GEO-ELECTRICAL RESISTIVITY INVESTIGATION OF MINERAL ...

GEO-ELECTRICAL RESISTIVITY INVESTIGATION OF MINERAL BEARING

ROCKS IN RONGO GOLD MINING AREA IN MIGORI COUNTY

OMBATI DENNIS [B. Ed Science (HONS)]

I56/CE/23417/2012

KENYATTA UNIVERSITY

DEPARTMENT OF PHYSICS

A thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree

of Master of Science (Physics) in the School of Pure and Applied Sciences of

Kenyatta University

JULY, 2018

ii

DECLARATION

This thesis is my original work and has not been presented for the award of a degree at any other

university.

Ombati Dennis [B. Ed (Sc.)] Signature…… ………………….Date …………………….

(I56/CE/23417/2012)

Department of Physics

Kenyatta University

P. O. Box 43844

Nairobi, KENYA

This Thesis has been submitted with our approval as University Supervisors.

Dr. Willis. J. Ambusso Signature…… ………………….Date …………………….


Kenyatta University

P. O. Box 43844

Nairobi, KENYA

Dr. John. G. Githiri Signature…… ………………….Date ……………………….


Jomo Kenyatta University of Agriculture and Technology

P.O BOX 62000-00200

Nairobi, KENYA

iii

DEDICATION

This thesis is dedicated to my wife and children, my mother and sisters the ESWA fraternity and

Ekioga Seventh Day Adventist Church members.

iv

ACKNOWLEDGEMENTS

I take this solemn opportunity to thank our Almighty God for His rich grace to have guided me

in this study thus far. I register my appreciation to Dr. Ambusso Willis for his keen and focused

guidance in the development of this work. As my first supervisor, he has been my constant

source of motivation, direction and encouragement.

I also wish to register my heartfelt gratitude to my second supervisor, Dr. John Githiri, for his

attitude and devotion in this study. He has been available all time, very understanding and

generous in advice giving. I wish to also appreciate all the lecturers who have participated during

my seminar presentations at the department of physics.

Finally, I thank all my friends, including Mr. Hezekiah Komen Cherop and Charles Mogunde for

their readiness when I needed consultation. I once again glorify God for all who had a positive

contribution in this study.

Any discrepancies, inconsistencies, inaccuracies in this study remain my sole responsibility.

v

TABLE OF CONTENTS

DECLARATION........................................................................................................................... ii

DEDICATION.............................................................................................................................. iii

ACKNOWLEDGEMENTS ........................................................................................................ iv

TABLE OF CONTENTS ............................................................................................................. v

LIST OF FIGURES ................................................................................................................... viii

LIST OF TABLES ........................................................................................................................ x

ABBREVIATIONS, SYMBOLS AND ACRONYMS .............................................................. xi

ABSTRACT ................................................................................................................................. xii

CHAPTER ONE: INTRODUCTION ......................................................................................... 1

1.1 Background to the study ........................................................................................................... 1

1.2 Regional geological setting ....................................................................................................... 2

1.3 Statement of research problem .................................................................................................. 3

1.4 Objectives ................................................................................................................................. 4

1.4.1 General objective ................................................................................................................... 4

1.4.2 Specific objectives ................................................................................................................. 4

1.5 Rationale of the study ............................................................................................................... 4

CHAPTER TWO: LITERATURE REVIEW ............................................................................ 6

2.1 Gold ore deposits ...................................................................................................................... 6

2.2 Mineral exploration ................................................................................................................... 9

2.3 Mineral exploration techniques............................................................................................... 10

2.4 Related studies in the area ....................................................................................................... 11

vi

CHAPTER THREE: THEORY OF RESISTIVITY METHOD ............................................ 13

3.1 Resistivity method .................................................................................................................. 13

3.2 Electrode Configurations ........................................................................................................ 16

3.2.1 General array ........................................................................................................................ 16

3.2.2 Wenner configuration .......................................................................................................... 17

3.2.3 Schlumberger configuration ................................................................................................. 18

3.3 Rock Resistivity ...................................................................................................................... 19

3.4 Current flow in the ground ...................................................................................................... 20

CHAPTER FOUR: MATERIALS AND METHODS ............................................................. 22

4.1 Introduction ............................................................................................................................. 22

4.2 The Measuring Instruments .................................................................................................... 23

4.2.1 Terrameter ............................................................................................................................ 23

4.2.2 Global positioning system (GPS)......................................................................................... 24

4.3 Resistivity data processing ...................................................................................................... 24

4.4 Curve Matching ...................................................................................................................... 25

4.5 Characteristic Wenner HEP curves ......................................................................................... 27

4.6 Introduction to IP2 Win Software and partial curve matching ............................................... 29

CHAPTER FIVE: RESULTS AND DISCUSSION ................................................................. 30

5.1 Qualitative Interpretation ........................................................................................................ 30

5.1.1 Contour Map ........................................................................................................................ 30

5.1.2 Log-Log plots....................................................................................................................... 31

5.1.3 Wenner HEP Curves using IP2Win Software ..................................................................... 35

vii

5.2 Discussion and Results ........................................................................................................... 40

5.2.1 IP2WIN Curve Fitting.......................................................................................................... 40

5.2.2 Pseudo cross-sections models .............................................................................................. 47

5.2.3 Ore Potential Primers ........................................................................................................... 51

5.2.4 Area Lithology ..................................................................................................................... 55

CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS ...................................... 57

6.1 Conclusion .............................................................................................................................. 57

6.2 Recommendations ................................................................................................................... 58

REFERENCES ............................................................................................................................ 59

APPENDIX I: MAP OF OYUGIS SHOWING KAMWANGO ............................................. 62

APPENDIX II: WENNER CONFIGURATION MAP ........................................................... 63

APPENDIX III:WENNER AND VES CONFIGURATION MAP ........................................ 64

APPENDIXIV: WENNER READINGS ................................................................................... 65

APPENDIX V: CONTOUR MAP SHOWING WENNER STATIONS AND

SCHLUMBERGER TRANSECTS ........................................................................................... 66

APPENDIX VI: SCHLUMBERGER EXCEL (VES 1-VES 8) .............................................. 67

APPENDIXVII: SCHLUMBERGER IP2WIN CURVES: ..................................................... 71

APPENDIX VIII: VES LAYERING ......................................................................................... 75

APPENDIX IX: SCHLUMBERGER SOUNDING FOR 8 STATIONS. .............................. 77

APPENDIX XI: FIELD PHOTOS ............................................................................................ 78

APPENDIX XII: TABLE OF RESISTIVITY AND CONDUCTIVITY OF MATERIALS 79

APPENDIX XIII: BORE HOLE LOGS IN THE VICINITY ................................................ 80

viii

LIST OF FIGURES

Figure 1.1: Geological map of Kenya locating Kamwango area of Rongo, Migori County. ......... 3

Figure 2.1: Placer deposits formed by the weathering of hard rock ............................................... 8

Figure 3.1: General electrode Configuration (Sultan, 2010) ........................................................ 16

Figure 3.2: Wenner Array and formula for calculating apparent resistivity ................................. 17

Figure 3.3: Schlumberger Array and formula for calculating apparent resistivity ...................... 18

Figure 3.4: Resistivity value ranges for various earth materials ................................................... 19

Figure 4.3 The Measuring Instruments ......................................................................................... 23

Figure 4.3: HEP curves type-H, A, K and Q (Courtesy of http://faculty.ksu.edu.sa) ................... 28

Figure 5.1: A contour map showing profiles for wenner and transects for schlumberger. ........... 30

Figure 5.2 a:VES1 Log-Log plot along transect T1 ..................................................................... 31

Figure 5.2 b: VES 2 Log-Log plot along transect T1 .................................................................. 32

Figure 5.2 c: VES 3 Log-Log plot along transect T2 ................................................................... 32

Figure 5.2 d: VES 4 Log-Log plot along transect T2 ................................................................... 33

Figure 5.2 e: VES 5 Log-Log plot along transect T3 ................................................................... 33

Figure 5.2 f: VES 6 Log-Log plot along transect T3 .................................................................... 34

Figure 5.2 g: VES 7 Log-Log plot along transect T4 ................................................................... 34

Figure 5.2 h: VES 8 Log-Log plot along transect T4 ................................................................... 35

Figure 5.3 A: A combination of both H type and A type. ............................................................ 36

Figure 5.3 B: An A type curve ...................................................................................................... 37

Figure 5.3 C: A combination of Q type and H type ...................................................................... 37

Figure 5.3 D: A combination of H type and A type of curve ....................................................... 38

Figure 5.3 E: H type and Atype .................................................................................................... 38

ix

Figure 5.3 F: K type and H type ................................................................................................... 39

Figure 5.3 G: K type and Atype ................................................................................................... 39

Figure 5.4 a: VES 1curve matching (RMS=7.36%re ................................................................... 42

Figure 5.4 b: VES 2 curve matching (RMS=6.8% ...................................................................... 43

Figure 5.4 c: VES 3 curve matching (RMS=4.21%) .................................................................... 43

Figure 5.4 d: VES 4 curve matching (RMS=4.83%) .................................................................... 44

Figure 5.4 e: VES 5 curve matching (RMS=4.99%)30 ................................................................ 44

Figure 5.4 f: VES6 curve matching (RMS=6.51%) ...................................................................... 45

Figure 5.4 g: VES7 curve matching (RMS=4.42%) ..................................................................... 45

Figure 5.4 h: VES8 curve matching (RMS=5.96%) ..................................................................... 46

Figure 5.5: Pseudo cross-section spatial layer distribution for all VES 1-8 ................................. 48

Figure 5.5 a: Pseudo cross-section spatial layer distribution between VES 1 and VES 4. ........... 48

Figure 5.5 b: Pseudo cross-section spatial layer distribution between VES 2 and VES 3. .......... 49

Figure 5.5 c: Pseudo cross-section showing spatial layer distribution between VES 5 and VES 7.

