A study of the geology of the Vaalbank and Lady Frere areas in the Karoo Basin of South Africa using gravity, magnetic and gamma-ray spectrometry data: implications of groundwater potential
- Khalimashe, Sinesihle, Gwavava, Oswald
- Authors: Khalimashe, Sinesihle , Gwavava, Oswald
- Date: 2020
- Subjects: Gamma ray astronomy
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/11983 , vital:39124
- Description: The Vaalbank and Lady Frere areas belong to the Elliot, Molteno and Burgersdorp Formations, that are part of the sedimentary succession of the Beaufort Group in the Karoo Basin of South Africa. There is Quaternary alluvium covering the mudstone, sandstone and shale rocks of the Beaufort Group. Dolerite and gabbro sills of the Karoo age have intruded the whole area. A number of investigations were carried out for the study namely field observations, petrographic, X-ray diffraction, airborne gamma-ray spectrometry, aeromagnetic and gravity analyses. Twenty four rock samples were collected in the field from fresh outcrops of the Karoo dolerites, Burgersdorp and Molteno formations. The measured densities and porosities show that the Karoo dolerite suite has the highest average dry density of 2.771 g/cm3 and the lowest average porosity of 3%. The Burgersdorp Formation has an intermediate average density of 2.458 g/cm3 and an intermediate average porosity of 5.4%. The Molteno Formation has the lowest average density of 2.190 g/cm3 and the highest average porosity of 14.5%. Petrographic and geochemical investigations were carried on 19 rocks samples collected in the field to determine the mineralogy character using microscopic and XRD analyses. Both petrographic and X-ray diffraction analyses revealed that the sandstones of the study area are composed of quartz as their primary mineral and feldspars as the secondary mineral. The dolerite consists of euhedral structured minerals such as magnetite, pyroxene, plagioclase and amphibole. The gamma ray maps show high spectrometric values are associated with the Burgersdorp Formation, alluvium cover and dolerite dykes. The low spectrometric values are associated with dolerite sills and ring complexes. The boundaries of the sill/ring complexes are clearly delineated by the K/U ratio and ternary maps. The magnetic maps show ring like patterns of magnetic high anomalies that are due to the sills/ring complexes whilst the numerous, narrow, linear magnetic highs are due to faults and dolerite dyke swarms. The majority of the dykes trend in a NW-SE direction and a few dykes are in a NE-SE direction. The magnetic power spectrum indicates four depths of the magnetic sources at average depths of 0.13 km, 1.60 km, 2.83 km and 12.40 km. The magnetic depth iii slices maps show that both the circular/ring like and linear anomalies extend from shallow to deeper depth of 12.4 km. The gravity map is dominated by a long wavelength gravity anomaly that increases from about -120 mGals in the northwestern corner of the study area to -110 mGals in the southeastern corner of the study area. Results from 2½D gravity modelling show that this long wavelength anomaly is due to a horizontal Moho at a depth of 47 km in the study area, which shallows outside the study area near the coast. Superimposed on it are short wavelength gravity anomalies due to low density sediments and high density dolerite intrusions. The simple 2½D models generated from five profiles traversing the study area reveal that the sediments of the Karoo Supergroup extend from the surface down to a depth 5 km below sea level attaining a maximum thickness of about 6½ km. These sediments are dykes, sills and ring complexes. The dykes and sills/ring complexes identified from gamma ray spectrometry, magnetic and gravity data results are likely to be associated with fractures, joints, cracks and fissures in the host rocks, which form preferential pathways for groundwater transmission. Hence, they could be suitable targets for groundwater.
