Ground Magnetic Survey for Geothermal Exploration in Menegai Area, Kenya

Abstract

Menengai is located in the central part of the Kenyan Rift. It is a massive shield volcano with an elevation of 2278 m.a.s.l. Within the caldera, geothermal manifestations in form of fumaroles suggest a geothermal potential. Ground magnetic survey has been carried out to delineateareas associated with high temperature reservoirs in the area and establish whetherit relates with the occurrence of fumaroles. The field stations were positioned using Global Positioning System (GPS) device. Total magnetic field intensities were measured using G-856 Proton Precession Magnetometer with an accuracy of ± 0.5 gamma.The magnetic field intensities were corrected for both diurnal and geomagnetic variations then residual anomaly isolated from the regional field. Having reduced the data, gridding was done using Surfer 8 software then contour map computed to establish the anomaly signature of the area. Qualitative and quantitative interpretations have been made from reduced magnetic intensity contour map of the area. Qualitative interpretations involved delineating anomalous regions in the study area based on the contourmap while Quantitative interpretations involved both direct interpretation and forwardmodeling along selected profiles in the study area to estimate the depths of the causative bodies. Direct interpretation methods utilized included Parasnis' method, Peters' Half-slope and Euler De-convolution techniques. Forward modeling was done using Mag2dc for windows which involved fitting a calculated model on the observed data along selected profiles repeatedly until a good fit was found. Intrusions at depths rangingfrom 0.257km to 0.888km to the top and extending up to 3km were found. The depths to the bottom where the causative bodies cease to be magnetic were considered shallow suggesting a Curie point depth. Comparing the model results with the geology andearlier studies done in the area there was a good correlation