....................................................................................................................................................... 49

Figure 5.5 d: Pseudo cross-section spatial layer distribution between VES 6 and VES 8. .......... 50

Figure 5.5 e: Pseudo cross-section spatial layer distribution between VES1 and VES2 .............. 50

Figure 5.5 f: Pseudo cross-section spatial layer distribution between VES 4 and VES 55 .......... 51

x

LIST OF TABLES

Table 5.1: Summary of layer thickness with corresponding resistivity for the VES stations ...... 46

Table 5.2: Layer Lithology ........................................................................................................... 54

Table 5.3: Layer Lithology of bore hole for VES 2 about 4 km from the study area ................... 54

Table 5.4: Kamwango drill results (adopted from www.stockportexploration.com) .................... 55

xi

ABBREVIATIONS, SYMBOLS AND ACRONYMS

ρa Apparent resistivity(Ωm)

σ Conductivity (Ωm)-1

J Current density (A/M2)

E Electric field vector

V Electric potential

G Geometrical factor

GPS Global Positioning System

HEP Horizontal electrical profiling

ρ Resistivity measured in (Ωm)

S.A.S

Signal Averaging System

The constant of configuration / array constant

VES Vertical electrical sounding

xii

ABSTRACT

Rongo Gold field forms part of the Lake Victoria greenstone belt and is a highly prospective

area. However, it has to date been underexplored due to overburden which obscure the

mineralized zones beneath. An electrical resistivity survey was used to detect gold bearing rocks

and dense bodies of rocks within host formation in Kamwango area of Rongo district, Migori

County. To achieve this, a terrameter (ABEM SAS 1000) was used to determine apparent

resistivities using Wenner and Schlumberger configurations. For good vertical resolution,

Wenner array was employed to map horizontal structures where a total of 30 stations were done

with a probe depth of 45m. Values from Wenner array were used to plot a contour map using

Surfer 10 software. The eastern central part of the study area (40km2) is a region of low

resistivity as seen from the contour map. Sounding was done on this region of low resistivity

along transects using Schlumberger array where a total of 8 stations were sounded as identified

from the contour map. IP2WIN software was used to process and model the apparent resistivity

values to get true resistivity values. Soundings done on this region gave an average basement

depth of 21.86m and a steady rise depth of 32.68m which indicate the depth at which the country

rock was hit. High resistivity values indicate the compact volcanic Nyanzian system rocks that

are porphyritic, andesites and dacites. The values go up to 1000 Ωm in some parts of the study

and the depth is in the range between 40m and 130m. Depths with low resistivity are composed

of the highly fractured volcanics with resistivity as low as 13Ωm. The subsurface and the

weathered section also have low values due to presence of groundwater. The conductive zones

give resistivity values that correspond to mineral ores that bear gold and related minerals.

1

CHAPTER ONE

INTRODUCTION

1.1 Background to the study

Kamwango area of Rongo is 380 km west of the city of Nairobi in Kenya. It forms

part of the Lake Victoria greenstone belt which is endowed with gold deposits. This

area which is 60km to the north of the Tanzanian border covers Archaean age

metavolcanics and granites where records of gold production within the Nyanzian

system are historically known (Ogola, 1995). The gold mineralization in the area

occurs in quartz veins and in massive sulphide impregnations (Shackleton, 1946).

Artisanal mining is presently active on the Kamwango area. Gold mining has been

done in cross-cutting quartz veins, banded iron formation; strata bound horizons in

tuffs and alluvial deposits, with the main mines located at Macalder, Masara and

Kehancha (Shackleton, 1946).

Because of the stability of gold over a wide range of conditions, it is very widely

spread in the earth‟s crust. Rich gold ore deposits are concentrated throughout the

world though its overall concentration is very low (about 5 milligrams per tonne of

rock). The well-known saying amongst prospectors that “gold is where you find it”

suggests its occurrence is unpredictable, but it is now known that certain geological

environments favour gold‟s formation (Hill, 2006). The association of gold with

quartz forms one of the most common types of “primary gold types”. Veins and reefs

of quartz that bear gold can occur in many types of rock, for example, around granitic

rocks , volcanic rocks and in regions of black slate, but quite often these host rocks

are not the immediate source of gold (Ralph, 2003).

2

This study endeavored to employ resistivity in the geophysical investigation. The

approach consisted in collecting apparent resistivity data using Schlumberger and

Wenner. The interpretation of electrical soundings gives geological sections that

correlate the resistivity data and the geological background of the studied area (Loke,

1999).

1.2 Regional geological setting

The knowledge of the geological setting of the area will make the application of

resistivity method a success. Since interpretation of apparent resistivity can be

challenging because of the overlapping apparent resistivity values, understanding the

geology can guide in setting up restraints to help in the challenge of non-uniqueness

(Loke, 1999). The area is covered by volcano-sedimentary sequences and intrusive

rocks of the Migori greenstone belt which is part of the Archaean Tanzanian craton.

Gold is hosted in quartz veins and is associated with massive sulphides like pyrrhotite,

pyrite, chalcopyrite, and galena. (Ralph, 2003).

According to Shackleton (1946), intrusive granites have played an important role in

the mineralization of the south Nyanza gold field. The largest of these granites,

extending from Lake Victoria to the Isuria escarpment, is in contact with Nyanzian

rocks (banded ironstones and concentrations of basic rocks) along the entire length of

the gold field‟s southern boundary, and has mineralized a tract of Nyanzian rocks up

to three miles in width known as the Migori gold belt. Mineralization is not confined

to anyone particular rock type but certain bands are more susceptible to it, notably

shales and banded ironstones.

3

The figure 1.1 below shows the map indicating the study area which is magnified

alongside and bounded by the coordinates 675000-683000 Easting (m) and 9918000-

9928000 Northing (m).

Figure 1Figure 1.1: Geological map of Kenya locating Kamwango area of Rongo, Migori

County. (www.epgeology.com)

1.3 Statement of research problem

Despite the fact that large stocks of gold are stored deep in the underground bunkers,

to date the eagerness to search for gold is as ever before. While the Rongo gold field

has the potential to host major gold and related mineral deposits on the Lake Victoria

greenstone belt, it has not been fully explored to date as a result of overburden which

largely obscure the zones of mineralization underneath. However, artisanal mining

activity is presently happening in most parts of the Kamwango area. Local miners

have relied on „trial and error‟ to locate the ores bearing gold and associated minerals,

most of them exposing themselves to heavy metal poisoning during processing using

mercury (appendix XI). This implies that gold and other minerals in the area would be

4

alluvial deposits. Banded iron formation in the area is deeply weathered and therefore

magnetic survey could not be efficient as pointed out by Jacob Mukasa in his

recommendations. (Mukasa, 2001). Electrical Resistivity survey was, therefore, used

to detect gold bearing rocks and dense bodies of rocks within host formation in

Kamwango area.

1.4 Objectives

1.4.1 General objective

To determine the overall distribution of mineral bearing rocks and structures in

Kamwango area of Rongo region part of the Lake Victoria greenstone belt using

resistivity method.

1.4.2 Specific objectives

i. To measure apparent resistivities of Kamwango area using wenner and

schlumberger configurations.

ii. To determine resistivity measurements of Kamwango area.

iii. To determine the structural trend of the shear zones, veins and identify

the conductive zones that bear minerals.

1.5 Rationale of the study

As part of the rich Lake Victoria Greenstone Belt that extends northwards from the

Tanzanian border, Rongo gold field is known to be rich and hosting known class of

the world gold and associated mineral deposits. To establish occurrence of

commercial quantities of gold and related mineral ores at Kamwango area will

therefore serve as good news to locals, Investors and country at large. The value of

gold, if commercially mined, will contribute highly to economic development and

5

minimize dangers of heavy metal poisoning among the artisanal miners (appendix

XI).

This then, necessitates a thorough geophysical exploration survey in the area. Hence,

this study employed resistivity method which has been a solution to many problems

of the past because it is easy to determine the underground features without having to

dig it up.

6

CHAPTER TWO

LITERATURE REVIEW

2.1 Gold ore deposits

Naturally gold has four habitats of occurrence: crystalline masses, flat plates, nuggets,

and in grains. As grains, it can be so fine that its visibility to the naked eye is

impossible (Bonewitz, 2008). Gold, which is known as the most ductile and malleable

metal in the world, can also be found in compounds of several elements such as

sulphides and tellurides. It can be stretched and manipulated into many different

forms, which is helpful in metalworking. For instance, one gram of gold can be beaten

into a sheet of area1 m2. (Moharram et al., 1970)

Gold occurs very widely diffused in nature chiefly in the free or “native” state, but

invariably alloyed with some silver or copper (Bu bois, 1969). The methods employed

in the recovery of gold from its ores depend upon the way in which the gold occurs.

Gold occurring in veins may, if the grains are not too small, be won by fine grinding

of the ore followed by amalgamation with mercury. Ores of this type are known as

“free- milling ores”. The gold deposits fall into three categories depending on their

relationship to the enclosing rock. They occur in (a) quartz veins (b) strata bound

horizons, and (c) elluvial/ alluvial deposits. The more common of the two types of

gold bearing quartz veins in the belt are normally aligned sub-parallel to the strike of

the host Rock (Shackleton, 1946).

Gold particles which accumulate in the sands and gravels of streams and rivers give

rise to “alluvial” gold deposits. Extraction from these is relatively simple, and usually

involves gravitational concentration followed by amalgamation.

7

The mineral most commonly mistaken for gold is iron pyrites, a confusion so

worldwide that the alternative name for pyrites, is “fools‟ gold”. Gold is very soft

however, and a small piece may be cut in two quite easily with a sharp knife. Whereas

pyrites is very brittle, any attempt to cut it results in shattering and reduction to a

dark- coloured powder (Bu bois, 1969).

The South Nyanza goldfield, which lies to the south of the Kavirondo Gulf, covers an

irregular, somewhat triangular area, the approximate limits of which extend from

Komundo at the apex in the north, then south-westerly to Karungu on Lake Victoria,

thence south-easterly to Lolgorien, then very irregularly northwards west of Kisii

back to Komundo. Nyanzian rocks showing erratic gold mineralization occur also in

an isolated strip, elongated north- south, and a few miles to the west of Sotik.

Throughout the entire goldfield's area the commonest and most characteristic products

of mineralization are auriferous quartz veins. These are lenticular in habit and vary in

strike length from tens of 1 foot to over 2,000 feet, and in width from an inch or two

up to 30 feet. Persistence at depth is commonly greater than the surface strike.

Economically interesting concentrations of gold have been found in more or less well-

defined shoots rather than throughout the entire bulk of the veins (Bu bois, 1969).