- Full Text:
- Authors: Khalimashe, Sinesihle , Gwavava, Oswald
- Date: 2020
- Subjects: Gamma ray astronomy
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/11983 , vital:39124
- Description: The Vaalbank and Lady Frere areas belong to the Elliot, Molteno and Burgersdorp Formations, that are part of the sedimentary succession of the Beaufort Group in the Karoo Basin of South Africa. There is Quaternary alluvium covering the mudstone, sandstone and shale rocks of the Beaufort Group. Dolerite and gabbro sills of the Karoo age have intruded the whole area. A number of investigations were carried out for the study namely field observations, petrographic, X-ray diffraction, airborne gamma-ray spectrometry, aeromagnetic and gravity analyses. Twenty four rock samples were collected in the field from fresh outcrops of the Karoo dolerites, Burgersdorp and Molteno formations. The measured densities and porosities show that the Karoo dolerite suite has the highest average dry density of 2.771 g/cm3 and the lowest average porosity of 3%. The Burgersdorp Formation has an intermediate average density of 2.458 g/cm3 and an intermediate average porosity of 5.4%. The Molteno Formation has the lowest average density of 2.190 g/cm3 and the highest average porosity of 14.5%. Petrographic and geochemical investigations were carried on 19 rocks samples collected in the field to determine the mineralogy character using microscopic and XRD analyses. Both petrographic and X-ray diffraction analyses revealed that the sandstones of the study area are composed of quartz as their primary mineral and feldspars as the secondary mineral. The dolerite consists of euhedral structured minerals such as magnetite, pyroxene, plagioclase and amphibole. The gamma ray maps show high spectrometric values are associated with the Burgersdorp Formation, alluvium cover and dolerite dykes. The low spectrometric values are associated with dolerite sills and ring complexes. The boundaries of the sill/ring complexes are clearly delineated by the K/U ratio and ternary maps. The magnetic maps show ring like patterns of magnetic high anomalies that are due to the sills/ring complexes whilst the numerous, narrow, linear magnetic highs are due to faults and dolerite dyke swarms. The majority of the dykes trend in a NW-SE direction and a few dykes are in a NE-SE direction. The magnetic power spectrum indicates four depths of the magnetic sources at average depths of 0.13 km, 1.60 km, 2.83 km and 12.40 km. The magnetic depth iii slices maps show that both the circular/ring like and linear anomalies extend from shallow to deeper depth of 12.4 km. The gravity map is dominated by a long wavelength gravity anomaly that increases from about -120 mGals in the northwestern corner of the study area to -110 mGals in the southeastern corner of the study area. Results from 2½D gravity modelling show that this long wavelength anomaly is due to a horizontal Moho at a depth of 47 km in the study area, which shallows outside the study area near the coast. Superimposed on it are short wavelength gravity anomalies due to low density sediments and high density dolerite intrusions. The simple 2½D models generated from five profiles traversing the study area reveal that the sediments of the Karoo Supergroup extend from the surface down to a depth 5 km below sea level attaining a maximum thickness of about 6½ km. These sediments are dykes, sills and ring complexes. The dykes and sills/ring complexes identified from gamma ray spectrometry, magnetic and gravity data results are likely to be associated with fractures, joints, cracks and fissures in the host rocks, which form preferential pathways for groundwater transmission. Hence, they could be suitable targets for groundwater.
- Full Text:
Geological and geophysical investigations of groundwater resource in the area of Ndlambe Municipality, Eastern Cape Province, South Africa.
- Authors: Mpofu, Mthulisi
- Date: 2020
- Subjects: Groundwater Geophysical surveys
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/18755 , vital:42730
- Description: Groundwater is an essential resource contributing extensively to overall total annual supply. However, overexploitation has depleted groundwater availability significantly and also brought about land subsidence at some places. The evaluation of groundwater potential zones is essential in protecting the quality of water and managing of groundwater structures. The Eastern Cape Province is one of the provinces faced with the challenge of supplying clean fresh water to the communities residing in it. Ndlambe municipality is a case in point where people rely on groundwater for agriculture and domestic activities. Few studies have been undertaken to evaluate groundwater resource in the study area. This study aims to assess groundwater resources as a way of achieving the goal of water sustainability. In the southeast of the Cape Fold Belt (CBF), is the Ndlambe municipality underneath folded Cape and Karoo Supergroup rocks. The rock sequence in the region reflects the geological history over a considerable period. In general, the area of study comprises of the Bokkeveld and Witteberg groups. The Bokkeveld comprises of shale along with sandstone whilst the Witteberg Group consists predominantly of quartzites with minor interbedded shales. The aims of the study were to target potential zones for groundwater exploration, analyse zones of lineaments, investigate the networks of fractures and the mineralogy of the area of study. In line with studies for groundwater exploration, a number of methods were undertaken for obtaining the results. These included literature review, remote sensing and geographic information system, thin section analysis, scanning electron microscope (SEM), X-ray fluorescence (XRF), structural analysis and geophysical investigations (magnetic and vertical