Characterizing cobalt mineralization in the southeast orebody of Chambishi Cu-Co deposit, Zambia

• Sedimentary pre-enrichment and orogenic upgrading are likely key processes in Co mineralization. • Syngenetic Co-rich sedimentary pyrite was identified in argillite from the Chambishi SE orebody. • Independent Co minerals include carrollite, cobaltite, Co-pentlandite, and linnaeite. • Co-rich sulfide precipitation resulted by fluid reduction due to the organic material input. The Chambishi Southeast orebody in the Zambian Copperbelt is notable for its significant Co mineralization, particularly compared to the Co-poor Main and West orebodies. However, the mechanisms controlling Co distribution and enrichment remain unclear, as previous study have primarily focused on copper mineralization. Here, the Co-rich ore samples and wall rocks from the southeast orebody were analyzed using micro-X-ray fluorescence spectroscopy, Tescan integrated mineral analyzer, electron probe micro-analysis and whole-rock trace element analyses. Cobalt occurs mainly in the Copperbelt Orebody Member (COM) (mean Co = 321 ppm) and the footwall conglomerate (mean Co = 305 ppm), where it is hosted in two principal forms: discrete Co minerals (carrollite, cobaltite, cobalt-pentlandite, and linnaeite) and Co-bearing sulfides (pyrite, bornite, pyrrhotite, and chalcopyrite) through isomorphic substitution. Both modes, particularly in carrollite (mean Co = 44.5 wt%) and pyrite (mean Co = 3.3 wt%), represent significant Co resources. Two major stages of Co enrichment stages were recognized. The initial stage of synsedimentary–diagenetic pre-enrichment during the Neoproterozoic, is characterized by Co-rich framboidal and cubic pyrite in weakly alteration zones with average Co concentrations reaching 1520 ppm in cores and 3380 ppm in rims. The dominant epigenetic hydrothermal Co mineralization during the Lufilian orogeny, consists of disseminated Co-rich sulfide assemblages along schist foliation and Co-rich sulfides in veins. Mineral assemblages display a distinct oxygen fugacity zonation, with Co-rich minerals forming mainly under relatively reduced conditions. This redox change—likely driven by organic matter in the COM (mean total organic carbon content = 0.093 wt%)—was the principal control on Co precipitation and enrichment. These findings support a two-stage model that highlights the critical role of epigenetic hydrothermal processes in enhancing Co endowment and refine our understanding of Co mineralization in the Zambian Copperbelt.