The process of formation of gold found in the Smartville complex is known as

hydrothermal. Hydrothermal process involves ores of gold being brought to the

surface from deep within the earth through lava flows along mid-oceanic faults (Hill,

2006).

In most cases, ore-rich source rock was discovered entirely by chance. Many people

found gold known as placer deposits in rivers, where the ore was washed out from

8

hard rock deposits due to wind and water erosion as shown in figure2.1. (“Placer

deposit”, 2010). Stream placers, also known as alluvial placers, are the best known of

all placer deposits (“Placer deposit”, 2010). A stream placer is created when a

powerful body of water transports gold, along with other precious minerals and stones

far from its source within the hard rock deposit. In the course of time, miners

discovered that in most cases the gold that they were panning resulted from an initial

source in the earth known as a hard-rock deposit. The deposits in the Sierra Nevada

were mostly gold-quartz veins formed through hydrothermal deposition (Alpers et al.,

2005). Many prospectors claimed that a person could tell the difference between

potentially gold rich quartz (deemed “live” quartz) and “dead” quartz just by looking

at a sample (Hill, 2006). They claimed that the live quartz appeared less lustrous than

other non-ore-bearing quartz and also seemed more opaque (Hill, 2006). When they

traced the quartz back to its source they discovered different kinds of hard rock

deposits.

Figure 2.1: Placer deposits formed by the weathering of hard roc

(“Placer deposit”, 2010)

Silt formations are detectable in resistivity for their higher conductivity and thinness.

9

2.2 Mineral exploration

The application of ground geophysical surveys of induced polarization (IP) and

resistivity is very common and used for a varied range of applications, ranging from

environmental pollution studies (e.g. oil spills), lithological variation, hydrology in

locating aquifers to mineral exploration (Teikeu et al., 2012). The geology of the

Migori gold belt have been studied by Shackleton (1946), who noted that the

basement rocks are the oldest , followed by the Nyanzian system, Kavirondian

system, Bukobian system/Kisii series, tertiary rocks and Pleistocene and recent

deposits. This work however, covered a large area outside the study area.

Gold mineralization in the area studied exists mostly in the Nyanzian system rocks

which are divided into the following groups; salty and andesitic, greywacke and basic

volcanic. The structures in the area are described by Shackleton (1946); the

description is restricted to the Nyanzian rocks, perhaps due to gold mineralization in

it, the main ones are folds which are the main reason as to why nearly all the rocks dip

towards the granite, cleavage is not strongly developed in the rocks but many rocks

are sheared. Cleavage occurs in silty slates and shales near the granite, this cleavage is

possibly of post Achaean. Faulting is present in some parts such as near Kehancha

where phase faults are small thrusts along the bedding planes. The veins are normally

crossed by faults with no appreciable movements. In the study area, Gold is

embedded in rock often with quartz or sulphide minerals. The association of gold

mineralization with sulphides and oxides of metals, which are excellent electrical

conductors, makes it possible to target such ores using geoelectric exploration.

10

2.3 Mineral exploration techniques

Mineral exploration by remote sensing began in the early 1940's. In this method,

hand-held cameras were pointed out of aircraft windows (Agar, 1994). This method

advanced progressively to the use of gray shaded through color aerial photos in

geological mapping in 1952 to more sophisticated space technology using satellite

and airborne multispectral and hyper spectral digital imaging systems in use

today(Whaples, 2010). For a long while, multispectral remote sensing has been

successfully employed for that purpose especially with the advancement of remote

sensing sensors that give detailed information on the mineralogy of the different rock

types comprising the Earth's surface (Zhang et al., 2007).

Companies such as Abba, African queen mines and Stockport have done their

preliminary airborne geophysics in exploring the Odundu property in southwest

Kenya‟s Rongo Gold Fields. Highly potential and prospective targets have been

identified courtesy of the sampling and geochemical results from fieldwork with

positive results from ground and airborne geophysics. A zone of high chargeability

over an approximate strike of 1.5 kilometers by 0.5kilometers was detected over and

within the shear zone/fault system. (African queen Ltd, 2010)

Mineral and ground water exploration has been extensively done using electrical

resistivity method. Ogungbe et al. (2010) did a subsurface characterization using

electrical resistivity (dipole-dipole) method and gave reasonable results about the

subsurface layers and ground water potential. Electrical resistivity technique was also

used to delineate gold deposits in minna, Nigger state, Nigeria (Bello, 2012). Gold

and related minerals in Wadi El Beida area, South Eastern desert, Egypt were also

explored using geophysical methods by Sultan Awad Sultan using Wenner,

11

Schlumberger, dipole-dipole and chargeability (Sultan, 2010). Gold mineralization

channels identification was carried out in eastern Cameroon using resistivity and IP

(Gou et al., 2013). Fon et al. (2012) carried out electrical resistivity and chargeability

in mapping out auriferous structures in the prospective area of eastern Cameroon.

2.4 Related studies in the area

According to Mukasa (2001), the banded iron formations in the Nyanza greenstone

belt which host gold and other base metals were mapped geologically and found to be

intermittently exposed on the surface. This surface manifestation points solidly to the

type of volcanic activities that took place in the area and also to the type of forces

prevalent in the area prior to the volcanic activities. Both shearing and compressional

forces can lead to the intermittent nature of the structures as observed on the surface;

however no research has ever been designed to address this issue and therefore little is

known as to whether these banded iron formations are folded or faulted. Similarly

little is known as to whether this surface manifestation of the banded iron formations

extends into the bowels of the earth or whether a different manifestation does exist.

These issues which to date remain obscure are very important to gold prospectors and

miners. Mining of gold has been done from small deposits in entire region of the gold

belt by crosscutting quartz veins, banded iron formations; strata bound horizons in

tuffs, and alluvial/fluvial deposits. The most common gold-quartz veins are steeply

dipping structures aligned sub-parallel to the greenstones near the Migori granites.

Less common widely spaced veins (10's of km) have strike lengths of up to 8 km and

occur in strike slip faults oblique to the belt.

12

Oketch (2012) carried out a project in Kamwango; Rongo town in Migori county of

Kenya identified by coordinates 674000-680000Easting (m) and 992700-

993000Northing (m).

The project involved studying the distribution of the mineral pyrrhotite using entirely

geophysical methods of exploration. Pyrrhotite is a member of the sulphide group, it

is a mono-sulphide mineral and it is ferromagnetic. The methods that were used in

probing were magnetic and electrical which combined both Profiling and Sounding

techniques. The interpretations indicated that the mineral could be found in the

Northern Eastern tip of the study area. A vein was also detected. The vein exhibited

an East-West trend like all structures in the Archaean of the Tanzania craton. The

sounding technique also indicates that Pyrrhotite occurs at depths of 40mand above.

Several exploration follow-up exercises have to be conducted to evaluate the nature,

lateral and vertical extent of the mineralization.

13

CHAPTER THREE

THEORY OF RESISTIVITY METHOD

3.1 Resistivity method

Electrical resistivity is a geophysical method that is utilized in profiling geoelectric

structures to locate mineral deposits and aquifers. Hence, as one of the geophysical

methods of exploration, electrical prospecting methods have been used for a long time

in geological and geotechnical engineering (Keary and Brooks, 1991). The resistivity

method has its origin in the 1920‟s courtesy of the Schlumberger brothers but it still

suffices for initial investigations. The ground resistivity is related to various

geological parameters such as the mineral and fluid content, porosity and degree of

water saturation in the rock (Loke, 1999).

The geophysical method gives measurement for the apparent resistivity of the

underground. The field measurements of resistivity are known as apparent resistivity

since, without inversion, the field measurement of resistivity does not refer to any

particular geologic formation. Modeling of the subsurface is done by plotting graphs

of apparent resistivity against electrode separation. This provides detailed information

regarding the vertical distribution of layers in terms of thicknesses, depths and

resistivities (Loke, 2015). Resistivity method employs equipment which consists of a

transmitter and a receiver along with the electrodes and wires (Appendix XI). Two

electrodes are driven into the ground and constitute the transmitter part which sends a

low frequency square wave current signal. On the other hand, the two other electrodes

constitute the receiver part which is used to measure the resultant voltage. The

measured value of the apparent resistivity of the ground is then found by dividing the

voltage measured by the amount of current injected into the ground as in equation 3.1.

14

The product of the quotient (voltage divided by current) and the geometric factor,

which is derived from the geometry of the electrode configuration, gives the value of

the measured value of the apparent resistivity. The depth of investigation depends on

the configuration type and the size of the electrode separation. The more the current

electrode spacing, the deeper the depth of investigation. (Loke, 2015)

Materials such as poor conductors are known to have high resistivity as opposed to

good conductors which have high conductivity hence low resistivity. For

inhomogeneous bodies, average resistivity along the path of current flow is measured.

This is called the apparent resistivity. Good conductors include metals, graphite and

most sulphides. Intermediate conductors (called semi-conductors) include most

oxides, aquifers and porous rocks. Poor conductors (insulators) include most common

rock-forming minerals. Faults, joints, shear zones etc can produce “structural”

conductors. Gold mineralization around the world is usually associated with faults,

fractures and shear zones. Therefore this mineralization is controlled by structures

(Pitfield and Campbell, 1996).

Resistivity contrast exists beneath the surface, for example, between dry and water

bearing sediments, differing rock lithologies and differing weathering histories. The

apparent resistivity values are normally measured by injecting current into the ground

through two current electrodes, and measuring the resulting voltage difference at two

potential electrodes. From the current (I) and voltage (V) values, an apparent

resistivity ( a) value is calculated. (Reynolds, 1998)

a= k V / I (3.1)

where;

k is the geometric factor which depends on the arrangement of the four electrodes.

15

The value of resistance R = V/I, is normally given by the resistivity meters, so in

practice the apparent resistivity value is calculated by

a= k R (3.2)

The calculated resistivity value given by the formula (2) above is not the true

resistivity of the subsurface, but an “apparent” value which is the resistivity of a

homogeneous ground which will give the same resistance value for the same electrode

arrangement. The complexity of the relationship between the “apparent” resistivity

and the “true” resistivity necessitates an inversion of the measured apparent resistivity

values using a computer program to be carried out in order to determine the true

subsurface resistivity. The degree of fracturing, and the percentage of the fractures

filled with ground water affects the resistivity of these rocks. Because of high

porosity and high water content, sedimentary rocks normally have lower resistivity

values. Fresh underground water, moist and wet soils have even lower resistivity

values. Comparatively Clay soil normally has a lower resistivity value than sandy soil.

