The Açdif Gold-Bearing Shear Zone (Zenaga Inlier, Central Anti-Atlas, Morocco): New Petro-Structural and Geochemical Data

Abstract

The Açdif gold deposit is located in the Zenaga Inlier (central Anti-Atlas), approximately 120 km southwest of the city of Ouarzazate. It hosts gold mineralization associated with a shear zone affecting the metamorphic and magmatic formations of the Eburnean basement. It mainly consists of alternating micaschists, augen gneisses, and orthogneiss. These crystalline rock assemblages are intruded by a variety of granitoids. These are the Azguemerzi granitoids, which are locally affected by Eburnean deformation. Subsequently, these facies are intersected by a swarm of mafic dykes, which show a variety of rocks ranging from microgabbro-dolerite to quartz diorite. Detailed mapping, petro-mineralogical investigations, and geochemistry of the major and trace elements of these magmatic intrusions suggests the following: (i) for the granodiorite rocks (deposited before the basic dykes), a calc-alkaline affinity, with a chemical signature similar to a syn-collisional context; (ii) for mafic dykes, a contemporaneous emplacement of these mafic intrusions with an evolutionary process controlled by fractional crystallization of the same magma of continental tholeiites, whose chemical composition is comparable to that of enriched MORBs (EMORBs). These continental tholeiites are related to a distensive tectonic context that would have affected the Zenaga inlier prior to the Pan-African orogeny.