MAKERERE UNIVERSITY.
COLLEGE OF NATURAL SCIENCES (CoNAS).
SCHOOL OF PHYSICAL SCIENCES
DEPARTMENT OF GEOLOGY AND PETROLEUM STUDIES.
A REPORT ON THE GEOLOGICAL MAPPING PROJECT CARRIED OUT IN IGAYAZA, ISINGIRO DISTRICT, SOUTH WESTERN UGANDA IN MAY 2018
COMPILED BY;
OCENG IVAN OTIM
REGISTRATION NUMBER: 16/U/1009
STUDENT NUMBER: 216000414
CORDINATOR: Dr K AANYU
COURSE: BACHELOR OF SCIENCE PHYSICAL (GEOLOGY)
COURSE CODE: GLO 3203.
RESEARCH PROJECT
A research project report submitted to the Department of Geology and Petroleum Studies- Makerere University, in partial fulfillment of the requirements for the award of Bachelor of Science degree
29th May 2019
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DEDICATION This report is dedicated to my great lecturers who have greatly not only imparted but also enhanced and nurtured me in this field of geology. It also goes out to my loving parents for not giving up at any one point in my life and studies and to my lovely friends and all who have supported me in any way throughout my struggles to shape my future.
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ACKNOWLEDGEMENT I, first of all thank the Almighty God for the grace and protection provided throughout the execution of all parts of this mapping exercise Great gratitude is also extended to my hardworking and resilient field supervisors, Dr.K Aanyu, Dr.B Nagudi, Dr. A. G Batte, Dr J V Tiberindwa, and Mr. W Kawule who provided the necessary guidance and knowledge required for proper acquisition of data and field experience. Sincere appreciation also goes out to my group mates Ms. Ninsiima Bridget, Mr. Lingo Deogratius, Mr. Kakande Haruna, Mr. Buyinza Hannington and Mr. Sseruwaji for the tireless effort and sharing of the knowledge while carrying out this project. I also recognize the great love and commitment of my parents and family towards shaping my life so sincere gratitude for them
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ABSTRACT This geologic mapping exercise was carried out in Igayaza located in Isingiro district in south western part of Uganda. The area mapped is within the Karagwe Ankolean system of rocks which stratigraphically overly the Basement complex rocks. The Karagwe-Ankolean (K-A) system (1400-950Ma) in Uganda is the northern most extension of the Kibaran mobile belt. The sediments of this system occupy a continuous area in southern and central Kabale, southern Mbarara, Bushenyi, Isingiro, Rakai and south eastern Masaka districts. The Buhweju plateau and surrounding hills in Bushenyi district belong to this system as well. This field work was majorly aimed at imparting the skill required to carry out a geologic mapping exercise besides other aims such as familiarizing with field conditions and equipment, collection and interpretation of data among others. The area to be mapped was gridded and we exclusively mapped area A. Therefore, this report contains majorly data obtained within this region which includes the rock types, structures present, economic potential, stratigraphy, metamorphism of the area as well as the regional synthesis using the data obtained by other groups as well. In the area A mapped the major rock types observed include Quartzite, ferruginous shales, Phyllitic shale, Granite, phyllites and conglomerates. Mudstones and slates were also observed in other areas within the region that were out of the area A. All these rocks, being in a region greatly affected by various stress and deformation events such as faulting and folding possessed a number of structures such as quartz veins, boudins, foliation, lamination and mud cracks, joints, beds and folds and folds most of which trended in the NW-SE direction, the major regional trend and a few in the NE-SW direction, the cross-fold trend. Some of these structures not only existed in a macro but also in a micro scale as will be shown in the petrographic analysis. Economic activities in the area included quarrying of majorly quartzite and mining of sand for the construction industry. Agriculture through growing of majorly Bananas in the valleys and the arena and rearing of livestock was also carried out.
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TABLE OF CONTENTS DECLARATION...... Error! Bookmark not defined. APPROVAL ...... Error! Bookmark not defined. DEDICATION...... ii ACKNOWLEDGEMENT ...... iv ABSTRACT ...... v LIST OF FIGURES ...... viii CHAPTER ONE: INTRODUCTION ...... 1 1.1 BACKGROUND...... 1 1.2 OBJECTIVE OF STUDY ...... 1 1.3 LOCATION AND ACCESSIBILITY ...... 2 1.4 PHYSIOGRAPHY ...... 3 1.5 CLIMATE AND VEGETATION ...... 3 1.6 LAND USE AND SETTLEMENT ...... 4 1.7 DRAINAGE ...... 5 1.8 REGIONAL GEOLOGY ...... 6 1.8.1 Literature review ...... 6 1.8.2 General geology ...... 8 1.8.3 Structure of the K-A system...... 10 1.8.4 Stratigraphy and geochronology of the K-A...... 11 1.8.5 Tectonic evolution, intrusion and Metamorphism of the K-A...... 13 1.8.6 Mineralization and economic potential...... 14 1.9 MATERIALS AND METHODS USED ...... 14 1.9.1 Materials used...... 14 1.9.2 Methods...... 16 CHAPTER TWO: STRATIGRAPHY ...... 18 2.1 INTRODUCTION ...... 18 2.1.1 Types of stratigraphy ...... 18 2.1.2 Principles of stratigraphy ...... 19 2.2 PREVIOUS WORK...... 20 2.3 STRATIGRAPHIC DESCRIPTION...... 23 2.4 STRATIGRAPHIC ROCK SUCESSION AND DEPOSITION...... 27 vi | P a g e
2.4.1 Rock succession ...... 27 2.4.2 Depositional environment ...... 28 2.5 GEOCHRONOLOGY AND AGE DATING ...... 28 2.6 GEOLOGIC HISTORY...... 29 CHAPTER THREE: STRUCTURES...... 30 3.1 INTRODUCTION ...... 30 3.1.1 Primary structures...... 30 3.1.2 Secondary structures...... 30 3.2 STRUCTURAL DATA...... 30 3.2.1 Obtaining and analysis of Macro structural data...... 30 3.2.2 Stereographic analysis...... 31 3.3 STRUCTURAL DESCRIPTION...... 33 3.4 SUMMARY...... 38 CHAPTER FOUR: PETROGRAPHY AND METAMORPHISM...... 39 4.1 PETROGRAPHY ...... 39 4.1.1 Introduction ...... 39 4.1.2 Sample analysis ...... 39 4.2 METAMORPHISM ...... 48 4.2.1 Introduction ...... 48 4.2.2 Metamorphism of rocks in Area A ...... 48 4.3 SUMMARY...... 49 CHAPTER FIVE: REGIONAL SYNTHESIS...... 50 5.1 INTRODUCTION ...... 50 5.2 HOTSPOTS ...... 51 5.3 GEO-TRAVERSE ...... 56 5.4 SUMMARY...... 61 CHAPTER SIX: COMCLUSION AND RECOMMENDATIONS...... 63 6.1 CONCLUSION ...... 63 6.2 RECOMMENDATIONS...... 64 APPENDIX 1 ...... 67 APPENDIX 2 ...... 73 APPENDIX 3 ...... 78 vii | P a g e
LIST OF FIGURES Figure 1: Synthetic litho-chronostratigraphic logs of the KAB for the WD (a) and ED (b) with position of 4 dated samples (KI 2, KI 7, KI 8 and KI 25) ...... 9 Figure 2: An intensely fractured quartzite outcrop from station A32 (0253986, 9915279)...... 25 Figure 3: A conglomerate at station A30 (0253811, 9916472) on top of the quartzite hence forming an uncomformity...... 26 Figure 4: Ferruginous shale outcrop at station A3 (0252895,9915800) ...... 27 Figure 5: A Pi diagram representing the folds in area A from stereonet software...... 31 Figure 6: (Left) A density diagram and (right) A rose diagram representative of the bedding planes in area A from stereonet software ...... 32 Figure 7: (Left) A density diagram and (right) A rose diagram representative of the joint planes in area A generated by stereonet software...... 33 Figure 8: Joints in quartzites in the area that were mainly trending in the NW - SE (from station A19, (0253853, 9915202)) ...... 34 Figure 9: Bedding in shales at station A21 (0252300, 9915795) ...... 35 Figure 10: A synformal fold within shales (station A14 (0252770, 9915220)) ...... 36 Figure 11: Quartz veins in quartzites at station A17 (0253469,9915055) ...... 36 Figure 12: Twinning as observed in a phyllite sample from station A24 (0252824, 9916420). The two represent images on rotation at 45° ...... 37 Figure 13: A sinistral strike- slip fault in quartzite. (0253179, 9907838) ...... 38 Figure 14: Sample A22S1 ...... 40 Figure 15: Thin section view of sample A22S1(Left)PPL (right)XPL ...... 40 Figure 16: Sample A14S2 ...... 41 Figure 17: Thin section view of sample A14S2(Left)PPL (right)XPL ...... 42 Figure 18: Sample A23S1 ...... 43 Figure 19: Thin section view of sample A23S1(Left)PPL (right)XPL ...... 43 Figure 20: Sample A19S1 ...... 44 Figure 21: Thin section view of sample A19S1(Left)PPL (right)XPL ...... 44 Figure 22: Sample A4S1 ...... 45 Figure 23: Thin section view of sample A46S1(Left)PPL (right)XPL ...... 45 Figure 24: Sample A26S1 ...... 46 Figure 25: Thin section view of sample A26S1(Left)PPL (right)XPL ...... 46 Figure 26: Sample A1S1 ...... 47 Figure 27: Thin section view of sample A1S1(Left)PPL (right)XPL ...... 47 Figure 28: Elongation in quartz grains as highlighted in the thin section above under cross polarized light. (sample A1S1) ...... 49 Figure 29: Block diagram illustrating the style of folding of the K-A system of rocks...... 50 Figure 30: Bedding in shales of area E ...... 52 Figure 31: A water hole in a shale outcrop in area A ...... 56 Figure 32: Voids created from mining of quartz veins containing cassiterite at Kikagati tin mine...... 58 Figure 33: (Left)An enclave at Ibanda granites. (right)a xenolith of tourmaline ...... 58 Figure 34: A sinistral strike slip fault that can also be used in correlating the different ages of the structures. . 59 Figure 35: The granite tors of the Chitwe granites...... 59 Figure 36: The Mafuro crater lake ...... 61 Figure 37:Part of the western arm of the East African rift valley near lake George...... 61
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LIST OF ACRONYMS FY Financial Year
GPS Global Positioning System
K-A Karagwe-Ankolean
KAB Karagwe-Ankolean Belt
KIB Kibaran Belt
Ma Million years
NE North East NNE North-North East
NNW North-North West
NW North West
PPL Plane polarized light
P-T-X Pressure-Temperature-Time
SE South East
SSE South-South East
SSW South-South West
SW South West
XPL Crossed Polars
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CHAPTER ONE: INTRODUCTION 1.1 BACKGROUND Geologic mapping is a very important skill required for everyone in the field of geology therefore to cub this, Makerere University through the department of Geology and Petroleum studies sets up a mandatory field mapping exercise for every student where while in groups, they are required to map an area of about four-square kilometers to attain the necessary and vital skills in this area. A two weeks mapping exercise was organized from 23rd may 2018 to 8th June 2018 in Igayaza Isingiro district which lies within the Karagwe-Ankolean (K-A) system in Uganda which is the northern most extension of the Kibaran mobile belt. The sediments of this system occupy a continuous area in southern and central Kabale, southern Mbarara, Bushenyi, Isingiro, Rakai, SE Masaka districts, the Buhweju plateau and surrounding hills in Bushenyi district. This system is dated to between 1400 and 950 Ma. The system gives rise to mountainous or hilly country with intervening areas of lower relief normally occupied by metamorphosed rocks on the fringes with granites occupying the entire lowland. Quartzites run along the summits of the ridges with the rest of the argillaceous rocks occupying the slopes of the ridges and the valleys within and between the ridges. In the area SE of Mbarara in Isingiro, occurs one of the greatest concentrations of quartzites in Uganda. The quartzites in such massive concentration appear to have restrained the folding of the covering Karagwe-Ankolean rocks, because only broad synclines are recognizable. Phillips (1959) identified quartzitic horizons q1 to q4 of them q4 being the thickest which is underlying the Rugaga plateau and comprising numerous quartzite layers interspersed with thin argillaceous bands. To the N and W in the area underlain by the Igayaza syncline (Biryabarema, 1995), the rocks of the Karagwe-Ankolean system are largely argillaceous and the quartzites attenuate fairly abruptly. Plummer (1960) described thinning of the quartzites on the NW limb of the Igayaza syncline E of the Mbarara-Kikagati road. Up to the stratigraphic level of the Rugaga quartzite, the rocks are fairly metamorphosed, but sometimes sedimentary structures are still recognizable especially in a microscopic scale as observed during the laboratory petrographic analyses This region, having a very diverse geologic environment, creates an ideal condition for both educational and research purposes hence endeavoring a broad coverage by students during this field mapping exercise.
1.2 OBJECTIVE OF STUDY • This research project was majorly aimed at introducing and developing students’ skills in geological mapping, an important one in this field of geology. • To enhance and develop the students’ approach to research, data collection (lithologic and structural), presentation of various findings to an audience and compilation into a detailed report
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• To understand the background and potential of the Karagwe-Ankolean system of rocks in this field further proving the theoretical views learned off the field. • To obtain and gain expertise in the use of various geologic equipment such as the compass and the Global Positioning System (GPS). • To formulate consistent approximate models, basing on the data collected leading to reasonably simple inverse problems and direct deductions from them 1.3 LOCATION AND ACCESSIBILITY
Map 1: Location and accessibility of Isingiro district
Igayaza is located in Isingiro district in south western Uganda about 30km south of Mbarara. Isingiro District is located in southwestern Uganda. It lies between Latitude 1 - 30 degrees south and 0-30 degrees north Longitude 30-20 degrees east and 31-20 degrees east. Its altitude is at 1800 meters above sea level. It borders with the United Republic of Tanzania in the south, Rakai District in the east, Ntungamo District in the west, Mbarara District in the North and North West and Kiruhura District in the North. The area is well and easily accessed through major tracks such as the Mbarara-Kikagati highway that is an extension of the Kampala-Mbarara Highway which is joined by multiple motorable roads and footpaths at major towns and trading centers. Due to the rural and hilly nature of the region, some of the areas cannot easily or even not accessible through use of machinery such as vehicles and motorcycles or bicycles but may be accessed through hiking and climbing. Specifically, the area A mapped lies between coordinates Eastings 252000 and 254000 and Northings 915000 and 917000, a four-square kilometer area accessed through motorable tracks and foot paths and a little portion by the Mbarara-Kikagati highway. This is well represented in map 6 in appendix 3
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1.4 PHYSIOGRAPHY The study area gives rise to mountainous or hilly landscape with the lower lying areas containing metamorphosed rocks as a result of the granitic intrusion and the valleys containing the weathered granites themselves. Quartzites run along the summits of the ridges with the rest of the argillaceous rocks such as the shales and granites occupying the slopes of the ridges and the valleys within and between the ridges. Conglomerates were also found deposited on top of the quartzites hence were considered to be younger than the Quartzites. A type of discontinuity known as a non-conformity. The conglomerates are trending from the northwest to the southeast. The matrix in the conglomerates were found to support the grains hence called a para-conglomerate. The conglomerates were also found to be having clasts that seemed to have been derived from outside the basin of deposition and of different sizes hence considered to be extra-formational and polymictic respectively. 1.5 CLIMATE AND VEGETATION Isingiro has a tropical climate. It basically has two rainy seasons per year, each followed by a dry spell. The climate here is classified as Aw by the Köppen-Geiger system. The District enjoys equatorial climate and it receives average rainfall of 1200mm, temperature normally range from 17 to 30 degrees Centigrade averaging to a temperature of 20.7 °C. It has two main rainy seasons during the months of March to April and September to November in each calendar year. Some areas however have recently been faced with dry spells especially in Masha sub-county and Kikagati. Some parts of Bukanga are also sometimes unfortunate as they get hit by hail storms especially at the beginning of the September to November wet rainy season. The warmest month of the year is often July and August and the lowest average temperatures in the year occur in June. Wetlands in Isingiro District occupy 2.08percent of the total land area. Seasonal wetlands occupy at least 60percent, permanent wetland covers 40percent. The District’s ecological system is prone to chronic drought and the terrain is characterized by bare hills and rangelands. Thorny bushes and trees, grassland savannah, scattered swamps and valleys, and bare hills with stone deposits characterize the District vegetation. The soils are mainly of clay, late rite loam, and sandy nature. The District natural resources include fertile soils in almost all sub-counties. The district has two forest reserves under NFA and 1 natural forest which is privately owned. The district is embarking on an afforestation plan. In the financial year (FY) 2007/08, 119,965 trees were planted and in FY 2009/10, the District covered 120Ha of land with trees.
