Evaluation of groundwater potential using geological and geophysical methods in the University of Fort Hare Alice Campus, Eastern Cape Province of South Africa
- Adesola, Gbenga Olamide https://orcid.org/0000-0002-4151-5305
- Authors: Adesola, Gbenga Olamide https://orcid.org/0000-0002-4151-5305
- Date: 2022-04
- Subjects: Groundwater , Geology, Structural -- South Africa , Geographical Information Systems
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22490 , vital:52344
- Description: Geological and geophysical methods were used to evaluate the groundwater potential in University of Fort Hare (Alice campus), Eastern Cape Province of South Africa. Methodologies adopted for obtaining these results included a comprehensive literature review, thin section analysis, scanning electron microscopy, Geographical Information Systems (GIS), remote sensing and geophysical investigations (magnetic survey and vertical electrical sounding). The geology of the study area belongs to the Balfour Formation, which forms part of the Beaufort Group in the Karoo Supergroup. The rocks within the study area are composed majorly of sandstone and mudstone. Lineaments were automatically extracted using the PCI Geomatica 2018 software. Fifteen samples were collected at various locations within the study area and were analyzed using the petrographic microscope while others were analyzed with the Scanning Electron Microscopic (SEM) combined with an Energy dispersive x-ray spectrometry. The results show that the rocks are fractured, porous and contained minerals such as quartz, feldspar, calcite, mica and clay minerals. The occurrence of these fractures helps to improve the groundwater storage capacity in the study area. Out of the twenty seven (27) rock samples collected in the field, ten (10) rock samples were selected for densities (dry, wet and grain densities) and porosity measurements in the laboratory. The rocks density values range from 2.5763 – 2.6978 g/cm3. The average porosities of the rocks range from 0.85 – 2.56 percent. The density of the sandstone ranges from 2.5908 – 2.6820 g/cm3 whilst the porosity range from 0.85 – 2.02 percent. The density of the mudstone ranges from 2.5763 – 2.6978 g/cm3 whilst the porosity ranges from 1.84 – 2.56 percent. About 8458 magnetic measurements were taken at about 20 m spacing along linear and non-linear paths and road. A variety of magnetic maps were generated. Several magnetic highs were observed and the linear highs were interpreted to be due to dolerite dykes whilst the broader high zones were inferred to be due to dolerite sills. These Karoo dolerites intruded the sediments at various depths and must have fractured the sediments causing them to be more porous and permeable. The depth slices of magnetic data reveal that near surface magnetic bodies occur within the depth of approximately 19 m from the surface while deep seated ones occur as deep as 31 m and maybe deeper. The knowledge of the dolerite intrusions enabled the location of drilling targets for groundwater. Electrical resistivity data were collected at 28 sites using the Schlumberger array and a maximum cable length (250 m) from the centre point which achieved a maximum depth penetration of about 70 m to 162 m. The results from 1D modelling using WINRESIST software showed that the vertical electric sounding curves are composed of HA and HK curve-types, which show four geoelectric layers. The resistivity of the first layer which is the topmost layer has values ranging from 20 - 5752 Ωm and the thickness is between 0.4 – 1.8 m. The second layer which consists of clay, mudstone and sandstone has resistivity values varying from 3 - 51 Ωm and thickness varying from 0.8 – 17.5 m. The third layer which is interpreted to be the aquiferous layer of the study area is made up majorly of sandstone with resistivity that varies from 136 – 352 Ωm and thickness range from 9.9 – 143.9 m. The fourth layer of resistivity varying from 44 to 60428 Ωm is made up of mudstone and sandstone, which are in some places intruded by dolerites. Groundwater potential is favourably high in some of the areas investigated. Furthermore, the results of the research indicated that secondary porosity is the main porosity for the reservoir rocks in the study area. , Thesis (MSc) -- Faculty of Science and Agriculture, 2022
- Full Text:
- Authors: Adesola, Gbenga Olamide https://orcid.org/0000-0002-4151-5305
