KUFRE AKWANGA FIELD REPORT- Supervisors DR. S.C. OBIORA, DR. C.C. UGBOR

UNIVERSITY OF NIGERIA, NSUKKAFACULTY OF PHYSICAL SCIENCES

DEPARTMENT OF GEOLOGY

A FIELD REPORT ON THE STUDY OF SOME PARTS OF THE BASEMENT COMPLEXROCKS IN AKWANGA AND ITS ENVIRONS IN NASARAWA STATE, NORTH

CENTRAL NIGERIA

A REPORT PRESENTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE

COURSE GLG 351 (FIELD MAPPING AND SURVEYING)

BY

BASSEY, DANIEL KUFREREG. NO: 2010/170012

FIELD INSTRUCTORS:

DR. S.C. OBIORA (CO-ORDINATOR)

DR. C. C. UGBOR

MR. I. OKONKWO

MARCH, 2013

TITLE PAGE

A FIELD REPORT ON THE STUDY OF SOME PARTS OF THE BASEMENT COMPLEX

ROCKS IN AKWANGA AND ITS ENVIRONS IN NASARAWA STATE, NORTH

CENTRAL NIGERIA

DEDICATION

This work is dedicated to God Almighty for his grace, my

friends for their support, my lecturers and field supervisors for

their time and effort, and to my family members especially my

parents.

ACKNOWLEDGMENT

First, I remain grateful to Almighty God for his endless

grace and mercy upon my life. I wish to use this avenue to

express my sincere appreciation to my parents Mr. and Mrs. BASSEY

for their moral and financial support in my academics, my course

mates for their support and company during the field exercise,

and to the staff of geology department, UNN and most especially

Dr. Smart C. Obiora whose works I consulted in the process of

writing this report, and also to all our field supervisors. May

God bless and reward you.

Bassey, Daniel

Kufre

ABSTRACT

Akwanga and adjoining areas are underlain by the

migmatities, gneisses, schist, and Older Granites. Imagery

results of the area have been analyzed and interpreted to

determine the lineaments, lineament density, and ground water

potentials across the area. The drainage pattern is structurally

controlled and it influences groundwater and surface water flow

directions in the area. Rose (azimuth-frequency) diagram of the

lineaments delineated on the imagery shows trends in the NE-SW,

NNE-SSW, E-W, NNW-SSE and N-S directions with NE-SW and NNE-SSW

as the major trends.

Lineament density maps show that the lineament density is

high around areas such as Monkwar, Zamatak, Ninkade, Mugu,

Gwanzu, Wamba, Nakere, and Garko.

Areas having high lineament density represent areas with

relatively high groundwater potentials. Field observations agreed

with results from the imagery analysis.

Field work is a major aspect of geological investigations.

The ‘‘hard rock’’ terrain which is the Basement Complex is a

fundamental unit in the geology of Nigeria.The Basement Complex

which is Precambrian in age are the most resistant crystalline

rock upon which the sedimentary rocks are unconformably laid.

They constitute the oldest rocks in the Nigeria geological

record. Akwanga area and its environs is underlain by the

basement complex of Nigeria. This particular area of the Basement

Complex was studied with particular interest in the lithologic

units, structures, composition and mineralization. The area

consists of high hills of out crops of the basement rocks. Fresh

samples of these rocks were collected and studied megascopically

in hand specimen and microscopically in thin section.

LIST OF PLATES

PLATE PAGE

Plate 1: Outcrop of migmatitic banded gneiss along the Nassarawa Eggon

– Mada road…………

Plate 2: Outcrop of banded gneiss showing network of cross-cutting dykes………………………

Plate 3: Outcrop of banded gneiss at a river section showing faulted dyke…………………………

Plate 4: Outcrop of migmatitic banded gneiss showing quartzo-feldsparthic injection…………….

Plate 5: Outcrop of migmatitic banded gneiss showing xenolith on sill intrusion………………….

Plate 6: Outcrop of pegmatitic dyke showing characteristic large grains…………………………..

Plate 7: Outcrop of schist along Keffi road showing folding on

schistose foliation…………………

Plate 8: Outcrop of schist showing boidinage structure on quartzo-

feldspartic injection……………

Plate 9: Outcrop of schist showing pygmatic fold on quartzo-

feldspartic injection………………….

Plate 10: Outcrop of banded gneiss showing a fracture plane with

faulted injection………………..

LIST OF FIGURES

PAGE

Figure 1. Location and accessibility map of the study

area……………………………………….

Figure 2. Drainage map of the study area…………………………………………………………

Figure 3. Geological map of Nigeria, showing the 3 major rock

units…………………………….

in the Basement Complex, as well as the Jurassic granite

Which intruded the Basement (Oyawoye, 1972)

Figure 4. Outcrop map of the study area…………………………………………………………..

TABLE OF CONTENTS

Title page………………………………………………………………………………………

Dedication …………………………………………………………………………………….

Acknowledgement ……………………………………………………………………………

Preface ……………………………………………………………………………………….

List of plates ………………………………………………………………………………….

