Author:

Keywords:

dikulushi cu-ag deposit, lead isotopes, polysulphide vein-type mineralisation, lufilian arc, central african copperbelt, lead-isotope, neoproterozoic nguba, katanga supergroup, lufilian foreland, northern sweden, icp-ms, deposit, zambia, belt, Science & Technology, Physical Sciences, Geochemistry & Geophysics, Mineralogy, Dikulushi Cu-Ag deposit, Lead isotopes, Polysulphide vein-type mineralisation, Lufilian Arc, CENTRAL AFRICAN COPPERBELT, LEAD-ISOTOPE, NEOPROTEROZOIC NGUBA, LUFILIAN FORELAND, DEPOSIT, BELT, SUPERGROUP, PROVENANCE, KATANGA, LITHOSTRATIGRAPHY, 0402 Geochemistry, 0403 Geology, 0404 Geophysics, Geology, 3703 Geochemistry, 3705 Geology

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 (Pb-206/Pb-204 = 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 Pb-207/Pb-204 vs. Pb-206/Pb-204 diagram (Pb-206/Pb-204 = 18.66-23.65; Pb-207/Pb-204 = 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 Pb-208/Pb-204-Pb-206/Pb-204 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.