Dissertations / Theses on the topic 'Dolomite - South Africa'

Includes bibliographical references.
Sinkholes encompass the withdrawal of shallow sediment into deep hollow compartments located in karstic stratum. These subsequent surface openings associated with karst geology have inhibited multiple infrastructure developments. Sinkholes are triggered by the alteration of the existing groundwater level which erodes weathered altered dolomite (WAD) residuum into karst cavities. Substantial literature has explored the stability of sinkholes, with reliance on limit analysis and empirical data, to quantify the strength of the porous karst residuum. In this study, the appraisal of sinkhole propagation was facilitated with the geological data acquired along the Gautrain route through Centurion, South Africa. Sinkhole development was analysed through analytical theories and the application of numerical methods. The analytical study conceptualized the ‘angle of draw’ of dolomite overburden layers into cavities, with Terzaghi’s arching in soil equation. The analytical results illustrated constant vertical drawdown in the WAD and incremental cavity propagation in the frictional chert residuum.

Dolomitic land is known for subsidence and sinkhole formation, making development such as housing unsafe, especially when wad is found. Wad and residual dolomite are usually found at the bedrock-soil interface and in grykes, in an unsaturated, non- to highly-reworked, state. These are critical areas for ground stability of a dolomite site (Buttrick, 1986). This research aims to better understand the geotechnical properties and hydrological behaviour of unsaturated wad and residual dolomite in relation to the grading, fabric and geochemical composition and the microstructure of the particles of the material, and how the reworking processes alter these characteristic properties. The fabric of the residuum is inherent to the structure of the parent rock, which is determined by the stress history of the rock. The fabric influences the unsaturated behavioural characteristics and water holding capacity of the material. The high and variable liquid limits is dependent on the overall fine grading, and the nanoparticle structure and large reactive surfaces exhibited by the metal oxides in the material. The residuum is typically non-dispersive, possess a low density, when not reworked, that can be below that of water, mostly grades in the silt fraction and has hydraulic conductivities in the order of 1x10-6 m/s. The mobilisation potential is dependent on the presence of the fabric, variance of sorting of the material’s grain sizes and the disparity of the degree of saturation above and below the wetting front moving through the material. The material is considered reworked when mechanical processes destroy the structured or nonstructured inherent fabric and foreign material is introduced into the soil matrix. The factors influencing the consequential broad potential behavioural and characteristic properties of the material are the type and degree of reworking and the environment of reworking.
Dissertation (MSc)--University of Pretoria, 2019.
Geology
MSc
Unrestricted

Masters of Science
This study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Heuningnes Catchment. The role or influence of hydrogeochemical processes in groundwater quality in aquifer systems remains poorly understood. One of the ways of improving such understanding is to employ different techniques to explore key processes that govern groundwater quality in aquifer systems. Therefore, the present study investigated hydrogeochemical processes of groundwater resources and identified key processes that explained its quality from a spatiotemporal perspective. The quantitative approach that provides the ability to assess relationships between variables both spatially and temporally was applied. Groundwater sampling was done on four occasions during July 2017, October 2017, March 2018, and July 2018. Identification of hydrogeochemical processes controlling the evolution of groundwater chemistry and quality was done using various complementary tools. These tools included classification of the main water types, evaluation of water-rock interaction by means of stoichiometry analysis and bivariate correlation plots, inverse geochemical modelling, and statistical analysis (hierarchical cluster analysis and factor analysis). Physical parameters were measured in situ, while water samples were collected from boreholes, piezometers, springs, and artesian boreholes for laboratory analysis for major ions analysis. Descriptive and bivariate statistical methods were used to summarise and evaluate the strength of the relationship between variables, while multivariate statistical methods were applied to group similar samples based on their chemical compositions. Tri linear Piper diagrams were generated to characterize water type based on double normalizing the proportions of cations and anions, while correlation and stoichiometric analysis were applied to identify hydrogeochemical processes influencing groundwater chemistry. The results generated from the trilinear Piper diagrams confirmed the dominance of sodium and chloride ions in waters of the Heuningnes Catchment. Groundwater of a Na/Cl type is typical for a coastal aquifer characterised by saline, deep ancient groundwater. The lower parts of the Catchment were characterised by saline groundwater. The results indicated that shallow groundwater samples within the study area were more mineralised as compared to deep groundwater with EC values ranging between 20.8 and 2990 mS/m, with waters within the Table Mountain Group region (TMG), recording the lowest values. Deep groundwater for boreholes and artesian boreholes located upstream in the Catchment was fresh and yielded some of the lowest EC values recorded with an EC value below 50 mS/m. Generally, EC values increased from the upper TMG region of the Catchment towards the Bokkeveld shale region downstream and were highest during the dry season of 2018. The results indicated strong geological influences on water chemistry. Bivariate correlation and stoichiometric analysis identified cation exchange, adsorption, evaporation, weathering of carbonates, sulphates and silicate minerals as processes influencing the chemistry of groundwater in the Heuningnes Catchment. The Saturation Index (SI) results showed a change