List of figures …………………………………………………………………………………

CHAPTER ONE

1.0 INTRODUCTION

1.1 Scope and objectives ……………………………………………………………………..

1.2 Location and Accessibility ………………………………………………………………..

1.3 Physiography ……………………………………………………………………………...

1.3.1 Vegetation and Soil ……………………………………………………………………..

1.3.2 Topography and Drainage ……………………………………………………………...

1.3.3 Climate …………………………………………………………………………………

1.4 Procedure / Methodology ………………………………………………………………..

1.4.1 Preliminary Studies …………………………………………………………………….

1.4.2 Detailed Study ………………………………………………………………………….

1.5 Literature Review ………………………………………………………………………..

CHAPTER TWO

2.0 REGIONAL GEOLOGY

2.1 Regional Tectonism …………………………………………………………………………

2.2 Tectonic history ……………………………………………………………………………..

2.3 Regional geology of study area ……………………………………………………………..

2.4 Regional Stratigraphic setting ………………………………………………………………

2.5 The Basement Rocks ………………………………………………………………………..

2.5.1 Gneisses and Migmatites/Migmatitic gneisses

……………………………………………

2.5.2 Schist Belt (Meta-sediment) ……………………………………………………………...

2.5.3 Pan-African (Older) Granite ………………………………………………………………

2.5.4 Intrusion and Extrusion Associated with the Basement

rocks ……………………………

2.6 Grade of metamorphism and protolith ……………………………………………………..

CHAPTER THREE

3.0 FIELD DESCRIPTION

3.1 Gneiss ………………………………………………………………………………………..

3.2 Schist ………………………………………………………………………………………...

3.3 Granite ……………………………………………………………………………………….

CHAPTER FOUR

4.0 PETROGRAPHY

4.1 Megascopic Analysis ………………………………………………………………………

4.2 Microscopic Analysis ……………………………………………………………………..

4.3 Modal Analysis ……………………………………………………………………………

CHAPTER FIVE

5.0 STRUCTURAL GEOLOGY

5.1 Discussion and Interpretation …………………………………………………………….

5.2 Summary and Conclusion ………………………………………………………………...

CHAPTER ONE

1.0 INTRODUCTION

Nassarawa State is a state in North-Central Nigeria, with

Lafia as its capital. Nassarawa State is bounded in the North by

Kaduna State, in the West by Abuja the Federal Capital Territory,

in the South by Kogi and Benue States and in the East by Taraba

and Plateau States. There are thirteen Local Government Areas in

Nassarawa State which are Akwanga , Awe, Doma, Karu, Keana,

Keffi, Wamba, Nassarawa, Nassarawa-Eggon, Lafia, Obi, Toto.

The field work study was in Akwanga and its environs. It

extends to towns like keffi, Nasarawa Egon, and Lafia. Akwanga

possess features and structures that are useful to this field

work report on the bases that it is characterized by Basement

Complex of Nigeria. The field work in Akwanga took place between

8th and 11th of March, 2013. The following discuss outlines the

various features and structures in Akwanga and its environ.

1.1 SCOPE AND OBJECTIVES

The objectives of this study is vast, one of which is to

expose students to fieldwork in hard rock terrain and also to

observe and identify mappable exposed rock untis.

It also enables students to describe the various geological units

in details of the different lithology which entails measurement

of attitude of some planar surfaces, trends of foliation, and

trend of intrusions such as pegmatites.

It also provides students with a practical knowledge of the

Basement Complex rocks with clear understanding of their geologic

boundaries on geologic maps.

It also enables the student to produce an outcrop map from a base

map of the study area.

1.2 LOCATION AND ACCESSIBILITY

Akwanga and its environs in the North-Central part of

Nigeria is located within latitude 8o55’0”N and 8o23’0”E. This

extends to places such as Nassarawa-Eggon, Akwanga and Keffi. The

accessibility of Akwanga is easy as regards to network of roads

and urbanization in the area. The major routes to the area are

through Nsukka –Otukpo-Makurdi – Lafia – Akwanga Expressway and

the Abuja –Keffi – Akwanga Expressway. The outcrops are located

along road cuts like Nassarawa-Eggon road, Akwanga-Keffi road,

and Akwanga-Lafia road. Some are river sections while others are

quarry sites. The accessibility map of the area is as shown

below.

Fig 1: Location and accessibility map of the study area.

1.3 PHYSIOGRAPHY

1.3.1 SOIL AND VEGETATION

Akwanga area is composed of undulating lowlands and a

network of hills developed on granites, migmatites, pegmatites

and gneisses and also characteristic high lands.

The major soil units of Nassarawa State belong to the

category of oxisols or tropical ferruginous soils. The soils are

derived mainly from the Basement Complex and sedimentary rock.

Akwanga is characterized by tall grasses and trees. The

trees form a canopy over sparse populated grasses. Dense forests

are few and far apart. Such forests are found in lowland areas

particularly where population pressure is less on land. Trees of

economic value include locust bean, shea butter, mangoes citrus

and banana.

1.3.2 TOPOGRAPHY AND DRAINAGE

The landscape of Akwanga is composed of undulating lowlands

and a network of hills developed on granites, migmatites,

pegmatites and gneisses.

The state is drained by numerous fast flowing streams/rivers

that take their source from the Jos Plateau and flow into the

River Benue which also marks the state’s Southern boundary. Some

major rivers are the Mada, Dep, Ayini, and Farin- Ruwa rivers.

Imagery results of the area have been analyzed and

interpreted to determine the lineaments, lineament density, and

ground water potentials across the area. The drainage pattern is

structurally controlled and it influences groundwater and surface

water flow directions in the area. Lineament density maps show

that the lineament density is high around areas such as Monkwar,

Zamatak, Ninkade, Mugu, Gwanzu, Wamba, Nakere, and Garko; and

areas having high lineament density represent areas with

relatively high groundwater potentials.

1.3.3 CLIMATE

Akwanga area is characterized by a tropical sub-humid

climate with two distinct seasons (wet and dry seasons). The wet

Fig 2: Drainage map of the studyarea.

seasons lasts from about the beginning of May and ends in

October. The dry season is experienced between November and

April. Annual rainfall figures range from 1100mm to about 2000mm.

1.4 PROCEDURE/METHODOLOGY

1.4.1 PRELIMINARY

Prior to departure, a 3 day preparatory lecture was

organized by our field instructor Dr. Smart Obiorah. At the

lecture he gave us maps, materials and also a lecture on what we

were expected to do and come with. We were given a road map of

the Nsukka- Akwanga and a base map of the study area to guide in

locating our positions.

1.4.2 DETAILED STUDY

The detailed study commenced on Saturday 9th march 2013. The

methods employed during the field mapping are of great

importance. For accurate interpretation, each outcrop was

properly examined and different measurement taken.

The tools and equipment taken to the field include:

1) Brunton and silver compasses for the measurement of

attitude of foliation planes.

2) Geologic hammer for breaking out a fresh surface of the

rocks and cutting out collectable samples.

3) GPS-Global Positioning system gives information on the co-

ordinates at a particular location.

4) Ruler, measuring tape, used for the measurement of

dimensions and thicknesses.

5) Base map aids in the location of stations and outcrops.

6) Field note and pen for writing down readings and

descriptions of outcrops observed in the field.

7) Sample bags for the collection of the samples.

During the field work, every outcrop encountered was

described with guidelines from our field instructors. These

guidelines on how to describe an outcrop include:

Numbering the outcrop showing clearly, day and date.

Describing the location of the outcrop.

Taking the GPS reading.

Plotting the position on the base map.

Describing the kinds of rock exposed.

Describing salient features on the outcrop.

Measuring the attitude of planar structures.

Plotting the outcrop and the attitude where applicable

on the base map.

Collecting fresh samples of exposed rocks.

These samples were then taken to the lab where hand

specimens and thin sections were

made and analyzed appropriately.

The above mentioned materials with observations of the geologic units helped establish the different lithological units that makeup the Basement Complex of Nigeria.

1.5 LITERATURE REVIEW OF PREVIOUS WORKS

Various researches and investigations have been made

on the Nigeria Basement Complex by lecturers of geosciences,

petrologists and International agencies.

