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Major Element Analysis of Basement Complex Rocks Around Bajabure Area Maiha L.G.A Adamawa State North-Eastern Nigeria

Projektarbeit 2014 56 Seiten

Geowissenschaften / Geographie - Geologie, Mineralogie, Bodenkunde

Leseprobe

TABLE OF CONTENT

Dedication

Acknowledgement

Table of content

List of Figures

List of Tables

Abstract

CHAPTER ONE: INTRODUCTION
1.0 Background
1.1 Location and Accessibility
1.2 Climate and Vegetation
1.3 Relief and Drainage
1.4 Previous Work
1.5 Aims and Objectives

CHAPTER TWO: LITERATURE REVIEW
2.0 The Nigerian Basement Complex
2.1 Review of the Geology of the Basement Complex of Northeastern Nigeria
2.1.1 Metasediments
2.1.1.1 Hornblende and Biotite-Gneiss
2.1.1.2 Quartzo-Feldspathic Gneiss
2.1.1.3 Quartzites
2.1.1.4 Calc-Silicate Rocks
2.1.1.5 Sericite Rocks
2.1.2 Older Granite
2.1.2.1 Syntectonic Granite
2.1.2.2 Fine Grained Granite
2.1.2.3 Basic and Intermediate Rocks-
2.1.3 The Burashika Group
2.2 Geology of Mandara Hill

CHAPTER THREE: METHODOLOGY
3.0 Geological mapping
3.1 Field instrumentation
3.1.1 Uses of instruments
3.1.2 Traversing
3.2 Laboratory work
3.2.2 Geochemistry
3.2.3 Analytical method

CHAPTER FOUR: PRESENTATION OF RESULTS
4.0 Local geology of the study area
4.1 Major rock types
4.1.1 Coarse grained granite
4.1.2 Coarse porphyritic biotite granite
4.1.3 Medium-coarse grained granite
4.2 Minor rock types
4.2.1 Granite gneiss
4.2.2 Mylonite
4.2.3 Pegmatite
4.3 Structural features
4.3.1 Foliation and Lineation
4.3.2 Joints
4.3.3 Veins
4.4 Field relationship
4.5 Geochemical results
4.6 Plotting of geochemical data

CHAPTER FIVE: Discussion, Summary, Conclusion and Recommendation
5.0 Discussion
5.1 Summary
5.2 Conclusion
5.3 Recommendations

REFERENCE

LIST OF FIGURES

Fig.1: Map of Nigeria showing location of the study area

Fig.2: Coarse porphyritic biotite granite

Fig.3: Mylonite

Fig.4: Pegmatite

Fig.5: Geological map of the study area

Fig.6: Foliation

Fig.7: Joint

Fig.8: Feldspathic vein

Fig.9: Wt% of Calcium oxide CaO and (Na2O + K2O) against wt% of silica (SiO2)

Fig.10: Wt% of all oxides against wt% of Silica(SiO2)

Fig. 11: Variation Diagram of (Na2O + K2O) against wt% of Silica (SiO2)

Fig.12: Cao-Na2O-K2O plot of sample L46C

Fig.l3: Cao-Na2O-K2O plot of sample L17B

Fig.14: Cao-Na2O-K2O plot of sample L46

Fig. 15: Cao-Na2O-K2O Diagram showing the position of Bajabure rocks

Fig.16: Al2O3-CaO-(Na2O + K2O) Plot of sample L17B

Fig.17: Al2O3-CaO-(Na2O + K2O) Plot of sample L46

Fig.18: Al2O3-CaO-(Na2O + K2O) Plot of sample L46C

Fig.19: Al2O3-CaO-(Na2O + K2O) Diagram showing the position of Bajabure rocks

LIST OF TABLES

Table 1: Geochronology of various rock types around the study area (Maiha)

Table 2: Major oxides composition of rock samples from Bajabure area, Maiha LGA of Adamawa State, NE Nigeria

Table 3: Classification based on silica percentage

Table 4: Classification based on Alumina saturation

DEDICATION

This project is dedicated to Almighty Allah for His infinite mercies, divine guidance and to my late father Dr. Usman Abba Tukur and to my mum Mrs. Aishatu U.A Tukur.

ACKNOWLEDGEMENT

I wish to acknowledge the contribution of some personalities who have helped and encouraged me through this phase of life.

My most profound gratitude goes to the almighty Allah for his divine love, guidance and empowerment throughout my time in Unimaid, most especially as am conscious of many who started this race with us and never got to see the end for one reason or the other.

I sincerely acknowledge the contribution of my supervisor Dr. J.V. Millitus for his tolerance, understanding and patience towards the success of this work.

With my heart filled with contempt and gratitude, I say a big thank you to mum, Mrs Aishatu U.A Tukur for all that she has done for me in my times of need and to my brothers and sisters; Sadiq Usman, Nabila Usman, Hafsat Usman, Atiku Usman, Hajara Usman and Abdulmajeed Usman. Also Sa’adah Akeel Umar for her unconditional love, Dr. Saidu Baba, Alh. Abubakar Sadiq and mama Azumi. Thanks for the unconditional love, moral and financial support and most of all of your tolerance. All of you just define what it is to have a family, I love you all.

