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A Case Study from Lake Victoria Gold Fields, Tanzania

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A Case Study from Lake Victoria Gold Fields, Tanzania A NEW APPROACH FOR DETECTING HYDROTHERMAL ALTERATIONS USING REMOTE SENSING DATA: A CASE STUDY FROM LAKE VICTORIA GOLD FIELDS, TANZANIA Thesis submitted for fulfillment of a Doctoral Degree in Natural Sciences (Dr. rer. nat.) to Faculty of Natural Sciences (III) Martin-Luther-University Halle-Wittenberg by Elisante Elisaimon Mshiu Born on 25.09.1978 in Hai, Kilimanjaro, Tanzania Reviewers: Prof. Dr. Gregor Borg (Martin-Luther-University Halle-Wittenberg) Prof. Dr. Cornelia Gläßer (Martin-Luther-University Halle-Wittenberg) Prof. Dr. Hartwig Frimmel (Julius-Maximilians-Universität Würzburg) Halle (Saale), 14.07.2014 ACKNOWLEDGEMENTS I am grateful for the support from the Deutscher Akademischer Austausch Dienst (DAAD) and the Ministry of Education and Vocation Training (MoEVT) of the Government of Tanzania for paying my living costs in Germany during my study. Also, my deepest appreciation goes to the University of Dar es Salaam for a research fund used to purchase remote sensing ASTER data, for fieldwork costs, and geochemical analyses. My sincere gratitude also goes to Martin Luther University Halle-Wittenberg, to both Departments of Economic Geology and Petrology and Remote Sensing and Cartography for providing laboratory facilities and office space during the project. I would like to extend my special thanks to my supervisors, Prof. Dr. Gregor Borg and Prof. Dr. Cornelia Gläßer for their support and constructive scientific contributions that have enabled me to reach the objectives of this project. I have learned a lot of things from them, which for sure have contributed to the quality of this work. I acknowledge the support of Prof. Dr. Dr. Herbert Pöllmann from the Department of Mineralogy and Geochemistry for XRD analyses and his contribution during discussions with him. My sincere gratitude also goes to other members of staff from Department of Economic Geology and Petrology, and Department of Remote Sensing and Cartography, both in the Institute of Geosciences and Geography. Specifically, my appreciations to Dr. Thomas Degen, Andreas Kamradt, Dr. Manuela Frotzscher, Danilo Wolf and Sabine Walther in the Economic Geology and Petrology Department, and Dr. Christian Götze and Dr. Markus Möller, in the Department of Remote Sensing and Cartography, for their valuable support at different stages of the project. Thanks goes to M.Sc students Astrid Kauert, Kai Wellnowski, Sebastian Heitzer and Antje Migalk, for their help during laboratory work and analyses. I am also indebted to my fellow students, Christian Marien, Tim Rödel, Raik Döbelt, Sten Hüsing, Elisa Burmester, Melanie Krüger, Simon Sachwitz, Helen Kolai, Michael Denk, Daniel Schwefel, Florian Beyer, and Henning Gerstmann, in both the Department of Economic Geology and Petrology and the Department of Remote Sensing and Cartography. We have been together during my study in both research and social aspects. Last but not least, I extend my special thanks to my family for their support, courage and patience during the whole period when I was away from home. ii ABSTRACT Remote sensing hydrothermal alteration mapping has been employed in mineral exploration for decades. Both multispectral and hyperspectral data have been the most used remote sensing data, this is because of their ability in identifying spectrally the individual hydrothermal alteration minerals. Depending on spectral resolution of these data sets, it has been possible to map specific mineral alterations, which are related to base or precious metal mineralization. Different approaches have been applied for the mapping of the hydrothermal alterations, for example, the extraction of the key alteration minerals from the alteration assemblage, band rationing, composite images, and various statistical methods are some of these techniques. However, there has been a challenge in the quality of the results obtained. For example, it is still difficult to differentiate the hydrothermal minerals and minerals of non-hydrothermal origin such as minerals from weathering and metamorphic processes. The best example is the problem to differentiate hydrothermal chloritization from the chloritic metamorphosed basalts. This ambiguity normally leads to misinterpretations of the mapped alterations and can create challenges or problem for the identification of exploration targets. This study presents an approach for hydrothermal alteration mapping by satellite remote sensing data. The method has shown to improve the quality of alteration mapping and also to simplify the identification of precious metal exploration targets. Geological maps and SRTM data were used as the sources of information to identify tectonic structures, since structural elements such as fractures and shear zones are known as the crustal features or conduits for mineralizing fluids. Landsat ETM+ data were used to map areas, which may have been affected by hydrothermal alterations and the statistical method “Feature Oriented Principal Component Analysis (FOPCA)” was used as the extracting tool of these altered areas. Identification of the lineaments that were potentially involved in carrying hydrothermal fluids was achieved by applying the GIS functions clumping and sieving, which led to particularly interesting results. The analysis has revealed linear alteration patches that coincide with regional and local crustal lineaments. In this study the linear alteration patches are interpreted to have acted as hydrothermal fluid conduits. The linear alteration patches are consistent with both tectonic structures and gold occurrences and locally gold deposits in the study area. ASTER data was used to map the individual alteration minerals and their systematic zoning in the study area. The mapping of alteration zones was achieved through the technique that uses more than one key mineral for each hydrothermal alteration assemblage. In addition, the supervised classification as well as the mathematical rules applied has made it possible to realize the systematic alteration zoning around mineralization zones. Results from ASTER data also have revealed the correlation between alteration zoning and gold deposits, and fit the most accepted Archaean granite-greenstone gold deposit models. Moreover, the size and shape of proximal alterations are consistent with the reported size range for hydrothermal alteration zones in orogenic gold deposits as well as the associated tectonic structures. The mapped alteration zones have shown their differences in the spectra measured by TerraSpec (VNIR-SWIR) spectroscopy instrument in samples taken from each alteration zone. Also samples from the mapped alteration zones have revealed differences in mineralogy through light microscopy thin section studies, Scanning Electron Microscopy (SEM) and X- ray Diffraction Analysis (XRD). The conducted geochemical analyses have revealed Au anomalies in the selected test sites, which also associate with the proximal alteration zones. Furthermore, Au corresponds with its most known pathfinder elements such as Ag, Sb, Hg, Tl, Bi, Mo and B. iii TABLE OF CONTENTS 1 INTRODUCTION............................................................................................................... 1 1.1 Hydrothermal System .......................................................................................................................... 1 1.2 Hydrothermal Alteration Mapping....................................................................................................... 2 1.3 Objectives of the study ........................................................................................................................ 3 1.3.1 Specific objectives ............................................................................................................................ 3 1.3.2 Significance of the Study .................................................................................................................. 3 2 METHODOLOGY .............................................................................................................. 3 2.1 Objective I ........................................................................................................................................... 4 2.2 Objective II .......................................................................................................................................... 4 2.3 Objective III ......................................................................................................................................... 4 2.4 Result Validation ................................................................................................................................. 5 3 THE GEOLOGY OF THE STUDY AREA ................................................................................ 6 3.1 The Study Area .................................................................................................................................... 6 3.1.1 Climate, Topography and Vegetation Cover ...................................................................................... 6 3.1.2 Location and Accessibility ................................................................................................................. 7 3.2 Geological Background ........................................................................................................................ 7 3.2.1 Geology of the Lake Victoria Gold Field (LVGF) .................................................................................. 7 3.2.1.1 Dodoman Supergroup
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