The Aquifer System Within the Crystalline Rocks of the Jos - Plateau and Environs

Abstract

An investigation into the aquifer system of the crystalline rocks within Jos and
environments was carried out. The area covered some selected sites from the
northern senatorial zone down to southern senatorial zone of the state. The
geology of each site was study to establish the grain size, texture and geological
structures associated with each of the rock type. The rock types in the area are:
migmatites, gneisess, granites, and basalts. Vertical electrical sounding (VES)
using the Schlumberger full electrode spread was adopted for the geophysical
investigation. The spread ranged from 95m-215m. the software IX1D Package
developed by Interpex Limited was used for plotting data and iteration of the
curves. Thereafter drilling of favourable sites were carried out as the clients could
afford at that time using PAT DRILL 301, 401, and Indian Motor Rigs. The VES
curves showed that the basement rocks are characterized by A, KHA and KHK
curves types. Most of the VES points have four geoelectric layers whose apparent
resistivities range from 19Ω -344Ω. The younger granites are characterized by H
and HA curves of which the H curves dominate. Here, the geoelectric layer and the
apparent reistitvies range from 4-5 and 21 Ω -834Ω respectively. Within the
basement complex, drilling revealed that the aquifers are located mainly within
the basement rocks, while within the younger granites, they are located at the
contact between the regolith and the crystalline rocks and also within the
crystalline rocks as fractures. In terms of drillabiblity, the aquifers within the
crystalline rocks have low drillability than the unfractured or fresh rocks. Whereas
within the regolith, the aquifers have high drillability than the non aquiferious clay.
Drilling also showed that coarse grain rocks are more aquiferious than fine grain
rocks when weathered. From the investigations, the chances of getting
groundwater is higher within the basement complex than the younger granites as
the basement complex are more deformed and altered.