UNIVERSITY OF GHANA

DEPARTMENT OF EARTH SCIENCE

A REPORT ON AN INTERNSHIP PROGRAM AT THE GEOLOGICAL

SURVEY DEPARTMENT.

BY: ATIEMO OWUSU CHRISTOPHER

ID: 10486584

DATED: JUNE 30TH, 2016

TABLE OF CONTENT PAGE

Chapter 1

1.0 Introduction………………………………………………………………...4

Chapter 2

2.0 General introduction………………………………………………………..5

2.1.0 Ceramics and clay Mineralogy Division………………………………....5

2.1.1 How clays are located/sites ………………………………………….......6

2.1.2 Line of activities for acquiring clay samples…………………….............6

2.1.3 At the laboratory ………………………………………………………...7

2.1.4 Test pieces..................................................................................................7

2.1.5 The Bricket test..........................................................................................7

2.1.6 The MOR test............................................................................................7

Chapter 3

3.0 The XRF laboratory......................................................................................8

Chapter 4

4.0 The museum.................................................................................................9

4.1.0 The Western unit......................................................................................10

4.1.1 The Birimian.............................................................................................10

4.1.2 Economic significance..............................................................................10

4.1.3 The Tarkwaian Group...............................................................................10

4.2.0 The Dahomeyide.......................................................................................11

4.2.1 The Buem structural unit..........................................................................11

4.2.2 The Togo structural unit............................................................................11

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4.2.3 The Dahomeyan......................................................................................12

4.3.0 The Voltaian Supergroup........................................................................12

4.3.1 The Kwahu Group..................................................................................12

4.3.2 The Oti Group.........................................................................................12

4.3.3 The Obosum Group.................................................................................13

4.3.4 Economic significance.............................................................................13

Chapter 5

5.0 The mineral laboratory...............................................................................13

5.1.0 Thin-section preparation..........................................................................13

5.2.0 Polished section.......................................................................................16

5.3.0 Sample impregnation................................................................................16

5.4.0 Abrasives..................................................................................................16

5.5.0 Sample preparation...................................................................................17

5.5.1 Sieve analysis............................................................................................17

Chapter 6

6.0 Geophysics...................................................................................................19

6.1.0 radiometric method....................................................................................19

6.2.0 Electrical Methods.....................................................................................20

6.2.1 Electrical Resistivity..................................................................................20

6.2.2 Induced Polarization...................................................................................20

7.0 Gravity Method..............................................................................................20

8.0 Magnetic Method...........................................................................................20

9.0 Conclusion...................................................................................................21

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CHAPTER 1

1.0 INTRODUCTION/BACKGROUNG

The Geological Survey Department (GSD) was established in 1913 by the colonial

administration under the Directorship of Sir Albert Kitson to investigate and establish more

exactly the extent and quality of both existing and yet undeveloped areas of mining activity

and to prepare for their exploitation. The first office of the department was located at the

River Ankobra Junction in Prestea. The Department finally settled at Accra where major

policy decisions on mining are taken. It headed by Dr. Daniel Boamah the director and

assisted by two deputy directors Dr. Solomon Anum (technical) and Mr. Emmanuel Mensah

(administrative).

This report captures four weeks of internship program at the Geological Survey Department,

Accra–Ghana. It entails the line of activities or training I received from the Geological

Survey Department from the 6th of June to the 30th of July 2016.

As part of the training, I was attached with the Ceramics and Clay mineralogy division, the

X-Ray Flourescent laboratory, the Museum, the minerals laboratory and the geophysics

division where I learnt wide categories of things clearly spelt out in this report.

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CHAPTER 2

2.0 GENERAL INTRODUCTION

On my first day at the Department, I was introduced to all the various divisions.

Some of these places are the Ceramics and Clay Mineralogy Division, the X-R

Fluorescent laboratory, the Minerals Laboratory, the Museum, the Geophysics

Division, the stores, the Geochemical Laboratory and the library.

2.1.0 THE CERAMICS AND CLAY MINERALOGY DIVISION

Mr. Amoako Asare and Mr. Ofori Nyarko as his assistant head this division.

At this division, I learnt how clays are classified based on color, mineralogy,

response to heat and the place of formation of these clays.

The following are the various classes of clay with different bases (rationale) of

classification:

Place: primary (in-situ) clays and secondary/transported clay

Mineralogy: Montmorillonite (Smectite), Kaolinite and Illite group.

Response to heat: earthenware clay, refractory clay, stone-ware clay and bowl

clay.

Colour: brown clay, white clay and black clay (more rare).

Other classes may further be obtained on elemental basis.