However, different categories of rocks and soils have resistivity values that overlap.

This is because porosity, the degree of water saturation and the concentration of

dissolved salts determines the resistivity of a particular rock or soil sample. Ground

water‟s resistivity varies from 10 to 100 Ωm. This is affected by the level of

concentration of dissolved salts. The resistivity of sea water is low (about 0.2 Ωm)

due to the relatively high salt content. This makes the resistivity method an ideal

technique for mapping the saline and fresh water interface in coastal areas (Loke,

1999).

16

3.2 Electrode Configurations

Depending on the electrode array, electrical resistivity methods are categorized into

two basic types: the profile, or traverse, method and the sounding method. In

electrical profiling, lateral resistivity variations information is obtained. In this case

the electrode separation is fixed. In the electrical sounding method, gradual increase

in electrode spacing while maintaining the center of the electrode spread is done at a

fixed location. Information about the subsurface at increasing depths is provided

whereas limited lateral changes information is given. A combination of profiles and

electrical soundings are now often practiced for relatively shallow surveys. In these

cases, at regular intervals, a series of electrodes are positioned and connection using

cables done to the transmitter and receiver. The transmitter and receiver collect data,

by means of an automated switching mechanism. This switching mechanism

automatically selects the positioned electrodes appropriately. Repetition of this

procedure for different electrode sets ensures recording of the whole line. Ohm-m is

the common unit for electrical resistivity.

3.2.1 General array

The figure 3.1 below shows the general arrangement of the electrodes. The red

coloured represent the potential electrodes and the green coloured represent the

current electrodes.

2Figure 3.1: General electrode Configuration (Sultan, 2010)

17

Mathematical Formulation

Resistivity studies in geophysics (Sultan, 2010) begin with:

(3.3)

where G = geometrical factor =

-

-

+

(3.4)

3.2.2 Wenner configuration

Figure 3.2 below shows Wenner configuration. In this configuration, the separation

between adjacent electrodes are equal to a. the four electrodes; potential electrodes M,

N and current electrodes A, B, are collinear

3Figure 3.2: Wenner Array and formula for calculating apparent

resistivity (Sultan, 2010)

The formula for determining apparent resistivity can be derived as shown in equations

3.5, 3.6, and 3.7 below.

ρa=

(3.5)

ρa=

(3.6)

ρa=

(3.7)

18

3.2.3 Schlumberger configuration

In Schlumberger configuration, The M, N electrodes are between A, B and they are

placed symmetrically at the center. The interelectrode spacing is not constant as

shown in figure 3.3 below

R e4Figure 3.3: Schlumberger Array and formula for calculating

apparent resistivity (Sultan, 2010)

Using the total potential at a point on the array equation (Parasnis, 1997)

V =

(

) (3.8)

V =

(

) (3.9)

= -

)

) ] = -

(3.10)

ρa = -

(3.11)

ρa = -

(3.12)

where

is the constant of configuration / array constant.

19

Deduction of the variation of resistivity with depth beneath a given point on the

ground is the object of VES. This resistivity is then correlated with the geological

information available in order to make an inference of the resistivities of the layers

present with depths.

3.3 Rock Resistivity

Rocks conduct electricity by electrolytic rather than electronic. Porosity is therefore a

major control of resistivity of rocks and resistivity increases as porosity decreases

(Loke, 1999). The geological parameters which are related to ground resistivity

include; porosity, the mineral and fluid content, and extent of water saturation in the

rock.

Figure 3.4: Resistivity value ranges for various earth materialsFigure5

(Reynolds, 1998)

The resistivity range of most rock forming minerals is 108−10

16 Ωm and they are

insulators. However, measurement insitu gives the following resistivity range values;

sedimentary rocks: 5−1000 Ωm, metamorphic/crystalline rocks: 100−1050 Ωm. The

20

range of the resistivity is due to the fact that rocks usually have pores and the pores

are filled with fluids, mainly water. This explains the reasons why rocks are

electrolytic conductors. This means that the flow of current in rocks is mainly by

means of passage of ions in pore waters.

3.4 Current flow in the ground

Earth materials typically have varied mechanisms of conduction. Pure metals, for

instance, conducts electronically. The metals have very low resistivity (<10-8

Ωm) due

to the high mobility of the electrons which are the charge carriers in metals. Minerals

such as sulphides are semiconductors. The charge carriers in semiconductors include;

electrons, ions or holes. Comparatively, in semiconductors the mobility and number

of charge carriers are lower than in metals, and thus the resistivity of semiconductors

is higher (typically 10-3

to 10-5

Ωm). For example this type of conduction occurs in

igneous rocks where the temperature dependence is of the form (thermally activated).

(Keary and Brooks, 1991).

(3.13)

where

T is the temperature in K,

E is an activation energy and

K is the Boltzmann constant.

Molten rocks or aqueous fluids conduct ionically. In this case the charge carriers are

ions that freely move through the fluid. Since it is rare to find pure materials in the

Earth and given that most rocks are a mixture of two or more phases (solid, liquid or

gas), serious consideration is made on the individual resistivities order to compute the

21

overall electrical resistivity of a rock. Take, for instance, sandstone saturated with salt

water. The grains are quartzite and have a high resistivity (> 1000 Ωm).

An empirical formula was developed for this scenario by Gus Archie in 1942.

Archie‟s Law states that the resistivity of a completely saturated whole rock (do) is

given by equation 3.14: (Reynolds, 1998)

(3.14)

Where

F is called the formation factor,

ρw is the resistivity of the pore fluid (water) and

Φ is the porosity. On a log-log plot of ρ0 as a function of Φ, a straight line should

result with slope–m. The exponent m is a constant termed the cementation factor.

22

CHAPTER FOUR

MATERIALS AND METHODS

4.1 Introduction

In this study, A GPS (global positioning system) was used in locating the various

stations. A total of 30 (thirty) stations were done using the wenner configuration

(appendix II) as indicated using the blue asterix, 8(eight) stations were done using

configuration as indicated using the green small triangles of figure 4.1.

Figure 4.1: Shows profiles (blue marks) and VES transects (green marks)

(Courtesy of ARCGIS software) Figure6

23

An ABEM terrameter SAS 1000 as shown by figure 4.2 was used to measure the

apparent resistivity values which were recorded (appendix VI).

Figure 4.2: ABEM Terrameter SAS 1000 (ABEM instruction manual, 2010).Figure

The total area of study was approximately 40 km2.After collection of data through the

equipment, the data was tabulated and arranged in excel sheets (appendix VI) and

thereafter conversion of the geographical coordinates from GPS system to UTM

(appendix IX). The data was then plotted on Surfer, and a contour map was generated

(appendix V). The map ideally forms patterns that describe the resistivity of all the

regions in the study area. Colours gave a clear distribution of the resistivity values as

indicated on colour scale in appendix V.

4.2 The Measuring Instruments

4.2.1 Terrameter

ABEM Terrameter SAS 1000, shown in figure 4.2, is a highly competent Resistivity/IP

system suitable for many different types of applications. By measuring both resistivity

and IP simultaneously it minimizes expensive field time and it is expandable with a

variety of accessories.

24

ABEM Terrameter SAS 1000 comprises a powerful built-in constant current transmitter

that runs on either a clip-on battery pack or an external power

According to the instructional manual,(ABEM instruction manual, 2010),the terrameter is

fast and hence safes time besides having a high precision in data acquisition with an

accuracy better than 1% over whole temperature range. ABEMS S.A.S gives absolute

values. This makes the results obtained using the terrameter more reliable compared to

those obtained using single short systems. In this method, consecutive readings are taken

automatically and the results are continuously averaged.

4.2.2 Global positioning system (GPS)

The global positioning system (GPS) is a satellite-based navigation system that provides

location and time information anywhere on or near the earth where there is an

unobstructed line of sight to four or more GPS satellites. The GPS was very vital during

the research in locating desired points along profiles and transects.

4.3 Resistivity data processing

The collected data in the study area were processed so as to prepare the dataset for

interpretation. Wenner field data including coordinates and apparent resistivity values

were input into computer and processed using Microsoft office Excel and Golden

software surfer 10 (appendix V). The data from the Microsoft office excel was used to

plot a contour map using the software. Then from the contour map, points of low

resistivity were located by plotting transects and this is where vertical electrical sounding

was conducted. Along the transects, two VES points on each, where sounding was done,

were marked as shown in figure 4.1 and appendix IV since they correspond to the weak

25

zones which are likely to be faults or fractures where mineralization of gold and related

minerals occur. Entry of VES data (Schlumberger Configuration) into the computer

software was done and curves were plotted using excel and IP 2WIN software for

inversion.

Details of the lithological information on each point that was profiled and later sounded

was made available digitally based on the type of electrical configuration used as shown

in appendix VII and VIII. Pseudo cross sections were formed through the inversion of the

VES data courtesy of the many soundings along the transects (Loke and Barker, 1996).

Lateral variation of resistivity gave description for the geoelectric structures and

formations.

4.4 Curve Matching

Curve matching is a substantially accurate and dependable method of interpretation in

electric sounding and involves the comparison of field profiles with characteristic

curves.Then on-linear inverse problems are solved using the standard linearized inversion

approach based on iterative processes. Inversion processes update the model parameter at

each step to best fit the observed data by using damped least-squares equation 4.1

(Menke, 1984).

m (GTG+

2 I) 1 GT d (4.1)

where m is the parameter correction vector, d is the data difference vector, G is the

Jacobian matrix containing partial derivatives of data with respect to the initial model

26

parameter, I is the identity matrix, and the term is called the damping factor which is a

scalar quantity that controls both the speed of convergence and solution.

The deduction of the variation of resistivity with depth beneath a given point on the

ground is possible with VES. The correlation of this resistivity with the geological

information available provides inference of the depths and resistivities of the layers under

consideration. DC current flow in most rocks occurs by relatively slow migration of ions

in a fluid electrolyte. This is known as electrolytic conduction. The factors that affect this

conduction include; type of ion, ion concentration, and ionic mobility. The matrix of the

mineral grains has little contribution safe for metal ores. Geological materials have a big

range (1024

) in resistivities: 1.6 x 10-8

Ωmfor native silver to 1.6 x 1016

Ωm for pure

sulphur. It is obvious that the resistivity measure over horizontal resistivity in the beds is

larger than actual horizontal resistivity in beds, but smaller than the vertical resistivity.

