MEASUREMENT OF MAGNETIC SUSCEPTIBILITY OF GRANITOIDS OF SOME SELECTED AREAS IN THE ASHANTI REGION OF GHANA. MINI PROJECT AT KNUST- KUMASI

1. MEASUREMENT OF MAGNETIC SUSCEPTIBILITY OF GRANITOIDS AND MAFIC MINERAL CONTENTS OF
SOME SELECTED AREAS IN THE ASHANTI REGION OF GHANA.
ADONGO VINCENT (PG6900716)
January 7, 2017
ABSTRACT
This survey was geared towards the measurement of magnetic susceptibility of granitoids at three
different widespread locations in the Ashanti region of Ghana specifically, Boadi, Mankranso and Ohwim.
The Bartington magnetic susceptibility system (MS2) instrument was used to take readings on different
granitoid samples broken into considerable sizes (4 cm × 3 cm) with flat cutting surfaces. With the help of
the MS2E sensor, the magnetic susceptibilities of the various samples from these locations were
determined. Also, the amount of mafic mineral contents in the granitoid samples were estimated as well
as the various mineral types confined in granitoids. The results obtained for the magnetic susceptibilities
were very significant to ascertain the amount of mafic mineral contents present in these rock samples.
Rock samples at Boadi were found to contain small amount of mafic minerals in them, whiles rock samples
from Ohwim had the highest mafic content. This was so because, rock samples from Ohwim recorded the
highest values of magnetic susceptibility (5.3-11.2×10^-6) SI, followed by those from Mankranso (2.6-
5.3×10^-6)SI and Boadi recording the least values of magnetic susceptibility, which is (1.1-3×10^-6)SI. The
decrease in susceptibility values of granitoids at Boadi was as a result of factors such as weathering,
rainfall, anthropogenic activities and climate change. These values were used to ascertain the mafic
mineral content present in the individual rock samples.The estimated mafic mineral contents in
percentages were found to be 10-20%, 20-30% and 50-90% for Boadi, Mankranso and Ohwim granitoids
respectively. It was therefore concluded that, high magnetic susceptibilities correspond to high mafic
mineral contents and vice versa.
1.0 Introduction
The amount of magnetic crystals which exhibit the magnetic properties of minerals present in a particular
rock sample is measured by the magnetic susceptibility. Magnetic properties exhibited by rocks are
basically attributed to the presence of iron-containing compounds such as ironic oxides and iron sulfides.
However, there are several factors that affect the susceptibility signal within a sample which includes
topography, parent materials, weathering, climate etc. A study of the magnetic susceptibility of granitoids
at different locations in the Ashanti region of Ghana was undertaken. These variations in the susceptibility
are attributed to nature of different types of granitoids, weathering activities as well as climatic conditions
in the different locations. Changes in environmental conditions such as rainfall, temperature and pressure
of overlying Earth materials strongly affect the susceptibility of rocks. Concurrently, magnetic
susceptibility of rocks relates very well with the amount mafic mineral contents present in the rocks.
Magnetic susceptibility analysis has been applied in different geophysical fields such as mineral
exploration, geophysical prospecting, archaeology, finding magnetic content of ground water, rocks etc.
Magnetic susceptibility can be used primarily as a relative proxy indicator for changes in composition that
can be linked to paleoclimate-controlled depositional processes. The high precision and sensitivity of
susceptibility loggers make these measurements extremely useful for core-to-core and core down-hole
log correlation (Tarling and Hrouda, 1993). It is found so far that magnetite is a very dominant magnetic

2. mineral in granitoids, and hemo-ilmenite or hematite replacing magnetite which may increase or
decrease, respectively, magnetic susceptibility of rock sample is seen in rare occasions on certain type of
granitods (ISHIHARA, 1979). Thus, magnetic susceptibility has a positive correlation with the content of
magnetite and its measurement is most convenient way to identify regionally distributed magnetite in
granitoids. Under a routine ore-microscopic magnification, magnetite is commonly seen on granitoids
having a susceptibility of more than 50×10^-6 (SI) (ISHIHARA, 1979). Magnetic susceptibility again can be
related to the mafic mineral content present in granitoids. These may include olivines, pyroxenes, K-
feldspars, plagioclase, amphibole, biotite, melilites etc. The bulk of ferric/ferrous ratio is an expression of
different content of magnetite in granitoids (TSUSUE & ISHIHARA, 1974). Magnetic susceptibility indicates
the degree of magnetization of a material in response to an applied magnetic field.
