The Key Role of Neoproterozoic Rifting in Cu–Co Enrichment of the Central African Copper Belt: Indications From the Gabbro Origin of the Chambishi Cu–Co Deposit in Zambia

ABSTRACT The Zambian Copperbelt, which is the southern part of the Central African Copperbelt (CACB), contains numerous large to super‐large Cu–Co deposits. However, mafic magmatic rocks in this region are poorly understood, and their tectonic setting remains controversial. To address this and to explore their relationship with mineralisation, we investigated the Chambishi Cu–Co deposit in Zambia, presenting mineralogical data of the ores together with precise geochronological and geochemical analyses of gabbro intruded into the Upper Roan Subgroup. LA‐ICP‐MS zircon U–Pb dating indicates the Chambishi gabbro emplacement at ca. 767 Ma. The rocks exhibit pronounced negative Eu anomalies (δEu = 0.17 to 0.24) and Sr depletion, but no significant negative anomalies in Nb, Zr or Hf. They have low Nb/U (17.17 to 25.96) and Ce/Pb (7.64 to 7.88) ratios, high V/Sc (8.7 to 11.8), with εNd( t ) values ranging from −0.70 to +0.67, initial 87 Sr/ 86 Sr ratios of 0.70619 to 0.70859 and zircon εHf( t ) values from +0.6 to +12.6. These features of the Chambishi gabbro indicate a sub‐alkaline basaltic magma. This magma derived from moderately partially molten enriched mantle one (EMI) type lithospheric mantle metasomatised by subduction‐related fluids. Tectonic discrimination diagrams (Zr/Y vs. Zr, Th/Hf vs. Ta/Hf, Zr/Y vs. Zr/Nb) consistently indicate an intraplate tholeiitic affinity formed in an extensional setting. Integrating age data from rift‐related Cu–Co deposits across the CACB and the predominance of rift‐stage ores at Chambishi, we propose that syn‐rift period represents the main mineralisation period for the CACB. The rift extension event recorded by the Chambishi gabbro constitutes a deep‐seated response to this main mineralisation period. Later orogenic events only caused localised overprinting.