International Journal of Engineering Applied Sciences and Technology, 2021 Vol. 5, Issue 10, ISSN No. 2455-2143, Pages 55-59 Published Online February 2021 in IJEAST (http://www.ijeast.com) 55 QUALITATIVE AND QUANTITATIVE INTERPRETATION OF HAND-DIGITIZED AEROMAGNETIC DATA FROM IDAH Robert Bassey Umera Odong Peter Department of Physics Earth Sciences Arthur Jarvis University Arthur Jarvis University Abstract— Qualitative and Quantitative interpretation of hand-digitized aeromagnetic data from Idah has been carried out by applying forward and inverse modeling technique. Qualitatively, wavelength and amplitudes of source bodies reveal lithologic contrast, basement structure and sedimentary magnetization contrast. The maximum depth to top of the magnetic source body obtained is 16.8m and minimum depth is 0.5m. The anomalous bodies’ total magnetic intensity ranges from a minimum negative peak value of -153.5nT to maximum value of 162.7nT. Susceptibility values obtained reveals the presence of rocks such as granite, diabase, olivine-diabase, basalt/gabbro, quartzite and diorite. Results obtained shows that hand-digitized data competes favorably with computer digitized data Keywords— Basement complex; Anomaly; Rock units; granite, diabase, olivine-diabase, basalt/gabbro, quartzite, diorite; suprabasement; Magnetic; Modeling; Susceptibility; basic igneous rocks I. INTRODUCTION Magnetometry is a potential field method of geophysical survey whose basic task in prospection geophysics is to differentiate the subsurface according to its magnetic properties. Its operative physical property is magnetic susceptibility. Magnetic survey carried out on air is normally termed aeromagnetic survey. It is a common type of geophysical survey that employs the use of a magnetometer toed behind an aircraft. The principle of the survey is similar to that carried out on land (ground magnetic survey) except that it allows coverage of larger area for regional reconnaissance. The end result being an aeromagnetic map, nowadays digitized using computer tools, upon which interpretation is made. The main use of any aeromagnetic data and their derivative maps in mineral prospecting is to make geological deduction from them Dobrin & Savit, (1988). This article however looks at the interpretation of hand digitized aeromagnetic map with a view of showing its effectiveness in interpreting aeromagnetic data. II. THE STUDY AREA Fig. 1.0 Geology map of the study area after Obiora et. al., (2006) Idah is a town in Kogi state, Nigeria, which lies between latitude 7 0 00, N and 7 0 30,N and longitude 6 . 00E and 6 , 30.E. Geologically, the study area (figure 1.0) is located partly in Anambra basin and partly within the basement complex of South Western Nigeria. The geology of Nigeria is dominated by crystalline and sedimentary rocks both occurring approximately in equal proportions Woakes et. al, (1987). The crystalline rocks are made up of Precambrian basement complex and the phenerozoic rocks which occur in the eastern region of the country and the north central part of Nigeria. The Precambrian basement rocks in Nigeria consist of the migmatite, gneissic-quartzite complex dated archean to early proterozoic (2700-2000ma). Other units include the NE-SW trending schist belts mostly developed in the western half of the country and the grantoid plutons of the older granite suit dated late proterozoic to early phanerozoic (750 – n450 Ma). Kogi, (2005) reported that the eastern flank of the state is on