My special appreciation goes to my friends throughout the course of my life m my primary school days through secondary school and now the university as they are precious to me the names remain close to my heart as I don’t want anyone to be left out. My grandmother and the entire Abba Tukur family I say a big thank you for all you have done.

My appreciation goes to my course mates, whose contributions to my academic excellence cannot be overemphasized and remains evergreen to my heart. To many I couldn’t mention, I have you all at heart. Thank you all.

ABSTRACT

Geological field mapping was carried out within the study area (Bajabure). Basement rocks known as the older granite suite were the dominant occurring rocks which varies texturally from the fine grained granite to medium grained granite to coarse grained granite to coarse porphyritic biotite granite. Minor suites of granite gneiss, and pegmatite were also observed in the study area. Mylonite was also observed that trend in N-S direction.

The samples collected were subjected to geochemical analysis for major oxide composition using the X ray fluorescence spectrometer. Geochemical results indicates that Silica (Si02) content ranges from 72.l4wt% to 74.53wt% while Aluminium oxide or Alumina (A1203) ranges from 13.26wt% to 14.57wt%. Calcium oxide (CaO) ranges from 0.53wt% to 1.00wt%. Sodium oxide (Na20) ranges from 2.03wt% to 3.63wt% while Potassium oxide (K20) ranges from 4.91wt% to 6.48wt%. Haematite (Fe203) ranges from O.63wt% to l.59wt%, Manganese oxide (MnO) ranges from 0.005wt% to 0.017% while Magnesium oxide (MgO) ranges from 0.14wt% to 0.58wt%. Titanium oxide (Ti02) ranges from 0.109wt% to 0.441wt%. Phosphorus Pentaoxide (P205) ranges from 0.04wt% to 0.16wt%. Loss of ignition (LOI) ranges from O.46wt% to 1.35wt%. Chemical variation plots indicate that the rocks are mostly Calc.alkaline and Peraluminous. The silica content of the samples (> 66%) suggests that all the rocks are acidic and that the rocks from Bajabure are cogenetic and compares favourably with those from the Northern Cameroon volcanic line and other parts of the basement complex of Nigeria.

CHAPTER ONE

INTRODUCTION

1.0 BACKGROUND

Bajabure forms part of Maiha Local Government Area (LGA) of Adamawa State. The study area is shown to be located within the basement complex of Nigeria. Bajabure is also part of the Mandara hill which lies within the northeastern sector of the Nigerian basement complex. The Mandara hill occurs within the pan African mobile belt which lies between the West African craton and the Congo craton to the east. The southern part of the Mandara hill is situated in Adamawa State forming part of the northeastern sector of the basement rock of Nigeria. The Mandara hills are composed mostly of hill forming rocks approximately trending North-South.

Generally, the basement complex of Nigeria is grouped into three lithological units: the migmatite-gneiss-quartzite complex, the metasedimentary schist belts and the older granite. The basement complex rocks in Bajabure belong to the older granite suite. The rocks are believed to have been emplaced during the pan African orogeny (600 + 150) million years ago. After a period of sedimentation orogenic cycles occurred during which the older granites were emplaced. The subsequent interaction between the older granite and the preexisting rocks produced a variety of migmatite and gneissic rocks with dominantly North-Easternly trending foliation. Dominant among the older granite rocks are coarse porphyritic biotite granite, medium to coarse grained biotite granite, fine grained biotite granite, pegmatites and Aplite.

1.1 LOCATION AND ACCESSIBILITY

The study area is within Maiha Local Government in Adamawa State, Nigeria. It forms part of the southern sector of the Mandara hills of the basement complex of Nigeria and it lies between latitude 1O°8’30”N to 1O°6’20”N and longitude 13°11’OO”E to 13°14’O&E.

The area is accessible through the Maiduguri-Mubi road, covering a distance of about 195km. Although there are many hills in the study area due to high topographic relief with terrain elevation above sea level at 156m but yet the availability of footpath and routes joining the villages made it possible

illustration not visible in this excerpt

Fig.1: Map of Nigeria showing location of the study area.

1.2 CLIMATE AND VEGETATION

Bajabure in Maiha L.G.A has a tropical climate of dry and wet season. The wet (rainy) season usually commences late April and ends late October to early November with an average precipitation of 759mm (Adamawa State diary 1993). The wettest period being the months of August and September. The dry season starts late November and ends early April, this is the period of harmattan; a period when dust laden North-Eastern winds from the Sahara desert have a marked effect on the climate of the area. The period is cold and the driest months are January and February when the relative humidity is 13%. Temperature varies from time to time, the minimum average for the year being 24°C and maximum being 39.7°C.

The area is a typically semi-arid zone characterized by shrubs and thorny trees with few grasses of the lowland area with flat topography.

1.3 RELIEF AND DRAINAGE

The area is characterized by high relief ranging from 2000m in the western part to 3900m above the sea level in the southern part of the area. The Northern hills range starts with the Bagale group of Synclinal folds (about 600m above sea level), development in the series Cretaceous sandstorms described by Dio, (1999).