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1.6 LAND USE AND SETTLEMENT The 2002 census classified land tenure as; customary, free hold, mailo land, leasehold and others. The table below shows Land Tenure of Occupancy by sex of Household Head in the District. Information in the table indicates that 76.23 percent of the land is held under customary land tenure system while 1.49 percent is under Mailo land. Table 1: Land Tenure of Occupancy by sex of Household Head
Land Tenure Male Head Female Head Total Percentage Total Customary 40,828 10,566 51,394 76.23 Free hold 3,253 781 4,034 5.98 Mailo land 788 219 1,007 1.49 Lease hold 2,607 533 3,140 4.66 Other 6,129 1,718 7,847 11.64 Total 53,605 13,817 67,422 100.00
Source: District census analytical report-2002 The major activity carried out in this area is Agriculture. Agriculture activities in the area include; traditional Agriculture namely crop growing, livestock rearing or herding especially, fishing, hunting and gathering The sector provides employment for 72 percent of the labour force in the entire national economy. However, most the Agriculture is of a subsistence nature. This is generally characterized by the engagement in crop production, livestock rearing and other associated activities mainly for ‘own consumption’. Subsistence farming is usually associated with risk, uncertainty (when based on seasonal rains) and low productivity. Subsistence farmers produce primarily for own consumption but may sell some of the produce. There is growing of mainly bananas in the valleys and other annual crops like maize and beans. Along some gentle slopes crop growing is also carried out due to the abundance of potassium rich soils obtained from the weathering of shales. Animal rearing such as cattle and goats plus sheep are also carried out majorly on the rocky hill tops that would not support easy cultivation. . Mining is also done majorly through quarrying to obtain aggregate and stones for the construction industry. Mining of economic mineral ores such as cassiterite is also carried out at Mwerasandu and Kikagati Isingiro District has a total land area of about 3010 square kilometers. The population density of Isingiro District is on has raised from 104 persons per square kilometer of each land area to the current projection of 124 person per square kilometer (2002 national census). Particularly population density becomes of fundamental importance in Isingiro district being an agricultural District since together with people’s settlement patterns affect commercial farming. It is also imperative to note that that as much as the population density of Isingiro is below the national
4 | P a g e one (127 persons per square kilometer), the district has a lot of inhabitable high lands, wet lands and lakes. A vast land area of about 135km is also preserved as a refugee and settlement camp. Settlement is seen along main roads and feeder roads and clustered around the trading centers and Isingiro town. Below is a map showing population density in Isingiro district as per the 2002 population and housing census. Map 2: Map showing Population Density in Isingiro district
1.7 DRAINAGE Isingiro district has a variable nature in its drainage pattern which is largely dependent on the nature of the underlying rocks. It is also greatly affected by the tectonism of the area that created the complexities in the folding, jointing and faulting. The District is blessed with 2 permanent rivers and 1 stream. The two rivers are Kagera and Rwizi. R. Kagera flows through the sub counties of Kikagate, Ngarama and Kabuyanda yet R.Rwizi flows through the Sub-Counties of Masha and Kabingo. The stream flows through Kabibi Town Council. The lakes are 4 and are all permanent. The biggest ones are L. Nakivale and L.Mburo. L. Mburo is shaired with Kiruhura District yet Nakivale is inside the district. The other lakes are Oruchinga and Misyera. L.Nakivale boarders the Sub counties of Isingiro town council, Ngarama, Kashumba and Rugaaga. L.MBuro boarders Masha and Rugaga. Misyera is also found in Rugaaga. Water holes are very numerous and widely spread throughout the whole region mostly in the valleys These main water bodies create a complex drainage pattern which can be locally classified as dendritic drainage pattern for the areas underlain by more competent rocks such as those of
5 | P a g e higher grade of metamorphism such as schists, gneisses and the weathered granitic rocks of the arena whereas for the case of areas where ridges were formed due to the alternating competent(quartzites) and less competent rock(shales) patterns follow a parallel to sub-parallel drainage pattern which is the most evident nature of drainage pattern in area A which on a regional scale falls back to dendritic drainage pattern 1.8 REGIONAL GEOLOGY 1.8.1 Literature review The earliest classification of formations in Uganda after the inception of the Geological Survey was necessarily on a lithological basis. Although the term Karagwe Series had already been applied by Scott Elliot and Gregory (1895) to certain predominantly argillaceous formations occurring in and around north-western Tanganyika, Wayland preferred initially to employ the non-committal term Argillite Series (1921a, 9-10). This was applied to all typically low- grade and non-metamorphic sedimentary assemblages, which, however, included extensive developments of arenaceous as well as argillaceous formations, and was in contrast to the mica- schists, metamorphic quartzites and gneisses which were placed in the Archaean or Basement Complex. Meanwhile Combe had established the individuality of the Argillites of the south-west, which then became known as the Ankolean Series (Wayland, 1923; Combe, 1925). Thereafter further investigation showed their identity with the formations of the adjacent parts of Tanganyika, and the name Karagwe -Ankolean applied to the whole group (Combe, 1926, 15). Thus it was that term " Argillite Series " was abandoned (Wayland, 1925, 9), and its place there appeared a number of systems or series of widely differing ages: Karroo, Bunyoro Series (Wayland, 1931, 13), Mityana and Butologo Sandstones (later to be included (King, 1943, 35)), and the Karagwe- Ankolean be noted, however, that the Karagwe-Ankolean, to the structurally continuous formations Masaka districts, also included non-metamorphic morphosed sediments of Singo county and parts the Jinja area, parts of Bunyoro (and later of the Sese Islands (Simmons, 1927, 19-21), Kenya border in south-eastern Uganda. This on the virtual or complete lithological identity these more or less widely separated areas localities to the south-west. Although in many places, notably Karagwe and Kigezi, the stratigraphy and structures of the Karagwe-Ankolean rocks are comparatively simple and could be effectively elucidated, a very general problem that presented itself was the nature of the base of the system and its relations with the Archean Complex which originally on quite general grounds had been inferred to underlie it (Wayland, 1921a, 9).
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. Map 3: Sketch map (Cahen and Snelling, 1966), showing the Karagwe-Ankole Belt (KAB) and the Kibara Belt (KIB) as redefined by Tack et al. (2010). Inset after Brinckmann et al., 2001 showing the Kibara Belt as one single and continuous belt. Ki Mt, Kibara Mountains type locality; M, Mitwaba town; Ka, Kalima town.
The K-A system rocks in Uganda were first described by Speke in 1863, consisting of shales and sandstones west of Lake Victoria. Elliot (1893) passed through southwest Uganda and Karagwe from where he collected samples of rock specimens which were subsequently described in his joint paper with Gregory (Elliot and Gregory, 1895) bringing up the name the ‘Karagwe series’ before after an extensive mapping of the Ankole Kigezi region plus Karagwe in Tanzania, Combe in 1926 came up with a term Karagwe Ankolean. His work was published later in 1932. Wayland (1919) carried out some reconnaissance across southern, south-western and western Ankole and from it the most important lithologies, features and structures were recorded.
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Combe (1932) also described two local successions occurring in the eastern part of Kigezi (Rukiga-Mpalo area) and in the western Ankole (Ntungamo-Kafunzo-Dwata area). He used six quartzite horizons in an attempt to correlate the successions between the two areas and as a basis for assigning lower, middle and upper divisions. Stheeman (1932) wrote about the geology of the wider region of southwest Uganda which was majorly directed towards economic geologic aspects. Phillips (1959) reported that south of Mbarara were the greatest quartzite concentration which appeared to have restrained the folding of covering K-A rocks. This was attributed to only broad synclines being recognizable. He further identified quartzite horizons q1 to q4 with q4 being the thickest of all, underlie the Rugaga plateau and comprises numerous quartzite layers interspersed within argillaceous horizons. Biryabarema (1995) noted that to the north and west of the area underlain by the Igayaza syncline, the rocks of the K-A system are largely argillaceous with quartzites attenuating fairly abruptly. These argillaceous rocks of the K-A system showed a progressive increase in metamorphism towards the base from shales and slates through phyllites to muscovite or sericite schist. This progressive trend in metamorphism also corresponds with their proximity to granites in anticlinal cores. These massive argillaceous rocks were intercalated with thinner arenaceous bands of quartzites and quartzitic-sandstones and the succession had been intruded by the granites. 1.8.2 General geology The K-A system rocks is characterised by an eastward decrease of both deformation and metamorphism (Tack et al., 1994). A basal conglomerate in this system unconformably overlies either gneissic basement, which is part of the Archaean Tanzania Craton, or the Paleoproterozoic Ruwenzori Fold Belt. In contrast to the Kibaran belt, the K-A belt is devoid of S-type granitoids and economic mineralisation.
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The Karagwe-Ankolean is also characterized by argillaceous units intercalated with thinner bands of quartzites and quartzitic sandstones. It is composed of acid gneisses, migmatites and folded metasedimentary rocks. This area generally contains rocks such as shales, slates, phyllites, quartzites, and some conglomerates that often occur as lenses. The system is also composed occasionally of conglomeritic basal members and minor volcanic and calcareous sequence, pegmatites, quartz veins and basic dykes (Ucakuwun, 1989)
Figure 1: Synthetic litho-chronostratigraphic logs of the KAB for the WD (a) and ED (b) with position of 4 dated samples (KI 2, KI 7, KI 8 and KI 25)
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1.8.3 Structure of the K-A system The major folds of the K-A are generally comparatively simple, but the associated structures on a smaller scale are often very much more complex. The major structures depend mainly for their recognition on the understanding of the stratigraphy. Thus, in SW Ankole and Kigezi, owing to the uncertainty in places of correlating the critical quartzite horizons, Combe (op. cit., 79) showed that there were corresponding ambiguities in interpreting the major folds. In Koki and Buhweju, the K-A occurs in broad synclinal basins, the form of which is clear not only from the deposition of the sedimentary formations themselves but also from the behavior of the unconformable base, the position of which can be more or less readily mapped. In Kigezi the major structures consist of a series of rather open anticlines and synclines, the axial planes of which are nearly vertical and the axes trending around NNW-SSE (Combe, op. cit., 78). In Ruampara and the adjacent part of Isingiro, Ankole, the dominant structures have a similar style, while in the intervening terrain of Kazara, in the extreme SW of Ankole, the basement is extensively brought up in a prevalently anticlinal area, the Ankole Anticlinorium of Barnes (1956, 42). Refolding of the primary cleavage or schistocity has occurred in many localities, notably towards the base of the succession where deformation has often evidently been more intense and especially in the vicinity of the arenas. A second planar structure often having character of a strain-slip cleavage, has usually developed in relation to refolding. A most important observation by Phillips (op. cit., 62-78) is that as metamorphism increases, there develops a pervasive phyllitic schistocity which lies near to the original bedding, combined with mild regional metamorphism, since it is folded, together with the bedding, by the smaller NNW-SSE folds which produced the axial plane flow cleavage and strain slips. The connection between cleavage and folding is emphasized by the fact that at certain localities, generally high in succession, and where folding is slight, the shales or mudstones are devoid of cleavage. Examples are to be found near Nsika, Buhweju, North of Igayaza in Isingiro and at many places in Koki. The argillaceous formations display almost everywhere a true flow or slaty cleavage. This has commonly been described as agreeing with the bedding and indeed, close or even precise agreement can frequently be demonstrated. However, where fold closures are visible it is clear that the structure in an axial plane cleavage. The arenaceous formations which predominate in the northern part of the Buhweju plateau are broadly flat-lying. Reece, in order to reconcile these observations, has suggested that the dips generally represent current bedding, implying deposition under deltaic conditions a conclusion that he regards as supported by the prevalently southerly dips in parts of the area. The most important feature of the fold pattern of the K-A is that it conforms to two directions approximately at right angles to each other. Indeed, the notion of “main” and “cross” folds was employed by both Combe and Steeman in 1932, long before it was a familiar one of the geologic
10 | P a g e literatures. Whereas in the Caledonites of NW Europe or the Alps, the direction of the main folding is quite clear, for it is that of the great recumbent structures, in the K-A the choice is less obvious since the folds on both directions possess a similar style. Considering SW Uganda as a whole, the prevailing fold direction is around NNW-SSE, sometimes more nearly NW-SE as in Buhweju. This main trend is even more dominant southwards into Tanganyika, although here the directions swings towards N-S. the direction of cross folding varies from about NE-SW to NNE-SSW, a major fold of this type being the broad syncline of Isingiro. Others apparent to the north and south of the Marsha arena and traversing the Ankole anticlinorium. Reece concluded that in Buhweju cross-folding on NE-SW axes preceded the main folding on NW-SE axes. Phillips similarly finds that the structures which regionally are to be regarded as cross-folds antedate the NNW-SSE (main) folding. Here the major cross-fold is a complex syncline in thick quartzites which dominates the Isingiro area. This formed a massive block that resisted the main folding which is thus developed principally in the largely argillaceous formations farther east in Koki. The later folding has had the effect of deflecting earlier fold axes and on a small scale the sequence of movements can be seen in the presence of refolded folds and superimposed cleavages.
1.8.4 Stratigraphy and geochronology of the K-A. The type area of the K-A (1400-950Ma) may conveniently be regarded as south western Ankole and Eastern Kigezi since it was concerning this region that Combe (1932, 22-35) presented the first detailed account. He described the system as consisting “dominantly alternating strata of thinly bedded and unbedded mudstones, thinly bedded and laminated phyllitic shales and phyllites, with sandstones and quartzites “(op. cit., 22). The sandstones and quartzites often show current bedding and ripple marks, sometimes contains lenses of conglomerate, are rather regularly spaced throughout the succession and are remarkably persistent over considerable distances. In eastern Kigezi arenaceous formations constitute over 2500ft. out of a total estimated thickness of more than 26000ft. In SW Ankole, the total thickness is less than 16000ft. Individual quartzite horizons vary in thickness from a few tens to several hundreds of feet. Throughout Ruampara, the succession appears to be approximately similar, although it has not been worked out in details. Farther east in Isingiro, however, Phillips (1959, 53) has estimated a thickness of no less than 8000ft. of quartzites around the middle of a succession totaling over 22000ft. Still farther to east in Masaka district, these quartzites thin very rapidly and indeed the only quartzites in the entire sequence become discontinuous lenses. In this area, moreover, Philips infers that successively higher members of K-A overlap on to the basement formations. Small quartz pebble conglomerates are developed at or near the base in a number if localities. A prominent example is seen on the outlier forming Simba hill in south Budda.