- Date: 2022-04
- Subjects: Groundwater , Geology, Structural -- South Africa , Geographical Information Systems
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22490 , vital:52344
- Description: Geological and geophysical methods were used to evaluate the groundwater potential in University of Fort Hare (Alice campus), Eastern Cape Province of South Africa. Methodologies adopted for obtaining these results included a comprehensive literature review, thin section analysis, scanning electron microscopy, Geographical Information Systems (GIS), remote sensing and geophysical investigations (magnetic survey and vertical electrical sounding). The geology of the study area belongs to the Balfour Formation, which forms part of the Beaufort Group in the Karoo Supergroup. The rocks within the study area are composed majorly of sandstone and mudstone. Lineaments were automatically extracted using the PCI Geomatica 2018 software. Fifteen samples were collected at various locations within the study area and were analyzed using the petrographic microscope while others were analyzed with the Scanning Electron Microscopic (SEM) combined with an Energy dispersive x-ray spectrometry. The results show that the rocks are fractured, porous and contained minerals such as quartz, feldspar, calcite, mica and clay minerals. The occurrence of these fractures helps to improve the groundwater storage capacity in the study area. Out of the twenty seven (27) rock samples collected in the field, ten (10) rock samples were selected for densities (dry, wet and grain densities) and porosity measurements in the laboratory. The rocks density values range from 2.5763 – 2.6978 g/cm3. The average porosities of the rocks range from 0.85 – 2.56 percent. The density of the sandstone ranges from 2.5908 – 2.6820 g/cm3 whilst the porosity range from 0.85 – 2.02 percent. The density of the mudstone ranges from 2.5763 – 2.6978 g/cm3 whilst the porosity ranges from 1.84 – 2.56 percent. About 8458 magnetic measurements were taken at about 20 m spacing along linear and non-linear paths and road. A variety of magnetic maps were generated. Several magnetic highs were observed and the linear highs were interpreted to be due to dolerite dykes whilst the broader high zones were inferred to be due to dolerite sills. These Karoo dolerites intruded the sediments at various depths and must have fractured the sediments causing them to be more porous and permeable. The depth slices of magnetic data reveal that near surface magnetic bodies occur within the depth of approximately 19 m from the surface while deep seated ones occur as deep as 31 m and maybe deeper. The knowledge of the dolerite intrusions enabled the location of drilling targets for groundwater. Electrical resistivity data were collected at 28 sites using the Schlumberger array and a maximum cable length (250 m) from the centre point which achieved a maximum depth penetration of about 70 m to 162 m. The results from 1D modelling using WINRESIST software showed that the vertical electric sounding curves are composed of HA and HK curve-types, which show four geoelectric layers. The resistivity of the first layer which is the topmost layer has values ranging from 20 - 5752 Ωm and the thickness is between 0.4 – 1.8 m. The second layer which consists of clay, mudstone and sandstone has resistivity values varying from 3 - 51 Ωm and thickness varying from 0.8 – 17.5 m. The third layer which is interpreted to be the aquiferous layer of the study area is made up majorly of sandstone with resistivity that varies from 136 – 352 Ωm and thickness range from 9.9 – 143.9 m. The fourth layer of resistivity varying from 44 to 60428 Ωm is made up of mudstone and sandstone, which are in some places intruded by dolerites. Groundwater potential is favourably high in some of the areas investigated. Furthermore, the results of the research indicated that secondary porosity is the main porosity for the reservoir rocks in the study area. , Thesis (MSc) -- Faculty of Science and Agriculture, 2022
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The investigation of groundwater potential zones in the Neotectonic area of Ntabankulu Local Municipality, Eastern Cape Province, South Africa
- Nonkula, Zenande https://orcid.org/0000-0002-3858-7703
- Authors: Nonkula, Zenande https://orcid.org/0000-0002-3858-7703
- Date: 2021-09