of calcite, dolomite, aragonite, gypsum, anhydrite, halite, melantinterite, siderite and sylvite from being undersaturated to oversaturated at some areas for the different seasons along the flow path. The mass-balance modelling results indicated that ion exchange and reverse ion exchange processes were more dominant at low elevations along the same flow path during the dry periods. However, at high elevations along the flow path, silicate weathering was the dominant process taking place. The findings of this study demonstrated the influence of hydrogeochemical processes in changing the water chemistry along the flow paths. In conclusion, the study showed the value of utilising various assessment tools as complementary techniques to improve the understanding about hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality. Based on the findings of the study the following recommendations were made for future studies; the sample points or sample boreholes in the study Catchment should be increased; and to have more sampling trips to enable better comparison between the possible processes

The Gautrain Rapid Rail Link is a state-of-the-art rail route and one of the ten Spatial Development Initiatives planned in Gauteng Province, South Africa. The route comprises two links, namely a link between Tshwane (Pretoria) and Johannesburg and a link between OR Tambo International Airport and Sandton. A total of 10 stations are linked by approximately 80 kilometres of rail along the proposed route. Between Johannesburg and Pretoria in the southern Tshwane region, the rail alignment is underlain by dolomite bedrock for approximately 15km in the vicinity of Centurion between Nelmapius Drive and The Fountains, including nearly 6km elevated on a viaduct. The stability of the rapid rail link constructed over the dolomitic sections was considered a major project risk due to its proneness to sinkholes and subsidences along this route. Construction on heterogeneous soils, pinnacled bedrock and other geohazards posed major challenges to the construction team. To facilitate detailed design and adapt proper foundation options for the viaducts founded over the dolomitic terrain, rigorous and comprehensive ground investigations were conducted by the Bombela Civils Joint Venture (BCJV). This work presents the different ground investigation methods used and how the results have led to the adoption of five suitable foundation solutions namely: large diameter shafts to rock, piles to rock, floating foundations over grouted ground, spread footings on shallow bedrock and concrete U shaped structures. Additional information available on a CD stored at the Merensky Library on 3rd Floor
Dissertation (MSc)--University of Pretoria, 2012.
Geology
unrestricted

Extensive research has been done on the investigation, evaluation, development and management of land underlain by dolomite to prevent the formation of sinkholes and subsidences. Little emphasis is, however, given to the various processes and methodologies with respect to the investigation and rehabilitation of sinkholes or subsidences. In South Africa most sinkholes and subsidences have been recorded on dolomite of the Malmani Subgroup of the Chuniespoort Group on the Far West Rand and in an area south of Pretoria within the City of Tshwane, with numerous studies done on the occurrence of sinkholes and subsidences in these two areas. However, a large number of sinkholes and subsidences have also been recorded on the East Rand in the Ekurhuleni Metropolitan Municipal area, which is the focus of this research. Very little is published on the occurrence of sinkholes and subsidences, the related geological models, investigations and rehabilitation work done in the Ekurhuleni Metropolitan Municipal area. It has been attempted with this thesis to document the various processes and methodologies applicable to the investigation and rehabilitation of dolomite-related sinkholes and subsidences within a non-dewatering environment. This is based on experience gained during the investigation and rehabilitation of various sinkholes and subsidences within the Ekurhuleni Metropolitan Municipal area on the East Rand, over the past ten years. Various methods of investigation, including non-intrusive and intrusive methods have been tried and tested to determine the extent of subsurface erosion within an affected sinkhole or subsidence area. The gravity geophysical method in association with the drilling of percussion boreholes; exposure of the affected area by means of excavation and the use of the Dynamic Probe Super Heavy (DPSH) method, in areas not accessible for a drilling rig where gravel, cobbles and boulders are absent in the subsurface profile; is the most appropriate methods for sinkhole or subsidence investigations on the East Rand. The gravity method is, however, not always successful in delineating narrow grykes in a shallow dolomite environment. The use of a specific method or methods of investigation is prescribed by the accessibility of a site. Accessibility constraints within a build-up area, may lead to the use of an investigation method other than what is generally preferred. The specific method or combination of methods used to rehabilitate a sinkhole or subsidence will depend on the available funds, current and proposed land use, subsurface conditions, accessibility constraints caused by existing infrastructure for equipment and the impact of the rehabilitation procedure on existing infrastructure. The various sinkhole and subsidence rehabilitation methods used on dolomite in South Africa and their applications are discussed, including: the Inverted Filter Method, Dynamic Compaction Method, combination of the Inverted Filter and Dynamic Compaction Methods, Compaction (backfill) Grouting Method, Combination of the Inverted Filter and Compaction Grouting Methods, Combination of the Dynamic Compaction and Compaction Grouting Methods and the use of Self- Compacting Concrete or Soil-cement Mix. Nearly half of the Ekurhuleni Metropolitan Municipal area is classified as dolomite land. A total of 241 ground movement incidents had been recorded, since 2005 to mid-2013. The Ekurhuleni Metropolitan Municipal area of jurisdiction is divided into three regional areas, namely:  Southern Regional area: More than 50% of the region is directly underlain by dolomite and chert of the Monte Christo Formation of the Malmani Subgroup of the Chuniespoort Group. A total of 141 ground movement incidents had been recorded, with all dolomite-related sinkholes and subsidences caused by ingress of water. Approximately 85% were caused by sewer lines, 7% by leaking water lines and valves, 4% by surface water ponding and 3% by concrete stormwater lines.  