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The disconnected area of K-A forming the Buhweju plateau in NW Ankole again shows a great development of arenaceous formations which thicken rapidly northwards. Here, however, the main development of these sediments lies at or near the base of the succession and contains grits and conglomerates as the lowest members. Reece (1959, 78) has estimated the maximum thickness of these arenaceous formations at 5000 ft. and infers a deltaic mode of formation, the material originating from the north. Southwards and SW, they are overlain and in part replaced by up to 3000ft. of shales and a higher group of quartzites which attain a maximum of 1200ft. This is therefore summarized in three major sub-divisions (Modified after Combe, 1932; and Bugrov et al., 1982) as shown in the table below
Sandstone horizon
Ihunga Quartzite
Boundary Quartzite
If the Buganda series (1700-1800Ma) is excepted, the only formations in central and western Uganda which have been correlated with the K-A are those occurring on the great northern spur of Rwenzori and at Kabuga in south Toro. The former occurrence consists of sediments resting uncomfortably on inferred basement gneisses. That at Kabuga is composed almost entirely of a distinctly cleaved quartzitic sandstone, closely comparable with the dominant formation of northern Buhweju. If, as now appears likely, the Buganda series is not to be correlated with the K-A, a problem arises with regard to the status of the shales and phyllites which are poorly exposed farther to the NE around L. Kyoga. These have generally been referred to the K-A (cf. Bisset, 1939; Roberts, 12 | P a g e
1940) on grounds of their lithology. It is thus not possible to draw any reliable conclusions as to the original limits of the K-A system. The great development of arenaceous formations in northern Buhweju may suggest an approach to the margins of the area of deposition in a NW direction, but a not dissimilar development in Isingiro passes laterally into argillaceous formations in all directions. A phenomenon which is so widespread as to be inseparable from the stratigraphic description in the almost ubiquitous progressive metamorphism of the sediments downwards in the succession, most apparent in the argillaceous formations so that whereas the highest members may have the character of shales, those lower down are slates and phyllites and the lowest formations may be schists. Therefore, the rocks that make up the K-A system in southwestern Uganda include mudstones, shales, slates, phyllites, grits, schists, quartzites and intrusive rocks such as granites and granodiorites. Granites form eroded domes referred to as arenas since they are easily weathered. 1.8.5 Tectonic evolution, intrusion and Metamorphism of the K-A. The Kibaran belt (Karagwe –Ankolean) evolved as a result of the movement between continental plates what is referred to as the Kibaran Event that proceeded the Pan-African Event between the 1400 and 900 Ma (Pohl and Gunther (1991)). This type area was basically made up of sediments (both clayey and sandy) mixed up with volcanic rocks and in a few instances carbonate rocks. Early tectonic forces then led to thrusting and a large mass of rock thrust over other rocks. A major folding phase in the Kibaran event (about 1200 Ma) which produced a wide anticlinorium and a narrow synclinoria. The anticlinoria were then intruded by the G1 and G2 granites causing metamorphism of the country rocks, a type known as contact metamorphism hence formation of a contact aureole with degree of metamorphism increasing towards the intrusive body. G1and G2 (two-mica) granites are the oldest granites and formed through muscovite and minor biotite dehydration melting of a greywacke source at moderate temperatures and pressures (731-806°C, >5 kbar). Melting was driven by the emplacement of mantle-derived mafic igneous rocks into the lower crust. This intrusion was followed by a later intrusion (1100 Ma) of the Alkaline biotite granites (G3). G3 (biotite) granites are younger and formed by biotite-dominated melting of a similar source under slightly higher temperature but decreased pressure conditions (768- 847°C, <4 kbar) consistent with the ongoing emplacement of mantle-derived melts and crustal melting during lower plate exhumation. This in NW Tanzania and SW Uganda formed what is referred to as Burundian – Tanzanian ultramafic belt. Later the country rocks within this belt were then intruded by numerous small bodies of the granites, pegmatitic granites and pegmatites (G4). G4 granites (or the so called ‘Sn granites’) formed at 986 ± 10 Ma (Tack et al., 2006) and it is in this type of granite that most of the mineralization in this belt is associated.
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The intrusive granites, due to their intensely high temperatures also caused metamorphism of the country rocks majorly allochemical in nature. The KA rocks are metamorphosed to various degrees. There is a progressive increase in metamorphism towards the base, from shales or slates, through phyllites (sericite-chlorite) to mica schists (muscovite and finally biotite-bearing). At the same time this progression corresponds to increasing proximity to the granitic rocks of the arena. In the west, basal rocks have undergone high-grade metamorphism to phyllites and fine muscovite schists. The sandstones have been metamorphosed to form hard quartzites and conglomerates have been metamorphosed and pebbles flattened. The quartzites have also been sheared and mylonitized.
1.8.6 Mineralization and economic potential. The Kibaran belt is best known for its richness of different granite-related rare element deposits that contain cassiterite (SnO2), columbite-tantalite (also called coltan, (Nb,Ta)2O5), wolframite ((Fe,Mn) WO4), beryl (Be3Al2Si6O18), spodumene (LiAlSi2O6), amblygonite ((Li,Na)AlFPO4), monazite ((Ce,La,Y,Nd,Th) PO4), gold (Au) and many others as typical mineralisations (Pohl, 1994). The Sn-Nb-Ta-W mineralisations mainly occur in pegmatites and quartz veins (Varlamoff, 1972; Pohl and Günther, 1991; Dewaele et al., 2007, accepted). The mineralized pegmatites and quartz veins are interpreted to be related to the ‘Sn- or G4-granites’ which were the last of the intrusive bodies in the K-A system. It was not until in 1924, the occurrence of tin as Cassiterite was discovered and documented in NW Tanzania by J.S. and D.S Kargarotos at Kyerwa where the first export was made in 1927 (Barnes 1961). The tungsten deposits in this system are present in the central part of Rwanda and occur as mineralised quartz veins that are hosted by graphite-rich black shales. Wolframite minerals formed after the precipitation of the main quartz vein. The pegmatites are dated at 968 ± 8 Ma and the Nb-Ta-mineralisation in the pegmatites at 962 ± 2 Ma (Romer and Lehmann, 1995) and 965 ± 5 Ma (Brinckmann et al., 2001). The pegmatites are sometimes crosscut by mineralised quartz veins (Varlamoff, 1972; Pohl, 1994). The tin-mineralised quartz veins formed at 951 ± 18 Ma (Brinckmann et al., 2001) which can be realized at the cassiterite deposit near Kikagati where small scale artisanal mining is being carried out along sub-parallel to parallel quartz veins The K-A system has also provided a lot of potash rich soils derived from the weathering of shales hence encouraging agriculture through growing of crops like bananas and maize and also rearing of animals such as cattle and goats besides the mining through quarrying that actively occurs throughout the whole region for attaining of various construction materials. 1.9 MATERIALS AND METHODS USED 1.9.1 Materials used. ➢ Global Positioning System. (GPS)
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This was used to determine the current location at that point. It needs access to the satellites for it to operate hence works best under limited cloud cover and in open space. The reading we took were of UTM (Universal transverse Mercator)
➢ Geological, topographic and base maps
This was used to locate current positions relative to other locations on the map using the coordinates obtained from a GPS which further aided in the plotting in the base maps provided
➢ Geological Compass
This was used in determining directions for example in the determination to the strike and angle of dips of various structures such as plane of joints
➢ hand lens
This was used to observe some of the textural characteristics present in rocks that cannot easily be seen using the unaided eye.
➢ geological and Sledge hammer
This was used for breaking rock samples to observe the fresh parts. A sledge hammer was used in cases where the rock was so rigid and the sample hard to obtain hence much more force needed.
➢ Sample bag
This was used to carry and store the obtained samples for later analysis such as laboratory analysis
➢ Tape measure. This was used to standardize the pace length and also measuring some distances whose accuracies were a priority. The pace length was important for the estimation of the extent or dimensions of outcrops and features of interest ➢ Camera
This was used to take the pictures of geologic structures and features observed in the field for example the foliation and the joints
➢ pens and pencils
They were used as scales for the geologic pictures as well as noting down the observations in the field
➢ Field bag
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This was used to handle and keep all equipment and tools while in the field for example the GPS, geological compass notebooks and many others while not in use.
1.9.2 Methods.
The methods used may be divided into two main parts, that is, fieldwork and then data analysis and report writing
a) Fieldwork The field work during this mapping project involved used of various skills and methods which called for particular tools as well. First of all, to obtain good and fast estimation of extent of various outcrops and features, pacing hade to be done over standardized paces which was done prior to the actual mapping activity. This was proceeded by the mapping exercise that included locating the area A on the map and then using the general area map, lithologic boundaries, and stations and their locations plotted onto the base map using the coordinates obtained by the GPS and the attitudes of the structures obtained using the geological compass also mapped. These structural features included folds, faults, joints, beds, cleavage, veins and ripple marks. In cases where these features and structures had to be referred to in later analyses, pictures were taken using a digital camera with various tools and equipment such as the geologic hammer and compass acting as the scale. At each of these stations, samples were obtained for later petrographic analysis, both micro and macro features. The coordinates obtained were there after used to locate the area on the geologic or topographic maps hence obtaining the relative location with respect to others. The lithostratigraphic boundaries can be recognized through observation of places with a change in vegetation cover, break in slope, difference in soil cover plus the floats. To sum up the mapping exercise, a station with representative features and structures that summarize the study area was selected at location (0253811, 9916472) at an elevation of 1511m which had intensely brecciated quartzite with joint planes majorly corresponding to the regional trend of structures (NW-SE) with a few others corresponding to the minor regional trend (NE- SW)
b) Data analysis and Report writing The obtained data from all stations were statistically analyzed using Stereonet software to obtain the relationships between the different data sets for example the density and rose diagrams for joint and bedding planes and pi plots for fold analysis. ArcGIS was also used to digitize the obtained detailed maps created from the base maps and this was used to obtain stratigraphic sections and also observe the various trends in the features in the area A. The obtained samples were also exclusively analyzed in the laboratory both macroscopically (texture and mineralogy) and microscopically using the thin sections obtained from the macroscopic samples through observing different characteristics of grains under plane polarized
16 | P a g e and also crossed polarized light in a polarizing microscope. Their mineralogic and structural features and therefore relationship with the regional geology was then ascertained hence drawing of conclusive deductions. The finding and these deductions were then compiled into a comprehensive report which contains five major chapters which included; introduction which covered the literature review, general geology methods and materials used; stratigraphy; structures; petrography and metamorphism; regional synthesis and finally conclusions and recommendations
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CHAPTER TWO: STRATIGRAPHY 2.1 INTRODUCTION Stratigraphy refers to the study of rock layers and layering through observation of the different sediments and rocks that are stratified, their description, relationship with other layers and rocks and how all the observations are interpreted. A single rock layer is called a stratum and it’s a combination of all these that brings up the stratified nature of rocks. 2.1.1 Types of stratigraphy Stratigraphy is divided into various arms based on how one wishes to study the rock strata seven of which are highlighted as follows
➢ Lithostratigraphy This is the study and organization of strata on the basis of lithologic characteristics. The lithology includes the rock type, color, mineral composition, and grain size. This variation can occur laterally and vertically as layering and it reflects changes in the environments of deposition and hence the variation provides the lithologic stratigraphy of the rock unit in the study area. ➢ Biostratigraphy This refers to the organization of strata on the basis of the fossils they contain. Biological stratigraphy is based on William Smith’s principle of faunal succession. It provides strong evidence of formation and extinction of species. The geological record provides an evidence of biologic stratigraphy and faunal succession. ➢ Magneto-stratigraphy The earth is magnetic in nature and during deposition of the sediments, they may get aligned corresponding to the magnetic dipoles hence getting magnetic. Each episode of deposition may have a unique signature hence organization and study of strata on the basis of their magnetic characteristics is what is referred to as Magneto-stratigraphy. ➢ Chemo-stratigraphy Basing on the fact that even elements under different conditions may tend to form isotopes or variation in composition in a particular medium, rock strata can be analyzed in this way hence distinguishing them using their isotopic characteristics and composition. ➢ Seismic stratigraphy Seismic stratigraphy is the study of seismic data with the purpose of extracting information on rock layers(strata) and layering(stratigraphy). This may include refraction or reflection seismics depending on the nature of the underlying rocks
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➢ Chronostratigraphy This refers to the arrangement and study of rock strata in relation to time. This is due to the variation in the deposition of the different sediments. This aids in organizing the rocks systematically, that forms the earth crust into named units corresponding to intervals of geologic time. ➢ Sequence stratigraphy This is the study of rock relationships within a time-stratigraphic framework of repetitive, genetically related strata bounded by surfaces of erosion or non-deposition, or their correlative conformities (Posamentier et al., 1988). These sequence boundaries may be generated by relative rise and fall in sea level or the variation in the energy of the transporting medium 2.1.2 Principles of stratigraphy However, all these arms of stratigraphy operate on definite principles that were defined by Nicholas Steno in 16669 which include the law of superposition, the principle of original horizontality and the principle of lateral continuity. Other workers proposed the law of cross cutting relationship, principle of inclusion and the principle of faunal succession ➢ Law of original horizontality This states that in an undisturbed sequence of rock strata, the beds of sediment deposited in water/ basin form as horizontal (or near horizontal) hence aiding in the analysis of tilted or folded rock strata. ➢ Law of superposition In an undisturbed stratum, the oldest layers lie at the bottom and the youngest on top. ➢ Lateral continuity Horizontal strata extend laterally until they thin to zero thickness (pinch-out) at the edge of their basin of deposition or unless they are cut by younger rock units. ➢ Law of cross-cutting relationship It states that an event that cuts across existing rock is younger than that rock (Charles Lyell) This principle aids in the relative age dating of the rocks ➢ Principle of inclusion Fragments of rock that are contained (or included) within a host rock are older than the host rock. ➢ Faunal succession This is also known as the Smith-Cuvier discovery.
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The Smith-Cuvier discoveries are termed the “Principle of Faunal Succession” states that fossils and groups of fossils exist for limited amounts of time, and that fossil plants and animals appear in the rock record in a definitive pattern hence the older the rock, the more primitive the fossil forms that were present. In area A, no fossils were observed.
2.2 PREVIOUS WORK.
Igayaza falls under the Karagwe-Ankolean (K-A) system which in some literature places it under the Kibaran belt. The Mesoproterozoic Kibara Belt (also Kibaran Belt or Kibarides in some references) of Central Africa is often portrayed as a continuous, about 1500 km long orogenic belt, trending NE to NNE from Katanga, Democratic Republic of Congo (DRC) in the south, up into SW Uganda in the north (e.g. Brinckmann et al., 2001). Satellite imagery however, supports older schematic representations (e.g. Furon, 1958; Cahen and Snelling, 1966) showing that this belt consists of two distinct northern and southern segments (Map 3). These two are separated in the DRC between the Katanga and Kivu-Maniema regions by a NW-trending basement rise, partially consisting of a Karoo-age (Late Carboniferous to Early Jurassic) rift, itself superimposed on the Palaeoproterozoic Rusizi Belt (Lepersonne, 1974; Lavreau, 1985), which extends beneath Lake Tanganyika, and links up with the Palaeoproterozoic Ubende Belt of SW Tanzania (Klerkx et al., 1987; Theunissen et al., 1996).
The apparent paradox of Palaeoproterozoic belts cross-cutting a Mesoproterozoic Kibara Belt results from repeated, to the present day, crustal-scale structural reactivation along the pre- existing Ubendian-Rusizian structures (Klerkx et al., 1998).
The two segments of the Belt, north and south of the basement rise, have been redefined by Tack et al. (2010) as; the Karagwe- Ankole Belt (KAB), spanning Rwanda and Burundi, SW Uganda and NW Tanzania as well as the Kivu-Maniema region of the DRC and then the Kibara Belt (KIB) further SW in the Katanga region, including the Kibara Mountains type area near Mitwaba town (Map 3).
In Uganda, the Karagwe-Ankolean Supergroup is also characterised by argillaceous units intercalated with thinner bands of quartzites and quartzitic sandstones. The northern boundary of the Karagwe-Ankolean is poorly constrained but the supergroup is considered to overlie the Palaeoproterozoic Buganda-Toro Supergroup of the Ruwenzori fold Belt (Cahen et al., 1984; Master et al., 2008).
The unconformity is apparent in the Mashonga sedimentary outlier of Uganda (Pohl and Hadoto, 1990). Contacts with the Archaean Tanzania Craton have not been observed.
Highly characteristic of the landscape of Ankole are the " arenas," which Wayland (1921a, 10) quickly appreciated were topographic expressions of dome-like structures in the Karagwe- Ankolean, in which erosion had exposed the underlying supposed Archaean floor. Combe's later
20 | P a g e mapping showed, however, that in most cases the arenas were partly, and in a few cases wholly, occupied by post-Karagwe-Ankolean granite, and that the gneisses and schists, instead of being pre-Karagwe-Ankolean in age, could often be shown to be gneissose phases of the later granite and schists formed by metamorphism of the Karagwe-Ankolean itself (1926, 20).
Nevertheless, it was clear from the behaviour of quartzites which can be employed as marker horizons that in very many places the arena floors approximate to the base of the Karagwe- Ankolean, and it is normally this basal part of the succession which is progressively metamorphosed (Combe, 1932, 31). Locally, as where two arenas are in close proximity, the intervening Karagwe-Ankolean may show metamorphism extending to high stratigraphic horizons and in parts of Kigezi, especially in the north, the entire development of Karagwe- Ankolean is highly metamorphosed (Combe, 1941, 11-14.).
It had long been recognized that granites of at least two ages existed; the one supposedly associated with the Basement later than the Karagwe-Ankolean showed that the provisional, the Basement, was unjustified that in the arena areas of south, foliated or not, post-date the A landmark in defining. This was the discovery by Simmons formity. Here, in Koki, Masaka virtually unmetamorphosed, and seen overlying steeply inclined granite evidently belonging rocks were observed elsewhere observation, however, awaited around the Buhwezu Plateau.
Buhwezu had been shown by Combe (1933, 23-26) to consist of great thicknesses of quartzite with underlying grit and conglomerate, only very gently folded in the north, which are overlain and replaced southwards by shales and slates, and increasingly strongly folded in the same direction. Although not contiguous with the main area of the Karagwe-Ankolean, there could be no doubt that the Buhwezu rocks form part of this system. Surrounding the plateau and evidently underlying the Buhwezu formations are schists with some quartzites, more or less extensively invaded by granite.
