final editted dissertation dukuray
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GEOLOGICAL MAPPING OF
PART OF SHEET 103 JORU
KENEMA DISTRICT, EASTERN
SIERRA LEONE
BY
MOHAMED ABDULAI DUKURAY
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GEOLOGICAL MAPPING
OF UPPER SHEET 103 JORU
KENEMA DISTRICT
EASTERN SIERRA LEONE
BY
MOHAMED ABDULAI DUKUAY
REG. NO: 28535
A DISSERTATION PRESENTED TO THE GEOLOGY DEPARTMENT
FOURAH BAY COLLEGE, UNIVERSITY OF SIERRA LEONE IN PARTIAL
FULFILMENT FOR THE DEGREE OF BACHELOR OF SCIENCE
WITH HONORS IN GEOLOGY
FEBRUARY 2016
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DEDICATON
Dedicated to my Late Father, Alhaji Abdulai Dukuray, whose advice has been with me
throughout my studies.
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ACKNOWLEGEMENT
Thanks and appreciations to the Lord Almighty for making it possible for me to go through this
milestone of academic struggle. To my family, thank you for encouraging me in all my pursuits
and inspiring me to follow my dreams. I am especially grateful to my parents, who supported
me emotionally and financially. I know that you believe me and want the best for me. Thank
you for teaching me that my job in life is to learn, to be happy and to know and understand
myself. Only after that could I know and understand others. As such, special thanks goes to my
late Dad, Alhaji Abdulai Dukuray,Mum, Hawa Sheriff, sister Massa Dukuray and Big brother
Mohamed Kaikueh Dukuray.
Thanks to all the Lecturers, I have worked with over the last four years. In each of their own
unique ways, they have shown me what it means to be dedicated to my work. Each of you has
given your time, energy and expertise and I am grateful for it. Dr. Mustapha O. Thomas Ag Head
of Department (HOD), Dr. Sahr Fillie (former HOD), Dr. Kelvin Anderson, Mrs. Salmatta Sandi,
Mr. Buba Turay, Mr. Yussif A. Lahai, Mr. Molai Kanu, Mr. Tamba Kumba, Mr. Sahr Kellie and Mr.
Santigie K. Sesay. To the Laboratory Technicians and our former departmental Secretary, Aunty
Kadie, thank you all.
Special appreciation goes to my able supervisor and Lecturer Dr. Kelvin F.E. Anderson, for his
relentless efforts and guide in helping me complete this dissertation. Thank you so much and I
pray that the lord continue to guide and protect your family. To my friends scattered around
the Globe, thank you for your thoughts, well-wishes, prayers, phone calls and texts. Thanks go
to my course mate, Mohamed A. Thoronka, for his selflessness and for sharing his ideas with
me.
Finally my conscience will judge me if I fail to mention Mr. and Mrs. Vandi Kallon for the
support rendered to me throughout my staying in the field. Allah will surely reward your good
gesture; you treated me as your son .Thank you and may the lord continue to guide and protect
us all, Amin!
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ABSTRACT
The project entails geological mapping of an area in Kenema District, Sierra Leone which is part
of sheet 103. According to previous work on the geology of Sierra Leone, the project area
outcrops in the Basement complex, which is also referred to as granite greenstone terrain. It
can be therefore being divided into three categories.
Basement granites
Greenstone supracrustals
The Intrusive/syn kinematic rocks
The Basement complex is the largest of the units and houses older formations. The rocks of the
Kenema assemblage occupy the greater part of Eastern Sierra Leone. It is a metamorphic
plutonic assemblage and includes a geosynclinal sequence known as the Kambui Group, which
was deposited upon an ancient basement and geosynclinals sediments were invaded and
modified by granite rocks associated subsequent orogenic movements. These have obliterated
the structure of the ancient basement so that the original crystalline rocks are no longer
recognizable. The greater part of eastern Sierra Leone is composed of complex intimately
associated granite, migmatite and gneisses.
The basement granites are normally the host rock, which houses all other rock units. They
include granites, migmatites and gneisses. The greenstone supracrustals consists of mica schist
and amphibolites. The intrusive granites are referred to the synkinematic granites. Most of the
intrusive follow shear zones, fault planes and foliation planes. They normally occur as dolerite
dykes. The general foliation trend in this region is Northeast direction and majority of the rocks
are trending in the same direction of the foliation. Structures were minors, but few
microstructures like schistossity, foliation, gneissosity and macrostructures like fault, fold, vein
and fractures were observed. The metamorphic grade is up to the granulite facies.
The project area, Greenstone terrain host the general gold mineralization of the country and
possible minerals are; Diamond, Chromites and Construction materials. Therefore this area is of
high economic importance to the country.
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TABLE OF CONTENTS
DEDICATON ................................................................................................................................................... ii
ACKNOWLEGEMENT .................................................................................................................................... iii
ABSTRACT ..................................................................................................................................................... iv
TABLE OF CONTENTS ..................................................................................................................................... v
LIST OF FIGURES .......................................................................................................................................... vii
LIST OF PLATES ........................................................................................................................................... viii
LIST OF TABLES ........................................................................................................................................... viii
CHAPTER ONE ............................................................................................................................................... 1
INTRODUCTION ............................................................................................................................................. 1
1.1 INTRODUCTION ................................................................................................................................... 1
1.2 AIMS AND OBJECTIVES ........................................................................................................................ 1
1.3 LIMITATIONS ....................................................................................................................................... 2
1.4 RISKS .................................................................................................................................................... 3
1.5 METHODOLOGY .................................................................................................................................. 3
1.6 LOCATION AND ACCESSIBILITY ............................................................................................................ 4
1.7 SETTLEMENT, OCCUPATION, COMMUNICATION, EDUCATION AND HEALTH .................................... 5
1.7.1 Settlement.................................................................................................................................... 5
1.7.2 Occupation ................................................................................................................................... 6
1.7.3 Communication ............................................................................................................................ 7
1.7.4 Education ..................................................................................................................................... 7
1.7.5 Health ........................................................................................................................................... 8
1.8 PREVIOUS WORK ................................................................................................................................. 8
1.9 CONTENT ORGANIZATION .................................................................................................................. 9
CHAPTER TWO ............................................................................................................................................ 11
PHYSIOGRAPHY OF THE AREA ..................................................................................................................... 11
2.1 CLIMATE AND VEGETATION .............................................................................................................. 11
2.2 SOIL ................................................................................................................................................... 12
2.3 DRAINAGE ......................................................................................................................................... 13
2.4 TOOGRAPHY ...................................................................................................................................... 13
CHAPTER THREE .......................................................................................................................................... 14
SUMMARY OF THE GEOLOGY OF SIERRA LEONE ........................................................................................ 14
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3.1 THE BASEMENT COMPLEX ................................................................................................................ 15
3.1.1 The Loko Group .......................................................................................................................... 15
3.1.2 The Kambui Supergroup ............................................................................................................ 16
3.2 THE KASILA GROUP ........................................................................................................................... 16
3.2.1 The Tapr Formation ................................................................................................................... 17
3.2.2 The Magbele Formation ............................................................................................................. 17
3.3 THE MARAMPA GROUP .................................................................................................................... 18
3.4 THE ROKEL RIVER GROUP ................................................................................................................. 19
3.4.1 Tabae Formation ........................................................................................................................ 20
3.4.2 Makani Formation ...................................................................................................................... 21
3.4.3 Teye Formation .......................................................................................................................... 21
3.4.4 The Mabole and Taia Formation ................................................................................................ 21
3.4.5 Kasewe Hills Formation .............................................................................................................. 21
3.5 THE SAIONYA SCARP GROUP (SSG) ................................................................................................... 21
3.6 BULLOM GROUP................................................................................................................................ 22
3.7 THE FREETOWN IGNEOUS COMPLEX ................................................................................................ 22
CHAPTER FOUR ........................................................................................................................................... 26
GENERAL GEOLOGY OF THE PROJECT AREA ............................................................................................... 26
4.1 DESCRIPTION OF THE GEOLOGY OF THE PROJECT AREA .................................................................. 26
4.2.2 The Greenstone Supracrustal .................................................................................................... 41
4.2.3 Late Kinematic/Intrusive Granites ............................................................................................. 43
CHAPTER FIVE ............................................................................................................................................. 47
STRUCTURES, DEFORMATION, AND METAMORPHISM .............................................................................. 47
5.1 STRUCTURES ..................................................................................................................................... 47
5.1.1 Micro Structures ........................................................................................................................ 48
5.1.2 Macro Structures ....................................................................................................................... 49
5.2 DEFORMATION .................................................................................................................................. 54
5.2.1 Effects of Deformation in the Project Area ................................................................................ 55
5.3 METAMORPHISM .............................................................................................................................. 56
5.3.1 Effects of Metamorphism on the Project Area .......................................................................... 57
CHAPTER SIX ................................................................................................................................................ 59
THE ECONOMIC AND HYDROGEOLOGIC POTENTIAL OF THE AREA ............................................................ 59
6.1 THE ECONOMIC GEOLOGY OF THE AREA .......................................................................................... 59
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6.1.1 Mineral Deposits ........................................................................................................................ 59
6.1.2 Construction Material ................................................................................................................ 62
6.2 HYDROGEOLOGIC POTENTIAL OF THE AREA .................................................................................... 63
6.2.1 Access to the Groundwater ....................................................................................................... 64
6.2.2 Impact of the Rocks to Ground Water Quality Assessment ...................................................... 65
6.2.3 Geologic Activity of Groundwater.............................................................................................. 65
CHAPTER SEVEN .......................................................................................................................................... 66
CONCLUSION AND RECOMMENDATIONS ................................................................................................... 66
7.1 CONCLUSION ..................................................................................................................................... 66
7.2 RECOMMENDATIONS........................................................................................................................ 67
BIBLIOGRAPHY ............................................................................................................................................ 69
LIST OF FIGURES
FIGURE 1.1 Author taking the dip of a bed in the field at the Moa River (O252347/0853498 Elevation-
122m) ............................................................................................................................................................ 4
FIGURE 2.1 Vegetation at the Fefewai Hill (0271558 /0846577 elevation -211m) .................................... 12
FIGURE 3.1 The Geologic Map of Sierra Leone ........................................................................................... 24
FIGURE 4.1 The geology of the project Area, Sheet 103 Joru .................................................................... 26
FIGURE 4.2 Microcline Granite at Kebewana village .................................................................................. 29
FIGURE 4.3 Granite gneiss .......................................................................................................................... 29
FIGURE 4.4 Biotite granite showing exfoliation .......................................................................................... 33
FIGURE 4.5 Showing Swarm of dolerites at an outcrop in Mani Village (0254155 / 0845677) .................. 44
FIGURE 5.1 A Fracture at Fefewai Hill (0271558 / 0846577) ...................................................................... 50
FIGURE 5.2 A Vein at an outcrop close to Gama Village (0256223 / 0855890) .......................................... 51
FIGURE 5.3 A Normal fault plane at an outcrop around Diame village (0266032 / 0853310) ................... 52
FIGURE 5.4 A fold observed at Goma Village (0256651 / 0848362)........................................................... 53
FIGURE 6.1 A local Diamond pit at koma village and the Insitu materials (O253065 / 0845558, Elevation
134m) .......................................................................................................................................................... 61
FIGURE 6.2 A Reservoir at Tikonka Gaura Chiefdom (0263839 / 085O130 Elevation-142m) .................... 64
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LIST OF PLATES
PLATE 4.1 Cross-Polar Biotite Granite ........................................................................................................ 32
PLATE 4.2 Plane polar Biotite granite ......................................................................................................... 32
PLATE 4.3 Cross- polar granite schist .......................................................................................................... 34
PLATE 4.4 One-polar granite schist ............................................................................................................. 34
PLATE 4.5 Cross polar microcline granite ................................................................................................... 36
PLATE 4.6 One polar microcline granite ..................................................................................................... 36
PLATE 4.7 Cross-polar granite gneiss .......................................................................................................... 38
PLATE 4.8 one-polar granite gneiss ............................................................................................................ 38
PLATE 4.9 Cross polar migmatite ................................................................................................................ 40
PLATE 4.10 One polar migmatite ................................................................................................................ 40
PLATE 4.11 1 cross polar amphibolite ........................................................................................................ 42
PLATE 4.12 1 one polar amphibolite........................................................................................................... 43
PLATE 4.13 Cross polar amphibolite ........................................................................................................... 45
PLATE 4.14 1 one polar dolerite ................................................................................................................. 45
LIST OF TABLES
TABLE 3.1 Provisional stratigraphic table ................................................................................................... 25
TABLE 4.1 Modal Percentage Table of the Minerals in Biotite granite ...................................................... 31
TABLE 4.2 Modal Percentage of the minerals in granite schist .................................................................. 33
TABLE 4.3 Modal percentage of the minerals in microcline granite .......................................................... 35
TABLE 4.4 Modal Percentages of the minerals in granite gneiss................................................................ 37
TABLE 4.5 Modal Percentage of the minerals in migmatite ....................................................................... 40
TABLE 4.6 Modal Percentage of the minerals in Amphibolite.................................................................... 42
TABLE 4.7 Modal Percentage of the minerals in dolerite ........................................................................... 44
TABLE 5.1 A summary of the different metamorphic conditions from which the metamorphic rocks in
the area were formed. ................................................................................................................................ 57
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CHAPTER ONE
INTRODUCTION
1.1 INTRODUCTION
Geological mapping is the process of selecting an area of interest and identifying all the
geological features such rock units, faults, fold, etc. with the purpose of preparing a detailed
report which includes maps unit that can be identifiable by the presence or absence of some
characteristics. The mapper then marks which of the map unit is found at each place where the
rocks are exposed. Other information such as the orientation of the area of contact between
different rocks may also be recorded. Where obvious, contacts are drawn as solid lines; where
only inferred as dashed lines (if one find a gneiss at point A and migmatite at point B a short
distance away, one can infer a contact between A and B even if the spot is covered by soil).