- Subjects: Groundwater , Water-supply , Neotectonics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22875 , vital:53068
- Description: Ntabankulu extends from latitude 30° 51' 09"S to 31° 09' 10" S and from longitude 29° 06' 51"E to 29° 23' 49"E in the Eastern Cape Province of South Africa. Ntabankulu Local Municipality has 141 villages with 125 976 population size. About 36% of villages do not have water sources, 38% have partial functional water sources, 6% have non-functional water sources, and 20 % have reliable water sources, primarily rivers (Mnceba, Caba and Mzimvubu). Water is scarce in this area, especially in the dry season when perennial rivers and springs become dry. This research investigates groundwater potential zones and identifies suitable aquifers that can be developed to augment the water resources. The study involved: literature review, remote sensing, borehole and springs data, geological, petrographic and geophysical (gravity, magnetic and electrical resistivity) analyses. Each method has its purpose in finding the potential groundwater zones. Ntabankulu Local Municipality is located on the Karoo Supergroup in Ecca and Beaufort Group, Adelaide Subgroup and Balfour Formation. During field analysis, it was observed that this area consists of sandstone, shale and dolerite sills, dykes and complex rings. Fining up sequences, massive bedding, concretions, and spheroidal weathering were observed in sandstone, shale, and dolerite, respectively. Groundwater seepages are found within these structures. Sandstones are yellow due to the presence of limonite because of the continuous seepage. Red coloured laminated shale reflects that the rock has an iron oxidation state with hematite (Fe2O3) on the sediments. The Geographical Information Systems (GIS) method was used to extract lineaments. Lineaments dominate Ntabankulu with an NW-SE direction. Some of the lineaments are due to Karoo igneous intrusions, and others are due to neotectonic activities. Ntabankulu is located on the eastern and northern neotectonic belts. Geological maps and lineament maps were compared; it was observed that sandstones and shales are found on high liinament density areas. High yielding boreholes and springs coincide with lineaments, and some lineaments are faults. Hence areas that have high lineaments density could be groundwater potential zones. There are geological structures (faults, joints, and fractures) that are present. Systematic and non-systematic joints are found on sandstones which are due to extensional stress. These joints have been reactivated and acted as strike-slip faults. All these geological structures increase the porosity and permeability of the rocks. It was observed that the area of Ntabankulu consists of coarse-grained and medium-grained sandstone with quartz and orthoclase minerals. Dolerite consists of labradorite, clinopyroxene, olivine, oxide minerals with twinning formed during cooling and magma crystallisation. The gravity and magnetic methods were used to study the subsurface rock density contrasts and susceptibilities, respectively. The gravity and magnetic maps were generated in Geosoft Oasis 8.3 software. High gravity zones coincide with some of the mapped Karoo intrusions. Unmapped dolerite intrusions, lineaments and faults were inferred. The magnetic method delineated the subsurface structures (lineaments and faults), which are known to control groundwater accumulation. These structures and inferred dolerite intrusions helped in identifying groundwater potential zones. Groundwater potential zones were inferred in sedimentary rocks between dolerite intrusions and areas where sills and dykes intersect. A total of six vertical electrical soundings (VES) were conducted at Mzalwaneni and Tabankulu town areas using the Schlumberger configuration array with a maximum penetration depth of about 25- 33 m. The VES data were modelled in Winresist and Surfer 9 software to obtain 1D models and geoelectric sections, respectively. These 1D models have three layers with response curves of H-type. The top layer is about 0.4 - 0.7 m thick, with resistivity values from 12.3 – 1885.9 Ωm and is topsoil (sand and clay). The second layer of thickness 5.2 – 13.3 m has low resistivity values from 23.1- 44.9 Ωm. This layer is interpreted to be fractured shales and sandstones possibly containing water. The third layer of high resistivity values of 145.9 – 727.4 Ωm is inferred to be sandstone. The simultaneous interpretation of resistivity and normalised chargeability revealed that groundwater potential zones are characterised by low resistivity values and low normalised chargeability values for layers from 0.7 - 13.3 m depth. The groundwatwer in the area of Ntabankulu can be found on unconfined aquifers. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Authors: Nonkula, Zenande https://orcid.org/0000-0002-3858-7703
