Title Page i
Approval Page ii
Dedication iii
Acknowledgments iv
Abstract v
Table of Contents vi
List of Tables x
List of Figures xi
List of Plates xii
List of Appendices xiii
List of Abbreviations xiv
1.1 Background to Study 1
1.2 Statement of Problem 3
1.3 Aim and Objectives of the Study 3
1.4 Scope of Study 4
1.5 Significance of the Study 4
1.6 Location and Accessibility 5
1.6.1 Location of study area 5
1.6.2 Accessibility to study area 5
1.7 Climate and Vegetation 7
1.8 Relief and Drainage 10

2.1 History Mining in the Study Area 12
2.1.1 Existing Genetic Models on the Nigerian Lead-Zinc Field 14
2.1.2 Mineralogy of the Benue Trough Deposits 16
2.1.3 Geologic Structure of the Host Rocks 18
2.3 Regional Tectonic and Structural Setting 19
2.2 Regional Stratigraphic Setting of Ishiagu Area 24
2.4 Geology of the Ishiagu Area 27
2.4.1 Shale Unit. 27
2.4.1 The Intrusive: 28
2.5 Concept and Theories of Stable Isotope Geochemistry 29
2.5.1 The Principles of Stable Isotopes and Ore Genesis 30

3.1 Materials 40
3.1.1 Field Work Material s 40
3.1.2 Laboratory Materials 40
3.2 Methods of Study 40
3.2.1 Field Method 40
3.2.1.a Geological Field Work 40
3.2.1.b Sample Collection 41

3.2.2 Laboratory Studies 42
3.2.3 The Working Principles of the Analytical Methods 43
3.2.4 Sample Preparation for Isotope Studies 44
3.2.5 Sample Preparation for XRF Analysis 45
3.3 Laboratory Analysis 45
3.3.1 Sulphur Isotope Analysis 45
3.3.2 Oxygen and Carbon Isotope Analysis 45
3.3.3 XRF Analysis 46

3.4 Data Analysis 46
3.4.1 Geochemical Plots 46
3.4.2 Isotope Data Analysis 47
3.4.2a Sources of the Hydrothermal Fluid 47
3.5.2b Formation Temperature of the deposit 47
3.5.2c Level of Equilibrium Attained by the Deposit 48

4.1 Field Results 49
4.1.1 The Geology of the Area 49

4.1.2 Geologic Structure 54 51
4.2 Geology of the Deposits 52
4.3 Geochemical Analysis Results. 59

4.3.1 Intrusive Rocks 59
4.4 Results of Isotope Studies 61
4.4.1 Sulphur Isotope 61
4.4.2 Carbon and Oxygen Isotope 63
4.5 Discussion of Results 64
4.5.1 The basic – ultrabasic Igneous Rock 64
4.5.2 The Sources of Sulphur in the Hydrothermal Fluid 67
4.5.3 The Source of Oxygen in the Hydrothermal Fluid 73
4.5.4 The Source of Carbon in the Hydrothermal Fluid 76
4.5.5 The Effect of the Immediate Host Rock on the Source of the Ore Fluid. 80
4.5.6 Conditions of Formation of the Hydrothermal Deposit 81 Condition of the Ore forming fluid. 81 The Close Nature of the Hydrothermal System of the deposit 83 Temperature of Formation of the Deposit 84 Fractionation between the Mineral Pairs. 86 Isotopic Equilibrium Nature of the Deposit 89
4.6 Genetic Model for the Ishiagu Lead Zinc Deposit. 92

5.1 Summary 95
5.2 Conclusion 97

5.3 Contributions to Knowledge 98
5.4 Recommendations 99
2.1: Stratigraphic framework for early Cretaceous-Tertiary
strata in southeastern Nigeria (modified from Nwajide, 2013) 27
3.1 Lists of ore samples for isotope studies 42
3.2 Rock samples collected for geochemical analysis 42
4.1 Major element content in weight percent of the carbonate from the study
area 51
4.2 Major element content of intrusive rocks from the study area 60
4.3 Sulphur isotope partition function and compositional ratios of the
samples 62
4.4 Oxygen and carbon isotope compositional ratios of the siderite 63
4.5. The computed temperature of formation of the sulphide mineral of the

study area using equation 2.12 70

4.6 Results of the sulphur isotope compositional ratios of the deposits of the
Benue Trough as compared to that of this study (in 0 / 00 ) 72

4.7 Results of oxygen isotope compositional ratios of the deposits of the

Benue Trough as compared to this study (in 0/00) 76

4.8 Results of the carbon isotope compositional ratios of the deposits
Of the Benue Trough as compared to that of this study
(in 0/00) 80