electrical sounding). Potential zones for groundwater were identified using remote sensing techniques and geographical information systems (GIS). Maps were generated using GIS tools. Geology, slope, lineaments and Normalised Difference Vegetation Index (NDVI) were considered as parameters for determining groundwater potential zones. A geological and geophysical study was conducted in the Ndlambe municipality. Twelve samples for thin sections, 12 samples for XRF analysis and 4 samples for SEM analysis were collected at different locations in the area of study and were analysed. Thin section analysis revealed that quartz arenite has been metamorphosed to quartzite due to high pressure and temperatures and the cracks in the quartz grains are due to pressure and brittle deformation that has in turn enhanced secondary porosity resulting in joints and fractures which are good for groundwater movement. Scanning electron microscopy complemented the findings from optical microscopy by revealing splatter pores which are due to intense fracturing and these contribute to increasing permeability of the rock structures. XRF revealed the chemical composition of various rock types in the area of study. The analysed samples were dominated by silica reflecting their source from weathering of silicate rocks. The Chemical Index of Alteration (CIA) and Al2O3 values of the analysed samples reflected moderate to intensive weathering. In the study area, three main hydrogeologically important structures were taken into account. These included primary structures (bedding), contacts (geological) and secondary structures like fractures and folds. The study area comprises of several faults that are an important factor for porosity and permeability. The study area is dominated by blocky quartz veins that have been crushed due to compression hence higher permeability of groundwater. The Syscal Pro multichannel resistivity equipment was used to conduct the survey using the Schlumberger- Dipole-dipole array on three lines of varying length (350 m, 530 m and 340 m). Data collected were processed using RES2DINV software, producing a subsurface 2-D geoelectrical model from the pseudosections of apparent resistivity. Low resistivities in the study area were inferred to be weathered moist sandstone while low resistivities with depth indicated an overlying zone of fractured sandstone and quartzite which may be hosting some groundwater. An area of low resistivity zones between two large bodies suggests that the massive rock bodies are being weathered and fractured and fractures act as conduits for groundwater. High resistivity values indicate hard rock bodies that are unweathered hence low potential zone for groundwater localisation. The ground magnetic survey was used to delineate the subsurface structures as these control groundwater potential.
- Full Text:
- Authors: Mpofu, Mthulisi
- Date: 2020
- Subjects: Groundwater Geophysical surveys
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/18755 , vital:42730
- Description: Groundwater is an essential resource contributing extensively to overall total annual supply. However, overexploitation has depleted groundwater availability significantly and also brought about land subsidence at some places. The evaluation of groundwater potential zones is essential in protecting the quality of water and managing of groundwater structures. The Eastern Cape Province is one of the provinces faced with the challenge of supplying clean fresh water to the communities residing in it. Ndlambe municipality is a case in point where people rely on groundwater for agriculture and domestic activities. Few studies have been undertaken to evaluate groundwater resource in the study area. This study aims to assess groundwater resources as a way of achieving the goal of water sustainability. In the southeast of the Cape Fold Belt (CBF), is the Ndlambe municipality underneath folded Cape and Karoo Supergroup rocks. The rock sequence in the region reflects the geological history over a considerable period. In general, the area of study comprises of the Bokkeveld and Witteberg groups. The Bokkeveld comprises of shale along with sandstone whilst the Witteberg Group consists predominantly of quartzites with minor interbedded shales. The aims of the study were to target potential zones for groundwater exploration, analyse zones of lineaments, investigate the networks of fractures and the mineralogy of the area of study. In line with studies for groundwater exploration, a number of methods were undertaken for obtaining the results. These included literature review, remote sensing and geographic information system, thin section analysis, scanning electron microscope (SEM), X-ray fluorescence (XRF), structural analysis and geophysical investigations (magnetic and vertical electrical sounding). Potential zones for groundwater were identified using remote sensing techniques and geographical information systems (GIS). Maps were generated using GIS tools. Geology, slope, lineaments and Normalised Difference Vegetation Index (NDVI) were considered as parameters for determining groundwater potential zones. A geological and geophysical study was conducted in the Ndlambe municipality. Twelve samples for thin sections, 12 samples for XRF analysis and 4 samples for SEM analysis were collected at different locations in the area of study and were analysed. Thin section analysis revealed that quartz arenite has been metamorphosed to quartzite due to high pressure and temperatures and the cracks in the quartz grains are due to pressure and brittle deformation that has in turn enhanced secondary porosity resulting in joints and fractures which are good for groundwater movement. Scanning electron microscopy complemented the findings from optical microscopy by revealing splatter pores which are due to intense fracturing and these