The project area entails geological mapping of an area in Kenema District, Sierra Leone. This is
part of Sheet 103. The study area covered an area of 81km2, which consist of twelve grids at the
upper part of sheet 103 and it fall within the following coordinates X=857 & Y=252,
X=857&Y=259, X=845 & Y=252 and X=845& Y=279. The mapping exercise was divided into two
phase. The First phase lasted for a month (from May to June) and it was purely a
reconnaissance Survey. During this period information about the area were gathered from
maps and reports from geological survey of Sierra Leone.
The last and final phase compliment the first phase and it was the mapping of the entire sheet
and lasted for three months (July to September 2015).This phase was able to correct most of
the features such as villages and forests that were on the maps and reports made in 1958 and
1961 respectively. The final phase which involve in the microscopic analysis of all rock samples
was able to unravel the deformation, metamorphism and Evolutional history all the samples
collected in the project area.
1.2 AIMS AND OBJECTIVES
To mark the locations of rocks exposure encountered in the field on the field map.
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To identify the different type of rocks encountered based on their mineralogy
To describe and measure certain parameter e.g. strike, dip, etc. of the outcrops and
study their geologic structures (Folds, veins and faults).
To describe the age relationships of the different geologic units and geologic events that
affected the area.
To produce infer boundaries at the contacts of different rock units.
Help to produce a comprehensive report in the dissertation. This report will include:
Petrological and petrographical analysis of rocks within the project area.
Structures including both micro and macro textures.
Deformation, Metamorphism and evolution of the area.
To give an economic and hydrogeology account on the mapped area.
1.3 LIMITATIONS
There were many constrains in carrying out this field mapping. Some of which are highlighted
below.
There was not enough literature about this area, because it has taken a long time field
mapping has not being done there.
Accessibility to the outcrops was a major problem, and even though some accessible
ones were located in the farms with certain geological features, most have been missing
as a result of human activities. Mostly the rocks were weathered; therefore getting
fresh sample was very difficult.
Using this topo-sheet caused us a lot of problems because it was prepared in the year
1962 and as a result some of the features such as rivers and villages on map were not
found in the field. In fact some of villages on the map were no longer in existence
Example Koribundu (GPS X=0260417/ Y=0856738 Elevation-145m).
Another limitation was poor GPS reading mostly in areas with very dense vegetation
cover and forested terrain. Acquiring satellites in these areas was difficult.
Cultural belief and tradition meant restrictions to certain bushes
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Language barrier was another problem for my colleague but fortunately I speak mende
so therefore I was the one talking to the locals throughout our research.
Financial constrains was a factor because of high cost of living. Most of the local people
asked for compensation before taken us to the outcrops.
1.4 RISKS
Some of the risks faced during the mapping exercise are:
Crossing of large rivers e.g. Moa River without life jacket or properly made canoes.
Traversing through thick forest and bushy footpaths, which can also be habitat for wild
animals.
Using motorcycles which were not road worthy and are usually overloaded, increasing
the tendency of road accident.
1.5 METHODOLOGY
The procedure or method employ during this exercise was been divided into two;
DESK STUDY: This lasted for almost a month. Information and literature was obtained
from already prepared sources and were used to draw logical interpretations for the
field work. This information helps us to know the nature of the terrain and the Geology
of the area. They were obtained from different places such as:
Geology Department, Fourah Bay College, University of Sierra Leone.
Geological Surveys, New England Ville, Freetown.
National Mineral Agency (NMA), Wilkinson road, Freetown.
Consultation and interview of indigenes in the area.
Websites.
FIELD WORK: The main equipment used in the field are; Compass, Global Positioning
System (GPS),geological hammer, Hand lens, field notebook, tape rule ,pencils, ruler,
pens, sample bags, digital camera, topographic map and field kits.
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Field notebook: Have a hard cover and strongly sewn hinges. All observations
were recorded in the field notebook.
Hand lens: a magnifier and aided in the identification of minerals.
Geological Hammer: weigh about 200g made with wooden handle. It is use to
chip fresh samples, in order to make thin section for later analysis.
Global positioning system: was use to mark the position of outcrops.
Topographic Map: Use to mark the location of out crops. Its works in line with
the GPS Coordinates.
Tape rule: use to measure the length and breadth of interesting features such as
the displacement of fault plane, veins and folds.
Lead pencil: used for rough plotting on the map and sketching features in the
field book.
FIGURE 1.1 Author taking the dip of a bed in the field at the Moa River (O252347/0853498 Elevation-122m)
1.6 LOCATION AND ACCESSIBILITY
The project area comprised basically of 12 Grids, at the upper end of sheet 103,Joru.It cover
four chiefdoms, which are ;Dama, Gaura, Koya and Tunkia all in Kenema District, Eastern
province, Sierra Leone. This area is two hundred ant ten miles from the capital city, Freetown.
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The area is located along motorable highway to our neighboring country, Liberia. It is found at
the South-East part of Sierra Leone. This area belongs to the interior plateau and Hill region,
which coincides to form the Kenema Assemblage, with an elevation between 100-450m above
Sea level.
Joru town is the reference point for the project area, which is the chiefdom headquarter town
of Gaura Chiefdom and its name is given to the Sheet (Joru Sheet 103). Joru is approximately
twenty miles away from the provincial headquarter town, Kenema city. The Major towns on
this sheet fall within Gaura Chiefdom, and the other villages are found in the other three
chiefdoms (Dama, Koya, and Tunkia).The towns are Joru, Peri, and Kpuwabu all in Gaura
Chiefdom respectively. Small villages are Nwalargo, Mamboma, are in Koya chiefdom and
Fayima and Mani are found in Tunkia Chiefdom.
During our field mapping, Joru town was our base center for our logistics. We decided to move
from Joru and begin our mapping from Nwalargo (koya chiefdom), where we crossed the Moa
River and we later returned to Baraka (Dama chiefdom). Most of the villages and towns are
connected by roads which are either motorable or have become so dilapidated, that the only
means of transportation was by Motorcycle (Okada), bicycle or on foot. It must be emphasized
that road to Kenema from Freetown is tarred and from Kenema to Liberia is not tarred. .
Accessibility to Okada was very difficult and as such we normally walk for the whole day thus
making it difficult. In regions where rivers were found like in the Mabiye River, they usually
have locally made bridges and thereby making crossing risky.
1.7 SETTLEMENT, OCCUPATION, COMMUNICATION, EDUCATION AND HEALTH
1.7.1 Settlement
The project area is located in four chiefdoms i.e. Dama, Koya, Gaura and Tunkia. There are over
fifty villages in this area and thirty of these villages are found in Gaura chiefdom, two in Koya,
two in Tunkia chiefdom and the ten in Dama chiefdom. This studied area is one of the mostly
sparsely populated part of Sierra Leone with density of about 50 people perkm2 (2004
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population and Housing census).Some villages in this area may have a population about 10-15
people living in a village and it became nearly empty during the Farming period. Villages such as
Goma and Koribundu have integrated into other villages.
Most of the houses are mostly made of mud and thatch roof with few houses built with cement
and zinc roof which are found only in the chiefdom headquarter towns we came across. These
towns serve as an administrative center from which the supply of food and other items can be
obtained. The housing system reflects the general configuration of houses in rural communities
of Sierra Leone, except in major towns.
The road networks are poor even though most of the villages are interconnected and a single
route can lead to several villages. The roads are not tarred and during the rainy seasons they
are impassable. Most of the roads are lateritic and can be transverse only with bikes. This have
serious effect during the rainy season as the roads become very bad, the access to food in the
administrative towns become very difficult leading to hunger in the affected villages.
The common social activities of the people are secret societies and traditional dances, even
though they are done occasionally. The people in this area are mostly Muslims with few to non-
Christian. I only saw a single opened place, which they referred to as a church. Even though
there may be Christians, they perform their various worships at homes. However, some people
are still holding firmly to their traditional religion, for instance in a town called Peri, some
people worship the Hill called Fefewai which they strongly believed will give them everything
they want.
1.7.2 Occupation
Majority of the people, about 90% are involved in farming (subsistence) and only few influential
people are doing commercial farming. Some have plantations such as cocoa, coffee and palm
trees. The soil condition is good and favor large crop yield as was evidence by the number of
plantations and garden seen during the exercise. The king crop is rice (our staple food), and
they also grow pepper, cassava, groundnuts, beans, corn and much more. The few farmers that
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are engaged in mechanized farming use equipment such as tractors, wheel barrows, while
those involved in subsistence farming use hoes, pickaxe, cutlass and shovel because they
cannot afford expensive tools. Since their farm products are mostly used in their homes.
Few people are petty traders, selling foodstuff, clothes and household items. Many of the able
young men have abandon farming for more lucrative jobs as okada Ridding whilst others
provide labor for digging pits in artisanal mining in koma village had also in road construction.
Inhabitant close to river areas, such Moa river is engage in fishing as their source of livelihood.
1.7.3 Communication
The generally spoken language in this area is Mende, even though few speak Krio, English,
Fullah and Temne. In some villages, it is very difficult to see someone who speaks Krio or
English.
Despite the much advancement and positive strides mobile network companies have made,
this area is still finding it difficult to relate messages from one place to other. I made an
interviewed with one of the chiefdom heads and he confirmed to me mobile communication is
a problem and when they are ready to send messages is through a messenger or by letters.
1.7.4 Education
The Educational standard in this area is below matching standard. The whole area cannot boast
of a senior secondary school but there is at least one junior secondary school in each of the four
chiefdoms. When pupils have acquired their Basic Education Certificate Examination (BECE),
they are transferred to Kenema city to acquire their senior secondary school Education. The
performances in both the National Primary School Examination (NPSE) and Basic Education
Certificate Examination (BECE) are below average and this is because of untrained and
unqualified teachers in this schools. This has caused a massive number of dropouts in this area.
The major issue affecting girl child Education in the area is teenage pregnancy. I was able to
interview one of the teachers and he told me that teenage pregnancy is occurring at an
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alarming rate. He also assured me that the schools, the police, and the Ministry of Education
are working in collaboration to combat this act by punishing anyone found victim.
1.7.5 Health
The health system in the country is not favorable at this specific time due to the recent Ebola
outbreak in the Mano river sub regions. Ebola is a virus which is transmitted from an affected
person to another through body fluid. Kenema District was one of the worst affected regions.
According to World Health Organization (WHO) a region can be an Ebola free, when it has gone
42 days without a new confirmed case(s).This region at this time has gone more than 100days
without any new case and in fact it was one of the reasons this area was selected for Geological
Field Mapping.
The entire four chiefdoms (Dama, Tunkia,Koya and Gaura) cannot boast of a sophisticated
Hospital but rather they have local health centers in the major towns. This Health Centre lack
the necessary Equipment characterized by other Good Hospitals. Because of this, the major
cases have to be transferred to Kenema town or the capital city, Freetown.
One of the chiefdoms i.e. Gaura chiefdom has pipe borne water and in the other three
chiefdoms they have Hand dug wells. Therefore the water facility in this region is favorable.
Malaria is an Eveready adversary all over the country i.e. also a major disease in this area.
Malaria parasite is transfer by the female Anopheles Mosquito; this breed readily in every
stagnant water. In addition, this had been reduced drastically by the supply of treated mosquito
bed net, although many inhabitants in river area are using them as fishing net rather than bed
nets.
1.8 PREVIOUS WORK
Detailed work has not been yet been done on the area before present survey was done. The
Geology of Sierra Leone by D.D. Hawkes, former Head of Department (HOD) at Geology, Fourah
Bay College and Dixey (1925) and the physiography (Dixey, 1922).
9
An Aero geophysical survey about 8,000square miles in the South-Eastern Sierra Leone was
done by the Directorate of overseas Geological survey in 1958, and has helped to outline the
areas covered by alkali complex. Although the complex itself and the radioactive mineralization
connected, which had been discovered just previously by the Division might or might not have
found the Monazite Mineralization at Lalehun and Belebu, but would almost certainly have
missed the Tewo.
Additional traverse were been made where necessary up streams and along paths of payable
minerals or rock seemed possible in an area, J.V Hulta, then the Division mining Geologist, was
called upon for a detailed examination. That meant in practice cutting intermediate traverse
lines, geochemical sampling or rate meter or magnetic surveys. This work was followed where
necessary by trenching and pitting .Additional geological features disclosed by the
supplementary lines were incorporated in 1/30,000 or 1/40,000 scale maps. At Bagla Hill and
the Neighborhood of Bagbe Alkali complex, enough was accumulated to plot rough Geological
maps on the scale 1/20,000.
