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Physical and Chemical Characterization of the Manganese Ore Bed at the Mamatwan Mine, Kalahari Manganese Field

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Physical and Chemical Characterization of the Manganese Ore Bed at the Mamatwan Mine, Kalahari Manganese Field Physical and chemical characterization of the manganese ore bed at the Mamatwan mine, Kalahari Manganese Field By PAULA CRISTINA CANASTRA RAMOS PRESTON DISSERTATION Submitted in fulfillment of the requirements for the degree MAGISTER SCIENTAE in GEOLOGY in the FACULTY OF SCIENCE at the RAND AFRIKAANS UNIVERSITY Supervisor: Prof. N.J. Beukes Co-supervisor: Prof. J. Gutzmer AUGUST, 2001 TABLE OF CONTENTS Acknowledgements i Abstract ii Chapter One: Introduction 1.1 Geographical setting 1 1.2 The Kalahari manganese field 2 1.3 Mamatwan mine 3 1.4 Previous work 4 1.5 Objective of this study 8 1.6 Analytical methods 8 Chapter Two: Geological Setting 2.1 Stratigraphy of the Transvaal Supergroup in Griqualand West 12 2.2 Geology of the Kalahari deposit 13 2.3 The geology at Mamatwan mine 17 Chapter Three: Lithostratigraphy 3.1 Introduction 19 3.2 Existing subdivision of the ore bed 20 3.3 New subdivision of the ore bed 22 3.4 Lateral variation 29 3.5 Discussion 29 Chapter Four: Petrography and Mineralogy 4.1 Introduction 35 4.2 Oxide mineralogy 37 4.3 Carbonate mineralogy 38 4.4 Petrographic description of lithostratigraphic zones 42 4.5 Discussion 52 Chapter Five: Geochemistry 5.1 Introduction 55 5.2 Major elements 55 5.3 Trace elements 61 5.4 Loss on ignition 63 5.5 Depositional Geochemical signatures 63 5.6 Carbonate stable isotope geochemistry 64 5.7 Discussion 70 Chapter Six: Density and Washability 6.1 Density measurements 74 6.2 Washability 77 6.3 Discussion 79 Chapter Seven: Conclusions 7.1 The diagenetic evolution of the Mamatwan-type ore 85 7.2 Cyclicity and lateral consistency of the ore bed 88 7.3 Recommendations for future mining and beneficiation at Mamatwan mine 90 References 96 Appendix I: Drill core logs 102 Appendix II: Whole rock geochemical data 127 Appendix III: Carbonate stable isotope geochemistry 130 Appendix IV: Density measurements 135 i Acknowledgements Without the participation and support of the following people and organizations, this study would not have been possible. A very special thank-you to my supervisors Prof. J. Gutzmer and Prof. N.J. Beukes. For a geologist, life is too short as there are too many unanswered questions to resolve. They somehow managed to find time in between their many travels and conquests to answer mine. I will always be indebted to my parents who supported me and encouraged me to continue to learn new things. To my husband Douglas who has always been there and always will be. The staff and students at the RAU Geology Department provided excellent ‘tea-time’ stories. Special thanks to Lisa Carter, Lynnette Greyling, HermanVan Niekerk, Adrian van Bart, Herman Dorland, Dr. J.M.Huizenga, Angus McIntyre and El-El Coetzee. SAMANCOR for financial support and E. Swindell, R. Arnot and E.P. Ferreira for their continued interest and participation. Special thanks to Janet Oosthuizen from Mintek, Uwe Horstmann at the Council for Geoscience and personel from Billiton Process Research for providing valuable information. ii Abstract The Mamatwan mine is situated at the most southern end of the world’s largest land- based resource of manganese, the Kalahari manganese field. The mine is operated by South African Manganese Corporation Limited (SAMANCOR) and is the largest open pit manganese mine in the world. The sedimentary manganese ore bed is interbedded with iron-formation of the Hotazel Formation of the Early Paleoproterozoic Voëlwater Subgroup of the Transvaal Supergroup. The open pit Mamatwan mine has a proven economic ore reserve of between 300 and 400Mt and produces 1.2Mt of manganese ore annually, of which 0.5Mt of ore is beneficiated and shipped through the harbour at Port Elizabeth. The remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle. Carbonate-rich manganese lutite mined at the Mamatwan Mine is widely known as Mamatwan-type ore. It has a manganese content ranging from 30 – 38%. Only a small portion (15m of a total thickness of 49m) of the ore bed, containing an average of 38% Mn, is being mined and processed at present. The larger portion of the ore bed is not utilized. This study focuses on the physical and chemical characteristics of the ore bed in more detail in order to make suggestions on how to a) reduce waste by upgrading the upper parts of the lower manganese ore bed, or b) to improve the current recovery from the present economic zone. A second part of this study pays special attention to the lithostratigraphy of the lower manganese ore bed. The focus is on the paragenetic sequence and the diagenetic evolution of the braunite lutite that constitutes the manganese ore. The Mamatwan-type ore can be described as diagenetic