The geology of aframtwo, dabaa, wioso and their environs in the ashanti region of ghana

Field mapping report 2015 group one
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Contents
ACKNOWLEDGEMENT..........................................................................................................................................2
ABSTRACT:............................................................................................................................................................3
INTRODUCTION:...................................................................................................................................................4
CHAPTER 1. BACKGROUND OF STUDY AREA.......................................................................................................5
1.1 LOCATION:..................................................................................................................................................5
1.2 TOPOGRAPHY:............................................................................................................................................5
1.3 CLIMATE:.....................................................................................................................................................5
1.4 VEGETATION:..............................................................................................................................................5
1.5 DRAINAGE...................................................................................................................................................5
1.6 LAND USE....................................................................................................................................................5
CHAPTER 2. MAPPING EQUIPMENT AND PROCEDURE.......................................................................................6
2.1 EQUIPMENT AND TOOLS USED..................................................................................................................6
2.2 MAPPING PROCEDURE...............................................................................................................................7
CHAPTER 3. MAPS AND SECTION.........................................................................................................................8
3.1 BASE MAP...................................................................................................................................................8
3.2 TRAVERSE MAP ..........................................................................................................................................8
3.4 OUTCROP MAP...........................................................................................................................................8
3.5 STRUCTURAL MAP......................................................................................................................................9
3.6 GEOLOGICAL MAP....................................................................................................................................10
3.7 CROSS SECTION ........................................................................................................................................11
CHAPTER 4. GEOLOGICAL SETTING....................................................................................................................12
4.1 REGIONAL GEOLOGY................................................................................................................................12
4.2 ECONOMIC GEOLOGY: .............................................................................................................................12
4.3 STRATIGRAPHY:........................................................................................................................................12
4.4 STRUCTURES:............................................................................................................................................13
4.5 IGNEOUS ACTIVITY:..................................................................................................................................15
4.6 METAMORPHISM:....................................................................................................................................16
CONCLUSION ......................................................................................................................................................17
RECCOMMENDATION ........................................................................................................................................17
REFERENCES........................................................................................................................................................17
APPENDICES........................................................................................................................................................18
APPENDIX ONE: SAMPLE IDENTIFICATION....................................................................................................18
APPENDIX TWO: ATTITUDES OF STRUCTURES FOR ROSE PLOTS .................................................................20

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ACKNOWLEDGEMENT
We first thank the Almighty God for his guidance and protection during the course of the field mapping.
Our sincere gratitude also goes to the lecturers who were with us on the field during the mapping
process. We also thank Dr S. K. Y Gawu, and Madam Lydia for providing necessary guidance during
the preparation of our maps and report. This field mapping exercise would not have been the same
without your selfless commitment.
We also wish to express our sincere appreciation to the teaching assistants for their help and solid
illustrations on rock analysis.

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ABSTRACT:
Geological field mapping is the process of obtaining surface and sub-surface information on rock types
underlying the different parts of a terrain as well as significant features such as faults, fold structures,
mineralization zones, etc. Our geological field mapping exercise was carried out at Adankwame,
Afrantwo and their environs covering 1 ̊37 ̍40’’ - 1 ̊45 ̍W and 6 ̊45 ̍ - 6 ̊48’38’’N on the base map.
Samples from outcrops encountered on the field were taken to the laboratory for further analysis.
Information obtained from the field and laboratory was used to produce a geological map of the area.
From the analysis made it can be inferred that the area mapped is generally underlain by granitoids, as
lithological materials encountered were mainly intrusive igneous rocks.

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INTRODUCTION:
In June 2014, mapping was done around the northern part of Kumasi in the Ashanti Region of Ghana
covering 1 ̊37’40’’ - 1 ̊45 ̍W and 6 ̊45 ̍ - 6 ̊48’38’’N. The area assigned to our group was traversed using
the roads and footpaths on the base map. During traversing, detailed description and attitude
measurement of geological structures, outcrops and exposures were recorded in field notebooks.
Samples of outcrops were taken to the laboratory for further analysis.
The aim of this field mapping exercise is to enable students to obtain the necessary practical knowledge
needed for the job world in the identification of geological structures, outcrops and exposures, the
measurement of the attitudes of structures in these outcrops and exposures and using acquired field
information and their theoretical knowledge to produce a geological map.
This report gives a detailed overview, of all activities and information gathered over the two week
period spent studying the geological features present at Afrantwo, Adankwame, Dabaa, Wioso and
their environs. It also encompasses results from the laboratory analysis of the samples taken from this
area. It should however be noted that laboratory analysis as mentioned throughout this report refers to
only the physical analysis of rock samples, as Petrographic and Chemical analysis could not be made
due to lack of necessary instrumentation.