Among the various works that have been done in Akwanga and

its environs is the Field Description of Hard Rocks by Dr. Smart

C.Obiora who stated that the Basement rocks is Precambrian in

age and are mostly related to the Pan- African (900-450ma)

thermo-tectonic event. He explained that the Basement Complex is

exposed in five major location namely: North-Central zone, South-

Western zone, South-Eastern zone (extension of Bamenda Massif),

Northeastern zone (the Hawal Massif) and South southeastern zone

(the Oban Massif). He further stated that there are three major

rock units that make up the Nigeria Precambrian Basement Complex.

These units are Gneisses and Migmatites/Migmatitic gneisses,

Schist belts, and the Pan-African (older) granites.

Umeji (1987) classified the basement complex of Nigeria into

two parts viz the Western part is predominated by hornblende

composition, the Eastern part which comprises of pinkish granitic

gneiss and Migmatites.

Obiora (2005) referred to the Migmatitic gneisses as the

Basement “sensu stricto” meaning the Migmatitic gneisses are the

Basement Complex strictly speaking.

Obiora (2006), Obiora and Ugwora (2011) assigned a pellitic,

with some arkosic and grey wacke protolith to the gneiss and

migmatitic gneiss complex from geochemical analysis on the

mineral assemblages.

Jacobson and Webb (1946) carried out a geologicsurvey of the area and also sampled parts of Akwanga. They

noticed that pegmatites occurred as veins striking in NW-SE

direction. McCury (1971) studied the evolution of the

Nigeria basement and the imprints left by the four orogenic

cycles of the Liberian, the Eburnean, the Kibarian and the Pan –

African.

Ajibade (1979) classified the basement rocks into two

provinces, the eastern province, which comprises migmatitic

gneisses, and pan-African granites that intruded then, and

the western provinces which are made up of north-south

trending low grade schist belt.

CHAPTER TWO

REGIONAL GEOLOGY

2.1 REGIONAL TECTONISM

The Basement complex is defined as the igneous, metamorphic,

granitized or highly deformed rock underlying sedimentary rocks

(Lapidus, 1987). It can also be regarded as the more resistant,

generally crystalline rock beneath layers or irregular deposits

of younger, relatively undeformed late Proterozoic early

Paleozoic sedimentary sequence.

The basement complex underlies the entire area and includes

all rock older than the late Proterozoic metasediments. It

includes metasediments of high metamorphic grade such as

paragneiss, calcerous and basic schist, marble and quartzite, as

well as orthogneiss. The whole basement complex has been through

at least two tectono-metamorphic cycles, and consequent

metamorphism, migmatisation and granitisation has extensively

modified the original rocks so that they generally occur as

relict rafts and xenoliths in migmatites and granites. More

extensive areas of gneiss and metasediments occur in northern

Nigeria. The matasediments in the basement complex are believed

to be relicts of an old supracrustal cover.

2.2 TECTONIC HISTORY

The understanding of the complex deformation and metamorphic

history has been quite difficult because the older deformation

has been largely overprinted by the Pan-African Orogeny of

870myrs – 540myrs. The basement rocks in West Africa as a whole

are products of four major tectonic events. They are:

Liberian Orogeny (3.0byrs – 2.4byrs)

Eburnean Orogeny (2.4byrs – 1.6byrs)

Kibarian Orogeny (1.6byrs – 900myrs)

Pan-African Orogeny (900myrs – 450myrs)

The basement complex `sensu stricto` is very old and is

believed to be metamorphosed sedimentary unit deposited around

2.5byrs ago or earlier. Metasediments of this age are known in

other parts of West Africa as ``Birrimian”.

Evidence of the Eburnean Orogeny come from a Granite-Gneiss in

Ibadan dated by Grant (1970) at 2,205±70 myrs. This event may be

related to E-W trending structures in the Basement Complex.

The presence of the Kiberian orogeny is more contentious, and

is based on a 1120 myr age given to the Ile-Ife Granite Gneiss by

Grant et al (1972). These ages have been reviewed up to

1825±27byrs by Rahaman et al (1983). Hence, there is little or no

evidnce of the Kiberian event, especially in the schist.

The sediments of the schist belt are believed to have been

deposited around 1.1byrs – 800myrs ago in a closing oceanic basin

leading up to a continental collision in the Pan-African.

The Pan-African event was as a result of a collision of a

number of continental masses to form the ancient Gondwana Lands.

This event was very extensive and the effect can be found in most

part of Africa, Arabia, India, Australia, South America, and

parts of Europe. The collision in Africa was as a result of the

convergence of the West and Central African cratons after

subduction along the N-S zone.

The intensity of this event in Nigeria overprinted other

deformation events and “reset” most of the ages of the rocks, as

well as leading to the emplacement of the older granite, and

migmatization.

The Precambrian geology of West African is divided into

“Mobile belts” and “cratons” with the Nigerian basement a part of

the pan-African mobile belts. Precambrian relates to pan African

(900-450ma). The Kibarian event was restricted to Africa about

(1600-900ma). The last major event was the Pan-African orogeny

which occurred about 900-450 million years ago affected almost

the whole continent except the cratons.

The evolution of the Nigeria Basement Complex follows a

series of tectonic events that occured in Africa. These tectonic

events included

The Watian event

The Leonean event.

The Migmatitic gneisses are the basement ‘sensu stricto’

they exhibit a great variation in composition, the variation

being a result of the protolith from which they were derived and

the grade (Pressure- Temperature, P- T) conditions under which

they were formed. The Migmatitic gniesses were formed by the

effect of heat from the series of orogenic cycles mentioned above

on the country rock. The effects of crustal deformation,

magmatism and metamorphism of the country rock gave rise to the

Migmatitic gneisses.

Most parts of the Basement Complex are underlain by belts of

roughly N-S trending metamorphosed ancient Precambrian

sedimentary and volcanic rocks known as the younger

Metasediments. The younger metasediments contains most of the

gold deposits in the NW around Maru and Arika and at Zuru near

Kaduna and also at Ilesha in SW Nigeria.

The Older granites are widespread throughout the basement

complex and occur as large circular masses within the Schist’s

and the Older Migmatitic gneiss complexes. The Older granites

vary extremely in composition.

The younger granites complexes in Nigeria are found mainly

on the Jos plateau forming a distinctive group of intrusive and

volcanic rocks that are bounded by ring dykes.

About two phases of tight isoclinals folding have been

recognized in both the younger meta-sediments and the basement

gneisses. These deformational episodes were accompanied by

progressive regional metamorphism and separated by a phase of

static metamorphic pressure-temperature condition, which remained

essentially constant throughout both deformations. Before the

static metamorphism took place, the first episode folded the

east-west foliation along the north-south axes.

