DELINEATING AND INTERPRETING THE GOLD (MINERALISATION) VEINS AROUND BIDA AND ZUNGERU AREA OF NIGER STATE, NIGERIA USING AEROMAGNETIC AND RADIOMETRIC DATA

ABSTRACT

Both Airborne Magnetic and Radiometric dataset were employed to interpret the geology and geological structures that serve as host to gold and other solid minerals within the Bida (Sheet 184) and Zungeru (sheet 163). An area of 55 by 110 km square is contained within the cretaceous sediments of Bida Basin and the meta-sediments of Zungeru- Sarkin-Pawa schist belt. Data interpretation adopted concentrated on mapping geological structures, boundaries and possible gold mineralisation veins that arises from hydrothermal altered zones. Application of mathematical algorithm for data enhancing such as, Reduce-to-the-Equator and Analytical signal, to the magnetic data, Potassium (K), Thorium (Th), Uranium (U) and Ternary image of the radiometric data helps in delineating the NW-SE trending contact separating the cretaceous sedimentary formation from the meta-sediments. This trend takes off from the Southern end Bida and terminates at the Western end of Bida. The first vertical derivative and the CET analysis help in mapping the fractures, folds and contact zones. Majority of the structures delineated exist around the meta-sediments. Primarily at the Northern end of the study area are linear faults and fractures trending NE-SW around Zungeru – Yakila – Katako axis and ranges from 2 to 5 km in length within mylonite formation. Also, below Federal University of Technology Minna main campus around Minkwogi, Sunbwagi, Sabon-Dagga, Kakagi and Bobo Shiri area, are chunk of interconnected short fracture zones that exist within the magmatite. Belt type meta-sediment complexes. Results from the Analytical signal, vertical derivative, Eular Deconvolution and CET-plugin showed that most of these structures and their depth were located with in northern part and south-western region of the study area. The coordinate of these major structures and lineaments that shows degree of mineralisation were mapped on CET map most interestingly is between longitude 6˚20E to 6˚30E and latitude 9˚10N to 9˚30N. Where the meta-sediments have been intruded by medium to coarse grain biolite granite, is an evidence of structural control veins, which coincided with regions of hydrothermally, altered zones on the ternary map.

CHAPTER ONE

1.0       INTRODUCTION

1.1       Background to the Study

Mineral is a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. Common minerals include quartz, feldspar, mica, amphibole, olivine and calcite. The physical properties of minerals such as their hardness, lustre, color, cleavage, fracture and relative density can be used to identify minerals. These general characteristics are controlled mainly by their atomic structure crystal (HKGS, 2009). In geology and mineralogy, the term “mineral” is usually reserved for mineral species, crystalline compounds with a fairly well-defined chemical composition and a specific crystal structure. Mineral without a definite crystalline structure such as opal or obsidian are then more properly called mineraloids. If a chemical compound may occur naturally with different crystal structures each structure is considered different mineral species example quartz and stishovite are two different minerals consisting of the same compound silicon dioxide. Minerals being natural chemicals are classified according to their chemistry and crystal form. A basic classification for minerals is native element are gold, silver, mercury, granite, diamond. Oxides (Corundum, hematite, spine) Sulfides (pyrite, galena), Hydroxides (Goethite, brucite) Carbonates (calcite, magnesite, dolomite) Sheet silicates (Muscovite mica, biotite mica, clay minerals) Framework silicates (quartz, feldspar).

Silicate minerals are the most abundant components of rocks on the earth’s surface, making up over 90 percent by mass of the earth’s crust. The fundamental chemical building  block  of  silicate  minerals  is  the  chemical  compound  silicon  tetra  oxide �����4. (HKGS, 2009). Rocks are made of mineral element; element are simple substances that cannot be broken down into any other substance. Only a few  minerals are rock forming and most rock is made from a combination of the component of these such as feldspars, quartz, mica, olivine, calcite, pyroxene, and amphiboles. Most other minerals of which there are over 3000 different types are rarely present in a quantity that is large enough to be considered as rock forming. To consider a common rock forming mineral must be one of the most rock abundant mineral in the earth crust, be one of the original minerals presents at the time of a crustal rock formation and an important mineral in determining a rock’s classification (Hobart, 2005).