The drainage pattern in the area is basically the dendritic type with stream valleys joining each other to form a river in the lower course of the channels. Two drainage systems occur in the area (Opeloye et al., 1999) the Yadzeram system which is mainly formed in the western part of the area and is an inland drainage system that empties its content into Chad while Killange system empties its content into river Benue.

1.4 PREVIOUS WORK

The geology of North-Eastern basement complex of Nigeria into which the study area falls has not been studied in details as compared with other basement areas of the country. However, Carter et al., (1963) have studied the geology of part of Adamawa, Borno and Bauchi provinces and classified the North-Eastern region into;

1. Metasediment
2. Older granite
3. Burashika group

Islam, et al., (1986), and Islam and Baba (1989), carried out geological studies on the Northern and North-Eastern part of Mandara hills. Islam et al., (1986) also described the occurrence of some members of the polymetamorphosed migmatite-gneiss-quartzite complex and various members of the older granite suite on the Mandara hills.

The work of the Geological Survey of Nigeria (1996), though not in detail, is relevant to this study as they identified and differentiated the major rock units comprising the older granite based on texture and mineralogy. Many research works carried out by students of the department of Geology University of Maiduguri on the basement complex rocks have also helped in the completion of this research work.

1.5 AIMS AND OBJECTIVES

The aim of this work is to produce the geological map of Bajabure area that will contribute to the knowledge of the geology of the area. It is also aimed at the geochemical study of the rocks with the following objectives in mind:

i. Identify and distinguish the major rock units in the area.
ii. Identify definite or approximate geologic contact of the main rock units.
iii. Carry out a major element analysis of the minerals.
iv. Produce a final year B.Sc (Geology) project.

CHAPTER TWO

LITERATURE REVIEW

2.0 THE NIGERIAN BASEMENT COMPLEX

The Nigerian basement complex covers about 50% of the entire country, (Islam, et al., 1986) underlying mainly the Southeast, Northwest, Central and Northeastern parts of the country and these comprises a wide range of rock types. The other 50% of the country’s land surface is covered by Cretaceous and younger sediments overlying the basement complex. Towards the central part of the country high level intrusive granites of Jurassic age intrudes into the basement complex referred to as the younger granite suite or ring complexes. Tertiary volcanics also cover a small portion in the Northeastern part of the country.

The Nigeria basement complex rocks is a group of crystalline igneous and metamorphic rock of Precambrian to lower Proterozoic in age. The rocks are generally grouped into three lithological units;

1. The migmatite-gneiss-quartzite complex
2. The schist belt
3. The older granites.

While Rahaman (1976) grouped the basement in Southwestern part of the country as follows;

1. The migmatite-gneiss complex
2. Slightly migmatized to unmigmatized paraschist and metaigneous rocks
3. Charnokitic rocks
4. Older granites
5. Unmetamorphosed doloritic dykes.

McCurry (1976) classified the Paleozoic and Precambrian rocks in the Northwestern part as;

1. Older metasediments
2. Younger metasediments
3. Older granites
4. Volcanic rocks.

These rocks ranges from acid to basic in composition and are massive to foliated in texture, the grain size ranges from fine to medium to coarse grained and porphyritic.

The Nigerian basement complex has been worked on by different authors, these includes;

1. Rahaman (1976) and Odeyemi (1981) in the Southwest.
2. McCurry (1973), and Ajibade (1981) in the Northwest.
3. Barber and Carter (1963), Islam, Ostafrezuk and Baba (1986) in the Northeastern part.

2.1 REVIEW OF THE GEOLOGY OF THE BASEMENT COMPLEX OF NORTHEASTERN NIGERIA

Not much is known about the basement complex of Northeastern Nigeria. Carter et al., (1963) classified the crystalline basement complex rocks of the region as;

1. Metasediments
2. Older granite
3. Burashika group

2.1.1 METASEDIMENTS

The metasediments in this region are completely granitized and transformed into anatexis migmatite and granite. The oldest rock unit is the migmatite-gneiss which is exposed at the eastern margin of the batholiths near Pukka area (Islam, et al., 1990). This group exist only as xenoliths and small pendant in the granitic rocks, gneiss being the most frequently occurring type; their mineral assemblage is that of amphibolites faces. Carter et al., (1963) divided the metasediments into;

1. Hornblende and biotite gneiss
2. Quartzo- feldspathic gneiss
3. Quartzites
4. Calc. Silicate rock
5. Sericite rocks

2.1.1.1 HORNBLENDE AND BIOTITE-GNEISS

These rocks occur as xenoliths and are widely spread. They are foliated with amphiboles and biotite as the characteristic minerals largely as rifts and pendants in anatexis migmatite bodies are found near Bahamu.

2.1.1.2 QUARTZO-FELDSPATHIC GNEISS

The gneisses are poorly foliated, leucocratic and fine grained in texture. They consist of fine grained granoblastic aggregate of quartz, plagioclase and potash feldspars. They also occur as small pendants and xenoliths in granites near Wuyo. Quartzo-feldspathic gneiss are best exposed in Takaskara hills associated with quartzites (Islam, et al., 1990). This rock forms a number of hills near Manawa.

