Structural, Petrographical and Geochemical Characterization of Tin-Tantalum Bearing Pegmatites from Chessu Area, North Central, Nigeria

Granodiorite, medium grain granite gneiss, medium grain banded gneiss with pegmatite intrusion, comprise the Basement Complex rocks of Chessu. The primary geological structures that emerge from the Pan Africa ductile and brittle deformation stages are fold, strike slip fault, dextral shear plane and fractures in Chessu and environs. Tin and tantalum containing pegmatites are found in the main E-W and NE-SW fault. Field observation demonstrate NE-SW, NNE-SSW and N-S structural trend with dipping values ranging between 19-52 in accordance with data collected, displayed on rose plots and equally supported by lineaments. In terms of petrography, medium grained banded gneiss, medium grain granite gneiss and granodiorite all contain quartz, plagioclase, biotite and muscovite. Pegmatite contains muscovite, biotite, quartz and orthoclase among other opaque minerals. The protoliths of the gneisses, which may be from granite are revealed by the geochemical data used on Middlemost plots (Na2O + K2O vs SiO2), which suggest that the rocks are members of the granitoid family. The Harker’s variation Plots of SiO2 vs Na2O, K2O, CaO, MgO, TiO2, P2O5, reveals intense alteration and contamination during fractionation of the rock, as displayed by the scattered/non-linear trends. The primitive mantle (spider plot) indicates the depletion of some compatible less mobile elements (Ti, Y, Zr and Sr) and enrichment of incompatible elements (Th, Rb, Nb, Ta, Sr and Pb), which reveal the mineralization potential in these incompatible elements. The enriched elements Th, Nb, Ta and Pb are used as the pathfinder elements for Tin and Tantalum mineralization in Chessu area. The deformation processes and structures created in the latter phase of Pan Africa Orogenic event resulted in the pegmatite emplacement, this could infer a connection between the mineralizing fluid and the rocks.