Potassium (K) is a building block of some of the most widespread minerals but despite that, it is actually surprisingly rare in the whole Earth. It can be even said that potassium is a trace element. It forms only 160 ppm (0.16%) of the bulk earth. It is an important constituent of k-feldspar and mica and these are among the major component of granitic. Granite rhyolite, stale, shale, arkoses and so on, are the common rock and potassium is abundant there and found abundant in the upper continental crust. It belongs to the alkali metals group. Other geological significant metals in this group are sodium and lithium. These elements are very reactive because they contain only one outermost electron. They are therefore always on  the lookout  for the potential partners. We will never find uncombined potassium in nature because of that potassium tends to form ionic compound. Potassium and sodium are very similar to other chemically and their behavior in geological materials in analogous as well (Mittlefehldt and David, 1999).

Radioactive decay is an important source of earth’s internal heat, because the concentration of potassium is so much higher in the continental crust than in the mantle. The geothermal gradient and heat production is also higher there. It is not the only heat producing element but other heat producers such as uranium and thorium are also highly incompatible in the mantle and therefore gather in the continental crust just as potassium does.  Potassium  readily dissolves  in  water during weathering of  potassium-bearing minerals and enters the hydrosphere for a long time. It goes relatively easily into the water, but it is not easy to take it back. All it takes is to vaporise the water until potassium precipitates out of its as evaporate mineral sylvite (KCL), but very high rate of evaporation is needed for it to occur. Therefore, potassium tends to stay in the hydrosphere for a long time (Mittlefehldt and David, 1999).

This work focuses on the analysis and interpretation of the aeromagnetic and radiometry data over some parts of Niger State (Minna and part of Central Bida Basin). The outcome of the analysis is expected to throw more light on the geological features, minerals and other linear features as related to the mineralisation potential of the study area.

1.2       Statement of the Research Problem

In line with the current trend in Federal Government policy which is encouraging state governments agencies and parastatals to find means of improving on their internally generated revenue fund (IGRF), rather than relying on Government funding. This prompts the authorities of the Federal University of Technology Minna to look into the possibility of exploring the solid mineral (especially gold) potentials that are located within his neighborhood so as to generate more funds (FUTMinna Book of Speeches, 28th Convocation Ceremony). This idea is not out of place as the University is situated within the contact/boundary between the Bida sedimentary basin and the Zungeru/ Sarkin-Pawa Schist belt. These regions are marked by several volcanic activities which give rise to the structures that serve as host to this mineral.

1.3       Justification of the Study

Both aeromagnetic and radiometric methods are very effective in environmental monitoring and  geological  mapping.  The result  from  radiometric and  aeromagnetic survey will delineate the geology structure like fault, fold, basement structure for mineral which are possible host, target and assist in locating some intrusive body related to mineral deposits and its magnitude. The outcome of this research will provide solution to address where exactly the mineral of interest is located and also their depth so occurrence. Exploring these minerals would in no doubt increase the internally generated revenue of the University.

1.4       Aim and Objectives of the Study

The aim of this project is to delineate delineating and interpreting the gold (mineralisation) veins around Bida and Zungeru area of Niger State, Nigeria using aeromagnetic and radiometric data.

The objectives are to;

i.          Interpret the Total Magnetic Intensity (TMI) of the area to indicate regions of high and low magnetic susceptibilities.

ii.         Obtain the horizontal derivatives, analytical signal, vertical derivative and Central Exploration Targeting (CET) in order to position anomalies directly above the causative body, delineate both deeper and shallow structures that could be faults, fracture, intrusive bodies, lineament that are veins.

iii.        Produce ternary map by combining the data of Potassium K (in red), Thorium Th (in green) and Uranium U (in blue) to map geology contact, while correlate with Geology map of the study area and delineate the regions of highs and lows for the three (3) elements namely Potassium, Thorium and Uranium
iv.        correlate  the  structure  obtain  from  the  magnetic  field  with  that  of  the radiometric interpretation to delineate the mineralisation zone.

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