2.1.1.3 QUARTZITES

In Grashina beds of impure quartzites ranging 5-7cm are found interbedded with layers of biotite and gneiss. The quartzite is grayish with grey luster. Accessories of pyroxene, sphene, apatites, clinozoosites and epidote are often present (Carter et al., 1963) while also quartzite cobbles and pebbles are also encountered in the Liga Hills (Islam, et al., 1990).

2.1.1.4 CALC-SILICATE ROCKS

The calc.silicate rocks are dark, strongly foliated and medium grained. They occur as small outcrops of diopsides scapolite rock associated with granite near KwayaTera. They are composed of equal amount of diopsides and andesine with sphene and epidote as accessory minerals.

2.1.1.5 SERICITE ROCKS

These rocks are non-polluted composed almost entirely of sericites with little quartz. The rocks are greenish-grey in colour, fine grained in texture, dense and structureless. They are found at two localities near Hyema and Manawaji. They are composed of massive aggregate and sericites and fine white mica. Interstitial quartz, orthoclase, secondary hematite and a little magnetite are also present. The rocks may be hydrothermal alteration of intermediate lavas such as trachytes.Sericite schist are also exposed in the Takaskara hill associated with quartzite (Islam, et al., 1990).

2.1.2 OLDER GRANITE

This is found in all parts of the Nigerian basement complex, this rock intruded during the pan African orogenic cycle. They vary in structure, texture and mineralogy and show diverse relationship with metasediments. This can be attributed to the various stages of granitization anatexis and migmatization undergone by rocks (Carter, et al., 1963). The earliest members of the older granite are characteristically rich in potash, which are basic and intermediate intrusive represented by small irregular bodies of quartz and pyroxene diorites and gabbro. Three main divisions of the older granites are recognized in the Northeast region (Falconer, 1911). This includes;

1. The syntectonic granite
2. Fine-grained granite
3. Basic and intermediate plutonic rocks

2.1.2.1 SYNTECTONIC GRANITE

These were emplaced during the early stage of Pan African orogeny. They are described as concordant granite produced by granitization of preexisting rocks. They are composed of diverse series of potassic rocks including porphyritic granite, anatexis migmatite and equigranular granite, Marmo (1955) summarized the potassic rocks.

2.1.2.2 FINE GRAINED GRANITE

These are discordant rocks occurring as small irregular bodies rarely exceeding 180m in extent and 27m in width. There is little variation in colour and appearance. They are generally pale brown grey equigranular fine grained rocks. Foliation is defined by parallel alignment of mica. They resemble the syntectonic granite through the feldspartization of fine grain granite and is believed to have taken place during the later granitization (Falconer, 1911). Their composition ranges from granite to adamalite.

Gradational contacts are rare, several occurrences have been described by Carter et al., (1963) in localities of Lawaya, Tera, Zona, Bayema and Zobe etc.

2.1.2.3 BASIC AND INTERMEDIATE ROCKS

These rocks are divided into three parts;

1. Gabbro
2. Diorite
3. Pyroxenite

Quartz diorite and feldspathic basic rocks are related rocks. Carter et al., (1963) described twenty one small bodies of gabbros, diorite and quartz-diorite which are older than the syntectonic granite. They are usually poorly exposed and their presences in the field are indicated by a few scattered boulders. They occur as irregular massive and discrete pendant in the syntectonic granite. They are found east of Kokua and west of Daushi and the Garigari inlier (Carter et al., 1963), several patches are also found near Billiri in the Kaltungo inlier. The rocks are generally massive, fine grained and show granular textures with no directional tendency.

Gabbro, diorite and pyroxene occur in the Garigari inlier forming hills and are highly altered, granitised and grades into ferromagnesian constituent. The pyroxenite is also granitized. Quartz diorite and other related rocks of this group present a wide range of composition from granodiorite to quartz diorite. Accessory minerals includes; sphene and epidote. These are common rocks of basic and intermediate varieties.

Islam et al., (1990) differentiated the basement complex of Northern part of Mandara hills and established that;

a. The Precambrian basement rocks are the older metasediments represented by migmatite gneisses, schist and quartzites which were intruded by the older granite suite during the Pan African orogeny. The older granite emplacement is responsible for the conversion of some gneisses into migmatites.
b. The banded gneiss has resulted from simple metamorphic differentiation.
c. The sequence of diorite, various types of granite and pegmatite possibly suggests a fractional trend.
d. The feldspathic megacrysts of coarse porphyritic granites are essentially of magmatic origin.
e. The faulting episode has played a significant role in the modification of some older granite suite.
f. The N-S faults in the Liga hills resulted in the intrusion of pegmatitic quartz and feldspar bodies which are being mined.

Details of the geological setting of Northern part of the Mandara hills have been dealt with by Islam and Baba (1989) and Islam and Baba (in press) respectively. They found out that the rocks are predominantly made of hill forming older granite suite enveloped by low lying migmatite gneiss, schist and quartzites.