contribute to increasing permeability of the rock structures. XRF revealed the chemical composition of various rock types in the area of study. The analysed samples were dominated by silica reflecting their source from weathering of silicate rocks. The Chemical Index of Alteration (CIA) and Al2O3 values of the analysed samples reflected moderate to intensive weathering. In the study area, three main hydrogeologically important structures were taken into account. These included primary structures (bedding), contacts (geological) and secondary structures like fractures and folds. The study area comprises of several faults that are an important factor for porosity and permeability. The study area is dominated by blocky quartz veins that have been crushed due to compression hence higher permeability of groundwater. The Syscal Pro multichannel resistivity equipment was used to conduct the survey using the Schlumberger- Dipole-dipole array on three lines of varying length (350 m, 530 m and 340 m). Data collected were processed using RES2DINV software, producing a subsurface 2-D geoelectrical model from the pseudosections of apparent resistivity. Low resistivities in the study area were inferred to be weathered moist sandstone while low resistivities with depth indicated an overlying zone of fractured sandstone and quartzite which may be hosting some groundwater. An area of low resistivity zones between two large bodies suggests that the massive rock bodies are being weathered and fractured and fractures act as conduits for groundwater. High resistivity values indicate hard rock bodies that are unweathered hence low potential zone for groundwater localisation. The ground magnetic survey was used to delineate the subsurface structures as these control groundwater potential.
- Full Text:
Mineralogy, geochemistry and pebble morphology of the Katberg Formation around Graaff Reinet and East London, Eastern Cape province of South Africa
- Authors: Ndlazi, Nondumiso Zandile
- Date: 2020
- Subjects: Mineralogy|
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/18631 , vital:42615
- Description: The Katberg Formation forms the upper part of the Tarkastad Subgroup in the Beaufort Group of the main Karoo Supergroup. The Katberg Formation consists of siliciclastic sedimentary rocks mostly dominated by greyish sandstone, red mudstone with minor siltstone occurrences. The Katberg Formation also consists of calcareous and ferruginous concretions that formed during diagenesis. Braided streams deposited the Katberg Formation with a predominantly sand bed load. The Katberg Formation sandstones contain pebbles with no true conglomerates identified in the study area. This study was conducted in the Katberg Formation to understand the mineralogy, geochemistry, and pebble morphology around Graaff Reinet and East London areas. The major and trace elements were analyzed through X-Ray Fluorescence (XRF) to deduce the source rock provenance, tectonic setting, paleo-weathering conditions, climatic conditions, and sediment maturity. The X-Ray Diffraction (XRD) was used to highlight a detailed distribution and variation of mineralogical polymorphs of the minerals present in sandstones and mudstones. The pebble morphology was used to confirm the depositional environment of the Katberg Formation. The use of The bivariate plots of the Maximum Projection Sphericity Index (MPSI) and the Oblate-Prolate Index (OPI) showed that 79 % of pebbles fall in the fluvial environment, whereas 21 % of pebbles fall in the beach environment. A small proportion of beach pebbles within the Katberg Formation suggests that the river reached the marginal marine environment during its flow. The majority of the pebbles yielded a bladed shape with a dominating Sphericity Index symptomatic of fluvial sediments. All the bivariate plots illustrate the fluvial depositional environment for the sediments of the Katberg Formation. Petrographic studies based on the prepared 15 thin sections indicated that the Katberg Formation rocks are dominated by quartz, feldspar, and clay minerals. However, they show more plagioclase feldspar than k-feldspars. The grains are poorly sorted and immature, with irregular grain sizes and shapes. The angularity of clasts indicates that the grains have travelled shorter distances. The abundance of feldspar minerals suggests that the arkose sandstone was derived either from situ or from a short distance. The albitization of plagioclase to illite and the replacement of plagioclase feldspars by calcite and laumontite is very common in the Katberg Formation, which points out deep burial diagenesis. The XRD analysis revealed the occurrence of 14 minerals in the siliciclastic rocks of the Katberg Formation, namely: quartz, albite, clinochlore, muscovite, phlogopite, annite, illite, orthoclase, anorthoclase, laumontite, calcite, and ankerite. Amongst these minerals, albite, clinochlore, muscovite, and phlogopite show variation in crystal forms known as polymorphs. Geochemical analysis of the Katberg Formation sandstones and mudrocks revealed that all samples show a high concentration of SiO2, Al2O3, Fe2O3, K2O, Na2O, CaO, and MgO. The trace elements: TiO2, MnO, P2O5, BaO, SrO, ZrO2, and V2O5 are depleted with values ranging below 1 wt %. The geochemical classification of the Katberg Formation sandstones revealed the origin from wacke and arkose sources. The geochemical diagrams and indices of paleoweathering conditions suggested that the Katberg Formation underwent a moderate degree of chemical weathering. The geochemistry revealed that the sediments were 4 Final Submission of Thesis, Dissertation or Research Report/Project, Conference or Exam Paper deposited during the arid climate conditions. The studied sandstone and mudstone samples pointed an active continental margin and passive margin tectonic setting of the Katberg Formation.