There was migmatization and granitization of the basement

gneisses which resulted in the intrusion of a syn-tectonic

granite suite. During the late Proterozoic there was initial

continental rifting crustal displacement at the West African

cratons. The closing stages of the orogeny were marked by

cooling, uplift and fracturing and by the intrusion of the high

level volcanic rocks.

2.3 REGIONAL GEOLOGY OF STUDY AREA

Akwanga, Northcentral Nigeria is underlain by pelitic

to semipelitic Schists which totally grade up to the Silimanite

zone of regional metamorphism. Other rock types include

Migmatitic gneisses, small metaquartzitic bodies, Augen-gneiss,

Granite gneiss, Granite pegmatites and dolerites.

The dominant trends of linear and planar structures are

largely N-S. These cross-cut earlier structures. Complex

deformation culminating in superimposed folding suggests that the

deformation is polyphase and most likely polycyclic. Brittle

deformation in the area is manifest by cataclasis in the Sabon-

Gida augen-gneiss and by the numerous near vertical joints in

virtually all lithological units.

2.4 REGIONAL STRATIGRAPHIC SETTING

Akwanga, Nigeria is underlain by basement rocks which are

bounded by sediments of the Sokoto basin in the North eastern

Nigeria. The Basement Complex in Nigeria is made up of igneous

and metamorphic rocks. It consists of hard rocks which are the

foundations on which the sedimentary rocks are laid; and thus

constitute the oldest rocks in the Nigerian geological record.

The metamorphic rocks have been intruded by the igneous older

granite series.

2.5 THE BASEMENT ROCKS

The Basement Complex is exposed in five major locations in

Nigeria namely:

Northcenrtal zone

Southwestern zone

Southeastern zone (extension of Bamenda Massif)

Northeastern zone (The Hawal Massif)

South southeastern zone (The Oban Massif)

The three major rock units that make up the Nigerian

Precambrian Basement Complex are as follows:

Gneisses and Migmatites/Migmatitic gneisses

Schist belts

Pan-African (Older) granite

Fig 3: Geological map of Nigeria, showing the 3 major rock units

in the Basement Complex, as well as the Jurassic granite which

intruded the Basement (Oyawoye, 1972)

2.5.1 GNEISSES AND MIGMATITES/MIGMATITIC GNEISSES

These are the basement “sensu stricto”. They constitute the

oldest rocks in the Basement Complex, and consist mainly of

Migmatitic gneisses which are usually banded, Augen gneisses, and

Pophyroblastic gneisses. They exhibit a great variation in

composition; the variation being a result of the protolith from

which they were derived and the grade (pressure-temperature, P-T)

conditions under which they were formed. The protoliths could be

pelitic, psammitic or igneous, where the pellitic types are

characterized by the presence of pellitic minerals such as

garnet, cordierite, sillimanite, kyanite, and staurolite.

Gneisses: These are generally medium to coarse-grained, felsic

rocks which show alternating layers or bands of light and dark

colored minerals, described as gneissose foliation. The foliation

may be weak to well-pronounced. They are said to be banded when

the foliations are well pronounced (mm scale). The mineral

components in the light layers are commonly orthoclase and/or

microcline, plagioclase (andesine/oligoclase) and quartz while

biotite, with or without hornblende dominate the dark layers.

Accessory amounts of zircon, apatite, sphene and epidote may be

present. Some deformed varieties of the gneisses which consist of

eye-shaped quartzo-feldspathic components are described as augen

gneisses.

Most of the gneisses are meta-sedimentary rocks as shown by

their mineral constituents of the aluminosilicates (kyanite,

andalusite and sillimanite), cordierite, staurolite and garnets,

as well as their geochemistry. They had attained the amphibolite

grade of metamorphism.

Migmatites/migmatitic gneisses: Migmatites are mixtures of

gneisses/schistose rocks with more or less foliated granites or

granitoids. They occur as concordant and discordant pods, lenses

and layers which are often contorted. These are frequently cut by

granitic components.

The name, “migmatite” is actually a field name for rock body

in which two to three rock components are recognizable. The

components include:

i) Light-coloured, quartzo-foldspathic portion: the leucosome

or the neosome.

ii) Dark-colured, mafic portion: the melanosome or the

paleosome, which is the unaltered, resistant country rock.

iii) Average-colured, mesocratic portion: the mesosome.

The melanosome and the mesosome are comparable ordinary

metamorphic rocks while the leucosome compares with igneous

rocks.

In a nutshell, the migmatites are composed of metamorphic

host materials (commonly schists and gneisses) which is streaked

and veined with granitic materials (quartzo-feldspathic veins).

When the metamorphic material that is streaked and veined is

gneiss, the term, “migmatitic gneiss” is used to describe the

rock. The quartzo-feldspathic materials are commonly products of

anatexis.

The possession of gradational contacts with high grade

metamorphic rocks by the migmatites suggests that they are

transformed or granitized rocks

2.5.2 SCHIST BELTS

The schist belts are mapped as predominantly meta-sediments

with subordinate mafic-ultramafic units. The schistose components

of the migmatitic terrain were designated, the “Older meta-

sediments”, while distinct N-S trending belts of schist which are

clearly younger than the gneisses and migmatites were mapped as

the “Younger meta-sediments”. Outcrops of these Younger meta-

sediments are pronounced, and so appear to be restricted to the

western half of Nigeria. The meta-sediments consist of low to

medium grade mica-schists, quartz schists, quarzites and

concordant amphibolites. The rock name, “amphibolite” is a

hornblende-rich rock. It is often a meta-igneous (basic), but

sometimes meta-sedimentary rock (shale).

In places, especially in the Southwestern Basement Complex,

the schist belts are associated with marbles, dolomites and calc-

silicate rocks (e.g. Calc – schists) which are the products of

the metamorphism of limestones, marls and calcareous sediments.

Banded Iron Formation (BIF) is also rarely associated with the

schist belts such as the Muro schist belt. They also outcrop in

the South Eastern part of Nigeria where they appear to have been

intruded by concordant quartzo-feldsparthic injections

(especially in the Ogoja province).

2.5.3 PAN-AFRICAN (OLDER) GRANITES

These Pan-African granites intruded the basement “sensu

stricto” and the schist belts. The rocks of this unit include

porphyritic/porphyroblastic muscovite-granites, biotite-granites,

hornblende-biotite-granites, non-prophyritic/non-porphyroblastic

granites, aplites, granodiorites, diorites, quartz-diorites,

hypersthene-granites (charnockites), and quartz-hypersthene-

diorites. They are often weakly foliated, i.e., they show weak

alignment of the constituent platy minerals. Such types are

sometimes described as foliated granites and gneissic granites.

