Theses and Dissertations

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Browsing Theses and Dissertations by Author "Amponsah-Dacosta, F."

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    Assessment and management of environmental and socio-economic impacts of small-scale gold mining at Giyani Greenstone Belt
    (2017-09-18) Magodi, Rofhiwa; Amponsah-Dacosta, F.; Mhlongo, Emmanuel
    Artisanal and small-scale gold mining (ASGM) has devastating impacts on different parts of the environment and is a source of environmental degradation and contamination. ASGM degrades water resources, contaminate soil, sediments and water and lead to serious land degradation problems. ASGM activities are also associated with socio-economic issues such as child labour, prostitution and health and safety concerns. Insufficient understanding of the environmental and social problems of ASGM in Giyani Greenstone Belt has led to lack of mitigation strategies to reduce such problems. The main aim of this research was to assess and manage the environmental and socio-economic impacts of ASGM in Giyani Greenstone Belt. Remote sensing and GIS and Normalised Differential Vegetation Index were used to assess the effects of mining activities on vegetation cover. Assessment of the effects of ASGM on water, sediments and soil quality involved collection of samples in order to establish their physical and chemical properties. The concentration of toxic and trace metals were determined using Atomic Absorption Spectrometer (AAS) and X-ray Fluorescence (XRF) instruments. The pH meter was used to determine the pH level of the collected samples. Questionnaires, interviews and SPSS were used to assess socio-economic impacts of ASGM. The study culminated in devolvement of NDVI maps and this was used to assess the effects of ASGM on vegetation cover. Results showed that the mining activities in the area had caused extensive environmental degradation due to serious removal of vegetation cover in the site. ASGM had serious effects on soil, water and sediments quality such as environmental contamination by toxic and trace elements. Soil samples were found with high concentration of As, Cr, Cu, Ni, Pb and Zn as compared to the recommended South African Soil Quality and WHO threshold values for plants. It was found that Klein Letaba had high concentration of Ba, La, V, and Ce above the World Soil Averages for plants. Sediments were heavily contaminated with Cr, Ni, Pb, Zn, As and Ba as compared to the recommended standards prescribed by US EPA and WHO. The pH of water, soil and sediments samples collected from both mining sites were found to be strongly alkaline which affects the plants growth as well as aquatic flora and fauna. Socio-economic issues such as child labour, injuries, educational problems, health and safety issues, police disturbance, creation of jobs and income generation were identified at mine sites. ASGM had serious effect on vegetation cover through environmental degradation. ASGM also had serious environmental contamination by toxic and trace elements. ASGM had both positive and negative socio-economic issues at mining site which include employment opportunities, income generation, occupational health and safety, police disturbance and arrests and the use of child labour. Mine site rehabilitation is recommended in this study to reduce environmental degradation. The remediation of contaminated area by concentrated toxic and trace elements should be applied at both mining sites. ASGM should be legalised to enhance positive aspects of the mining such as increase in income generation and creation of more employment opportunities. However, there should be enforcement of mining policies to reduce social and environmental problems.
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    ItemOpen Access
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    An integrated approach of determining shale gas potentiality of carbonaceous shale of the Permian Tuli Basin, Limpopo Province of South Africa
    (2022-11-10) Akintola, George Oluwole; Amponsah-Dacosta, F.; Rupprecht, S. M.; Mhlongo, S. E.