- Date: 2021-09
- Subjects: Groundwater , Water-supply , Neotectonics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22875 , vital:53068
- Description: Ntabankulu extends from latitude 30° 51' 09"S to 31° 09' 10" S and from longitude 29° 06' 51"E to 29° 23' 49"E in the Eastern Cape Province of South Africa. Ntabankulu Local Municipality has 141 villages with 125 976 population size. About 36% of villages do not have water sources, 38% have partial functional water sources, 6% have non-functional water sources, and 20 % have reliable water sources, primarily rivers (Mnceba, Caba and Mzimvubu). Water is scarce in this area, especially in the dry season when perennial rivers and springs become dry. This research investigates groundwater potential zones and identifies suitable aquifers that can be developed to augment the water resources. The study involved: literature review, remote sensing, borehole and springs data, geological, petrographic and geophysical (gravity, magnetic and electrical resistivity) analyses. Each method has its purpose in finding the potential groundwater zones. Ntabankulu Local Municipality is located on the Karoo Supergroup in Ecca and Beaufort Group, Adelaide Subgroup and Balfour Formation. During field analysis, it was observed that this area consists of sandstone, shale and dolerite sills, dykes and complex rings. Fining up sequences, massive bedding, concretions, and spheroidal weathering were observed in sandstone, shale, and dolerite, respectively. Groundwater seepages are found within these structures. Sandstones are yellow due to the presence of limonite because of the continuous seepage. Red coloured laminated shale reflects that the rock has an iron oxidation state with hematite (Fe2O3) on the sediments. The Geographical Information Systems (GIS) method was used to extract lineaments. Lineaments dominate Ntabankulu with an NW-SE direction. Some of the lineaments are due to Karoo igneous intrusions, and others are due to neotectonic activities. Ntabankulu is located on the eastern and northern neotectonic belts. Geological maps and lineament maps were compared; it was observed that sandstones and shales are found on high liinament density areas. High yielding boreholes and springs coincide with lineaments, and some lineaments are faults. Hence areas that have high lineaments density could be groundwater potential zones. There are geological structures (faults, joints, and fractures) that are present. Systematic and non-systematic joints are found on sandstones which are due to extensional stress. These joints have been reactivated and acted as strike-slip faults. All these geological structures increase the porosity and permeability of the rocks. It was observed that the area of Ntabankulu consists of coarse-grained and medium-grained sandstone with quartz and orthoclase minerals. Dolerite consists of labradorite, clinopyroxene, olivine, oxide minerals with twinning formed during cooling and magma crystallisation. The gravity and magnetic methods were used to study the subsurface rock density contrasts and susceptibilities, respectively. The gravity and magnetic maps were generated in Geosoft Oasis 8.3 software. High gravity zones coincide with some of the mapped Karoo intrusions. Unmapped dolerite intrusions, lineaments and faults were inferred. The magnetic method delineated the subsurface structures (lineaments and faults), which are known to control groundwater accumulation. These structures and inferred dolerite intrusions helped in identifying groundwater potential zones. Groundwater potential zones were inferred in sedimentary rocks between dolerite intrusions and areas where sills and dykes intersect. A total of six vertical electrical soundings (VES) were conducted at Mzalwaneni and Tabankulu town areas using the Schlumberger configuration array with a maximum penetration depth of about 25- 33 m. The VES data were modelled in Winresist and Surfer 9 software to obtain 1D models and geoelectric sections, respectively. These 