Understanding Precambrian Komatiite Petrochemistry from talc bodies within the Ilesha Schist belt, Southwestern Nigeria
The nature of parentage of talc bodies from the northern part of Ilesha schist belt was investigated and compared with altered ultramafic – Komatiite. Observations from thin sections revealed altered serpentine with included nodular olivines. Talc, chlorite and tremolite were other minerals present. Geochemical analysis of five (5) rock samples taken from talc bodies outcropped from both sides of the Ifewara Shear Zone (ISZ) revealed magnesia (MgO) > 18% and Al2 O3 /TiO2 values ~ 40. MgO values ranged from 23.01 – 32.79 wt. %. Al2 O3 and TiO2 values averaged 2.34 and 0.04wt. % respectively. Mg# values (87.93 – 90.71) supported ultramafic precursor. Major oxide variation plots against magnesia revealed negative correlation in Al2 O3 TiO2 vs MgO. Co, V, Ni and Cu concentrations were significantly higher than the incompatible elements. Maximum Ni and Co values were 1765.10 ppm and 108.60 ppm respectively. The rare earth element (REE) concentrations showed relative enrichment in light rare earth element (LREE). The values of Gd/Yb(N) ranges from 0.94 – 1.86. The Gd/Yb(N) and Al2 O3 /TiO2 suggested that the precursor to the talc bodies were possible Gorgona group IIItype komatiite. Plot of V vs Ti indicated an Island arc environment for the emplacement of these talc bodies.
Keywords: Gorgona-type-Komatiite, Talc-bodies, ISZ, Serpentine, Magnesia