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CHAPTER 1. BACKGROUND OF STUDY AREA
1.1 LOCATION:
Located in the northern part of Kumasi in the Ashanti Region of Ghana covering 1 ̊37 ̍40’’ - 1 ̊45 ̍W
and 6 ̊45 ̍ - 6 ̊48’38’’ ̍N.
1.2 TOPOGRAPHY:
The area has alternating highlands and lowlands. The highlands are mostly to the east of the mapped
area.
1.3 CLIMATE:
The climate is that of the semi-equatorial belt characterised by double rainfall maxima occurring in
July and November. The dry season occurs between December and April and is associated with drought
conditions. Temperature is found to be uniformly high all year round with a mean annual temperature
of 26 ̊c. (www.ghanadistricts.gov.gh)
1.4 VEGETATION:
Mostly semi-deciduous forest comprising open forests and closed forests. However most of the original
forest has degenerated into secondary forest and grassland due to indiscriminate felling of trees and
poor farming practices. (www.ghanadistricts.gov.gh)
1.5 DRAINAGE
The area is well drained. The drainage patterns are mostly sub-dendritic.
1.6 LAND USE
The most common use of land in the area is for agricultural purposes. Common crops include maize,
cassava and plantain.
Also, the exposed granitoids are being quarried for aggregates.

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CHAPTER 2. MAPPING EQUIPMENT AND PROCEDURE
2.1 EQUIPMENT AND TOOLS USED
The equipment and tools used during the field mapping exercise include;
base map for the mapping exercise. This had prominent features such as roads, footpaths, schools,
churches, etc. which aided in the determining of our positions on the field. The traverse, structural,
outcrop and geological maps were all drawn on the base map.
Compass and clinometer for measuring attitudes (dip and strike) of structures on the field.
hammer for breaking the rocks as samples and also to expose fresh surfaces.
Hand lens to examine the mineral grains of the rocks more closely.
Field notebook for recording information and observations, such as, strike and dip values, outcrop
description, sample names, etc.
Markers for the marking and naming of the samples.
Field bag for holding samples.
Camera for taking photographs of the outcrops and other significant features.
Fig. 1. Some of the equipment used during the mapping exercise.(measuring tape, compass, hand lens,
geological hammer, cutlass, field notebook, from left)

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2.2 MAPPING PROCEDURE
The following procedure was used during the field mapping exercise;
along roads and footpaths to find outcrops and/or exposures. We would traverse
the nearby bushes if outcrop or exposures are rare to find along the roads.
etermine the location coordinates of the outcrop or other feature using the GPS.
easily
recognisable minerals, and suggest a field name for the outcrop in our field notebooks.
attitude measurements of the structures in the outcrop, noting which structures they
are.
ure to aid future analysis.
We took fresh samples of the outcrop or exposure for further analysis to confirm the field name or
otherwise.

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CHAPTER 3. MAPS AND SECTION
3.1 BASE MAP
A base map of the area was provided for the exercise. It simply shows geographic features of interest
and relief of areas, using contours. It is the base on which the other maps were developed.
3.2 TRAVERSE MAP
This map was developed to show the route of traverse in the field. The paths of each day were
differentiated using different colours.
Fig 2 Traverse map
3.4 OUTCROP MAP
It shows the locations of outcrops seen in the field. The different types of outcrops were also
differentiated using colours. (Yellow for metasediments, pink for fine grain granitoids and purple for
coarse grain granitoids)

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Fig 3 Outcrop map
3.5 STRUCTURAL MAP
A map showing the structural measurements recorded on the field. Since these structures are usually
taken on outcrops, their locations should coincide with the locations of outcrops on the outcrop map.
Fig 4 Structural map

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3.6 GEOLOGICAL MAP
The primary aim of the mapping exercise is to produce a geological map of the area and write a report.
The geological map shows the rock units underlying the area. It is essentially a combination of the
outcrop map and the structural map. The similar rock outcrops are connected and boundaries of
different rock units are shown or inferred where they were not seen on the field.
Fig 5 Geological map

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3.7 CROSS SECTION
We took a cross section along 6 ̊ 47’ from “A” to “B” as shown on the geological map. The cross
section shows the progression of rock units in moving from “A” to “B”.
Fig 6 Cross section at 6047'