The Tongo dykes have been bulk sampled and drilled in the past by SLST and NDMC. The
evaluation work was summarized in the study carried out by seltrust Engineers in the 1970`s by
NDMC. The richest grades were encountered in the lando dyke zone. The lando dyke zone may
have grades of 2 to 3 carats/ tone, in the Kimberlite over an aggregate kimberlite width of 0.3m
and total length of 2,600m. The Peyima and Panguma dykes are lower grade of the o.5 to 1
carat/tone in pure kimberlite. Much work has not been done within the project area. The
Stellar Diamond Limited has done their explored some few years. At Tongo, stellar has
completed an independent preliminary Economic Assessment over the 1.45 million carat Dyke
resource. This delivered robust economic which justifies the application for a mining license,
which is still ongoing.
1.9 CONTENT ORGANIZATION
The dissertation is been divided into six chapters.
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Chapter 1 gives brief introduction about the project area, aims & Objectives, limitations, Risks,
Methodology, location& accessibility, settlement, occupation, communication, education
&Health and Previous Work.
Chapter 2 Gives information about the Physiography i.e. Climate& Vegetation, soil, Drainage
and Topography.
Chapter 3, knowledge of the Geology of Sierra Leone and chapter 4, Explained about the
geology of the project area, the petrogenesis of the different rock type is been examined based
on analysis of both hand specimen and thin sections. Information of these rocks, certain
geological condition such as stress and the environment of formation leads to the development
of structures including fold, fault, veins etc are noted in Chapter 5, which further explains the
deformation and metamorphism of the project area.
Chapter 6 described the economic and aquifer potential of the area, this chapter purely
explained the importance of economic minerals and the accessibility to aquifer.
The last and final phase unravels the Evolutional history of the project area and then the
conclusion.
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CHAPTER TWO
PHYSIOGRAPHY OF THE AREA
2.1 CLIMATE AND VEGETATION
The climate of area is tropical to most areas of Sierra Leone (Gwynne-Jones, 978).The climate is
characterized by south-Westerly winds coming to the land off the coast of Guinea. These are
the main-laden winds of the region. The dry harmattan winds which are the N-E trade winds
that are experienced in this part of West Africa stretch from December to February. The climate
in the project area is typically tropical with two seasons. The wet season, lasts from May to
November, and record of about 255mm has been recorded. The dry season lasts from
December to April and rainfall record 30mm is achieved. A diminution in rainfall occurs in
September. This is referred to as the” September Break”. Humidity is high. The mean annual
humidity at 12:00GMT is 60% and lowest monthly mean is 40% this type of climate favors
laterization.
East of Mahoi, the country is covered with primary forest reserve in which there are few
villages and footpaths .They valleys of the Moro–Gbewa and Koye (Faiama), however, are
almost free of primary forest and are farmed on the shifting cultivation system. That is to say,
portions of the bush are cut down on a rotational basis in which they are farmed, allowed to lie
fallow for a few years and revert to bush, burnt and farmed again. Due to this rotation, when
three or four years have elapsed since the taking of air photographs, farm outlines on the
photographs are of little use in establishing positions on the ground. West of the Maho there is
little or no primary forest near Bagbe and this stretches towards the Zimmi-Kenema road for
about two miles.
Geological traverse along straight lines area impossible anywhere in the country mapped unless
the lines are cut,but without much trouble one can walk up most of the larger streams and
meander through parts of the primary forest that are at some distance from the valleys. The
thickest bush is invariably on farms that remained fallow for a few years. The forest glades that
mark the highest doricrusted erosion surface in the Kangari and Nimini Hills are not to be seen
12
in the Gola forests,though some of the granite hill tops South of Lalehun and East of Beobu are
bare except for tussock grass. The Liberian bank of the Moro-Gbewa is farm intensively for
sugar cane. Below is the picture in Fig-2 of a very thick forest in Peri town which is close to the
Gola forest with coordinates X=0270767/Y=0847305, elevation 173 m.
FIGURE 2.1 Vegetation at the Fefewai Hill (0271558 /0846577 elevation -211m)
2.2 SOIL
In most of the area, the dominant soils are of the weathered and leached lateritic type which is
red to yellow brown in color. They contain oxides of iron and aluminum Kaolin clay are
important in some area; when cultivated, they are light, readily workable and free draining,
with productivity that depends large on the nutrients provided by the vegetation previously
cleared and burned. In the coastal plains, lateritic soils that have developed on a sandy deposit
are agriculturally poor but those derived from basic igneous rock fare somewhat better. Swamp
soils occur over large area on the coastal plain where drainage is a problem. In coastal and
estuaries areas where mangrove is the natural vegetation, production soil can be acquired by
clearance but careful water control is sometimes needed to prevent toxicity from fertilizers. At
the foot of the main escarpment on the sula mountain plateau and elsewhere on iron rich
laterite crust forms a surface that is intractable for agricultural production.
13
2.3 DRAINAGE
Drainage refers to the arrangement and the distribution of streams, direction and pattern of
water flow resulting in the removal of excess water from the ground. This is controlled by
several factors including:
Initial slope(gradient)
Climate
Amount of precipitation
Geomorphology
Lithological variation
Surface process
The project area has a relatively good drainage system, with a major river called river moa and
a number of streams and streamlets. These streams empty their load into the moa river, and
most of the streams flow in a meandering pattern. Most of the streams flow-throughout the
year, although the year, although the velocity of their flow depends on the volume of water
they carry which in turn depends on whether it is the rainy(wet) season or dry season. The
streams flow with very high velocity during the rainy season when the water volume is high.
The ancient drainage system is of direct economic importance because part of it may be
connected with the diamantiferous gravel at Waima.
2.4 TOOGRAPHY
This region comprise of both the interior plateau and Hill region that coincides to form Kenema
Assemblage. Erosion is immense and therefore three erosion surface are represented in the
country -.The erosion surface has height of 1,200 to1, 500ft like in fefewa hill and is
represented only by duricrusted relief preserved on the of Gieboy hill in Sierra Leone. The
surface continuous Northwards and may touch the crests of Bomui, Bembeye and Togbin
Ridges, which are on sheet 90.It could be of the same age as duricrusted (supposedly African)
surface capping parts of the Sula mountains and Kangari Hills at height of from 1,700 to 2,000ft
at the Gieboy hill. The terrain is slopping on the both opposing sides of the Moa River and
shows some surface features such as intense weathering and mass movement.
14
CHAPTER THREE
SUMMARY OF THE GEOLOGY OF SIERRA LEONE
Sierra Leone is underlain by rocks of the Precambrian age(Archean and Proterozoic),with a
coastal strip of about 50km in width, comprising of marine and estuarine sediments that are of
tertiary and quaternary to recent age .The Precambrian (mainly Archean) outcrop over 75% of
the country and typically comprise Granite-greenstone terrain. It represents part of ancient
continental nuclei located on the edge of the West Africa craton. Regional reconnaissance
Mapping indicates that the Archean basement are been subdivided into
Infracrustal rocks (gneisses and granitoids)
Supracrustal rocks(containing greenstone belts)
Basic and ultrabasic igneous intrusion
The infracrustals gneisses and granitoids were been formed and reworked during two major
orogenic cycles. These are:
An older Leonean Episode( ≈2950-3200m.a)
Young Liberian Episode(≈2,700 m.a)
The Leonean oregenic episode commenced with intrusion of basic igneous suit (the pre-
Leonean amphibolites) and the formation of a greenstone belt, represented by the Loko Group
which is now deeply eroded. The Liberian oregenic Episodes (pre-Liberian amphibolites) are
considered to be metamorphosed basic igneous intrusion. They are distinguished from the pre-
Leonean amphibolites by the presence of Liberian tectonite fabric only. Leonean fabrics are
absent and the emplacement of the igneous suite is regarded as subsequent to the Leonean
oregenic episode but predating the Liberian deformation. Amphibolites of this age occur within
the Sula Group and on it Western and Northern margins.
Sierra Leone forms part of the West Africa craton. The basement complex consist mainly
archean granite-greenstone terrain bounded in the west by a westwards. Dipping zone of
intense ductile simple shear, deformation zone of very fine grain high grade metamorphic rocks
and this forms the Kasila group and it has been interpreted as suture. Eastwards the granite-
15
greenstone terrain is bounded by low grade metamorphic rocks of the Marampa Group. The
geology of Sierra Leone is divided into;
7. Bullom group
6. Freetown complex (Basic and Alkali intrusion)
5. Saionya scarp Group (SSG)
4. Rokel River Group (RRG)
3. Marampa Group
2. Kasila Group
1. Basement complex (Granite-greenstone terrain)
3.1 THE BASEMENT COMPLEX
This is the largest of the units and it a house other formations. It is also refers to as the Granite-
greenstone terrain. The basement complex composed of three types of granites.
Syn-kinematic granite
Homogeneous Syn-kinematic migmatites
Late sync-kinematic granite
The supracrustal unit within the basement complex includes greenstone belts of two ages. The
older unit, the Loko Group, pre-dates the Leonean oregenic episode; the younger unit, the
Kambui super group post-dates the Leonean episode but was involved in the events of the later
Liberian oregenic episode.
3.1.1 The Loko Group
Dixey (1925) considered these rocks type as components of the “older schists and gneiss”
within the “younger granites”. Amphibolites, quartzites and banded Ironstones together form
the Loko group. The older (Leonean ≈Ca 2900ma) forms the Loko hills and adjacent area is
known as the Loko group. Hence, the age of the Loko group is at 2900m.a.
16
On structural and textural grounds, the group is referred to as a Supracrustal assemblage
deposited prior to the Leonean orogenic episode on a basement floor of migmatites rocks
containing the elements of the pre-Leonean granitization event. The Loko group is very poorly
exposed so that subdivision into formations is not possible.
3.1.2 The Kambui Supergroup
The Kambui Super group is defined to include those greenstone belts whose origin pre-dated
the Liberian orogenic episode and which were laid down on a basement floor of gneisses and
granitoids that have been imprinted with the events of the Leonean episode. The later episode
is been equated with the 2700ma, Liberian age province (Hurley et al, 1971) hence the age of
the Kambui super group is 2700ma.In the Northern part of the country, this group includes the
greenstone belt of the Sula group.
The Sula group is the more dominant of the greenstone belts and forms the Kangari hills, Sula
Mountains, Nimini hills, Gori hills and the Kambui hills. This group is subdivided into:
UPPER TONKOLILI FORMATION-This formation consists of a series of meta-sedimentary
rocks such as quartzite, mica schists, charts and banded iron formation.
LOWER SONFON FORMATION-This formation consist of meta volcanic such as talc
schists, tremolite, schists, amphibolites, ultramafics (chromiferous serpertinite-
sometimes called pillow lava).
3.2 THE KASILA GROUP
This is NW-SE trending between Sierra Leone and Guinea in the North and Liberia in the South,
as shown in the geological map below in Figure3 .The rocks belonging to this group were firmly
recognized as part of gneiss belt compositionally different from the gneiss of the east,
successively referred to as the older schist and gneiss (Dixey, 1925), the Kasila series, (Pollet,
1951) and the Kasila group, (Allen, 1969). The Kasila consists of series of basic granulites,
metasedimentary granulites and migmatites, banded iron formation, and meta-leucogabbroic
17
intrusions, (Williams, 1988). It is a linear belt dominated by high-grade metamorphism
supracrustals rocks of Archean age, (Tysdal and Thorman, (1988).
Outcrops within the Kasila are poorly exposed; as a result, lithological boundaries have been
drawn between major rock types such as the basic granulites and metasedimentary.The other
lithologies such as the banded iron formation occur as lenses rather than continuous layer,
elongated along the NW-SE foliation trend. Keyser and Mansaray (2004) recognized to two
formations within the Kasila group as the source of bauxite, rutile, illmenite, and iron ore. The
two formations are:
Magbele formation
Tapr formation
3.2.1 The Tapr Formation
The Tapr formation occupies the eastern portion of the belt and is dominated by metabasic
rocks with subordinate metasedimentary granulite containing thin layers and lenses of banded
iron formations, quartzite and leuco gabbro. These may be distinguishing from the western
portion containing amphibolites, sedimentary migmatites and gneisses. The basic rocks are
strongly deformed and mylonitised with no traces of pillows or igneous structures. They have
layered and massive leucogabbro andanorthosite occurs as deformed and metamorphosed
sheets, disconnected layers and lenses within these predominantly mafic rocks (Williams,
1988). Relicts of the original igneous layering and mineralogy can be seen in coarse-grained
leuco gabbro rocks, despite being metamorphosed to the Granulite facies.
3.2.2 The Magbele Formation
The western part of the group is composed of gneisss, migmatites and granulites of quartzo-
feldsparthic composition which are interbanded with calc-silicates, banded iron formation and
quartzitic materials. Keyser and Mansaray (2004) recognized this lithology as member of the
Magbele formation. The quarzo-feldsparthic rocks have been interpreted based on their
composition and association as being dominantly of sedimentary origin (Vallance, 1874,
18
Williams, 1975; Macfarlene et al, 1981).However, Williams, (1988) from field evidence
suggested an igneous origin for some of thinner, discordant units of quartzo-feldsparthic
composition.
3.3 THE MARAMPA GROUP
A strip of low grade supracrustal rocks lying west of the main group of supracrustals. This
represents argillaceous and ferriferous metasedimentary sequence. It lies adjacent to and on
the western side of the Rokel River Group. This lithology is divided into two divisions.
A LOWER META VOLCANIC MATOTO FORMATION-This consists of pillow basalts, meta-
andesite, hornblende-epidote-schist and subordinate meta-volcanic. These meta-ultramafic
consist chiefly of serpentinite, talc, chlorite and hornblende. The top of the Matoto
formation is gabbroic in the west and is pillow andesitic in the east.
