Comparative Geochronological, Isotopic, and Petrographic Constraints on the Bou Azzer Co-Ni and Bleïda Cu Deposits in Morocco
Abstract
The Bou Azzer and Bleïda deposits in the Anti-Atlas of Morocco are geographically close and occur within the same Neoproterozoic Pan-African tectonic framework, yet they host contrasting styles of metal mineralization. Bou Azzer hosts economically important Co–Ni mineral deposits linked to serpentinized ultramafic formations, whereas Bleïda is mainly characterized by Cu–Fe sulfide mineralization hosted in volcanic units. Despite their close geographic and tectonic relationship, the geological and geochemical controls responsible for these different mineralization styles remain insufficiently understood. This study integrates geological and petrographic observations with compiled published geochronological data, fluid-inclusion microthermometry, and S isotopic compositions to better understand the evolution of mineralizing systems and ore formation processes. The results suggest that Bou Azzer is a polyphase serpentinite-hosted Co-Ni hydrothermal system with high-temperature, saline fluids, and sequential arsenide and sulfarsenide deposition. Bleïda, in contrast, is associated with a structurally controlled volcanic-sedimentary copper system characterized by low-salinity hydrothermal fluids, fluid–rock interaction, and remobilization of pre-existing sulfide mineralization. Despite their contrasting mineralization styles, Bou Azzer and Bleïda exhibit broadly similar S-isotope ranges and possibly overlapping mineralization ages. Their wide isotopic variations are interpreted to reflect redox-controlled fractionation under relatively oxidizing conditions rather than differences in sulfur source. The contrasting metal assemblages were therefore probably controlled by differences in fluid–rock interaction, local redox evolution, structural setting, and metal precipitation mechanisms. The genetic model integrating magmatism, structural deformation, and hydrothermal mineralization is proposed in this study.