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CHAPTER 4. GEOLOGICAL SETTING
4.1 REGIONAL GEOLOGY
Regionally, the area is in the Ashanti uplands. The geology is that of the lower Birimian series. The
lower Birimian forms part of the Birimian system. The Birimian system is one of the units forming the
West African cratonic region.
The Birimian terrains in the West African craton are a mixture of highly metamorphosed volcanic and
plutonic rocks with low grade metavolcanic and metasediments. The Birimian is divided into the older
“lower Birimian”, consisting of predominantly metasedimentary rocks, and a younger “upper
Birimian”, consisting chiefly of metavolcanic rocks.
Our area falls within the Lower series which consist of metasedimentary rocks mainly phyllites,
greywackes. Also associated are intrusives of felsic (granitic and granodiorite) and mafic (dolerite)
compositions.
4.2 ECONOMIC GEOLOGY:
The granitoids of the area are suitable for use as aggregates for construction. There is a quarry,
operating on the Achinsi classification range.
The phyllite can also be used for decoration purposes.
4.3 STRATIGRAPHY:
The major rock units encountered were the birimian granitoids and metasediments. From the principle
of original horizontality, sediments would be laid horizontally or almost horizontally. The fact that the
sedimentary rocks have been metamorphosed and also inclined provide evidence of deformation. The
metamorphism was most likely due to heat from a magmatic intrusion. The intrusion could also be the
cause of the dipping nature of the metasediments. Combining these, we can infer that sedimentary
rocks were laid, they got intruded by the granitoids. The force of the intrusion disturbed the sedimentary
beds, causing them to incline. The heat from the magma metamorphosed the sedimentary rocks. There
are two types of granitoids, differentiated on the basis of grain size into coarse grain and fine grain
types.

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4.4 STRUCTURES:
The major geological structures encountered were joints. Some of the joints have provided space for
vein intrusions. Some of the veins were quartz and others were pegmatite veins. The joints strike in the
North – East direction, generally. The foliations of the metasediments strike in the North – East
direction and dip generally in the North – West.
Stereo plot of foliation strike showing a general direction of NE-SW.

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Rose diagram showing general strike direction of quartz veins (NE-SW)

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Rose diagram showing general strike of pegmatite veins (almost N-S).
4.5 IGNEOUS ACTIVITY:
The most prominent igneous bodies are the granitoids. There were quartz and pegmatitic vein and
veinlet intrusions in both the fine and coarse grained granitoids.
Fig.2. Granitoid with quartz and pegmatite intrusions at Asuofua.

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4.6 METAMORPHISM:
The presence of phyllite in and around Dabaa, Kapro and Kumi is an evidence of a medium grade
metamorphism. Again there were areas in Ntiribuoho and Nkukua where the minerals in the granitoids
have started aligning themselves. Thus, the area is moderately metamorphosed.
Fig.2. Outcrop of phyllite seen near Dabaa.

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CONCLUSION
The area is underlain by three major rock types, thus, fine grain granitoids, coarse grain granitoids, and
metasedimentary rocks (phyllite). The granitoids intruded original sedimentary rocks, metamorphosing
them. Therefore, even though the area appears dormant and stable at present, it must have undergone
remarkable igneous activity in the past.
RECCOMMENDATION
1. The pre-mapping training should done over a longer duration to allow students to really grasp
the concepts of mapping, especially determining attitudes of structures.
REFERENCES
1. GEOLOGY AND MINERAL DEPOSITS. Ghana Ministry of lands forestry and lands (Mines
section). Retrieved 2009-03-17.
2. “Geological evolution and metallogeny through the Birimian”. (PDF). Prospectors and
Developers Association Canada.2009. Retrieved 2009-03-17.
3. J.P. Miles, P. Ledru, P. Ankrah, V. Johan, E. Marcoux and Ch. Vinchon. “The metallogenic
relationship between Birimian and Tarkwaian gold deposits in Ghana”. SpringerLink.
Retrieved 2009-03-16.
4. www.ghanadistricts.gov.gh (website), accessed on 8th
April, 2015.

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APPENDICES
APPENDIX ONE: SAMPLE IDENTIFICATION
SPECIMEN PICTURE COLOUR TEXTURE MINERAL
COMPOSITION
ROCK
NAME
TA
050/14
Black,
white
Fine to
medium
interlockin
g grains
Quartz, Biotite
and Feldspar
Basin
type
granitoid
(felsic)
TA
140/14
Black,
white
Medium to
coarse
interlockin
g grains
Biotite, Feldspar
and Quartz
Basin
type
granitoid
(felsic)
TA
136/14
White,
black
Medium to
coarse
interlockin
g grains
Biotite, feldspar
Quartz and
muscovite
Basin
type
granitoid
(felsic)

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TA
099/14
Grey, Fine
grained and
Foliated
Mica and Chlorite Phyllite
TA
032/14
Light grey
with dark
specks
Fine
interlockin
g grains
Biotite,
muscovite,
feldspar and
Quartz
Basin
type
granitoid
(felsic)
TA086/
14
Milky
white
glassy Quartz quartz

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APPENDIX TWO: ATTITUDES OF STRUCTURES FOR ROSE PLOTS

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The geology of aframtwo, dabaa, wioso and their environs in the ashanti region of ghana

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