Geophysical Exploration for Iron Ore Prospect using Gravity Method in Meru County, Kenya
Nguru, Joseph Mugacia
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Ground gravity survey covering an area of 60km2 in Kimachia and Mbeu, area of Tigania- West Sub-County of Meru County, Kenya was conducted to establish iron ore extent in the area. A Sodin 410 gravimeter was used to measure the gravity field‟s variations in the 278 established stations. At each station the location coordinates and elevation were obtained using Global Positioning System, Garmin 45 model. The time of measurement at each station was also recorded. Gravity reductions and removal of regional trends was done. Computer software Surfer 11 was used to plot Bouguer anomaly contour map. Qualitative interpretation was used to discern positive Bouguer anomalies in the map. Five profiles were drawn on discerned anomalies, one oriented in the SW-NE direction and the other four in NW-SE direction. Half width and Gradient amplitude ratio methods together with Euler de-convolution were used to image the sub-surface and to establish limiting depths of anomalous bodies which were later used for start models. Modeling using Grav-2 dc software was done in fitting models, which established bodies at depths ranging 0-200m below surface. The anomaly map was also used in estimating the excess mass at 3.078109×10 13 kg. Chemical analysis of rock samples from selected stations mainly within gravity highs was done to determine the percentages of major minerals, magnetite included. The analysis indicated an average of 19.1 % of iron content. Gravity models indicated high density bodies and chemical analysis confirms presence of iron ore.