ASSESSING THE MINERAL AND GEOTHERMAL POTENTIALS OF PART OF KOGI STATE, NIGERIA

ABSTRACT

The Mineral and Geothermal Potentials of part of Kogi State was investigated through the interpretation of aeromagnetic and radiometric data of the study area. Vertical and horizontal derivatives, Analytical Signal, CET, Euler deconvolution and Spectral depth analysis were used for the interpretation of the aeromagnetic data while the Concentration, Ratio and Ternary images of the three radiogenic elements were used for the interpretation of the radiometric data. The analysis of both the Vertical and Horizontal Derivatives revealed features of two major components of Nigerian geology construed in the study area based on the degree of distortion to the magnetic signatures. The NW and SW portion of the area is basement covered by short wavelength magnetic anomalous signatures that are the characteristic of outcrop and shallow intrusive magnetic bodies, while the remaining part of the study area is characterized by medium to long wavelength magnetic signatures that are attributes of sedimentary formations. 1VD map was helpful in delineating mineral potent lineaments. Result of the Analytical Signal amplitude revealed regions with shallow intrusive magnetic rocks having high amplitudes ranging from 0.174 to 0.579 nT/m, while regions with magnetic rock intruding into sedimentary formations at greater depths, have medium to low amplitudes ranging from 0.021 to 0.157 nT/m. Analyses due to Central Exploration Targeting grid revealed lineaments and structures trending NE-SW and E-W. Euler depth analysis revealed structures with greatest depth of 1252 metres and least depth of 27 metres. Radiometric signatures from the K/Th ratio map revealed portions around Latitude 8°00’  NW and 7°30’ SW having values above known threshold of 0.2 %/ppm for un-altered rocks, to be hydrothermally altered due to K enrichment. Mapping of lithology from Ternary map revealed K-Feldspar mineral bearing rocks dominated the NW and SW regions, while sandstones, ironstones, mudstones, shale, alluvium and other fluvial sedimentary lithologies dominated the sedimentary North-east and South-Eastern regions. Structures trending NE-SW and E-W mapped in the basement region of study area which also coincided with the zones of hydrothermal alterations and thus represents the zones of significant mineralisation in the study area. Result of Spectral depth analysis on the aeromagnetic data showed that peak values of geothermal gradient and Heat flow were 66 °C/km and 166 mW/m2 respectively, and occurred at the western edge of study area with a Curie point depth of 8 Kilometres.

CHAPTER ONE

1.0      INTRODUCTION

1.1       Background to the Study

Geophysical investigations of the interior of the Earth involve taking measurements at or near the Earth’s surface that are influenced by the internal distribution of physical properties. Analysis of these measurements can reveal how the physical Properties of the Earth’s interior vary vertically and laterally (Kearey et al., 2002).

Various Geophysical methods for mapping the earth subsurface includes Electrical Resistivity, Induced Polarization, Self-Potential, Electromagnetic, Gravity, Magnetic, Radiometric and Seismic. The application of these methods and their underlying principles has remained the bedrock for mineral exploration and other Geophysical investigations of economic importance.  Airborne Geophysical survey  makes use of majorly Magnetic, Radiometric and Gravity methods. It is very efficient in mapping out large areas and is cost effective for regional surveys. Airborne geophysical surveys are applicable in oil and mineral exploration, engineering projects, geothermal mapping and land management; they are excellent tools for mapping exposed bedrock, geological structures (such as basements, faults, dikes, sills, kimberlites), sub-surface conductors, paleo-channels, mineral deposits and salinity (Adagunodo et al., 2015).

An aeromagnetic survey is a common type of airborne geophysical survey carried out using a magnetometer on board or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger areas of the earth’s surface to be covered quickly for regional reconnaissance. The aircraft typically flies in a grid like pattern with height and line spacing determining the resolution of the data and cost of the survey per unit area (Allis, 1990).

Aeromagnetic survey is a veritable tool for probing the presence and distribution of magnetic minerals in mineral bearing rocks. Colin (2005) indicated that, the Magnetic properties of any rock are, to some extent, determined by the grain size of the magnetic minerals present.

Radiometric data is collected above the ground by flying an airplane with a spectrometer for regional surveys. The parameter of interest measured during a radiometric survey is gamma radiation which results from the decaying of unstable radioactive elements present in the rocks. Potassium, Uranium and Thorium are the only naturally occurring elements with radioisotopes that produce gamma rays of sufficient energy and intensity to be measured at airborne survey heights (Minty, 1997).

Airborne gamma-ray measurements are a fast way of surveying and monitoring radioactivity of subsurface rocks for the determining of uranium, thorium and potassium concentrations. The radiometric method is one of the most cost-effective and rapid techniques for geochemical mapping based on the distribution of the radioactive elements: potassium, uranium, and thorium. Nowadays, the method is mainly applied for geological mapping and exploration of economic minerals; geochemical and environmental monitoring such as localization of radioactive contamination from fallout of nuclear accidents and plumes from power plants; the method allow the interpretation of regional features over large areas, and is   applicable in several fields of science (International Atomic Energy Agency, IAEA, 1990; 2003).

1.1.1    The earth’s magnetism

Generally, the Earth is structurally divided into three major components; the Crust, Mantle and Core. The Core is further divided into molten outer-core and solid inner core. Magnetism of the Earth is said to originate from the molten outer core.

Colin (2010) inferred that the movement of the charged electric particles within the molten core produces a magnetic field around the Earth. This magnetic field enveloping the Earth give rise to the magnetic features of the various rocks found within or on the surface of the Earth. The cause of the geomagnetic field is attributed to a dynamo action produced by the circulation of charged particles in coupled convective cells within the outer, fluid, part of the Earth’s core (Colin, 2005).