On the other hand, if the beds have a steep dip and the measurement is made with a

spread perpendicular to strike, the apparent resistivity will be smaller than the true

resistivity normal to the bedding, just the opposite to the result over horizontal layers; this

is known as the “paradox of anisotropy” (Bhattacharya et al, 2003). If the array is parallel

to the strike of the dipping beds, the apparent resistivity may be too large, depending on

the current-electrode separation. The conversion of the apparent resistivity which is a

function of electrode spacing to the true resistivity being as a function of depth is

achieved by the Ip2win software using the equation (4.2). (Reynolds, 1998)

(4.2)

dsJTssa )()()( 1

0

2

27

where,

S is half of the current electrode spacing (AB/2)

T (λ) is the resistivity transform function

J1 denotes the first order Bessel function of the first kind

λ denotes the integral variable

4.5 Characteristic Wenner HEP curves

The detection of lateral variations of the ground like lithological changes, near- surface

faults, shears and ore bodies is the object of HEP. In the wenner configuration procedure

of HEP the current and potential electrodes array is moved as a whole in determined

suitable steps with a constant array spacing “a” (figure 3.2). For Three layers resistivities

in two interface case, four possible curve types exist as shown in figure 4.3;

28

Figure 4.3: HEP curves type-H, A, K and Q (Telford et al., 2004)Figure7

Q – Type curve as shown in figure 4.3 (D) above is where, ρ1>ρ2>ρ3; and K-type in

figure 4.3 (C) is where ρ1<ρ2>ρ3. These imply formations that cannot be easily predicted

since the apparent resistivity is continuously decreasing with increase in electrode

spacing. On the other hand, H – Type where, ρ1>ρ2<ρ3 figure 4.3(A); and A – Type

where, ρ1<ρ2<ρ3 figure 4.3(B), indicates depths at which steady rise begins. These imply

depths at which country rock or basement is hit. The shape after hitting the country rock

shows a steady rise at an angle of 450

which is very informative in giving geological

formation of a given point under study.

29

4.6 Introduction to IP2 Win Software and partial curve matching

Data from Schlumberger configurations, Wenner configurations and from some other

kinds of electrode configurations can be analyzed byIP2 Win software. There are steps

followed in using the IP2 Win software. Data is fed into the software, error in data is

corrected, addition of data point follows in and lastly, the cross section is the created.

Data from the field can be directly input (sounding data consist of AB/2, V, I, and K) or

the field data converted so as to find the apparent resistivity (sounding data consist of

AB/2 and a) before inputting. IP2 Win software can be used to analyze the output of

sounding data such as; resistivity‐depth table, resistivity layer, log resistivity graph, and

pseudo cross section. There are data formats that can be used to export the output.

Restarting the software is necessary in solving the problem of a bug that frequently

prompts when analyzing data. Analysis of the output from IP2 Win software can be done

based on Loke‟s book, Electrical Imaging Survey for Environmental and Engineering

Studies (Loke, 1999).

30

CHAPTER FIVE

RESULTS AND DISCUSSION

5.1 Qualitative Interpretation

5.1.1 Contour Map

The data that was collected through the equipment was tabulated and arranged in excel

sheets and thereafter conversion of the geographical coordinates from GPS system to

UTM. The data was then plotted on Surfer, and a contour map generated as shown in

Figure 5.1.

Key:

Figure 5.1: A contour map showing profiles for wenner and transects for schlumberger. Figure8

Apparent resistivity

In Ωm

Wenner stations:

Schlumberger transects:

Drill hole

31

The central and Eastern regions have the lowest resistivity values and this indicates a

conductive buried ore body as shown in figure 5.1. Metallic and conductive minerals may

be disseminated in the said regions. Gold that is conductive occurs at the probe depth of

45m. The northern tip has the greatest resistivity values. The sounding was conducted on

the values with the least resistivity values from the profiles within an area of

approximately 10 Km2.

5.1.2 Log-Log plots

The figure 5.2 shows log-log plots indicating the trend of the curves and steady rise

beginning depths for the different VES.VES 1, VES 4 and VES 6. They show a steady

rise depth of 40m, VES 2 and VES 3 show a steady rise depth of 20m, VES 5 shows a

steady rise depth of 31.4m.VES 7 and VES 8 indicate a steady rise depth of 30m

Steady rise begin at 40m

Figure 5.2 a: VES1 Log-Log plot along transect T1Figure 9

1

10

100

1000

1 10 100 1000

VES1

Ap

p. R

esis

tivi

ty

AB/2

32

1

10

100

1000

1 10 100 1000

VES3

AB/2

Ap

p. R

esis

tivi

ty

Figure 5.2 b: VES 2 Log-Log plot along transect T1Figure10


Figure 5.2 c: VES 3 Log-Log plot along transect T2Figure 11


1

10

100

1000

1 10 100 1000

VES2

Ap

p. R

esis

tivi

ty

AB/2

33


Figure 5.2 d: VES 4 Log-Log plot along transect T2Figure12

Steady rise begin at 31.4m

Figure 5.2 e: VES 5 Log-Log plot along transect T3Figure13

1

10

100

1000

1 10 100 1000

VES4

Ap

p. R

esis

tivi

ty

AB/2

1

10

100

1000

1 10 100 1000

VES5

Ap

p. R

esis

tivi

ty

AB/2

34


Figure 5.2 f: VES 6 Log-Log plot along transect T3Figure 14


Figure 5.2 g: VES 7 Log-Log plot along transect T4Figure15

1

10

100

1000

1 10 100 1000

VES6

AB/2

Ap

p. R

esis

tivi

ty

1

10

100

1000

10000

1 10 100 1000

VES7

Ap

p. R

esis

tivi

ty

AB/2

35


Figure 5.2 h: VES 8 Log-Log plot along transect T4Figure16

5.1.3 Wenner HEP Curves using IP2Win Software

The sounding data collected were plotted on the IPI2win software. Line graphs of vertical

depth downwards (AB/2) against resistivity (ρ) were plotted and sounding curves

generated. The basic concept is that any lithological properties or unit has its own

identical resistivity value that is generated by the components i.e. minerals, moisture

content, clay content, compactness and other properties. High resistivity values indicate

the compact volcanic Nyanzian system rocks that are porphyritic andesites and dacites

the values go up to 1000 ohms-m in some parts of the study and the depth is in the range

of 40m upto130m. Depths with low resistivity are composed of the highly fractured

volcanic with resistivity as low as 13 Ωm. The subsurface and the weathered section also

have low values due to presence of groundwater. Figure 5.3 A is a combination of both H

type and A type. This curve shows a section representing compact Nyanzian volcanics

1

10

100

1000

1 10 100 1000

VES8

AB/2

Ap

p. R

esis

tivi

ty

36

and the zone of lowest resistivity in the study area that imply a buried auriferous

structure. Figure 5.3 B is an A type curve similar to the one in figure 4.3 (D) which

indicates the compact Nyanzian volcanic section and a highly fractured zone. Figure 5.3

C is a combination of Q type and H type (see also figure 4.3). It indicates a Zone of

oxidation and weathering. Figure 5.3 D and Figure 5.3 E shows a combination of H type

and a type of curve. This implies good formations that could be hosting mineral ores at a

dipping of 450 .Figure 5.3 F and Figure 5.3 G; K type and H type, K type and A type

respectively (compare with figure 4.3), indicate areas covered by compact formations that

could be fresh to slightly weathered volcanics or granitic rocks.

VES 1

Figure 5.3 A: A combination of both H type and A type.Figure17

Compact

volcanics

The depth with lowest

resistivity in the station

37

VES2

Figure 5.3 B: An A type curveFigure18

VES 4

Figure 5.3 C: A combination of Q type and H type Figure19

Compact Nyanzian

volcanics

Highly

fractured

zone

Zone of

oxidation and

weathering

38

VES 5

Figure 5.3 D: A combination of H type and A type of curve Figure20

VES 6

Figure 5.3 E: H type and A typeFigure21

39

VES7

Figure 5.3 F: K type and H typeFigure22

VES8

Figure 5.3 G: K type and AtypeFigure23

40

5.2 Discussion and Results

5.2.1 IP2WIN Curve Fitting

The tables alongside the curves in figures 5.4a, 5.4b, 5.4c, 5.4d, 5.4e, 5.4f, and 5.4g give

information about resistivity layer. Resistivity value in each ground layer is displayed in

ρ column. Alt column is altitude column or depth from VES point elevation. Information

of depth from surface is displayed in d column. Information of each layer thickness with

different resistivity value is displayed in g column. The black curve is the observed while

the red is the calculated. Red and Blue curve give information about the relation between

AB/2 and apparent resistivity value. Blue curve give information about resistivity value

variation.

This curve fitting achieved an average basement depth of 21.86m at accuracy of 5.635%

(good fit with average correlation of 94.365%). This accuracy is less than the maximum

accepted 10%. It therefore implies that the curves are accurate enough to be used in

deduction of the different layers‟ depth and resistivities at the sounding station. For VES

1, the curve outlines three layers: the first layer with a resistivity of 49.9 Ωm has a

thickness of 1.17m; the second layer with a resistivity of 6.87Ωm has a thickness of 1.31

m; the third layer with a resistivity of 148 Ωm has a thickness of 28.6m and a basement

being hit from depth of 31.1m. The fitting has an accuracy of 7.36% (Figure 5.4 a). For

VES 2, the curve outlines three layers: the first layer with a resistivity of 38.2 Ωm has a

thickness of 0.451m; the second layer with a resistivity of 2.1Ωm has a thickness of 0.862

m; the third layer with a resistivity of 32.2 Ωm has a thickness of 15.5m and a basement

being hit from a depth of 16.8m. The fitting has an accuracy of 6.8%as in figure 5.4 b.