Variations in rock magnetic properties, which is the magnetic susceptibility values are responsible for the
many magnetic anomalies that are spatially associated with faults and mineral deposits in their host rock.
Susceptibilities of rocks and density logs are primarily used as porosity logs, identification of minerals in
evaporite deposits, detection of gas, determination of hydrocarbon density, evaluation of shaly sands and
complex lithologies, determinations of oil-shale yield, calculation of overburden pressure and rock
mechanical properties (Schlumberger, 1989). Basically, high density granitoids have high values of
magnetic susceptibility recorded by the Bartington instrument which is the magnetic susceptibility meter
(MS2). This research work seeks to determine the magnetic susceptibilities of granitoids and the amount
of mafic mineral present in these rocks at some selected areas in the Ashanti region of Ghana.
1.1 Research Problem
Geophysical exploration is very costly now a days. There has been the need to bring on board, a less
expensive but effective method for exploration work. In this survey, magnetic susceptibility
measurements of granitoids at different locations in the Ashanti region would be determined which would
also help in quantifying the amount of mafic minerals present in the various rock samples using MS2E
sensor to probe the rocks.
1.2 Objectives
The main objective of this work is to measure the variations of the magnetic susceptibilities of granitoids
at different locations in Ashanti region. Also, I would seek to find; The amount of mafic minerals present
in the granitoids at the areas where the samples were collected which are of importance to a geologist as
well as a geophysicist.
1.3 Literature Review
Intuitions about the magnetic susceptibility and mineral contents are essential tools used in mapping
several rock units which includes granitoids and for delineating both mineralized and non-mineralized
zones. Major work done on magnetic susceptibility of rocks are as follows.
Tsiboah and Arko (1999) performed a Magnetic Susceptibility measurements on young and fresh rocks of
the Birimian volcanic greenstone belt of the Ashanti Belt. Their findings were such that, a genetic between
magnetic susceptibility and gold mineralisation within the Birimian rocks of Ghana were observed. Some
areas which were magnetically anomalous were also noted. Measurements of magnetic susceptibility
made on the new rocks in sulfide zones within the anomalous areas indicated high variables of
susceptibility, with about 2-3 orders of magnitude in the metavolcanics.

3. Kuma et al. (1999) used mineralogical and statistical analysis to estimate the magnetic susceptibility of
rocks in Bogosu Gold Limited’s concession. The results indicated that the susceptibility of the rocks was in
the range of (31-170) x 10^-6 SI. Metatuff revealed the lowest susceptibility of 31 x 10^-6 SI while dolerite
dyke, had the highest susceptibility value of 170 x 10^-6 SI. The work also showed that weathering had
significantly reduced the susceptibility of the rocks. The presence of graphite in the rocks had no effect
on their overall susceptibility but pyrite had a small positive effect on them.
Sanger (2003) performed a survey on density and magnetic susceptibility analysis on rocks from south-
central Alaska. Results demonstrated that the average grain density of the rocks in the study area
increases from sedimentary rocks to intermediate igneous rocks to mafic igneous rocks and to
metamorphic rocks. The magnetic susceptibility measurements on rock outcrops and six hand samples
ascertained comparatively lower magnetic susceptibilities for sedimentary and felsic intrusive rocks,
moderate susceptibility values for metamorphic, felsic extrusive and intermediate igneous rocks and
higher susceptibility values for mafic igneous rocks. The magnetic properties of rocks in the study area
were consistent with the trend expected for certain rock types.
Henry et al. (2003) performed a survey on the Anisotropy of magnetic susceptibility of heated rocks.
Heating produced changes, which did not always correspond to simple enhancement of the magnetic
fabric. Two methods were proposed to determine the anisotropy of magnetic susceptibility of the
ferrimagnetic minerals formed or that have disappeared by chemical change during persistent heating.
They first looked at the difference between each tensor term before and after heating. The second
deployed linear regression for each tensor term made with the values obtained throughout a thermal
treatment. Instances where heating simply enhances pre-existing fabrics form and those where thermal
treatment induces a different fabric, were distinguished by comparing the ferromagnetic material with
the initial rock fabric
Oniku et al. (2008) carried out a low field magnetic susceptibility measurements within Zaria granite
batholiths. Magnetic susceptibility was within the range of (29 - 3505) x 10^-6 SI with an average value of
684 x 10^-6 SI. The large variation in the susceptibility values were as a result of a large variation of
magnetic mineral content within an outcrop and the different rock types within individual suite. Major
minerals found were feldspar, quartz and biotite while magnetite, ilmenite and hematite occur as trace
minerals.
