CHAPTER ONE
INTRODUCTION
1.1
Statement of the problem
Granite is a common type of
felsic intrusive igneous rock that is granular and phaneritic in texture.
Granites can be predominantly white, pink, or gray in color, depending on their
mineralogy. The word “granite” comes from the Latin granum, a grain,
in reference to the coarse-grained structure of such a holocrystalline rock.
Strictly speaking, granite is an igneous rock with at least 20% quartz and up
to 60% alkali feldspar by volume. The term “granitic” means
granite-like and is applied to granite and a group of intrusive igneous rocks
with similar textures and slight variations in composition and origin. These
rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which
form an interlocking, somewhat equigranular matrix of feldspar and quartz with
scattered darker biotite mica and amphibole (often hornblende) peppering the
lighter color minerals. Occasionally some individual crystals (phenocrysts) are
larger than the groundmass, in which case the texture is known as porphyritic.
A granitic rock with a porphyritic texture is known as granite porphyry. Granite
differs from granodiorite in that at least 35% of the feldspar in granite is
alkali feldspar as opposed to plagioclase; it is the potassium feldspar that
gives many types of granite a distinctive pink color. The extrusive igneous
rock is equivalent to granite rhyolite. Granite is classified according to the
QAPF for coarse grained plutonic and named according to the percentage of
quartz (Harvey Blatt & Robert J. Tracy 1997).Granite is nearly always
massive (lacking any internal structures), hard and tough, and therefore it has
gained widespread use throughout human history, and more recently as a
construction stone.
The study area lies within the Western region of
Nigeria. Nigeria can broadly be subdivided into three major geological
components and these are: the Basement, Granites and Sedimentary Basins (Obaje,
2009). The basement (Precambrian in age) is further subdivided into five
regions on the basis of the occurrence of sedimentary basins. These are the
Western Nigerian Basement, North Central Nigerian Basement, Adamawa Highland,
Eastern Nigerian Basement and the Oban Massif. As discussed by Obiora et al
(2009) and references cited within, the basement consists of “migmatitic
gneisses, including banded varieties; the schist belts constituted by
mica-schists, tremolite-schists, graphite-schists, with occasional marbles and
dolomites, calc-silicate rocks, meta-conglomerates and banded iron formation
(BIF) and Precambrian granites including porphyritic/porphyroblastic muscovite
granites, biotite granites, hornblende-biotite granites,
non-porphyritic/non-porphyroblastic granites, aplites, granodiorites, diorites,
quartz diorites, syenites, quartz-enstatite granites and enstatite granites
(charnockites).”
Two generations of granites can be identified and these
are prominent within the basement rocks. The older granites as termed by
Falconer (1911) range widely in composition and age from 750 Ma to 450 Ma
(Obaje, 2009). The younger granites (Jurassic in age) are prominently
distributed in the North Central Nigerian Basement and occur as ring complexes
which form part of a wider province of alkaline anorogenic magmatism (Obaje.,
2009). Broadly speaking, the sedimentary
basins can be stratigraphically divided into formations, the older Cretaceous
sedimentary basins of which the Benue Trough, Bida-, and Sokoto Basins are the
most prominent. The youngest sequence is the Tertiary Sedimentary Basins of
which the Chad Basin is the most prominent as well as the sedimentary sequences
of the Niger Delta. The geology of the area of interest in this present study
falls within the Western Nigerian Basement of which the basement rocks cover
almost 100% of the total land surface in this state (Oyedokun and Igonor,
2013). The study presents the results of the characterisation of granite
samples obtained from a deposit site in Gbaleosu, South Western Nigeria and
focused on the geology, major elements and composition of granite.
1.2
Aim and objectives of
study
The main aim of this study is to undertake the trace elements study
of granite from Gbaleosu. Other objectives of this study include:
·
To produce an accurate
geological map of the area.
·
To identify the different rock
lithologies present in the study area.
·
To understand and establish the
geologic history of the area.
·
To analyze structural data
acquired and their relevance to the current geology of the study area.
·
To generally analyze the
economic value of the rock lithology found in the area
·
To examine and report all
structural features
1.3
Justification of study
A lot of studies have been undertaken in this area, but this study
specifically aims to investigate the trace elements composed of granite from
Gbaleosu the study area.
1.4 Scope and Method
This study is restricted to the
relationship between geology and trace elements studies of granite at Gbaleosu
south western Nigerian. Geological field mapping was undertaken in order to collect, identify
and study the field occurrences of granite in Gbaleosu, the method use are the
thin section preparation for petrographic analysis and sample preparation for geochemical
analysis. 10 fresh rock samples which were cut into thin section will then be
move further for the laboratory studies.
1.5
Study Location and
Accessibility
The study area, Gbaleosu is in Oluyole local government of south
western Nigeria Oyo state, Gbaleosu is situated southeast of Ibadan in South
western Nigeria which is part of the Precambrian basement complex of Nigeria,
it’s bounded by latitudes 7.76’00N to 7.93’00N while the longitudes 3.54’00E to
4.00’00E within Ibadan (fig 1.1). The area is bounded by Lagunji at the Western
part while Akintola ogibun is at the North eastern part. Motor cycle is the
major means of transportation in Gbaleosu Community. There are minor road
linking Gbaleosu with some other neighboring villages. In general the study
area is easily accessible through a network of minor, major and footpath
Figure1.1: Map of south western Nigerian
showing the location of study area
1.6
Physiographic setting
Physiographic setting is the study of the features of the area which
occur by certain effect of geographical factors such as drainage pattern,
climate and vegetation, relief and topography.