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2.1.1 HOW CLAYS ARE LOCATED SITES

Through geological activities River mouth

Samples of clay brought for investigation River banks

The factory site Deltas

In the course of work

2.1.2 LINE OF ACTIVITIES FOR ACQUIRING CLAY SAMPLES

Do Topographic sheet work

Take GPS co-ordinates.

Assess the size of the deposit.

Make grid line for the deposit on the map and/or the ground.

Dig 1m×1m or 1m×1.5m pits.

Examine the pit for clay layers.

Take block samples of clay from the pit.

The weight of the samples should be between 3Kg-5Kg.

Identify the pit by a name and label the samples from the pit with the same

name.

Bring samples to the laboratory for analysis.

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2.1.3 AT THE LABORATORY

The samples are grounded to make them fine, dried, sieved with 30 mesh size and

tested.

At the Ceramics Division, the analysis is usually centered on their response to

heat or their behaviour after heating. Hence the two tests conducted are the

Bricket and Modulus Of Rapture (MOR) tests.

2.1.4 TEST PIECES

2.1.5 THE BRICKET TEST

Add a measured amount of water to the clay powder to obtain a paste-like

mixture. Press the body into a mould and smoothen the surface. Make diagonal

marks on the moulds to measure the percentage shrinkage of the clay when dry.

Gently dry the paste-like body to prevent deformation. Determining the shrinkage

percentage helps in knowing the amount of clay material to use for making a clay

artifact or it determines the composition of material for making a clay product.

2.1.6 THE MOR TEST

Repeat the procedure above but use an MOR mould to to obtain the bars. The bars

are then tested for their strength. Under this test the bars are heated to 10000C-

11000C to make them mature. This clay that are used for commercial ceramics

works are heated to this temperatures. Pressure is the mounted on the bars until

the rapture. The tension in the bar can be calculated using the formula below

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T = 3WL/2BT

Where W= breaking load, L= distance between support points,

B= width T= thickness

At the Ceramics Division they study or examine the physical properties such as the

raw color, fired color, moisture content, wet and dry sieve analysis, density,

shrinkage and porosity of the clay samples.

In the ceramics industry the production techniques employed in making ceramics

products are throwing, pressing, slip casting and hand building.

One important thing I learnt from the ceramics Division is the making of Plaster

Of Paris from gypsum.

CHAPTER 3

3.0 THE X-RAY FLOURESCENT LABORATORY

Mr. Mohammed Awan A. Rashid heads this Division.

The XRF laboratory’s main function is to find the compositions of major elements

and minor elements that make up a rock sample. The manner in which the test is

done is laid down below:

Take a 4g sample of a labeled powdered rock sample using the electronic

balance.

Add 0.9g of powdered wax to the sample

Rinse the sample cups with acetone to avoid contamination of sample by

impurities in the cup.

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Pour the sample into the cup and put in a homogenizer for about 3 minutes to

obtain a uniform mixture.

Pour the sample into the castor and apply pressure under a hydraulic press

after rinsing the castor with acetone.

Remove the pellet from the castor.

Put the sample into the sample plate and insert into the XRF spectrometer

which is synced with a PC.

The result of the test is displayed on the PC, which could then be printed and

interpreted.

CHAPTER 4

4.0 THE MUSEUM

Mr. Anani Ayitey is the one in charge of the museum.

At the museum, I was introduced to the geology of a Ghana and the rock samples

of the respective rock types that were present. The geology of Ghana is broadly

divided into five main lithostratigraphy based on geochronological, lithotectonic,

lithology, and structural data. They are the paleo-supracrustal known as the

Birimian or the Western units (including the Tarkwaian and the intrusives), the

Pan-African Mobile belt or the Dahomeyide, the Voltaian supergroup, the coastal

sedimentary deposits, and the recent deposits.

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4.1.0 THE WESTERN UNIT

4.1.1 THE BIRIMIAN

The Birimian is known to have an average age of 2.1Ga. It consists of

metasedimentary basins and metavolcanic belts. The belts have a NE general

trend except the Lawra belt, which trends NS, and they are separated by the basins

giving rise to an undulating regional topography.

The belts and the basins were formed contemporaneously. The Birimian rocks are

weakly metamorphosed with an amphibolites facies metamorphism. The belts are

known globally as the green stone belt. The metasediments are mainly made up of

phyllite, schists and greywacke and the metavolcanics are made up of mainly

tholeitic basalts, andesites, rhyolite and dacite.

The Birimian rocks are intruded by the basin type syntectonic, deformed

granitoids also known as the Cape-Coast type granitoids and the belt type post-

tectonic, undeformed granitoids also known as the Dixcove type granitoids.

