Manganese mineralization in the northern Middle Atlas (Aderj mining zone, Morocco): Petro-structural and geochemical analysis

Abstract

The Aderj area, part of the northern Middle Atlas of Morocco, is characterized by significant manganese oxide mining potential. These are associated with calcite components and iron oxides mainly hosted by Upper Triassic doleritic basalts, Liassic flint limestones and Vallesian (Middle-Upper Tortonian) lacustrine formations. However, the petrographic and mineralogical characteristics of this mineralization, along with its origin and emplacement mode, remain poorly defined in the study area. Addressing these gaps is essential for assessing the mining and economic potential of this region. This paper involves a meticulous field work approach, including detailed geological surveys of the different host series, as well as careful analysis of the mineralogical typology and morphology. Moreover, the petrography, mineralogy and geochemistry of these Mn(-Fe) mineralization allows to characterize the composition and geochemical features in order to propose an emplacement model of the Mn mineralization, which haves never been the subject of previous investigation. X-ray diffraction combined with light and scanning electron microscopy reveal a polyphase manganese and iron oxide sequences mainly formed from Mn²⁺ rich-hydrothermal fluids derived from leaching and hydrothermal alteration of ferromagnesian minerals from Upper Triassic basalt flows. This sequence is also enriched in geochemical elements such as Pb, Zn, and Ba resulting from the alteration of K-feldspar, probably derived from deep magmatic rocks. Fluids flow along the fractures and faults which affect this area, and deposited mineralization in fracture zones as veins and veinlets during their ascent and mixing with low-temperature, well-oxygenated surficial waters.