Zeitschrift für Geologie und Geophysik
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Comparison of Magnetic Basement Depth Values from Spectral Technique, SPITH and Slope Techniques using HRAM

Nwosu OB, Umego MN and Onuba LN

The quantitative results obtained from the use of spectral analysis technique, Source parameter Imaging technique and empirical depth rule method (maximum and half slope techniques) in interpreting High Resolution AeroMagnetic of middle Benue trough data have been presented and compared. Before employing each technique, the regional residual seperation was done with least square method using polifit program to get the residual data for onward processing. The slope technique usually require that the residual values be contoured into map and then profiled along the most prominent anomaly to obtain the depth curves from where depth to magnetic sources could be calculated. The Spectral requires that the residual values be sub-divided into spectral blocks and radial energy spectrum be generated from where depth would be calculated from the slopes of the straight line plots. The SPI requires the griding of the residual values and the conversion of this to image map from where depth could be read off easily. The deep magnetic anomally source gotten ranges from 2.00 km to 6.29 km with an average depth of 3.25 km for SPI technique; 2.33 km to less than 5.66 km with an average depth of 3.65 km for Spectral analysis technique; and average of 3.74 km and 3.66 km for Half-slope and maximum slope technique respectively. These average depth could be taken as the magnetic basement depth and has the significant that if other conditions are met, this study area of marine sedimentary layer of the Albian Age is favourable for hydrocation accumulation. The shallow source depth gotten ranges from 0.02 km to 2.00 km with an average depth of 1.08 km for SPI; 0.05 km to less than 0.42 km with an average depth of 0.21 km for spectral analysis; and an average depth 0.80 km for Half slope technique. This can be viewed as magmatic intrussion into the sediment and could be responsible for the lead-Zinc mineralization found in the area. These methods thus compares favourably well and moreso the slope technique though empirical has compared favourably with more modern automatic source depth methods.