Petrological and geochemical constraints on the origin of apatite ores from Mesozoic alkaline intrusive complexes, Central High-Atlas, Morocco

Five main apatite deposits from the Moroccan Central High-Atlas —including Anemzi, Tirrhist-Inouzane, Tassent, Ait-Daoud-Toumliline and Tasraft— have been investigated through integrated field, petrographic, mineralogical, geochemical studies. The ore occurs as veins, few mm to several cm thick, spatially associated with syenite-quartz monzonite (dominant) monzodiorite-gabbrodiorite bodies emplaced during Atlas Jurassic-Cretaceous alkaline magmatic event. Gem-quality crystals, up 15 in size, are albite, clinopyroxene (hedenbergite–augite–diopside), amphibole (hornblende–edenite–actinolite), K-feldspar, quartz, magnetite, titanite, epidote, prehnite, calcite. Two types of distinguished according their halogen contents: F-rich Cl-rich apatites. Both enriched REE (up 2 wt% ΣREE), major trace element contents consistent a origin, corroborated by chemical similarity accessory host intrusions, well other reference igneous However, hydrothermal fluids percolating country sedimentary rocks were also involved, indicated striking Na enrichment observed apatites, likely inherited Triassic evaporites, showing close spatial relationships intrusions. These would account for pervasive Na-metasomatism rocks, wall veins.