The carbonatites of South Morocco: Unusual occurrences and associated REE-Nb-Ta-Fe mineralization

The Oulad Dlim massif in the southernmost part of Morocco hosts several carbonatite bodies of different ages. The older carbonatite (1.85 Ga) occurs in the eastern Oulad Dlim massif in the Gleibat Lafhouda area and consists of three juxtaposed magnesiocarbonatite outcrops. They are associated with glimmerite, hosted by Archean gneiss, and unusually intruded by massive IOA deposits. The latter contains up to several wt% REE related to numerous monazite-(Ce) inclusions within large apatite crystals. Columbite-(Fe) is the main Nb-mineral and occurs closely associated with Fe-phases, whereas microlite and Ta-rich columbite-(Fe) are mainly associated with coarse-grained apatites hosted by Fe-oxides and silica breccia. Geochemical characteristics and textural relationship suggest that they are genetically linked to the carbonatite and likely formed by late hydrothermal fluids at multiple stages. Small outcrops of nepheline syenite occur at several km from this carbonatite and might be genetically related. The youngest carbonatite (104 Ma) is a soevite and crops out within a ring structure composed of silica breccia and Fe-oxide mineralization at the Twihinat area of the western Oulad Dlim massif without visible associated alkaline rocks. All outcropping rocks at Twihinat show epigentic REE-Nb mineralization, mainly as bastnaesite within the carbonatite and silica breccia and monazite within the Fe-oxides. Pyrochlore senso-stricto occurs within the carbonatite, whereas cerio-pyrochlore is dominant in the silica breccia. The mineralogical and geochemical signatures of all Twihinat rocks suggest ore precipitation from multistage REE-Nb-rich hydrothermal fluids that percolated through the carbonatites and the associated rocks.