Understanding Precambrian Komatiite Petrochemistry from talc bodies within the Ilesha Schist belt, Southwestern Nigeria

Abstract

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