Reconnaissance geochemical study of a part of Igarra Schist Belt, southwestern Nigeria

Abstract

Geochemical exploration of Orle district within the Igarra schist belt in southwestern Nigeria was carried out using reconnaissance stream-sediment survey. A total of 56 samples were collected and chemically analysed for 22 trace elements including Au, Ag, As, Pb, Zn, Cu, Co, Mo, Hg, Sb, Tl, Sc, Cr, Ni, La, W, V, U, Th, Sr and Ga. The analytical results were subjected to univariate statistical analysis in order to determine statistical parameters such as means, standard deviation, etc. that allow the calculation of thresholds for individual elements. Geochemical distribution and anomalous-concentration maps were plotted for the elements, so as to have an insight into their distribution patterns. The geochemical  distribution maps of the elements reveal that Cu, Pb, Zn, Co, Sc, Ni, Cr, Au, Sr, Hg and Tl show similar distribution patterns, and their anomalous-concentration maps also reveal that they have some common sites of anomalous concentrations; also, U, Th, La and W show similarity in their geochemical distribution and have some anomalous concentration sites in common, which may indicate close associations among the elements in each of these two groups in the study area. Comparison of the  anomalous values derived for the different elements with their mean contents in geological materials  suggests that the anomalous values for Co, Mo, Cr, Ni, Bi, Sr, Sb, V and Ga reflect underlying lithologies;  while those for Au, Hg, U, Cu, Pb, Zn, Th and La indicate possible mineralization in the study area. Precious-metal (Au-Hg), base-metal (Cu-Pb-Zn etc) and U-Th-La mineralization potentials are high in the study area. The occurrence of pathfinder elements such as As and W; and of rock units, such as amphibolites and pegmatites, within the schist belt that could serve as hosts for mineralization of these elements, provides a strong basis for this assertion.

Keywords: Reconnaissance, Stream Sediment, Geochemical Distribution, Anomalous Concentration, Igarra Schist Belt