The Genesis of the Kenticha rare-metal granite-pegmatite, Southern Ethiopia

Abstract

The Kenticha pegmatite field comprises suites of barren to fertile pegmatite swarms. It shows textural, mineralogical, and geochemical variations. The pegmatites are structurally controlled and emplaced in mafic–ultramafic belts during the Neoproterozoic. This study aims to constrain the genetic and tectonic setting of the Kenticha rare-metal (RM) pegmatite and the associated granite. The presence of minerals such as biotite, muscovite, spodumene, spessartine-almandine garnet, gahnite, beryl, tourmaline, cordierite, and topaz indicate the peraluminous nature of the granite and associated pegmatites. The Kenticha rare-metal granite-pegmatite shows ASI > 1.1, low V, Y, very low Sr, Ba, Th, Zr and REE, very high Be, Li, Rb, Cs, Ga, Nb, and Ta than the upper continental crust. The parental two-mica granite has higher Co, Rb, Ba, and Ce and lower V, Zr, Y, Nb, Ni, La, Pb, Sr, and Th than the upper continental crust. The Ta/Nb value in the two-mica granite is nearly equal to the average upper crustal value. In both parental granite and pegmatites, the normative corundum (C) is greater than 1%. The P2O5 content is low in the assumed parental granite. However, in the main ore body, the P2O5 content increases towards the more fractionated pegmatite. Due to its peraluminous character and high content of Be, Cs, Li, Ta, and Rb, we can categorise the granite-pegmatite under the LCT subclass of the rare-element pegmatite. It's associated with S-type granite. HFSE and LIL elements show characteristics of bulk continental crust composition and syn-collisional felsic magmatism. Biotite composition suggests partial melting of the metasedimentary protolith as the source of the two-mica granite. The plots of Y vs. SO2, P2O5 vs. SiO2, % normative C vs. Rb, Y vs. Rb, and Th vs. Rb support the S-type magma source. Geochemical and mineralogical data show a nearly vertical evolutional trend of the granite-pegmatite. It varies from the basal granitic unit to the pegmatite core unit. The mineralization of rare metals in the granite-pegmatite was mainly controlled by genetic (processes).