Petrology and Geochemistry Study of the Basaltic Rocks of Tchaga South East of Fitri Lake-Chad: Metallogenic Implication

In this paper, we present the new data from the study area. Located in the Southeast of Fitri Lake, at the center of the Republic of Chad in the Batha region, our study sector is an excellent metallogenic province, characterized by the presence of meta-volcano-sedimentary rocks. Based on petrography and geochemistry findings, these meta-volcano-sedimentary rocks are: the metavolcanites (metabasaltes, metadacites) and the metasediments (metaconglomerates, and marbles), covered by quaternary sedimentary formations (clay and sandstone). These rocks are crosscut by quartz-veins and a vein network hosting pyrite, chalcopyrite and gold mineralization. In the TAS classification we identify two lithological rocks of basaltic and dacitic composition. In the AFM ternary diagram, some rocks plot into the tholeitic field and others in the calco-alkaline domain, but have higher tholeitic tendency suggesting that the rocks have been crystallized from a similar parent magma. The high loss on ignition (LOI) values from 2.26 to 11.65 wt. % suggesting probably the contribution of secondary hydrated and carbonate phases. The variable contents of MgO, Mg# (36.09 - 67) and transition elements (Sc, Cr, Co, Ni) of the meta-volcanic rocks studied suggest that a certain degree of fractional crystallization occurred during the emplacement of meta-volcanic rocks. The Haker diagram shows a trend of negative evolution with the exception of the Al2O3vs SiO2 diagram which shows a positive trend. The high enrichment of Th, Rb, Cs, K and Y, Zr, Hf, Sr shows a negative anomaly and subduction tectonic setting. Based on Chondrite and primitive mantle spider diagrams, LREE have been enriched to HREE in this area. The Th/Yb VS Nb/Yb diagram shows that, these rocks are original MORB of the oceanic arcs which have been enriched to the Metadacites of the continental arcs.