Karst-Associated Bauxite Deposits of Parnassos-Ghiona, Central Greece: Ore Genesis and Structural Evolution
Total Page：16
File Type：pdf, Size：1020Kb
KARST-ASSOCIATED BAUXITE DEPOSITS OF PARNASSOS-GHIONA, CENTRAL GREECE: ORE GENESIS AND STRUCTURAL EVOLUTION RICHARD JAMES WILLIAMS A thesis submitted in partial fulfilment of the requirements of the University of Brighton for the degree of Doctor of Philosophy June 2014 Karst-associated bauxite deposits of Parnassos-Ghiona, Central Greece: Ore genesis and structural evolution The karst-associated bauxites of the Parnassos-Ghiona zone in Central Greece are part of the large Mesozoic age Mediterranean Karst Bauxite belt. Greece is responsible for around 50% of European bauxite production, and has an estimated 600 million tonnes of bauxite reserves. This investigation focuses on the bauxites of Mount Iti and Mount Ghiona, two mountains in the west of the Parnassos- Ghiona zone that are currently being explored and mined by Greek bauxite producer, Elmin S.A. The aim was to develop a better geological understanding of the ore genetic history and regional structural evolution to aid ore deposit science and bauxite exploration. Within the Parnassos-Ghiona zone the bauxites were deposited as three separate ore horizons intercalated with thick limestone layers during the early Jurassic, late Jurassic and late Cretaceous. Only the upper two bauxite horizons are economic and therefore formed the focus of this investigation. Studies of the texture, mineralogy and lithogeochemistry provide information on the origin and evolution of the ore bodies over time and the temporal and spatial variations between ore bodies. It is proposed that many of the observed textures and geochemical variations are representative of a complex, dynamic and continuously evolving, self-organising system. Models are presented here to show how complex textures of bauxite can be formed through long periods of episodic transport, involving alternating periods of concretion texture development followed by mobilisation and partial destruction of the developed textures. Mineralogical analysis of the bauxites has identified a wide range of Al and Fe phases within the second and third horizons which can be linked primarily to variability in redox conditions. Particular attention was given to the sulphide mineral-bearing bauxites of Mount Iti, as these sulphides (predominantly pyrite) cause problems during ore processing. Three generations of pyrite were identified, each with distinctive textural characteristics, trace element concentrations and sulphur isotope concentrations. Sulphide formation utilised predominantly bacterially reduced sulphate in a closing system. Epigenetic meteoric fluid flow caused oxidation of pyrite in the third horizon bauxite generating acidic fluids that mobilized iron and several trace and rare earth elements creating zones of bleached bauxite. This investigation has shown that this mobilized iron was re- deposited at the base of the ore bodies and within fractures. A portion of this mobilized iron penetrated deeper into the underlying limestones, significantly enriching them in Fe, Ni, Si and Mn, and creating a distinctive red/yellow colour. This limestone alteration is detectable for up to 50 metres from the ore bodies and could be used as an exploration tool. The structural evolution of the Parnassos-Ghiona geotectonic zone has a strong control on the orientation, inclination and dislocation of ore bodies. Lineament analysis of remotely sensed LANDSAT 7-TM data helped to identify major structural trends and aided structural interpretations. Compressional deformation during the Eocene created southwest-verging folds in the Parnassos- Ghiona carbonates along the northern edge of Mount Iti, resulting in inclined, vertical and even overturned ore lenses. In the northern Mount Ghiona area, west dipping thrust faulting inclined and imbricated the ore horizons. Later extensional deformation fragmented and offset ore bodies, and provided conduits for alteration fluids. This investigation concludes by presenting an updated ore genetic model for the formation history of the bauxite deposits of the Parnassos-Ghiona zone, drawing together the results of this study and previous data and models for the region. The author is indebted to Elmin S.A. for their financial, practical and logistical support throughout this project, with particular thanks to Mr. Lyberis Polychronopoulos and Mr. Vasilis Yfantis for their support and positive cooperation. I am also grateful to the invaluable co-ordination and guidance received from Professor Stavros Kalogeropoulos throughout the design and operation of this research programme. At the University of Brighton, I am grateful to my UK supervisory team of Professor Andy Cundy, Dr. Norman Moles and Dr. Martin Smith for help, advice and