The rocks of the Older granites are medium to coarse-grained,

containing both biotite and muscovite, plagioclase (albite to

oligoclase) and microcline. Petrographcally and geochemically,

the Older granites are calc-alkaline; thus they representing

products of subduction/collision or mountain building events,

characteristic of convergent/compressional tectonism. They are

therefore orogenic granite.

2.5.4 INTRUSIONS AND EXTRUSIONS ASSOCIATED WITH THE BASEMENT

ROCKS

Certain rocks occur as intrusions into the Basement Complex

rocks. These include:

1) Quartzo-feldspathic veins

2) Pegmatites,

3) Basic intrusives,

4) Rhyolite dykes,

5) Alkaline granite complexes and

6) Tertiary volcanoes.

Quartzo-Feldspathic Veins

These are veins (1cm to 20cm across) composed essentially of

quartz and feldspars. They cross – cut, as well as follow the

trends of foliation in the basement rock. They are common in all

the basement rocks units, especially the gneisses and

migmatities, and the schist belts. They are generally younger

than the Basement Complex within which they are emplaced along

weak planes.

Pegmatites

These are extremely coarse-grained granitic rocks consisting

essentially of quartz, feldspars (microcline, Na-plagioclase),

muscovite and biotite. They occur as dykes which cross-cut the

basement rocks. Their thicknesses can be up to 3m. In some cases,

the thicknesses range between 500 and 1000 m.

Some of the pegmatities contain numerous economic minerals,

principally cassiterite and columbite-tantalite.

Basic Intrusives

These are commonly basaltic sills/dykes and dolerite dykes.

They are often microporphyritic to porphyritic and dark coloured.

Occasionally, they occur as spheriodally weathered boulders. They

are composed of plagioclase (labradorite), augite, and olivine.

Rhyolite Dykes

These are acid hypabyssal intrusives that cut across the

major trends of foliation in the Basement Complex rocks. The

rocks are characteristically, fine grained and porphrytic. The

phenocrysts are quartz and feldspars which constitute the ground

mass. The rocks are generally leucocratic (pink coloured).

Alkaline Granite Complexes

These Jurassic rocks otherwise known, as Younger Granites of

Nigeria are exposed in the eastern parts of the north central

Basement Complex, mainly in the Jos Plateau. They are emplaced in

small individual or composite complexes and in essentially NE-SW

direction.

Tertiary Volcanoes

Tertiary volcanoes of mainly basalt compositions extruded

unto the Basement Complex rocks. They are found mainly in the

North-central basement in the Jos Plateau, the Hawal massif

around the Biu Plateau and parts of the southeastern Basement

Complex.

2.6 GRADE OF METAMORPHISM AND PROTOLITH

“Grade” as a term refers to the temperature attained during

metamorphism as indicated by the mineral assemblages. A rock

containing high temperature assemblages is designated “high-

grade”, and a rock with low-temperature assemblages is designated

“low-grade”. A medium grade rock has an assemblage intermediate

between low-grade and high-grade.

Low temperature metamorphism generally produces fine-grained

rocks, while prolonged metamorphism tends to result in coarse-

grained textures. Very coarse-grained rocks such as marbles and

calc-silicates are generally formed under the influence of active

pore fluids such as CO2. Some high temperature minerals include

garnet, sillimanite, pigeonite, hypersthene, omphacite, larnite,

spurrite and mullite. Low-temperature minerals include chlorite,

albite, epidote, zeolites, and actinolite.

In the migmatitic gneiss complex, the grade of metamorphism

attained is generally middle to upper amphibolite facies, and

rarely granulite facies. In the schist belt, the grade of

metamorphism is upper green schist to upper amphibolite facies.

Obiora (2006), Obiora and Ugwora (2011) assigned a pellitic,

with some arkosic and grey wacke protolith to the gneiss and

migmatitic gneiss complex from geochemical analysis on the

mineral assemblages, where the pellitic types are characterized

by the presence of pellitic minerals such as garnet, cordierite,

sillimanite, kyanite, and staurolite The schist are unmistakably

of metasedimentary origin

CHAPTER THREE

FIELD DESCRIPTION OF LITHOLOGIC UNIT AND THEIR FIELD OCCURRENCES,

AND SALIENT STRUCTURAL FEATURES

Various outcrops were visited during the field work in

Akwanga, and different lithologic units were encountered. These

lithologic units are:

Gneisses

Schists

Granites

Fig 4: Outcrop map of the study area

3.1 GNEISSES: The gneisses were encountered at locations 1, 2, 3,

7 and 8. There were some salient features associated with the

gneisses encountered. These are gneissose foliation, pinch and

swell structures, fractures, quartzo-feldsparthic intrusions,

dyke intrusions, presence of xenolith in intrusions, and

ptygmatic folding on the quartzo-feldsparthic injections. The

ptygmatic folding is almost perpendicular to the direction of

boudinage. The foliations trend essentially NE-SW. There were

networks of cross cutting, and in some cases, faulted dykes in

some locations. The gneisses had some other characteristics from

being fairly porphyroblastic, weakly foliated, to being

melanocratic. The porphyroblastic gneisses consist of porphrys of

euhedral to subhedral feldspars, with medium to coarse grained

ground mass which consist of quartz, biotite, and muscovite. The

minerals associated with the gneisses are quartz, characterized

by its conchoidal fracture; feldspar, which shows characteristic

two directional cleavage; biotite and muscovite, characterized by

their flaky nature.

The gneisses encountered are biotite-muscovite banded

gneiss, muscovite-biotite banded gneiss, micaceous banded gneiss,

porphyroblastic gneiss, migmatitic banded gneiss, and mela-

gneiss. The attitudes of foliations were measured and recorded as

follows:

SN STRIKE DIP DIRECTION DIP AMOUNT

1 440NNE - 2240SSW 1340ESE 620

2 400NNE - 2200SSW 1300ESE 650

Plate 1: Outcrop of migmatitic banded gneiss along the Nassarawa

Eggon – Mada road

Also, associated with the gneisses were xenolith in

intrusions, and pegmatitic dykes trending essentially NW – SE,

and basaltic sill trending essentially NE – SW. The basaltic sill

has almost the same orientation as the host rock. The pegmatite

is extremely coarse grained, and the minerals associated with the

pegmatite are quartz, characterized by presence of conchoidal

fracture; feldspars, showing characteristic two directional

cleavages, biotite, lepidolite and muscovite, characterized by

their flaky nature, and tourmaline characterized by presence of

striations. There were also fine grained, and in most cases,

highly fractured rhyolitic dykes associated with the gneisses.