1D models have three layers with response curves of H-type. The top layer is about 0.4 - 0.7 m thick, with resistivity values from 12.3 – 1885.9 Ωm and is topsoil (sand and clay). The second layer of thickness 5.2 – 13.3 m has low resistivity values from 23.1- 44.9 Ωm. This layer is interpreted to be fractured shales and sandstones possibly containing water. The third layer of high resistivity values of 145.9 – 727.4 Ωm is inferred to be sandstone. The simultaneous interpretation of resistivity and normalised chargeability revealed that groundwater potential zones are characterised by low resistivity values and low normalised chargeability values for layers from 0.7 - 13.3 m depth. The groundwatwer in the area of Ntabankulu can be found on unconfined aquifers. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
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Characterization of sandstone reservoirs and hydrocarbon generation potential of selected four wells in the Pletmos basin, offshore South Africa
- Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Authors: Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Date: 2021-06
- Subjects: Hydrocarbon reservoirs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22512 , vital:52387
- Description: This study focused on the use of data from four wells (Ga-M1, Ga-S1, Ga-Z1, and Gb-J1) comprises of the Late Jurassic to Early Cretaceous shallow marine clastic sandstones consisting of wildcat wells located in Block 11 of the Pletmos Basin, a sub-basin of the Southern Outeniqua Basin, south offshore South Africa. This research evaluates the hydrocarbon potential in the Pletmos Basin by integrating core and well log data to characterize the source and reservoir rock potential. The methods implemented consist of a mineralogical and petrological analysis of about 300 thin section slides from four wells were studied. Stratigraphic profile computation from core logging, geochemistry analysis focusing on total organic carbon (TOC), geophysical wireline logs, conventional core analysis, geological well reports, and petrophysical analysis (water saturation, porosity, permeability, and volume of clay) were done using Interactive Petrophysics software. The different datasets were used to delineate how the mineralogy, total organic carbon content, poro-perm properties, fluid saturation, and volume of clay impact the hydrocarbon production potential. The evaluated sandstones have depths ranging from 2523.9 m to 3397.2 m with varying thickness depending on the position of the well. The results indicate that the study area consists of shallow marine clastic sandstones with sparse siltstones and mudstone that are fine-grained to silty in texture. The sedimentary sequence is characterized by moderate to intense bioturbation. Depositional environment was in a reducing condition indicated by plenty of glauconites. The tight fine-grained sandstones have low porosity values ranging from 4.5% to 13.8% in the selected intervals. The low porosity values may have been caused by the quartz cement that is observed from the thin sections. Low permeability values ranging from 0 mD to 0.16 mD are present throughout the studied wells caused by calcite cement and clay matrix. Source rock in the studied wells have inferior TOC values ranging from 0.31 wt% to 0.51 wt%. The van Krevelen indicates that the analysed samples have very low hydrogen index (HI) values and are consistent with Type III Kerogen (gas prone). A total of six reservoirs were identified. For well Ga-M1, one reservoir interval (2988.2 m – 30281 m) was selected and is located at BCII formation and was classified as a nonproducing reservoir due to its high water saturation content of 94.2%, even though it has an average porosity of 10.6%. Two reservoirs were selected for well Ga-S1, reservoir one (3026.3 m – 3107.7 m) is located within the 13AT1 formation and was classified as a producing reservoir with an average porosity of 11.9%, water saturation of 38.3%, and volume of clay of 29.5%. Reservoir 2 (3380.7 m – 3397.2 m) and the reservoirs (2970.20 m – 2993.0 m and 3006.80 m – 3049.50 m) from well Ga-Z1 located between the 9AT1 – BCVI formations were classified as non-reservoirs. One selected reservoir from well Gb-J1 had promising gas shows with an average porosity of 19%, water saturation value of 34.8%, and volume of shale of 33.1%. However, well Ga-S1 has a large interval with hydrocarbon potential compared to the well Gb-J1. Results indicate that the absence of hydrocarbon accumulation may result from non-effective seals due to the silty texture of the reservoir sandstones. Also, the presence of calcareous cement, clay minerals, and the argillaceous matrix reduce the porosity and permeability characteristics. To better understand the hydrocarbon potential of the Pletmos Basin, 3D seismic data is recommended to perform seismic well tie analysis for correlation between well log and seismic data to understand the basin‟s potential better. