Electronic Theses and Dissertations (ETDs) - Items to be moved to 3. Electronic Theses and Dissertations (ETDs).
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Item A study of VCR multi-reef remnant extraction in the Carletonville area(2017) Esterhuyse, Johann ChristoffEven after years of mining, a vast gold resource remains in the Carletonville area of the Witwatersrand basin. Mining in this area nevertheless predates 1934 and the accessible ore-reserves on the primary reefs are being depleted. Mining of secondary reefs and remnants has therefore become important in recent years. Of particular interest is multi-reef mining as it will become much more prevalent in this part of the gold mining industry. Very little rock engineering research on multi-reef mining scenarios at great depth is available in the literature. Owing to the lack of proper understanding and guidelines for remnant selection and extraction in a multi-reef environment, a study was conducted by the author of this dissertation. The key references of earlier work are discussed in the literature survey. This study compared two displacement discontinuity boundary element codes, MINSIM and TEXAN, to simulate multi-reef environments. The preliminary analysis proved to be valuable and indicated that a small middling with a large overlap of mining is required to achieve a significant effect on ERR and average pillar stress on the remnant pillar. Care should be exercised with the so-called “45° rule” when destressing pillars and modelling is required in all cases. The study found that there is no significant difference between the results obtained from the two numerical modelling codes. To better understand the process of understoping, a simplified geometry of a pillar being understoped was investigated. An analysis of the incremental stress evolution in the middling between two reef horizons, as the pillar was being incrementally understoped, revealed valuable information. A zone of very high major principal stress and low minor principal stress develops between the two reefs. This indicates a high risk of violent shear failure between the two reefs. The reason for successful historic extractions of actual multi-reef remnants was therefore explored in more detail. As part of this analysis, an “extended” ERR concept introduced by Napier in 1991, was investigated. It was found that bedding planes and lithology played a crucial part in the stable dissipation of energy in these multi-reef remnant geometries. The study indicated that the stope convergence and the various energy components are affected by the presence, position and properties of a bedding plane. The energy solutions are very complex and sometimes counterintuitive. Care should be exercised when modelling specific cases. The modelling was nevertheless valuable to indicate that energy dissipated on weak layers, such as bedding planes, may reduce the risk of violent failure in a multi-reef mining scenario. This is an important novel contribution of this study. As a further step, actual multi-reef remnants were selected and back analysed to verify the hypothesis of weak layers being useful to make multi-reef mining less hazardous. Aspects such as seismic history, numerical modelling and photographic records were studied. From the analysis it was found that multi-reef extraction was successful in cases where a weak rock type was present in the immediate stratigraphy or where pertinent bedding planes were found. This supported the hypothesis as presented above. An important practical outcome of this study is that much greater emphasis needs to be placed on studying the rock mass surrounding multi-reef environments at depth to determine the risk of extraction in these conditions. This should be added to the list of remnant selection criteria.Item The appropriateness of the localised uniform conditioning technique for high-nugget Birimian-style gold deposits(2017) Maritz, EmmarentiaThe localized uniform conditioning (LUC) technique converts conventional Uniform Conditioning (UC) grade-tonnage curves into single grade values attached to each smallest mining unit (SMU). This is achieved by ranking the SMUs within a panel in increasing order of their grade based on the local grade patterns predicted by direct kriging of the SMUs. However, the quality of this localization process will depend heavily on the validity of the predicted grade patterns. A study was undertaken to determine how valid the predicted grade patterns of a typical Birimian-style gold deposit (with high nugget effect and strong short-range variability) might be expected to be. The direct SMU kriging rankings (based on sparse data) were compared with the grade control model ranking (based on close-spaced data and the best available estimate of the deposit). The results showed a satisfactory correlation and relationship between these rankings. It was concluded that the application of the LUC technique is still useful and appropriate for this style of deposit.Item Evaluation of mercury accumulation and biotransportation in wetland plants affected by gold mining and industrial activities(2017) Mbanga, OdwaSix different plant species that grow in a natural wetland impacted by old gold mining and other industrial activities were randomly selected with surface sediments. These included: Cyperus eragrostis (Nutgrass), Datura stramonium (Jimson weed), Melilotus alba (White sweetclover), Panicum coloratum (Blue panicgrass), Persicaria lapathifolia (Pale smartweed) and Phragmites australis (Common reed). These were used to investigate the levels of mercury in the wet and dry seasons, as well as to evaluate which of the species could be utilized for the remediation of mercury contaminated areas. The results obtained indicated that metal contamination could be determined