AN UPPER METASEDIMENTARY ROKTOLON FORMATION - This is subdivided into three
members.
a. THE MABOLE MEMBER- Consist of quartz that is coarse-grained saccoroidal in texture.
b. THE MASIEMRA MEMBER: This consists of quartz-chlorite-serpentinite-albite± epidote
schist in the East. In the West where metamorphic grade is high, the Masiemera member is
represented by quartz-biotite-gneiss and corderite-quartz paragenesis. This member is the
most widely outcropping rock of the Marampa group and is about 200m thick.
c. THE MASSABOIGN MEMBER-this is predominantly hematite-quarz and hematite-serecite-
schist.
The hematite–serecite–schist is soft and flexible. The Massaboign is about 150m thick and
constitute of the iron ore deposits formally mined in the Marampa. A prominent mylonite zone
about 1-6m wide at the contact between the Matoto formation and granite greenstone terrain
has been identified.
19
THE ECONOMIC POTENTIAL
The Marampa comprises mainly iron ore which occurs as schist comprising hematite and/or
magnetite with quartz. About 50% of iron ore was mined between 1970-80`s by DECCO mining
company and has been mined again by London mining, which is presently not in operation
(2015).
3.4 THE ROKEL RIVER GROUP
This occurs adjacent to the Marampa Group. It is a late Precambrian sedimentary and volcanic
assemblage deposited unconformably on the basement complex. It is imprinted with the
Leonean and Rokellide events. The Rokel River extends southwards from Guinea into Sierra
Leone where it occupies a belt of 30km wide trending South-East from 225km onto Southern
Sierra Leone. It consists of calc-alkali rocks and it is proposed to have developed as a result of
plate collision orogeny. It is younger than the Marampa group. The sediments at the base of the
Rokel River Group comprise of conglomerates, feldparthic sandstone and clays which are
interpreted as glacial and fluvo-glacial in origin, recording advances and retreats of the ice
sheet that move over the region from the East. The Rokel River group has been subdivided into
six formations by Allen (1968). Further re-definition of part of the Rokel River group was
proposed by Culver and Williams (1979) and McFarlane et al (1981).
Fossils are lacking in the Rokel River group and hence paleontological dating cannot be used on
the basis of lithologic correlation and limited radiometric data. The Rokel River group is
considered to be late Proterozoic to early Cambrian in age. They were deposited prior to the
pan Africa event and they were folded and slightly metamorphosed by the Rokellide event.
Allen (1968) recognized the following stratigraphy in the Rokel River group.
6. Kasewe hills formation
5. Taia Formation
4. Mabole formation
3. Teye formation
2. Makani formation
20
1. Tabae formation
Culver further subdivided the Tabae formation into three members
–
I. Dodo member
II. Taban member
III. Tibai member
3.4.1 Tabae Formation
It rest unconformably on the granite basement and it extends along the east and south-west
margins of the main Rokel River group outcrop belt where it comprise, the Tiban and Dodo
members. A smaller elongated outcrop occurs 50km to the west of the main belt in the North
and is been represented as the Dodo, Tibai and Taban members.
The Dodo Member: Overlies the Tibai member but it maybe laterally equivalent in some area. It
consists essentially of feldsparthic sandstone pretends as cross bedded and ripples marks,
sandstone and they are of shallow marine origin. This represent postglacial rise in sea level and
subsequent marine transgression.
The Taban Member: Is composed of crossed bedded feldsparthic sandstone interpreted as spot
orogenic molasses. The fluvial nature of this sandstone further suggests fluvial glacial deposit
origin of this deposit. Tabae formation records a glacial condition over Sierra Leone in the late
Proterozoic.
The Tibai Member: consists of three lithologies.
Poorly sorted conglomerate interpreted as glacio-marine tillite
Laminated silt-stone and fine sandstone with isolated granitic clasts interpreted as glacio-
marine deposits. These contain ice rafted dropped stone.
Lenticular graded feldsparthic sandstone interpreted as channel turbidites.
21
3.4.2 Makani Formation
This overlies the Tabae formation and is composed of grey silty clays which are interbedded
with orthoquartzite and sub-arkoses. They are referred to as well work sediments.
3.4.3 Teye Formation
This is composed of a thick sequence of interbedded shales and sandstones interpreted as
turbidites. The overall lithological characteristics of the Makani and Teye formations which
contain shales and turbidites reflect the depth of water under which this sediment was
deposited.
3.4.4 The Mabole and Taia Formation
These are lateral equivalent and they overlay the Teye formation. The Mabole formation is
dominantly shale with siltstone, and well-rounded orthoquartzites meaning that they were
been deposited in shallow water deltaic environment.
3.4.5 Kasewe Hills Formation
It consists of volcanic tuff sand lavas of varying compositions
3.5 THE SAIONYA SCARP GROUP (SSG)
This outcrop in the northern part of Sierra Leone and cover an area of about 60km2 and extends
north wards to Guinea. It rests uncomformably on the Archean granitic rocks and on the Rokel
River Group conglomerate. It is said to be at late Ordovician in age ( Reid and Tucker, 1972)
Consisting of Sedimentary sequence about 190m thick. Two formations are recognized. They
are:
The Moria Formation: Consists mainly of feldsparthic and cross-bedded, basal conglomerates
and shale.
22
The Waterfall Formation: Consist of laminated mudstone with angular fragments coarse
sandstone bed. The Saoinya Scarp group was intruded by mesozoic dolerite sill up to 90m thick.
Within the intruded rocks, fossils have been found that are of Silurian age.
3.6 BULLOM GROUP
The Bullom group underlies the broad, often swampy coastal strip of Sierra Leone. It comprises
a sequence of poorly consolidated near horizontal sediments which rests with marked
unconformity upon the Kasila-Marampa Group and, in the vicinity of Freetown, upon the
layered basic complex. The sediments, which are deposited in a marine or estuaries
environment consists of series of gravels, sand and clays with occasional thin beds of
argillaceous limestone and calcareous grit. Lenticular lignite seams are interbedded with
kaolinitic clays at several horizons.
The sediments of the Bullom Group are well expose in the sea cliff of the Bullom shore but
elsewhere they are largely concealed and are known imperfectly from borehole data. Thickness
of the group is variable but appears to attained maximum thickness on land of about 120m,
east of the Freetown Peninsula, offshore the deposits may be much thicker and may be in
excess of several thousand meters (Sheridan et al, 1969).
A spare fish and mollusk fauna obtained from boreholes suggest a probable Eocene age for the
horizon which gave radiocarbon dates of 30,250±690 years and 4,840±1200 (Raufub, 1946). It is
probable future work will permit a subdivision into a lower, concealed, tertiary serecite
succeeded by disconformities and overlapped toward the East by a quaternary sericite.
3.7 THE FREETOWN IGNEOUS COMPLEX
The Freetown Igneous complex (also called the Peninsula complex), forms an intrusive body on
the coast, with acute outcrop concave toward the west. It is composed of a layered complex of
gabbro, norite, troctolite and anorthosite. Platinum occurs in the gravel of many streams that
cuts the outcrop of anorthosite and anorthositic gabbro complex of the Freetown peninsula.
23
The relation of this complex with the other units is obscured by the coastal veneer of tertiary
sediments of the Bullom group which lies unconformably on the basement. Tertiary and more
recent weathering lead to laterisation across a large part of Sierra Leone, affecting mainly the
greenstone belts and extensive dolerite intrusions.
The Freetown intrusive complex is a funnel shaped intrusion, forming parallel ranges of
mountains (Freetown Peninsula and Banana Island). The greater part of the complex is
submerging in the Atlantic Ocean and it intrudes the Kasila Group and is covered by Cenozoic
sediment. The age of the Complex is put at 193±3ma (Beckinsale et al 1977).Within the
Freetown Igneous complex, several units are recognized. The Ideal sequence is as follows:
6. Anorthosite ->90%plagioclase
5. Leucogabbro-plagioclase, hypersthenes.
4. Gabbro/Norite-plagioclase, augite, hypersthenes
3. Olivine gabbro-plagioclase, augite, hypersthenes
2. Troctolite- plagioclase, olivine
1. Dunite->90%olivine.
The rocks show sedimentary structures such as layering, cross bedding, slumping etc. The
complex is cut by a series of dykes and veins. It forms part of the Peninsula and Banana Island;
it also contains anorthosite and magnetite sands. It is thought to have been due to multiple
injections of magma that occurred intermittently. The Freetown complex of rocks belongs to
region we referred as layered basic complex and examples of other basic layered complexes are
Skaergoard intrusion (Greenland), Bushveld complex (South Africa) and The Great Dyke
(Zimbabwe).
Features they exhibit are as follows:
They form a major vertical column
Igneous lamination
Cryptic variation
24
FIGURE 3.1 The Geologic Map of Sierra Leone
25
TABLE 3.1 Provisional stratigraphic table prepared by D. D Hawkes (1970)
Quaternary
Bullom Group
Tertiary
Great unconformity
Cretaceous Intrusion of kimberlites
Jurassic Triassic Intrusion of Dolerites
Permian
Carboniferous
Devonian
Silurian
Ordovician Saionya Scarp Group
Unconformity
Cambrian Taban Formation
Unconformity
Rokel Assemblage
Late tectonic and syntectonic
Igneous activity?
Rokellide orogeny
Rokel River Group
Great Unconformity
Intrusion of Freetown Lopolith
Portloko Assemblage
Late tectonic and syntectonic
Igneous activity
Marampa orogeny
Kasila-Marampa Group
Great unconformity
Kenema Assemblage
Late tectonic and syntectonic Igneous activity
Kambui Orogeny
Archean Kambui Group
Obliterated Basement (now
granitized)
Approximate radiometric ages:
Rokellide Orogeny (±500 m.a)
Marampa orogeny (±2,000 m.a ) Kambui Orogeny (±3,000 m.y. )
26
CHAPTER FOUR
GENERAL GEOLOGY OF THE PROJECT AREA
4.1 DESCRIPTION OF THE GEOLOGY OF THE PROJECT AREA
The project area comprised basically of 12 Grids i.e. at the upper end of sheet 103,Joru.It cover
four chiefdoms, which are ; Dama, Gaura, Koya and Tunkia respectively all in Kenema District,
Eastern province, Sierra Leone. The area is located along a motorable Highway to our
Neighboring country, Liberia at the Southeast part of Sierra Leone. Here a geological map
showing the project area in Figure 4.1
FIGURE 4.1 The geology of the project Area, Sheet 103 Joru
The geology of the project area intrudes the Granite greenstone terrain. It is also refer to the
kambui supergroup. The kambui hills forest reserve occupies an area 14,335 hectares in the
Eastern province of Sierra Leone. It is located about 25km from kenema with terrain consisting
of steep slopes that reach an attitude of between 100 and 400m. The area mainly consist of
PROJECT AREA
27
forest habitat but there is also some savannah and wetland. The project area is formed by the
basement granite which range in composition from hybridize, migmatite, metasediment ,
gneissic rocks, quartz-diorite, granodiorite and foliated or massive to medium grade
homogenous granites. The Greater part of eastern Sierra Leone is composed of a complex of
intimately associated Granites, Migmatites, and Gneisses. All these rocks are loosely granitic in
composition and are assume to have been formed by granitization of the deeper parts of the
kambui geosynclines. Two phases (Marmo, 1955) of the granite formation have been
established. The Syntectonic granitization accompanied the main orogeny and the intrusion of
late tectonic granites, with some granitization following the main orogeny.
Syntectonic granites range in composition from diorites to the true granites;
granodiorites are commonest rocks. They tend to be coarse-grained and gneissose with
foliation, Parallel to the enclaves of the kambui Group. Two mica granodiorites, with the
assemblage quartz-oligoclase-microcline (biotite –muscovite) are typical sphene and
apatite are common accessory minerals. Porphyroblastic granites, with porphyroblasts
of microcline are locally abundant, Particularly near fracture zones and appear to reflect
a later potash metasomatism of syntectectonic granites.
The late-tectonic granites have a restricted occurrence and occur as small bosses and
dykes. They form medium-grained usually massive intrusion, which are frequently
discordant to the enclosing rocks. Chilled margin occur in composition, they are potassic
granites with assemblage quartz-microcline, albite-epidote and muscovites are common
accessories minerals. A phase of pegmatitic and aplitic intrusion accompanied by
potassium Boron and Fluorine metasomatism is associated with the late tectonic
granites.
The general trend of geology in the project area is northeast and few strikes north-west with an
approximate dip of 65°. It is in zone 29 of the UTM coordinate. The main tectonic event that
affected the area is the Liberian event of age approximately 2700ma years. The geology of
Sierra Leone is been divided into seven Groups. Based on these seven groups the project area
falls into three groups. These are:
I. The basement granite
28
II. The Greenstone supracrustal
III. The late-kinematic/intrusive granites
The basement granites: the basement is normally the host rock, which houses all other rock
units. Concerning the project area, the basement is predominantly granitic and the granite
rocks show various colors between felsic (leucocratic), mafic (mesocratic) and different
compositional grains. The grain size ranges between medium to coarse grained. Based on
microscopic studies in the project area, five different types of granitic rocks were encountered.