1.6.1 Climate and vegetation
The study area falls within the tropical humid climate region where
the wet and dry seasons are noticed prominently in the area. Just like any
other part of the south western region of Nigeria, wet season Gbaleosu runs
from march through October while dry season is between November and February.
The mean maximum temperature observed is 21.42°C to 26.46°C while the annual rainfall ranged from 150 to 2500mm. Generally the
vegetation of major part of southwestern Nigerian represents that of the humid
forest. The vegetation of the area is similar to that of tropical rain forest
where they are high tree and shrub (fig 1.2), the vegetation is characterized
by the presence of thick tropical greenish forest made up of different trees
and grasses e.g. pawpaw, palm tree, etc.
Fig. 1.2 Showing Ecological Map of
Nigeria
(CIA, 1979)
1.6.2 Relief and topography
The relief and topography of the study area is randomly an
undulating feature. The eastern part of the study area has higher elevation;
the upper part of the study area has elevation between 100-120m feet’s (above
the mean sea level).
1.6.3 Drainage pattern
The drainage system in the area is usually marked with a
proliferation of many smaller streams which are wet for some few months,
especially from march to October. There is a Major River in the study area
called river Omi which flow from north to the southern part of the area.
1.7 Review of Related Previous Works.
Nigeria
lies approximately between longitude 40N and 150N and latitude 30E and 140E.
Within the pan African mobile belt in between the west African craton in
the region of late Precambrian to early
Paleozoic orogenesis. The basement complex is made up of Precambrian rocks and
consists of schist belts folded in them. Previous works have been carried out
on a regional scale on the basement complex of Nigeria and it has been shown
that this is the most abundant lithology in Nigeria such work includes, Rahaman
(1988), Odeyemi (1977) and Oyawoye (1964), Grant (1978), Anifowose (2006),
oyinloye (2011) among others. They gave an account of the geology of this area
under a broader work.
Ejimofor et al., (1996) worked on the petrography and
major element geochemistry of the basement rocks of northern Obudu area,
eastern Nigeria. It was shown mineralogically that, the preference of igneous
fields by the granite gneisses suggest their affinity for igneous progenitors.
Elueze et al., (2004) determined the petrochemistry and petrogenesis of granite
from Abeokuta area, southwestern Nigeria.
The geology of the basement
complex of southwestern Nigeria Oyawoye (1964), Rahaman (19176), Odeyemi (1977)
noted that the rocks in the study area show eveidence of polyphase deformation
with the plutonic episode of the pan African event being the most pervasive
Undeformed Acid and Basic Dykes or The minor felsic and mafic intrusives.
One of the most famous publications on the pegmatitic veins in
Nigeria is that of Jacobs and Webb (1946) which identified that the pegmatites
are confined to a 400km NE-SE trending belt. Recently however, Okunlola
and Somorin (2006), Okunlola, (2005),
Garba (2003), Okunlola and King (2003), have shown evidence that they
may not be restricted to only this confine. Geochronological data from previous works (Rb
– Sr whole-rock and U-Pb zircon) of Pan-African granitoids intruding the
reactivated Archean to Lower Proterozoic crust of central and southwestern
Nigeria show that intrusive magmatic activity in these areas lasted from at
least 630 to 530 Ma (van Breemen et al., 1977; Rahaman et al.,
1983; Dada et al., 1987; Matheis and Caen-Vachette, 1983; Umeji and
Caen-Vachette, 1984; Akande and Reynolds, 1990). Results of the rock ages also
show that pegmatites’ emplacement in the southwestern Nigeria occurred mainly
after the peak of the Pan-African orogenic event in this area. Several others have carried out extensive research on geochemical
and petrochemical analysis on pegmatites from southwestern Nigeria. Akintola et
al (2011) examined pegmatite around Awo and concluded that the pegmatite
contains accessory minerals such as tourmaline, garnet, beryl and spodumene
together with some rare metals. Okunlola (2005), while studying the rare metal
Ta-Nb pegmatites of Nigeria outlined seven (7) broad fields namely
Kabba-Isanlu, Ijero-Aramoko, Keffi-Nasarawa, Lema- Ndeji, Oke Ogun, Ibadan-
Oshogbo and Kushaka-Birnin Gwari. The Olode-Gbayo pegmatites occurrences are
presumed to be members of the Ibadan-Oshogbo field occurrences. Elueze et. al.
(2004) embarked on a preliminary investigation of the industrial properties of
the Olode-Falansa pegmatites in southwestern Nigeria and they concluded that
the pegmatites have good potential for use in refractory, glass, ceramic and
construction industries. Okunlola and Jimba (2006) carried out petrographic and
geochemical evaluation of pegmatite bodies around Aramoko, Ara and Ijero area
and concluded that majority of the samples are subclass and magmatic pegmatite
while some pegmatite may have undergone mild post-magmatic alteration distinct
petrologic units especially those outcropping around Ijero area.