Mineral Assemblages, Regional Zonation, and Geochemical Characterization of the Sidi Bou-Othmane Pegmatite Field (Jebilet Massif): An Example of Li-Enrichment in the Moroccan Meseta

Abstract In the Jebilet Hercynian Massif (Moroccan Meseta), granitic pegmatites are widespread in the Sidi Bou-Othmane region, where they form a subvertical dike swarm intruding cordierite and andalusite-bearing mica schists. Based on the abundance of the accessory minerals, eight types of pegmatites are distinguished, with increasing degrees of fractionation: T1 – pegmatites that are poor in accessory minerals; T2 – schorl-rich; T3 – schorl-garnet-rich; T4 – garnet-rich; T5 – Fe-Mn phosphate-rich; T6 – green tourmaline-rich; T7 – Fe-Mn- + Li-Al-phosphates and Nb-Ta-oxide-rich; and T8 – lepidolite-elbaite-rich pegmatites. Mapping of these different types of pegmatites shows a zonal distribution marked by an evolution from barren pegmatites (pegmatites T1, T2, T3, and T4), bearing schorl and garnet in addition to quartz, feldspar, plagioclase, and muscovite, through intermediate pegmatites (pegmatites T5 and T6) characterized by the abundance of Fe-Mn phosphates, to fertile pegmatites (pegmatites T7 and T8) that contain Li-rich minerals. Lithium (Li) can be found in a large number of minerals in Sidi Bou Othmane pegmatites. In addition to the already identified ferrisicklerite, other primary Li-bearing minerals have been found in this region for the first time in this study, including triphylite, lepidolite, elbaite, and amblygonite-group minerals. The detailed mineralogical study and whole-rock geochemistry indicates that the Sidi Bou Othmane pegmatites can be classified within the REL-Li subclass of rare-element class pegmatites of the lithium-cesium-tantalum family. Their genesis can be related to fractional crystallization of a highly peraluminous S-type leucogranitic melt.