Ayidin and Ceryan (2005) carried out Magnetic variation measurements on the Harsit granitoid and their
findings were that, the Harsit granitoid can be divided into three main groups. The first group was
characterised by the magnetite content, ilmenite, biotite and amphibole. The second group was
characterised by having mineral content in which magnetite is less frequent; therefore the minerals then
become ilmenite, biotite and amphibole. In a case like this, contribution of ilmenite to MS (650–350 x 10^-
6 SI) and magnetic fabric could be significant as underlined by Borradaile and Henry (1997). In the last
group biotite and amphibole are the dominant minerals. In this case the MS (100–350×10^-6 SI) is
controlled by the ferromagnesian minerals (Borradaile and Werner, 1994; Benn et al., 1998).
1.0 Theoretical Background
Minerals are naturally occurring, solid materials which are mostly organic with orderly crystal structure
and fixed chemical composition. Some minerals are magnetic whiles others are non-magnetic. Magnetism
is caused by unpaired electrons in atoms. The ease at which a material can be magnetized is termed as

4. magnetic permeability. Magnetic permeability is denoted by µ. Atoms within a material have electrons
which rotates in their various orbitals around the nucleus whiles spinning about their axes. This rotation
of electrons, in reference to atomic physics may make a material have a net magnetic moment which in
turn makes the material exhibit some magnetic properties. Magnetic susceptibility, χ is the degree at
which a material can be magnetized in response to an external magnetic field. Both J and H have the same
unit (A/m), hence they cancel out; making the magnetic susceptibility, χ a dimensionless parameter. The
induced magnetic field and the inducing field are in the same direction if the value of χ is positive and vice
versa. During magnetic survey or prospecting, χ is a numerical constant that is determined by the physical
properties of a magnetic material. Materials can be grouped into diamagnetism, para-magnetism,
ferromagnetism, ferrimagnetism and anti-ferromagnetism based on their magnetic susceptibilities.
Materials whose electronic orbitals are fully filled with no unpaired electrons will have no magnetic
moment and also negative values of magnetic susceptibilities are referred to as diamagnetic materials.
Examples of such materials are quartz, marble, graphite etc. Paramagnetic materials have unpaired
electrons in their lattices and poses a net magnetic moment but magnetic interaction between atoms is
weak. Their magnetic susceptibility values is weak but positive. Examples are gneiss, dolomite, pyrite
(FeS2). Ferromagnetic material have a net magnetic moment in the absence of an inducing field, H. They
have large positive values of magnetic susceptibilities. Their susceptibilities interact strongly in an
imposed magnetic field. Examples are Iron, Cobalt and Nickel. Ferrimagnetism in materials occurs when
atoms within a material have net magnetic moments which are anti-parallel to each other but are of
different magnitudes. Due to this, Ferrimagnetic materials have a weaker magnetism than ferromagnetic
materials. Magnetic susceptibility, χ for ferrimagnetic material is strongly positive. Examples are
magnetite (Fe3O4), maghemite (γ−Fe2O3) (M.S. Tite, 1975). Anti-ferromagnetism in materials occurs
when magnetic moments of equal magnitudes in a material are anti-parallel to each other. Hence, anti-
ferromagnetic materials have magnetic susceptibility which are moderately positive (J. Dearing, 1999).
