GEO-ELECTRICAL RESISTIVITY INVESTIGATION OF MINERAL ...
Transcript of 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
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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 …………………….
Department of Physics
Kenyatta University
P. O. Box 43844
Nairobi, KENYA
Dr. John. G. Githiri Signature…… ………………….Date ……………………….
Department of Physics
Jomo Kenyatta University of Agriculture and Technology
P.O BOX 62000-00200
Nairobi, KENYA
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DEDICATION
This thesis is dedicated to my wife and children, my mother and sisters the ESWA fraternity and
Ekioga Seventh Day Adventist Church members.
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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.
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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
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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
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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
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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
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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
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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
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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
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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.
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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).
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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.
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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
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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
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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.
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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.
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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
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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.
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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.
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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,
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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.
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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.
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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.
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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
Steady rise begin at 30m
Figure 5.2 c: VES 3 Log-Log plot along transect T2Figure 11
Steady rise begin at 20m
1
10
100
1000
1 10 100 1000
VES2
Ap
p. R
esis
tivi
ty
AB/2
33
Steady rise begin at 40m
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
Steady rise begin at 40m
Figure 5.2 f: VES 6 Log-Log plot along transect T3Figure 14
Steady rise begin at 30m
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
Steady rise begin at 30m
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
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.
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:
http://www.britannica.com/EBchecked/topic/462598/placer-deposit
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.
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
76
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
81