Mass balance modelling of cobalt sources in the Tenke-Fungurume copper-cobalt district, Democratic Republic of the Congo

Abstract Sedimentary rock-hosted copper-cobalt deposits of the Central African Copperbelt (CACB) supply over 70% of global cobalt production. Cobalt source rocks proposed in the literature include Katangan red beds and mafic igneous rocks, and mafic-ultramafic rocks in the pre-Katangan basement. Given the limited exposure of potential source rocks in cobalt-rich CACB deposits, mass balance modelling is developed to evaluate cobalt sources in the Tenke-Fungurume copper-cobalt district (TFMD), Democratic Republic of the Congo, with an estimated total cobalt budget of 25.1 Mt. Modelled parameters are source rock volume and composition, and cobalt leaching efficiency. Assuming 20% leaching efficiency, the Katangan basal units thickness required to supply the cobalt budget greatly exceeds observed values across the CACB, with over 3,800 m and 1,900 m for red beds and gabbro, respectively. In forward models combining Katangan basal units and pre-Katangan basement, the cobalt budget was achieved by a scenario with basement containing over 63% lherzolite. In this context, ultramafic rocks associated with the NE Kibaran belt extension may occur within the pre-Katangan basement. The cobalt budget was also achieved by increasing basement leaching efficiency from 5% to 23% and to 10% for felsic-intermediate and mafic compositions, respectively. These results and the parameter sensitivity analysis highlight a fundamental control of leaching efficiency on cobalt sourcing. Such efficient leaching may have been driven by hypersaline residual brines, with major structural pathways facilitating fluid flow into the basement. Overall, the modelling underscores the key roles of ultramafic basement rocks and leaching efficiency in effective cobalt sourcing.