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 4̊5 ̍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.

http://www.ghanadistricts.gov.gh/



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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

Education