The older granites are made up of coarse porphyritic grained granites, medium-coarse grained fine grained granites tectonised granite, pegmatite and aplites with minor basic and felsic dykes and veins.

Contact relationships within the various rocks were found to be commonly sharp but gradational contact were also encountered. Numerous fault zones were mapped and trend generally approximately N-S (Islam, and Baba, 1989).

2.1.3 THE BURASHIKA GROUP

This group of rocks comprises of granite, porphyries and lavas which intruded the near Burashika. They include the Kwaba hill granite, the Jamboran hill porphyry, the Bonga hill volcanic and felsic dykes. These rocks underlie an extensive area of about 19 square kilometers (Carter, et al., 1963). Lavas which occurs near Liya, Yimirdullen and Marland closely resemble certain members of the Burashika group and are therefore grouped with the Bonga hill volcanic. These rocks were intruded into the older granite and are overlain by the Cretaceous sand storm. McLeod, Jacobsen and Baick, (1958) described the Burashika group as Jurassic based on similar features it shows with the younger granite. This group is divided into four (Carter et al., 1963);

I. The felsic dyke being the youngest
II. The Bonga hill volcanics
III. The Jamboran hill porphyry
IV. The kwaba hill granite being the oldest.

2.2 GEOLOGY OF MANDARA HILL

The Mandara hill forms part of the crystalline basement complex of Northeastern Nigeria. The rock units of the area largely range from Precambrian to Tertiary (Islam, et al., 1990).

Recent work has succeeded in differentiating the various rock units in the study area. Baba, et al., (1990) carried out a detailed field work and laboratory study of aerial photograph around the Mandara hills to include the following feldspar, quartz, manganese ore, sulphide minerals, kaolin and granite.

The rock unit of Precambrian to Cambrian age largely comprises of migmatites and gneisses, quartzite, mylonites and pegmatites.

Among rocks of the tertiary age are agglomerate crystal tuff and minor granophyres (Islam et al., 1990). The oldest rock unit is the migmatite and gneisses, which is exposed at the eastern margin of the batholith near Pukka and Gwoza area of Borno State.

Table 1: Geochronology of various rock types around the study area (Maiha).

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CHAPTER THREE

METHODOLOGY

3.0 GEOLOGICAL MAPPING

Geological mapping is a technique employed in studying the geology of the particular area. In carrying out this work it involves reconnaissance survey of the study area using a topographic map as a guide. This was followed by detailed geological mapping using all the necessary field equipment’s such as: G.P.S, Compass, hammer, chisel, measuring tape, acid bottle, sample bag, field notebook, writing materials, magnifying lens, camera etc. needed for the exercise.

Description of all rock samples encountered was done on the field by hand observation and the basic properties noted are; texture, colour, mineralogy and structures based on which the rocks were named. It also involves the differentiation of geological structures as well as rock types and outcrops of the area.

Samples were collected at different locations of certain distance and were labeled to avoid mix up and are afterwards used to produce the geological map of the area as noted on the topographic map.

3.1 FIELD INSTRUMENTATION

The geological field mapping of basement (crystalline) environment involves the use of the following equipment:

I. Topographic map (i.e. base map)
II. Compass clinometers
III. Geological hammer
IV. Measuring tape
V. Hard cover field note book
VI. Sample bag
VII. Pencil, pen, colored pencil etc.
VIII. Hand lens
IX. Global positioning systems (GPS)
X. Masking tape and marker.

3.1.1 USES OF INSTRUMENTS

- Topographic Map (Base Map):

This is used as a guide to the location using geographical co-ordinates on the map (the top of the map is usually considered as the North). This map provides useful information such as drainage patterns, cultural features and vegetation etc. this base map is later developed or improved to the status of a geological map.

- Compass Clinometers:

This is used to measure the strike on a horizontal bed of an outcrop as well as the dip direction perpendicular to the strike on the same bed. It is enclosed in a circular casing designed with the four cardinal points and reads from O3 600.

- Measuring Tape:

This is used for measuring the lateral extents as well as the distance between two points; it is also used in measuring the distance to calculate pace.

- Geological hammer:

This is used for chipping rock samples from large out-crops for portability and identification with the aid of a masking tape.

- Chisel:

This is often used together with the hammer when carefully chipping a delicate sample without much fragmentation.

- Sample Bag:

This is used for carrying samples collected from the field to the laboratory for further analysis, polythene bags were used to prevent the samples from getting wet.

- Hand lens:

This is used for careful examination of a rock sample (usually a fresh sample chipped from an outcrop in the field) in order to identify a mineral so that it can be distinguished where the naked eye may not be able to identify them, and the hand lens comes in handy because it usually comes with a x 10 magnification power.

- Field Notebook:

This is used to record information and description of different rock samples collected in the study area, the field notebook is always accompanied by writing materials (pencil, biro, and colored pencil) used for sample description and inscription.

- Global Positioning Systems (GPS):

This is an instrument that sends signals to satellites in space to process data which as a result plots and tracks your exact position on the earth at any given time; it was used in the field to take coordinates of studied sections in the field as well as their elevation above the mean sea level.