Examples of anti-ferromagnetic materials are ilmenite (FeTiO4) and hematite (α−Fe2O3). If the ratio
between the induced magnetisation and the inducing field is expressed per unit volume, it is called volume
susceptibility, χv. Volume susceptibility is mathematically expressed as;
χ =J H
where J is the volume magnetization induced in a material of susceptibility χ by the applied external field
H. Volume susceptibility is also dimensionless quantity and depends on the measurement system used: χ
(SI) = 4πχ (cgs) = 4π G Oe−1 , where G and Oe are abbreviations for Gauss and Orstedt, respectively. The
SI system should be used. Mass or specific susceptibility is defined as;
χm =χ ρ
Where ρ is the density of the material. The dimensions of mass susceptibility are therefore cubic meters
per kilogram (m3kg−1)
3.0 Materials and Methodology of Survey
3.1 Description of the Areas of Survey
A magnetic susceptibility measurements were taken at three different locations in the Ashanti region of
Ghana, predominantly in areas where most granitoids are exposed to the surface. Rocks, specifically
granitoids were collected from Boadi, Mankranso, and Ohwim in the Ashanti region. A sledge hammer

5. was used to break these rocks into medium to small sizes with considerable densities which were almost
equivalent for all granitoids from each location. Granitoids from Ohwim were observed to be younger
since it looked coarser than those from Mankranso and Boadi. A lot of construction works have taken
place and some of these rocks have aided in the construction of these houses at Boadi. Heavy down pour
around the area have caused most of the granitoids to be weathered which made breaking of these rocks
easy. Rocks from Ohwim and Mankranso were collected from around the bush whereas those from Boadi
were collected from new site where a lot of construction works are taking place. Different rock outcrops
of about 100 m apart were taken from Boadi especially at the areas where the construction was taking
place. Figure 3.1.1 shows the three different locations where the granitoid samples were collected.
Figure 3.1.1: A map showing the locations where Granitoids were collected.
3.2 Instrumentation of Survey Equipment
3.2.1 Bartington Magnetic Susceptibility System
The equipment used in this survey is the Bartington Magnetic Susceptibility instrument (MS2). This
instrument over the years has been used mostly in geological and rock survey, soil survey, archeological
prospecting, paleomagnetics, paleoclimate studies, hydrology, sedimentology, core logging/correlation,
pollution surveys and magnetic fabric analysis. In archeology, this system has been used to probe the
enhancement of magnetic susceptibility in soils caused by human lifestyle with time (Tite and Mullins,
1971). The MS2 is a portable instrument which comprises of several sensors which includes MS2D Probe,

6. MS2K Probe, MS2B Dual Frequency Sensor and MS2E sensor. Since, this survey seeks to measure the
average susceptibilities of the granitoids, the MS2E sensor was deployed to carry out the susceptibility
measurements for the different granitoids. Also, the MS2E sensor is designed to perform high resolution
measurements on the surface of split drill or soft sediment cores. The sensitive area of the probe, as
defined by 50% maximum response, is in the form of a rectangle of 3.8mm x 10.5mm allowing very fine
resolution surface measurements. The position of the long axis is identified by marks on the circumference
of the sensor. The sensor is supplied in a protective case. The instrument setup comprises of an MS2
sensor (probe) connected to the susceptibility meter through the MS2 probe handle by a cable. The
susceptibility meter has a measuring range of 1×10^−5 to 9999×10^−5 in SI (volume specific χ) or 1×10^−8
to 9999×10^−8 in SI (mass specific χ).The susceptibility meter has five front panel controls: on-off switch,
sensitivity range switch, SI or cgs unit switch, zero button and continuous measurement switch. The range
switch is typically on the lower sensitivity (1.0), which allows rapid one second measurements. Readings
from the MS2E sensor is shown in the appendix.
3.2.2 Data Acquisition
The MS2E sensor was deployed in measuring the average susceptibilities of the granitoids from the three
different locations, which are Boadi, Mankranso and Ohwim outcrops. The rock samples were grouped
according to their locations. The Bartington instrument was fully charged and connected to the computer
as already described in the instrumentation and survey equipment. The MS2E sensor was used to probe
the granitoids. The sensor was used to probe the nearly flat to perfectly flat surfaces to ensure a proper
probing of sensor into the granitoids. Air readings were taken by nulling (zeroing) the susceptibility meter.
The first air reading was taken followed by the sample reading and also the last air readings for each of
the rock samples. The average susceptibility values of granitoids at the different locations were recorded
for each sample of granitoid. The standard deviations were recorded for each sensor reading. This was
repeated for all the samples collected from these locations. Also, drift was taken for the granitoid readings
before the actual readings were taken. The average susceptibilities were saved on the computer and later
collected for data processing and interpretation.
3.3 Rock Sample analysis
Granitoids from different locations were observed to have different grain sizes. The grain sizes of rocks
also has an effect on its magnetic susceptibility. The samples were cut to very flat surfaces before
measurement was undertaken. The samples were labelled based on their locations. For example,
granitoids from Boadi, Mankranso and Ohwim were labelled BD, MK and OH respectively. Each rock
Sample was also identified and several readings were taken on same sample to ensure that the value
recorded for the average susceptibility was the true value. Bigger grain size recorded high values of
magnetic susceptibilities than those of smaller grain sizes. Density of rock samples also has an impact on
the susceptibility of the rock samples.
