Metallogeny and Emplacement Conditions of Continental Terminal 3 (Ct³) Iron Formations of the Niamey Region (Western Niger)

Abstract

This study aims to characterize the different lithofacies of the Ct 3 formation in the Niamey region, and to determine the distribution of major and trace elements, in order to highlight the conditions for the establishment of iron mineralization. A lithological column, synthesizing sections of selected outcrops in the vicinity of Niamey, was produced. The chemical compositions of the selected samples were determined by X-ray fluorescence (XRF) spectrometry. Microscopic analysis of the thin sections determined the g œ thitic nature of the oolitic iron ore. The oolites show a quartz, limonitic or g œ thitic nucleus. Sometimes the nucleus is absent. From a morphoscopic point of view, two types of oolites have been distinguished: spherical-shaped and ellipsoidal-shaped oolites. The oolites are either contiguous or disseminated, as the case may be, in a limonitic to goethitic cement or in a fine sandstone matrix. The larger oolites (pisolites) are relatively friable. They reflect the influence of a relatively turbulent to submerged environment. The hardground of the iron mineralized horizons are covered by quartz grains. They are indicative of a submerged or emergent environment. X-ray fluorescence analysis shows high Fe 2 O 3 contents (50% to 80%) and variable contents of major elements SiO 2 , Al 2 O 3 , TiO 2 , MnO, MgO, CaO, K 2 O and P 2 O 5 associated with certain trace elements such as Th, U, V, Y, Zn, Zr and As. The results of the study are an important tool for decision-makers to adopt effective prevention/remediation measures for groundwater contamination in the Continental terminal aquifer systems.