Northwards, beyond Ankole, crystalline quartzites are massively developed and these, supposed by Combe to be pre-Karagwe- Ankolean, were referred to as the Toro quartzites. He emphasised the difference between the quartzite of Ibanda Hill and that of the Buhwezu plateau, in which original depositional structures are commonly present. It was, however, around the south-eastern part of the Plateau in Igara county, that the relations between the Karagwe-Ankolean of Buhwezu and the schists of the lower country were first examined in detail, and, although an intervening zone of problematic rocks was noted, Combe suggested that the arenaceous formations of the Karagwe-Ankolean rest unconformably on the underlying schists, which he referred to as the Igara Series (1935, 9; 1939, 6-10).
From the above deductions, Bisset (1939, 27-28), in reviewing the geology of Masaka district, suggested that the schists below the Lwanda correlated with those of the Igara Series. He also made an observation that these pre-Karagwe do not resemble the rocks of the " true " northern and north-eastern Uganda. The unconformable base to the Karagwe-was established beyond
21 | P a g e doubt by the subsequent (1942, 22) and Roberts (1943, 19; 1944, 19). Igara schists and Toro quartzites into a single (1942, 22), which was subsequently named the Toro System (Ann. Reptfor 1942 (1943), Bisset, 1947). King maintained (1947) that the which become increasingly abundant as the system southwards and eastwards from Buhwezu reflect granitisation rocks, acting selectively on the schists, so that quartzites are virtually the only members of the sequence to survive.
Phillips (1959) identified quartzite horizons q1 to q4, of them q4 being thickest which is underlying the Rugaga plateau and comprising of numerous quartzite layers interspersed with thin argillaceous bands.
Plummer (1960) described thinning of the quartzites on the NW limb of the Igayaza syncline east of the Mbarara-Kikagati road, up to the Stratigraphic level of the Rugaga quartzite (q4), the rocks are fairly metamorphosed, but sometimes sedimentary structures are still recognizable.
Biryabarema (1995) stated that to the N and W in the area underlain by the Igayaza syncline the rocks of the Karagwe-Ankolean system are largely argillaceous with quartzites attenuating fairly abruptly
Table 2: Generalized lithostratigraphy of K-A in Uganda.
UPPER K-A Mudstones, siltstones, sandy mudstones, sandstones, grits and occasional conglomerates Intercalations of quartzitic horizons, q3, q4, q5 and q6
MIDDLE K-A Sandstone with occasional itabiritic layers of micaceous hematite Predominantly mudstones, arenaceous mudstones and phyllites. The more argillaceous rocks are characterized by a colour banding in shades of grey, cream and pink
LOWER K-A Largely muscovite schists and phyllites with quartzites Occasional calc-silicate rocks derived from arenaceous limestones Thin quartzitic bands, semi persistent and frequently boudinaged, sheared or mylonitized. Intercalations of quartzitic horizons q1a, q1, q2a and q2 The area A that was exclusively mapped was of the lower K-A
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2.3 STRATIGRAPHIC DESCRIPTION. In general, the stratigraphy of area A was one that had quartzites at the top of the ridges and the shales at the slopes of the hills. There were some Phyllitic shales at the point of transitional stage of metamorphism. The quartzites were obtained through the metamorphism of the sand sized particles or sediments and rocks such as the sandstones The stratigraphy can be well visualized using the cross-section obtained from point A to point B in the map below.
Map 4: A digitized geologic map ofarea A created using ArcGIS software
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Map 5: A cross section from point A to B of the geologic map of area A generated using ArcGIS
A B
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Quartzites This is a hard, non-foliated metamorphic rock that is composed mainly of quartz It is derived from the metamorphism of the sand sized sediments due to heat and pressure due to the regional tectonic activity in the area. The conditions recrystallize the sand grains and as well as the silica cement that binds the grains together resulting in an interlocking network of quartz grains of great strength. This interlocking crystalline structure makes the quartzite hard, tough, and with great durability. Pure quartzite is usually white to grey but they can occur with shades of red due to the presence of varying amounts of iron oxide which was more often than not the case in area A. The quartzites, due to their stability and resistance to weathering and erosion formed ridges that stretched for several kilometer with a few discontinuities such as faults. They are low grade metamorphic rocks and as a result they show some relict sedimentary structures that were observed in some areas. They are composed mainly of silica hence are fine to medium grained and they are usually grey, white, dark brown in color (brown due to presence of iron oxide). Many of the quartzites were fractured and joints were also present. There were some quartz veins found in some of the areas with quartzites where they cut through the quartzites. In some of the area the quartzites were intensely weathered too form the laterite soils.
Figure 2: An intensely fractured quartzite outcrop from station A32 (0253986, 9915279).
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Conglomerates Conglomerates are consolidated coarse-grained clastic sedimentary rock, made up of larger than 2mm-diameter particles cemented together. The conglomerates observed in the area A uncoformably lie over the quartzites hence an unconformity. They are polymitic composed of a variety of clasts, sub rounded, matrix supported (para conglomerates). they are extra formational since the clasts are derived from outside the basin of deposition. There is imbrication that is a preferred orientation of sediments to direction of currents.
Figure 3: A conglomerate at station A30 (0253811, 9916472) on top of the quartzite hence forming an uncomformity.
Shales This is fine grained clastic sedimentary rock that consists of mud mixed with flakes of clay minerals and silt sized particles of other minerals like quartz. It is fissile in nature hence distinguishing it from the other clay particle sized sedimentary rocks The shales observed in the area A were found in the slopes of the ridges. They were below the quartzites and exhibit structures such as bedding, lamination in most areas. There was a variation in color and the composition of the different shales hence showing different kinds of shales we observed. The notable shales were grey shales, ferruginous shales and the phyllitic shales. The reddish colour of the ferruginous shale is as a result of oxidation of the iron. ➢ Phyllitic shale: This is a type of foliated metamorphic rock created from partly metamorphosed shales so that the very fine-grained white micas achieve a perfect orientation and becomes lustrous in nature. These are rocks that contain phyllites in them. The Phyllitic shales observed were hard and grey in color. They are an indicator of low- grade metamorphism that occurred on a sedimentary rock that is the shales. However, this grade is higher than that of ferruginous and grey shales.
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➢ Grey shales: They are soft and grey in colour containing little amount of organic matter. The grey colour is as a result of the composition of the shale to consist mainly of clay minerals such as kaolinite, illite and other minerals. and the shade of grey depends on the clay and organic matter content and are more abundant that phyllitic shales in area A. They often are softer than ferruginous shales. They also contain very little or no iron solutions recrystallized within the lines of weakness present in them. ➢ Ferruginous shale: This is a metasedimentary rock that contain mainly iron oxide that gives it the brown color hence the name “ferruginous”. They were found on the gentle slopes of the ridges
Figure 4: Ferruginous shale outcrop at station A3 (0252895,9915800)
Granites Granites is a type of felsic intrusive igneous rock with a granular texture hence phaneritic. In area A the granites were predominantly pink and white to grey in color suggesting a mineralogy compost majorly of 50% quartz, 40% alkali feldspars and 10% micas. The outcrops were found below the shales on the lower areas of the hills and some of the outcrops were greatly weathered. The products from the weathering provide well-conditioned soils that facilitate the growth of crops such as bananas in the features formed from their weathering (Arenas) 2.4 STRATIGRAPHIC ROCK SUCESSION AND DEPOSITION. 2.4.1 Rock succession The deposition within this area was due early deposition of the clay sized particles then followed by the sand sized particles. There was also alternating deposition of sand sized and clay sized particles (cyclic deposition). The clay sized particles were compacted and lithified into shales whereas the sand sized particles into sandstones. Due to the high temperature and pressure conditions, the sandstones were metamorphosed into quartzites and the shales to slates and then phyllites. This nature of metamorphism was further enhanced through the later intrusion by
27 | P a g e granitic bodies into the country rocks hence contact aureole formed around these bodies. In area A this is evidenced by the Masha arena where there is progressive increase in metamorphism of the rocks towards the granitic body. 2.4.2 Depositional environment In the area A mapped, there is intercalations of both arenaceous and argillaceous rocks in the area. This in due to the change in energy or medium of transportation of the sediments. The low energy favoured the deposition of the fine suspended sediments like clays in quiet water. These were areas or periods of low kinetic energy in quiet and calm waters that favor the sediments to settle out at the bottom of the sea. The deposited sediments were compacted and cemented as they underwent diagenesis to form a sedimentary rock which are the shales in this case. For the quartzites, the sediments were carried by water that has high energy that favoured transportation and deposition of the sediments. Diagenesis occurred with compaction and cementation of the silt to sand sized particles and hence the sedimentary rock which was sandstone was formed. These sandstones underwent low grade metamorphism to form the quartzites that consists of the medium sized quartz particles. The sandstones grains were subjected to high pressure and temperature where recrystallization of the minerals to form new crystals of the quartzites that are more favourable and stable under the new conditions. The quartzites were medium grade metamorphic rocks where there were no primary structures of the original rock the sandstone. The conglomerates were formed when sediments of different clast sizes that were carried by turbulent flow and deposited in a depositional area when the velocity of the current decreased as the energy of the water reduced. These however occurred after the formation of the quartzites and they were deposited over these quartzites in local basins. After deposition of the sediments then they were compacted and cemented in order to form the conglomerates that are hard rocks. The preferred orientation of the clasts gives an indication of how the clasts were carried during transportation for example the elongated big pebbles moving along the river bed with the long axis perpendicular to the direction of current hence the pebbles were carried by rolling. The tilted pebbles had the long axis in the direction of the current hence the pebbles were carried by suspension.
2.5 GEOCHRONOLOGY AND AGE DATING Since no fossils were encountered in the study area, it was difficult to tell the ages of the different lithologic formations. However, using radiometric dating techniques, absolute ages of rocks can be found. These were used by previous workers to approximate ages of the granites of southwestern Uganda.
Radiometric (isotropic) dating is an absolute age dating technique. Radioactive isotopes such as uranium rubidium, thorium and potassium undergo systematic change with time through
28 | P a g e radioactive decay to turn into new atoms with emission of radiations. All these reactions proceed as an exponential function of time, which can be characterized by the half time abundance of the parent nuclei. This is what is referred to as half-life of the atom. Several workers dated the granites of southwestern Uganda using radiometric age dating technique for the K/Ar and Rb/Sr isotropic ratios and got the following results (Vernon; 1972, Cahen et al; 1984)
Granites Age (m.a) Masha 1827 Rwentobo 1318 Kamwezi 1201 Chitwe 119.5 Chabakonzo 939 Ntungamo 117 2.6 GEOLOGIC HISTORY. Most of the rocks in area A are sedimentary though some are slightly metamorphosed. These rocks slightly under went regional metamorphism and have also been affected by contact metamorphism that resulted from granitic intrusion. The major compressional forces that affected the area brought about the formation of regional folds trending in the NW-SE direction and cross folds trending in the NE-SW direction that can be observed in Kamuli hill. Tensional tectonics also affected the area especially through the faulting and jointing in the rocks of area A.
Granites intruded anticlinoria between 1330 and 1250Ma (Schluter, 1997) and because of the composition of the unstable minerals under surface conditions, severe erosion on the granites took place resulting into topographic inversion. As a result, the original anticline is now a low- lying area (Masha arena) and the syncline is now a raised ground. Due the increased temperatures and pressures, these rocks were worked on by regional metamorphism and it increases from shales to phyllites. The metamorphism that occurred in the area increased towards the base. Metamorphism was enhanced by the increase in temperature and pressure due to burial of sediments. All consolidated rocks of SW Uganda are non-fossiliferous and they are of Precambrian age. The stratigraphical hierarchy in the formation of SW Uganda greatly relies on the way up criteria indicated by depositional structures that are available such as bedding structures and cross cutting relationships of lithology and geochronology.
Due to the intense fracturing and jointing, the rocks were exposed to the agents of weathering hence the rocks within this region were intensely weathered until the granites were exposed. These granites having a less stability compared to country rocks caused differential weathering in the area hence the formation of an arena. This then left a relief characterized by low lying areas of granites flanked by shales and sandstone ridges formed at the top if the hills since they are more resistant to weathering and erosion.
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CHAPTER THREE: STRUCTURES. 3.1 INTRODUCTION Structures refers to the features that are formed or developed through deformation due to tectonic forces that cause tensional, compressional and shear forces. These may be formed on the surfaces of the rock body and should be distinguishable from the undisturbed rock appearance. This may be in form of how the different faces or planes are oriented both to each other and to others as well. The structures may also be lines developed on the surface or may be referred to as the texture of the surface. There are two main types of structures which include primary structures and secondary structures.
3.1.1 Primary structures. These are structures that are developed in the rock during the period of formation of the rock itself for example bedding, mud cracks and many others. These structures aid in the reconstruction of the conditions that were present during the period of formation of the rocks and the right order of deposition of the rocks for the case of volcanic and sedimentary rocks hence important in absolute age dating. They also, through comparison with other structures, aid in understanding the different tectonic events and other physio-chemical actions that have occurred in the area since the formation of the rocks. 3.1.2 Secondary structures. These are those that are formed within an already existing rock body. This may be due to external stress, physical conditions of temperature and pressure as well as chemical reactions within the rock or with its environment. These may include folds, faults, joints, striations and many others. Contrary to the primary structures, these ones are important in relative age dating and also aids in correlating geologic events that have taken place during the existence of the rocks. In this chapter, a full descriptive account of all the structural data is given all from those observed in the field and during the laboratory analysis where the symmetry and geometry (from microscopic analysis) of the rocks in area A is done. The characteristics while in situ are correlated to that of the samples collected such that a relevant conclusion is reached through deduction of the tectonic history and knowledge of the development and evolution of the structures in the rocks in area A. 3.2 STRUCTURAL DATA. 3.2.1 Obtaining and analysis of Macro structural data. Various parameters of the different structures such as the plunge, trend, strike or dips of structures like joints, beds, fault, veins and folds were taken using a diverse collection of equipment majorly a compass and ruler. This data was there after obtained and analyzed using
30 | P a g e various software such as GIS and stereonet to obtain digitized maps, contour diagrams and rose diagrams.
Table 3: Measurements of plunge and fold axial trends in the area mapped A formatted by the stereonet software.
Dip Strike Dip Quadrant 53 18 S 174 28 W 306 25 N 15 20 E 318 20 E 102 24 S 110 30 S 68 15 S 20 68 E 116 41 S 320 23 E
The measurements for the attitudes of joint planes and bedding planes are as shown in appendix 1. 3.2.2 Stereographic analysis. The data obtained from macroscopics analysis and measurements during field visits are as shown above and deductions were made through development of rose diagrams for all the different sets of structures as well as contour(density) diagrams each of which aids in a fairly conclusive result. The stereographic projections are used for the display of geometries and orientations of lines and planes without regarding their spatial relations. ➢ Analysis of folds
Figure 5: A Pi diagram representing the folds in area A from stereonet software.
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Interpretation Poles of the various axial planes were plotted using the stereonet software to provide the Pi diagram as shown above. From the plot it is observed that the folds generally dip in the 76°NW direction and strike in S62°W direction hence correlating with the cross-fold direction of the K-A system that generally trends in the NE-SW direction ➢ Analysis of bedding planes
Figure 6: (Left) A density diagram and (right) A rose diagram representative of the bedding planes in area A from stereonet software
Interpretation From the stereographic analysis of the bedding planes in the area. it’s found that the beds show a general trend in the NE-SW as shown in the figure above. The different colors in the contour diagram are indicative of the different poles of the bedding planes in a given area. The concentration of the poles decreases outside towards the colour blue. The red colour contains the highest concentration of poles whereas the blue colour, the least poles. Since poles are perpendicular to planes, therefore the region with the highest density of poles is considered to have the least number of planes oriented in that direction. Therefore, from the density diagram above it can be conclusively deduced that planes increase outwards from the red color towards the blue hence generally trending in the NE-SW direction. From the rose diagram the length of the petals gives the frequency of the bedding planes in an area and are directly proportional hence in this case showing that most of the bedding planes were oriented in the NE -SW as shown by the petals while a few trended towards the NW-SE. This general orientation of the beds can later aid in the determination of direction of transportation of the sediments that were later deposited there. The general orientation of the beds as observed from the rose diagram is in the direction N320E and the frequency of plots is highest in this direction shown by the petal size in this direction meaning that most of the bedding planes trend in this direction.
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➢ Analysis of joint planes
Figure 7: (Left) A density diagram and (right) A rose diagram representative of the joint planes in area A generated by stereonet software.
