Tectonic environments and rare metal mineralization in pegmatites of Komu Area, Southwestern Nigeria

Abstract

The discrimination diagrams: Rb versus Nb +Y and Nb versus Y, and Th/Ta ratio combined with field observations and empirical information from the literature were used to infer the tectonic environments and sources of the rare metal mineralization in the pegmatites of Komu area, southwestern Nigeria. The discrimination diagrams show that the pegmatites were mainly emplaced in tectonic environments similar to those of syn-collisional granites (Syn COG) and within plate granites (WPG). Volcanic arc environment was not pronounced. The emplacement of the pegmatites was structurally controlled by the predominantly Northeast (NE)– Southwest (SW) and North northeast (NNE)-South southwest (SSW) fault systems that were developed during the Pan-African orogeny. The upwelling of the mantle at the beginning and faulting systems associated with the active and closing stages of the Pan-African orogeny elevated rare metals from the mantle to higher crustal levels where they were incorporated into the pegmatitic fluids. The Th/Ta ratios of less than 1.00 which resemble that of the oceanic ridge tectonic environment is attributable to the upwelling of mantle material. The variation in the tectonic environments of the pegmatites may be attributed to the long span of the Pan-African orogeny (750-450 Ma).

KEY WORDS: Komu. Nigeria. Pegmatites. Rare metals. Tectonic environments.