Origin of High-Grade Hematite Ores at Thabazimbi Mine, Limpopo Province, South Africa
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ORIGIN OF HIGH-GRADE HEMATITE ORES AT THABAZIMBI MINE, LIMPOPO PROVINCE, SOUTH AFRICA by SIMON THIZWILONDI NETSHIOZWI DISSERTATION Submitted in the fulfillment of the requirement for the degree MAGISTER SCIENTAE in GEOLOGY in the FACULTY OF SCIENCE at the RAND AFRIKAANS UNIVERSITY SUPERVISOR: PROF N. J. BEUKES CO-SUPERVISORS: PROF J. GUTZMER : PROF C.A. SMIT JULY, 2002 ii DECLARATION I declare that this research is my own work and that it was conducted under the supervision of Professor N.J. Beukes, Professor J Gutzmer and Professor C.A Smit. No part of this research has been submitted in the past, or is being submitted, for degree at another university S.T. Netshiozwi iii ACKNOWLEDGEMENTS There are many people and organizations to acknowledge for their contribution to this thesis. The National Research Foundation of South Africa and ISCOR (now Kumba Resources) are gratefully acknowledged for their financial support. I am greatly indebted to Prof N. J Beukes for his inspirational guidance and patience during this study. Thank you Prof Jens Gutzmer for valuable criticism, suggestions and not only for your continued support but also for your interest in this project. Prof C.A Smit is acknowledged for his advise concerning the structural work. Markus Schaefer and Dr Jan- Marten Huizenga are thanked for valuable assistance during fluid inclusion studies. The Thabazimbi Mine provided the necessary logistical support required to conduct this study and the staff of the geology department at Thabazimbi, especially Harry Leister, Marius Van Niekerk and Torren Klinge are gratefully acknowledged. Dr Joydip Mukhopadhyay and Prof Carlos Rosiere are acknowledged for their input and discussion regarding the origin of high-grade hematite ores. Dr Uwe Hortstmann (Council of Geosciences, Pretoria) for assistance in carbon and oxygen stable isotopes analyses. Dr Andreas Pack at the University of Cologne, Germany is thanked for oxygen isotopes analyses. Thank you also to staff and students in the Department of Geology at RAU for their support and friendship. Special thanks to Oom Hennie, Tannie Elsa, Mike Knoper, Herman van Niekerk, Herman Dorland, El-el Coetzee, Rene Boshoff, Dr Willie Oldewage, Dries du Plooy, Michiel de Kock, Yvonne Flattery, Chris Twiggs, Chris Harding, Shaun van Kal, Anelda van Staden, Kimi, Eiko, Sergio Mkhaza and Dr. Frank Nyame. And last but not least Munaka Maumela for his friendly advices, encouragement and support throughout my studies at RAU. Nnditsheni, Tshifhiwa, Buyiswa, Takie, I had a stunning time with you guys at RAU. The love goes to my brothers, Maanda, Shumani, Joshua, Taki, Mom and especially my late father J. M. Netshiozwi to whom this thesis is dedicated. Table of contents v Table of Contents 1. Introduction 1.1 Rationale………………………………………………………………………1 1.2 Geographic Setting………………………………………………………….…3 1.3 Mining activity………………………………………………………………...5 1.4 Previous Work………………………………………………………………...8 1.4.1 Supergene model…………………………………………………..9 1.4.2 Combined metasomatic-supergene models………………………..9 1.4.3 Magmatic model…………………………………………………10 1.4.4 Combined metasomatic hydrothermal model……………………10 1.5 Objective and Methods of study……………………………………………..11 2. Geological Setting 2.1 Introduction………………………………………………………………….12 2.2 Stratigraphic setting………………………………………………………….12 2.3 Structural setting……………………………………………………………..15 2.3.1 Regional setting……………………………………………………15 2.3.2 Thabazimbi Mine…………………………………………………..19 3. Description of the deposit 3.1 Introduction…………………………………………………………………… 3.2 Northern Range……………………………………………………………………...27 3.2.1. Kwaggashoek East Deposit………………………………..27 3.2.2 East Mine Deposit……………………………………..…...29 3.2.3 Van der Bijl Deposit………………………………….……30 3.2.4 Donkerpoort Deposit……………………………………….32 3.2.5 Donkerpoort West Deposit…………………………….…..32 3.3 Middle Range, the Bobbejaanwater Deposit ………………………………….….....35 3.4 Southern Range………………………………………………………………………36 3.4.1 Buffelshoek East Deposit………………...………………...36 3.4.2 Buffelshoek West Deposit…………… Table of contents vi 4. Mineralogy and Petrography 4.1 Unaltered Penge Iron Formation……………………………………………..39 4.1.1 Mesoscopic description……………………………………… ……39 4..1.2 Microscopic description…………………………………………...39 4.2 Oxidized Penge Iron Formation……………………………………………...43 4.2.1 Mesoscopic description ……………………………………………43 4.2.2 Microscopic description……………………………………………45 4.3 High grade hematite ores…………………………………………………….48 4.3.1 Hard hematite ore…………………………………………………..48 4.3.1.1 Mesoscopic description ………………………………….48 4.3.1.2 Microscopic description………………………………….51 4.3.2 Carbonate-hematite ore…………………………………………….55 4.3.2.1 Mesoscopic description ………………………………….55 4.3.2.2 Microscopic description………………………………….58 4.2.3 Supergene modified ore……………………………………………60 4.2.3.1 Mesoscopic description ………………………………….60 4.2.3.2 Microscopic description………………………………….60 4.4 Summary and discussion……………………………………………..