Geochemical Soil Survey for Base and Precious Metals in Dagbala-Atte District, Southwestern Nigeria

Geochemical survey of residual soils was undertaken in Dagbala-Atte District of Igarra Schist Belt, southwestern Nigeria to explore for base and precious metals (Cu, Pb, Zn, Au and Ag). It involved sampling residual soil from 49 sites in a grid pattern;analyzing the soil samples for the base and precious metals and other commonly associated elements including As, Cd, Fe, Hg and Sb;subjecting the geochemical data generated to statistical analysis;and preparing the geochemical distribution map of the district for each element.? On the basis of the multivariate statistical analysis (correlation matrix and factor analysis) of the soil geochemical data, three mineralization types were inferred to be present in the district. The suspected types of mineralization consist of: 1) Cu-Pb-Zn-Ag mineralization with associated As, Hg, Sb and Fe;2) Au-Cu mineralization with associated As;and 3) minor Hg-bearing Au-Pb mineralization. With the aid of the elemental geochemical distribution maps, the suspected mineralization was linked to rock types from which the sampled residual soils were apparently derived. Hence, the suspected Cu-Pb-Zn-Ag mineralization is linked to the quartz-biotite schist at the southwestern part of the district while the suspected Au-Cu mineralization is located on the silicified sheared rock at the northern and southern parts and the minor Hg-bearing Au-Pb mineralization within the granitic gneiss at the northeastern and eastern areas of the district. Based on the foregoing findings, it is recommended that lithogeochemical survey for the base and precious metals should be done in the area.

Geochemical Classification and Geotectonic Setting of Granitic Gneisses from Southeastern Margin of Western Nigeria Basement

Chemical whole-rock major oxides and some trace element analyses were done on granitic-gneiss rocks from Dagbala-Atte District,located on the southeastern margin of western Nigeria Basement Complex.This was meant to classify the rocks and to understand the tectonic setting in order to evaluate their crustal evolution.The chemical analyses were done using inductively-coupled plasma mass spectrometer.From the results obtained,these rocks classified into calc-alkaline to shoshonite series with metaluminous to peraluminous varieties.They are I-type granitoids of feroan composition.The granitic gneisses formed from metamorphism of granite and granodiorite.Tectonically,most of the rock samples plotted in the field of island arc,continental arc and continental-collisional granitoids,which indicated that the protolith granite and granodiorite are orogenic and are arc related inferring arc tectonic setting.