- Full Text:
- Authors: Ndlazi, Nondumiso Zandile
- Date: 2020
- Subjects: Mineralogy|
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: http://hdl.handle.net/10353/18631 , vital:42615
- Description: The Katberg Formation forms the upper part of the Tarkastad Subgroup in the Beaufort Group of the main Karoo Supergroup. The Katberg Formation consists of siliciclastic sedimentary rocks mostly dominated by greyish sandstone, red mudstone with minor siltstone occurrences. The Katberg Formation also consists of calcareous and ferruginous concretions that formed during diagenesis. Braided streams deposited the Katberg Formation with a predominantly sand bed load. The Katberg Formation sandstones contain pebbles with no true conglomerates identified in the study area. This study was conducted in the Katberg Formation to understand the mineralogy, geochemistry, and pebble morphology around Graaff Reinet and East London areas. The major and trace elements were analyzed through X-Ray Fluorescence (XRF) to deduce the source rock provenance, tectonic setting, paleo-weathering conditions, climatic conditions, and sediment maturity. The X-Ray Diffraction (XRD) was used to highlight a detailed distribution and variation of mineralogical polymorphs of the minerals present in sandstones and mudstones. The pebble morphology was used to confirm the depositional environment of the Katberg Formation. The use of The bivariate plots of the Maximum Projection Sphericity Index (MPSI) and the Oblate-Prolate Index (OPI) showed that 79 % of pebbles fall in the fluvial environment, whereas 21 % of pebbles fall in the beach environment. A small proportion of beach pebbles within the Katberg Formation suggests that the river reached the marginal marine environment during its flow. The majority of the pebbles yielded a bladed shape with a dominating Sphericity Index symptomatic of fluvial sediments. All the bivariate plots illustrate the fluvial depositional environment for the sediments of the Katberg Formation. Petrographic studies based on the prepared 15 thin sections indicated that the Katberg Formation rocks are dominated by quartz, feldspar, and clay minerals. However, they show more plagioclase feldspar than k-feldspars. The grains are poorly sorted and immature, with irregular grain sizes and shapes. The angularity of clasts indicates that the grains have travelled shorter distances. The abundance of feldspar minerals suggests that the arkose sandstone was derived either from situ or from a short distance. The albitization of plagioclase to illite and the replacement of plagioclase feldspars by calcite and laumontite is very common in the Katberg Formation, which points out deep burial diagenesis. The XRD analysis revealed the occurrence of 14 minerals in the siliciclastic rocks of the Katberg Formation, namely: quartz, albite, clinochlore, muscovite, phlogopite, annite, illite, orthoclase, anorthoclase, laumontite, calcite, and ankerite. Amongst these minerals, albite, clinochlore, muscovite, and phlogopite show variation in crystal forms known as polymorphs. Geochemical analysis of the Katberg Formation sandstones and mudrocks revealed that all samples show a high concentration of SiO2, Al2O3, Fe2O3, K2O, Na2O, CaO, and MgO. The trace elements: TiO2, MnO, P2O5, BaO, SrO, ZrO2, and V2O5 are depleted with values ranging below 1 wt %. The geochemical classification of the Katberg Formation sandstones revealed the origin from wacke and arkose sources. The geochemical diagrams and indices of paleoweathering conditions suggested that the Katberg Formation underwent a moderate degree of chemical weathering. The geochemistry revealed that the sediments were 4 Final Submission of Thesis, Dissertation or Research Report/Project, Conference or Exam Paper deposited during the arid climate conditions. The studied sandstone and mudstone samples pointed an active continental margin and passive margin tectonic setting of the Katberg Formation.
- Full Text:
- «
- ‹
- 1
- ›
- »