4.1.2 ECONOMIC SIGNIFICANCE

The Birimian rocks have huge economic significance. They host the main gold

resources and reserves that are being mined currently. Other minerals such as

bauxite, manganese and diamonds are present.

4.1.3 THE TARKWAIAN GROUP

The Tarkwaian rocks are about 1.65-1.85Ga old. They are found mainly in the

synformal belts of the volcanic belts in the Birimian in Ghana. They are

considered to be the erosional product of the Birimian rocks. it is divided into the

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Kawere group, the Banket series , Tarkwa phyllites and the Huni sandstone. They

are well exposed in the Ashanti belt and the Bui belt. It weakly metamorphosed

and weakly deformed than the Birimian rocks but at some places they are

interfolded with the metasediments. The Banket unit is the most economic unit of

the Tarkwaian group. It hosts commercial quantities of gold mineralization.

Manganese is also mined from the Tarkwaian rocks at Nsuta.

4.2.0 THE DAHOMEYIDE

The Dahomeyide is divided into the western unit, the sure zone and the internal

unit.

4.2.1 THE BUEM STRUACTURAL UNIT

This is the western most unit of the Dahomeyide. It is dated to be around 600-

650Ma old. The Buem consist of metasandstones, limestone, jasparoids, and meta

basalts. They are the least metamorphosed among the Dahomeyide.

4.2.2 THE TOGO STRUCTURAL UNIT

This forms part of the western unit of the Dahomeyide. It is bounded by thrust

faults. The Togo rocks are highly deformed and highly metamorphosed. They are

made of phyllites, schists, quartzites, and phyllonites.

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4.2.3 THE DAHOMEYAN

The Dahomeyan consists of the Ho augen gneisses, the

pyroxene/hornblende/garnetiferous gneiss of the suture zone and the migmatite

gneiss of the internal unit. They are dated to be around 2.1Ga old.

4.3.0 THE VOLTAIAN SUPERGROUP

This divided into the Kwahu group, the Oti group and the Obosum group.

4.3.1 THE KWAHU GROUP

This is the oldest of the Voltaian dated to about 1.0Ga old. It is mainly made up of

massive cross-bedded feldspathic sandstones. They outcrop along the margins of

the basin. They are correlated with Togo structural unit based on age and

lithologic similarities. They are responsible for the Kwahu and Gambaga

escarpments.

4.3.2 THE OTI GROUP

This lies unconformably over the Kwahu group by a basal conglomeritic layer

which marks a period of glaciation. They consist of tillite, limestone and silexites

which forms the triad and some shales and siltstones. It is correlated with Buem

structural unit of the Dahomeyide on the basis of lithological similarities.

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4.3.3 THE OBOSUM GROUP

This is occupies the central part of the basin. They are molasse sediments which

increase in thickness towards the Dahomeyide. It lies unconformably on the Oti

group.

4.3.4 ECONOMIC SIGNIFICANCE

The Voltaian, mined for limestone and currently petroleum explorations are under

way to discover oil reservoir(s) in the basin. The Sheini Iron ore deposits is also

found within the voltaian.

CHAPTER 5

5.0 THE MINERALS LABORATORY

5.1.0 THIN-SECTION PREPARATION

A thin-section is prepared for the purpose studying the rocks under the

mineralogical microscope. They are done o as to identify the various minerals, the

microstructures and the texture which make up the rock. Below are the

summarized steps for preparing a thin-section:

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PARENT MATERIAL

SAMPLE SAMPLE IDENIFICATION

IMPREGNATION

(Weathered material

Soils, sediments etc)

TRIMMING/SLABBING

BEST FACE FLAT LAPPING

BONDING OF SLAB TO THE PREPARED

SIDE

REMOVAL OF BULK SPECIMEN

FRONTAL THINNING OF BONDED SPECIMEN

COVER-SLIPPING OF THIN SECTION

READY FOR ANALYSIS

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A sample thin section was analyzed and the details are presented below. The sample

number is GA1014B obtained from the archives of the Department.

Muscuvite

Biotite

Biotite

Muscuvite

Quartz

Feldspar

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Fig.1 PPL view of the sample.

Fig.2 XPL view of the sample.

From the mineral association in the sample, it can be inferred that the rock sample

may be a granite. The crystals show slight trend in a certain direction and this may be

indicative of the beginning of deformation of the rock. The locality from which the

rock was analyzed may not have undergone intense or severe tectonic stress due to

the absence of microstructures like microcrennulations, fractures, banding foliation

etcetera. However due to the slight alignment of the crystals tectonic stresses may be

very prominent in the course of time.

