Phosphate resource evaluation in the eastern Dahomey Basin: A 3D litho-constrained gravity inversion approach

Abstract

This study presents an assessment of the phosphate resource in the eastern Dahomey basin using 3D litho-constrained gravity inversion. The inversion results identified notable density anomalies within the Oshosun formation, primarily in the vicinity of Ifo and Faleke towns. To validate the association of these anomalies with phosphate-bearing rocks, three exploration pits were dug in the Ifo area, reaching depths of 9–10 m. Subsequent investigations confirmed that the density anomalies corresponded to two phosphatic shale beds, ranging in thickness from 0.6 to 1 meter, exhibiting an average phosphorus concentration of 32 percent. Estimation of the phosphate resource within the Ifo area employed a comprehensive approach integrating geochemical data derived from phosphatic shale analysis, net to gross ratios obtained from the exploratory pits, and mass and volume calculations from the 3D density model of the phosphatic shales. The resulting estimate for the phosphate resource in the Ifo area amounted to approximately 4.3 million tonnes. Disappointingly, the estimated phosphate resources in Ifo town amounted to a mere 119 tonnes per acre, falling significantly below the requirement for large-scale mining to be considered economically viable. Nonetheless, these study findings hold potential value for local artisanal miners, who may engage in small-scale phosphate mining in Ifo town to produce localized fertilizers. Further investigations and exploration are encouraged to enhance understanding of the phosphate resources in the region and explore potential applications for sustainable local development.