3.4 Data Processing
The average values of magnetic susceptibilities obtained were generated and processed using excel
software. Two columns were shown in excel that is, sample number and average magnetic susceptibilities
of the various rock samples (SI). The Grapher software was used to plot a graph as shown in the figure
4.1.1.

7. 3.0 Results and Discussion.
4.1 Results of Magnetic Susceptibilities of Granitoids and Mafic mineral content
This survey was conducted to ascertain the magnetic susceptibility distribution in granitoids as well as
mafic mineral contents present in the rocks. Magnetic susceptibility, however, is a descriptive parameter
of a mineral and also very useful in the determination of the amount of magnetic materials present in the
rocks. Rock samples were sorted out base on their locations. In figure 4.1.1 Samples at Boadi were first
measured and the average magnetic susceptibility values were obtained as shown in the appendix.
Granitoids at Boadi recorded the minimum average susceptibility values ranging from as low as 1.1-
4.3×10^-6 (SI). Samples with very low susceptibilities can be attributed to the fact that, weathering
activities have caused most of the magnetic minerals to be absent. Also, tectonic events have occurred
predominantly in the area. At Boadi, most of the rock samples were taken from different points, yet there
were no much variations in the susceptibilities of the individual rock samples. The maximum value of
susceptibility at Boadi, which is 4.3×10^-6 SI was probably due to the fact that, granitoids were found
above sloppy areas and hence weathering at those areas was very minimal. Rock samples at Mankranso
recorded susceptibilities closed to one another and ranges from 2.6 – 5.3×10^-6 (SI) as shown in figure
4.1.1.That is, there were no much variations in the average susceptibilities recorded. This indicated that
the rock samples were broken from only one rock unit hence, consistent values of magnetic susceptibility.
However, granitoids from Ohwim recorded the highest susceptibility values which ranged from 5.3 –
11.2×10^-6 (SI) as shown in figure 4.1.1. These values recorded from Ohwim can be attributed to the fact
that the rocks have not been exposed to the environment where there is weathering, climatic conditions
and other tectonic activities. Also, burning and deposition of excess waste materials could be a factor.
Rock samples were very difficult to break due to the excess magnetic mineral content present in the rock
samples. The extent of magnetic minerals present can be related to the susceptibilities of the various
magnetic minerals present. A similar work was done to ascertain magnetic susceptibilities using grinded
minerals and it showed a good correlation of the above values obtained. Magnetic Susceptibility
measured shows very good correlation with the content of mafic minerals present. The graph of the
magnetic susceptibilities for the three different locations took the same trend using the Grapher software
as shown in figure 4.1.1 below. A graph of average magnetic susceptibilities of rock samples with their
corresponding sample numbers were plotted as shown below. This profile plot helped us to predict the
mafic minerals content present in the various rock samples collected from all the three different location.
Some of these mafic minerals present are olivines, pyroxenes, plagioclase, hornblende, amphibole,
biotite, melilites etc. Granitoids at Boadi recorded the least mafic mineral content which were between
the ranges of about 10-20%. This low percentage of mafic minerals may be attributed to the low average
magnetic susceptibility values recorded when taking measurement with the MS2E sensor, plagioclase and
apatite were likely to be common due to its light-coloured nature. However, granitoids at Ohwim recorded
the highest values of magnetic susceptibilities, hence the most mafic minerals were present in these
samples. Minerals likely to be present included olivines and pyroxenes. The range of percentage of mafic
minerals was between 50-90% ascertaining its high magnetic susceptibilities. Also, rocks from Mankranso
had small to moderate amount of mafic minerals. These minerals are biotite and apatite minerals. Their
mineral content were nearly 3.0-4.2 SI, with a percentage of 20-30%. (La Trobe University Catalogue)

