Example of a structurally controlled copper deposit from the Hercynian western High Atlas (Morocco): the High Seksaoua mining district

Abstract

Abstract The mineralized district of the High Seksaoua (Western High Atlas, Morocco) is characterized by a lithological succession marked by an alternation of schists and limestones attributed to the Cambrian and affected by at least five deformational events. The copper mineralization herein analysed is systematically localized close to a dolomite/black schist level in which a top-to-the-NNW décollement-type tectonics (D d ) has been identified. We demonstrate that the economic mineralization is a syn-tectonic stockwork formed in response of this top-to-the-NNW shearing event (D d ). This tectonic event can be reasonably correlated with the late Hercynian tectonics responsible, in the same area, for the Tichka granite emplacement at c. 291 ± 5 Ma, also under the control of a NW-SE shortening direction. Indeed, the Tichka granite represents a good candidate to explain the origin of the mineralized fluid. Such an hypothesis is confirmed by the Permo-Triassic age ( c. 270 Ma) given by 40 Ar/ 39 Ar dating realized on white micas related to the stockwork formation (this study). This important result questions the syn-genetic interpretation accepted until now for this mineralization and allows us to propose a new model of formation for this kind of deposit that could contribute to exploration programmes.