Interpretation The joints have a general trend of NW-SE shown by the contour diagram. there are 190 plotted points in total and they are distributed allover shown as the poles to the planes in the area A and from which countering is done. the red color shows the area with the highest number of poles all the way up to the blue with a smaller number of poles. From the rose diagram its seen that the petals are trending in the NW-SE direction with varying frequencies shown by the varying lengths of the petals. A few of the joints trend in the NE-SW direction. the average orientation of the joints is S52°E. The general direction of the joints, NW-SE, is similar to the direction of the regional folding hence it may be deduced that the same event or nature of forces that caused the folding led to the formation of these joints as well. The ones that trend in the NE-SW direction correspond to the cross-fold trend hence might have been due to the event that led to the formation of this folds as well. 3.3 STRUCTURAL DESCRIPTION. As we mapped the area A we encountered different kinds of structures; the major and the minor structures. Structures such as folds and faults found on the rocks show that it was acted by compressional and tensional forces and hence were formed by deformational processes. There are other structures such as bedding planes as well. Structures majorly aid in determining the processes under which the rocks have undergone with time, their provenance and the P-T-X paths especially for the metamorphosed rocks.
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3.3.1 Major structures These are the structures that occur on a large scale on the rock. These include the faults, joints, beds. ➢ Joints These are fractures along which there is no displacement. The rocks deform when the applied stress exceeds the rock strength. Joints are found in brittle rocks. In the area A we mapped, joints were the most dominant structures found mainly on the quartzites that were located on the ridges. Most of the joints in the area were nonsystematic those that are irregular in form and in spacing and in their orientation. The joints had an aperture ranging from a few millimeters to about 20cm. The joints that we encountered were of two different sets that show the different episodes of deformation that deformed the rock to form the joints. Those in the NW-SE direction that correspond to the regional fold and those in the NE-SW direction that correspond to the cross fold. These joints could have been formed during a period of folding were brittle rocks fracture forming the joints and even faulting occurred after the folding as shown by the faults.
Figure 8: Joints in quartzites in the area that were mainly trending in the NW - SE (from station A19, (0253853, 9915202))
➢ Bedding A bed is the smallest lithostratigraphic unit that ranges in thickness from a centimeter to several meters and is distinguishable from the bed above or below in terms of size of particles and mineral type or rock. It is the smallest division of the geological formation or stratigraphic rock marked by well-defined divisional planes separating it from layers above and below. In area A mapped the beds were found mainly in the shales and the beds were varying in terms of the thickness. The beds differ from each other in terms of the colour, texture. Some of the beds were folded due to the tectonic forces mainly the compressional forces that acted on them. Some of
34 | P a g e the beds in the ferruginous shales were folded beds dipping in the NW-SE direction and trending in the NE-SW direction conforming to the trend of the cross fold while other beds were trending in the NW-SE direction conforming to trend of the regional fold.
Figure 9: Bedding in shales at station A21 (0252300, 9915795)
Faulting This is a fracture or fissure on the earth’s crust along which there is relative displacement on the either side of the fracture. Faulting Karagwe-Ankolean system is wide spread in the rocks where some of the faulting appears to have occurred together with the folding or in the closing stages of the folding whereas some faulting is clearly much later (King and Swardt, 1967). Evidence of faulting in area A was seen through the presence of the fault breccia, linear vegetation seen in certain areas.
3.3.1 Minor structures These are the structures that occur on a small scale on the rock and they include folds, veins filled quartz or with iron. ➢ Folds A fold occurs when one or a stack of originally flat and planar surfaces like sedimentary strata are bent or curved as a result of permanent deformation. Folds can range from microscopic to hundreds of kilometers across. The Karagwe-Ankolean being part of Kibaran belt is dominated majorly by two-fold sets: the pronounced regional with the fold axes trending NNW and cross folds with the fold axes trending NNE (Barnes, 1956; King and De Swardt, 1967; Cahen and Snelling, 1966).
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In the area mapped the folds were found to occur in argillaceous rock units like shales which are ductile in nature and so are easily bent when acted on by the compressional forces.
Figure 10: A synformal fold within shales (station A14 (0252770, 9915220))
➢ Veins The two veins found in the area mapped A were the quartz veins and the veins filled with iron fluids. The structures are formed when the hydrothermal solutions penetrate and solidify along the lines of weakness in quartzite and shales. These quartz veins are mainly composed of silica minerals. Some of the veins were fractured showing that the rock hosting them underwent some period of deformation.
Figure 11: Quartz veins in quartzites at station A17 (0253469,9915055)
➢ Ripple marks Ripple marks are primary structures in a sedimentary rock formed due to the action of currents and flows of sediments prior or during their deposition. These environments are often quiet and calm. Due to the variability r the consistency of the energy, they may be termed symmetrical or asymmetrical. The ripple marks observed in area A were current ripple marks and was trending in the NE-SW direction which is believed to be the current direction.
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3.3.1 Micro structures Through the analysis of thin sections various structures that could not be observed with the unaided eye were observed which further aided in the description of the history and nature of the rocks ➢ Elongation. This is very evident especially within the quartzites where by the grains are seen to attain a particular alignment of their longer axis. Ideally, quartz grains are equidimensional but in cases where the elongation is observed, it suggests that these grains underwent some strain which might have even cased the metamorphism. Therefore, the elongation in the quartz grains in quartzite is an evidence that the quartzites underwent metamorphism. This is observed in figure 28 in chapter four ➢ Twining This is also a feature observed in the phyllite. When crystals are stressed, they may be deformed plastically by gliding or sliding along planes between rows of atoms within the crystal structure. This may take the form of ‘translation gliding’, whereby one or more rows of atoms may be displaced laterally along the glide plane, or ‘twin gliding’, where a smaller displacement is taken up by each row within the lattice. This leads to what is referred to as twins and it can be observed in thin sections using XPL whereby they exhibit undulose extinction
Figure 12: Twinning as observed in a phyllite sample from station A24 (0252824, 9916420). The two represent images on rotation at 45° Discussion Like the Eastern or Main Rift, the East African rift valley system, Western Rift is superposed on an old crustal weakness zone, that is, a Paleoproterozoic suture between the Archaean Tanzania and Congo Cratons that was rejuvenated during Mesoproterozoic extension and compression, resulting in formation of the intra-cratonic North Kibaran Belt, and subsequently reworked again during the Pan-African. The basin formed then favoured sedimentation where various sediments of varying sizes were deposited over time hence on lithification, beds were formed. The later reworking led to the formation of tilted beds. The compressional forces acted later in the northwest-southeast 37 | P a g e direction. The compressional forces acted on the area led to the formation of regional folds trending in the northwest-southeast direction and cross folds trending in the northeast-southwest direction. Structures like folds, joints, faults, beds, quartz veins with the associated mineralization were probably triggered by the compressional and tensional forces that affected the area. Plastic deformation usually first occurs especially in the sediments and rocks such as the ones in K-A system and when the forces are intense, it may result into rupture which is what is referred to as rupture. This therefore suggests that faulting within this system follow the folding Due to the increase in pressure and temperature changes that might have been caused by the burial or the intrusive granite body, there was metamorphism which was however low grade in nature. This is evidenced by the presence of relict structures such as relict beds within the quartzites. During the analysis of the thin sections, the quartz was found to be elongated and also having an undulose extinction hence further evidence of metamorphism. The age relations within these structures can only be distinguished in the cases where the actual
N
Fault plane
Quartz veins about 4- 10mm thick in Quartzite rock
Figure 13: A sinistral strike- slip fault in quartzite. (0253179, 9907838) structures are being observed and they vary from locality to locality hence no general relationships. The principles of stratigraphy aid a lot in these comparisons for example in the sketch below, the faulting occurred after the formation of the quartz veins. 3.4 SUMMARY The area studied has major structures including joints, beds, faults and the minor structures include laminations, folds, quartz veins, ripple marks, cleavage and foliations. These structures were interpreted after drawing the rose, contour and pi diagrams and getting their lines of best fit. These structures were formed at different periods due to the different tectonic episodes that occurred with varying magnitude and direction. These forces were majorly tensional and/or compressional forces but rarely shear forces. This led to the cross-cutting structures and features as observed that greatly modify the landscape of the K-A system.
Micro structures such as elongation and twinning were also observed
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CHAPTER FOUR: PETROGRAPHY AND METAMORPHISM. 4.1 PETROGRAPHY 4.1.1 Introduction Petrography is a branch of petrology that focuses on the detailed description and classification of rocks, especially by microscopic study though macroscopic study is also essential. It is useful in establishing the mineral content and textural relationships within the rock. Petrographic description started from the field with the filed notes at the out crop including macroscopic description in the hand specimens. The chapter gives the description of the samples obtained and the thin sections got from representative samples in the laboratory. It describes the macroscopic, microscopic properties of the samples got from mapped area A. 4.1.2 Sample analysis This is majorly divided into two major types which include the microscopic and macroscopic analysis. ➢ Macroscopic analysis This involves mainly the field description of a fresh sample obtained in the field by use of a hand lens and the naked eye. It is the description of mineralogical compositions, colour, grain shape, texture, structures present, and field name. ➢ Microscopic analysis This is the description of the sample determined by studying it under a petrographic microscope, as a thin section for detailed analysis of minerals, micro texture and structure. Microscopic properties were obtained both under plane polarized light for example pleochroism, colour, habit, inclusions, cracks, relief or under crossed polars for example birefringence, interference colours, extinction, sign of elongation as some properties are only visible in latter and not in the former. Individual minerals that the rock sample is composed of can be studied. In this case seven representative samples from the area A were chosen and analyzed as shown below, two of which are exclusively discussed in this chapter. For the microscopic analysis of each of the other samples not discussed in this chapter, check the appendix 2 Representative rock samples
• For the quartzites
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Field name: A22푆1 Rock name: Quartzite Rock type: Metamorphic Precursor rock: Sandstone Color: Grey, brown, colorless Rock form: Sub-hedral Cleavage: Perfect (2-direction) Texture: Phaneritic Heft: Moderate Grain size: Fine grained Hardness: Hard(7) A22S1 Structure: Joints Mineralogy: Quartz, clay minerals, muscovite Comment:
Figure 14: Sample A22S1
A
B
C
Figure 15: Thin section view of sample A22S1(Left)PPL (right)XPL
Table 4
MICROSCOPIC OBSERVATION FOR SECTION A22푺ퟏ PROPERTIES MINERALS OBSERVED ANALYSED A B C
Color Colorless Colorless Colorless
Percentage composition 70 20 10
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Form (Habit) subhedral subhedral Anhedral
Relief Low Strong Strong
Cracks Absent Absent Absent
Alteration Absent Absent Absent
Inclusion Present Absent Absent
Cleavage Absent Imperfect Basal
Anisotropy/ Isotropy Anisotropic Anisotropic Anisotropic
Twinning Absent Absent Absent
Inference colors 1st order grey 2nd order blue Pale green
Birefringence Weak Strong Strong
Interference figure Uniaxial positive Biaxial negative Biaxial negative
Extinction angle Present Absent Absent
Zoning absent absent absent
Pleochroism Absent Absent Present
Mineral proposed name Quartz chlorite Muscovite
• For the shale
Field name: A14푆2 Rock name: Shale (slaty shale) Rock type: Sedimentary rock Precursor rock: Claystone Color: Grey, pink Rock form: Anhedral Cleavage: Imperfect Texture: Aphaneritic Heft: Moderate Grain size: Fine to moderate Hardness: Low Structure: Lamination, minor structures Mineralogy: Quartz, kaolinite, muscovite, hematite, illmenite Comment:
Figure 16: Sample A14S2
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A
B
C
D
E
Figure 17: Thin section view of sample A14S2(Left)PPL (right)XPL
Table 5
MICROSCOPIC OBSERVATION FOR SECTION A14푺ퟐ PROPERTIES MINERALS OBSERVED ANALYSED A B C D E
Color Colorless Colorless Green Brown Black
Percentage 20 35 15 20 10 composition Form (Habit) Subhedral Anhedral Euhedral Euhedral Euhedral
Relief Low Low Strong Strong Low Cracks Absent Absent Absent Absent Absent
Alteration Present Absent Present Present Absent
Inclusion Absent Absent Present Absent Absent Cleavage Imperfect Imperfect Perfect Imperfect Imperfect (one direction)
Anisotropy/ Anisotropic Anisotropic Anisotropic Anisotropic Anisotropic Isotropy
Twinning Absent Absent Absent Absent Absent Inference 1st order 1st order 1st order 2nd order 1st 0rder colors grey grey white red blue 1st order 4th order 2nd order 1st order white green black grey Birefringence Weak Weak Strong Moderate Weak
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Interference Uniaxial Not Biaxial Uniaxial Uniaxial figure positive obtained negative negative negative
Extinction Absent Absent Absent Absent Absent angle
Zoning Present Absent Absent Present Absent
Pleochroism Absent Absent Absent Absent Absent Mineral Quartz Kaolinite Muscovite Hematite Illmenite proposed name
For the samples below, only the macroscopic analysis is discussed in this chapter. For the microscopic analysis, refer to the appendix 2
Field name: A23푆1 Rock name: Phyllitic shale Rock type: Sedimentary rock (metasedimentary) Precursor rock: Claystone Color: Grey, brown Rock form: Anhedral Cleavage: Imperfect Texture: Aphaneritic Heft: Moderate Grain size: Fine to medium grained Hardness: Moderate Structure: Joints, lamination Mineralogy: Clay minerals, chlorite Comment:
Figure 18: Sample A23S1
B
A
C
Figure 19: Thin section view of sample A23S1(Left)PPL (right)XPL
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Field name: A19푆1 Rock name: Quartzite Rock type: Metamorphic Precursor rock: Sandstone Color: Grey, white Rock form: Sub-hedral Cleavage: Perfect Texture: Phaneritic Heft: Heavy Grain size: Medium-coarse Hardness: hard (7) Structure: Joints Mineralogy: Quartz, chlorite, muscovite Comment:
Figure 20: Sample A19S1
A
B
C
Figure 21: Thin section view of sample A19S1(Left)PPL (right)XPL
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Field name: A4푆1 Rock name: Quartzite Rock type: Metamorphic rock Precursor rock: Sandstone Color: Grey to colorless Rock form: Sub-hedral Cleavage: Perfect Texture: Phaneritic Heft: Heavy Grain size: Medium-coarse Hardness: High Structure: Joints Mineralogy: Quartz, muscovite, clay minerals (kaolinite) Comment:
Figure 22: Sample A4S1
A
B
C
Figure 23: Thin section view of sample A46S1(Left)PPL (right)XPL
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Field name: A26 S1 Rock name: Phyllitic shale Rock type: Sedimentary rock Precursor rock: Claystone Color: White Rock form: Anhedral Cleavage: Imperfect Texture: Aphaneritic Heft: Moderate Grain size: Fine-medium Hardness: Moderate Structure: Layered Mineralogy: Clay minerals (Kaolinite), chlorite, quartz Comment:
Figure 24: Sample A26S1
A
B
C
D
Figure 25: Thin section view of sample A26S1(Left)PPL (right)XPL
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Field name: A1푆1 Rock name: Quartzite Rock type: Metamorphic Precursor rock: Sandstone Color: Grey to colorless Rock form: Sub-hedral Cleavage: Perfect Texture: Phaneritic Heft: Heavy Grain size: Medium to coarse Hardness: High Structure: Joints Mineralogy: Quartz, muscovite, clay minerals Comment:
Figure 26: Sample A1S1
A
B
C
Figure 27: Thin section view of sample A1S1(Left)PPL (right)XPL
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4.2 METAMORPHISM 4.2.1 Introduction
Metamorphism may be referred to as the mineralogical and structural adjustments of solid rocks to physical and chemical conditions that are imposed at depths below the zones of weathering and diagenesis and which differ from conditions under which the rocks originally were. This definition, therefore, excludes alteration at or just beneath the surface, such as weathering and diagenesis which is very significant in area A. However, diagenetic changes grade into metamorphic changes in burial metamorphism therefore making a distinct boundary for determination of metamorphic rocks nonexistent.
Rocks, therefore, metamorphose in order to re-establish equilibrium (stability) under the new conditions, mainly of increased temperature with increase or decrease in pressure and influx of fluids into the rock body. They may do this mainly by the constituent minerals reacting with one another to form new product minerals that are more stable under the changed conditions such as the case of the contact metamorphism in the granitic intrusions or by undergoing structural re- adjustments to accommodate the constraints, such as strain imposed by the new conditions, especially pressure. Lithostatic pressure on its own does not really cause metamorphism. It is deviatoric stress that causes deformation. Interpretation of the conditions and evolution of metamorphic bodies, mountain belts, and ultimately the state and evolution of the Earth's crust is a cardinal goal of a comprehensive study of metamorphism of this region. 4.2.2 Metamorphism of rocks in Area A
The Karagwe-Ankolean rocks are metamorphosed to various degrees. The metamorphism progressively increases from the top to the base ranging from shales or sometimes slates at the top through phyllites and then to muscovite schist and finally biotite schists at the bottom. The metamorphism also increases with proximity to the granite intrusions hence rocks closest to the granite intrusions have been metamorphosed to a higher degree compared to those farther from the granite intrusions. The sandstones have been metamorphosed to form hard quartzites and conglomerates have been metamorphosed and pebbles flattened. Quartzites have been sheared and mylonitised.
