages given by rhenium-osmium (Re-Os) isotope data for individual Cu-Co sulphides (carrolite and bornite) from the Cu-Co Kamoto deposit. The initial Os isotope composition of carrolite is compatible with the leaching of Os and Cu(-Co) from Mesoproterozoic Cu sulphide deposits hosted in fertile basement. In contrast, the ca. 473 Ma Cu-Au mineralisation stage, which is coeval with late-to post-compressional deformation, may be a distal expression of fluid flow and heat transfer caused by magmatic intrusions in the core of the collisional orogen. The Re-Os ages support a model for mineralisation driven by evaporite dissolution and percolation of large volumes of dense brines in the Katangan Basin during the Lufilian Orogeny. The most important source of copper (Cu), beyond that of giant and supergiant porphyry Cu deposits, is sedimentary rock-hosted stratiform and vein-type Cu deposits. Mining of economical mineralisation is centred on the Udokan deposit in the Palaeoproterozoic Kodaro-Udokan Basin in Siberia, Russian Federation 1 , the Central African Copperbelt in the Neoproterozoic Katangan Basin in Zambia and the Democratic Republic of Congo 2 (DRC, Fig. 1a ) and the Permian Zechstein Basin of Central Europe 3 . Containing ca. 200 Mt of Cu and a significant supply of cobalt (Co), the Central African Copperbelt along the Lufilian fold-and-thrust belt (i.e., Lufilian Arc, Fig. 1a) is the world's most important metallogenic province of this kind 4 . Recent uranium-lead (U-Pb) and rhenium-osmium (Re-Os) geochronological studies have revealed that several major sediment-hosted stratiform and vein-type Cu deposits formed during orogenesis and the associated metamorphism (e.g., Udokan and Nussir in Norway) 1,5 , or mineralisation coincided with the timing of basin-wide intersecting folding of basinal strata (e.g., Dzhezkazgan in Kazhakstan) 6 . In parallel, Re-Os ages of molybdenite, which is paragenetically associated with Cu-sulphides, were combined with previous structural, mineralogical and geochemical evidence in several ore deposits in the Zambian part of the Central African Copperbelt, where the host rocks were metamorphosed to the greenschist to amphibolite facies 4,7,8 (Fig. 1b ). An epigenetic introduction of Cu as stratiform and veinlet-type sulphide mineralisation during the peak and post-peak stages of the Lufilian collisional orogeny in those Zambian deposits was proposed (540-490 Ma) 4,7-10 . Although the most effective time for fluid mobilization, overpressuring, and expulsion of metal-bearing brines is related to contraction and fault inversion 4,11,12 , this genetic model was criticised 13,14 in favour of the popular paradigm of older, primary syndiagenetic Cu introduction followed by possible orogenic overprint/remobilization 2,15-18 . Published: xx xx xxxx OPEN www.nature.com/scientificreports/
doi:10.1038/s41598-018-33399-7 fatcat:k7qb2wpadbbrzo6drpocby63xy