corundum, Cameroon.12, gems

The gem corundum deposits of detrital origin were studied along the Mayo Kewol in the Adamawa mining region (Cameroon). The region was affected by the Pan-African cycle producing abundant granitoid intrusions, metamorphism, and important tectonic movements that occurred due to two main structural features: the Central Cameroon Shear Zone and the Cameroon Volcanic Line. The gem sapphires found in the gravel layer are mostly blue and broken, but retain their typical primary habits. Zircon, ilmenorutile, and ilmenite are the solid inclusions observed within these gem corundum. Their oxygen isotopic signatures range from 4.7 to 5.4‰, with a mean δ¹⁸O of 5.0 ± 0.3‰ (n = 3). Geochemical signatures show significant values up to 5320 ppm FeO, 570 ppm Ga₂O₃, and 3270 ppm TiO₂. These results suggest that the sapphires mainly crystallized within the mantle in a magma of syenitic composition. They were incorporated as xenocrysts in basaltic magma during the ascent from the mantle to the surface. These phenomena are structurally linked to the Central Cameroon Shear Zone and the Cameroon Volcanic Line, reactivated within the rifting continental surroundings.