These are:
Microcline granites
Biotite granites
Granitic gneiss
Granitic Schist
Migmatite
Microcline granites: Microcline granites outcrop in the following areas: Kebewana (X=0263654,
Y=0845657), Kanga (X=0268963, Y=0853645), Baoma (X=0277736, Y=0856563), Nyandehun
(X=0273816, Y=0855381), Jago (X=0272416, Y=0854980), Koila (X=0264787, Y=0846691) etc.
They range from medium to coarse grain. It consists of varieties of colors, which are; pink, grey,
white (mesocratic). It main composition in hand specimen includes quartz, microcline,
plagioclase and biotite. Figure 4.2 shows microcline granite at Kebewana village
Biotite granites: This outcrop in the following area; Senehun now called Jawavulahun
(X=0278729, Y=0853559). It grain size ranges from medium to coarse grain. The color varies
from mafic to felsic (mesocratic). That is, white, black. The composition is quartz and Biotite.
Granite gneiss: This outcrops in the following areas: Boyama (X=0268650, Y=0850185),
Taninahun (X=0262387, Y=0856991), kanela (X=0257342, Y=0855761), Koribundu (X=02595302,
Y=08563504). Granite Gneisses consist of alternate bands of mafic and felsic minerals. The grain
size ranges from medium to coarse grain with a gneissose texture. The composition varies from
plagioclase and quartz. Figure 4.3 shows a granite gneiss.
29
FIGURE 4.2 Microcline Granite at Kebewana village
FIGURE 4.3 Granite gneiss
Granite schist: These outcrop at the middle of the Moa River (X=0252347, Y=0853498). It shows
foliation of the grains. The grain size ranges from medium to coarse grain. It has variety of
colors such as white, black, grey, green etc. The texture is schistose and it main composition is
quartz, biotite, muscovite.
30
Migmatite: This outcrops in Jagbwema (X=0275662, Y=0845388). It is a medium to coarse grain
mixed rock. It consists of both metamorphic and igneous composition. It has variety of colors
such as: grey, pink, black, white etc. It also has a migmatitic texture. The main composition is
hornblende, biotite, quartz and feldspar.
The Greenstone Supracrustal: The supracrustals usually consists of two groups. These are; the
Loko group and Kambui super group. The Loko group is the oldest whilst the Kambui
supergroup youngest. This supracrustal also form part of the Greenstone belt. The Greenstone
belt consists of two major sequences. These are:
The metavolcanic sequence
The metasedimentary sequence
The metavolcanics: Is a type of metamorphic rock that originates from volcano as lava. The
common minerals are; quartz, feldspar, microcline, amphibole etc. the metavolcanic rocks in
the project area are: Amphibolite, which outcrops at the northeast end of the map across the
Moa River. The town located there is Nyawalago (X=0251056, Y=0853113). It grain size ranges
from medium to fine grain. Another metavolcanic rock is dolerite which outcrops in the
following areas: Koma (X=0252603, Y=0845396), Mani (X=0254155, Y=0845677), Maboma
(X=0253449, Y=0844298) etc. it shows an ophitic texture under the microscope. That is
plagioclase forms an intergrowth with feldspar. The grain size ranges from fine to medium. The
main composition of dolerite is plagioclase, feldspar etc. The dolerite in the project area occurs
as dykes/ massive rocks.
The metasedimentary: Is a sediment or sedimentary rock that appears to have been altered by
metamorphism. The overall composition of a metasediment can be used to identify the original
sedimentary rock even where they have been subjected to high-grade metamorphism and
intense deformation. However, no metasedimentary rock is been found in the project area.
The Late Kinematic Granites: They are also referring to as intrusive granites. The intrusive
granites outcrop mostly on the hills. It can be found almost everywhere in the field. Most of the
intrusions follow shear zones, fault planes and foliation planes. They are believed to have been
31
emplaced during the Liberian tectonic events, the intrusive granites normally occur as dolerite
dykes.
THE BESEMENT GRANITES: The basement in this project area is predominantly granites and the
granites show various color index; ranging from leucrocratic, mesocratic and melanocratic,
based on the dominant minerals. There is also compositional variation of these basement
granites and their grain size range from fine grained, through medium grained to coarse-
grained. The basement granite is the largest unit in the project area. The petrographic
characteristics of these rocks are been explained in detailed.
Biotite Granite: These rocks are found in several areas but large outcrops. The rock is medium
to coarse-grained leucocratic, halocrystalline. Microscopic analyses show quartz having grains
that are subhedral to anhedral, quartz forms an essential constituent of the rock showing strain
shadowing, it also show cracks and free from alteration .Plagioclase (albite to oligoclase
compositional range ) shows twinning white others cloudy because of seriticization. Biotite was
been recognized by its obvious dichroic property (dark brown to pale brown) and its distinctive
pleochroic halos. Quartz has inclusion, which results to the formation of poikilitic texture.
TABLE 4.1 Modal Percentage Table of the Minerals in Biotite granite
Biotite Quartz Plagioclase Hornblende Microcline
35% 40% 10% 3% 7%
The minerals are not aligned neither in hand specimen nor thin section; this proves that the
rocks were formed at the late phase deformation.
32
Quartz
Biotite
Plagioclase
Microcline
PLATE 4.1 Cross-Polar Biotite Granite
Biotite
PLATE 4.2 Plane polar Biotite granite
Paragenesis: The rock is granitic, therefore plutonic. This also means that the rock crystallized
at some depth below the surface. This also evidence by the exfoliation structure of the rock as
it is seen in Figure 4.4 below.
This confirms that fact that the rock crystallized at some depth below the surface. It may
possible that although the rock crystallized at depth, continual erosion of the top soil and uplift
33
eventually exposed the rock. As this happens, there is considerable deduction in pressure, at
depth the rock is under confining pressure by the overlying material. The part of the rock
exposed to the surface will peel off. Homogenous Biotite granite is attributed to low
temperature (quartz, biotite, albite –oligoclase) homogenization of migmatite gneiss.
FIGURE 4.4 Biotite granite showing exfoliation
Granite Schist; These rock form extensive bodies characterized by preponderance of quartz
rubbles. They are white to light grey in color, coarse grained with large crystals of quartz and
large intergranular muscovite. The rock displays well-formed schistosity that makes it splits
easily and contains mica flakes. The rock is light in color, fine to medium grained and consists of
quartz, muscovite, biotite, chlorite and opaque minerals. Table 4.2 shows the modal percentage
composition of each mineral.
TABLE 4.2 Modal Percentage of the minerals in granite schist
Quartz Plagioclase Biotite Muscovite Opaque
minerals
30 15% 35% 5% 15%
34
Under the microscope, quartz occurs as a colorless mineral usually cloudy and anhedral in
shape with a low relief. It shows no cleavage, alteration and pleochroism. It also does not show
any twinning but display undulose extinction. Biotite occurs as subhedral grains in between
crystals of other minerals. It exhibit pleochroism, moderate relief and one direction of cleavage.
It has no twinning.
Quartz
Muscovite
Biotite
PLATE 4.3 Cross- polar granite schist
Opaque minerals
PLATE 4.4 One-polar granite schist
Paragenesis of Granite Schist A rock that originates from igneous processes it found at
hyperbysal depth. It consists of fine to medium grain with foliations and lineation. It shows
35
schistosity. During the time of crystallization, it encounters an igneous melt as a result it
crystallizes together.
Microcline Granite: The microcline granite is mesocratic and range from fine to medium grains
the dominant minerals are; microcline, biotite and quartz .Some of the microcline granites are
observed to have quartz bands alternating with microcline. In hand specimen the microcline
shows a variety of colors such as white, grey, pink etc. The main mineral composition in hand
specimen are; quartz, microcline, biotite and plagioclase. Under the microscope the dominant
minerals present are; microcline, quartz, plagioclase, biotite and opaque minerals as shown in
the table below
TABLE 4.3 Modal percentage of the minerals in microcline granite
Microcline Quartz Plagioclase Biotite Opaque
minerals
55% 30% 5% 5% 5%
The shape of microcline can be anhedral or euhedral grains are common elongate with a
tabular appearance. It has perfect cleavage but it is difficult to see cleavage in thin section due
to microcline low relief. It typically displays albite twinning and pericline twinning. It also shows
Carlsbad twinning or crosshatched twinning in cross-polarized light. It is because of these
twinning characteristics that differentiate it from the other minerals. It shows inclined
extinction to cleavage and commonly alters to sericite or clay. Quartz grains show anhedral
grains with diffuse grain boundary. It has no cleavage but it also has low relief. Quartz does not
show any twinning. Quartz display undulatory extinction wherein when the stage is rotated it
shows white alternate with black bands. Quartz occurs as colorless minerals with inclusions of
unidentified minerals. Plagioclase shows elongate crystals in one direction with a low relief. It
shows polysynthetic twinning of alternate white and grey grains. Biotite occurs as brownish
colored crystals. It is anhedral in shape and sometimes shows prismatic crystals with a perfect
cleavage in one direction. It has moderate to high relief. It exhibit pleochrosim characterized by
a dark pleochroic haloes.
36
Microcline
Biotite
Quartz
PLATE 4.5 Cross polar microcline granite
Biotite
PLATE 4.6 One polar microcline granite
Paragenesis of Microcline Granite: The rock is plutonic in origin. That is form at great depth in
the earth surface. Granites are composed wholly of crystals and are therefore term
holocrystalline medium to coarse grain are mostly plutonic coarse grain (phaneritic). They
crystallize from bodies of magma that intrudes at temperatures below about 800°c and that
cooled and lost gas slowly because of their shape or their depth of emplacement. During the
final stage of consolidation of such magma, the residual liquids may be enriched. The microcline
has been formed by the potassium metasomatism and replaces the earlier oligoclase. The
microcline developed along the foliation planes and fractures cracks forming the metacryst
37
than the oligoglase; some have been seen up to 3.0cm in length. Microcline has very irregular
boundaries and frequently encloses quartz, biotite, and remnant plagioclase. It exhibits typical
replacement textures. Microcline may form microperthite in which the insets are irregular and
maybe untwined.
The Granite-Gneiss; The Granitic contain mafic and felsic minerals that intermingle with each
other but are not separated in bands ,where the zebra gneiss contain mafic and felsic minerals
intermingle with each other are separated in bands. The texture varies considerably. Some fine
even-grained occur, but the majority are medium to coarse grained and are frequently
gneissose. The rock displays well-formed schistosity that makes it splits easily and contains mica
flakes. The rock is light in color; fine to medium grained and consists of quartz, microcline,
biotite, and it accessory minerals are serecite, epidote and chlorites. Under the microscope,
quartz occurs as a colorless mineral usually cloudy and anhedral in shape with a low relief. It
shows no cleavage, alteration and pleochroism. It also does not show any twinning but display
undulose extinction. Below is a table showing the percentage modal composition of each
mineral. Biotite occurs as subhedral grains in between crystals of other minerals. It exhibit
pleochroism, moderate relief and one direction of cleavage. It has no twinning
TABLE 4.4 Modal Percentages of the minerals in granite gneiss
Biotite Quartz microcline Accessory minerals
30% 35% 15% 20%
38
Biotite
Quartz
Opaque minerals
Microcline
PLATE 4.7 Cross-polar granite gneiss
Opaque minerals
PLATE 4.8 one-polar granite gneiss
Parageneiss of Granite Gneiss; It a metamorphic rock that originate from an igneous rock.
Metamorphic rocks, on the other hand, form in the absence of a silicate melt by re-
crystallization and reaction between minerals that are solid though at high temperature. In the
deeper levels of the earth’s crust, igneous and metamorphic phenomena merge imperceptibly.
39
A common cause of the banding is the subjection of the protolith (the original rock material
that undergoes metamorphism) to extreme shearing force. Gneiss is a common and widely
distributed type of rock formed by high-grade regional metamorphic processes from pre-
existing formations that were originally either igneous. High temperature and pressure causes
igneous rocks to become what type of rock. Gneisses that are metamorphosed igneous rocks
are termed granitic gneiss.
Migmatites: The migmatite rock belong the granulite group that has been granitised by the
enderbite and some extent by the microlinisation process. This rock was seen in an outcrop
close to Jagbema (GPS X=027616, Y=0844886). In hand specimen migmatite often appears as
tightly incoherently folded (ptygmatic fold), dikelets, vein and segregation of light colored
amphibole and biotite rich mineral called melanosome. The mesosome is intermediate in color
between leucosome and melanosome, which is mostly a more or less unmodified remnant of
the original parent rocks (protoliths).The light-colored materials has the appearance of having
been mobilized or molten. In thin section the migmatites resemble charnockites, and the
porphyroblasts are set in fine grained matrix varying in grain size up to 1.5mm. They contain a
higher proportion of ferromagnesian minerals including hornblend and pyroxene. The essential
minerals of migmatites under the microscope are hornblende, pyroxene, and microcline. The
amphibole is six sided(orthorhombic) and display a cleavage in two orientations meeting at
angle of 125˚.The color is green and show pleochroism from light to dark green, microcline is
identified under cross polar in which it displays tartan twinning. The accessory minerals are
chlorite, and calcite. The migmatite is characterized by coarse pink microcline porphyroblasts
which contrast strongly with fawn metacryst of the charnokites. The pink microclines show
carlbad twinning similar to the charnockitic porphyroblasts. The coarse pink microcline,
representing the metasome, may have sharp contacts; however, the porphyroblasts have
frequently developed along shattered cracks and have followed foliation planes. Nucleation
occurred at points along these planes, and coarse microcline developed which is very strongly
xenoblastic and may envelop the earlier formed minerals. Hence, the long axes of the
porphyroblasts have a strong lineation parallel to the foliation, and are separated by fine,
granular, dark, material which varies greatly in proportion. The individual porphyroblasts are
frequently elongated up to several centimeters in length; alternatively they may form augen.