Northern Regional area: The northern portion of the region is directly underlain by dolomite of the Malmani Subgroup; from west to east by, chert-poor dolomite of the Oaktree Formation, chert-rich dolomite of the Monte Christo Formation, chert-poor dolomite of the Lyttelton Formation and chert-rich dolomite of the Eccles Formation. Dolomite of the Monte Christo Formation is also encountered in the south-eastern portion of the region. A total of 83 ground movement incidents had been recorded. Ground movement incidents are related to both ingress of water and dewatering of dolomite groundwater compartments including the Bapsfontein, Elandsfontein and Sterkfontein-East Dolomite Groundwater Compartments and Sub-Compartment.  Eastern Regional area: More than 50% of the region is regarded as dolomite land, with large portions of dolomite of the Monte Christo Formation and the Oaktree Formation of the Malmani Subgroup covered by the Karoo Supergroup. Dolomite of the Monte Christo Formation also occurs in the south-western portion of the regional area. A total of 17 ground movement incidents had been recorded. None of the recorded ground movement incidents are, however, related to dolomite. Incidents are related to poorely backfilled old wet services, natural erosion of subsurface soils, collapse of shallow coal workings and collapse of mine shafts and ventilation shafts. The sinkhole and subsidence rehabilitation method mostly used in the Ekurhuleni Metropolitan Municipal area is the Inverted Filter Method accounting for 85% of rehabilitation work, 10% for compaction grouting and 5% for the use of the Dynamic Compaction Method. The sinkhole and subsidence rehabilitation method should not be prescriptive, given the vast number of variables involved. A comprehensive understanding of the affected area is essential although for cost effective and practical rehabilitation measures. A site specific set of criteria for the rehabilitation of the features and affected infrastructure must be developed to ensure proper stabilisation and safe future use of the area. Basic principles can however be applied to each sinkhole or subsidence, such as: Ensuring the trigger of the sinkhole or subsidence has been identified and removed; the position and extent of the receptacles have been determined as best as possible and erosion paths sealed; the known eroded area, possible voids and cavities properly backfilled and densified; a proper impervious or engineer designed earth mattress created; ensuring that all affected subsurface wet services are replaced and comply with industry standards; and that proper surface drainage exists.
Thesis (PhD)--University of Pretoria, 2017.
Geology
PhD
Unrestricted

This study was undertaken to investigate the genetic relationships of allopatric populations of the cichlid fish, Tilapia sparrmanii (A. Smith 1840) inhabiting the sinkholes and springs of the North West Province, South Africa. It also examined the genetic relationships of T sparrmanii to its polychromatic sister species, Tilapia guinasana (Trewavas 1936) which is endemic to the Guinas sinkhole in Namibia. Finally, the study investigated whether there is a genetic basis for T guinasana's colour polymorphism. The research was prompted by the concern of conservation authorities about the possible loss of unique fauna given the high demand for use of the subterranean waters for agricultural, domestic and industrial purposes. Such demands have the potential to drain these habitats. Further concerns related to habitat destruction and the introduction of alien species in the ecosystems inhabited by both fish species. Three approaches were adopted in attempting to answer the above questions. First was the investigation of Sodium dodecylsulphate (SDS)-Polyacrylamide Gel Electrophoresis (PAGE) of total cellular proteins as a fast and relatively inexpensive indicator of genetic relatedness between the fish populations. Secondly, genetic differentiation between the T sparrmanii populations and its relationship to T guinasana were assayed using restriction endonuclease analysis of Polymerase Chain Reaction (PCR)-amplified regions of the cytochrome b gene and the d-Ioop of mitochondrial DNA, coupled with Temperature Gradient Gel Electrophoresis (TGGE) analysis of the same regions. The third approach involved the use of Random Amplified Polymorphic DNA (RAPD) fingerprinting of the populations ofT sparrmanii as an indicator of genetic differentiation between them. RAPD fingerprinting was further used to investigate the genetic relationships between T sparrmanii and T guinasana and to probe the genetic basis of the polychromatism of the latter. SDS-PAGE did not reveal any genetic differentiation between the T sparrmanii populations, nor could the analysis detect variation within them. It however clearly distinguished at a species level between T sparrmanii and T guinasana as well as between these and other fish species, thus indicating its possible utility as an indicator of genetic relatedness at a species level. Mitochondrial studies employing the Restriction Fragment Length Polymorphism (RFLP) of Polymerase Chain Reaction (PCR)-amplified cytochrome b (1.1 kb) and d-Ioop regions (0.9 kb) with six and five restriction enzymes respectively, failed to reveal genetic differences within and between the allopatric populations. TGGE of500 bp of the d-Ioop and 400 bp of the 12sRNA PCR-amplified fragments did not reveal any differences between the populations of T. sparrmanii, nor did the analysis reveal any differences between T. sparrmanii and T. guinasana. The lack of differentiation between the T. sparrmanii populations by these mitochondrial Dna analysis techniques, despite habitat fragmentation, indicated a recent origin of the populations from a common ancestral population. Failure to distinguish between T. sparrmanii and T. guinasana may be related to the sensitivity of the techniques utilized. RAPD fingerprinting analysis indicated that the populations are genetically differentiated from each other. Using a measure of coefficient of variation, the population with the highest