Cu–Au vein mineralization related to the Talat n’Imjjad shear zone (western High Atlas, Morocco): geological setting, ore mineralogy, and geochemical evolution

The Cu–Au deposit of the Talat n’Imjjad occurrence, southwestern Azegour mine, western High Atlas of Morocco, is situated in a NW trending quartz vein along a shear zone in quartz diorite host rocks. The recently discovered shear zone, ~200-m long, NW–SE trending, so-called Talat n’Imjjad vein system of Cu–Au–Bi–Te–Se mineralization that crosscuts the Al Medinet quartz diorite, represents a landmark in regional metallogeny. This region has long been known for its polymetallic ore deposits, with the historical Mo–Cu–W mine of Azegour and Pb–Zn–Ag mine of Erdouz. The economic sulfide enrichment is often hosted by breccias and quartz veins in the ductile shear zone. Samples from the field surface and boreholes show macro- and microscopic evidence of shearing such as S-C fabrics and microshear planes. The quartz diorite was deformed and mylonitized, then the igneous texture was modified. On the basis of textures, mineral assemblages, and hydrothermal alteration, four stages were documented and could be distinguished: (1) quartz I–sericite–chlorite–epidote pre-ore stage; (2) chlorite–quartz II–calcite–pyrite ore stage; (3) native bismuth–bismuthinite–emplectite–wittichenite–(tsumoite–laitakarite)–chalcopyrite–sphalerite–native gold–calcite ore stage II; and (4) bismuthite–hematite–malachite–covellite post-ore stage. Bi-chalcogenides are considered as pathfinders for gold in Au–quartz veins. The association of gold with Bi-minerals is linked to the role of Bimelt as scavenger for gold. Tellurides and selenides are also the best indicators of the magmatic signature. The alteration types of the wall rocks include seritization, silicification, chloritization, carbonatization, and propylitization. The auriferous shear zone of Talat n’Imjjad represents a newly discovered occurrence in the western High Atlas characterized by its mineralogy, paragenetic sequence, hydrothermal alteration, and magmatic and structural control of the deposit of sulfide minerals.