    Shale gas displays signs of future potential for energy generation. Apart from the fluctuating prices of liquid fuel and energy resources, the recent national load shedding of electricity supply is probably the most obvious sign of the energy security crisis in South Africa. To expand energy security, there is a need for an energy mix to complement existing sources. Despite extensive studies on stratigraphic, sedimentology, and coal investigations, the source rock potential of organic-rich shale for gas generation remains elusive in the Permian Tuli Basin. As a result, this research aims to investigate the shale gas potentiality of the carbonaceous shale of Madzaringwe and Mikambeni Formations in the Tuli Basin of Limpopo Province, South Africa. A total of Twenty (20) representative core samples are selected to determine the whole rock major and trace elements using X-ray fluorescence (XRF) and Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) respectively. In addition to the mineralogical characterisation using X-ray diffraction (XRD), the functional groups of organic compounds in studied samples are identified using Fourier Transform Infrared Spectrometry (FTIR). Furthermore, the porosity networks of the shale samples are determined using the Scanning Electron Microscopy-Energy Dispersive X-Ray Analysis (SEM-EDX). Lastly, the total organic carbon content (TOC), Kerogen type and thermal maturity of the studied samples to generate hydrocarbon are determined using the Rock-Eval 6 programmed pyrolysis. The major oxides results indicate a varying amount of Al2O3 (19.37–20.32%), CaO (0.20-0.22%), Fe2O3 (0.85-0.94%), K2O (1.59-1.66%), MgO (0.25-0.28%), Na2O (0.12-0.15%), P2O5 (0.04%), SiO2 (50.37-51.90%), TiO2 (0.69-0.73%) in the studied Mikambeni samples. The compositional trend of other major components is comparable, except for the lower average value of loss-on-ignition (LOI), which averages 15.04% in the Madzaringwe shale, indicating a lower TOC content. The average LOI values of Mikambeni shales (25.02%) show a higher TOC content which correspond to the actual TOC test. The elemental ratio K2O / Al2O3 (0.08) of the studied samples showed values ≤ 0.5, which suggests a moderately mature shale since a significant amount of Al2O3 is typical of immature sediments. The LA-ICP-MS analysis reveals trace elements Ba (294.16-560.88 ppm), Zn (57.46-121.63 ppm), Zr (189.02–341.72 ppm), Rb (67.69-102.26 ppm), V (81.24-156.88 ppm), Sr (92.02-344.91ppm), Cr (47.50–86.66 ppm), Pb (11.25-35.22ppm) in all studied samples. The presence of Ba suggests the dissolution of mineral barite in the black shale by the action of sulphate-reducing bacteria while Zn indicates paleo-productivity of abundant organic matter. Furthermore, Mo concentration > 2.5ppm of Mikambeni, suggests a marine sediment input in the Mikambeni samples apart from terrigenous sources in all studied samples. The interpretation of the anoxic environment is consistent with the V/(V+Ni) average value of 0.84ppm which exceeds the 0.54 limit for anoxic conditions for all studied samples. The XRD analysis shows the presence of montmorillonite, mixed illite/smectite (I/S), illite, chlorite, and non-clay minerals such as dolomite, albite, microcline, pyrite, and quartz in the studied samples. The presence of pyrite suggests activities of sulphide-reducing bacteria on parent organic matters to generate biogenic gas. The presence of illite and chlorite suggests illitisation and chloritization at greater depths of Madzaringwe samples, suggesting a high thermal alteration level for sediments. The functional group of all studied samples shows infrared absorption peaks between 2800 and 3300cm-1 wavelength attributed to an aliphatic C-H stretching vibrations. The sp2 C-H hybridization found with absorption peak between 3000-3100 cm-1 wavelength indicates the aliphatic methane gas stretching of methyl and methylene vibration. Bubble-like porosity resulting from organic matter decomposition typifies most of the studied samples, suggesting a gaseous release from organic matters. However, isolated-irregular pattern of matrix-mineral pores are displayed apart from preferred-oriented linear pores exhibited by the micro-fracture pore types in all studied samples. The EDX elemental compositions indicate intragranular grains composed of quartz, feldspars, carbonate, and pyrite minerals to form interconnected matrix. Furthermore, a non-spherical, closely packed polyframboidal-pyrite is observed, having multiple presence of Fe contents on the EDX composition. Thus, this suggests an anaerobic condition that favours organic matter degradation that initiates methanogenesis. The Rock-Eval 6 programmed pyrolysis and TOC of the studied shale samples revealed a TOC content that exceeds threshold limit of 5.0 wt %, indicating an excellent source rock in both formations. The hydrocarbons produced from the thermal breakup of kerogen (S2) ranged from 101.64 to 122.75mg HC/grock with an average value of 115.7mg HC/g rock in the Mikambeni samples. The S2 content of Madzaringwe shale ranged from 15.25 to 16.47 mg HC/g rock averaging at 1.82 mg HC/g rock. The plot of Hydrogen Index (HI) against TOC indicates a mixed kerogen TYPE II-III for the Mikambeni samples and TYPE-III for the Madzaringwe samples, which is gas prone. The maximum temperature, Tmax, corresponding to the peak of hydrocarbon yield (S2) range between 430 to 434°C, averaging at 431.8°C thus indicating a thermally immature source in the Mikambeni samples. On the other hand, the Madzaringwe shale samples yield a thermally mature condensate wet-gas, with Tmax values (464 - 470°C) averaging at 467.2°C. The studied samples have an average Productivity Index (PI) value of 0.1 which indicates a moderately mature source, generating a mixed biogenic-thermogenic gas. As such, the petroliferous indicators of the studied Mikambeni shale generates thermal immature biogenic gas while Madzaringwe shale produces a matured condensate wet-gas in the Tuli Basin.