variation was the Wondergat population (13.99%), followed by the Klerkskraal popUlation (8.29%), the Malmani and Marico Oog populations (each with 5.88%) and the least variation (4.95 and 4.83%) was with the Amalinda and Molopo Oog populations respectively. This high degree of intra population similarity points to the fact that this differentiation is still confined within the limits of con specificity. The genetic distances between all of the T. sparrmanii populations across all primers ranged from 0.09 to 0.234 and averaged 0.146, a value that falls in the upper end of conspecific population differentiation. Such results indicate populational sub-division below the species level. RAPD fingerprinting therefore proved more sensitive than protein or mitochondrial studies. The differentiation it detected between the populations is a reflection of their adaptation to local conditions of the unique ecosystems they inhabit. A comparison with a subset of primers between T. guinasana and T. sparrmanii confirmed the separate species status of the former from the latter. The mean genetic distance between the T. sparrmanii populations was 0.136, compared to that between T. sparrmanii and T. guinasana which was found to be 0.374. Statistical analysis of the difference between the mean genetic distances indicated significance with 95% confidence. The polychromatism of T guinasana was investigated to determine whether there were significant differences between its five colour morphs. RAPD fingerprinting indicated with 95% confidence that there were significant differences between the colour forms based on the genetic distances computed between them. These genetic differences appeared to correlate with the observed assortative mating between the colour forms of the species. The manifestation of the polychromatism at sexual maturity in T guinasana probably indicates that colouration plays an important role in the breeding process. The genetic uniqueness shown here between the populations of T sparrmanii and the colour forms of T guinasana indicate for protective measures to be put in place if the genetic resources of the isolated fish populations are to be preserved. These must be coupled with a thorough assessment of the temporal and spatial distribution of genetic variability of the populations as a guide to a long-term management strategy for the fish populations and the ecosystems they inhabit. This study therefore has shown that the allopatric populations of T sparrmanii in the sinkholes and springs of the North-West Province are genetically unique, as well as show that the colour forms of T guinasana are genetically distinct.

Karst related sinkholes and subsidence‟s occur on areas underlain by Chuniespoort Group dolomite bedrock in the Gauteng Province. Dolomite land occurs across several South African provinces; however sinkhole and subsidence formation in Gauteng is more well-known than in of the other provinces. Thousands of sinkhole and subsidence events have occurred in the past 60 years. In the past, data on sinkhole and subsidence occurrence has been amassed separately by various consultants, companies and state authorities. There is currently no legal requirement for sinkhole and subsidence events to be reported to a central authority, yet this data is crucial for future assessment of sinkhole hazards and decision making. This study focuses on the dolomitic land areas within four Gauteng municipalities, vulnerable to karst related sinkhole and subsidence formation. Historical as well as current information regarding the sinkhole record for Gauteng was compiled from various sources to develop as comprehensive an inventory of the study area as possible. The importance of sinkhole inventories are reviewed as well as the expediency and efficiency of Geographic Information Systems in data capturing and viewing. Data originates from numerous sources and compiling a comprehensive database presented many challenges, most importantly the large percentage of missing data that could not be retrieved and that the format and quality varies. Only karst related sinkhole, subsidences and crack events prior to 31 December 2011 were considered in this study. The data compiled is only an estimation of the number of events that has occurred in Gauteng. Once all the available sinkhole and subsidence data was collected and compiled, it was organized into multiwave frequency tables and various aspects were analyzed. The data collected, although limited in some cases, is used in statistical analysis to investigate the relationship between the formation of sinkholes and subsidences and underlying geology, size distributions, frequency of events and external influences. Results indicate that to date just over 3000 events (sinkholes, subsidences and ground cracks) are recorded within the study areas, and:  Sinkholes and subsidences are still regularly occurring in areas underlain by dolomite in Gauteng, however based on available data, events in the West Rand and Tshwane appear to show decreasing trend over the last decade.  More events occur in high rainfall months or years (due to increased ingress water entering the ground profile).  The most dominant type of event recorded is sinkholes.  Overall the largest percentage of events has occurred on the chert-rich Monte Christo Formation and Eccles Formation.  Triggering mechanisms were considered for the different areas: on the West Rand most occurrences before 1984 were due to dewatering while after 1984, most are attributed to ingress. The largest percentage of events on the West Rand has occurred in the Oberholzer Groundwater Compartment. In Tshwane almost all occurrences can be attributed to ingress, while in Ekurhuleni, just under a quarter of events were identified as due to dewatering.  When considering sinkhole and subsidence size and depth distributions; the largest percentage of sinkholes in the West Rand (>60%) are large to very large (i.e. from greater than 5m to greater than 15m diameter), the largest percentage of sinkholes in Tshwane (>60%) are medium to large (i.e. from greater than 2m to less than or equal to 15m diameter) and the largest percentage of events in Ekurhuleni (>70%) are small to medium (i.e. less than or equal to 5m diameter).  When considering size distribution on the different formations, it was not possible to determine if certain sizes were more prevalent for specific formations.