8. Figure 4.1.1: Magnetic susceptibility of different samples of Granitoids at three different locations.

9. 4.2 Discussion
The magnetic susceptibilities for the various locations, Boadi, Mankranso and Ohwim to be precise were
used to plot a simple graph as shown in figure 4.1.1 above. The average susceptibilities obtained for these
locations gives a very good indication of the type of rock (granitoids). The values obtained is comparable
to the volume susceptibility as well as the mass susceptibility, which ranges from about (0-50,000)×10^-6
and (0-1,900)×10^-6 (SI). The first plot in figure 4.1.1 shows the average magnetic susceptibilities of
granitoids at Boadi. It is observed that, the susceptibility values at these areas are widespread. Even
though, the average value obtained was significantly low as compared to the other locations. The values
were observed to be very closed. Interpretation of this plot would be very important since there was a
clear indications of small amount of magnetic minerals present in the granitoids at Boadi. The second plot
in figure 4.1.1 on the other hand, indicates a corresponding average magnetic susceptibilities of rock
samples at Mankranso. Granitoids at Mankranso indicated a small variation in the magnetic
susceptibilities. Their susceptibilities ranging from 2.5-5.3×10^-6 (SI). This can be associated to the fact
that, only a particular magnetic mineral was predominant in this type of granitoid. Rocks with the same
mineral composition may have the same values of magnetic susceptibilities. Contamination of non-
mineralized materials on rocks can also have an effect on its magnetic susceptibilities. However, plot 3
has high values of susceptibility, with a very wide variations in the values obtained. The plot showed very
strong variation peaking at an average of 11.2×10^-6 (SI). The lines plotted are far apart due to its widest
variations compared with the granitoids at Mankranso and Boadi. The standard deviations of the various
granitoids for each sample were recorded, which indicate how the magnetic susceptibilities were varying
for each rock sample. Again, rock samples from Boadi showed the lowest deviation followed by those
from Mankranso and Ohwim as seen from the appendix. Overall deviation was calculated for the
differentlocations as seen in the plots. These three different plots indicate that, there should be the need
to preserve granitoids from continuous exposure to the environment where weathering, tectonic
activities as well as climatic conditons like rainfall, atmospheric pressure and temperature variation can
have effect on the amount of magnetic minerals present in a rock sample. This is because, Boadi rocks
showed a very low magnetic susceptibility signature as a result of some weathering activities and also
human settlement within the area which have affected the magnetic mineral contents present in the
granitoids within the area. Areas like Mankranso and Ohwim showed values of high magnetic
susceptibility because of less weathering activities present in the rock samples. Interpretation of this data
indicates that areas of high magnetic susceptibilities will give rise to a corresponding high mineral content
which is applicable in determining the various magnetic materials such paramagnetic, ferromagnetic,
ferromagnetic, anti-ferro magnetic and diamagnetic materials. Each of which gives different magnetic
susceptibility signatures, which may be highly positive for ferromagnetic, negative for diamagnetic and
less positive for paramagnetic, anti-ferro and ferrimagnetic materials. These material types can be linked
up with the values as plotted in the figure 4.1.1 above.
5. Conclusion and Recommendation
5.1 Conclusion
In conclusion, geophysical survey method of prospecting especially with magnetic method employs a
broad range of instruments to probe various environmental materials in their pure (fresh) and polluted
state (Evans and Heller, 2003). With the application of these instruments, magnetic susceptibility
measurement were made at three different locations in the Ashanti region of Ghana. Granitoids samples

10. were obtained from three different locations, specifically Boadi, Mankranso and Ohwim. This survey also
predicted the estimated mafic magnetic minerals present in the various grantoids. There was a clear
correlation between the magnetic susceptibility values obtained as well as the mineral content present in
the samples measured. High values of magnetic susceptibilities corresponded to high magnetic minerals
present in the rocks and vice versa. The susceptibilities measured again enabled in estimating the mafic
mineral contents, that is, their percentage compositions as well as the different minerals present. High
amount of mafic minerals were found to be present in the Ohwim granitoids. However, granitoids from
Boadi had only small amount of mafic minerals present in them. This was attributed to the fact that, the
granitoids were mostly exposed to weathering and other climatic conditions, hence making the rock very
soft and frozen when probing to ascertain the magnetic susceptibility values. Anthropogenic occurrences
such as construction, well logging, walking and bathing have also contributed enormously in the low
susceptibility values of the granitoids at Boadi. From the results, conclusions can be made based on the
fact that, values of magnetic susceptibility decreases at areas with a lot of weathering activities making
rocks frozen when held. Not only that, but rock outcrop exposed to the surface where there are a lot of
human activities may also be a contributing factor.
5.2 Recommendation
This survey emphasized on the measuring the magnetic susceptibilities of granitoids on three selected
areas in the Ashanti region of Ghana and the mafic minerals present in these samples. I suggest if further
work could be done by considering a wider areas. More rock samples could be used in order to get more
data for this work and also, to predict the various structures for hosting oil and gas.