Plate 2: Outcrop of banded gneiss at a river section along the

Nassarawa Eggon – Mada road showing network of cross-cutting

dykes.

Plate 3: Outcrop of banded gneiss at a river section along Nassarawa Eggon

road showing faulted dyke.

The table below shows the trend and thicknesses of some dykes

measured and recorded;

SN

THICHNESS

(CM)

TREND

(degrees)

1 22

– 35

298 WNW –

118 ESE

2 28 –

35

320 WNW –

140 ESE

3 9 –

16

282 WNW –

102 ESE

4 20 –

23

290 WNW –

110 ESE

5 20 –

25

331 WNW –

159 ESE

6 11 –

40

299 WNW –

119 ESE

7 17 –

25

300 WNW –

120 ESE

8 GREATER THAN 500 20 NNE –

200 SSW

The dykes are much fractured due to their fine grains.

Plate 4: Outcrop of migmatitic banded gneiss along Nassarawa

Eggon – Mada road showing quartzo-feldsparthic injection

Plate 5: Outcrop of migmatitic banded gneiss showing xenolith on

sill intrusion.

Plate 6: Outcrop of pegmatitic dyke along Nassarawa Eggon -

Akwanga road showing characteristic large grains.

3.2 SCHIST: The schist were encountered at locations 10, 12, and

13. There were some salient features associated with the schist

encountered. These are quartzo-feldspartic injections showing

ptygmatic folding and boidinages, and presence of schistose

foliation. The minerals present in the schist are mostly

micaceous minerals such as biotite and muscovite showing

characteristic flaky nature, staurolite, characterized by its

elongated dark nature, and quartz which shows characteristic

conchoidal fracture. The schists encountered are mica schist with

injections of quartzo-feldsparthic materials, and garnet-mica

schist. The attitude of planar surfaces on the schist at each

location were measured and recorded as follows:


1 328̊ NNW - 142̊ SSE 232º

WSW

28º

2 332º NNW – 152º SSE 242º

WSW

52º

3 328º NNW – 142º SSE 232º

WSW

28º

4 324º NNW – 144º SSE 234º

WSW

30º

5 317º NNW – 137º SSE 227º

WSW

26º


1 276º WNW – 96º ESE 6º 22º

NNE

2 290º WNW – 190º ESE 2Oº

NNE

34º

3 274º WNW – 94º ESE 4º

NNE

19º

4 304º WNW – 124º ESE 210º

SSW

28º

5 306º WNW – 126º ESE 206º

SSW

22º


1 10º NNE – 190º SSW 100º

ESE

48º

2 5º NNE – 175º SSW 95º

ESE

44º

3 18º NNE – 175º SSW 108º

ESE

62º

4 21º NNE – 201º SSW 111º

ESE

53º

5 23º NNE – 203º SSW 113º 14º

ESE

The above dip directions and dip amount values indicate a

phenomenon of fold reversal.

Plate 7: Outcrop of schist along Keffi road showing folding on

schistose foliation

Plate 8: Outcrop of schist showing boidinage structure on

quartzo-feldspartic injection

Plate 9: Outcrop of schist along Keffi road showing pygmatic fold

on quartzo-feldspartic injection

3.3 GRANITES: the granite was encountered at location 5 where it

occurs as an intrusion into the basement complex. There is

presence of chilled margin at the periphery of the granitic

intrusion, and baking of the host rock. The granitic intrusion is

coarse grained and leucocratic (pinkish). The grains are

equigranular. The minerals present are quartz, showing

characteristic conchoidal fracture; feldspar (pink), showing

characteristic two directional cleavage, and biotite,

characterized by its flaky nature. At the chilled margins, the

grains are finer due to rapid loss of heat to the host rock, and

there is presence of fractures due to the fineness of the grains.

The granite encountered is Biotite-Granite.

CHAPTER FOUR

PETROGRAPHIC STUDIES

Fresh samples of exposed rock units in the field were taken

and studied megascopically in hand specimen, and microscopically

in thin sections under the petrographic microscope. Some however,

such as the pegmatites, could only be studied in the field at

their places of occurrence due to characteristic large grains.

The rock samples that were collected from Akwanga were sent to

Kogi State University to be cut into thin sections. These thin

sections were studied effectively using a standard petrographical

microscope.

The rock samples collected were studied effectively,these

samples include:

Migmatitic banded gneiss

Micaceous banded gneisss

Porphyroblastic gneiss

Quartz-mica schist

Garnet-mica schist

Biotite Granite

Pegmatite

Basalt

4.1 MEGASCOPIC DESCRIPTION

Migmatitic Banded Gneiss

The rock is mesocratic and coarse grained. The grains of the

rock are subhedral to euhedral. The rock shows gneissose

foliation which consist alternation of light and dark minerals.

The mineral components in the light layers are quartz,

characterized by its conchoidal fracture, plagioclase feldspar,

characterized by a characteristic two-directional cleavage,

while biotite, characterized by its flaky nature, and hornblende

dominate the dark layers. The rock shows the presence of a light

(leucosome) part, and dark (paleosome) part.

Micaceous banded gneiss

The rock is mesocratic and coarse grained. The grains of the

rock are subhedral to euhedral. The rock shows gneissose

foliation which consist alternation of light and dark minerals.

The mineral components in the light layers are quartz, ,

characterized by its conchoidal fracture, plagioclase feldspar,

characterized by a characteristic two-directional cleavage,

muscovite showing a characteristic flaky nature, while biotite,

characterized by its dark, flaky nature and hornblende dominate

the dark layers.

Porphyroblastic Gneiss

The rock is mesocratic and porphyroblastic with subhedral to

euhedral ground mass and euhedral porphyroblasts. The ground mass

is medium to coarse grained and consist of quartz, biotite,

muscovite, and feldspars. The porphyroblasts are euhedral to

subhedral plagioclase and

microcline.

Quartz-Mica Schist

The rock is fine to medium grained and leucocratic. The rock

constitutes mica minerals as its main mineral constituent and are

characterized by their flaky nature, and quartz. The rock shows

schistose foliation constituted by a preferred orientation or

allignment of the clay minerals.

Garnet-mica schist

The rock is fine to medium grained and leucocratic. The rock is

fairly porphyroblastic with a fine to medium grained ground mass,

and the grains of the rock are anhedral to subhedral. The rock is

hypocrystalline. The rock shows schistose foliation in which the

clay minerals are alligned in a preferred orientation. The

porphyroblasts constitute staurolite characterized by its dark

elongate nature, and garnet characterized by its dark

rhombohedral nature. The clay minerals, and quartz make up the

ground mass.