Dissertation (MSc)--University of Pretoria, 2013.
gm2014
Geology
unrestricted

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy in Town Planning. Johannesburg, 2016
Keywords/key concepts: Dolomite, Dolomitic ground, Disaster Risk Management, Physical Vulnerability, Low-income settlements, Housing Policy, Services delivery, Responsibility, Living with risk, Human Behaviour, Basic Human Rights Ground underlain by dolomite may be hazardous to development due to the potential occurrence of subsidence and sinkholes. These potentially disastrous occurrences are in many instances caused by human interaction with the soil through the ponding of water or leaking of wet infrastructure such as water and sanitation services. Construction materials and techniques, as well as effective maintenance of waterborne services have traditionally been acknowledged as having a significant bearing on the level of risk that communities face when living on such potentially dangerous land. The spatial distribution of settlements on dolomite in the Gauteng City Region (GCR) is already widespread and expected to increase as urbanisation intensifies. Similarly, the challenge of considering the physical vulnerability of low-income settlements is expected to intensify. Well- defined procedures and guidelines govern the development of human settlements on dolomitic ground. However, the classification and characterisation of low-income and informal settlements are not as advanced as that of formal residential developments. In addition, the guidelines regarding management of settlements on dolomite focus significantly on geotechnical interventions, leaving a gap in the influence that human behaviour can play in possible disaster risk reduction on such ground. The thesis considers the significance of different low-income settlement types on dolomite, relative to perceived human behaviour in association with principles of disaster risk reduction. It hypothesizes that an understanding of settlement type in relation to human behaviour and a stronger emphasis on monitoring via official channels could address some of the conflicts in the development-on-dolomite debate and thereby reduces settlement vulnerability. The research methods included quantitative and qualitative components, commencing with a literature review that spanned multiple disciplines and sectors. Fieldwork included spatial investigation and consideration of low-income settlement types with regard to, for example building material use, dwelling size and dwelling layout, and wet services infrastructure provision and location. The thesis subsequently identify and explore low-income settlement types in the study area. The research explores a number of sample settlements to consider the physical vulnerability and potential key areas of intervention and risk reduction, outside of the traditional geotechnical arena. The evaluation then applies the Analytical Hierarchy Process (AHP), a form of Multi Criteria Analysis (MCA), to identify important variables and indicators related to human behaviour and the physical vulnerability of settlements on dolomite that can be harnessed to intervene in the debate, and possible improve the safety of communities living with this risk. Although not affecting the research outcome directly, a specific observation during the course of engagement with specialists across disciplines was that experts in even closely related practice areas view low-income settlement development and upgrading on dolomite differently. The differences in viewpoints result in contradictions in approaches between housing officials, disaster managers, socio-environmental practitioners, engineers and geologists. Even small differences in approach have been shown to have significant effects on the practicalities surrounding decision making related to low-income settlements and especially informal settlement relocation or upgrading. The outcome is a set of prioritised indicators that could enable specialists, officials and the public to consider different elements of low-income settlements based on its physical vulnerability. By focussing on the indicators most likely to result in reduced vulnerability, actions that drive settlement development, upgrade and resettlement could be prioritised. Interestingly, one of the findings of the research is that it is not so much the settlement type based on informality that makes a difference in the exposure to risk - physical vulnerability is deemed to be significantly affected by official (municipal-sphere) actions, monitoring and awareness. Finally, the research enables the integration of technical knowledge with behavioural considerations when living on dolomite, thus highlighting opportunities to bring technical and non-technically skilled stakeholders in the debate closer together.
