Pb isotopic constraints on the formation of the Dikulushi Cu–Pb–Zn–Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo)
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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.
KeywordsDikulushi Cu–Ag deposit Lead isotopes Polysulphide vein-type mineralisation Lufilian Arc
Our gratitude goes to the exploration department of Anvil Mining, which has provided logistic support during sample collection in the Dikulushi region in 2003, 2004 and 2006. We acknowledge W. Heijlen who collected the first set of samples in 2003 and we thank W. Heijlen and S. Dewaele for information on the Cu occurrences in the Kundelungu Plateau region. The constructive comments of Åke Johansson (NHM Stockholm, Sweden), an anonymous reviewer, associate editor Rolf Romer and editor Bernd Lehmann greatly improved this paper. JS thanks RLR for massive, robust and stimulating inputs. This research is financially supported by research grant G.0585.06 of the FWO-Vlaanderen.
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