Magma fertility assessment of Cryogenian granitoids in the Bou Azzer–El Graara inlier (Central Anti-Atlas, Morocco): overview from whole-rock and tracer radiogenic isotopic geochemistry

The Bou Azzer–El Graara inlier records the transition from the Pan-African major collisional phase to the WACadomian transpressive phase of deformation, marked by ca. 650 Ma syn-collisional intrusions (e.g. Ait Ahmane) and the ~540 Ma post-collisional Bleida intrusion. Geochemically, the syn-collisional granitoids are highly potassic, calc-alkaline I-type bodies with adakitic signatures. Field investigations also reveal the presence of pegmatitic–aplitic dikes marking a magmatic–hydrothermal transition. The disseminated hypogene copper mineralization; along with potassic, phyllic, and propylitic alteration assemblages, are characteristic evidence of porphyry copper systems. While local geological factors influence mineralization and preservation, the fundamental controls on ore genesis are linked to large-scale geodynamic and plate-tectonic processes. In this case, the Bou Azzer–El Graara inlier exhibits an overprinting of magmatic, and hydrothermal events by tectonic processes that have partially obscured some field characteristics typically associated with porphyry systems. For these reasons, whole-rock and radiogenic-isotope geochemistry are used to aid in enhancing the overall interpretation, following the recent approaches of previous studies. The syn-collisional Cryogenian granitoids record an emplacement in a compressive regime linked to obduction and fore-arc closure, and display clear signatures of magma fertility conditions: major-element contents by SiO2 ≥60 wt%, Al2O3 ≥15 wt%, MgO-poor, low Y and Yb, and enriched in LILE (positive Rb and Ba anomalies). High Sr/Y ratios, favourable Zr–Y systematics, positive εNd(i), and oxidized adakitic affinities indicate deep (>50 km), mantle-influenced melting during crustal thickening. Trace-element ratios (e.g. Sr/Y, Dy/Yb, V/Sc) further support porphyry Cu fertility. These features suggest that the Bou Azzer–El Graara intrusions formed from a fertile parental magmatic system capable of generating Pan-African syn-collisional porphyry copper deposits (PCD) (ca. 647 Ma). A possible analogue, the Chapada Cu deposit, developed in a similar geodynamic setting between ca. 900 and 640 Ma during the Brasiliano Orogeny.