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Authors: Moloi, Busiswa https://orcid.org/0000-0001-6815-4901
- Date: 2021-06
- Subjects: Hydrocarbon reservoirs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22512 , vital:52387
- Description: This study focused on the use of data from four wells (Ga-M1, Ga-S1, Ga-Z1, and Gb-J1) comprises of the Late Jurassic to Early Cretaceous shallow marine clastic sandstones consisting of wildcat wells located in Block 11 of the Pletmos Basin, a sub-basin of the Southern Outeniqua Basin, south offshore South Africa. This research evaluates the hydrocarbon potential in the Pletmos Basin by integrating core and well log data to characterize the source and reservoir rock potential. The methods implemented consist of a mineralogical and petrological analysis of about 300 thin section slides from four wells were studied. Stratigraphic profile computation from core logging, geochemistry analysis focusing on total organic carbon (TOC), geophysical wireline logs, conventional core analysis, geological well reports, and petrophysical analysis (water saturation, porosity, permeability, and volume of clay) were done using Interactive Petrophysics software. The different datasets were used to delineate how the mineralogy, total organic carbon content, poro-perm properties, fluid saturation, and volume of clay impact the hydrocarbon production potential. The evaluated sandstones have depths ranging from 2523.9 m to 3397.2 m with varying thickness depending on the position of the well. The results indicate that the study area consists of shallow marine clastic sandstones with sparse siltstones and mudstone that are fine-grained to silty in texture. The sedimentary sequence is characterized by moderate to intense bioturbation. Depositional environment was in a reducing condition indicated by plenty of glauconites. The tight fine-grained sandstones have low porosity values ranging from 4.5% to 13.8% in the selected intervals. The low porosity values may have been caused by the quartz cement that is observed from the thin sections. Low permeability values ranging from 0 mD to 0.16 mD are present throughout the studied wells caused by calcite cement and clay matrix. Source rock in the studied wells have inferior TOC values ranging from 0.31 wt% to 0.51 wt%. The van Krevelen indicates that the analysed samples have very low hydrogen index (HI) values and are consistent with Type III Kerogen (gas prone). A total of six reservoirs were identified. For well Ga-M1, one reservoir interval (2988.2 m – 30281 m) was selected and is located at BCII formation and was classified as a nonproducing reservoir due to its high water saturation content of 94.2%, even though it has an average porosity of 10.6%. Two reservoirs were selected for well Ga-S1, reservoir one (3026.3 m – 3107.7 m) is located within the 13AT1 formation and was classified as a producing reservoir with an average porosity of 11.9%, water saturation of 38.3%, and volume of clay of 29.5%. Reservoir 2 (3380.7 m – 3397.2 m) and the reservoirs (2970.20 m – 2993.0 m and 3006.80 m – 3049.50 m) from well Ga-Z1 located between the 9AT1 – BCVI formations were classified as non-reservoirs. One selected reservoir from well Gb-J1 had promising gas shows with an average porosity of 19%, water saturation value of 34.8%, and volume of shale of 33.1%. However, well Ga-S1 has a large interval with hydrocarbon potential compared to the well Gb-J1. Results indicate that the absence of hydrocarbon accumulation may result from non-effective seals due to the silty texture of the reservoir sandstones. Also, the presence of calcareous cement, clay minerals, and the argillaceous matrix reduce the porosity and permeability characteristics. To better understand the hydrocarbon potential of the Pletmos Basin, 3D seismic data is recommended to perform seismic well tie analysis for correlation between well log and seismic data to understand the basin‟s potential better. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