The Earth’s magnetic field is made up of three parts namely;

i.   The major field, which differs comparatively gradually and originates within the Earth.

ii.  The minor field (compared to the major field), which varies rapidly and of external origin.

iii. The spatial variation of the major field which are usually lesser than the major field, are almost the same in time and place, and are brought about by local magnetic anomalies within the Earth’s crust. These are the areas of interest in magnetic surveying (Telford et al., 1990).

1.1.2    Basic radioactivity

Elements composing of same number of Protons but different number of Neutrons in their atomic structure are called Isotopes. This phenomenon (Isotopy) causes some nuclei to be unstable resulting in spontaneous emission of energetic ionizing radiations to become stable. These isotopes are called radioactive isotopes or radioisotopes. Nuclides with this feature are called radionuclide, and disintegration or nuclear decay is the breakdown of unstable nuclei (International Atomic Energy Agency, IAEA, 2003)

Each radioactive isotope has a distinctive chance associated with the radioactive disintegration of its nuclei. This is called as the isotope half-life and is the time taken for radioactive nuclei to decay to half its initial value. Hence, after one half-life, half the original radioactive isotopes remain, and after two half-lives, one quarter of the original radioactive isotopes remain (Minty, 1997).

Also, Minty (1997) indicated that radioactivity usually occurs as a sequence of the number of daughter products with a breakdown of the mother elements in order to have a stable isotope. At this period, the behaviours of all the radioisotopes of the decay series are the same. Hence, the extent of the quantity of any daughter nuclei can be helpful in estimating the quantity of any other radio nuclei in the breakdown series. Emanations of gamma rays from the Earth surface differ with many factors but most importantly depend on the amount of radionuclides in the top soil about 30 to 40 cm. The amount depends on the parent rock and the extent of weathering (Elawadi et al., 2004).

1.1.3    Mapping natural sources of radiation

Naturally occurring radiation sources can be suitably classified into three groups according to their origin. The first group includes 40K, 238U, 235U and 232Th, which are believed to have been produced during the creation of the universe and have half-lives of the same order as the Earth’s age. The second group comprises radioactive isotopes that are daughter products from the decay of isotopes in the first group. These have half- lives varying from small fraction of one 1 second to 104  to 105  years. The third group include isotopes created by external causes such as the reactions of cosmic radiations with the Earth and its atmosphere. The concentration of cosmic radiation at surface of Earth is comparatively small such that all of them are absorbed in the atmosphere (Minty, 1997).

1.1.4    Geothermal energy

Geothermal energy is the heat produced deep in the Earth’s core. It is a clean, renewable resource that can be harnessed for generation of electricity and other industrial heating requirements. The vast majority of Earth’s heat is constantly generated by the decay of radioactive isotopes, such as potassium, thorium and Uranium. As earth’s temperature rises with depth from the surface to the core, the gradual change in temperature is known as the Geothermal Gradient. Measurements have shown that a region with significant geothermal energy is characterised by an anomalous high temperature gradient and heat flow (Tselentis et al., 1991). The depth to bottom of magnetic sources (DBMS) or curie point depth (CPD) is known as the depth at which the dominant magnetic mineral in the crust passes from a ferromagnetic state to a paramagnetic state under the effect of increasing temperature(where magnetisation is lost) (Nagata, 1961). It is therefore expected that geothermally active areas would be associated with shallow Curie point depth (Nuri et al., 2005).

1.2       Statement of the Research Problem

One of the major problem bedevilling the country against benefiting immensely from its abundant solid mineral and other sub-crustal resources is the size of the country. With a land mass totalling about 923,768 Square Kilometres, exploration for solid mineral and appropriation of other natural resources such as geothermal energy could remain elusive until a comprehensive geophysical exploration is carried out that will delineate these resources locations in coordinate and depth. The availability of such a database will become a tool that will attract investors who are interested in mineral exploration and utilization of geothermal energy for electricity generation and other industrial processes.

This will not only solve electrification problem but also increase the revenue accrued to the nation, as well as help in diversifying the revenue base from crude oil to other sources.

1.3       Aim and Objectives of the Study

The aim of this research is to interpret the Aeromagnetic and Radiometric data of part of the confluence area in order to assess the mineral and geothermal potentials associated with it.

The objectives of the research include the following:

i.    Delineate structures, lineaments and depth to magnetic sources from Vertical derivatives, Horizontal derivatives Analytical Signal, Centre for Exploration Targeting (CET) and Euler deconvolution.

ii.  Compute Concentration maps, and use the result to produce Ratio and Ternary images to map lithologies and locate regions of Hydrothermal Alterations.

iii. Correlate  the  delineated  structures  with  mapped  lithologies  and  regions  of hydrothermal alterations to map zones of mineralisation.

iv. Employ spectral analysis technique on the aeromagnetic data to reveal underlying geothermal potentials of study area.

1.4       Justification of the Study

Nigeria is one of the Nations colossally blessed with solid minerals and other sub-crustal resources such as geothermal energy. Employing these resources will not only enhance her infrastructural development but will also boost her economic and revenue base. This research work will produce database of Geophysical information for the exact location (Coordinates and depth) of solid minerals and geothermal potential of study area. These information makes mineral exploration easier and will attract investors whose input will increase Internally Generated Revenue (IGR) of the country.

₦8,000.00 – DOWNLOAD FULL PROJECT DOWNLOAD FULL PROJECT Added to cart

---

---

---

---

Related Project Topics :