MT 2018

An estimated 2.5 million people live on dolomite and in excess of 1.2 billion Rands of property damage has been observed to date and in excess of 800 sinkholes have occurred in the Southern Tshwane area alone. Research on dolomitic terrain is hence crucial in the quest for releasing land for development that is deemed safe from a dolomite risk perspective. This thesis attempts to present a better understanding of the geology and stability of a carefully selected type area east of Irene town in Pretoria, Gauteng, South Africa, and to interrogate the current method of dolomite stability analysis. The study area is located partly on the Lyttelton and Eccles Formations, Malmani Subgroup, Chuniespoort Group, of the Transvaal Supergroup. The Transvaal Supergroup rocks were subjected to complex faulting and folding along the northeastern rim of the Johannesburg Dome. Displacement and duplication of the Transvaal rocks by faulting is common to the east and south east of Pretoria with the karst topography being well developed along these water exploited structural features. The karst development, in particular on the Eccles Formation, has lead to a highly variable dolomite and chert bedrock topography. Cavernous conditions can be expected both within the bedrock and the overburden. A summary is given of how instability occurs. Given sufficient time and the correct triggering mechanisms, instability may occur naturally but is expedited, by many orders of magnitude, by man’s activities. Various authors have over the years attempted to classify dolomitic land. The “method of scenario supposition for stability evaluation of sites on dolomitic land in South Africa”, which has been applied widely by the industry, certainly since 1995, was applied to the study area in 1996/7. The method was successful in focussing the attention of investigators of dolomitic land on the various factors that contribute to instability. However, with time it became evident that modification and further clarification of various concepts was necessary. The modified method was named “method for dolomite land hazard and risk assessment in South Africa”. This method was applied and comparison drawn between the two assessments. The latest investigative and evaluative methodology is explained. The gravity method as applied to dolomite studies is explained and its results interrogated. Shallow dolomite and its associated risks are analyzed. The karst types identified by Waltham and Fookes is considered and compared to the karst identified in the study area and in so doing placed in a South African context. The results of the new assessment are placed in context with current development type and density recommendations. The functions and requirements of the National Home Builders Registration Council are explained. It is concluded that the study area can be divided into 3 broad risk zones. Zone A represents the shallow dolomite areas and largely reflects a high risk of small to medium-size sinkholes and dolines with localized sub-areas reflecting a high risk of large sinkholes (i.e. inherent risk classes 5,3, 6 (7)). Zone B represents areas potentially reflecting a low to medium risk of up to large sinkholes and dolines (i.e. inherent risk classes 1 and 4). Here bedrock is relatively deep (40 m) and mantled by relatively thick stable material. Zone C represents transitional areas between shallow and deep bedrock where bedrock topography is often highly undulating and thick sequences of low density insoluble weathering product and cavernous conditions occur. Here the risk of all size sinkholes and dolines is high (inherent risk classes 5, 6, 7 and 8). The function of water precautionary measures and founding solutions is discussed. It is pointed out that these measures and solutions cannot change the inherent risk classification but rather change the development risk. Under certain circumstances an acceptable development risk may be established, however a stumbling block remains quality of workmanship, practicality of implementation and costs, the latter referring to the costs of some founding solutions, which render many developments unfeasible. Significant financial losses due to dolomite stability are recorded annually. The development present in this study area is 9 years old and already severe damage to structures have been observed. Despite the mounting costs associated with dolomite instability, local authorities and developers continue to develop dolomitic land. Sites such us these will continue to be targeted for development and investigators are under increasing pressure to come up with engineering solutions to the problem. It is essential to continue to better understand the sites earmarked for development from a geological perspective, so as not to leave future generations with large tracts of sterilized land and a community having to deal with injury to life and limb and fearful of dolomite. Many a geologist may continue to discover various generations of weathering products in this study area in the future and continue to grapple with the links between dolomite stability or rather lack thereof, the geotechnical properties of the various weathering products and the effects of geological structures. Copyright
Dissertation (MSc (Engineering and Environmental Geology))--University of Pretoria, 2007.
Geology
unrestricted

M.Sc.
Certain carbonate bearing formations in the Paleoproterozoic Pretoria Group and its Griqualand West equivalent exhibit remarkable geochemical and stable isotopic signatures. The 8'3Ccarb isotopic signatures from the Duitschland and Silverton Formations exhibit large positive excursions, which seemingly coincide with a significant increase in atmospheric oxygen between 2.4 and 2.0 Ga. The Duitschland Formation with its distinctive basal unconformity is composed primarily of limestone and dolomite units, interbedded with two compositionally different shale units and quartzite. Toward the base of the formation there is a distinct conglomeratic quartzite which forms a sequence boundary above which isotopic and geochemical signatures change dramatically. Normal marine isotopic signatures characterize the lower portion of the succession while above the sequence boundari, the carbonates are enriched in "C. This enrichment, however, appears to be the result of local processes occurring within a closed basin. Furthermore it is apparent that the Duitschland Formation (with its three distinct marker beds) is the equivalent of the Rooihoogte Formation and therefore constitutes the base of the Pretoria Group. The Mooidraai Dolomite Formation which outcrops only locally in the Northern Cape Province, is characterized by fenestral and microbially laminated dolomite. The geochemical properties are relatively homogeneous with increases in the FeO and MnO concentrations, resulting from post depositional diagenesis. The stable isotope signatures of these dolomites represent normal marine signatures. There is, however, a depletion in the 813C and 8180 signatures in the ankeritic and sideritic lithofacies, which suggests that this succession was deposited from a stratified water column with respect to the total dissolved CO2. The positive 6 13C excursion present in the carbonates of the Lucknow Formation in Griqualand West, traditionally grouped with the Olifantshoek Group can be correlated with carbonates near the top of the Silverton Formation in the Transvaal area. The latter also displays distinctly positive 6 43C values. One possibility is that if these successions were deposited in closed anoxic basins and that the isotopic anomalies are the result of local processes such as fermentive diagenesis and methanogenesis. However, the close association of the carbonates with shallow marine orthoquartzites suggests that these were deposited in an open marine system and that the positive 8 !3C values reflect a shift in the composition of the ocean water at the time of deposition of the carbonates at 2.2 Ga. Other carbonates present in the Pretoria Group, namely from the Vermont and Houtenbek Formations, display normal open marine 8' 3C values of close to zero. A systematic stratigraphic compilation of all 6 43C values available from the Transvaal Supergroup indicates that two clear-cut positive 5' 3C excursions are present. These excursions were apparently short-lived and well defined and did not occur over an extended period of time as suggested by earlier studies based on global compilations with large uncertainties in radiometric ages of deposits.

