Petrography and geochemistry of the pre-Mapedi “bostonite” dykes and sills in the Kalahari Manganese Field, Northern Cape Province
- Authors: Monareng, Batobeleng Fisah
- Date: 2016
- Subjects: Dikes (Geology) - South Africa - Northern Cape , Sills (Geology) - South Africa - Northern Cape , Intrusions (Geology) - South Africa - Northern Cape , Manganese ores - Geology - South Africa - Northern Cape
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235816 , uj:24123
- Description: M.Sc. (Geology) , Abstract: Mafic dykes and sills intruding and affecting ore deposits are a well-known phenomenon around the world. The role played by magmatic hypogene fluids globally in the genesis of high-grade hematite ore is well-recognized. In the Northern Cape Province of South Africa, a series of intrusions have been emplaced in association with various sedimentary-hosted iron and manganese deposits. In the Kalahari Manganese Field (KMF) of the Northern Cape Province, the intrusions are referred to as “bostonites”.These dykes and sills are pre-Mapedi in age and contact metamorphosed the ore resulting in a general decrease of ore quality. The main aim of the study is to characterize the “bostonite” dykes and sills more extensively than previously by determining whether they are related to the same magmatic event and by evaluating the style of alteration that affected the “bostonite” chemistry. Comparison with the previously studied “bostonites” and the well-known large igneous provinces of the Kaapvaal Craton was made to determine the comagmatism. A paleoweathering profile on the mafic intrusive rocks (so-called “Bostonite”) was intersected during the exploration drilling of the Avontuur Deposit and provides an opportunity to describe the behavior of major, trace and REE in weathered rock relative to the unweathered parent rock. This weathering profile developed below the basal Gamagara/Mapedi unconformity overlying the iron formation (IF) and manganese formation (MF) of the Hotazel Formation and marks the base of Olifantshoek group. The “bostonites” of the Main Kalahari Deposit are composed predominantly of pyroxenes (diopside and augite), plagioclase (labradorite and andesite), Fe-Ti oxides (ilmenite, titanomagnetite) and minor rutile. The “bostonites” of the Avontuur Deposits, on the other hand, are composed predominantly of pyroxene (augite), plagioclase (albite) and Fe-Ti oxides (ilmenite, titanomagnetite, titanite). Based on the geochemistry, “bostonites” of both the Main Manganese and Avontuur Deposits are characterized by low Mg# indicating an evolved nature of the magma, as well as low Cr, Co and Sc signifying fractionation of the mafic minerals within the magma chamber. These mafic intrusives are characterized by negative Sr, Nb and Ta anomaly and positive K and Pb...
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- Authors: Monareng, Batobeleng Fisah
- Date: 2016
- Subjects: Dikes (Geology) - South Africa - Northern Cape , Sills (Geology) - South Africa - Northern Cape , Intrusions (Geology) - South Africa - Northern Cape , Manganese ores - Geology - South Africa - Northern Cape
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235816 , uj:24123
- Description: M.Sc. (Geology) , Abstract: Mafic dykes and sills intruding and affecting ore deposits are a well-known phenomenon around the world. The role played by magmatic hypogene fluids globally in the genesis of high-grade hematite ore is well-recognized. In the Northern Cape Province of South Africa, a series of intrusions have been emplaced in association with various sedimentary-hosted iron and manganese deposits. In the Kalahari Manganese Field (KMF) of the Northern Cape Province, the intrusions are referred to as “bostonites”.These dykes and sills are pre-Mapedi in age and contact metamorphosed the ore resulting in a general decrease of ore quality. The main aim of the study is to characterize the “bostonite” dykes and sills more extensively than previously by determining whether they are related to the same magmatic event and by evaluating the style of alteration that affected the “bostonite” chemistry. Comparison with the previously studied “bostonites” and the well-known large igneous provinces of the Kaapvaal Craton was made to determine the comagmatism. A paleoweathering profile on the mafic intrusive rocks (so-called “Bostonite”) was intersected during the exploration drilling of the Avontuur Deposit and provides an opportunity to describe the behavior of major, trace and REE in weathered rock relative to the unweathered parent rock. This weathering profile developed below the basal Gamagara/Mapedi unconformity overlying the iron formation (IF) and manganese formation (MF) of the Hotazel Formation and marks the base of Olifantshoek group. The “bostonites” of the Main Kalahari Deposit are composed predominantly of pyroxenes (diopside and augite), plagioclase (labradorite and andesite), Fe-Ti oxides (ilmenite, titanomagnetite) and minor rutile. The “bostonites” of the Avontuur Deposits, on the other hand, are composed predominantly of pyroxene (augite), plagioclase (albite) and Fe-Ti oxides (ilmenite, titanomagnetite, titanite). Based on the geochemistry, “bostonites” of both the Main Manganese and Avontuur Deposits are characterized by low Mg# indicating an evolved nature of the magma, as well as low Cr, Co and Sc signifying fractionation of the mafic minerals within the magma chamber. These mafic intrusives are characterized by negative Sr, Nb and Ta anomaly and positive K and Pb...