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Application of geophysical methods to investigate the subsurface geology of Kuruman and Kono areas in Griqualand West Basin, South Africa
- Authors: Mthintweni, Sylvia Lwandisa
- Date: 2021-05
- Subjects: Geology , Soil surveys--Geophysical methods
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22555 , vital:52456
- Description: Kono and Kuruman areas belong to the geology of the Campbell Rand and Asbestos Hills Subgroups, Ghaap Group in the Griqualand West Basin. Campbell Rand Subgroup comprises interbedded chert, limestone and dolomite rocks of dominantly the Kogelbeen Formation covered with a thick regolith of red sand and weathered material. The Asbestos Hills Subgroup consists of a banded iron formation (BIF) of the Kuruman Formation overlain by the Kalahari sands. Petrographic and mineralogical analyses and various geophysical methods were utilised to investigate the surface and subsurface conditions of the study areas. This study was done to characterize and understand the geology of Kuruman and Kono and identify the structural lineaments. Rock samples of varying lithology were collected in the field for laboratory analyses that include preparation of thin sections and petrographic analyses and density and porosity determinations. Both the petrographic results and XRF analyses revealed that iron oxide (Fe2O3) and silica (SiO2) are the most abundant minerals in BIF. Iron oxide and silica percentages range between 21.17-39.97 wt % and 59.03-78.01 wt %, respectively. BIF has an average density of 3.0 g/cm3 and porosity of 2.51% and dolomite has an average density of 2.8 g/cm3 and porosity of 0.17%. The Bouguer anomaly values range between - 119.00 mGal and -1 17.29 mGals. High gravity anomalies are attributed to shallow fresh bedrock and this was confirmed by the seismic line that cuts across the map. The gravity high observed in the Kuruman profile coincides with the thick BIF body observed in the field. The gravity analytic signal indicates a width of about 1125 m for the BIF and inferred two normal faults at about 675 m and 1500 m. The high magnetic anomalies in the ground magnetic map correspond to chert rich dolomite ridges in the field and the intermediate to lows correspond to dolomitic terrains. A geological map was superimposed on an aeromagnetic map to correlate the two. The linear magnetic high trending from NW – SE coincide with BIF. Older dykes trending east-west were intruded by younger dykes trending north-south. The total counts channel map for Kono area shows the measured total gamma radiation count in the study area and the concentrations of radioelements range between 51.84 and 94.64 counts/sec. The concentrations of potassium, thorium and uranium range from 0.12 – 0.51%, 0.83 – 5.23 ppm and 0.06 – 2.27 ppm, respectively. A high concentration of radiometric elements cutting through the central part of the map stretching from northwest to southeast was observed in a ternary map and this could be associated with chert rich dolomite outcrops. Seismic refraction tomography (SRT) cross-section for study area 1 in Kono revealed 3 different layers. The topmost layer comprises sand and loose material and has a velocity ranging from 614 – 1194 m/s. It is underlain by highly to slightly weathered dolomite with a velocity that ranges from 1774 – 2354 m/s. Layer 3 is the fresh bedrock dolomite and has a velocity of 2934 m/s. Three layers were observed in study area 2 for Kuruman. Layer 1 had a velocity of 300 – 750 m/s, the second layer had a velocity of 1200 – 2100 m/s and the bottom layer’s velocity was 2500 – 2999 m/s. An inferred fault is indicated on the western side of the seismic section at about 650 m. The dipole-dipole resistivity model for the main survey line in Kono revealed that the area is underlain by fractured bedrock with high resistivity in places. A thick conductive stratum was observed at the beginning of the line. The resistivity models for the sinkhole in Kono were characterized into three resistivity zones. High resistivity values (1000 – 134202 Ωm) are due to slightly weathered to fresh bedrock, intermediate values (24 – 5770 Ωm) are interpreted to be due to highly weathered dolomite and compacted dolomitic soils and very low resistivity zones (4 – 397 Ωm) are inferred to be karstic cavities. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Authors: Mthintweni, Sylvia Lwandisa