5.2 POLISHED SECTION

Polished sections are made to study ore minerals. They can be made in 10 cm × 10

cm or 10cm × 5cm based on specification. The parent rock sample are cut and

polished to give a very smooth surface that can support maximum reflection of light.

5.3 SAMPLE IMPREGNATION

This is done to samples other than solid fresh rocks such as soils, sediments,

weathered rocks and so on. The material is obtained in a powdered form, this is then

mixed uniformly with resins and pressed into a mould. It is then dried to obtain a

solid sample in the shape of the mould. This can be used subsequently for polished

section or thin-section.

5.4 ABRASIVES

The abrasives used are sand papers of various grit sizes (60, 180, 240, 320, 400, 600,

800 and 1200), diamond abrasive of various sizes (100 mesh, 220 mesh, 45 microns,

and 30 microns).

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5.5 SAMPLE PREPARATION

Sample preparation is means of preparing a sample for analysis. Soil samples are

dried, sieved and the final pulverized form is used for analysis. Rock samples are first

crushed in the Jaw cracker before they are sieved and used for analysis. The product

may be used for chemical analysis, elemental analysis (very fine sample) or for sieve

analysis (various size ranges).

5.5.1 SIEVE ANALYSIS

Sieve analysis investigation is done for many reasons. It helps to identify the type soil

at a locality, for engineering analysis and for agricultural analysis. A sieve analysis

exercise was taken in order to acquire the skill for doing the investigation. The result

is shown below:

Sieves No.

(µm)

Weight of

sieves(g)

Weight of

sieves and

sample(g)

Deduced

weight of

sample(g)

Percentage

retained

(%)

Percentage

passed.

(%)

425 464.8 591.7 126.9 69.2 30.8

300 453.7 458.7 5.0 2.7 27.3

250 439.3 448.1 8.8 4.8 22.5

180 257.7 275.5 17.8 9.7 12.8

Pan 438.7 462.8 24.1 12.8 0

Total mass of sample= 183.3 g the sample was shaked for 5 minutes.

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CHAPTER 6

6.0 GEOPHYSISCS

Geophysics is the application of the basic principles of physics for solving geological

problems. The methods measure physical properties of rocks and their contrast with the

Earth’s natural fields. Below is a table illustrating the physical properties measured and their

corresponding geophysical method.

Physical properties Geophysical method

Density Gravity Methods

Magnetisations Magnetic Methods

Radioactivity Radiometric Methods

Acoustic velocity Seismic Reflection

Electrical Conductivity Electromagnetic

Electrical Polarisation Electrical and Induced Polarisation

Geophysical data can be interpreted using the forward modeling or the inverse modeling.

These yield either a quantitative or a qualitative outcome. However, it must be stressed that

no one geophysical method can be used to make conclusive inferences of what is beneath the

subsurface as such at least two of the methods are used to corroborate the findings made in

an investigation.

6.1.0 RADIOMETRIC METHOD

This is the measurement of gamma radiations from the decay of unstable isotopes usually

within the soils. The method relies on the assumption that soils are the products of the

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bedrocks beneath them hence, the method is not suitable for desert and lateritic areas. The

radioactive elements whose signatures are usually measured are potassium, uranium and

thorium.

6.2.0 ELECTRICAL METHODS

6.2.1 ELECTRICAL RESSITIVITY

The method measures the ability of the rocks to conduct electricity. It is dependent on the

water content, porosity, dept of burial, fluid saturation, the lithology, the permeability,

presence, or absence of salt in the water and so on.

6.2.2 INDUCED POLARIZATION

The method measures the ability of a rock to hold electric charge for a period of time. They

are affected by sulphides in a rock will hold charge and discharge as well as clays will also.

7.0 GRAVITY METHOD

The gravity method is a passive geophysical method that measures variations in the Earth’s

gravitational field. Gravity measures are greatly affected by the densities of different rocks

and this creates an anomaly against the background gravity field.

8.0 MAGNETIC METHOD

The magnetic method like the gravity method also measures the variations in the Earth’s

magnetic field. They depend on the magnetic susceptibilities of the various rocks beneath the

subsurface. Also depending on the part of the world where the survey is undertaken the

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magnetic anomaly will take the shape of the effects the north and south pole of the Earth’s

magnetic field has on the measurements.

9.0 CONCLUSION

The internship program was well organized with many activities during the time that I was

attached with the Geological Survey Department. I have acquired many skills from the

program and therefore I deem my time with the Department as very helpful for my academic

career.

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