MAPPING PETROLOGICAL PATTERNS IN THE REFOUGE GRANITE BY INTEGRATING GEOCHEMICAL, VNIR-SWIR AND GAMMA- RAY SPECTROMETRY DATA Data Gabriel February, 2007 MAPPING PETROLOGICAL PATTERNS IN THE REGOUFE GRANITE BY INTEGRATING GEOCHEMICAL, VNIR-SWIR AND GAMMA-RAY SPECTROMETRY DATA by Data Gabriel Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation, Specialisation: (Earth Resource Exploration) Thesis Assessment Board Prof. Dr. F. D. van der Meer Prof. Dr. S. B. Kroonenberg Dr. E. M. Schetselaar Dr. S. P. Vriend Dr. M. van der Meijde Drs J. B de Smeth INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Abstract The VNIR-SWIR and gamma-ray spectroscopic techniques are cost effective mapping tools as compared to the conventional methods in geological mapping and mineral exploration. The techniques were applied to map petrological and geochemical patterns on the Regoufe granite. The Regoufe granite is a specialized Sn-W granite in the North of Portugal belonging to the Hercynian massifs. Petrological units in the Regoufe granite are porphyritic two-mica granite grading through a transition zone into the muscovite-albite granite. Hydrothermal alteration recognized in the granite include albitization, muscovitization and apatitization. The objective of this study is to establish the relationship between VNIR-SWIR and gamma-ray spectral signatures and petrological/geochemical patterns and determine their significance with respect to Sn-W exploration. Laboratory reflectance spectra of rock samples taken from the Regoufe granite were determined and analyzed to obtain mineralogical information and derive spectral patterns on the granite. ASTER satellite image data of Regoufe was processed and analyzed by band ratioing and Spectral Angle Mapper to extract spectral signatures related to geology. A ground gamma-ray survey was conducted on the Regoufe granite to acquire radioelement concentrations of K, Th and U so as to map gamma-ray signatures related to petrology and hydrothermal alteration. The data obtained were integrated and compared with petrological and geochemical data using GIS software and spatial and multivariate relationships were evaluated. The laboratory reflectance studies showed significant variations in the absorption wavelength position and depth in muscovite and showed some correlation with the petrological zonation and geochemical data. Although the Regoufe granite can clearly be distinguished from its hosting metasediments, the ASTER data poorly correlates with petrological and geochemical zonations within the granite itself. This is mainly a result of poor spatial resolution and influence of vegetation and soil cover that modify spectral features and lack of minerals diagnostic for differentiating muscovite-albite granite from porphyritic two-mica granite. The position of the muscovite absorption feature, however, may be related to its composition and potentially can be used to differentiate Fe-Mg rich muscovite that is an alteration product of biotite from primary muscovite that crystallized from evolved magmatic differentiates. Gamma-ray data significantly correlates with the petrological and geochemical data: the Th/K ratio clearly discriminates between the petrological zonation in the Regoufe granite while the U/Th ratio is associated with hydrothermal alteration. VNIR-SWIR spectral methods require ground knowledge to interpret the signatures correctly while the gamma-ray survey methods provide good and effective means of mapping patterns on the granite related to petrology, hydrothermal alteration and mineralization. Key words: Hercynian granite, wavelength, absorption, radioelement concentrations, hydrothermal alteration, correlation and minerals. i Acknowledgements I acknowledge the staff members of AES programme in ITC for giving me the skills in earth science exploration and research. Special acknowledgments go to my supervisor’s Dr. E. Schetselaar, Drs. B. de Smeth., and drs. F van Ruitenbeek for their guidance towards the data acquisition and writing of my MSc. Research Thesis, thanks for their critical comments. I salute Dr. S. Barritt who critically reviewed my interpretations of gamma-ray data. Dr. M. van Meijde is recognized for guiding me on gamma-ray spectrometry. I must extend special thanks to Dr Boudenwijn de Smeth who accompanied and supervised me during the field work and experienced the field hazards of my time; I will leave to remember my time with you on the specialized granite of Regoufe, God bless you. Special tribute is paid to Dr. Vriend S. of Utrecht University, Department of Geochemistry who provided the basic the research materials, geochemical data and organised preparation of thin sections. I will not forget my sponsor, the Ministry of Energy and Mineral Development of Uganda for giving me this opportunity to study further for Masters of Science degree in ITC. Enschede, the Netherlands. ii Table of contents 1. Introduction .....................................................................................................................................9 1.1. Background.............................................................................................................................9 1.2. Research problem .................................................................................................................10 1.3. Motivation.............................................................................................................................11 1.4. Research objectives ..............................................................................................................11 1.4.1. Specific objectives .......................................................................................................11 1.4.2. Research questions.......................................................................................................11 1.4.3. Hypothesis....................................................................................................................12 1.5. Research methods .................................................................................................................12 2. Literature review ............................................................................................................................14 3. Geology and Geochemistry of the Regoufe area............................................................................18 3.1. Regional geology ..................................................................................................................18 3.2. Local geology........................................................................................................................20 3.3. Petrography of Regoufe granite............................................................................................22 3.4. Geochemical characteristics of the Regoufe granite ............................................................25 3.4.1. P, CaO, Sr, Na2O and K2O group.................................................................................26 3.4.2. SiO2, the alkali and alkaline earth elements.................................................................26 3.4.3. Ore related elements.....................................................................................................26 3.5. Weathering of Regoufe granite.............................................................................................27 3.6. Mineralization events in Regoufe granite.............................................................................27 4. Petrological and geochemical patterns...........................................................................................28 4.1. Petrological pattern...............................................................................................................28 4.1.1. Method .........................................................................................................................28 4.1.2. Results..........................................................................................................................28 4.2. Geochemical signatures and trends ......................................................................................32 4.2.1. Method .........................................................................................................................32 4.2.2. Results..........................................................................................................................32 5. VNIR-SWIR reflectance spectroscopy ..........................................................................................40 5.1. Laboratory reflectance spectroscopy....................................................................................40 5.1.1. Method .........................................................................................................................40 5.1.2. Results..........................................................................................................................41