- Date: 2021-05
- Subjects: Geology , Soil surveys--Geophysical methods
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22555 , vital:52456
- Description: Kono and Kuruman areas belong to the geology of the Campbell Rand and Asbestos Hills Subgroups, Ghaap Group in the Griqualand West Basin. Campbell Rand Subgroup comprises interbedded chert, limestone and dolomite rocks of dominantly the Kogelbeen Formation covered with a thick regolith of red sand and weathered material. The Asbestos Hills Subgroup consists of a banded iron formation (BIF) of the Kuruman Formation overlain by the Kalahari sands. Petrographic and mineralogical analyses and various geophysical methods were utilised to investigate the surface and subsurface conditions of the study areas. This study was done to characterize and understand the geology of Kuruman and Kono and identify the structural lineaments. Rock samples of varying lithology were collected in the field for laboratory analyses that include preparation of thin sections and petrographic analyses and density and porosity determinations. Both the petrographic results and XRF analyses revealed that iron oxide (Fe2O3) and silica (SiO2) are the most abundant minerals in BIF. Iron oxide and silica percentages range between 21.17-39.97 wt % and 59.03-78.01 wt %, respectively. BIF has an average density of 3.0 g/cm3 and porosity of 2.51% and dolomite has an average density of 2.8 g/cm3 and porosity of 0.17%. The Bouguer anomaly values range between - 119.00 mGal and -1 17.29 mGals. High gravity anomalies are attributed to shallow fresh bedrock and this was confirmed by the seismic line that cuts across the map. The gravity high observed in the Kuruman profile coincides with the thick BIF body observed in the field. The gravity analytic signal indicates a width of about 1125 m for the BIF and inferred two normal faults at about 675 m and 1500 m. The high magnetic anomalies in the ground magnetic map correspond to chert rich dolomite ridges in the field and the intermediate to lows correspond to dolomitic terrains. A geological map was superimposed on an aeromagnetic map to correlate the two. The linear magnetic high trending from NW – SE coincide with BIF. Older dykes trending east-west were intruded by younger dykes trending north-south. The total counts channel map for Kono area shows the measured total gamma radiation count in the study area and the concentrations of radioelements range between 51.84 and 94.64 counts/sec. The concentrations of potassium, thorium and uranium range from 0.12 – 0.51%, 0.83 – 5.23 ppm and 0.06 – 2.27 ppm, respectively. A high concentration of radiometric elements cutting through the central part of the map stretching from northwest to southeast was observed in a ternary map and this could be associated with chert rich dolomite outcrops. Seismic refraction tomography (SRT) cross-section for study area 1 in Kono revealed 3 different layers. The topmost layer comprises sand and loose material and has a velocity ranging from 614 – 1194 m/s. It is underlain by highly to slightly weathered dolomite with a velocity that ranges from 1774 – 2354 m/s. Layer 3 is the fresh bedrock dolomite and has a velocity of 2934 m/s. Three layers were observed in study area 2 for Kuruman. Layer 1 had a velocity of 300 – 750 m/s, the second layer had a velocity of 1200 – 2100 m/s and the bottom layer’s velocity was 2500 – 2999 m/s. An inferred fault is indicated on the western side of the seismic section at about 650 m. The dipole-dipole resistivity model for the main survey line in Kono revealed that the area is underlain by fractured bedrock with high resistivity in places. A thick conductive stratum was observed at the beginning of the line. The resistivity models for the sinkhole in Kono were characterized into three resistivity zones. High resistivity values (1000 – 134202 Ωm) are due to slightly weathered to fresh bedrock, intermediate values (24 – 5770 Ωm) are interpreted to be due to highly weathered dolomite and compacted dolomitic soils and very low resistivity zones (4 – 397 Ωm) are inferred to be karstic cavities. , Thesis (MSc) -- Faculty of Science and Agriculture, 2021
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