………62 5. Fluid Inclusion Studies 5.1 Introduction…………………………………………………………..………69 5.2 Sampling and analytical procedure…………………………………………..70 5.3 Fluid Inclusion Petrography………………………………………………….71 5.4 Microthermometry …………………………………………………………..71 5.5 Discussion……………………………………………………………………76 6. Stable Isotope Geochemistry 6.1 Introduction…………………………………………………………..…… 6.2 Carbonates……………………………………………………………………78 6.2.1 Sampling and analytical procedure………………………………..78 6.2.2 Results……………………………………………………………...79 6.2.3 Discussion………………………………………………………….81 6.3 Oxygen isotope geochemistry of hematite……………………………….….82 Table of contents vii 6.3.1 Introduction………………………………………………….…….82 6.3.2 Sampling…………………………………………………….…….83 6.3.3 Results………………………………………………………..……83 6.3.4 Discussion……………………………………………………..…..83 7. Genetic Model 7.1 Introduction…………………………………………………………….…….89 7.2 Deposition of the Penge Iron Formation……………………………….…….90 7.3 Metamorphic alteration………………………………………………….…...90 7.4 Intrusion of sills and dykes…………………………………………….…….92 7.5 Structural deformation………………………………………………….……92 7.6 Hydrothermal alteration…………………………………………… 7.7 Uplift, weathering and erosion along the old African land surface………….95 7.8 Physical erosion in geologic recent times……………………………..……..96 7.9 Comparison with previous metallogenetic models…………………………..97 7.10 Exploration criteria…………………………… 8. References……………………………………………………………………………100 Appendix I. Sample list A.1.1 Northern Range…………………………………………………………………..110 A.1.3 Southern Range…………………………………………………………………..113 A.1.2 Middle Range ……………………………………………………………………114 Appendix II. Analytical Methods A.2.1Field Work………………………………………………………………………..115 A.2.2 Sample preparation………………………………………………………………115 A.2.3 Cathodoluminescence…………………………………………………………....116 A.2.4 X-ray powder diffraction analysis………………………………………………..116 A.2.5 Microscopy……………………………………………………………………….116 A.2.6 Scanning electron microscopy…………………………………………………...117 A.2.7 Carbonated staining………………………………………………………………117 A.2.8. Fluid inclusion studies…………………………………………………………..117 Table of contents viii A.2.9 Reference list……………………………………………………………………..118 Appendix III. Analytical Results A.3.1 XRD results………………………………………………………………………119 A.3.2 Microthemometric results………………………………………………………..122 Appendix IV. Core logs A.4.1KW264……………………………………………………………………………123 A.4.2KW 287…………………………………………………………………………...124 A.4.3KW 295…………………………………………………………………………...125 A.4.4KW 308…………………………………………………………………………...126 A.4.5KW 309…………………………………………………………………………...127 A.4.6BH 607B………………………………………………………………………….128 A.4.7BH 1608…………………………………………………………………………..129 A.4.8BH1706…………………………………………………………………………...130 A.4.9BH2056…………………………………………………………………………...131 A.4.10BH2093………………………………………………………………………….132 A.4.11BH2107………………………………………………………………………….133 A.4.12DKP442………………………………………………………………………….134 A.4.13DON 396………………………………………………………………………...135 List of figures ix List of Figures Page Fig. 1.1 World production of iron ores in 1998 (USGS, 1999). 1 Fig. 1.2 Location of the Thabazimbi Iron Ore Mine relative to the Sishen and Beeshoek 3 Iron ore Mines, major steel works of Vereeniging, Pretoria, Newcastle and Saldanha Bay Fig. 1.3 Profile illustrating the position of the Thabazimbi iron ore deposit within the 4 Transvaal Supergroup (Modified from Dorland, 1999). Fig. 1.4 Simplified stratigraphic columns illustrating the fundamental difference between 5 the ancient unconformity-bounded supergene high-grade iron ore deposit on the Maremane dome at Sishen and Beeshoek and the structural (fault?) controlled “hydrothermal” ore bodies at Thabazimbi. Fig. 1.5 Satellite image of Thabazimbi area showing the Rosseaupoort, Northern and 7 Southern ranges and position of different open pits of the Thabazimbi Iron Ore Mine. Fig. 2.1 Distribution of the Transvaal Supergroup hosting the high-grade hematite ores at 13 Thabazimbi, Sishen and Beeshoek (modified after Dorland, 1999). Fig. 2.2 Sedimentary facies relationships of the Transvaal and Olifantshoek Supergroups 14 preserved in the Griqualand West and Transvaal Basins (modified after Beukes, 1986, and Dorland, 1999). Fig. 2.3 Correlation of profiles from the Penge Iron Formation in the northwest Transvaal 16 at Thabazimbi Mine and in the northeastern Transvaal at Mafefe. Fig. 2.4 Sketch diagram illustrating the loss of the stratigraphy from the discoidal marker 17 in the Malmani dolomite to the ore in the basal part of the Penge Iron Formation. Fig. 2.5 Geological map illustrating the regional geological setting of the Thabazimbi 18 hematite deposits. Note the Crocodile River fragment with a smaller high-grade hematite deposit. Fig. 2.6 Geological plan and cross-section of