40
Below is a table showing the modal percentage of each mineral.
TABLE 4.5 Modal Percentage of the minerals in migmatite
Biotite Plagioclase Hornblende Quartz
25% 30% 20% 25%
Plagioclase
Hornblende
Biotite
Plagioclse
Quartz
PLATE 4.9 Cross polar migmatite
Pleochroic halos
Biotite
PLATE 4.10 One polar migmatite
Petrogenesis: Migmatite is a rock that is a mixture of metamorphic and igneous rock. It is
formed when metamorphic rock, such as gneiss partially melts and that melt re-crystallize into
41
an igneous rocks creating a mixture of unmelted metamorphic part with recrystallized igneous
part. They are also known as diatexites. Migmatites from under extreme temperature condition
during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatite
are not crystallized from a totally molten material, are not generally the result of solid state
reactions. In extremely deformed rocks that represent the base of eroded mountain chain in
cratonic blocks. For migmatised argillaceous rocks, the partial or fractional melting would first
produce a volatile and incompatible-element enriched partial melt of granitic composition.
Such granites derived from sedimentary rock protolith would be termed S-type are typically
sometime containing leucite and would be termed ademelite, granite and syenite. Volcanic
equivalent would be rhyolite and rhyodacite. Migmatised igneous or lower crustal rocks which
melt do so to form a similar granitic I-type granite melt but with distinct geochemical signature
and typically plagioclase dominant mineralogy forming monzonite, tonalite and granodiorite
compositions. Volcanic equivalents would be dacite, trachyte and trachydacite. It is difficult to
melt mafic metamorphic rocks expect in the lower mantle, so it is rare to see migmatitic
textures in such rocks. However, eclogite and granulite are roughly equivalent mafic rocks.
4.2.2 The Greenstone Supracrustal
The main sequence of the greenstone supracrustal is the metavolcanics which involves
amphibolites.
Amphibolite; The amphibolites are composed bluish-green hornblende; it is confined to the
extreme northwestern of sheet 103NW. It outcrop just after Nwarlargo (GPS X=0251056,
Y=0853113) close the river moa. Close the granite contact, the amphibole of the amphibolite
becomes brown and slightly gneissose but the rock cannot be called a granulite by any any
stretch of imagination. Bands of quartz-mica schist few tens of feet wide interacted in the
amphibolite, but the area mapped was far too small to permit any inclusion to be drawn about
their origin. Amphibolite in hand specimen, vary in texture from a fine grained uniform variety
to foliated gneissose types, some of which contain porphyroblast of hornblende metacryst are
randomly orientated . Most amphiboliotes are remarkably uniform in grain size and texture.
The rock is composed mainly hornblende and plagioclase small grains of opaque minerals occur
42
throughout the rock and some Biotite, epidote, pyroxene and chlorite are present. As shown in
the table below.
TABLE 4.6 Modal Percentage of the minerals in Amphibolite
Amphibole Plagioclase Biotite Quartz Accessory
minerals
55% 25% 10% 5% 5%
The hornblende show pleochroism from green to brown and the biotite is from a dark brown to
pale brown .The good cleavage usually associated with pyroxene does not shown up in these
crystals.
Plagioclase
Amphibole
Quartz
Opaque minerals
PLATE 4.11 1 cross polar amphibolite
43
Amphibole
PLATE 4.12 1 one polar amphibolite
Petrogenesis; Amphibolites are formed by regional metamorphism of range of protolith. Ortho-
amphibolite has igneous protolith, which are generally mafic igneous rocks (Basalt, gabbro).
Para-amphibolites have sedimentary protolith and in a particular argillaceous carbonate or
marl. Amphibolites are consider medium grade metamorphic rocks and formed under
amphibolites facies metamorphism.
4.2.3 Late Kinematic/Intrusive Granites
They are also referred to as late kinematic granite. They have restricted occurrence and occur
as bosses and dykes. They form medium grained, usually massive, intrusions, which are
frequently discordant to the enclosing rocks. The Common example is dolerite dyke. Swarms of
dolerite dykes trending NW to SW trend are common in all parts of Sierra Leone. A well-
documented swarm (Wilson 1965) occurs in the gola forests. In the eastern plateau and hill
region and on the saionya scarp, dolerite to sills up to 150m, in thickness occurs. It is probable
that the dykes and sills form a single interconnected suite, which is tholeitic in character and
Triassic (185±10,230±10ma) in age.
Dolerites: The dolerites are similar to olivine dolerites but tend to be little finer grained. The
olivine is absent, although a few small green serpentinous may occur. The texture is often
44
strongly porphyritic, labradorite and occasionally clinopyroxene form the phenocryst. The
pyroxene is also similar to that of the olivine dolerites, forming aggregates which are frequently
recystallized. Individual grains rarely exceed 1.0mm in diameter in the groundmass, but the
phenocryst usually exceeds 1.5mm. They are similar smoky brown color increase in
birefringence. The pyroxenes are again pegeonitic in composition, but the stronger zoning
reflects a greater marginal increase in the optical axial. The rim may occasionally be augitic in
composition. All known dolerites in the project area form dykes and not sheet, sills or flows .It
occur in places such as Mani (GPS X=0254155,Y=0845677), Benduma (GPS X=0261748,
Y=0851824). The dykes are typically shallow intrusive bodies and often exhibit fine grained to
aphanitic chilled margin, which may contain tachylite (dark mafic glass).
FIGURE 4.5 Showing Swarm of dolerites at an outcrop in Mani Village (0254155 / 0845677)
Dolerite in hand specimen has a visible texture of anhedral lath shaped plagioclase crystals.
Under thin section, the essential minerals are plagioclase and finer matrix pyroxene. Accessory
and alteration minerals included Biotite, chlorite and calcite. Below is a table showing the
modal percentage of each mineral.
TABLE 4.7 Modal Percentage of the minerals in dolerite
Serpentine Pyroxene Biotite Accessory minerals
40% 30% 20% 10%
45
Pyroxene
Serpentine
Biotite
PLATE 4.13 Cross polar amphibolite
Fine grains (massive rock)
Biotite
PLATE 4.14 1 one polar dolerite
Petrogenesis: The various rock types under the heading of “late dolerites” all occur as dyke
swarms following the same WNW regional fracture system. This, together with their close
association within the swarms, suggests that they have been intruded at same time and are
closely related genetically. The similarity in mineral content supports this contention. Indeed,
the pyroxenes show a gradational change in composition throughout the doleritic range from
pigeonites with a very small optic axial angle to clinopyroxenes with pigeonite core and an
46
augitic rim. This increase in optic angle in the pyroxene is accompanied by the disappearance of
olivine. Hence the dykes were probably derived from the same magma source, but slightly
different levels in the magma chamber, and were injected during the same igneous episode.
The olivine dolerites were derived from the lower levels in the chamber, the dolerite from
intermediate levels, and the basalts from the upper levels. The gradational increase in the optic
axial angle of the pyroxenes reflects this sequential origin. There does not appear to be a
relationship between the grain size and the thickness of the dyke. But there is a general
relationship in the mineral composition and the coarseness. Thus the olivine dolerites tend to
form the coarsest rocks, and contain the most pigeonitic clinopyroxene, whereas the fine
grained basalts contain the more augitic clinopyroxenes, and show the greatest degree of
alteration. There is perhaps a relationship between level of origin in the magma chamber,
residual fluid content, initial temperature, and volume of the injected material. The age of the
dolerite suite has been determined at between 185-230m.y from two dykes cutting the Rokel
River Series to the west. This is equivalent to ages determined for the dolerite dykes of Karroo
age in East Africa. The dolerite dyke of Sierra Leone are therefore of upper Paleozoic age. This is
in agreement with postulated age of the dolerite sills of the Saionya Scarp Series.
47
CHAPTER FIVE
STRUCTURES, DEFORMATION, AND METAMORPHISM
5.1 STRUCTURES
Structural geology is the study of the change in the position or attitude of bodies of rock
achieved by the application of unbalanced pressure and varying amount, it is after the rock was
formed. Structural fabrics and deflects such as fault, and folds, fractures (joint & cracks) and
veins are internal weakness of rocks. Some of the most common terms, that is involved in the
study of geologic structures.
Outcrop- The area of exposure of bed on the earth surface
Strike Dip & Dip Direction- Strikes & dip are terms use by geologists to describe the
orientation of strata. The strike is a compass direction of stratum (bed) relative to the
horizontal. There are two measurements for dip direction and the dip angle. The dip
direction is the compass direction in which the layer is inclined downward from the
horizontal. The direction of the dip is always at angle to the direction of the strike. The
dip angle is the angle between the horizontal plane and the bedding plane, which is
measure in degree.
Bedding Plane-The planes that divide one bed from the other are called bedding plane.
Based on a new stratigraphic table of Sierra Leone is presented and the geology of the country
summarized (D.D Hawkes). Four structural units are recognized, they are
The eastern unit
The western unit
The Atlantic coast
The Freetown peninsula
The geology of the project area intruded the eastern unit. The Eastern unit, which coincides
with the interior plateau and hill region, formed the kenema assemblage. This structural unit
forms part of the West Africa craton and consists of very ancient (±3,000m.a) crystalline rocks
in Sierra Leone a dominant northeasterly foliation. The rocks of the kenema assemblage
(Andrew-Jones, 1966) occupy the greater part of Sierra Leone. It is a metamorphic –plutonic
48
assemblage and a geosynclinal sequence, Known as the kambui group, which was deposited
upon and ancient basement (perhaps primaeval sialic crust) or crystalline rocks. The basement
and geosynclinal sediment were invaded and modified by granitic rocks associated with
subsequent orogenic movements. These have obliterated the structures of the ancient
basement so that the original crystalline rocks are no longer recognizable. The strikes veers
from due north at the northern edge of sheet 103NE to North northeast at the western edge of
sheet 107SW. The area has an average dip angle above 45˚ dipping west. The dolerites dykes
tend to form swarms and most of them strikes 110˚ and 130˚. Many of them follow pre-existing
mylonites that could be related to forces acting from the north-east and south-west that
compressed the rocks in the country mapped, cross folded them when the compression relaxed
and was superseded by tension the mylonite zones may have provided paths of least resistance
of the dolerite intrusions. The dykes swarms could mark zones where tension was greatest and
beneath which mafic magma chambers formed within a few thousand feet of the surface. In
general, the dykes dip vertically but in detail, there are many departures from the vertical and
at the same time although the average strike is southeast or east-south-east dyke offshoot
diverge from the direction by up 90˚. In fact, the dolerite filled any crack the happened to be in
tension and accessible from fractures.
Both microstructures and macrostructures were observed in the project area.
5.1.1 Micro Structures
Structures such as foliation, schistossity, gneissosity that are all evidence of deformation in the
rocks of the project area were observed. The development of the structures during
deformation is governed by the rate at which grains were internally deformed. Thus, these
microstructures are a function of the strain rate and the temperature at which deformation
occurred.
Foliation: This is a penetrative or repeated planar feature in a rock and is been defined by
Biotite flakes, hornblende, lecticular quartz and feldspars. In certain areas of the project area,
compositional layering of migmatites was observed. The supercrustals show a wider variation
within the same lithologies.
49
Schistosity: Schistosity in the project area is defined by the preferred alignment of micas and
amphibole-typically hornblende and tremolite .This a dominant features in some amphibole
and Meta ultramafics minerals.
Gneissosity: Gneissosity in the project area was mostly observed in the synkinematic granites,
which were seen as compositional layering. This was seen in the basement granite gneiss with
bands chiefly of few millimeters that were rich in both mafic and felsic composition trends NE-
SW and dips at 60˚ west. This sample must have suffered plastic deformation.
5.1.2 Macro Structures
A number of microstructures (some of which are linear) are apparent within the project area.
Microstructures observed in the project area include; fault, fractures, veins, folds etc and can
be discuss as follows.
Fractures (Joint & Cracks): Joint and cracks are fractures in rocks along which there has been
little or no movement. They are the most common but still the most difficult of the geological
structures to analyze. Fracture development is related to three main geological processes:
Deformation at depth (orogenic processes)
Deformation (epeirogenic process)
Shrinkage (caused by cooling)
This structures (fractures) was the most dominant of the geological structures observed i.e. it
almost occurred in all the outcrops, but the most noticeable ones were at the moa River (GPS
X=0252347, Y=0853498), and Fefewai hill(GPS X=0271558, Y=0846577). The cracks range from
different centimeters. This types of fractures are refers to Irregular or concoidal fracture
because the joint are not parallel but they have just have their own set of orientation .They are
also refers to as non- systematic fractures.