support throughout the 3.5 years of this research project. My thanks to Stanislav Strekopytov and John Spratt (Natural History Museum), Adrian Boyce and Alison McDonald (SUERC), Jennifer Holter and Mike Helias (University of Brighton), Graham Souch, Matt Hunt and Adrian Watson (University of Derby) are thanked for their support with ICP- MS analysis, electron microprobe analysis, sulphur isotope analysis, SEM analysis and thin sectioning. Thanks also to my fellow PhD students at the University of Brighton, who have provided great friendship and support throughout my research. Finally, my thanks go to my Family and wonderful Fiancée, for the support and encouragement throughout this project, for adjusting to difficult situations and for helping me through difficult times. The organisation, structure and views expressed in this thesis are those of the author, and do not necessarily reflect the views or policy of the supporting organisations and individuals. Declaration I declare that the research contained in this thesis, unless otherwise formally indicated within the text, is the original work of the author. The thesis has not been previously submitted to this or any other university for a degree, and does not incorporate any material already submitted for a degree. Signed Dated Table of Contents Chapter 1 : Thesis Introduction 1 1.1 Thesis Outline 1 1.2 Bauxite 1 1.3 The Greek Bauxite Deposits 1 1.4 Research Aims and Objectives 3 1.5 Contribution to mineral deposit science and exploration strategy 4 1.6 The structure of this thesis 5 1.7 Bauxite as a global resource 5 1.8 Greek Bauxite 11 1.9 Elmin S.A. 11 References 12 Chapter 2: The Geology of the Karst-associated bauxites of the Parnassos-Ghiona zone 15 2.1 Regional Background 15 2.2 The Parnassos-Ghiona Zone 16 2.3 The Geology of the Parnassos-Ghiona Zone 16 The Geology of the Parnassos-Ghiona zone 16 Stratigraphy 18 2.4 Mediterranean Karst-associated bauxites 22 2.5 A summary of current understanding of the Parnassos-Ghiona Bauxites 22 2.6 Observations of the bauxite in the Iti and Ghiona Mountains 26 Observations from the bauxites of Iti and North Ghiona 26 Observations from the karstified footwalls of Iti and Ghiona 34 Implications for exploration and extraction 35 2.7 Conclusions 38 References 38 Chapter 3: Methodology 41 3.1 Introduction 41 3.2 Microscopy 41 3.2.1 Sampling 41 3.2.2 Equipment 41 3.2.3 Purpose of method 41 3.3 X-Ray Diffraction 42 3.3.1 Sampling 42 3.3.2 Equipment and analytical parameters 42 3.3.3 Cluster Analysis 42 3.3.4 Purpose of method 43 3.4 Portable X-Ray Fluorescence 44 3.4.1 Sampling 44 3.4.2 Equipment 45 3.4.3 Data accuracy and precision 45 3.4.4 Purpose of method 45 3.5 Inductively Coupled Plasma-Mass Spectrometry 46 3.5.1 Sampling 46 3.5.2 Equipment and analytical parameters 47 3.5.3 Data accuracy and precision 47 3.5.4 Purpose of method 47 3.6 Electron Microprobe 48 3.6.1 Sampling 48 3.6.2 Equipment and analytical parameters 48 3.6.3 Data accuracy and precision 48 3.6.4 Purpose of method 49 3.7 Sulphur Isotope Analysis 49 3.7.1 Conventional analysis sampling 49 3.7.2 Equipment and analytical parameters 49 3.7.3 Data accuracy and precision 50 3.7.4 Laser analysis sampling 50 3.7.5 Equipment and analytical parameters 50 3.7.6 Data accuracy and precision 51 3.7.7 Purpose of Method 51 3.8 Scanning Electron Microscope 51 3.8.1 Sampling 51 3.8.2 Equipment and analytical parameters 52 3.8.3 Data accuracy and precision 52 3.8.4 Applications 52 References 53 Chapter 4: The texture, mineralogy and geochemistry of the bauxites of Mount Iti and 55 Mount Ghiona 4.1 Introduction 55 4.2 Literature Review 55 4.2.1 The texture of the Parnassos-Ghiona bauxites 56 4.2.2 Bauxite Mineralogy 56 4.2.3 Bauxite Geochemistry 57 4.2.4 Ooids, pisoids and clasts in bauxite 58 4.2.5 The focus of this chapter 59 4.3 Results 60 4.3.1 The texture of the Parnassos-Ghiona bauxites 60 4.3.2 The Mineralogy of the Parnassos-Ghiona Bauxites 66 4.3.3 Textural Controls on Mineralogy 75 4.3.4 Bauxite Geochemistry 79 4.3.5 Results summary 99 4.4 Discussion 101 4.4.1 Pisolith formation 101 4.4.2 Bauxite pisolith formation as a Self-organizing process 101 4.4.3 Model for bauxite texture formation 102 4.4.4 Bauxite mineralogy and implications for ore formation 104 4.4.5 Bauxite mineralogy and implications on exploration 111 4.4.6 Bauxite geochemistry and implications for ore formation 111 4.4.7 Bauxite geochemistry and its implications for exploration 113 4.4.8 The effects of the scale of observations on bauxite exploration 113 4.5 Conclusions 114 References 114 Chapter 5: The formation of sulphide minerals within the Parnassos-Ghiona bauxites and subsequent epigenetic alteration associated with their destruction 119 5.1 Introduction 119 5.2 Background 119 5.2.1 Sulphide minerals associated with bauxite 119 5.2.2 Economics of sulphide bearing