Role of Triassic tectonics in the emplacement and distribution of hydrothermal mineralizations in the Aouli mining district (Upper Moulouya, Morocco)

Abstract

Hydrothermal mineralizations (Pb–Zn, Ba, F, Cu) of the Aouli mining district are hosted by Paleozoic schists and granitoids, as well as Triassic arkoses and basalts. These mineralizations are geographically distributed in five vein systems that are spread out over the Paleozoic Aouli inlier. Geological mapping, structural analyses and paleostress reconstruction were carried out in each of these vein systems, and they show that mineralizations are mainly controlled by three fracture networks: (i) NNE-SSW to NE-SW system; (ii) ENE-WSW to E-W system; (iii) WNW-ESE system. All of these fractures are developed under an extensive tectonic regime consistent with a NW-SE to NNW-SSE sub-horizontal σ3 axis and a subvertical σ1 axis. This extensive tectonic regime, related to the Atlas rifting stage during the Upper Triassic-Early Liassic period, allowed the development of vein structures along NNE-SSW to E-W trending normal faults and tension gashes, as well as WNW-ESE trending normal faults with strike-slip component. The relative age of mineralizations emplacement is interpreted to be the end of the Triassic period, with veins cross cutting Upper Triassic detrital and volcanic formations, but never affecting Early Liassic formations.