41

For VES 3, the curve outlines three layers: the first layer with a resistivity of 72.6 Ωm

has a thickness of 48.9mm; the second layer with a resistivity of 19.5Ωm has a thickness

of 71.4cm; the third layer with a resistivity of 31.4 Ωm has a thickness of 15.3m and a

basement being hit from depth of 16.1m. The fitting has an accuracy of 4.21% as shown

by figure 5.4 c. For VES4, the curve outlines three layers: the first layer with a resistivity

of 500 Ωm has a thickness of 0.629m; the second layer with a resistivity of 15.8 Ωm has

a thickness of 2.85 m; the third layer with a resistivity of 31.8 Ωm has a thickness of

23.7m and a basement being hit from depth of 27.1m.The fitting has an accuracy of

4.83% (Figure 5.4 d).

For VES 5, the curve outlines three layers: the first layer with a resistivity of 505 Ωm

has a thickness of 0.627m; the second layer with a resistivity of 16Ωm has a thickness of

2.9 m; the third layer with a resistivity of 31.7Ωm has a thickness of 23.2m and a

basement being hit from depth of 26.8m. The fitting has an accuracy of 4.99% (Figure

5.4 e). For VES 6, the curve outlines three layers: the first layer with a resistivity of

148Ωm has a thickness of 1.74m; the second layer with a resistivity of 19.2Ωm has a

thickness of 6.54 m; the third layer with a resistivity of 30304 Ωm has a thickness of

12.4m and a basement being hit from depth of 20.7m. The fitting has an accuracy of

6.51% (Figure 5.4 f). For VES 7, the curve outlines three layers: the first layer with a

resistivity of 286Ωm has a thickness of 1.81m; the second layer with a resistivity of

2025Ωm has a thickness of 3.13 m; the third layer with a resistivity of 189Ωm has a

thickness of 5.21m and a basement being hit from depth of 10.2m. The fitting has an

accuracy of 4.42% (Figure 5.4 g). In figure 5.4 h (VES 8) the curve outlines three layers:

42

the first layer with a resistivity of 2632 Ωm has a thickness of 0.566m; the second layer

with a resistivity of 243Ωm has a thickness of 5.08 m; the third layer with a resistivity of

22.2 Ωm has a thickness of 14.5m and a basement being hit from depth of 20.1m. The

fitting has an accuracy of 5.96%.

Figure 5.4 a: VES 1curve matching (RMS=7.36%re24

43

Figure 5.4 b: VES 2 curve matching (RMS=6.8% Figure25

Figure 5.4 c: VES 3 curve matching (RMS=4.21%)26

44

Figure 5.4 d: VES 4 curve matching (RMS=4.83%)27

Figure 5.4 e: VES 5 curve matching (RMS=4.99%)28

45

Figure 5.4 f: VES6 curve matching (RMS=6.51%) F igure29

Figure 5.4 g: VES7 curve matching (RMS=4.42%) Figure30

46

Figure 5.4 h: VES8 curve matching (RMS=5.96%) Figure31

Table 5.1: Summary of layer thickness with corresponding resistivity for the VES

stations

VES LAYER 1 LAYER 2 LAYER 3 LAYER 4 ERROR

No.

(Ωm) h (m)

(Ωm)

h (m)

(Ωm)

h

(m)

(Ωm) h (m) %

1 49.9 1.17 6.87 1.31 148 28.6 14891 ∞ 7.36

2 38.2 0.451 2.1 0.862 32.2 15.5 5607 ∞ 6.80

3 72.6 0.0489 19.5 0.714 31.4 15.3 16406 ∞ 4.21

4 500 0.629 15.8 2.85 31.8 23.7 6718 ∞ 4.83

5 505 0.627 16 2.9 31.7 23.2 3288 ∞ 4.99

6 148 1.74 19.2 6.54 30304 12.4 30304 ∞ 6.51

7 286 1.81 2025 3.13 189 5.21 2169 ∞ 4.42

8 2632 0.566 243 5.08 22.2 14.5 12903 ∞ 5.96

47

5.2.2 Pseudo cross-sections models

The pseudo section is useful as a means to present the measured apparent resistivity

values in a pictorial form, and as an initial guide for further quantitative interpretation.

Red colouration is representative of litho-layers with high resistivity values while those

with blue are designated to those of less resistivity values. Different colours by the model

are assigned to geological layers that have similarities in geo-electric properties. Red

colour (near the surface) corresponds to regions of less electrical conductivity (figures 5.5

a, 5.5 d, and 5.5 f). This could be an implication of holes left by artisanal miners or

outcrops of the granites and volcanics of the Nyanzian system. The rocks are intruded by

granites and dolerites and in other places are overlain by tertiary volcanics (Ogola, 1995).

Blue colours are indicative of metallic minerals that are conductive. The region between

VES 1 and VES 3 there is a near surface formation of very low resistivity to a depth of

about 14m and directly below VES 2 .This is a highly conductive material that can be an

auriferous structure or a sulphide impregnation that hosts gold and related minerals. The

region of low resistivity has a big spread between VES 1 and VES 6 especially the area

bounded by the yellow colouration in the figure 5.5 and figure 5.5 (a) below. The highest

resistivity in this area is about 70 Ωm. This is still low and it matches with most mineral

ores gold inclusive. The region between VES 7 and VES 8 is a region of high resistivity

which is about 500 Ωm (figure 5.5 c). This is indicative of a volcanic or granitic intrusion

which could be slightly weathered. The region however is a narrow strip that may not be

easily detected following the principle of suppression. This is particularly a problem

when three or more layers are present and their resistivities are ascending or descending

with depth. The middle intermediate layer may not be evident on the field curve.

48

Figure 5.5: Pseudo cross-section showing spatial layer distribution for all VES 1-8Figure32

Figure 5.5 a: Pseudo cross-section showing spatial layer distribution between VES 1 and

VES 4.Figure 33

49

Figure 5.5 b: Pseudo cross-section showing spatial layer distribution between VES 2 and

VES 3.Figure 34

Figure 5.5 c: Pseudo cross-section showing spatial layer distribution between VES 5 and

VES 7.Figure 35

50

Figure 5.5 d: Pseudo cross-section showing spatial layer distribution between VES 6 and

VES 8.Figure 36

Figure 5.5 e: Pseudo cross-section showing spatial layer distribution between VES1 and

VES 2Figure 37

51

Figure 5.5 f: Pseudo cross-section showing spatial layer distribution between VES 4 and

VES 55 Figure38

5.2.3 Ore Potential Primers

Previous related studies in the area, lithological information from prospectus companies

and the geological knowledge of Kamwango area was used in constraining model

interpretation of the VES curves and pseudo-cross sections. In Figure 5.4 a, the first layer

has a thickness of 1.17m which corresponds to soil formation of resistivity 49.9 Ωm. The

next layer has a reduced resistivity of 6.87 Ωm with a thickness of 1.31m that matches

with the moist sub-base. In the third layer, the resistivity shoots to 148 Ωm with a

thickness of 28.6m. At this point the basement is hit at a depth of 31.1m corresponding to

the compact formation of the Nyanzian volcanic. In Figure 5.4 b, the first layer with 38.2

Ωm of 0.451m thickness confirms the loose soil formation. Beneath the moist sub-surface

52

of resistivity 2.1 Ωm and thickness 0.862m of layer two, lies a layer of highly weathered

and fractured volcanic of resistivity 32.2 Ωm and thickness 15.5m. The basement here is

hit at a depth of 16.8m.

Figure 5.4 c begins with a thin layer of dry volcanic soil with alluvial deposits having a

resistivity value of 72.6 Ωm which is 0.0489m thick. This is followed by a layer of moist

volcanic soil of resistivity 19.5 Ωm of 0.714m thickness. At 16.1m, the resistivity

changes to 31.4 Ωm with a thickness of 15.3m. This is a layer of weathered and fractured

volcanic. The first layer of VES4 has a very big value of resistivity of 500 Ωm which is

0.629m thick. This is due to the holes left by the artisanal miners. Figure 5.4 d was

located near artisanal mining activity. The second layer has a reduced resistivity of 15.8

Ωm and 2.85m thick which corresponds to moist sub-base formation (table 5.2). This

overlies 31.8 Ωm layers, 23.7m thick that marks a highly weathered and fractured tuff

formation, structure or ore body. In figure 5.4 e, a thin layer, 0.627m, with a resistivity of

505 Ωm overlies a 16 Ωm, 2.9m thick layer. This is a wet clay formation beneath which

lies a highly fractured or weathered layer of resistivity 31.7 Ωm which is 23.2m thick and

occurs at a depth of 26.8m.Dry sandy soil with alluvial deposit formation with resistivity

148 Ωm and 1.74m thick characterizes the first layer of Figure 5.3 f. This is followed by

a slightly fractured layer of resistivity 19.2 Ωm and occurs at a depth of 8.28m.At a depth

of 20.7m, occurs, a 12.4m thick layer with a very high resistivity (30304 Ωm). This could

be due the fresh volcanic formation. However, this reduces again at a depth of 45m to

below 100 Ωm. In Figure 5.4 g there was a salient outcrop of some rock. Here, the first

layer of thickness 1.81m has a resistivity of 286 Ωm. This could be because of the

53

slightly weathered outcrop which could be an exposed volcanic formation of the

Nyanzian system. At a depth of 4.94m ends a layer with a thickness of 3.13m with

resistivity of 2025 Ωm.

This is a layer of compact fresh volcanic formation (table 5.2). From the depth of 4.94m

to 11.15m comes a 5.21m thick layer with resistivity of 189 Ωm. This signifies a layer

which is weathered and fractured. The first layer of figure 5.4 h has resistivity measure of

2632 Ωm. Like VES 4, this was also located near an active artisanal mining point.

Therefore the high resistivity layer of thickness 0.566m is due to many holes left by the

artisanal activity (table 5.3). The second layer has thickness of 5.08m and resistivity 243

Ωm. This is partly because the voids left by artisanal activity and soil formation. At a

depth of about 20.1m ends a layer of resistivity 22.2 Ωm which is 14.5m thick. This is a

conductive layer because it is highly weathered and fractured (table 5.2).