- Masking Tape and markers:

The masking tape was used to seal the polythene bags and they also serve as a platform of marking and labeling the samples with the aid of a marker which contains undeletable ink.

3.1.2 TRAVERSING

Traversing is a method of mapping where the person involved, physically walks in the area of study through defined routes. Pacing is an important aspect of traversing which is a measurement of length of foot step which is done by walking a known distance of about 100m and counting the pace for about 20 different times and the average length of the pace is calculated.

3.2 LABORATORY WORK

3.2.1 GEOCHEMISTRY

Sample of granite (biotite granite of pan African older granite), pegmatite and gneiss were collected, crushed, pulverized and analyzed for their major elements (oxides) composition.

3.2.2 ANALYTICAL METHOD

The analytical method adopted for this study is X-ray fluorescence (XRF). This method works based on the behavior of atoms when they interact with radiation. When materials are excited with high energy, short wavelength radiation for example X-rays, they can become ionized. If the energy of the radiation is sufficient to dislodge a tightly held inner electron, the atom becomes unstable and an outer electron replaces the missing inner electron. When this happens, energy is released due to the decreased binding energy of the inner electron orbital compared with an outer electron one. The emitted radiation is of lower energy than the primary incident X-rays and is termed fluorescent radiation. Because of the energy of the emitted photon is characteristic of a transition between specific electron orbitals in a particular element, the resulting fluorescent X-rays can be used to detect the abundances of elements that are present in the sample.

The analysis begin with creating an application calibration and validating the calibration before measurement of prepared samples.

Manufacture set standards were adhered to, so as to ensure accuracy of results.

CHAPTER FOUR

PRESENTATION OF RESULTS

4.0 LOCAL GEOLOGY OF THE STUDY AREA

The study area (Bajabure) is part of the northern Cameroon volcanic line situated in Maiha local government area of Adamawa state. The area is entirely underlain by the basement complex rocks and exposure of such rock in the area makes it part of the North-eastern sector of the Nigeria basement complex. The rocks encountered consist mostly of granite with textural variation ranging from the fine grained granite to medium grained granite to coarse grained granite to coarse porphyritic biotite granite. Other minor rocks occurring within the older granites of the study area are granite gneiss, mylonite and pegmatite. All the rock types have comparatively similar mineralogy containing quartz, microcline, plagioclase biotite, sericites, andesine and accessory minerals such as zircon and iron oxide.

4.1 MAJOR ROCK TYPES

4.1.1 COARSE GRAINED GRANITE

It is the most abundant rock type of the study area covering substantial portion of the mapped area occurring at two different locations. Its occurrence at the northern region of the study area covers from north-western region (Bedda surrounding) down to the north central region and up to the northeastern region. It shows a gradational contact with the coarse porphyritic biotite granite. This rock type is also prominent around the western sector of the study area and extends up to the southeastern region.

It shows a gradational contact with the coarse porphyritic biotite granite and sharp to gradational contact with the medium grained granite at the southeastern sector. It also occupies southwest part of the study area (Tappare) up to the SE region.

4.1.2 COARSE PORPHYRITIC BIOTITE GRANITE

The coarse porphyritic biotite granite is the second most abundant rock type of the study area. Its texturally coarse to very coarse grained with large white or pinkish feldspar phenocrysts normally measuring 2cm in length. This rock type is typical of older granite as the name implies with white and pink prismatic phenocrysts of microcline normally averaging 2cm in length but locally up to 5cm. It is leucocratic in colour with minerals such as quartz which are whitish, feldspars which are pinkish and biotite which are dark coloured minerals.

In general, the size and proportion of the phenocrysts varies considerably and largely determine the colour and texture of the rock. It is very massive in structure with a gradational contact with the medium-coarse grained granite. Its general appearance tells of its mode of formation, i.e. it is formed at a deeper level with extremely slow cooling of magma. It occupies the central part of the study area including Bedda, Sanda, and Wadakin.

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Fig.2: Coarse porphyritic biotite granite

4.1.3 MEDIUM-COARSE GRAINED GRANITE

This covers a relatively small portion of the study area and shows a gradational contact with the surrounding coarse grained granite and the granite gneiss. It is leucocratic and very massive in structure. It occupies mostly SE part of the study area.

4.2 MINOR ROCK TYPES

4.2.1 GRANITE GNEISS

The granite gneiss forms a very small proportion of the study area just at the south central showing a gradational contact with the surrounding coarse grained granite. The granite gneiss consists of the fine grained granoblastic aggregate of quartz and feldspar with biotite which appears grayish in colour. It is found around Mbaundi at the south central.

4.2.2 MYLONITE

It contains high amount of mafic mineral and is dark grey in colour. When observed under hand specimen; it’s composed of minerals like quartz, k-feldspar and biotite. It’s highly crushed and foliated thereby showing sign of metamorphism. Texturally its fine-medium grained must probably due to the effect of crushing and shearing as a result of dynamic metamorphism.

