Yizhe Hu

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.

The Xiangshan ore field is characterized by extensive alkali metasomatism, which represents the early-stage hydrothermal event before the acidic metasomatism during major U mineralization. However, the mineralogical and geochemical characteristics of alkali metasomatism, as well as its association with uranium mineralization, remain poorly understood. This study evaluates these scientific problems by conducting petrographic and geochemical analyses on feldspar, together with thermodynamic modeling. Hydrothermal feldspars are present as veinlets, differing from the magmatic ones with granular and subhedral structures. Hydrothermal albites have lower Na but higher K content than magmatic ones, while hydrothermal K-feldspars have lower K but higher Na content than magmatic ones. In addition, hydrothermal feldspars are significantly depleted in Ca and Sr, likely associated with the consumption of Ca in fluids by fluorite and calcite precipitation. Furthermore, alkali metasomatism is accompanied by intense hematitization, indicating the oxidized properties of ore fluids that are favorable for uranium transport. Thermodynamic modeling further demonstrates that continuous K⁺ consumption during fluid–rock interaction leads to a pH increase in the fluid, which is buffered by quartz–muscovite–K-feldspar (QMF). Given that quartz solubility is positively correlated with pH, this process induces extensive quartz dissolution in the host rocks. Such dissolution significantly enhances the porosity and permeability of the host rocks, creating ideal physical traps for the subsequent accumulation of uranium-bearing fluids. Consequently, alkali-metasomatized rocks associated with quartz dissolution and hematitization serve as critical indicators for regional uranium exploration.