Unraveling and modeling the role of Neogene tectonic fracturing in the emplacement of Mn mineralization in the Northern Middle Atlas, Morocco

The Neogene period in Morocco was characterized by polyphasic tectonic activity, extending from the Late Miocene to the Quaternary. These tectonic dynamics led to the formation and structuring of recent fluvio-lacustrine basins, as well as the emplacement and remobilization of hydrothermal mineralization within the Atlas Mountains. Understanding the evolution of this tectonic system is crucial for guiding and facilitating mineral exploration in the Middle and High Atlas ranges. The northern zone of the folded Middle Atlas was selected for a tectono-structural study, accompanied by a modeling of the mineralizing system evolution during this period. This study considers the impact of different tectonic phases on the Neogene terrains fracturing and the manganese mineralization emplacement. The results reveal three distinct tectonic phases responsible for structuring the study area and for establishing a system of tension gashes and mineralized fault-veins. The first phase, attributed to the Upper Tortonian–Early Pliocene, led to the formation of Late Miocene deposits. This phase is subdivided into three episodes: two compressional episodes-oriented NW–SE, separated by an extensional episode-oriented NE-SW. The second compressional episode is characterized by manganese veins associated with dextral (WNW-ESE) and sinistral (N–S) strike-slip faults, along with tension gashes oriented N140 to N160, filled with manganese and iron oxides. This phase was followed by a NNW-SSE extensional phase in the Middle to Late Pliocene, marked by normal faults that facilitated the development of Pliocene lacustrine deposits. Finally, a third and more recent compressional phase, dating to the Quaternary, oriented NNE-SSW to N-S, manifested through NW–SE and NE-SW strike-slip faults, offsetting earlier dextral and sinistral structures. The tectonics in this region also influence the paragenesis of manganese mineralization within the tension gash systems. Structural and mineralogical analyses reveal a paragenesis beginning with the formation of two types of calcites, corresponding to the early stages of tension gash opening. These structures are subsequently filled in the center by carbonates and manganese oxides, concluding with the precipitation of iron oxides.