Petrographic Analysis of the Palaeocene-Eocene Phosphate-Bearing Rocks of Eastern Dahomey Basin, Southwestern Nigeria.

Abstract Phosphorus is ubiquitous for its essential function in plant growth. Phosphate-bearing rocks include phosphorites and rocks that host phosphate mineral. Phosphorites, rocks containing ≥18 % phosphorus-pentoxide (P2O5), are essential sources of phosphorus. Due to the vast application of phosphorites in the manufacture of fertilisers and industrial products, the study of phosphate bearing rocks is crucial. This article examines the mineral component and structure of phosphate-bearing rocks in the Eastern Dahomey Basin, Southwestern Nigeria. Eleven pulverised samples of phosphatic rocks were analysed, employing a microscope, for petrographic studies. Three major types of phosphorites exist in the Eastern Dahomey Basin: Granular (which are composed of oolitic and pelletal structures), Nodular (which comprises cylindrical, rectangular, ellipsoidal shapes), and the vesicular (which either have coarse or fine forms) varieties. The phosphorites contain fluorapatite (as the dominant mineral), calcite, quartz, and glauconite. Generally, the phosphorites are fossiliferous (lamellibranches, echinoderms, shell, and bone fragments are observable). The phosphatic limestones are micrite (allochems) hosting collophane (specks of fine-textured fluorapatite) and glauconite. While fluorapatite occurs in the phosphatic claystone, it is glauconitic, just as the gypsum. The results of the petrographic analysis indicated the influence of seawater in the deposition of the phosphate-bearing rocks in an oxic environment.