4.9. The estimated fractionation factor and temperature of the sulphide

mineral pairs from the study area 85


1.1: Location and accessibility map of the study area 6
1.2 Map of Nigeria showing the vegetation belts 9
1.3: Drainage map of the study area 11
2.1 Geologic map of the Benue Trough Showing the Lead-Zinc Deposit 13
2.2 Tectonic map of southeastern Nigeria from Albian to Eocene
(modified from Murat, 1972) 20
2.3: Structural map of Southeast Nigeria showing folds and faults around
the study area (adapted from Reyment, 1965) 23
2.4 Stratigraphic map of South East Nigeria 26
4.1 Geologic map of the study area 50
4.2: Rose diagram of the faults and Joints in the study area 52
4.3 Total alkali versus silica diagram (after Cox et al.,1979) 65
4.4: Total alkali versus silica (TAS) (after Kuno, 1968) 66
4.5 Natural Sulphur Isotope Reservoir (adapted from Hoefs, 1973) 69
4.6 Natural Oxygen Isotope Reservoir (adapted from Hoefs, 1973) 75
4.7 Natural Carbon Isotope Reservoir (adapted from Hoefs,1973) 78
4.8 The plot of fractionation factor against temperature of formation of the
sphalerite – galena mineral pair in the study area 89
4.9 Equilibrium nature of the deposit of the study area to that of
different deposits of the world. (modified from Barnes, 1967) 90

4.10 Proposed genetic model of Ishiagu deposit 94 LIST OF PLATES
1.1 Typical Vegetation of the Area 9
4.1 Greenfield Mine 2 showing the ore vein and the host rock 54
4.2 Greenfield Mine 4 showing the mined Lead- Zinc vein in the intrusive 55
4.3 Picture showing the mine pit geometry of RSP mine 57
4.4 Picture showing the oxidized ore zone overlying the primary ore. The supergene
ore lode is flanked by islands of shale rocks and disseminated ore. 58
4.5 Picture showing the bluish grey unbaked shale host of the Palladium deposit 58 LIST
i Derivation of the formula for the calculation of the fractionation factor and temperature of
formation from isotope mineral pairs ii Computation for the temperature of the mineral pairs
from the study area using the formula LIST OF ABREVIATIONS

∆ Change
0/00 Per mil
32 S Lighter sulphur Isotope
34 S Heavier sulphur Isotope
34 S/ 32 S Sulphur Isotope partition function
ATMN Amalgamated Tin Mines of Nigeria
BMS Base Metal Sulphide
C Carbon
CaO Calcium oxide
CI China Intrusive
Cu Copper

E East
Eq Equation
Fe Iron
G Gabbro
GF2 Greenfield Mine 2
GF3 Greenfield Mine 3
GF4 Greenfield mine 4
GFI Greenfield Mine 1
GI Greenfield Intrusive
H Hydrogen
H 2 S Hydrogen sulphide
I Ijolite
Km Kilometers
Ln Mathematical log
Mn Manganese
MVT Mississippi Valley Type
N North
NaCl Sodium chloride
NGSA Nigeria Geological Survey Agency
O Oxygen
o C Degree centigrade
OH Hydroxyl

Pb Lead
Pbs Galena
Ppm Parts per million
RSP Palladium Mine
S Sulphur
S 1 South
Sd Syenodiorite
SiO 2 Silica
SO 2 Sulphate
T Temperature
TA Total Alkalis


Temperature of

VLF-EM Very Low Frequency Electromagnetic
W West
Wt % Weight Percent
XRF X-ray Fluorescent
Zn Zinc
Zns Sphalerite
ZPE Zero Point Energy
α fractionation faction
δ Isotope compositional ratio


1.1 Background to Study
One of the main agenda of the current political administration is the diversification of the
crude oil monopolized economy into solid mineral development. Nigeria is endowed with vast
and varied solid mineral resources among which are galena and sphalerite. Mineral deposits
are complex in nature and no two mineral deposits are alike (Jensen and Bateman, 1979). The
galena-sphalerite (lead-zinc) mineralogical province of Nigeria stretches across the Benue
Trough with the deposit in each part of the trough exhibiting a slight difference in the
mineralogy of the ore and the gangue (Olade,1976 ; Okezie, 1965). The Ishiagu lead-zinc
deposits are located at the southwestern extreme of the trough. The mineralization is
hydrothermal in nature and hydrothermal deposits are known for their limited range of
minerals, mostly sulphides. (Rose and Hawles, 1979).

The Benue Trough mineralization province therefore affords a good opportunity to examine
the detailed characteristics of one of the lead-zinc districts in order to establish its specific
origin. The slight variability in habitat noted among the deposits of the Benue Trough may
have accounted for the difference in the mineralogy of the ore and gangue. The ore-hosting
sediments of the Benue Trough range from deep marine carbonaceous shale in the Southern
Benue Trough to platform carbonate in the Central Benue Trough and fluvial to deltaic
sandstone in the Northern Benue Trough (Akande, 1992). The close proximity of

Ishiagu deposits to some intermediate-basic intrusives more than the other deposits of the
Benue Trough, should not be overlooked. There is also remarkable difference in the barite
content of the Benue Trough deposits from the southwest (Ishiagu district) to northeast (Gabu
district) of the Trough (Oha, 2017). Establishing the specific origin and conditions of

formation of these deposits is therefore paramount for its characterization and may give an
answer to differences mineralogy between the deposits.