In general, the older granitic rocks are overlain by less metamorphosed cover rocks and though not necessarily of equivalent stratigraphical age these rocks were probably originally deposited during the same episode and later metamorphosed, mylonitized and intruded by granites to different degrees and at different tectonic levels. In some areas, regional metamorphic effects cannot be distinguished from those due to granitic emplacement. Therefore, in this area A, metamorphism in the area is generally regional and of low grade. The metamorphism that influenced the area is also shown by the petrographic analysis quartz grains are elongated in a particular direction. These quartz mineral grains also exhibit undulose
48 | P a g e extinction and sutured boundaries which are evidences of metamorphism within the rocks in this area. In other rocks such as shales and quartzites, during the field observations relict bedding was observed which is an evidence of low-grade metamorphism where metamorphism has not attained completion.
Figure 28: Elongation in quartz grains as highlighted in the thin section above under cross polarized light. (sample A1S1)
4.3 SUMMARY It can therefore be conclusively deduced that two major types of metamorphism occurred in area A which are contact metamorphism and regional metamorphism. The metamorphism of this area is generally of low grade with rocks varying from shales, slates, phyllitic shales and phyllites. Rocks of higher grade of metamorphism such as muscovite and biotite schist are found outside area A and were observed during the geo-traverse around the whole region. Relict structures such as relict beds are observed and also elongation of quartz grains and undulose extinction in thin sections provide evidence of metamorphism in these rocks.
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CHAPTER FIVE: REGIONAL SYNTHESIS. 5.1 INTRODUCTION
In this chapter, various features from the entire Igayaza area are discussed and related to the general features that were both interacted with or not during the geo-traverse. This will not only prove the results and deductions made from the areas exclusively mapped but also observe the general trend of geology in the K-A system, that is, the metamorphism, structural trends, mineralization and how all these are related to each other over the whole region.
5.1.1 General Geologic setting The Karagwe-Ankolean System comprises mainly argillaceous formations that have been slightly metamorphosed to argillites, phyllites and schists. There are also arenaceous formations represented by quartzite. Ultramafic, mafic rocks and granites intruded the Karagwe-Ankolean rocks. The mafic and ultramafic intrusions recorded majorly in NW Tanzania are layered and comprise peridotites, pyroxenites, norites, anorthosites and granophyre. The metamorphism in the Karagwe-Ankolean System is very low and mainly increases towards the base of the Karagwe-Ankolean System. The general structural trend of the Kibaran belt is in the NE-SW direction in the south. In Tanzania the belt trends in N and NE direction. The prominent Kibaran trend in SW Uganda is NW called Ankole fold trend (Barnes, 1956)
Fold trends in the K-A ➢ Arching (Ankole Arch, Shema Arch, Nakivali Arch ➢ Regional folding (NW- SE) ➢ Cross folding (NE-SW) ➢ Minor folding (Argillites) Other structures ➢ Cleavage ➢ Faulting ➢ Jointing ➢ Bedding ➢ Lamination Figure 29: Block diagram illustrating the style of folding of the K-A system of rocks. ➢ foliation
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Mineral resources associated with the Karagwe-Ankolean System include cassiterite, wolframite, nickel, copper, gold, silver, niobium-tantalum, magnetite, talc, ochre, mica, uranium, thorium, beryllium, lithium, bastnaesite, semi-precious stone, cobalt, platinum, chromium, titanium, vanadium and iron. Some of the minerals occurring in the same system in neighbouring countries have not been located in Uganda. 5.1.2 Granite and Arena phenomena An arena is a broad stadium like low ground. This term was used by Wayland in1920 to describe these features that were very common in the K-A system of southwest Uganda. He realised each structure was an anticlinal dome, intensely eroded to expose the underneath granite Granites are grouped according to available Rb/Sr data, tectonic evolution and petrographic characteristics. In East Africa, they include;
• G1 Granites: Rwantobo (1318±84 Ma), Ntungoma (1170±66 Ma), Kamwezi (1201±134 Ma) and Lugalama (age?). • G2 granites: Chitwe (1107±39 Ma), Chabakonzo (939±39 Ma), Masha, Akabeba. • G3 granites: Ultramafic rocks of Kabanga. • G4 granites: lbanda, Dwata, Rwabaramira, Karenge. Two main theories are suggested about the granites that led to the formation of the arena; a) The first one suggests that the granites invaded the already formed anticlines which then underwent first uniform weathering and then differential weathering that resulted into formation of these features b) The second one suggests that the granites are older than the cover formations, that there was just an episode of thrust faulting and the granite was remobilized where it invaded the cover formations to fill the void created by doming which squeezed the cover rocks causing mylonitization and low-grade metamorphism. This was then proceeded by the uniform and then differential weathering that led to the formation of the arena. As structural depth increases, the granites tend to increase in size, become less regular in shape and to show greater disturbing effects on the surrounding sedimentary structures (Barnes, 1956). 5.2 HOTSPOTS 5.2.1 Area B Location: (0255725, 9918203) at an elevation of 1471m above sea level This area majorly consists of Quartzites, shales (ferruginous, grey, and phyllitic), and granites. It has a hinge within the arena hence contact metamorphism affected the area. The contact metasomatism intensified the metamorphism of the rocks close to the arena leading to rocks deep in succession such as phyllites and the phyllitic shale. The structures present included folds, joints, cleavage, boudinage, foliation and mineral lineation.
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The general trend for the folds within this area was the NE-SW hence corresponding to the cross folds of the K-A system The non-folded regions strongly developed foliation and mineral lineation due to compressional forces that generated a local tension. The cleavage was majorly axial planar cleavage and fracture cleavage having a general trend in the NE-SW Conclusively, this area represents representative information about the metamorphism and the cross structural trend of the K-A. The most distinct structure in this area that can’t be easily be found in other areas are the boudinage.
5.2.1 Area E Location: (0256974, 9916303) at an elevation of 1434m above sea level This area contained quartzites, grey shales, ferruginous shales and phyllitic shales with the quartzites forming sub parallel ridges flanked by the argillaceous rocks. These quartzites were intensely fractured leading to the formation of the water hole due to the fracture porosity. These further evidences the occurrence of faulting within the area. Other structures in this area included cleavage, folding and also bedding
Figure 30: Bedding in shales of area E
5.2.2 Area G Location: (0254951, 9916628) at an elevation of 1457m above sea level The lithologic unit is within this area includes brecciated quartzites hence evidence of faulting in the area, multiply fractured shales which are the ferruginous, grey and phyllitic shales. The major structures within this area included folds, faults, joints, bedding, and quartz veins.
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Just like it is in the K-A system, this too exhibits two phases of folding. These forces also led to the intense jointing within this region. Fissures were created before being later filled by the silica rich minerals hence formation of the quartz veins. The joints majorly trend in the NE-SW direction. The granite intrusion within this region is found to be of G1 and G2 type hence the oldest type but with no mineralization. The presence of fine materials or sediments imply a lacustrine, terrestrial environment of deposition of sediments.
5.2.3 Area H Location: (0254666, 9913016) at an elevation of 1457m above sea level. The rocks in this location were majorly grey shales, ferruginous shales, and quartzites The structures that were present majorly included bedding, folding, faulting, jointing and cleavage. The folding within the shales had an axil trend of N42°W and S78°E hence corresponding with the regional fold trend (NW-SE direction). The bedding planes had a general trend in the NE-SW direction for example N30°E/ 70°SE.
5.2.4 Area I Location: (0250770, 9915859) at an elevation of 1430m above sea level. This area is located on the northern slopes of Nabugando hill. Being close to the arena or the granitic intrusion, a number of rocks are recognized which include quartzitic sandstones, grey and dark grey colored quartzites, phyllitic, grey and ferruginous shales, aplite, phyllites, granites and mylonitic granites. Applite: is an intrusive igneous rock in which the mineral composition is the same as granite (Quartz and feldspars), but in which the grains are much finer, under 1 mm width. This is often due to the fast cooling that does not provide enough time for the fully developed large crystals to occur. Porphyritic granite has the same chemistry and mineralogy as ordinary granite, but differs in the size range of its crystals. Granites are coarsely crystalline igneous rocks, having a phaneritic texture. Porphyritic granites have a mix of large and small crystals, but all crystals are still fairly decent-sized. Large crystals in a porphyritic rock are called phenocrysts. The smaller crystals make up the groundmass. Porphyritic granites typically have K-feldspar phenocrysts (pinkish). The groundmass is typically quartz (greyish), sodic plagioclase feldspar (whitish- gray), amphibole (black), plus sometimes biotite mica and/or muscovite mica. Mylonitic Granites: The characteristic feature of mylonites is grain-size reduction through crystal-plastic deformation that results in a rock with a strong foliation produced by ribbon
53 | P a g e structures. Larger crystals within mylonites are porphyroclasts that are relict grains that have experienced less grain-size reduction than the surrounding matrix. Porphyroclasts in mylonites often form eye-shaped augen due to the development of pressure shadows during rotation of the crystal. The metamorphism grade of the rocks in this area is low grade which corresponds to the grades in the other areas visited and the K-A at large. This area possesses a characteristic centripetal type of drainage. Structures in this area include joints, folds, cleavage, bedding and faulting. The plutonic rocks have overburden pressure acting on them, but due to weathering and erosion of the plutonic body, the overburden is released and due to the sudden release in pressure, the rocks expand upwards hence forming the flat surface joints so that we observe the joints in the area being nearly horizontal in dip. Quarrying is actively carried out in this area in addition to the growing of bananas and rearing of majorly goats, cows and sheep.
5.2.5 Area L This area is located at Kichwekano along Kigarama road at (0251364, 9914142) 1577m above sea level. The general area L has two sub parallel ridges of quartzite, flanked by grey, ferruginous and phyllitic shales located on the slopes and valleys Breccias are very evident in this area with iron oxide acting as the cement in this case. This is an evidence of faulting within this region. The fault observed in this area is a sinistral strike-slip fault which was trending in N50°W Jointing is also observed with an average spacing of about 15-18cm for those close to the fault zone and 1-1.5m for those far away. These joints majorly trend in the NE-SW direction. The joints close to the fault zone are also filled up with iron oxide unlike those far away from the fault zone. Joints and faults increase the porosity and permeability of rocks hence improving their potential as reservoir rocks. The change in mineralogy and structure of the rocks in this area was also observed to be of isochemical metamorphism where no new components are added to or removed from the protolith during the metamorphic reactions Other structures observed include cleavage and folds. The major economic activity in this area is quarrying and brick laying to obtain construction material. Just like most areas in this region, there is growing of majorly bananas and rearing of animals such as cows.
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5.2.6 Area J Location: (0255511, 9914904) at an elevation of about 1380m above sea level. This area consists of majorly three hills which are Buchuba hill, Busenga hill and Kisitu hill The rocks in this area include quartzites, and shales (ferruginous, grey and siliceous). The shales are of uniform thickness due to the uniform rates of deposition of fine sediments within this region. The square shaped voids within the shales shows the removal of a mineral from the shales and in this case, it was the Pyrite which exist in reducing conditions only and in case oxidizing conditions they get altered and leads to voids The major structures in this area includes joint majorly trending in the NE-SW and NW-SE direction and the bedding planes which strike in the NE direction and dip in the NW direction and faults whose planes trend in the NE direction. It was further observed that the quartzites at Busenga hill had been displaced to the left of the fault as observed from the location of the hotspot which is a hanging wall. Faulting is further evidenced by the brecciated quartzites and siliceous shale that are intensely fractured. Folding is also present in this area with a general strike and dip of NW-SE direction and NW direction respectively. Boudinages are also observed. Just like most areas in this region the major economic activity in this area is agriculture and quarrying.
5.2.7 Area C Location: (0257340, 9917154) at an elevation of 1569m above sea level. This area like many others has quartzite horizons with slopes majorly containing shales and also in the valleys. A plateau is also present in this area. This plateau formed due to the presence of a dome which was proceeded by even weathering and erosion hence formation of the flat raised topped area. The products of the weathering (sandy clays) were deposited in the valleys and some also remained on the plateaus which made the area favourable for agriculture due to the fertile soils present. The evidence of low-grade metamorphism within this area is shown by the presence of the relict bedding which dip towards the water hole (N50°W/ 25°NE) The faults are also present in this area due to the presence of brecciation in quartzites and gradually widens in aperture as it fades out. These faults generally trend in the NW-SE direction.
5.2.8 Area A Location: (0253811, 9916472) at an elevation of 1511 at the playground near the rest house.
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This was also recorded as station A30 and inclusive of the areas we fully mapped. The outcrop here is intensively shattered, large and highly weathered. The major rocks here are quartzites and conglomerates which have quartzite pebbles and iron oxide cement. In other parts of area, A, rocks present include ferruginous shales, grey shales, Phyllitic shales, and granites. The conglomerates are angular to sub angular hence they might have travelled over a short distance or in a short period of time hence less period of reworking. The structures in this particular location include joints that majorly has two trends, the NE trending joints and the NW trending joints. The dips are generally high (greater than 50°) Other structures in area A include folds, cleavage, lamination, foliation, bedding and occurrence of quartz veins.
Figure 31: A water hole in a shale outcrop in area A
5.3 GEO-TRAVERSE
STOP 1: A hanging wall at Nyabwiiruka Hill Location: (0255966,911390) This are had an evidence of a reverse fault occurrence and the hanging wall could be observed. A cyclic nature of bedding is also present with iron oxide minerals between the different layers in addition to the coarse-grained silica minerals. in too The outcrop was grey in colour with brown stains or iron oxide minerals due to hydrothermal fluid intrusion. A process which may be referred to as paragenesis. The large dips of bedding and joint planes imply the axis of folding is far away from this area. Silica rich drop stones were also found and observed. A sinistral strike-slip fault was also observed as shown in the figure 13 in chapter 3 56 | P a g e
STOP 2: Road junction near Kabingo subcounty head quarters Location: (0253012, 9914436) at an elevation of 1404m above sea level. This roadcut is large and benching is done in order to prevent failure of the road cut. The two far ends of the road cut were seen to change in dip directions, that is, NW direction in one and SE in the other hence possibility of a synclinoria due to the opposite directions of dip. The major rocks here were shales. STOP 3: Mabona small scale folds. Location: (0253179, 9907838) This was also a moderately large outcrop and a road cut made up of majorly bedded grey shales in addition to the characteristic micro folds. These folds are on an almost vertical limb of a major fold. A white mineralization of canadite (NaSO3) occurs within the shales. Structural measurements
• Fold N42°E/ 52°NE and N15°E/ 20°NE • Joints N68°W/ 88°NE and N52°W/ 84°NE • Beds N20°E/ 78°SE and N14°E/ 66°SE
STOP 4: Kikagati tin mine Location: (0240535,0994842) This mineralization is said to have occurred as a result of intrusion of G3 and G4 granites bearing the mineralized fluids which occupied the fractures before being precipitated to form the minerals. Those minerals expected to occur in this manner include Gold, tin, tungsten tantalum, columbite and many others. Here cassiterite, a tin ore, occurs within Quartz pegmatitic veins that run parallel to sub parallel to each other. Other rocks noted in this area include graphitic schist, shales and quartzite with the structures such as joints and beds (majorly striking in NW and dipping in the NE), quartz veins, schistocity and lamination. At this site, poor methods of mining are evident where by the veins mined and the blocks are left hanging hence endangering lives. The best method of mining should have been part by part where the wastes are put back in the spaces created. Tin is used manufacture of tin plates, alloys (solder), textile dying and in ceramic industry. The tailings are used as construction material hence quarrying for aggregate is also carried out.
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Figure 32: Voids created from mining of quartz veins containing cassiterite at Kikagati tin mine. STOP 5: Ibanda granite at Kikagati. Location: (0238324, 9882454) at an elevation of 1248 m above sea level This granite is of G4 type (900-950Ma) and naturally outcrops at the boarder of the Uganda and Tanzania. They are responsible for the mineralization of tin in Kikagati. The granite has a mixture of white (quartz sodium rich felspars and muscovite) and dark minerals (biotite). The alkali feldspars are grey to milky in colour and are coarse grained whereas the granite is generally pegmatitic and porphyritic with a cleaved surface. These surfaces appear fresh due to exfoliation Joints that majorly trend in the SE direction with a steep dip are characteristic of these granites for example (S86°E/ 78°SW) Xenolith of tourmaline and enclaves are observed.
