The Chambishi Cu-Co deposit is one of the important giant Cu-Co deposits in Copperbelt province, Zambia, Central Africa, consisting the Main, West and Southeast orebodies. Its ore-bearing horizon is mainly the Mindola and Kitwe formations of the Lower Roan group, and its lithology includes argillaceous slate, argillaceous quartzite, slate, quartz sandstone, etc. The existing data on the cobalt occurrence mode is relatively weak and the genesis of Co-bearing minerals is not well understood, which directly hinders cobalt prospecting in the deposit. Focusing on the Co-rich minerals in this study, we conducted EPMA, Micro-XRF and S isotope analyses to investigate the Co occurrence modes and formation mechanism of Co-bearing minerals, in the Chambishi deposit, aiming to provide a theoretical basis for the future exploration of Co resources in the region. Our study shows that cobalt occurs as stand-alone minerals (mainly carrollite and linnaeite) or in Co-bearing minerals via isomorphism. In pyrite (Py2) and pyrrhotite formed from hydrothermal fluid, the cobalt content was up to 4.9% and 1.5%, respectively. Cobalt enrichment via isomorphism is evident by the inverse proportion between Co and Fe contents and by the relatively even distribution of Co components in the Co-bearing minerals. Moreover, the Co/Ni ratio in pyrite and pyrrhotite differs between the Chambishi deposit and skarn or other deposit types. Together with the hydrogen and oxygen isotope studies of fluid inclusions in the hydrothermal mineralization stage, it is implied that the Co-rich ore-forming fluid might not be magmatic-hydrothermal fluid but medium-high temperature metamorphic-hydrothermal fluid. The δ34S values of bornite from the West orebody and pyrrhotite from the Southeast orebody were 6‰-6.9‰ and 7.2‰-12.6‰, respectively, indicating that thermochemical sulfate reduction is the main formation mechanism of reductive sulfur in the Chambishi deposit; the similar δ34S values is also an indication of late metamorphism in the sulfide minerals. Based on this and previous studies, we suggest that the main mineralization stage of cobalt is closely related to the Lufilian orogeny. During the orogenic process, Co, Cu and other metal elements tend to enrich in the medium-high temperature metamorphic hydrothermal fluid. The hinge area formed by a NE-SW compression and the connecting area of specific strike faults can be the favorable prospecting targets for cobalt, and the pyrite-pyrrhotite assemblage in the hydrothermal veins can be used as mineral markers for cobalt prospecting. © 2021, Editorial Office of Earth Science Frontiers. All right reserved.