Some variants of genetic theories of the deposits have been propounded using trace elements
and fluid inclusions (Olade & Morton, 1985: Akande, 1988). Stable isotopic studies
have been used on some of the Benue Trough deposits but has not been applied for lead-zinc
deposits in Ishiagu. Microthermometry was in some cases used to specifically determine the
range of temperatures ( Olade and Morton, 1985 ; Akande et. al., 1988; Christopher and
Baldassare, 2014). However, it is a well known fact that temperatures estimated from fluid
inclusions can be affected by pressure variability (Barnes, 1979). Hydrothermal deposits are
group of deposits which have been investigated and mined far more than any other group and
have given rise to many of the great mining districts of the world (Jensen and Bateman, 1979).
They are formed when aqueous fluids move through a defined channel and precipitate under
favorable conditions to form ore deposits. Hydrothermal fluid can take its source from
connate, metamorphic, meteoric and magmatic waters. Though all aqueous solutions are
brines of some sort, they vary in their stable isotopic composition which is a function of the
different sources of the fluid as well as the conditions of formation of the deposits.
Hydrothermal fluids also vary in their major and minor elemental compositions and
concentrations and this variance has led to the formation of hydrothermal deposits of different
mineralogy (Rose and Hawles,1979; Jackson,1979).

This study therefore primarily used stable isotopes to generate a detailed scientific-based
genetic model for the Ishiagu Lead-Zinc deposits .The study also looked at the use of an
alternative method in estimating the temperatures of formation of each of the deposits. The
information got can be harnessed, documented and used for search for more Lead-Zinc

1.2 Statement of Problem
The genesis and conditions of formation of the Ishiagu Lead-Zinc deposit has not been
properly defined as there are still some controversies trailing the origin of the ore deposit.
Establishing the genesis of a deposit is paramount for its characterization. The higher
concentration of intermediate – basic intrusives in the Ishiagu area more than other parts of
the Benue Trough may have some effect on the origin of Ishiagu deposit. Akande et.
al.,(1992) suggested that the ore hosting shales in the Southern Benue are slightly more
metamorphosed than that of the Middle Benue Trough. Many scholars have studied the
genesis of the lead-zinc deposit of Ishiagu but on a regional scale (Central and Southern

Benue Trough) (Tattam,1944 ; Mc-Connel, 1949; Bogue & Renold, 1952; Farrington, 1952;
Olade and Morton, 1985; Wright, 1985 ; Akande et. al., 1988). There is therefore need for
more detailed study using stable isotope compositions of the deposit. The temperatures of
formation of the deposits need to be addressed using a different method (isotope
geothermometry). Better understanding of the spatial/trend of isotope distribution and the
physico- chemical conditions of ore deposition within a metallogenic belt is also important for
proper characterization of the ore deposit (Krauskopf, 1967).

1.3 Aim and Objectives
The aim of this study is to re-appraise the genesis of the Ishiagu Lead-Zinc deposit of the
Southern Benue Trough. The objectives are to:

Carry out geological mapping of the study area
Carry out a geochemical study of the intrusives and ore deposit.
Carry out sulphur, oxygen and carbon isotope studies on the ore

Establish the source and conditions of formation of the ore deposit and
Create a genetic model for the Ishiagu deposits
1.4 Scope of Study
The scope of this work includes:
Geologic mapping of the Ishiagu Lead-Zinc Sub-district Southern Benue Trough
Geochemistry of the intrusive rocks.
Establishing the source of the ore fluid using sulphur, oxygen and carbon isotope studies.
Computing the temperature of formation of the deposit using isotope geothermometry.

Use of equilibrium curve to establish the level of isotopic equilibrium attained during the
formation of the deposit.
Establishing the effect of the direct host to the deposits using stable isotopes.
Proposing a genetic model for the formation of Ishiagu deposit.

1.5 Significance of the Study
This present work is important considering the fact that:

The deposit is worth studying as hydrothermal deposits have given rise to many of the great
mining district of the world and their ores are of good grade.

The understanding of the source and other genetic parameters of the deposit can be of
assistance in the development of effective exploration model and thus enable finding of more
deposits in the Benue Trough.

The study will also help to widen the already existing academic knowledge on not only the
source of the lead-zinc mineralization but also the temperature and conditions of formation
This research will contribute in the development of the solid minerals industry in Nigeria by
motivating investments in the industry and creating jobs for the youth by finding more
deposits in the area.
1.6 Location and Accessibility of Study Area
1.6.1 Location of Study Area
The study area lies between latitudes 5 0 54 1 00 11 N and 5 0 57 1 00 11 N and longitudes 7 0 28 1 00 11
and 7 0 32 1 00 11 E (Fig. 1.1 ). The lead – zinc mines are located precisely in Ihetutu village of
Ishiagu town, Ivo Local Government Area of Ebonyi State, Southeast Nigeria. The study area
covers approximately 48 square kilometers.