VES 4, VES 5, VES 6, VES 7 and VES 8 indicated very high values of resistivity in their

first layer: 500Ωm, 505Ωm, 148Ωm, 286Ωm, 2632Ωm with a thickness of 0.629m,

0.627, 1.74m, 1.81m, and 0.566m respectively. This is because of either the holes left by

artisanal activity or the outcrops of the volcanic and granite formations. It can also be as a

result of the top sandy soils which are not conductive. The second layer is conductive

because of the moist sub-surface (table 5.2). The third layer has a slightly higher

resistivity value because of the weathered or highly fractured volcanics.at layer four the

country rock is hit and therefore resistivity rises steadily

54

Table 5-2 below shows the summary of the layer lithology of the study area and the

implied formations

Table 5.2: Layer Lithology

DEPTH (in meters) RESISTIVITY

(Ohm) FORMATION

0-1.7 120-90 Soil formation

1.7 – 7.00 13.85 Moist sub-base

7.70 – 10.5 50-70 Weathered volcanics

10.5 – 40.30 16.2-50 Highly Fractured volcanic (water bearing)

40.30– 120 70-100 Compact formation of the volcanics

Table 5.3: Layer Lithology of bore hole for VES 2 about 4 km from the study area

A borehole is recommended to be drilled at the site of VES- 2 to a maximum depth of

about 200 m bgl. This will ensure that the deeper aquifer will be fully penetrated.

55

Table 5.4: Kamwango drill results (adopted from www.stockportexploration.com)

Shallow drilling: All current intercepts run between 25 m – 60 m vertical depth.

5.2.4 Area Lithology

The sounding data collected were plotted on the IP2win software. Line graphs of vertical

depth downwards (AB/2) against resistivity (ρ) were plotted and sounding curves

generated. The basic concept is that any lithological properties or unit has its own

identical resistivity value that is generated by the components i.e. minerals, moisture

content, clay content, compactness and other properties. High resistivity values indicate

KG-11-02

Elevation 4548 feet;

-0.69883, 34.59661

http://www.stockportexploration.com/

56

the compact volcanics Nyanzian system rocks that are porphyritic andesites and dacites

the values go up to 1000 Ωm in some parts of the study area and the depth is in the range

of 40m upto130m. Depths with low resistivity are composed of the highly fractured

volcanics with resistivity as low as 13 Ωm. The subsurface and the weathered section

also have low values due to presence of groundwater. Geological structures related to

gold bearing quartz veins appear as low-resistivity anomalies because almost all of the

gold mineralization occurs in fractured areas associated with faults or shear zones.

Minerals associated with gold in the study area include: banded iron formations,

pyrrhotite, metal sulphides, granites and quartz vein formations. Rocks in this area are

greenstone belt type and mineralization is by intrusive granites.

57

CHAPTER SIX

CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusion

Mapping out of auriferous units and a better comprehension of ore characteristics in Kamwango

area, using profiling and sounding, has been made simple. Ore characteristics include; the

thickness, depth to bedrock and fractured/faulted zones which are required for locating points

with high potentials for ore body occurrence. From the contour map the central eastern part of

the study area at a probe depth of 45m covering an approximate area of 10 Km2 indicated low

resistivity anomaly. On this region eight soundings were done from which VES1 to VES 6 can

be postulated to be having an ore body at shallow depths between 10m to about 70m and

covering an approximate area of 6 Km2.VES 7 indicates a granitic intrusion of resistivity of

about 500Ωm. Soundings done on this region gave an average basement depth of 21.86m and a

steady rise depth of 32.68m, which indicate the depth at which the country rock is hit.

From the pseudo cross-sections, auriferous structures, having an east-west trend like all

geological structures in the Archaean of the Tanzania craton, have been delineated in deeply

weathered volcanic rocks. Related studies in the area are in agreement with this study. Banded

iron formations by Mukasa (2001) and pyrrhotite by Oketch (2012) are all hosts for Gold. The

drills done by exploration companies such as Stockport, Table 5.5, and African Queens give

results that very well match with the findings of this study. Shallow formations that indicate an

economically viable deposit have been intercepted. The low resistivity anomaly generally

exhibits an East-West to North West-South East range of trend similar to all structures in the

Archaean of the Tanzanian craton.

58

The association of gold with metallic sulphides and oxides which are excellent electrical

conductors made it possible to target such ores using geoelectric exploration.

6.2 Recommendations

Because any exploration geophysics requires complementary geophysical surveys integrated

with geochemical, environmental geophysics and geologic insight, the resistivity survey carried

out in Kamwango area cannot be regarded as an end but as a valuable piece of work for further

research and development. This study probed a maximum depth of 130m. However, drilling is

recommended at VES 1,2,3,5 and 6 to depths of about 60m which have resistivity range between

2 Ωm to about 50 Ωm. There is need to probe greater depths because some mines in the world

are as deep as 4km. Therefore, it is recommend Magnetotelluric method to be employed. Major

advantages of Magnetotelluric (MT) method is its unique Capability for exploration to very great

depths (hundreds of kilometers) as well as in shallow investigations without using of an artificial

power source.

In addition, it is recommended that the geological information of the Kamwango area be updated

since the available information is pre-colonial that concentrates on the lower part of Migori

greenstone belt leaving out the upper part, Kamwango inclusive. Finally drilling will assist in

confirming the presence and exact location in depth of the main ore body which might have

potential economic value.

59

REFERENCES

ABEM instruction manual (2010). Terrameter SAS 4000/SAS 1000.Retrieved from

http://www.abem.se/files/upload/manual-terrameter.pdf.

African queen mines’ agreement for Rongo gold project in Kenya lake Victoria greenstone

belt, may 17 2010 issue.

Archie, G.E. (1942).The electric resistivity log as an aid in determining some reservoir

characteristics. Trans. AIME 146, 54-62.

Agar, R.A. (1994). Geoscan airborne multi-spectral scanners as exploration tools for Western

Australian diamond and gold deposits. Geophysical Signature of Western Australia

Mineral Deposits: 435–447.

Alpers, C.N., Hunerlach, M.P., May, J.T., and Hotheim, R.L. (2005). Mercury contamination

from historical gold mining in California. USGS Publications. Retrieved from

http://pubs.usgs.gov/fs/2005/3014/

Bello, A.and Funtua I. I., (2012). Characterization of Lead (Pb) poisoning gold ores from North

Western Nigeria using PIXEtechnique. The IUP Journal of Physics.58J

Bhattacharyya, B.B., Shalibahan and Sen, M.K., (2003), Use of VFSA for Resolution,

Sensitivity and Uncertainty Analysis in 1D DC Resistivity and IP Inversion,

Geophysical Prospecting, 51, 393–408

Bonewitz, R.L. (2008). The definitive guide to rocks, minerals, gems, and fossils. New York,

United States. Rock and gem: DK Publishing, Inc. Britannica Online:

http://www.britannica.com/EBchecked/topic/462598/placer-deposit

Bu bois, C.G. (1969).Minerals of Kenya Geological survey bulletin. Geological survey of

Kenya: 11: 25-32.

Fon, A.N, Che, V.B, and Suh, C.E (2012).International Journal of Geosciences.3 960-

971http://dx.doi.org/10.4236/ijg.2016.325097.Published Online October 2012

(http://www.SciRP.org/journal/ijg)

Gou, D.H, Marga, T.N, Meying, A, Pepogo, A.D.M (2013) International Journal of

Geosciences, 4: 643-655http://dx.doi.org/10.4236/ijg.2013.43059.Published Online May

2013 (http://www.scirp.org/journal/ijg)

Hill, M. (2006). Geology of the Sierra Nevada. Berkeley and Los Angeles, CA: University of

California Press.

Hume, M.E. (1937). Geology of Egypt, 2 Part II. Geological Survey of Egypt.

http://www.abem.se/files/upload/manual-terrameter.pdf

http://pubs.usgs.gov/fs/2005/3014/


http://dx.doi.org/10.4236/ijg.2016.325097

http://dx.doi.org/10.4236/ijg.2013.43059

60

Keary, P and Brooks, M. (1991).An Introduction to Geophysical Exploration, 2nd Edition,

Blackwell Scientific Publications, London, 254.Minerals of Kenya. Geological survey

bulletin

Loke, M.H. (1999). Electrical imaging surveys for environmental and engineering

studies,2nd

edition. A practical guide to 2-D and 3-D surveys.

Loke, M. H and Barker, R.D (1996). Rapid Least-squares deconvolution of apparent resistivity

Pseudosections. Geophysics Prosp. 44: 131-152.

Loke, M.H., P. B. Wilkinson, P.B., Chambers, J.E., Uhlemann, S.S. and Sorensen, J.P.R, 2015. Optimized arrays for 2-D resistivity survey lines with a large number of electrodes. Journal

of Applied Geophysics, 112, 136-146.

Menke, W. (1984). Geophysical data Analysis, Discrete inverse theory, Academic press Inc.

New York.

Moharram, O., El-Ramly, M.F., Amer, A.F., Ivanov, S.S., Gachechiladze, D.Z.(1970).

Studies on Some Mineral Deposits of Egypt. Geological Survey of Egypt.

Mukasa, J.K (2001). Magnetic survey of banded iron formation in Migori segment of Nyanza

greenstone belt. Master‟s thesis. Kenyatta University.

Ogola, J.S.(1984). Geological Structure and Mineral Composition of Massive Sulphide Ores of

Macalder Deposit, Kenya, Moscow, 285 pp. (unpublished thesis).

Ogola, J. S., (1995). Geology and mineral resources of Nyanza province, Western Kenya. Geol.

Soc. Afr. 95, pp. 407 - 430.

Ogolla, J. S., Winnie, V., Omulo, M. A. (2002). Impact of gold mining on the environment and

human health: A case study in the Migori Gold Belt, Kenya. Environmental geochemistry

and health journal 24 141–158.

Ogungbe, A.S, Olowofela, J.A, Oresanya, O.O and Alabi, A.A, (2010) Archives of Applied

Science Research2: 24-34

Oketch, F.O. (2012). Exploration of pyrrhotite mineral and its distribution in Kamwango area.

Geology project. Nairobi University

Parasnis D. S. (1997). Principles of Applied Geophysics, 5th Edition, Chapman and Hall,

London, England, 104-176.

61

Pitfield P. E. J and Campbell S. D. G. (1996) .Significance for Gold Exploration of Structural

Styles of Auriferous De-posits in the Archaean Bulawayo-Bubi Greenstone Belt of

Zimbabwe, Transactions of the Institution of Mining and Metallurgy. Section B Applied

Earth Science, Vol. 105: B41-B52.

Placer deposit.(2010). In Encyclopedia Britannica. Retrieved June 04, 2015, from encyclopedia

of California Press. Britannica Online:


Ralph, C. (2003). The Geology of coarse gold formation. Retrieved from

http://www.nuggetshooter.com/articles/CRGeologyofcoarsegoldformation.html\

Reynolds, J. M. (1998).An Introduction to Applied and Environmental Geophysics. Wiley.