M.Tech. (Extraction Metallurgy)
The discovery of gold at Langlaagte in 1886 led to the development of gold mining in the Far West Rand in 1934. When shafts were sunk, water from the dolomites posed a serious threat to mining. Despite cementation that sealed the many fissures, water still found its way into the underground workings. This led to the “uniform” policy of dewatering. The farming communities in the area that were dependent on the ground water had to be considered, as they had lost their livelihood. As the water levels lowered, dolines and sinkholes were formed, posing a serious threat to life and property. When the mines eventually cease to operate, be it due to high working costs, or the declining grade of the ore body, the re-watering of the dolomitic compartments will occur as a natural consequence. When water comes to within six metres of the original water level, ground instability, the formation of dolines and sinkholes, both new and existing, will occur, threatening the important rail link between Pretoria and Cape Town as it passes through Far West Rand, as well as the N12 between Johannesburg and Potchefstroom, as well as the N14 which lies to the east connecting the Gauteng Province and the North West Province. The dewatering of the compartments caused the soil which formed the roof of the cavities to dry. Re-watering will cause this dry, stable material to become wet and unstable. Where mixtures of slime and/or other material, which is not part of the geological composition of that area was used, the same phenomenon will apply. A further complication is caused by the slimes dams which are unlined. In fact, some of the slime dams were deliberately constructed over cavernous dolomite. This large mass of mine tailings over the dolomitic aquifers will “liquefy”. If the re-watering is not carefully managed the rising water table will undoubtedly trigger a rash of new sinkholes, with catastrophic consequences for unsuspecting communities that may have been established in sensitive areas. The results of previous investigations by the Departments Minerals, Energy and Water Affairs who, due to the loss of institutional memory, might not be able to find the relevant information. Other organizations such as the Council for Geoscience could be using the results for consultancy. The information should be digitized and be available to the broader South African public. FWRDWA is currently in charge of monitoring events in the area. Levelling observations have been carried out quarterly and, so far the movement of ground is minimal. The potential hazard of ground instability will recur with the re-watering of the dolomitic compartments of the Far West Rand. To support what could happen, reference is made to events which took place in the late seventies when the Far West Rand had an above average rainfall. The Donaldson Dam overflowed into the Wonderfontein Spruit and into the dewatered Venterspost compartment. As a result, the water level of the Venterspost Compartment rose rapidly which led to the re-activation of sinkholes and the formation of new ones in the Venterspost area. In the present work levelling has been carried out along most of the loops affected and the results of the levelling give an impression that the surface is currently relatively stable. This Dissertation is presented as an attempt to alert the authorities to the potential dangers if the post mining period is not carefully monitored and insufficient provision made to deal with potential contingencies.

The Uitkomst Complex is located within the Great Escarpment area close to the town of Badplaas, approximately 300 km due east of Pretoria, in the Mpumalanga Province, South Africa. This complex is believed to represent a layered conduit system related to the 2.06 Ga Bushveld Complex. The succession from the bottom up comprises the Basal Gabbro- (BGAB), Lower Harzburgite- (LHZBG) and Chromitiferous Harzburgite (PCR) Units, collectively referred to as the Basal Units, followed by the Main Harzburgite- (MHZBG), Upper Pyroxenite-(PXT) and Gabbronorite (GN) Units, collectively referred to as the Main Units. The Basal Unit is largely hosted by the Malmani Dolomite Formation, in the Pretoria Group of the Transvaal Supergroup sediments. The Lower Harzburgite Unit contains numerous calc-silicate xenoliths derived from the Malmani Dolomite. The Basal Units host the economically important nickel-bearing sulphide and chromite deposits exploited by the Nkomati Mine. An area of extensive localized talc-chlorite alteration is found in the area delineated for large scale open cast mining. This phenomenon has bearing on the nature and distribution of the sulphide minerals in the Chromitiferous Harzburgite and to a lesser extent the Lower Harzburgite Units. The Basal Unit is comprised of both near pristine areas of mafic minerals and areas of extensive secondary replacement minerals. Of the olivine minerals, only fosterite of magmatic origin is found, the fosterite suffered hydrothermal alteration resulting in replacement of it by serpentine and secondary magnetite. Three different types of diopside are found, the first is a primary magamatic phase, the second is a hybrid “transitional” phase and the third, a skarn phase. Hydrothermal alteration of the matrix diopside led to the formation of actinolite-tremolite pseudomorphs. This secondary tremolite is intergrown with the nickeliferous sulphide grains. Chromite grains are rimmed or replaced by secondary magnetite. Pyrrhotite grains is also rimmed or replaced by secondary magnetite. Talc