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Nature of Occurrence and Economic Potential of Granitic Pegmatites of Mzimba District in Northern Malawi

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Nature of Occurrence and Economic Potential of Granitic Pegmatites of Mzimba District in Northern Malawi NATURE OF OCCURRENCE AND ECONOMIC POTENTIAL OF GRANITIC PEGMATITES OF MZIMBA DISTRICT IN NORTHERN MALAWI By Jalf William Joseph Salima SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE (GEOLOGY) In the Department of Geology Facaulty of Science and Agriculture University of Fort Hare 2014 DECLARATION I declare that this dissertation is a result of my own research work and no part of it has previously been submitted at any other academic institution for the awarding of a degree. Proper acknowledgement has been given wherever work from other authors has been used. Jalf William Joseph Salima Signature…………………… Date………………………… University of Fort Hare Department of Geology Alice 5700 Eastern Cape Republic of South Africa. i DEDICATIONS To my dear wife and children, your love, patience and encouragement deserve my special recognition. To the memory of my late father Mr Joseph Grasciano Salima. Am still treading on the path of knowledge you showed me. ii ABSTRACT A swarm of granitic pegmatites occurs in Mzimba district from northern Kasungu to Kafukure near the western international border with Zambia. The granitic pegmatites are hosted by a mobile belt, within the Mozambiquan orogenic belt (c. 900 - 1800 Ma). They have been dated as 485 Ma. They intruded metasediments of high to medium grade metamorphic rocks of a Precambrian Basement Complex. The dominant trend of the pegmatites is NW - SE, exhibiting a cross-cutting relationship with the country rocks and their contacts with the latter are usually sharp. The six pegmatites investigated in this study are inhomogeneous, composed of a massive quartz core, an intermediate zone composed of a blocky pink K-feldspar rich sub-zone and muscovite rich sub-zone and a wall zone composed of quartz - pink K-feldspar - muscovite mineral assemblage. The Mzimba pegmatites are classified as lithium-caesium-tantalum (LCT) family of rare element granitic pegmatites as described by Černý and Ercit (2005). They belong to the beryl-columbite subtype and beryl-columbite-phosphate subtype of the rare element pegmatites. It is suggested that the pegmatites are the product of magmatic differentiation and that they form roofs of granite plutons lying deep below the current level of erosion. The six pegmatites were sampled and minerals analysed using standard analytical methods such as petrographic microscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. Mineralogy of the granitic pegmatites indicates that they are predominantly composed of perthitic K-feldspar (perthite), Na-plagioclase (albite), quartz and muscovite as main mineral phases and accessory minerals including beryl, tantalite-columbite (ferrotantalite), iron-titanium oxides (ilmeno-rutile and ilmenite), tourmaline (schorl), garnet iii (almandine-spessartine) and triplite. Triplite is a very rare mineral found in a few pegmatites around the world, and this is the first reported account of this mineral in the Mzimba pegmatites and probably in Malawi. These minerals are being exploited by artisanal and small scale miners. Trace elements in K-feldspar and muscovite are significant indicators for the evaluation of economic potential of pegmatites as well as for the differentiation degree and origin of the magma. The K/Rb ratio for K-feldspars ranges between 12.72 and 109.38, while for muscovites it is between 16.66 and 82.36 indicating that the pegmatites are moderately evolved. The Ta versus Cs and the Ta versus K/Cs discrimination diagram indicates that all the investigated pegmatites plot above the 20 ppm threshold suggesting that the pegmatites have potential for Ta and Nb mineralization. iv ACKNOWLEDGEMENT This dissertation is a product of two years of hard work. I would like to give honour and praise to my Lord and saviour Jesus Christ for being by my side at all times. I would like to express my heartfelt gratitude to my supervisor, Mr C.J. Gunter, for his tireless guidance and encouragement throughout the period of this work. I am very grateful to the Government of Malawi for offering me a scholarship to pursue the Masters Degree under the Malawi Government Scholarship Development Funding Programme (MGSDF). Also, grateful to the director and members of staff of the Department of Public Service Management and Development, for all the financial and logistical support given over the period of my studies. My special thanks go to the director of the Geological Survey Department, Dr Leonard S.N. Kalindekafe, for granting me a study leave and for all the material, technical and financial support towards my studies. I am also grateful to a number of people who rendered a hand in the research work. Worthy of special mention are Mr Huxton Phiri, prospector, Mr Paul Kipandura, driver, Mr S. Kaluphya, senior laboratory technician as well as Mr Gama and Mr Chikomeni of the Mzimba Gemstone Miners Cooperative for their time and assistance during field investigations. Am also grateful to the following mine owners for allowing me to visit their mines; Mr Gama, Mr Mshashi, Mr Thole, Mr Mahowe, Mrs M. Banda, Mr C. Moyo, Mr Phiri. Am also grateful to Maria Atanasova, Jack Mxongwana, M. Crowley, H. Cloete and Nondumiso Dhlamini of Council for Geoscience for their wonderful work in the production of thin sections, XRD and XRF sample analyses for the project. To the staff of the Geology Department and my friends at the University of Fort Hare, of whom there are too many to mention, I salute you for your material and moral support during my studies. v TABLE OF CONTENTS DECLARATION....................................................................................................................... i DEDICATIONS ....................................................................................................................... ii ABSTRACT ............................................................................................................................ iii ACKNOWLEDGEMENT ....................................................................................................... v LIST OF FIGURES ................................................................................................................ xi LIST OF TABLES ................................................................................................................ xiv LIST OF PLATES ................................................................................................................. xv ACRONYMS AND ABBREVIATIONS ............................................................................ xvii CHAPTER 1: INTRODUCTION ........................................................................................... 1 1.1.Background information .................................................................................................. 1 1.1.1. Granitic pegmatites as potential mining targets ....................................................... 1 1.2. Research problem............................................................................................................ 3 1.3. Rationale of the study ..................................................................................................... 3 1.4. Specific objectives of the research .................................................................................. 4 1.4. Delineations and limitations ........................................................................................... 4 1.5. Significance of the study ................................................................................................. 5 1.6. Structure of the dissertation ............................................................................................ 5 1.7. Location of the study area ............................................................................................... 5 1.8. General Geology ............................................................................................................. 6 1.8.1. Geological Setting of Malawi .................................................................................. 6 1.8.2. Lithology and Stratigraphy .................................................................................... 10 vi 1.8.3. Regional Geology of Mzimba District ................................................................... 12 1.8.4. Structure and Metamophism .................................................................................. 14 1.8.5. Geological setting of the granitic pegmatites of the Mzimba District ................... 15 1.9. Exploration history of the Mzimba granitic pegmatites ............................................... 16 CHAPTER2: LITERATURE REVIEW ............................................................................ 19 2.1. Introduction ................................................................................................................... 19 2.2. Classification of granitic pegmatites ............................................................................. 20 2.3. Genesis of granitic pegmatites ...................................................................................... 21 2.3.1. Granitic pegmatites formed by fractional crystallisation ....................................... 21 2.3.2. Granitic pegmatites formed by anatexis ................................................................ 24 2.4. Textures and internal consolidation of granitic pegmatites .......................................... 25 2.5. Geological and tectonic settings of granitic pegmatites ..............................................
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