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Fig.3: Mylonite

4.2.3 PEGMATITE

They are extremely coarse grained igneous rocks consisting essentially of quartz and feldspar. Quartz has a very fine-glassy texture and it’s resistant to weathering while the feldspar portion is highly susceptible to weathering. That is the reason why the quartz can be found scattered around the hill of Wadakin.

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Fig.4: Pegmatite

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4.3 STRUCTURAL FEATURES

4.3.1 FOLIATION AND LINEATION

The features were mostly observed in granite gneiss and some other rock types with parallel alignment of minerals (platy mineral). Gneissic foliation is known by the alignment of the minerals, mainly biotite and light minerals like quartz and feldspar. They indicate product of deformation caused by regional and dynamic metamorphism.

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Fig.6: Foliation

4.3.2 JOINTS

They concentrate and around contact zones between igneous bodies and the host rock. They trend north-south in direction.

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Fig. 7: Joint

4.3.3 VEINS

The veins generally trend N-S, NE-SW, and NNE-SSW and they range in thickness from 1-3cm. Such veins were formed possible as a result of the late magnetic crystallization of low temperature minerals around a fractured zone.

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Fig.8: Feldspathic Vein

Bandings were also observed which may suggest local migration of components during metamorphic differentiation.

4.4 FIELD RELATIONSHIP

All the rocks in the study area were present during the Pan African orogeny. The attachment of appropriate temperature and pressure, coupled with zone of weakness in the country rock must have enhanced the emplacement of such rocks. Silicate melts crystallizes as quartz, feldspar and micas to form dominant constituent of the parent magma by the process of magmatic differentiation. Late formation of felsic mineral results in the formation of pegmatite and other quartzo-feldspathic veins cross cutting the fine medium grained granite pressure of low temperature mineral such as feldspar and quartz in veins seem to support this.

Structural features observed within the rock of the study area can be related to the cooling of the granite following its emplacement. Series of joints and veins occupying the features in rocks are of near vertical orientation. Banding observed can be attributed to metamorphic differentiation which may suggest local migration of components of potassium, sodium, and silicon might have migrated into layers which are now rich in feldspars while iron and magnesium into layers which are rich in ferromagnesian minerals.

4.5 GEOCHEMICAL RESULTS

Using the X-ray fluorescence analytical method, the concentration of the following major elements (oxides) in the samples were obtained viz; Al203, Si02, Fe203, MnO, MgO, CaO, Na20, K20, Ti02, P205 and LOl.

Table 2: Major oxides composition of rock samples from Bajabure area, Maiha LGA of Adamawa State, NE Nigeria.

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The major oxide composition are presented in table 2.

Silica (SiO2) ranges from 72.14% in biotite granite (L46) to 74.53% in pegmatite (L46C) with an average value of 73.34%.

Aluminium oxide or Alumina (A12O3) ranges from 13.26% in gneiss (L17B) to 14.57% in pegmatite (L46C) with an average value of 13.97%. Calcium oxide (CaO) ranges from 0.53% in gneiss (L17B) to 1.00% in biotite granite with an average value of 0.74%. Sodium oxide (Na2O) ranges from 2.03% in gneiss to 3.63% in pegmatite (L46C) with an average value of 2.91%. Potassium oxide (K20) ranges from 4.9 % in pegmatite (L46C) to 6.48% in gneiss (L17B) with an average value of 5.86%.

Fe203 ranges from 0.63% in pegmatite (L46C) to 1.59% in gneiss (L17B) with an average value of 1.25%. Manganese oxide (MnO) ranges from 0.005% in pegmatite (L46C) to 0.017% in gneiss (L17B) with an average value of 0.011%. Magnesium oxide (MgO) ranges from 0.14% in pegmatite (L46C) to 0.58% in gneiss (L17B) with an average value of 0.35%.Titanium oxide (TiO2) ranges from 0.109% in pegmatite (L46C) to 0.441% in biotite granite with an average value of

0.307%. Phosphorus pentaoxide (P2O5) ranges from 0.04% in pegmatite (L46C) to

0.16% in gneiss (L17B) with an average value 0.10%. Loss on ignition (LOl) ranges from 0.46% in biotite granite (L46) to 1.35% in gneiss (L17B) with an average value of 0.85%.

4.6 PLOTTING OF GEOCHEMICAL DATA

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CHAPTER FIVE

DISCUSSION, SUMMARY, CONCLUSION AND RECOMMENDATION

5.0 DISCUSSION

Silica (SiO2) ranges from 72.14% in biotite granite (L46) to 74.53% in pegmatite (L46C) with an average value of 73.34%. Based on the silica content the rocks are said to be acidic as it is shown in the table below;

Table 3: Classification based on Silica (SiO2) % (After Hyndman, 1985).

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The average values combined for Na2O, K2O and CaO are less than the average value of Al2O3 in the analyzed samples. This suggests for the designation of the rocks as peraluminous. See the table below; A12O3> Na2O + K2O + CaO, where Al2O3 = 13.97% and Na2O + K2O + CaO = 9.51%.

Table 4: Classification based on Alumina saturation (after Hyndman, 1985).