50
FIGURE 5.1 A Fracture at Fefewai Hill (0271558 / 0846577)
Veins: They are name for their resemblance to blood vessels, which are tubes. However, the
veins in rocks are actually sheet or tabular shapes. Which look like tubes only because outcrop
exposed them in cross-section. A Vein is a fracture that is filled with hydrothermal mineral
materials or a vein is a deposit of mineral or rock that fills the voids formed by a fracture or
fault in another rock. The mineralogy of the host rock surrounding the vein is often altering
where it is in contact with the vein of the country rock, because of the chemical reaction. The
two rocks types are: Two types of vein were encountered in the area and these veins are late
intrusion, intruded during the igneous activities caused by the Liberian tectonothermal event
(2700m.a) the veins cross cut the outcrops and in some the two veins are crosscutting
relationship, the outcrops are older they the veins cut each other. According to the principle of
cross cutting relationship, the outcrops are older than vein. Such structures were seen in Gama
(GPS X=0255141, Y=0855436) Quartz veins and in Kebawama (GPSX= 0263654, Y=0845657) and
kanga (GPS X=0268963, Y=0853645) pegmatitic veins were observed. Both pegmatitic veins and
Quartz veins are coarse in texture, in which the widths were ranging in different centimeters.
51
FIGURE 5.2 A Vein at an outcrop close to Gama Village (0256223 / 0855890)
Fault: A Fault is a fracture (evidence of brittle failure or breakage) in the Earth crust along which
measurable relative movement has occurred. When rocks are subject to great pressure, the
earth crust may have to withstand shear force in addition to direct compression. If the shear
forces induced is so excessive, failure will result, movement will take place along the plane of
failure until the unbalanced forces are equalized and a fault will be the result .Faults are
uncommon in the area and the only one fault was seen in the outcrop around Diame village
(GPS X=0264568, Y=0855585). The fault is a normal fault i.e., the hanging wall is displaced
downward relative to the footwall. The displacement of the hanging wall from the footwall is
3cm .The vertical component of the displacement between two originally adjacent point is
called the thrown of the faults, the blocks above the fault is called the hanging wall and the
underlying block is termed as footwall. The horizontal component of displacement is called the
heave.
52
FIGURE 5.3 A Normal fault plane at an outcrop around Diame village (0266032 / 0853310)
Folds: Fold refers to a bend or wave-like features in layered rocks. Many rocks contain planar
surfaces that bend during deformation forming folds of diverse shapes. Folds are mostly formed
in plastic deformation under tensional stress stretches or thin the rocks. When plastic
deformation results from compression or shear stress, the resultant crumpling of the rocks
commonly produces folds. They conditions under which fold forms are high temperature and
pressure, greater depth and high strain and stress intensity. Folds occur in many varieties and
sizes. Fold shape reflects the relative competence of the layers at the time of fold formation.
Folds in the project area are rare and not clearly observed. The type of fold seen is disharmonic
fold in which there is no relationship between shape and distance of the subsequent beds. This
type fold was in observed in Goma (X=0256651, Y= 0848362), Fayima (X=0259890, Y=0845776)
53
FIGURE 5.4 A fold observed at Goma Village (0256651 / 0848362)
IMPORTANT OF GEOLOGIC STRUCTURES
The study of geologic structure has seen of prime importance in economic geology both
petroleum and mining geology. Folded and faulted rocks strata commonly form traps for the
accumulation of fluids such as petroleum and natural gas. Faulted and structurally complex
areas are notable as permeable zones for hydrothermal fluids and precious metal are deposits
of gold, silver, copper, zinc, lead and other metals are commonly located structurally complex
areas. Environment and hydro geologist need to need to understand structural geology because
structures are sites of groundwater flow and petroleum, which may affects for instance,
seepage of toxic substances from dump of seepage of salty water into the aquifer.
EVOLUTION OF THE PROJECT AREA
The rocks of the Basement complex are metamorphosed from the granulite facies to the low
grade greenschist facies i.e. greenstone belt because of the presence of chlorite, which is
responsible for the green coloration. Greenstone belts generally follow the stratigraphic order
in which a sequence of basal ultramafic is overlained by mafic volcanic, metasedimentary and
the intrusive rocks all lying on or besides the granites (Basement rocks). However, because of
54
poor exposure and extensive duricrust cover, it was not easy to erect a stratigraphic column for
the project area. But structurally, it was observed that the intrusive rocks (dolerites) intruded
the late kinematic granites (Formed the basement rocks). The Basement rocks underlie the
metavolcanic and metasedimentary units. The rocks of the kenema Assembage (Andrew-Jones,
1966) occupy the greater part of Eastern Sierra Leone. It is a metamorphic plutonic rock
assemblage and includes a Geosynclinal Sequence, known as the kambui Group, which was
deposited upon an ancient Basement and Geosynclinal were invaded and modified by granite
rocks associated with subsequent orogenic movements. These have obliterated the original
crystalline rocks are no longer recognizable. The greater part of Easter Sierra Leone is
composed of complex intimately associated granite, migmatite and gneisses, all these rocks are
loosely granitic in composition and are assumed to have formed by granitization of the deeper
parts of the kambui Geosynclines. Isoclinal folds were developed as a result of East-west
compressional forces which are probably due to partial closure of the opening or the extrusion
of the late kinematic granites. A summarized sequence of the events is given below.
SEQUENCE
1. Deposition, in Northeasterly trending geosynclines of shaly and calcareous, sandstone
and iron bearing beds. Basic lavas were extruded as flow during deposition.
2. Metamorphism of the downfolded rocks to the granulite facies accompanied in places
by their partial hybridization and granitisation by a dry granitic magma, the granitic that
was synkinematic.
3. Faulting with a northeasterly strike in zones now accompanied by buckling and maho-
thrusting. During the movement all rocks were pervaded with potassic gneissose,
microcline granites that occur extensively except in granulites
4. Intrusion of the diabase complex into the fault zone and into the Diame-Jagbema
movement in the fault and thrust zones continued during the intrusion.
5.2 DEFORMATION
Deformation is the result of forces that are strong enough to change the shape and volume of
rocks. From observation and research (Sierra Leone Geological reconnaissance survey
55
publication 1989), two major episodes of deformation can be recognized within the project
area. The younger of this, the Liberian tecto-thermal event, is equated with the 2700ma age
the province of Hurley and others(1971) .This event imprinted E-W and NNW to NE
deformational trend associated with syntectonic and post tectonic mineral growth .The age of
the older or Leonean episode is approximated as >2700ma. This event gives rise to fold with E-
W trends. Thermotectonic event during the Liberian resulted to the formation of isoclinal
folding, which is evident in Goma village, faulting and metamorphosed region underlain by
sedimentary rocks, leading to migmatite formation and anatexis (partial melting). Tectonic
plate movement and subduction, volcanic and igneous activities, cause the displacement of
rock (fault), changes in shape and volume when strains causes rock to buckle and fracture. The
dolerite dykes tend to form swarms and most of them have strikes between 110˚ and 130˚.
When the compression relaxed and was superseded by tension the mylonite zones may have
provided paths of least resistance for dolerites intrusions .The dykes swarms could marks where
tension was greatest and beneath which mafic magma chambers formed within a few thousand
feet of the surface. The project area unravel that the area has undergone crystal plastic
deformation, rather than deformation by fracturing. The pattern of distribution of the
deformed rocks within the project area vividly indicates various episode of deformation. Two or
more lineation with different orientation do occurs in some rock samples (granitic) indicating
compound deformation. The project area shows parallelism of planar features over extension
areas, indicating some uniformity in deformation.
5.2.1 Effects of Deformation in the Project Area
Due to the deformation, the amplitude of Liberian F1, folds increases, the wavelength
decreases and fold style changes from warps to buckle. Accompanying the tightening of F1,
folds, a mineral elongation, mainly quartz grains, is replaced by a crenulation cleavage and
finally by schistosity axial planar to the F1, folds. This is largely coincident with the areas of
the kambui schist series and in the Intrusive granites.
The Liberian domains experienced strong deformation from elongate zones in which the S1
schistosity is intensely developed. Schistosity planes are closely spaced and form strong
56
augen structures and around earlier minerals, particularly the feldspars. These domains are
largely coincident with areas of granitic gneiss.
Folds in gneisses are cross cut by late Liberian pegmatoids.
5.3 METAMORPHISM
Metamorphic rocks may undergo re-crystallization either in respond to strains in the absence of
any chemical reaction, or because of reactions leading to the production of new phases. The
process is known as metamorphism. Rocks in the project area are generally metamorphosed in
the granulite to lower greenschist facies. There is a sharp contact from the amphibolites to
greenschist facies, which unravel the temperature and pressure in NE of Sheet 103. Indicating
that, there is drop in temperature and pressure. This region is affected by regional
metamorphism. Metamorphism to the granulite grade with sillimanite not kyanite or corderite
but pyroxene, microcline and anorthotite as typical minerals and scarcity of twinning requires
tranquil tectonic condition and according to Fyfe and others, a minimum temperature and
pressure of 650˚C and 6.5 kbs. If the pressure specified depend solely on the thickness of
overlying rock the depth of burial would have to be about 75,00ft. However, the beerchachites
in the Freetown layered basic igneous complex, which are for practical purpose, typical mafic
granites have formed at pressure the most have good deal lower than 6.5kbs although at
temperatures perhaps as high 1,050˚C. The difficulty in defining the field in which granulites
form in association with migmatite or granite may arise largely from the dryness of the magma
and the associated high temperature which little is known and much is conjectured. Except in
migmatite, granulite and hybrid belts, microcline bearing granite gneisses are the principally
rocks in the country mapped. The proportion of microcline rises generally towards zones of
fracturing and faulting. The deduction is that a long period of pervation with potassic fluids was
ushered in by fracturing and faulting and affected all permeable rocks. The late-kinematic
granites are dominantly potassic, but they probably include the Biotite-rich albite granite in
Teiwo (GPS 0267353, 0856708). Although the dolerite suite is microclinised and epidotised in
shear zones and fractures, it invariably cuts across the late-kinematic granites and is nowhere
intruded it. The basement gneisses on the other hand are of higher metamorphic grade with
the composition quartz-microcline-hornblende-albite to andesine. They late kinematic granites
57
however are considered to be of lower grade of metamorphism than the basement granites.
They consist of the assembly, quartz, muscovite, hornblende and plagioclase reflects the lower
temperature of late kinematic granites. Below gives a summary of the different metamorphic
conditions from which the metamorphic rocks in the area were formed.
TABLE 5.1 A summary of the different metamorphic conditions from which the metamorphic rocks in the area were formed.
ROCK TYPE TYPE OF
METAMORPHISM
FACIES/ZONES PROTOLITH
Biotite-Granite Medium pressure Greenschist
facies/Biotite
Ortho-protolith
Microcline-Granite Medium pressure Greenschist facies Ortho-protolith
Granite Schist Medium pressure Greenschist facies Ortho protolith
Granite Gneiss Medium pressure Greenschist facies Ortho protolith
Amphibolite Medium pressure Amphibolite facies Basic and
Intermediate
Igneous rocks
Dolerite High Pressure Pyroxene-Hornfel facies Ortho-protolith
Migmatite High Pressure Granulite facies Para/Ortho
protolith
5.3.1 Effects of Metamorphism on the Project Area
In gneisses and granites of the basement complex syntectonic mineral growth of micas,
epidote group minerals and amphibolites is commonly associated with cracking,
straining of earlier minerals. Earlier plagioclase are usually partially to completely
sericitized and some gneiss, orthoclase show partial to complete alteration to
58
microcline, quartz commonly has strain lamellae parallel to the S1 fabric defined by
some other syntectonic minerals.
In gneiss, there is some minor overgrowth by Biotite and muscovite while in amphiboles
there is growth of amphiboles and possibly some small garnet.
59
CHAPTER SIX
THE ECONOMIC AND HYDROGEOLOGIC POTENTIAL OF THE AREA
6.1 THE ECONOMIC GEOLOGY OF THE AREA
Economic Geology in this case simply describes the use of the material that where produced
through geologic processes to the people living around and the country as a whole. Economic
geology is concerned with earth material that can be used for economic and or industrial
purposes. The materials include precious and base metals, non-metallic minerals deposits and
mineral resources. The Techniques employed by other earth science disciplines (such as
Geochemistry, Mineralogy, Geophysics, Petrology and Structural Geology) might all be used to
understand, describe and exploit an ore deposit. Economic geology is studied and practice by
Geologist. However it is of prime interest to investment bankers, stock analysis and other
profession, such as Engineers, Environment scientists, and conservationist because of the far
reaching impact that extractive industries have on society, the Economy and the Environment.
The project area form part of the Greenstone belt, therefore base metals Mineralization such as
Cu, Pb, Au and Fe. They are the Indicator elements of Diamond, Gold, Chromite and
Construction materials. They can be divided into two types in this dissertation.
Mineral deposit and;
Construction materials
6.1.1 Mineral Deposits
A “Mineral deposit” is a mineral occurrence of sufficient size and grades that it might under the
most favorable of circumstance, be considered to have economic potential.
Gold - the Greenstone belt is the host of the general gold mineralization of the country. Low
gold values are fairly general east of the Moa in the rivers draining belts of rocks belonging to
the Granulite group. The values recorded were 48 small colors to the cubic foot of gravel in the
streams rising on the Eastern flank of Tosien Ridge in, the Tunkia chiefdom. One or two specks
of that might be molybdenite was noticed in the rock from the tosien Ridge. Gold was
discovered in several localities in the year 1926, mainly the South-Eastern part of Sierra Leone.
All Greenstone belts in Sierra Leone(with the exception of the marampa Group and perhaps the
60
kambui hills) are known to contains Gold-river and streams draining these area also carry Gold
–rivers and streams draining, these areas also carry Gold. Prospecting activities by the
Geological survey Established, the existence of the Gold in the following localities within the
Granite Greenstone terrain of Sierra Leone.