and chlorite is concentrated in the highly altered rocks, dominating the PCR unit. Primary plagioclase and calcite do not appear to have suffered alteration to the same extent as the other precursor mafic magmatic and hydrothermal minerals. It is suggested that the PCR was the first unit to be emplaced near the contact of the dolomite and shale host rock. The more primitive mafic mineral composition and presence of chromitite attest to this interpretation. The LHZBG and MHZBG units may have been emplaced simultaneously, the LHZBG below and the MHZBG above. Interaction and partial assimilation of the dolomitic country rock led to a disruption of the primary mafic mineralogy, resulting in the preferential formation of diopside at the expense of orthopyroxene and plagioclase. Addition of country rock sulphur resulted in sulphur saturation of the magma and resulted in the observed mineralization. The downward stoping of the LHZBG magma, in a more “passive” pulse-like manner led to the formation of the calc-silicate xenolith lower third of this unit. It is proposed that the interaction with, and assimilation of the dolomitic host rock by the intruding ultramafic magmas of the Basal Units are responsible, firstly, for the segregation of the nickeliferous sulphides from the magma, and secondly for the formation of a carbonate-rich deuteric fluid that affected the primary magmatic mineralogy of the Basal Unit rocks. The fluids released during the assimilation and recrystallization of the dolomites also led to the serpentinization of the xenoliths themselves and probably the surrounding hybrid and mafic- ultramafic host rocks. The CO2-rich fluids migrated up and outward, while the H2O-rich fluids remained confined to the area around the xenoliths and LHZBG unit. The H2O-rich fluid is thought to be responsible for the retrograde metamorphism of the precursor magmatic and metamorphic minerals in the Lower Harzburgite Unit. The formation of an exoscarn within the dolomitic country rocks and a selvage of endoskarn on the contact form an effective solidification front that prevented further contamination of the magma. It is also suggested that these solidification fronts constrained the lateral extent of the conduit. The CO2-enriched deutric fluid was able to migrate up to the PCR unit. Here the fluid was not removed as effectively as in the underlying parts of the developing conduit. This resulted in higher CO2-partial pressures in the PCR unit, and the stabilization of talccarbonate assemblages that extensively replaced the precursor magmatic mineralogy. Intrusion of the magma into the shales, which may have been more susceptible to assimilation and greater stoping, led to a broadening in the lateral extent of the Complex, in the Main units above the trough-like feature occupied by the Basal Units. Late-stage, hydrous dominated fluid migration is inferred to have been constrained to the central part of the conduit. This is demonstrated by the dominance of chlorite in the central part of the Uitkomst Complex in the study area. The Uitkomst Complex was further deformed by later intrusions of dolerite dykes. Weathering of the escarpment led to exposure of the conduit as a valley and oxidation of the surficial exposed rocks.
Thesis (PhD)--University of Pretoria, 2012.
Geology
unrestricted

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Hydrogeology. July 2017.
Hydrogeological research was undertaken in the transboundary Ramotswa dolomitic aquifer to provide understanding and quantification of the processes governing recharge mechanism and rates, in order to promote efficient and sustainable groundwater resource utilization and development, as well as to improve the Ramotswa transboundary aquifer management. Hydrochemical and tracer approaches were utilized to evaluate the processes governing the recharge mechanism while the chloride mass balance approach was further applied to assess groundwater recharge rates. Results indicated that all groundwater samples contained detectable amounts of tritium highlighting the renewability of the transboundary Ramotswa aquifer resources. Two distinct water types were characterised: sub-modern waters approximately recharge prior to the 1950s and a mixture of modern and sub-modern waters of recently recharge rainfall indicative of active recharge in the area through intensive rainfall. Correlation between δ18O and δ2H, and soil Cl- indicated that groundwater recharge in the Ramotswa dolomitic aquifer takes place mainly by two flow mechanisms: a displacement of moisture through a diffuse or piston flow through permeable soils and from concentrated runoffs due to surface depressions, and a preferential flow component through fractures that outcrop at surface and riverbed infiltration along the ephemeral Notwane River. Annual groundwater recharge estimates varied from 0.4% MAP to 12% MAP and from 5% MAP to 14% MAP within the northern parts and the southern parts of the study area, respectively. Recharge estimates correlated well with the proposed mechanism of flow both in the southern and in the northern parts of the study area as well as with the previous studies conducted within the greater Ramotswa area. A way forward to ensure the long-term sustainability of the transboundary Ramotswa aquifer resources is recommended, such as to preserve and protect potential recharge areas through carefully controlled land use planning and development, and to equate abstraction rates to average recharge rates, which has to be subjected to the Limpopo Watercourse Commission.
MT2018