from sediments and plant tissues. The pH values of the sediment samples were mostly neutral to slightly acidic and the redox potential was high in the wet season. On the other hand the dry season was characterised by very acidic and moderately oxidizing conditions. In summer all six plant species had higher concentration of HgT in sediments, whereas in winter the levels of HgT were elevated in the aerial tissues of the plants. The mercury accumulation patterns differed according to individual plant species and seasonality. Seasonal differences were significant but generally the MeHg concentrations in the wet season were higher in both surface sediments and plant tissues. Mercury methylation differed between species but concentration of MeHg was in general higher in plants with high concentration of mercury in sediments. The conversion of bioavailable HgT seemed more pronounced in tissues of the plants sampled in the wet season unlike those sampled in the dry season. Generally bioaccumulation factors were less than 1 in both the wet and dry seasons for all the plant species indicating that Hg was mainly retained in sediments. The translocation factor values were greater than 1 meaning metals were accumulated fundamentally in aboveground tissues for the plants D. stramonium, P. lapathifolia, P. coloratum and C. eragrostis in both the wet and dry seasons. The small bioaccumulation factors combined with translocation factor values greater than 1 were an indication that mercury present in the sediments was not the only source of mercury for the plant species growing in a contaminated environment. For P. australis the translocation of mercury was heavily influenced by seasonality, however this was not the case with M. alba. All the selected plant species demonstrated the capacity to grow in a heavily contaminated area, where P. australis and M. alba seemed to have developed an exclusion strategy to deal with toxic heavy metals therefore suitable for phytostabilisation. D. stramonium, P. lapathifolia, P. coloratum and C. eragrostis on the other hand exhibited characteristics of plants that can be successfully used for phytoextraction and phytovolatilization.Item Polygraph: a palimpsest pigment factory: a colour plant as a recording device for the sedimented scars on Johannesburg's mining landscape(2015-04-29) Vally, SumayyaThe mining that gave rise to Johannesburg as a city has left in its wake pieces of geologically disturbed, disused, and unusable land. These leftover fragments of landscape carry with them, not only memory of the city’s foundations, but scars of the mining processes that now render them unusable - Not only do these vaguescapes have potential for the memory within them to be unearthed, but they are highly polluted, and seek to be reimagined as productive city spaces. The chosen site, an abandoned piece of mineland with a concealed old mine shaft; on the edge of a highway on the fringe of the CBD, is simultaneously highly visible to the city, but forgotten to it. Its positioning is unique in that it allows for the potential for the extraction of the mine pollutants and site remediation to become a highly visible process. Understanding and uncovering layers and traces of the site as means of understanding what is possible on this highly polluted landscape became an important architectural and design generator. The architecture consolidates and reimagines the fragments of ruin, both physical and ephemeral, contained on the site, and curates the users experience through these forgotten traces. Its programme - a colour plant, which extracts useful metallic colour pigments from the contaminated earth, becomes a visceral reminder of these past traces ;and a recording device for the current consequences of past mining activity. The approach is an almost critical speculation. The age of the picturesque landscape is no more. Our effects on the land have depleted the earth and diseased its rhythms. But these unstable consequences hold possibilities that can be engaged with imaginatively; rather than merely re-mediated. How can architecture engage with this instability? The project accepts the presence of rising acid mine water; and imagines a new reality emerging from it. The project is a comment on our own epoch; one where waste, toxicity and radiation are so rife, that they are now a quiet, sinister backdrop to our world. More than an apocalyptic future, this project deals with a dystopian present. The precarious site conditions pose questions for an architecture which can engage with the instability, and not merely withstand it. The architectural concern is to render visible and intensify a consciousness of these traces, to investigate a palimpsest infrastructure. Colour, like architecture is a link between the conscious and the subconscious. It is a mediator between the realms. It holds possibilities for suggesting and molding atmospheres and perceptions. The architecture negotiates all the realms, concerned with past, present and future. It consolidates and makes apparent the traces but it is also developed with an awareness that it becomes part of these traces. It is an intervention which aims to heighten an awareness of the presence of the past in the life of the city; and also as palimpsest infrastructure; as a recording device for the geological happenings of the earth.Item A computer programme for the simulation of water reticulation systems in gold mines(2015-02-05) Holton, Mark CollinsThis report investigates the application of digital computer simulation models to the analysis and optimization of complex mine water reticulation systems- A simulation program is developed and documented, Guidelines in the construction and use of mine water models are applied in a case study of water quality and quantity aspects of Unisel Gold Mine.