Shackleton, R.M. (1946). Geology of the Migori Gold belt and adjoining

areas.Rep.geol.surv.kenya, 10.

Sultan, A.S. (2010).Geophysical exploration for gold and associated minerals, case study: Wadi

El Beida area, South Eastern Desert, Egypt.

Teikeu, W. A, Ndougsa-Mbarga, T., Njandjock , P. N., Tabod, T. C.( 2012). Geoelectric

Investigation for Groundwater Exploration in Yaoundé Area, Cameroon, International

Journal of Geosciences3: No. 3, 640-649. doi:10.4236/ijg.2014.33064.

Telford, W.M.,Geldart ,L.P and Sheriff ,R.E.(2004).Applied Geophysics 2nd

edition.

Cambridge University press. New York

Whaples, R. (2010). California Gold Rush. The Eh.net encyclopedia. Retrieved (2016, June 3)

from http://eh.net/encyclopedia/article/whaples.goldrush.

Zhang, X., Pazner, M., Duke, N. (2007). Lithologic and mineral information extraction for gold

exploration using ASTER data in the south Chocolate Mountains

(California).Photogrammetry and Remote Sensing 62 271–282.

http://www.nuggetshooter.com/articles/CRGeologyofcoarsegoldformation.html/

http://eh.net/encyclopedia/article/whaples.goldrush

62

APPENDIX I: MAP OF OYUGIS SHOWING KAMWANGO

63

APPENDIX II: WENNER CONFIGURATION MAP

64

APPENDIX III:WENNER AND VES CONFIGURATION MAP

65

APPENDIXIV: WENNER READINGS

NO_ Easting Northing res East_Dgr North_Degr

1 675507.76 9927027.98 402.749 34.57714737 -0.659948697

2 675487.918 9925063.596 204.423 34.57697478 -0.677714351

3 675507.76 9922980.157 193.962 34.57715922 -0.696556603

4 675587.129 9920976.088 282.446 34.57787838 -0.714680854

5 675646.656 9919011.703 241.903 34.57841931 -0.732446259

6 676876.877 9918872.808 205.504 34.58947208 -0.733698464

7 676837.193 9920976.088 330.393 34.58910894 -0.714676956

8 676698.297 9922960.315 127.42 34.58785501 -0.696732434

9 676658.612 9925103.281 156.488 34.58749209 -0.677351989

10 676757.823 9927027.981 508.936 34.58837779 -0.65994509

11 678186.467 9927008.139 945.269 34.60121255 -0.660120392

12 678206.309 9925063.596 153.648 34.60139651 -0.677706284

13 678404.732 9923059.527 73.501 34.60318515 -0.69582996

14 678603.155 9920956.246 302.158 34.60497427 -0.714850848

15 678484.101 9918872.808 201.822 34.60391133 -0.733693276

16 679773.849 9918813.281 130.8 34.6154985 -0.734227422

17 679615.11 9920916.562 128.372 34.61406567 -0.715206529

18 679575.426 9923019.842 68.452 34.6137026 -0.696185248

19 679476.214 9925142.965 67.708 34.61280486 -0.676984684

20 679476.214 9927087.508 153.284 34.61279913 -0.659398833

21 680627.066 9927226.404 111.532 34.62313766 -0.658139324

22 680587.382 9925043.754 31.956 34.62278763 -0.67787856

23 680805.647 9923019.842 51.375 34.62475465 -0.696181427

24 680904.858 9920837.193 87.062 34.6256528 -0.715920196

25 680924.7 9918733.912 184.44 34.62583784 -0.734941432

26 682135.079 9918793.439 230.476 34.63671147 -0.734399096

27 682154.921 9920837.193 53.853 34.63688309 -0.715916173

28 682115.236 9922980.158 42.355 34.63651979 -0.696536216

29 682016.025 9925103.281 32.402 34.63562197 -0.677335874

30 681956.498 9927305.773 109.738 34.63508062 -0.657417615

66

APPENDIX V: CONTOUR MAP SHOWING WENNER STATIONS AND

SCHLUMBERGER TRANSECTS

67

APPENDIX VI: SCHLUMBERGER EXCEL (VES 1-VES 8)

AB/2 RES

1.6 36.911

2 34.64

2.5 32.181

3.2 22.412

4 20.428

5 22.057

6.3 25.167

8 30.14

10 38.051

13 48.51

16 54.926

20 65.092

25 79.514

32 93.58

40 90.938

50 124.1

63 129.82

80 196.64

100 291.16

130 310.18

AB/2 RES

1.6 7.0927

2 5.5902

2.5 5.431

3.2 6.2908

4 7.4456

5 8.7552

6.3 10.625

8 13.41

10 16.364

13 20.951

16 20.726

20 21.328

25 27.286

32 33.696

40 40.843

50 52.885

63 69.143

80 90.939

100 117.34

130 167.65

1

10

100

1000

1 10 100 1000

VES1

1

10

100

1000

1 10 100 1000

VES2

68

AB/2 RES

1.6 23.807

2 23.691

2.5 26.182

3.2 27.459

4 28.76

5 30.096

6.3 30.608

8 30.758

10 32.651

13 38.224

16 35.4015

20 38.808

25 48.327

32 59.32

40 71.96

50 94.285

63 117.67

80 159.19

100 201.14

130 263.54

AB/2 RES

1.6 163.99

2 157.8

2.5 134.63

3.2 103.2

4 93.811

5 98.483

6.3 61.057

8 53.84

10 56.807

13 43.002

16 36.411

20 28.893

25 29.928

32 33.6395

40 36.062

50 43.055

63 53.25

80 68.386

100 87.596

130 107.88

1

10

100

1000

1 10 100 1000

VES3

1

10

100

1000

1 10 100 1000

VES4

69

AB/2 RES

1.6 151.19

2 75.822

2.5 46.014

3.2 27.849

4 21.322

5 18.673

6.3 19.799

8 23.142

10 23.801

13 30.572

16 30.131

20 28.122

25 34.592

32 37.103

40 44.032

50 55.532

63 63.585

80 87.086

100 111.38

130 147.46

AB/2 RES

1.6 131.41

2 119.36

2.5 108.38

3.2 90.21

4 71.839

5 49.919

6.3 36.153

8 31.018

10 33.002

13 41.896

16 50.566

20 56.011

25 66.171

32 84.017

40 125.2

50 155.95

63 179.07

80 219.16

100 251.4

130 321.61

1

10

100

1000

1 10 100 1000

VES5

1

10

100

1000

1 10 100 1000

VES6

70

AB/2 RES

1.6 333.44

2 340.52

2.5 335.29

3.2 409.29

4 499.28

5 574.98

6.3 621.15

8 689.14

10 733.1

13 809.71

16 727.355

20 672.89

25 672.76

32 757.1

40 821.92

50 958.7

63 1109.2

80 1282.9

100 1335.648

130 1388.396

AB/2 RES

1.6 794.9

2 490.24

2.5 363.61

3.2 288.3

4 267.19

5 242.26

6.3 197.1

8 146.18

10 119.06

13 98.34

16 71.6545

20 47.95

25 46.39

32 52.5395

40 58.947

50 71.864

63 90.884

80 110.57

100 131.25

130 251.51

1

10

100

1000

10000

1 10 100 1000

VES7

1

10

100

1000

1 10 100 1000

VES8

71

APPENDIXVII:SCHLUMBERGER IP2WIN CURVES:

VES 1

VES 2

VES 3

72

VES 4

73

VES 5

VES 6

74

VES 7

VES 8

75

APPENDIX VIII: VES LAYERING

77

APPENDIX IX: SCHLUMBERGER SOUNDING FOR 8 STATIONS.

AB/2 ves 1 ves 2 ves 3 ves 4 ves 5 ves 6 ves 7 ves 8

1.6 36.911 7.0927 23.807 163.99 151.19 131.41 333.44 794.9

2 34.64 5.5902 23.691 157.8 75.822 119.36 340.52 490.24

2.5 32.181 5.431 26.182 134.63 46.014 108.38 335.29 363.61

3.2 22.412 6.2908 27.459 103.2 27.849 90.21 409.29 288.3

4 20.428 7.4456 28.76 93.811 21.322 71.839 499.28 267.19

5 22.057 8.7552 30.096 98.483 18.673 49.919 574.98 242.26

6.3 25.167 10.625 30.608 61.057 19.799 36.153 621.15 197.1

8 30.14 13.41 30.758 53.84 23.142 31.018 689.14 146.18

10 38.051 16.364 32.651 56.807 23.801 33.002 733.1 119.06

13 48.51 20.951 38.224 43.002 30.572 41.896 809.71 98.34

16 54.926 20.726 35.4015 36.411 30.131 50.566 727.355 71.6545

20 65.092 21.328 38.808 28.893 28.122 56.011 672.89 47.95

25 79.514 27.286 48.327 29.928 34.592 66.171 672.76 46.39

32 93.58 33.696 59.32 33.6395 37.103 84.017 757.1 52.5395

40 90.938 40.843 71.96 36.062 44.032 125.2 821.92 58.947

50 124.1 52.885 94.285 43.055 55.532 155.95 958.7 71.864

63 129.82 69.143 117.67 53.25 63.585 179.07 1109.2 90.884

80 196.64 90.939 159.19 68.386 87.086 219.16 1282.9 110.57

100 291.16 117.34 201.14 87.596 111.38 251.4 1335.648 131.25

130 310.18 167.65 263.54 107.88 147.46 321.61 1388.396 251.51

78

APPENDIX XI: FIELD PHOTOS

79

APPENDIX XII: TABLE OF RESISTIVITY AND CONDUCTIVITY OF MATERIALS

80

APPENDIX XIII: BORE HOLE LOGS IN THE VICINITY

Site Name Grid Reference Elevation

Maximum

Recommended

Depth

Site reference

VES 1 034°30‟51S

00°38‟21S 1347 metres 200 metres

At the investigated

point, VES 1,at the

upper part of the

compound

GEO-ELECTRICAL RESISTIVITY INVESTIGATION OF MINERAL ...

Documents

Transcript of GEO-ELECTRICAL RESISTIVITY INVESTIGATION OF MINERAL ...