Investigations of electrical properties of weathered layers in the Yala area, western Kenya, using resistivity soundings

Abstract

Investigations in many parts of the world have indicated that resistivity of saprolite (a chloritization zone at the base of the weathering profile) depends uniquely on the underlying rock type. A study of electrical properties of the weathered layer was undertaken near Yala in the Nyanzian-Kavirondian greenstone belt in western Kenya. Resistivity soundings were systematically carried out in a 24 x 40 km area. Saprolite formed over basalt had the lowest resistivity (14 Qom), followed by andesite (27 Q*m) and rhyolite (67 Clem). Statistically meaningful data sets conclusively show, for the first time, that saprolite resistivity increases with the silica content of parent volcanic rocks. Plutonic and sedimentary rocks had higher average resistivities (granite 135 Q-m, mudstone 79 Q*m, grit 213 Qom). Thickness of the weathered layer varied between 10 and 40 m, with the largest values observed over grit (sandstone). Compared with other tropical regions, the saprolite layer in western Kenya appears relatively thin, possibly because of the relatively rapid tectonic uplift of the area which leads to fast erosion. As observed in earlier studies, resistivity and electromagnetic surveys can increase the speed and reliability of geologic mapping in tropical terrains.

DC resistivity survey for the assessment of groundwater potential in Oba Akoko, Southwestern, Nigeria

“…It investigates a geological medium via the consideration of its electrical properties or resistivity responses. While the vertical electrical resistivity sounding technique is usually considered more suitable for the subsurface depth probe of any geologic environment, abrupt lateral changes in lithology and electrical properties could constitute steeply dipping beds, fractures and fault zones, or highly variable thicknesses of weathered bedrock materials (Telford et al, 1990;Barongo and Palacky, 1991). This development usually makes interpretations difficult.…”

Geoelectric Investigation of Aquifer Vulnerability within Afe Babalola University, Ado –Ekiti, Southwestern Nigeria.

“…The most probable use of the electrical resistivity survey is in hydrogeological investigation in relation to aquifer delineation, lithologic boundaries and geological structures to provide subsurface information [3]. The method has been used extensively in groundwater investigation in the basement complex terrains [4], [5], and also in the sedimentary basins [6], [7], [8]. Hence, drilling programmes for groundwater development in areas of basement terrain are generally preceded by detailed geophysical investigations.…”

Deliniation of Weathering in the Çatalca Granite Quarry with the Very Low Frequency (VLF) Electromagnetic Method

“…Some former studies on weathering problems in tropic regions showed that electrical properties of the hard rocks and overlying weathered rocks are very different from each other different (BARONGO and PALACKY, 1991). In this case, resistivity or electromagnetic (EM) methods are powerful tools for measurement of in situ resistivities on weathered terrains.…”