Geology, geochemistry, and exploration of the Central African Copperbelt: a review

Data collated from the literature is used to summarize the petrogenesis of Central African Cu deposits located in the Neoproterozoic Katangan basin, the most mineralized basin on Earth with 8.7 billion tons of pre-mining Cu ore reserves grading 2.6% Cu. Deposits mostly occur within specific stratigraphic layers including the Mines-Kitwe and Mwale subgroups of the Roan and Nguba groups. Ore bodies occur as stratiform and vein-type deposits and display vertical and lateral zoning generally consisting of chalcocite + chalcopyrite + bornite upward/outward to chalcopyrite + pyrite and finally, pyrite. Chalcocite is more common within the Congolese ore bodies whereas chalcopyrite predominates within the Zambian ore bodies. The δ³⁴S sulphide values (−28 to +29‰) of Cu sulphide minerals display generally lighter sulphur isotopes in the Congolese part (−14 to +2‰) and become heavier within Zambian deposits (−16 to +23‰), implying bacteriological contribution and thermochemical reduction of sulphate contribution for the lighter and heavier S isotopes, respectively. The heavy δ³⁴S Cu sulphide values (−2 to +25‰) are consistent with the δ³⁴S data of Cu ore veins (−4 to +23‰). The δ¹³C and δ¹⁸O values (−23.1 to +8.7‰ and −1.8 to −28.0‰, respectively) of carbonate-related ores are consistently lighter than carbonate host values implying the oxidation of organic matter during carbonate deposition. The isotopic ratios of²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and²⁰⁸Pb/²⁰⁴Pb range between 17.885–23.650, 15.557–16.728 and 37.564–42.594, respectively, suggesting multiple sources of Pb in Cu ores. Uranium-Pb, U-Th-Pb, Pb-Pb, and Re-Os dating data of ore-related uraninite, brannerite, rutile, Cu-bearing sulphides, monazite, molybdenite, and mica fall within a ca. 670–490 Ma window, yielding two major episodes at ca. 670–645 Ma and 540–490 Ma for early stratiform and late vein stages of Cu mineralization. Two mineralizing stages were distinguished by fluid inclusions with the first deposited during diagenesis at low-temperature and moderate salinity, and the second ore stage that deposited metals at high-temperature and high salinity during the Lufilian orogeny. The Lufilian orogeny at ca. 590–465 Ma may have strongly influenced formation of the Central African Cu deposits, particularly the southern portion of the Copperbelt in Zambia. The sedimentary rocks display a prograde metamorphic trend varying from prehnite-pumpellyite facies in the DR Congo to greenschist-amphibolite facies in Zambia. Metamorphic processes during the orogeny may have led to metal redistribution characterizing the Zambian deposits. Common features include large ore reserves but relatively low grades (averaging 1.9% Cu versus 2.7% Cu in DR Congo), with chalcopyrite as the main Cu sulphide mineral, heavy δ³⁴S values for Cu sulphide minerals, and introduction of molybdenite into the ore system during the Lufilian event. Keys to finding new deposits in the Central African Copperbelt may require enhanced scientific research, integrating data-model approaches and advanced multi-layer and multi-scale technologies, focusing on the comprehensive characteristics of ore deposits.