Investigation of Magnetic Anomalies of Chibok and Damboa Areas in North Eastern Nigeria

 – Investigation of Magnetic Anomalies of Chibok and Damboa Areas in North Eastern Nigeria – 

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ABSTRACT

The aeromagnetic data of Chibok (sheet 134) and Damboa (sheet 112) areas, southern Chad basin were interpreted qualitatively and quantitatively.

Spectral Analysis, Source Parameter Imaging (SPI), Standard Euler deconvolution, Forward and Inverse modelling methods were used in the quantitative interpretation with the aim of determining depth to the magnetic source bodies,

magnetic susceptibilities and the possible mineralization in the area. Oasis Montaj 6.4.2, WinGlink 1.62.08, Surfer 11 and Microsoft Excel softwares were employed in the data analyses.

The estimated depths from the forward and inverse modelling methods for profiles 1-7 are 2749, 2201, 2088, 703, 521, 927 and 481 m respectively.

The respective susceptibility values were 0.20407, 0.47779, 7.8043, 0.1349, 0.0889, 0.3083 and 0.4820 SI, which indicate the presence of sedimentary intrusions (basalt or limestone), few  metamorphic  rocks (schist) and minerals (magnetite).

Spectral analysis revealed two depth sources with the  deep  sources  ranging  from  1485.3  4093.6  with  an  average depth value of2390.1 , while the shallow depth sources range from 405 844  with an average depth value of 567  .

The temperatures at these  depths range from 81.65°C to 169.16°C for the deeper sources and from 31.12°C to 32.82°C for the shallow sources.

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TABLE OF CONTENTS

Title page     i

Dedication    iii

Certification iv

Acknowledgment v

Table of contents vi

List of figures x

List of tables xiii

Abstract         xiv

CHAPTER ONE: GENERAL INTRODUCTION

• Geophysical survey 1
  • Magnetic survey 3
  • Gravity survey 4
  • Electrical method 4
    • Electrical resistivity method 4
    • Induced polarization method 4
    • Electromagnetic Method 6
  • Seismic method 6
• Location of the study area 7
• Geology of the study area 7
• Purpose of study 9

CHAPTER TWO: LITERATURE REVIEW

2.1 Review of previous geophysical surveys in the study area      10

CHAPTER THREE: MAGNETIC CONCEPTS AND METHODS

• Geomagnetic field 16
  • Geomagnetic components 17
• Basic ideas of magnetic prospecting 18
  • Magnetic force 18
  • Magnetic field strength 19
  • Intensity of magnetization 19
  • Magnetic susceptibility 19
  • Magnetic permeability 21
• Rock magnetization 21
• Magnetic order 24
• Remenant magnetism 25
• Magnetic anomaly 26
• Methodology 27
• Magnetic data correction 28
• Data processing and enhancement 28
• Removal of regional field data 28
  • Filtering of Aeromagnetic Data 29
  • Vertical Derivative 29
  • Upward and Downward continuation 30
  • Reduction to pole 30
• Data Interpretation 31
  • Qualitative Interpretation 31
  • Quantitative Interpretation 32
• Depth Estimation Methods 32
  • Spectral Analysis 32
    • Fundamentals of Spectral Analysis 32
    • Energy spectrum and depth to magnetic force 34
    • Spectral analysis method 35
  • Source parameter imaging method 38
  • Euler deconvolution method 39
• Estimation of temperature at depth 39
  • Theoretical background for geothermal exploration 39
  • Temperature inside the earth 41
  • Temperature distribution inside the crust 42
• Geophysical modelling software 43
  • The modelling shapes 44
  • Potent main concepts 46
• Source of Data         48

CHAPTER FOUR: RESULT AND DISCUSSION

4.1 Qualitative interpretation of result     50

• Sorting of data 50
• Filtering and gridding 50

• Total magnetic intensity map 50
• Regional and residual separation 52
• Vertical derivatives 54
• Upward and downward continuation 56
• Reduction to pole 57
• Analysis and result 59
  • Magnetic basement surface plot 59
• Euler deconvolution result 72
• Potent modelled result 75
  • Profile 1 (P1) result 77
  • Profile 2 (P2) result 78
  • Profile 3 (P3) result 79
  • Profile 4 (P4) result 80
  • Profile 5 (P5) result 81

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INTRODUCTION

Geophysical Survey

Geophysics means the physics of the Earth and its environment. Its subjects  include  the shape of the Earth, its gravitational and magnetic fields, the dynamics of the  Earth as  a  whole and of its component parts, the Earth’s internal structure,  composition and  tectonics.

Also, the generation of magmas, volcanism and rock formation, the hydrological cycle including snow and ice, all aspects of the oceans, the atmosphere, ionosphere, magnetosphere and solar-terrestrial relations, and analogous problems associated with the Moon  and  other planets (Cheminet al.,2006).

Geophysics is applied to societal needs, such as mineral resources, mitigation of natural hazards and environmental protection (Cheminet al.,2006).

Geophysical methods may be applied to a wide range of investigation from studies of the entire Earth, to exploration of a localized region of the upper crust.

Geophysical surveying, although sometimes is prone to major ambiguities or uncertainties of interpretation, provides a relatively rapid and cost- effective means of deriving an information about the subsurface  geology  (Keary  and  Brooks, 1984).

Geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, to locate groundwater and archaeological findings, to find the thicknesses of glaciers and soils, and for environmental remediation.

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REFERENCES

Ajana O., Udensi E.E., Momoh M., Rai J. K. and Muhammad S.B., (2014): Spectral depth estimate of subsurface structures in parts of Borno Basin, Northeastern Nigeria, Using Aeromagnetic Data. IOSR Journal of applied geology and geophysics (IOSR-JAGG), 2 (1):55-60.

Amigun, J.O., Afolabi, O. and Ako, B.D. (2012): Application of airborne magnetic data to mineral exploration in the okene iron- ore  province  of Nigeria.  International Research Journal of Geology and Mining 2(6): 132-140.

Baranov, V. (1957): A new method for interpretation of  aeromagnetic  maps: Pseudogravimetric anomalies: Geophysics 22:359-383.

Baranov, V. and Naudy, H. (1964): Numerical calculation of the formula of reduction to the magnetic pole: Geophysics 29: 67-79.

Barton, C.E., (1997): International Geomagnetic Reference Field. Journal of Geomagnetism Geoelectricity. 49:23-148.

Bath, M. (1974): Spectral Analysis in Geophysics, Elsevier, Amsterdam.