PETROGRAPHIC AND MINERALOGICAL CHARACTERIZATION OF GRANITOIDS AND PEGMATITES IN THE PAN-AFRICAN MASSIF OF HARAZE DJOMBO (BATHA, CENTRAL CHAD)

The Batha Massif, located in central Chad, occupies a key position at the transition between the Saharan Metacraton and the Central African Pan-African belt. The geodynamic evolution and metallogenic potential of this area remain poorly constrained due to the scarcity of modern analytical data. This study aims to characterize the mineralized granitoids and pegmatites of the Djombo and Gleb mounts (Haraze Djombo Department) through an approach combining field prospecting, optical petrography, and powder X-ray diffraction (XRD). Observations reveal two post-collisional magmatic facies emplaced during crustal relaxation (~570-560 Ma): a peraluminous biotite-muscovite granite (Djombo) and a calc-alkaline amphibole-biotite granite (Gleb). XRD analysis of the Djombo granite confirms a differentiated felsic assemblage (quartz, microcline, albite) and reveals the presence of secondary tremolite. The unprecedented identification of this amphibole indicates intense hydrothermal alteration in greenschist facies, demonstrating that the southern margin of the Saharan Metacraton corresponded to a reactivated and fractured margin that drained deep fluids. Furthermore, analysis of Gleb veins reveals a single-phase signature of exceptionally pure quartz (>95%) coupled with spectacular cataclastic texture. The conjunction of allanite-bearing fertile granites, marked hydrothermal alteration (tremolite), and injection of pure siliceous fluids into active shear zones constitutes the classic signature of orogenic gold mineralization, thus scientifically validating the strong regional economic potential.