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A petrographical and geochemical analysis of the upper and lower manganese ore bodies from the Kalahari Manganese Deposit, Northern Cape, South Africa – controls on hydrothermal metasomatism and metal upgrading
- Authors: Blignaut, Lauren Cher
- Date: 2017
- Subjects: Geology - South Africa - Northern Cape , Geochemistry - South Africa - Northern Cape , Mineralogy - South Africa - Northern Cape , Petrology - South Africa - Northern Cape , Manganese ores - Geology - South Africa - Northern Cape
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/233924 , uj:23893
- Description: Ph.D. (Geology) , Abstract: The Paleoproterozoic Kalahari Manganese Field (KMF) is the largest known land-based manganese (Mn) deposit on Earth. Of the five erosional relics that the KMF comprises within the Hotazel Formation, the Kalahari Manganese Deposit (KMD) is the largest. The Mn ores within the KMD are hosted in three beds that alternate with banded iron-formation (BIF) and hematite lutite. The low-grade ore (<38 wt% Mn), is mostly quartz-free and carbonate-rich, whereas the high-grade ore (>44 wt% Mn), is a carbonate-free, Mn oxide-rich ore. The drill cores analysed incorporate the Nchwaning (I, II and III), Belgravia and Gloria mines, as well as the Black Rock outcrop. This study provides a correlation of petrographical, mineralogical and geochemical data, in order to characterise and interpret the protolith, low-grade and high-grade ores of both the upper and lower Mn ore bodies. The source, transport, deposition, diagenesis, metamorphism, as well as hydrothermal alteration of the Mn ores have been addressed. The spatial distribution of the mineral assemblages, the mechanism of Mn enrichment, fluid characteristics and fluid-rock interactions, as well as the influence of epigenetic alteration processes and the erosional unconformity on the quality of the ore has been discussed. The fluid-rock interaction leads to the presence of boron (B), which is considered highly detrimental to the steel quality. Thus, the spatial distribution, location and the source of the B, as well as ways of dealing with its presence has been addressed. A regional model for the alteration of the Mn ores, based on the above results, has been produced. Five distinct drill core groups, based on mineralogical associations, textural features and geochemical characteristics were distinguished. The diagenetic textural features are comprised of carbonate minerals, and generally preserved within the lower grade ores. The higher grade ores show replacement of the carbonates with oxides and ‘secondary’ carbonate minerals, whilst the highest grade ore is almost completely devoid of the textural features. The upper ore bodies display higher Fe and Si contents, whereas the lower ore bodies show enrichment in Mn and Ca. This suggests pervasive and incipient oxidation, as well as carbonate leaching from the upper to the lower bed. An increase in grade is characterised by enrichment in Mn, Fe, Cu, Pb, Zn, Ni and Co, and depletion in Ca, Mg and Si. The high-grade ores are enriched in Ba, Sr, Li and B, with the upper ore beds generally exhibiting higher abundances of these elements relative to the lower ore bodies. Boron is mineralogically controlled and hosted by braunite, braunite-II, gaudefroyite, tephroite and the carbonate- and serpentine-group minerals. The trace elements were redistributed and locally concentrated
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- Authors: Blignaut, Lauren Cher
- Date: 2017
- Subjects: Geology - South Africa - Northern Cape , Geochemistry - South Africa - Northern Cape , Mineralogy - South Africa - Northern Cape , Petrology - South Africa - Northern Cape , Manganese ores - Geology - South Africa - Northern Cape
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/233924 , uj:23893
- Description: Ph.D. (Geology) , Abstract: The Paleoproterozoic Kalahari Manganese Field (KMF) is the largest known land-based manganese (Mn) deposit on Earth. Of the five erosional relics that the KMF comprises within the Hotazel Formation, the Kalahari Manganese Deposit (KMD) is the largest. The Mn ores within the KMD are hosted in three beds that alternate with banded iron-formation (BIF) and hematite lutite. The low-grade ore (<38 wt% Mn), is mostly quartz-free and carbonate-rich, whereas the high-grade ore (>44 wt% Mn), is a carbonate-free, Mn oxide-rich ore. The drill cores analysed incorporate the Nchwaning (I, II and III), Belgravia and Gloria mines, as well as the Black Rock outcrop. This study provides a correlation of petrographical, mineralogical and geochemical data, in order to characterise and interpret the protolith, low-grade and high-grade ores of both the upper and lower Mn ore bodies. The source, transport, deposition, diagenesis, metamorphism, as well as hydrothermal alteration of the Mn ores have been addressed. The spatial distribution of the mineral assemblages, the mechanism of Mn enrichment, fluid characteristics and fluid-rock interactions, as well as the influence of epigenetic alteration processes and the erosional unconformity on the quality of the ore has been discussed. The fluid-rock interaction leads to the presence of boron (B), which is considered highly detrimental to the steel quality. Thus, the spatial distribution, location and the source of the B, as well as ways of dealing with its presence has been addressed. A regional model for the alteration of the Mn ores, based on the above results, has been produced. Five distinct drill core groups, based on mineralogical associations, textural features and geochemical characteristics were distinguished. The diagenetic textural features are comprised of carbonate minerals, and generally preserved within the lower grade ores. The higher grade ores show replacement of the carbonates with oxides and ‘secondary’ carbonate minerals, whilst the highest grade ore is almost completely devoid of the textural features. The upper ore bodies display higher Fe and Si contents, whereas the lower ore bodies show enrichment in Mn and Ca. This suggests pervasive and incipient oxidation, as well as carbonate leaching from the upper to the lower bed. An increase in grade is characterised by enrichment in Mn, Fe, Cu, Pb, Zn, Ni and Co, and depletion in Ca, Mg and Si. The high-grade ores are enriched in Ba, Sr, Li and B, with the upper ore beds generally exhibiting higher abundances of these elements relative to the lower ore bodies. Boron is mineralogically controlled and hosted by braunite, braunite-II, gaudefroyite, tephroite and the carbonate- and serpentine-group minerals. The trace elements were redistributed and locally concentrated
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