Pb isotopic constraints on the formation of the Dikulushi Cu–Pb–Zn–Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo) |
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Authors: | Maarten Haest Jens Schneider Christophe Cloquet Kris Latruwe Frank Vanhaecke Philippe Muchez |
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Institution: | 1. Geodynamics and Geofluids Research Group, KULeuven, Celestijnenlaan 200E, 3001, Heverlee, Belgium 2. Centre for 3D Mineral Mapping, CSIRO, Dick Perry Avenue 26, WA-6151, Kensington, Australia 3. Department of Mineralogy, Technische Universit?t Bergakademie Freiberg, Brennhausgasse 14, 09596, Freiberg, Germany 4. Centre de Recherches Pétrographiques et Géochimiques, rue Notre Dame des Pauvres 5, 54501, Vandoeuvre lès Nancy, France 5. Department of Analytical Chemistry, Ghent University, Krijgslaan 281–S12, 9000, Ghent, Belgium
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Abstract: | Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed
during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago)
in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic
composition (206Pb/204Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides
were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a
chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of
lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the 207Pb/204Pb vs. 206Pb/204Pb diagram (206Pb/204Pb = 18.66–23.65; 207Pb/204Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead
and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation
also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided
Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides,
whereas the U most likely originated from external sources. Local metal sources are also suggested by the 208Pb/204Pb–206Pb/204Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate
host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu
Plateau clearly record a diachronous evolution. |
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