to very low-grade metamorphic carbonate-bearing braunite manganolutite. Based on geochemical and mineralogical data, the lower manganese ore body was previously subdivided into eleven lithogically distinct zones. Based on detailed diamond drill core logging and with the aid of geochemical and physical data of two selected drill cores, an additional thirteen subzones were identified in this study. These new subzones were found to be consistent across the entire study area, located to the west and north of the present Mamatwan open pit. The paragenetic sequence recognised in the ore of the lower manganese ore bed can be subdivided into four stages, namely: (a) sedimentation, which is represented by fine lamination and the presence of fine-grained “dusty hematite”. (b) early diagenesis as represented by micritic carbonate matrix and possibly braunite, (c) late diagenesis or low-grade metamorphism are represented by coarse grained hausmannite, specularitic hematite, partridgeite and Mn-calcite, and supergene alteration that occurs immdediately below the contact of the ore bed to the unconformably overlying Tertiary Kalahari Formation. This supergene altered zone is marked by the presence of Mn4+ oxides such as cryptomelane, manjiroite, romanechite and pyrolusite, in addition to barite. The results obtained in this study permit definition of two sedimentary cycles within the manganese ore bed at the Mamatwan mine. Both cycles are defined by a carbonate-rich finely laminated zone at the base, overlain by a central manganese-rich economic zone, ii iii capped by manganese lutite that is enriched in carbonate ovoids. The two manganese- rich zones are known as the M (lower) and X (upper) zone, and are characterized by the replacement of carbonate ovoids by hausmannite. The two Mn-rich zones are chemically and physically almost identical, with the M zone 7.5m thick and the X zone 5.5m thick. However, in the present mining configuration only the M zone is being mined. The most important result arising from the present study is the recommendation to restructure the future mining operation in order to mine not only the M zone, but also the X zone. iii Introduction 1 Chapter One Introduction The Mamatwan manganese mine is an open pit operation owned by Samancor Limited. It started operation in 1963 and was initially developed to provide ore with a high manganese to iron ratio, suitable for the local ferro-alloy industry. The mine currently produces approximately 100 000 tons of manganese ore a month (1.2Mt annually) of which some 0.5Mt of beneficiated ore is shipped through the harbour at Port Elizabeth and the remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle (Samancor, 1994). The manganese ore bed at Mamatwan mine contains low-grade ore with a manganese content ranging from 30 – 38 wt% Mn. The ore bed is some 49m thick but only a 15m thick section, containing on average 38 wt% Mn is currently being mined and processed. The remaining 35 meters of the ore bed are not being utilized. The focus of this project is to suggest a means of utilizing a larger thickness or more zones of the ore bed so as to reduce waste and possibly improve the manganese grade of the ore mined. This is to be achieved by carefully examining the physical and chemical characteristics of the manganese ore bed in the mine lease area. 1.1 Geographical Setting Mamatwan mine is located in the southern-tip of the Kalahari manganese field in the Griqualand West region of the Northern Cape Province, South Africa (Fig.1.1A). The mean elevation in this area is between 1100m to 1400m and the morphology is dominated by flat plains intersected by generally N-S striking ranges of the Asbestos Hills, the Klipfontein Hills and the Gamagara Ridge. The plains are covered by thick calcretes and wind blown Kalahari sands that obscure the sub-outcrop with the exception of Black Rock, a small hillock of the manganese-bearing Hotazel Formation (Fig.1.1B). Introduction 2 1.2 The Kalahari manganese field The Kalahari manganese field is made up of five structurally preserved erosional relics of the Hotazel Formation, consistng of iron-formation with interbedded units of manganese ore. The largest of the five deposits is the Kalahari deposit (Gutzmer, 1995) (Fig.1.1B), which contains 80% of the worlds known mineable manganese resource (Samancor, 1994). This deposit has a strike length of 41km and a width varying between 5 and 20km (Samancor, 1994). To the east of the Kalahari deposit, lie the Hotazel and Langdon- Annex deposits, which have virtually been mined out. The remaining two deposits, Avontuur and Leinster (Fig.1.1A) are small and of sub-economic grade and lie to the north of the main deposit. Several mines, presently in operation in the Kalahari deposit, are the Mamatwan Mine (open pit), Gloria Mine (underground), N’chwaning II (underground), Wessels (underground), and Langdon West (open pit) (Fig.1.1B).
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