The Sula mountain area including the lake sonfon, Maranda and yirisen.
The kangari hills area especially, Baomahun, makong and Makele.
The Loko groups schist in the kamakwie, lamanaria area, northern Sierra Leone.
The Gori hills.
Gold deposit in the studied area occurs as alluvial deposit. Only artisanal mining is present in
the area, most miners work river gravel whilst some prefer to trace the alluvial deposit back to
the origin.
Diamond: All known alluvial diamonds digging have been marked on the 1:50000 maps. As
mention in the previous research, indicator minerals like kimberlite type, illmenite has been
recovered in fair quantities. However, kimberlite that is barren or only slightly diamantiferous is
of little use and diamond prospecting and digging ought to be permitted and indeed encourager
throughout the country covered by sheets 99, 100 and 107. Then if payable diamantiferous
gravel were found, search for kimberlite sources could be started. The moro-gbewa gravels
have still to be tested thoroughly. Some diamonds are known to occur in them, for diggers
cleanout the potholes in the river bed annually and wash the gravel so obtained. The Sierra
Leone diamond fields cover an area of 20,000km2(about one quarter of the country) in the
South-Eastern and Eastern parts of Sierra Leone. The actual diamond producing areas are
concentrating in the Kono, Kenema and Bo Districts and are mainly situated in the drainage
area of Sewa, Bafi, mano and moa rivers. The primary host rock of diamond is Kimberlite and
the surrounding country rocks have probably been eroded by at least 1,000m. During this
erosion, diamonds in excess of 50Mcar have been released from the two kimberlites outcrop
areas at Koindu and Tongu and become widely dispersed down the Beri-sewa and moa river
systems and their antecedents throughout most of the cainozoic. Consequently the diamonds,
have been repeatedly sorted, deposited release by renewed erosion of alluvial deposit during
succeeding erosion cycles and then re-deposited. These mechanical processes have
61
concentrated the diamonds in the gravels and improved their quality. Diamonds have travelled
at least 100km in the river systems from their sources. The processes of concentration have
also affected other, resistant minerals particularly corundum, zircon, limonite, rutile, chromite
and tourmaline which have become trapped in depression in the beds of streams in joint,
behind rocks bars and crevices. In most cases the diamondiferous gravel line next to the bed
rock and may be covered by 20m of gravels, silt and clay. Artisanal mining and small scale
mining are widespread in this area. This is evidence by many abandon diamonds pits in the
area. Examples like in Koma Village small artisanal mining activities are taking place (Figure 6.1).
FIGURE 6.1 A local Diamond pit at koma village and the Insitu materials (O253065 / 0845558, Elevation 134m)
The diameter of this site (Figure 6.1) is 15m wide and the overburden is approximately about
4m thick, in which the materials are poorly sorted. Some gravel is well rounded and others are
62
sub-rounded. The color of the gravel is grey as shown in the picture and overburden is reddish
brown.
Chromite: Known chromites, occurrence are confined to the parts of sheet 103 NW and SW to
the west of line connecting Diame (GPS X=0263612, Y=0854727) prolonged Southwards. Except
for the outcrop 1,100yard South of Baraka (GPS X=0253922, Y=0853655) and about 200yards
East of Periwama-Pandebu road, all the chromites is laterised and consists of brown, oxidized
equidimensional chromite grains from 1 to 3mm in diameter, wrapped in chromian mica ,
anthohyllite and talc pseudomorphs after anthophyllite. The occurrence were found originally
by traces spaced 1,500yards apart, so that more closely, traces covering all the country
between the Moa and Diame-Tijoema line and southwards prolongation might disclose more
chromite. However, further prospecting seems quite pointless until the price of chromite rises
substantially.
6.1.2 Construction Material
Construction material is any material, which is used in construction purposes. Many naturally
occurring substances, such as soil (sand and clay) and rocks can be used in construction
purpose.
-Sand is a naturally occurring granular material composed of finely divided rocks and mineral
particles .The composition of sand is highly variable, depending on the local rock sources and
condition, but the most common constituents of sand is silica (SiO2) usually in the form of
quartz, sand as well as clay can be used in the manufacturing of bricks.
-Amphibolite which occur as lenses in the basement is widely use as construction material in
road building (Aggregate) and as railway ballast. Because amphibolites are heavier than
granites, the properties make it desirable for certain uses. Amphibolite is quarried and
construction as a ballast stone in rail road construction. It is also quarried and cut for uses
quarried and cut for dimension stones.
-Granite is an intrusive igneous rock, which form the Granite greenstone terrain. It is generally
strong rocks that make a good foundation for many structures such as dams and large
63
buildings. Blocks of these rocks are often resistant to weathering and used for variety of
construction purpose.
-Gneiss a coarse-grained banded metamorphic rock is usually a hard, tough rock similar in most
respect to granite and suitable for most engineering purpose. The uses of rocks are variable.
They could be used as building facing or as polish or just rough decorative. They could also be
used as protecting blanketing i.e. Embankment to minimize erosion or wave action especially
construction of road cuttings, dams, airport runways and particularly as embankment of soft
materials.
THE IMPORTANCE OF ECONOMIC GEOLOGY
The purpose of studies of the subject is as follows:
1. The subject Economic geology is aimed to provide detailed description of economic
minerals which may be little in numbers. Besides the detailed description of the
minerals, the subject also discusses the proper uses and development of the mineral
deposit. The foremost duty of Economic geologist is to suggest the suitability of the
mineral deposit for a particular industry.
2. The reserve of Economic mineral in a deposit are limited and their percentages are also
variable, which are not replenishable once they are extracted fully from the deposit,
their reserves are also exhausted forever. This fact require to borne in mine while
mining a deposit. A wise Economic geologist prepares a plan of mineral deposit for the
proper utilization before its extraction
6.2 HYDROGEOLOGIC POTENTIAL OF THE AREA
Hydrogeology (Hydro-meaning water and Geology-meaning the study of the Earth) is an area of
geology that deals with the distribution and movement of groundwater in the soil and rocks of
the Earth’s crust. When we wish to find a reliable supply of ground water, we search for an
aquifer-any geological material, rock or soil that is sufficiently permeable to yield significant
amount of water to pumping well is called an aquifer.
64
6.2.1 Access to the Groundwater
The project area is characterized by one major river which is the moa river and number of
streams and streamlets. The presence of the river and stream in the area are clear
manifestation of the groundwater systems. The groundwater is recharged during the rainy
season when it rains the water infiltrate into the soil and recharged the aquifer, the surface
runoff goes into streams and rivers. During the raining season, the project area overflows their
banks due to increase in water level. Water is the most essential mineral used for both primary
and secondary consumption majority of the people in the project area fetch drinking water
from those sources, others used water by settlers in the area are for agricultural, livestock,
natural resources development and other domestic purposes. About 50% of the villages in the
area have hand dug wells with hand pumps, like in a village called Tikonko Gaura the people are
using reservoir(where the water is recharged ) which has a series of connected pipes to supply
water for consumption as shown in the picture below.
FIGURE 6.2 A Reservoir at Tikonka Gaura Chiefdom (0263839 / 085O130 Elevation-142m)
The wells areas are maintained to prevent the water from pollution and keep it pure to drink.
The well are dug in order to ease the water erosion during the dry season , as major river get
dry or reduce in volume in a way that one gain easy access across the rivers. This main river is
65
polluted by various activities, fishing and also from the runoff. The main river is polluted by
various activities fishing and also from the runoff the encountered the weathered laterites and
plenty dust from the quarry, since there is no major mining of gold is present in the studied
area. This mean there is a low possibility of arsenic poisoning (arsenic is a pathfinder for gold).
In contracts, groundwater is the main source of drinking water in the project area. However,
fractures that occur in these rocks can allow water movement .The amount of water movement
through fractured rocks depends on the frequency and interconnectedness of the fracture.
6.2.2 Impact of the Rocks to Ground Water Quality Assessment
Groundwater can dissolve very harmful elements from rocks it follow through making the
water unsuitable for consumption water circulating through sulfur rich rocks many contain
dissolve hydrogen sulphide (H2S) that, though harmless to drink ,has disagreeable order of
rotten eggs.
6.2.3 Geologic Activity of Groundwater
As soon as rainwater reaches the Earth’s surface, it begins to react with minerals in regolith and
bedrock and weather then chemically. An important part of chemical weathering involves
minerals and rocks materials directly into solution through dissolution and hydrolysis. The
conversion of sediment into sedimentary rock is primarily the work of groundwater substance
in solution is precipitated as cement in the spaces between rock and mineral particles of the
sediment. This digenetic process transforms the loose sediment into minerals like calcite quartz
and Iron compound are the chief cementing substances.
66
CHAPTER SEVEN
CONCLUSION AND RECOMMENDATIONS
7.1 CONCLUSION
A Geological mapping was done on Sheet 103, Joru. Geological mapping is the process of
selecting an area and identifying all the geological aspects of that with the purpose of preparing
a detail report which include map units is that it can be idenfiable by the presence or absence
of characteristic and thus distinct from map unit chosen. During this process one geological
terrain was investigated in Archean rocks are the oldest rock unit in the Area (See stratigraphic
column in chapter 3). The Archean was approximated as > 2900 million years old. The Basement
complex comprises of the rocks of the Kenema Assemblage (Andrew-Jones, 1966) occupies the
greater part of Eastern Sierra Leone. The earliest recognizable orogeny in Sierra Leone is that
which involved the Kambui geosynclinals series forming the Precambrian Kenema assemblage.
This kambui orogeny has been dated at 2900m.y. and may correspond to the Dahomeyan
elsewhere in West Africa. It is metamorphic plutonic assemblage and includes Geosynclinal
Sequence known as the kambui group, which was deposited upon an ancient and the
geosynclinals sediment were invaded and modified by granite rocks, associated with
subsequent orogenic movements. These have obliterated the structure of the ancient
basement so the original crystalline rocks are no longer recognizable, which means they were
transforming by heat, and pressure and chemical reactions from older rocks into their present
form. The greater part of the project area composed of complex intimately associated granite,
migmatite and gneiss. All these rocks are loosely granitic in composition and assumed to have
formed by granitization of the kambui geosynclines. Structurally, it was observed that the late
kinematic granites underlie the greenstone supracrustal and the intrusive rocks. The strikes
veers from due north at the northern edge of sheet 103NE to North northeast at the western
edge of sheet 107SW. The area has an average dip angle above 45˚. The general foliation trend
in this region is Northeast direction and majority of the rocks are trending in the same direction
of the foliation. The presence of macrostructures (fold, fault, vein etc) and micro structures
(e.g. foliation, schistossity, Gneissosity) all are indications of deformation in the rocks of the
project area. The Liberian and Leonean episode is responsible for the present structure of the
area. Mountains were forming these rocks and great forces from below uplift them. Hot molten
67
Magma have injected into the rocks forming granitic rocks. The rocks are then uplifted and
exposed to surface by the tectonic process and erosion. This tectonic event pushed the rocks
well above the land surface and exposed them to the surface to weathering. As the mountains
were uplifted, swiftly forming stream carried floods of debris downward to the plain. Hot
magma invaded the older rocks of the mountains, and the forces of the mountain building
process cause the rocks to deform (Probably the Liberian and Leonean thermotectonic events).
This deformation event results to the faulting, fracturing and folding in the area. Deposited of
metallic ores where precipitated as hot mineralizing water flowed from the magma is well
mineralizing from both constructional material and mineral deposits. Active mountain building
continued after the deformation until it attained its lowest and highest level as seen today.
Observations from some artisanal pit plans provide evidences of the nature of mineralization in
the project area. Most of the structures (vein, fault and vein) have relation with mineralization
such as gold, hence the economic geology of the area. Therefore, if properly control, the
economic potential of the area is extremely promising.
7.2 RECOMMENDATIONS
Based on my experience throughout this field mapping exercise I thereby, summit the following
Most of the geological structures have been distorted, destroyed and completely erase
by human activities. Many of the outcrops at low elevation (valley), local burning
influenced deforestation. This leaves the land bare and prone to erosion; this eroded
material will move to the valleys and cover the outcrops. It is relevant and timely for the
university to advice the government on ensuring the protection of the rocks/outcrops.
A sophisticated detail mapping to be shall carried out in the areas that would be able to
enlighten students before going to the field, which will include not only geological
mapping but also geophysics and geochemical techniques.
As this year`s geological mapping was done during the rains from July-September
because of the late re-opening of college, as a result of the deadly ebola outbreak. Most
of the outcrops are cover with water and I recommend that field mapping must be
carried out during the dry seasons.
68
The Geology department is lack with equipment like rock cutter machine, sophisticated
microscope, XRF (X-Ray fluorescent) and enough textbooks that will enable students to
provide detail information on the samples collected from the field. It is still relevant and
timely for the university and the Government to work in collaboration to help provide
the appropriate materials.
Lastly, Geology is more of field works not theory and I therefore recommend the
department should be in good terms with the mining companies so that the students
would be able to gain vast knowledge of experience during their internship trainings.
69
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Andrew-Jones, D.A “Geology and mineral resources of the northern kambui schist belt”,
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Hawkes, D.D . “Order of abundant crystals Nucleation in Natural Magma”. Geol.Mag.Lond;
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