Figure 33: (Left)An enclave at Ibanda granites. (right)a xenolith of tourmaline
STOP 6: Akabeeba Granite Location: (0226441, 9891004) at an elevation of 1326m above sea level.
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Unlike the Ibanda granite, the Akakeeba granite is of G2 type, greatly foliated, with a weathered and exfoliated surface with medium to coarse grains. The foliation generally trends in the NW- SE direction corresponding to the joint trends in addition the large dips of joint planes for example N58°W/ 88°NE This granite body is a mixture of S and I type granite with an intermediate 87Sr/86Sr ratio hence generally associated with copper, gold and iron mineralization. Quarrying is carried out at this site.
Granite Fault line
Figure 34: A sinistral strike slip fault that can also be used in correlating the different ages of the structures.
2cm wide quartz vein trending in N38W
STOP 6: Chitwe Granite This too is a G2 type of granite that is weathered hence dark coloured and medium to coarse grained. Granite tors are very evident due to the exfoliation in an effort to attain the most stable shape or orientation, that is the spherical shape and it is from these spherical shaped rocks that the name Chitwe is derived which means “head” in the local dialect.
Figure 35: The granite tors of the Chitwe granites.
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STOP 6: Out crop of Kyanjyenyi series Location: (0202236, 9938613) This outcrop is of medium to coarse grained granite of the basement complex however much it is located in an area covered with the Buganda-Toro system of rocks. This is as a result of deep weathering of the initially overlying Buganda-Toro rocks hence exposing rose of the basement complex. The structures observed include quartz veins (trending in N84°W and N72°W), joints (generally trending in the NE direction) and foliation in the N-S direction. The foliation is due to the regional metamorphism. STOP 6: Kitagata hot springs Location: (0202236, 9938613) This hot spring is found in Kimondo 2 sub parish Sheema district. The locals have divided it into two parts that is the Mulago hot spring and Mugabe hot spring. The hot spring is an extension of the 5000km long East African rift system and lies within the basement complex. The water is about 25-40°C in temperature and rich in minerals such as Sulphur with emission of gasses such as hydrogen sulphide, chlorine and carbon dioxide Structures observed in the outcrops within this area include joints (N32°E/ 84°SE and S44°E/ 70°SW) and foliation trending in N74°W. There is also evidence of shearing due to the presence of mineral lineation within the rocks. This site majorly acts as a geosite hence of great importance in the economic, social and geologic fields STOP 6: Lake Mafuro in Bunyaruguru Location: (0177261, 9971162) This lake is a crater lake surrounded by tuffs and some pyroclastic rocks. This is due t the explosive nature of the magmatism that even the initial layer covering the lake area were thrown far away hence the lavas are very hard to find. It should be noted that in rift systems, volcanisms take place where the rocks that result have excess of potassium (3 to 5 times) more than sodium. These areas in Bunyaruguru volcanics have become world famous because of having potassium rich rocks instead of sodium rich. Even after recrystallization of the melt, there still exists an excess of potassium (ultra-potassic rocks form) The lavas around the Bunyaruguru volcanics include Mafurites, Katungites and ugandites
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Figure 36: The Mafuro crater lake STOP 6: Edge of the rift Location: (0176535, 9975109) at an elevation of 1777m above sea level This area contains pyroclastic rocks since it still lies within the volcanic field. Due to the rifting fragments of the older Buganda-Toro rocks are found in this area. There is also a high likelihood of fossils being found due to the presence of a sedimentary basin where clastic sediments and other eroded material may settle. Therefore, the rift valley basin has potential for hydrocarbon occurrence within them.
Figure 37:Part of the western arm of the East African rift valley near lake George.
5.4 SUMMARY
The area was developed before intrusion of G1 and G2 areas. However different intrusions and the later G1 and G2 intrusions coupled with the tectonic forces greatly shaped and moulded the observed physiology and relief of the area characteristic of quartzite ridges on to of the hills and shales making up the slopes and the valleys. In places close to the arena, metamorphosed rocks such as phyllitic shale, phyllites and schists are observed. Granites form arena structures in this region
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The metamorphism throughout the region is generally low grade of zeolite to greenschist facies. Sedimentary features and structures are also present even in the metamorphosed rocks (relict structures) Silica mineral veins, folds, joints foliation, beds, boudinages, cleavage and lamination dominate the rocks in the K-A system. The areas mapped is of the Upper division of Karagwe-Ankolean system. Most of these rocks have been affected by tectonic forces, predominantly the compressional forces associated with the regional and cross folding, and these are responsible for the dominant trends of most of the structures within the rocks. Unlike Kikagati, and other areas within the K-A system, Igayaza possesses no evidence of mineralization. The economic potential of these rocks can be seen in the quarrying of quartzites to obtain aggregates for road and building construction. They are poor source rocks due to limited organic matter, and bad reservoir rocks due to most joints being filled up by siliceous material and iron rich minerals. The hydrocarbons are instead expected in the sedimentary basins of the western arm of the East African rift valley.
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CHAPTER SIX: COMCLUSION AND RECOMMENDATIONS. 6.1 CONCLUSION Igayaza falls under the Karagwe-Ankolean (K-A) system which in some literature, place it under the Kibaran belt. The Mesoproterozoic Kibara Belt (also Kibaran Belt or Kibarides in some references) of Central Africa is often portrayed as a continuous, about 1500 km long orogenic belt, trending NE to NNE from Katanga, Democratic Republic of Congo (DRC) in the south, up into SW Uganda in the north (Brinckmann et al., 2001). Igayaza area specifically is found to give rise to mountainous or hilly landscape with the lower lying areas containing metamorphosed rocks as a result of the granitic intrusion and the valleys containing the weathered granites themselves. Quartzites run along the summits of the ridges with the rest of the argillaceous rocks such as the shales and phyllites occupying the slopes of the ridges and the valleys within and between the ridges having granites. The area A, studied has major structures including joints, beds, faults and the minor structures include laminations, folds, quartz veins, ripple marks, cleavage and foliations. These structures were statistically analysed using rose, contour and pi diagrams and getting their lines of best fit that aided in explaining and relating it to the regional trends of these structures. Bedding planes were found to be majorly trending in the NE SW direction and the joint planes in the NW-SE direction hence corresponding to the regional trend of the respective structures. The structures and granite phenomena of K-A in Uganda present features for which there is no close analogies in any described region elsewhere. Most notable are the widespread occurrence of two or more directions of folding with steep axial planes, the development of dome-like basement structures, often with associated later granite, and the progressive metamorphism of the sedimentary systems, increasing in general towards the basal portions of the successions, with proximity to the granite intrusions and towards the interior parts of their areas of development and often showing a dependence on regional migmatization It can be conclusively deduced that two major types of metamorphism occurred in area A which are contact metamorphism and regional metamorphism. The metamorphism of this area is generally of low grade with rocks varying from shales, slates, phyllitic shales and phyllites. Rocks of higher grade of metamorphism such as muscovite and biotite schist are found outside area A and were observed during the geo-traverse around the whole region. Relict structures such as relict beds are observed and also elongation of quartz grains and undulose extinction in thin sections provide evidence of metamorphism in these rocks. Mineral resources associated with the Karagwe-Ankolean System include cassiterite, wolframite, nickel, copper, gold, silver, niobium-tantalum, magnetite, talc, ochre, mica, uranium, thorium, beryllium, lithium, bastnaesite, semi-precious stone, cobalt, platinum, chromium, titanium,
63 | P a g e vanadium and iron. Some of the minerals occurring in the same system in neighbouring countries have not been located in Uganda. Cassiterite is being mined for tin near Kikagati. The major economic activity carried out in this area is agriculture through growing of majorly bananas and maize and also rearing of animals such as cattle and goats. Mining of aggregate through quarrying is also very commonly carried out especially on the quartzites to obtain construction materials. Therefore, the dynamic and diverse nature of the structures and features present in Igayaza and the K-A system makes it ideal for purposes of learning and deeper understanding of geologic processes. In general, however, the K-A system is both less metamorphosed and less structurally complex so that over wide areas its stratigraphy can be ascertained. In carrying out all the above exercises, the aims of the mapping project were met especially equipping the students with the required mapping knowledge and further understanding of geological processes.
6.2 RECOMMENDATIONS. Further exploration work should be done in the study area so that a clear picture of the mineral potential can be got for example the tungsten exploitation potential. There is need to quantify and qualify the amounts of various mineral deposits or occurrences hence need to encourage and fund geophysicists and geochemists in doing this. This can be done through use of wild cuts. To obtain the best geologic information around an area in a particular investigation, the results highly depend on the ease of access of the area. The area transverse though relatively well distributed with motorable tracks and footpaths turn out to be impassable in case of heavy down pour hence hindering geologic surveys in the area. The topography is also very ragged with very steep slopes. This has led to conclusions being drawn on inadequate investigations by researchers. I therefore recommend the construction of tarmac roads around these areas in order to ease accessibility hence encourage more exploration. Adequate preparation and information of the relevant authorities in the areas whose resources are going to be tampered with prior to carrying out the field work to avoid inconveniences. This is also found to be parts of the field surveying preparations which must be adhered to. For the case of students learning and experience, more mapping exercises or longer periods should be availed in order to exclusively equip geologists with practical and adequately required knowledge in this area which turns out to be very important in geology.
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REFERENCES
➢ Aanyu.K. (2015): structural geology lecture notes. Unpublished. ➢ Barifaijo. E, (2002), Regional Geology of Uganda. ➢ Barnes, J.W (1961) The Mineral Resources of Uganda. Geol. Sum Uganda Bulletin No 4. ➢ Barnes, J.W. (1956). Precambrian structures and the origin of granitoid rocks in South- West Uganda. PhD thesis, University of London, UK. ➢ Cahen, L., Snelling, N.J., Delhal, J. and Vail, J.R. (1984): The Geochronology andEvolution of Africa,Clarendon Press, Oxford, 512p ➢ Combe, A.D. (1932). The Geology of South Western Ankole and adjacent territories with special reference to tin deposits. ➢ Combe, A. (1984); The Geology of SW Ankole and Adjacent Territories with Special reference to the Tin deposits. Geological Survey, Entebbe. pg236. ➢ Davis, G.H. (1984). Structural Geology of Rocks and Regions. John Wiley and Sons. pp 492-495. ➢ Dewaele, S., Goethals, H., and Thys, T. (2013). Mineralogical characterization of cassiterite concentrates from quartz vein and pegmatite mineralization of the Karagwe- Ankole and Kibara Belts, Central Africa, Geologica Belgica [En ligne], volume 16, number 1-2, pp 66-70. ➢ Dutch, S., (2009). Natural and Applied Sciences, University of Wisconsin - Green Bay. Unpublished notes. ➢ Edwards R.P., 1964, Report on the Geology and Geochemistry of sheets 25/1 and 25/11, A Canadian Technical Team report. ➢ Holmes, A., Cahen, L. (1955). African geochronology. Col. Geol. Min. Res., 5, pp 1-30. ➢ King, B.C. (1947a). The mode of emplacement of the post-Karagwe-Ankolean granite of South-West Uganda. Geol. Mag., 84, pp 140-150. ➢ King, B. C. (1959). Problems of the Precambrian of Central and Western Uganda. – Science progress 47, pp 528-542 ➢ Kerr. P.F. (1977). Optical Mineralogy. (4th Edition). McGraw-Hill, New York. Pp 442 ➢ King, B.C., de Swardt, A.M. (1967). Problems of structure and correlation in the Precambrian systems of Central and Western Uganda. Geological Survey of Uganda, Entebbe, Uganda. pp127.
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➢ MacDonald_ R. (1969) Uganda - Geology: The Atlas of Uganda, 2nd Edition. ➢ Natural Resources and Energy Division, U.N. Department of Technical Co-Operation for Development, (1982). The Development Potential of Precambrian Mineral Deposits, pp 215–230. ➢ Petters, S.W. (1991): Regional Geology of Africa. Lecture notes in Earth Sciences 40, 1- 722, Berlin. ➢ Pohl, W. (1994). Metallogeny of the North-Eastern Kibaran belt, Central Africa- Recent Perspectives. Ore geology review, 9, pp100-130.
➢ Ocakuwun, K. (1989). Study of the Structural Control, Geology and Genesis of the Tin and Pegmatite Mineralization in SW Ankole, SW Uganda. PhD Thesis. ➢ Rumvegeri, B.T. (1991): Tectonic significance of Kibaran structures in Central and Eastern Africa. Journal of African Earth Sciences. 13, 267-276.
➢ Science Progress (1933-) Volume 47, No. 187 (JULY, 1959), pp. 528-542 (15 pages) Published by Science Reviews 2000 Ltd.
➢ Sinabantu, S. (1993): Variations in petrography of Rubanda, Chitwe and Masha Kibaran granites and its genetic significance.
➢ Tack, L., Fernandez-Alonso, M., De Waele, B., Tahon, A., Dewaele, S., Baudet, D. and Cutten, H., 2006. The Northeastern Kibaran belt (NKB): a long-lived Proterozoic intraplate history. Extended Abstract of oral communication submitted to session 1 (“Geodynamics of Africa”) of the 21st Colloquium of African Geology (CAG21) at Maputo (Mozambique), 3-5 July 2006, 149-151. ➢ Temple, P.H. (1967): E.J. Wayland and the Geomorphology of Uganda. Uganda Journal, 31, 13-31, Kampala.
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APPENDIX 1 Table 6: Attitudes of joint planes in area A as obtained using stereonet software.