Biotite granite

The rock is leucocratic(pinkish). The rock is coarse grained. The

grains are equigranular and subhedral to euhedral and are well

oriented. The minerals contained in the rock are quartz,

feldspar(pink), garnet, and muscovite. The presence of coarse

grains indicate that it is an intrusive body. In the field, there

was the presence of chilled margin at the periphery due to rapid

heat loss to the host rock and subsequent fineness of grains.

The Pegmatites

These are leucocratic granitic rocks with extremely large grains.

In the field, they occur as quartzo-feldsparthic veins with the

grains of the minerals ranging in diameter between 2cm to 10cm.

They consist essentially of quartz, feldspar, micas with

accessory amounts of tourmaline, lepedolite. Most of those

accessory minerals found within the pegmatite, such as tantalite

and tourmaline, are of economic value. The pegmatites include

both simple and complex pegmatites. The simple pegmatites consist

of quartz and feldspar while the complex pegmatites are made up

of quartz and feldspar in addition to muscovite, lepidolite,

apatite and some other accessory minerals.

Basalt

The rock is melanocratic and fine grained. Grains are extremely

fine and anhedral, and as such cannot be distinguished or studied

with the naked eye.

4.2 MICROSCOPIC (THIN SECTION) ANALYSIS

MIGMATITIC BANDED GNEISS

The rock is coarse grained and holocrystalline. The grains

of the rock are subhedral to euhedral, and are randomly oriented.

Mineral I

Dark colored mineral shows brown color. The mineral is strongly

pleochroic changing from light brown to dark brown. The mineral

shows an elongate prismatic shape. The mineral shows one perfect

directional cleavage and high relief. The mineral is anisotropic

showing interference color of second order red. The mineral shows

parallel extinction. With the above descriptions the mineral is

biotite.

Mineral II

Mineral II is a light colored mineral. The mineral has low

relief, that is, the outlines of the mineral are not visible in

plane polar. The mineral is anisotropic showing interference

color of first order grey. The mineral shows albite polysynthetic

twinning. The mineral shows maximum extinction angle of 28º

corresponding to An37 With the above description the mineral is

andesine.

Mineral III

The mineral is light coloured with rounded to irregular shape,

and low relief, that is, the outlines of the mineral are not

visible in plane polar. The mineral shows concoidal fractures.

The mineral is anisotropic showing interference color of first

order grey and shows undulose extinction. With the above

description the mineral is quartz.

Mineral IV



shows an elongate prismatic shape.The mineral shows one

directional cleavage. The mineral shows high relief. The mineral

is anisotropic showing interference color of second order red.the

mineral shows oblique extinction with extinction angle of 19º.

With the above descriptions the mineral is longitudinal section

of amphibole(hornblende).

Mineral V

The mineral is dark coloured and shows a somewhat rounded

outline. The mineral is isotropic, remaining dark in plane and

cross polars. The mineral shows high relief. With the above

description, the mineral is garnet.

Mineral VI

Mineral VI is a light colored mineral. The mineral has low

relief i.e. the outlines of the mineral are not visible in plane

polar. The mineral is anisotropic showing interference color of

first order grey. The mineral shows Carlsbad twinning. With the

above description the mineral is orthoclase.

MICACEOUS BANDED GNEISS

The rock is coarse grained and holocrystalline. The grains

of the rock are subhedral to euhedral. The light colored minerals

are segregated from the dark colored minerals into layers, and

each layer follows a preffered direction.

Mineral I

Mineral I is a light colored mineral. The mineral has low relief

ie the outlines are not visible in plane polar. The mineral shows

one directional basal cleavage. The mineral is anisotropic

showing interference colors of third order green. The mineral

shows parallel extinction. With the above description the mineral

is muscovite.

Mineral II







biotite.

Mineral III

The mineral is light coloured with low relief, that is, the

outlines of the mineral are not visible in plane polar. The

mineral shows concoidal fractures. The mineral is anisotropic

showing interference color of first order grey and shows undulose

extinction. With the above description the mineral is quartz.

Mineral IV

Mineral IV is a light colored mineral. The mineral has low






andesine.

Mineral V

Mineral V is a light colored mineral. The mineral has low relief

i.e the outlines of the mineral are not visible. The mineral is

anisotropic showing interference color of first order grey. The

mineral shows crosshatched twinning. With the above description

the mineral is microcline.

Mineral VI





PORPHYROBLASTIC GNEISS

The rock is hypocrystalline and medium grained. It contains both

felsic and mafic minerals. The rock grains are subhedral,

inequigranular, and fairly porphyroblastic. The ground mass is

medium to coarse grained and consist of quartz, biotite,

muscovite, and feldspars. The porphyroblasts are euhedral

plagioclase and microcline.

Mineral I

Mineral I is a light colored mineral. The mineral has low relief





is muscovite. It constitutes the groundmass

Mineral II





extinction. With the above description the mineral is quartz.It

constitutes the groundmass

Mineral III

The mineral is dark coloured (brown). The mineral is strongly






biotite. It constitutes the groundmass

Mineral IV







oligoclase. It constitutes the porphyroblasts.

Mineral V

The mineral is a light colored mineral. The mineral has low

relief i.e the outlines of the mineral are not visible. The

mineral is anisotropic showing interference color of first order

grey. The mineral shows crosshatched twinning. With the above

description the mineral is microcline. It constitutes also the

porphyroblasts.

GARNET-MICA SCHIST

The rock is fine to medium grained and fairly porphryoblastic.

The phenocrysts are subhedral to euhedral. The groundmass is

anhedral to subhedral. The groundmass consists predominantly of

platy minerals that are aligned in a preferred direction.

Mineral I

Mineral I is a pale-yellow colored mineral. The mineral is

pleochroic changing from pale yellow to deep yellow. The mineral

is elongate prismatic in shape. The mineral has high relief. The

mineral is anisotropic showing interference color of first order

yellow. The mineral shows some degree of penetration twinning and


is staurolite.

Mineral II

Mineral II is a light colored mineral. The mineral has low relief





is muscovite.

Mineral III

Dark, brown coloured mineral. The mineral is strongly






biotite.

Mineral IV



shows an elongate prismatic shape.The mineral shows one

directional cleavage. The mineral shows high relief. The mineral

is anisotropic showing interference color of second order red.the

mineral shows oblique extinction with extinction angle of 180.

With the above descriptions the mineral is longitudinal section

of amphibole(hornblende).