References
 AYDIN, A., and CERYAN, S. (2005), Geophysical evaluation of Hars¸it granotoid for marble sector
in, southwest of Trabzon, NE Turkey, In: (ed), O ¨ ZKUL, M., YAG ˘IZ S. and JONES B., Proceedings
of 1. International Symposium on Travertine; PAU, Denizli-Turkiye, p.309-314.
 BENN, K., HAM, N.M., PIGNOTTA, G.S., and BLEEKER, W. (1998), Emplacement and deformation
of granites during transpression: magnetic fabrics of the Archean Sparrow pluton, Slave Province,
Canada. J. Struct. Geol. 20, 1247-1259.
 BORRADAILE, G. J. and HENRY, B. (1997), Tectonic applications of the magnetic susceptibility and
its anisotropy. Earth Sci. Rev. 42, 49–93.
 BORRADAILE, G. J., and WERNER, T. (1994), Magnetic anisotropy of some phyllosilicates.
Tectonophysics 235, 223-248.
 E. M. Evans and F. Heller, “Environmental magnetism: Principles and applications of
enviromagnetism.” Amsterdam: Academic, 2003.
 Henry, B., Jordanova, D., Jordanova, N., Souque, C., and Robion P. (2003). “Anisotropy of magnetic
susceptibility of heated rocks”. (http://christine.souque1.free.fr/Travail/2003-henry-etal.htm)
 J. Dearing, I. Livingstone, M. Bateman, and K. White, “Palaeoclimate records from ois 8.0– 5.4
recorded in loess-palaeosol sequences on the matmata plateau, southern tunisia, based on
mineral magnetism and new luminescence dating,” Quatern. Int., pp. 76 – 77., 2001.
 Kuma, J.S., Al-Hassan, S., Stainforth, B., and Thompson, F.A. (1999). “Magnetic Susceptibility of
Rock Units in the Bogosu Gold Limited Concession, Western Region, Ghana”, Ghana Mining
Journal, vol 5, pp. 11-17.

11.  M. S. Tite and C. Mullins, “Enhancement of the magnetic susceptibility of soils on archaeological
sites,” Archaeometry, 1971.
 M. S. TITE and R. E. LININGTON, “Effect of climate on the magnetic susceptibility of soils,” Nature,
pp. 565 – 566, August 1975.
 Oniku, S. A., Osazuwa, I. B. and Meludu O. C. (2008). Preliminary report on magnetic susceptibility
measurements on rocks with the zaria granite batholith.
 Sanger, A.E. (2003). Density and Magnetic Susceptibility values for rocks in the Talkeetna
Mountains and adjacent, South-Central Alaska. Science for a changing world, pp 1-3.
 SASAKI, A. and ISHIHARA,S., 1979: Sulfur isotopic composition of the magnetite-series and
ilmenite-series granitoids in Japan. Contrr. Mineral. Petrol., 68, 107-115.
 Schlumberger, 1989 ”Log Interpretation Principles’’
 Tarling, D.H., & Hrouda, F. (1993). The magnetic anisotropy of rocks. Chapman &Hall, London,
U.K., XI + 217pp
 Tsiboah, T., and Arko, J.A. (1999). “Magnetic Susceptibility Index Measurement and Its Implication
for Gold Exploration at Ashanti Mine, Obuasi”, Ghana Mining Journal, vol. 5, pp 22-29.
 TSUESUE, A. and ISHIHARA, S., 1974: the iron-tiatanium oxides in the granitic rocks of South-west
Japan. Mining Geol., 24, 13-30*.
A. Appendix
A.1 Specifications of MS2 Sensor Used.
Table A.1 Specifications of the MS2E Sensor
Specification Range of values
Area of response 3.8mm x 10.5mm at the end of the ceramic
cylinder
Depth of response 50% at 1mm, 10% at 3.5mm
Measurement period - x 1 range - x 0.1 range 1.5s SI (1.2s CGS) to 15s SI (12s CGS)
Operating frequency 2kHz
Drift at room temperature <5 x 10^-5 SI (vol) (<5 x 10^-6 CGS) in 5 minutes
after 5 minutes operation
Enclosure material diecast aluminium and ceramic
Weight 0.22kg
Dimensions 150 x 50 x 25mm
Figure A.1. A Caption of the magnetic susceptibility sensor (MS2E) probe sensor.