Dip No. Strike Dip Quadrant Longitude Latitude Elevation Units Day Month Year 1 274 85 N 252000 9915515 1360 m 21 5 2018 2 272 87 N 252000 9915515 1360 m 21 5 2018 3 280 77 N 252000 9915515 1360 m 21 5 2018 4 154 73 W 252000 9915515 1360 m 21 5 2018 5 168 62 W 252000 9915515 1360 m 21 5 2018 6 64 64 S 252000 9915515 1360 m 21 5 2018 8 206 74 W 252012 9915523 1369 m 21 5 2018 9 185 72 W 252012 9915523 1369 m 21 5 2018 10 194 72 W 252012 9915523 1369 m 21 5 2018 11 316 83 E 252012 9915523 1369 m 21 5 2018 12 94 74 S 252012 9915523 1369 m 21 5 2018 13 125 74 S 252012 9915523 1369 m 21 5 2018 14 276 87 N 252012 9915523 1369 m 21 5 2018 16 188 70 W 252865 991610 1493 m 21 5 2018 17 110 68 S 252865 991610 1493 m 21 5 2018 18 194 80 W 252865 991610 1493 m 21 5 2018 19 102 30 S 252865 991610 1493 m 21 5 2018 20 104 26 S 252865 991610 1493 m 21 5 2018 21 165 84 W 252040 9915604 1375 m 22 5 2018 22 160 70 W 252040 9915604 1375 m 22 5 2018 23 172 78 W 252040 9915604 1375 m 22 5 2018 24 170 74 W 252040 9915604 1375 m 22 5 2018 25 248 66 N 252040 9915604 1375 m 22 5 2018 26 132 80 S 252040 9915604 1375 m 22 5 2018 27 80 85 S 252167 9915602 1408 m 22 5 2018 28 88 50 S 252167 9915602 1408 m 22 5 2018 29 278 50 N 252167 9915602 1408 m 22 5 2018 30 136 70 W 252167 9915602 1408 m 22 5 2018 31 310 85 N 253144 9916921 1502 m 22 5 2018 32 300 85 N 253144 9916921 1502 m 22 5 2018 33 322 82 E 253144 9916921 1502 m 22 5 2018 34 28 84 E 253144 9916921 1502 m 22 5 2018 35 250 72 N 253322 9915705 1493 m 23 5 2018 36 250 74 N 253322 9915705 1493 m 23 5 2018 37 58 64 S 253167 9915666 1489 m 23 5 2018 38 66 68 S 253167 9915666 1489 m 23 5 2018 39 82 54 S 253167 9915666 1489 m 23 5 2018
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40 238 76 N 253167 9915666 1489 m 23 5 2018 41 258 52 N 252770 9915220 1438 m 24 5 2018 42 48 20 S 252770 9915220 1438 m 24 5 2018 43 174 50 W 252770 9915220 1438 m 24 5 2018 44 176 54 W 252770 9915220 1438 m 24 5 2018 45 306 25 N 252770 9915220 1438 m 24 5 2018 46 52 52 S 252666 9915089 1442 m 24 5 2018 47 144 88 W 252666 9915089 1442 m 24 5 2018 48 160 86 W 252666 9915089 1442 m 24 5 2018 49 122 84 S 252666 9915089 1442 m 24 5 2018 50 188 86 W 253286 9915000 1515 m 25 5 2018 51 202 78 W 253286 9915000 1515 m 25 5 2018 52 190 68 W 253286 9915000 1515 m 25 5 2018 53 94 60 S 253286 9915000 1515 m 25 5 2018 54 70 48 S 253286 9915000 1515 m 25 5 2018 55 96 82 S 253286 9915000 1515 m 25 5 2018 56 294 84 N 253286 9915000 1515 m 25 5 2018 57 199 87 W 253286 9915000 1515 m 25 5 2018 58 312 88 N 253286 9915000 1515 m 25 5 2018 59 74 64 S 253286 9915000 1515 m 25 5 2018 60 258 30 N 253469 9915055 1541 m 25 5 2018 61 230 28 N 253469 9915055 1541 m 25 5 2018 62 198 42 W 253469 9915055 1541 m 25 5 2018 63 176 88 W 253469 9915055 1541 m 25 5 2018 64 274 44 N 253469 9915055 1541 m 25 5 2018 65 174 34 W 253469 9915055 1541 m 25 5 2018 68 258 30 N 253469 9915055 1541 m 25 5 2018 69 230 28 N 253469 9915055 1541 m 25 5 2018 70 198 42 W 253469 9915055 1541 m 25 5 2018 71 176 88 W 253469 9915055 1541 m 25 5 2018 72 274 44 N 253469 9915055 1541 m 25 5 2018 73 174 34 W 253469 9915055 1541 m 25 5 2018 76 22 74 E 253682 9915178 1541 m 25 5 2018 77 4 66 E 253682 9915178 1541 m 25 5 2018 78 34 62 E 253682 9915178 1541 m 25 5 2018 79 148 80 W 253682 9915178 1541 m 25 5 2018 80 66 40 S 253682 9915178 1541 m 25 5 2018 81 28 88 E 253682 9915178 1541 m 25 5 2018 82 192 50 W 253682 9915178 1541 m 25 5 2018 84 120 84 S 253853 9915202 1539 m 25 5 2018 85 350 60 E 253853 9915202 1539 m 25 5 2018
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86 172 68 W 253853 9915202 1539 m 25 5 2018 87 104 86 S 253853 9915202 1539 m 25 5 2018 88 30 45 E 253853 9915202 1539 m 25 5 2018 89 300 80 N 253853 9915202 1539 m 25 5 2018 90 122 82 S 253853 9915202 1539 m 25 5 2018 91 68 60 S 253853 9915202 1539 m 25 5 2018 92 70 56 S 253853 9915202 1539 m 25 5 2018 93 0 50 E 252300 9915795 1420 m 25 5 2018 94 152 84 W 252300 9915795 1420 m 25 5 2018 95 204 7 W 252626 9916020 1444 m 25 5 2018 96 244 20 N 252626 9916020 1444 m 25 5 2018 97 200 28 W 252626 9916020 1444 m 25 5 2018 98 222 30 W 252626 9916020 1444 m 25 5 2018 99 240 60 N 253144 9916212 1470 m 25 5 2018 100 145 52 W 253144 9916212 1470 m 25 5 2018 101 224 82 W 253144 9916212 1470 m 25 5 2018 102 198 86 W 253144 9916212 1470 m 25 5 2018 103 182 88 W 253144 9916212 1470 m 25 5 2018 104 218 64 W 253144 9916212 1470 m 25 5 2018 105 216 70 W 253144 9916212 1470 m 25 5 2018 106 260 78 N 253144 9916212 1470 m 25 5 2018 107 26 48 E 253144 9916212 1470 m 25 5 2018 108 26 50 E 252530 9916370 1350 m 25 5 2018 109 260 56 N 252530 9916370 1350 m 25 5 2018 110 148 260 W 252824 9916420 1369 m 25 5 2018 111 50 46 S 252824 9916420 1369 m 25 5 2018 112 210 78 W 252824 9916420 1369 m 25 5 2018 113 308 58 N 252824 9916420 1369 m 25 5 2018 114 318 70 E 252824 9916420 1369 m 25 5 2018 115 310 72 N 252824 9916420 1369 m 25 5 2018 116 154 84 W 252752 9916439 1379 m 26 5 2018 117 202 86 W 252752 9916439 1379 m 26 5 2018 118 114 68 S 252752 9916439 1379 m 26 5 2018 119 192 86 W 252752 9916439 1379 m 26 5 2018 120 168 88 W 252752 9916439 1379 m 26 5 2018 121 297 64 N 252752 9916439 1379 m 26 5 2018 122 322 74 E 253022 9916530 1371 m 26 5 2018 123 294 76 N 253022 9916530 1371 m 26 5 2018 124 322 75 E 253022 9916530 1371 m 26 5 2018 125 237 74 N 253022 9916530 1371 m 26 5 2018 126 342 75 E 253022 9916530 1371 m 26 5 2018
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127 42 30 E 253106 9916600 1359 m 27 5 218 128 56 48 S 253106 9916600 1359 m 27 5 218 129 44 48 E 253106 9916600 1359 m 27 5 218 130 42 30 E 253106 9916600 1359 m 27 5 218 131 44 70 E 253360 9916669 1372 m 27 5 2018 132 6 48 E 253360 9916669 1372 m 27 5 2018 133 72 14 S 253360 9916669 1372 m 27 5 2018 134 54 30 S 253360 9916669 1372 m 27 5 2018 135 28 36 E 253360 9916669 1372 m 27 5 2018 136 128 57 S 252994 9916290 1434 m 27 5 2018 137 24 47 E 252994 9916290 1434 m 27 5 2018 138 18 62 E 252994 9916290 1434 m 27 5 2018 139 21 56 E 252994 9916290 1434 m 27 5 2018 140 38 45 E 253811 9916472 1511 m 27 5 2018 141 338 86 E 253811 9916472 1511 m 27 5 2018 142 318 52 E 253811 9916472 1511 m 27 5 2018 143 24 0 E 253811 9916472 1511 m 27 5 2018 144 284 68 N 253811 9916472 1511 m 27 5 2018 145 346 74 E 253811 9916472 1511 m 27 5 2018 146 309 83 N 253811 9916472 1511 m 27 5 2018 147 30 62 E 253811 9916472 1511 m 27 5 2018 148 310 88 N 253811 9916472 1511 m 27 5 2018 149 304 59 N 253811 9916472 1511 m 27 5 2018 150 290 78 N 253811 9916472 1511 m 27 5 2018 151 288 88 N 253811 9916472 1511 m 27 5 2018 152 130 70 S 253425 9916237 1495 m 27 5 2018 153 194 78 W 253425 9916237 1495 m 27 5 2018 154 188 68 W 253425 9916237 1495 m 27 5 2018 155 10 80 E 253425 9916237 1495 m 27 5 2018 156 42 62 E 253425 9916237 1495 m 27 5 2018 157 183 74 W 253425 9916237 1495 m 27 5 2018 158 170 75 W 253425 9916237 1495 m 27 5 2018 159 185 72 W 253425 9916237 1495 m 27 5 2018 160 130 72 S 253425 9916237 1495 m 27 5 2018 161 115 82 S 253425 9916237 1495 m 27 5 2018 162 52 80 S 253986 9915279 1535 m 27 5 2018 163 68 86 S 253986 9915279 1535 m 27 5 2018 164 76 84 S 253986 9915279 1535 m 27 5 2018 165 34 62 E 253986 9915279 1535 m 27 5 2018 166 42 54 E 253986 9915279 1535 m 27 5 2018 167 48 68 S 253986 9915279 1535 m 27 5 2018
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168 36 72 E 253986 9915279 1535 m 27 5 2018 169 110 84 S 253986 9915279 1535 m 27 5 2018 170 312 88 N 253930 9915286 1545 m 27 5 2018 171 308 88 N 253930 9915286 1545 m 27 5 2018 172 52 82 S 253930 9915286 1545 m 27 5 2018 173 129 85 S 253930 9915286 1545 m 27 5 2018 174 106 66 S 253930 9915286 1545 m 27 5 2018 175 41 87 E 253930 9915286 1545 m 27 5 2018 176 124 86 S 253930 9915286 1545 m 27 5 2018 177 44 88 E 253930 9915286 1545 m 27 5 2018 178 126 82 S 253930 9915286 1545 m 27 5 2018 179 127 84 S 253930 9915286 1545 m 27 5 2018 180 214 89 W 253930 9915286 1545 m 27 5 2018 181 292 89 N 253930 9915286 1545 m 27 5 2018 182 127 74 S 253930 9915286 1545 m 27 5 2018 183 124 84 S 253930 9915286 1545 m 27 5 2018 184 124 86 S 253930 9915286 1545 m 27 5 2018 185 130 80 S 253930 9915286 1545 m 27 5 2018 186 130 84 S 253930 9915286 1545 m 27 5 2018 187 65 72 S 253930 9915286 1545 m 27 5 2018 188 309 88 N 253930 9915286 1545 m 27 5 2018 189 127 88 S 253930 9915286 1545 m 27 5 2018 190 307 85 N 253930 9915286 1545 m 27 5 2018
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Table 7: Attitudes of bedding planes in area A as formatted using Stereonet software
Dip No. Strike Dip Quadrant Longitude Latitude Elevation Day Month Year 1 290 30 N 252097 9915024 1395 23 5 2018 2 302 40 N 252097 9915024 1395 23 5 2018 4 268 40 N 252770 9915220 1438 24 5 2018 5 266 50 N 252770 9915220 1438 24 5 2018 6 268 58 N 252770 9915220 1438 24 5 2018 7 52 54 S 252700 9915440 1442 24 5 2018 8 48 45 S 252700 9915440 1442 24 5 2018 9 46 10 S 252700 9915440 1442 24 5 2018 10 204 32 W 252626 9916020 1444 25 5 2018 11 284 82 N 252626 9916020 1444 25 5 2018 12 10 72 E 252626 9916020 1444 25 5 2018 13 38 68 E 252626 9916020 1444 25 5 2018 15 42 50 E 252824 9916420 1369 25 5 2018 16 40 30 E 252824 9916420 1369 25 5 2018 17 44 52 E 252824 9916420 1369 25 5 2018 18 54 68 S 252824 9916420 1369 25 5 2018 19 46 62 S 252824 9916420 1369 25 5 2018 20 63 32 S 252752 9916439 1379 26 5 2018 21 64 42 S 252752 9916439 1379 26 5 2018 22 50 46 S 252752 9916439 1379 26 5 2018 23 66 44 S 252752 9916439 1379 26 5 2018 24 54 50 S 252752 9916439 1379 26 5 2018 25 58 60 S 253022 9916530 1371 26 5 2018 26 38 34 E 253022 9916530 1371 26 5 2018 27 22 58 E 253022 9916530 1371 26 5 2018 28 20 64 E 253022 9916530 1371 26 5 2018 29 50 64 S 253022 9916530 1371 26 5 2018 30 132 86 S 253106 9916600 1359 27 5 218 31 295 70 N 253106 9916600 1359 27 5 218 32 308 80 N 253106 9916600 1359 27 5 218 33 302 88 N 253106 9916600 1359 27 5 218 34 38 38 E 253106 9916600 1359 27 5 218 35 40 41 E 253106 9916600 1359 27 5 218 36 126 88 S 253360 9916669 1372 27 5 2018 37 56 78 S 253360 9916669 1372 27 5 2018 38 46 50 S 253360 9916669 1372 27 5 2018 39 48 75 S 252994 9916290 1434 27 5 2018 40 47 53 S 252994 9916290 1434 27 5 2018
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APPENDIX 2 Table 8
MICROSCOPIC OBSERVATION FOR SECTION A23푺ퟏ
PROPERTIES MINERALS OBSERVED ANALYSED A B C
Color Colorless Colorless Colorless
Percentage composition 20 40 40
Form (Habit) Anhedral Euhedral Euhedral
Relief Low/weak Strong Low/weak
Cracks Absent Absent Absent Alteration Absent Absent Absent
Inclusion Absent Absent Present
Cleavage Imperfect Imperfect Imperfect Anisotropy/ Isotropy Anisotropic Anisotropic Anisotropic
Twinning Absent Absent Absent
Inference colors 1st order grey 2nd order blue 1st order grey 1st order white
Birefringence Weak Strong Weak
Interference figure Uniaxial positive Biaxial negative Biaxial negative Extinction angle Absent Absent Absent
Zoning Present Absent
Pleochroism Absent Absent Absent Mineral proposed name quartz chlorite muscovite
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Table 9
MICROSCOPIC OBSERVATION FOR SECTION A19푺ퟏ PROPERTIES MINERALS OBSERVED ANALYSED A B C
Color Colorless Colorless Colorless Percentage composition 70 20 10
Form (Habit) Euhedral Euhedral Anhedral
Relief Low Strong Strong Cracks Absent Absent Absent
Alteration Absent Absent Absent
Inclusion Present Absent Absent Cleavage Absent Absent Basal
Anisotropy/ Isotropy Anisotropic Anisotropic Anisotropic
Twinning Absent Absent Absent Inference colors 1st order grey 2nd order blue Pale green
Birefringence Weak Strong Strong
Interference figure Uniaxial positive Biaxial negative Biaxial negative Extinction angle Present Absent Absent
Zoning absent absent absent
Pleochroism Absent Absent Present Mineral proposed name Quartz Chlorite Muscovite
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Table 10 MICROSCOPIC OBSERVATION FOR SECTION A33푫 PROPERTIES MINERALS OBSERVED ANALYSED A B C
Color Colorless Colorless Colorless Percentage composition 60 30 10
Form (Habit) Anhedral Euhedral Euhedral
Relief Low/weak Strong Low/weak Cracks Absent Absent Absent
Alteration Absent Absent Absent
Inclusion Absent Absent Absent Cleavage Imperfect Imperfect imperfect
Anisotropy/ Isotropy Anisotropic Anisotropic Anisotropic
Twinning Absent Absent Absent Inference colors 1st order grey 2nd order blue 1st order grey
Birefringence Weak Strong Weak
Interference figure Not determined Not determined Not measured Extinction angle Absent Absent Absent
Zoning Absent Absent Present
Pleochroism Absent Absent Absent Mineral proposed name phyllite Chlorite Quartz
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Table 11
MICROSCOPIC OBSERVATION FOR SECTION A1푺ퟏ PROPERTIES MINERALS OBSERVED ANALYSED A B C
Color Colorless Colorless Colorless Percentage composition 80 15 5
Form (Habit) Euhedral Euhedral Anhedral
Relief Low Strong Strong Cracks Absent Absent Absent
Alteration Absent Absent Absent
Inclusion Absent Absent Absent Cleavage Absent Imperfect Basal
Anisotropy/ Isotropy Anisotropy Anisotropic Anisotropic
Twinning Absent Absent Absent Inference colors 1st order grey 2nd order blue Pale green
Birefringence Weak Strong Strong
Interference figure Uniaxial positive Uniaxial negative Biaxial negative Extinction angle Absent Absent Absent
Zoning absent absent absent
Pleochroism Absent Absent Present Mineral proposed name Quartz Ilmenite Muscovite
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Table 12
MICROSCOPIC OBSERVATION FOR SECTION A4푺ퟏ PROPERTIES MINERALS OBSERVED ANALYSED
A B C
Color Brown Colorless Colorless
Percentage composition 10 60 30
Form (Habit) Euhedral Sub-hedral Euhedral
Relief Strong Low Low
Cracks Absent Absent Absent
Alteration Present Present Absent
Inclusion Absent Absent Absent
Cleavage Imperfect Imperfect Imperfect
Anisotropy/ Isotropy Anisotropic Anisotropic Anisotropic
Twinning Absent Absent Absent
Inference colors 2nd order yellow 1st order black-grey 1st order white 2nd order orange 4th order grey 1st order black Birefringence Moderate Weak Weak
Interference figure Uniaxial negative Uniaxial positive Uniaxial negative
Extinction angle Absent Absent Absent
Zoning absent absent absent
Pleochroism Absent Absent Absent
Mineral proposed name Hematite Quartz Clay minerals (Kaolinite)
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APPENDIX 3
Map 6: Location of the area A on the topographic map of Igayaza (highlighted in yellow)
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Map 7: Map of area A showing lithologic units.
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