Mineral V






Mineral VI





GRANITE

The rock is leucocratic and coarse grained. The grains are well

formed, equigranular, and subhedral to euhedral. The rock is

holocryatalline.

Mineral I

The mineral is dark coloured and brown with visible outline. The

mineral shows strong pleochroism from light brown to dark brown.

The mineral shows an elongate prismatic shape.The mineral shows

one directional cleavage. The mineral shows high relief. The

mineral is anisotropic showing interference color of second order

red.the mineral shows oblique extinction with extinction angle of

180. With the above descriptions the mineral is longitudinal

section of amphibole(hornblende).

Mineral II

Dark colored mineral shows brown color with clearly visible

outlines. The mineral is strongly pleochroic changing from light

brown to dark brown. The mineral shows an elongate prismatic

shape. The mineral shows one perfect directional cleavage and

high relief. The mineral is anisotropic showing interference

color of second order red. The mineral shows parallel extinction.

With the above descriptions the mineral is biotite.

Mineral III






Mineral IV







oligoclase.

Mineral V

Mineral V is a light colored mineral. The mineral has low relief

i.e the outlines of the mineral are not visible. The mineral is

anisotropic showing interference color of first order grey. The

mineral shows crosshatched twinning. With the above description

the mineral is microcline.

Mineral VI

Mineral VI is a light colored mineral. The mineral has low

relief i.e. the outlines of the mineral are not visible in plane

polar. The mineral is anisotropic showing interference color of

first order grey. The mineral shows Carlsbad twinning. With the

above description the mineral is orthoclase.

Mineral VII

Mineral II is a light colored mineral. The mineral has low relief





is muscovite.

4.3 MODAL ANALYSIS

BIOTITE

GRANITE

PORPHYROBLASTIC

GNEISS

MIGMATITIC

BANDED GNEISS

MICACEOUS

BANDED GNEISS

GARNET-MICA

SCHIST

QUARTZ 40 35 35 30 10

MICROCLINE 5 10 10 15 -

ORTHOCLASE 10 - 5 - -

ANDESINE - - 10 10 -

BIOTITE 25 20 15 10 15

MUSCOVITE 5 20 10 30 20

GARNET - - 5 5 20

HORNBLENDE 3 - 10 - 10

STAUROITE - - - - 15

OLIGOCLASE 12 15 - - -

CHAPTER FIVE

STRUCTURAL GEOLOGY

The Basement Complex is characterized by salient

structures, some of which were encountered in the field mapping

exercise. The structures include:

1. Foliation

2. Fractures

3. Folds

4. Veins/Veinlets

5. Pinch and swell structures (boudinages)

Foliation

Foliation is basically defined as the preferred linear

orientation of the mineral grains. The foliations encountered in

the field are the gneissose and the schistose foliations. The

gneissose foliation is characterized with the conspicuous

alternation of light and dark bands of minerals and is found in

gneisses whereas the schistose foliation characrerized by a

preffered orientation of the clay minerals and is found in the

schist. Attitude of these foliation are usually taken with a

compass. Foliation trends in the basement are used to make

different orogenic events.

Fractures

Fractures are to some extent the most prominent feature

observed and they indicates zones of weakness in rocks. The

fractures observed in the study area are of various orientations.

The presence of joints is arranged in a system order. The faults

are mostly normal fault. The fractures are filled with quartz-

feldspathic materials and basic intrusions in the migmatitic

rocks. Structures such as the basic intrusions and the quartzo-

feldspathic veins are faulted.

Plate 10: Outcrop of banded gneiss showing a fracture plane with

faulted injection

Folds

Folds are of various kinds in the field. They are evidence

of compressive tectonic forces. The migmatitic gnisses. Schist

pinch and swell structures and quartzo-feldspathic veins have

been strongly deformed into folds.

Their varities include Ptygmatic folds which are folds with

irregular wavelengths and are commonly found in the quartzo –

feldspathic injections.

Veins and veinlets

They are joint which have been filled with materials mostly

minerals, quartzo feldspathic veins that are less than 5mm are

referred to as veinlets but veins that contain extremely large

crystals are said to be pegmatitic veins. They can be lying

discordantly or concordantly to the host rock. Most of the vein

have been before med to pinch and swell structures and folds.

Pinch and swell structures (boudinages)

They are also called boudins and they occur as a result of

extension in a plane of band whereby the more competent (in this

case quartzo-feldsparthic) layer will resist compression or

extension like the in competent layer and might break into parts

going rise to pinch and swell structure. They characterized the

migmatitic gneisses and the schist.

5.1 DISCUSSION AND INTERPRETATION

The discussion and interpretation of this work would be

based on the analysis of those features and structures found in

the field and the application of structural geology.

The general trend of NE-SW orientation of the foliation

planes was as a result of the tectonic force probably acting in

the NW-SE directions while that inclined in the NW-SE direction

is probably as a result of stress acting in the NE-SW direction.

The occurrence of ptygmatic folds. Folding of gneissose

foliation and abundant quartzo feldspathic injections are all

evidence of plastic deformation and mobility together with the

tectonic fault analysis. Suggest that most part of the

metamorphic complex have reached the highest stage of

metamorphism. The presence of bands in the gneisses implies its

metamorphic origin with the coarse grains of gneisses and schist

indicating a regional high grade metamorphism. Also the mineral

assemblages of the migmatitic gneisses and schist in the study

area showed that they all originated from the same parent rock.

The presence of the pinch and swell structure suggests that

the basement complex have been subjected to high stress.

5.2 SUMMARY AND CONCLUSION

These basement complex of Nigeria have three lithologic

groups which range from Liberian to Pan-African thermo-tectonic

events.

Faults, folds boudinage structures, veins and quartzo

feldspathic materials are all indications that the gneisses have

undergone partial melting while the younger granites have

undergone magmatic processes.

The North central basement rocks in Nigeria are resistant to

the effect of weathering and erosion and this gives Akwanga and

its environs a higher elevation.

The pegmatites of the North central Nigeria are one of the

world’s most mineralized pegmatites with numerous economic

minerals like tantalite, staurolite, and columbite.

The lithologic variations of the gneiss include medium to

coarse grained bandad gneiss, augen gneiss, porphyroblastic

gneiss, and migmatitic gneiss. The lithologic variations of the

schist include coarse to fine grained clastics, pellitic schists,

phylites, banded iron formation, carbonates (marbles/dolomite

marbles), and the mafic metavolcanoes (amphibolites).

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KUFRE AKWANGA FIELD REPORT- Supervisors DR. S.C. OBIORA, DR. C.C. UGBOR

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