Implication of the Triassic–Liassic rifting and Pangea breakup on the geodynamic, tectonic and mineralogical evolution of the Zeida Pb–Zn, Ba deposit (Upper Moulouya, Morocco)

Abstract

The Zeida Pb–Zn, Ba stratiform deposit is part of the Upper Moulouya mining district at the junction of the Middle Atlas and the Central High Atlas. This paper aims to identify the geodynamic–tectonic setting of the emplacement of this ore deposit, using a multidisciplinary approach combining field and laboratory work associated with paleostress analysis. The lithostratigraphic and gitological studies enable descriptions of Pb–Zn, Ba mineralization impregnated in the Upper Triassic arkose beds unconformably overlying the Variscan biotite-bearing granites. The mineralogical study allowed determination of a primary paragenesis mainly composed of galena + barite with lesser copper and zinc sulfides (chalcopyrite, covellite and sphalerite). The supergene paragenesis is represented by galena oxidation products associated with iron and manganese oxides. The structural analysis revealed a complex fracture network controlling ore deposition with three main directional systems: (i) NNE–SSW to NE–SW system; (ii) ENE–WSW to E–W system, and (iii) WNW–ESE system. The reconstruction of the paleostress fields synchronous with the mineralization emplacement allowed to conclude that these fractures were developed under an extensional tectonic regime linked to the Atlasic rifting, and characterized by horizontal NW–SE-trending σ3 axis, and vertical σ1 axis. The relative age of the emplacement of the Zeida ore deposit is assigned to the Triassic–Liassic period during a regional metallogenic event related to the opening of the Central Atlantic and the Alpine Tethys in the framework of the breakup of the Pangea supercontinent.