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Also from the plot of Al2O3-CaO-(Na2O + K2O) in fig. 19 shows that the rocks are peraluminous.

The Wt% of silica (SiO2) vs calcium oxide CaO and (Na2O + K2O) as shown in figure 9 shows that as silica increases the value of Na2O + K2O also increases whereas the value of CaO decreases with increase in silica (SiO2).

The Wt% of all oxides against silica (SiO2) as shown in figure 10 shows that Alumina (A12O3), potassium oxide (K2O) and sodium oxide (Na2O) increases with the increase in silica with Fe203 remaining fairly constant while calcium oxide (CaO) and magnesium oxide (MgO) decreases with increasing silica as contrasted to their counterparts i.e. Al2O3, Na2O, K2O, and Fe2O3. The figure also shows the coherent nature of the data with increase in silica indicating that the rocks of the Bajabure area are essentially cogenetic (they are related in space and time).Figure 11 shows that all the rock samples are calc.alkaline. Cao-Na2O-K2O variation diagram shows that sample L17B falls within the granite field while sample L46 and L46C falls within the quartz monzonite field.

5.1 SUMMARY

The geological mapping and geochemical study of the rocks exposed in the Bajabure area reveals that the rocks are part of the basement complex of North Eastern Nigeria and are of the older granite suite. The area is essentially underlain by granitic rocks with few exposures of pegmatite and gneiss while mylonite band is restricted to the fault zone in the area. The rocks vary in texture from fine grained granite to coarse grained porphyritic biotite granites. The textures of the rocks was as a result of its cooling rate, composition, number of crystal nuclei and movement of magma. The mineralogy of the rocks of Bajabure area are quartz, muscovite, sericite, andesine and feldspars with quartz and feldspar as the dominant minerals.

5.2 CONCLUSION

Major oxide geochemistry of Bajabure area revealed that the rocks are cogenetic (they are related in space and time). The Cao-Na2O-K2O variation diagram shows that sample L17B falls within the granite field while sample L46 and L46C are quartz monzonite. All the rocks are peraluminous from the plot of Al2O3-CaO-(Na2O + K2O). The rocks are calc.alkaline in nature.

5.3 RECOMMENDATIONS

The study area is among those areas that are yet to be investigated in details in the Nigerian Basement complex. All the literatures used in this work is mainly based on regional synthesis and no recommended work is found that covers the area. There is need for an extensive and careful geochemical and geophysical study of the area. Also the granitic rock should be thoroughly studied to establish data with regards to economic potentials and evolutionary history of the area.

REFERENCE

Adamawa State Diary (l993) Published by Adamawa State Government.

Ajibade, A. C. (1981). Preliminary report of field relationship of the Basement Complex rocks around Igarra, Mid-West in C.A. Kogbe’s (editor) Geology of Nigeria. Elizabethan publishing Co. Lagos, Nigeria, 24-38.

Baba, S., Abaa, S.I. and Dada, S.S. (2006). Preliminary Petrogenetic study of some rocks from Gwoza Area, NE, Nigeria. Global Journal of Geological Science, Vol. 42, 147-155.

Baba, S., Islam, MR., El-Nafaty, J.M. and Annate M.X., (1991). Exploration and Evaluation of industrial minerals and rocks in the northern part of Mandara hills NE. Nigeria, Journal of Mining and Geology Vol. 27 [2], 11-14.

Carter, J.D., Barber, W. and Tait, E.A. (1963). The Geology of parts of Adamawa, Bauchi and Borno province in Northeastern Nigeria. The Geological Survey of Nigeria Bulletin, Vol. 30, 11-34.

Falconer, J.D. (1911). The Geology and Geography of Northern Nigeria, McMillan London 295p.

Hyndman, D.W. (1985). Petrology of Igneous and Metamorphic Rock (2°c’ Edition). McGraw 111111. Inc. New York 786p.

Islam, M.R. and Baba, S. (19S2). Some Geochemical studies of the older granite suites from the Northeth part of Mandara hills, Nigeria, Discovery and Innovation 4, 53-60.

Islam, M.R., Ostaticzuk, S. and Baba, S. (1989). The Geology of the Basement Complex of Northern part of Mandara hills, Nigeria. Annals of Borno 6/7, 99-105.

Jones, H.A. and Hockey, R.O. (1964). The Geology of part of South Western Nigeria. The Geological Survey of Nigeria Bulletin No.31, 15-18.

Rahaman, M.A (1976). A review of the Basement Complex Geology of Southwestern Nigeria. In Geology of Nigeria (edited by C.A. Kogbe, C.A) Elizabethan publishing company, Lagos, 41-58.

Details

Seiten
56
Jahr
2014
ISBN (Buch)
9783668728875
Dateigröße
3.6 MB
Sprache
Englisch
Katalognummer
v428430
Note
B+
Schlagworte
major element analysis basement complex rocks around bajabure area maiha adamawa state north-eastern nigeria

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Titel: Major Element Analysis of Basement Complex Rocks Around Bajabure Area Maiha L.G.A Adamawa State North-Eastern Nigeria