Theses and Dissertations (Geology)

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The engineering properties and road building characteristics of mudrocks, with special reference to Southern Africa
(University of Pretoria, 1980-05) Snyman, C.P.; Olivier, H.J.; Venter, Jacobus Petrus
English: Mudrocks occur in many parts of southern Africa and large quantities are used in road construction. This study involved research on the "state of the art" of the road construction aspects of mudrocks in southern Africa, as well as the general engineering-geological properties of such rocks and the assessment of the most appropriate tests for classifying mudrocks for road construction purposes. The "state of the art" investigation, done by means of interviews with users of the material, revealed much confusion about the terminology related to these rocks. It was therefore decided to use the term "mudrock" as the all-embracing term with "shale" and "mudstone" indicating fissile and massive varieties respectively. The survey also found mudrock to be an important construction material, especially in the Cape Province and Natal, where it is used up to subbase level. Large differences of opinion exist regarding the general road-building qualities of mudrocks. No particular problem pertaining to construction with mudrock was identified, but the break-down phenomenon on exposure gave rise to most of the concern expressed. It was felt that other tests, additional to the standard ones used in road construction, are necessary to characterize mudrocks. A wide variety of property investigations and tests was performed on 14 mudrocks, sampled as soon as possible after excavation, from different geological formations throughout South Africa. Although the samples were selected to cover a wide range of engineering geological properties, since they were limited in number it cannot be claimed that they are necessarily representative of the whole range of southern African mudrocks. Standard road construction tests showed some samples to be of subbase standard. Plasticity indices were usually low. The addition of four per cent lime generally caused a marked increase in the CBR strength. An "accelerated weathering" test, in which CBR compactions were followed by wet-dry cycles, indicated the different rates of break-down of the samples. Extensive free swell tests on cubes, pretreated differently before immersion in water, showed that the majority of samples expand less than one percent during immersion after oven-drying. tended to break down expanded more. Air-drying increased the expansiveness of the rocks to levels similar to those obtained after oven-drying. The mudrocks were found to absorb water at different rates. In an experiment during which test cubes were subjected to temperature and humidity changes, it was found that the mudrocks were more sensitive to humidity changes, both as far as volume changes and moisture adsorption were concerned. However, even large variations in temperature and humidity were not able to produce a visual break-down such as was observed for some samples when they were immersed in water. The results from classification tests were investigated and correlated to select tests which showed the best possibilities for mudrock classification. It is considered that a road construction material needs to be resistant to crushing, abrasion, and decomposition. The 10 per cent FACT, carried out on dried and soaked samples, is preferred for testing the resistance to crushing. A wet ball mill test was developed for testing resistance to abrasion. This test was more successful in separating samples of different qualities than the Los Angeles abrasion test and the results correlated well with those obtained from an ultrasonic disaggregation test. The sand equivalent test is recommended to determine the presence of deleterious material in the crushed mudrock. The break-down of mudrocks at various rates on exposure is not fully evaluated by the above tests, nor by the standard road construction tests. Two varieties of the break-down phenomenon were observed although there appears to be a gradation between the two processes, i.e. the break-down of the rock into hard fragments (disintegration) and the break-down into silt or clay-sized particles (slaking). It is considered that slaking can be measured by means of the slake durability test, but disintegration should be evaluated qualitatively by performing a five-cycle wet-dry test, using water. Tests, such as the Washington degradation, ethylene glycol soaking, methylene blue adsorption, sodium sulphate soundness, rate of slaking and conductivity, were found to be unsuitable for general classification purposes.
Hydrochemistry, hydrogen and oxygen isotopes, and radon in waters of the greater Timbavati catchment, South Africa
(University of Pretoria, 2024-05-16) Dippenaar, Matthys Alois; Diamond, Roger; kirstenraible@gmail.com; Raible, Kirsten
A baseline study was conducted to gain a better understanding of the relationship between groundwater, geology, and geography of the Greater Timbavati Area, to advance the knowledge of hydrostratigraphical settings affected by various socioeconomic and environmental factors. Samples were collected from both surface water and groundwater and were taken in both nature reserves and rural communities for comparison. An Aquaread AP-5000 probe was used to measure basic water chemistry parameters as well as nitrates, ammonium, and ammonia in the field. Samples were also taken and analysed for radon using a Durridge RAD7. Rainwater samples were also collected from two sites for hydrogen and oxygen isotope analysis using a Los Gatos Research (LGR) Liquid Water Isotope Analyzer. There are noticeable differences between the surface water and groundwater chemistry and isotopic signatures. Groundwater samples have a mean TDS of 1217 mg/l and pH of 7.5 while surface water samples have a mean TDS of 332 mg/l and pH of 8.3. A close correlation between land use and nitrate concentrations is observed with higher values being found in groundwater in the more developed areas, over 500 mg/l, suggesting human and agricultural contamination. Unfortunately, there also appears to be no relationship between radon concentration and the underlying geology with mean values in groundwater ranging from 188 Bq/m3 to 51400 Bq/m3 .
Mineralogical impact on the compaction of residual gabbro soils in the construction of Platinum Tailings Storage Facilities
(University of Pretoria, 2023-12-05) Dippenaar, Matthys Alois; jase.tunnell@gmail.com; Tunnell, Jason
Over the past decade, there have been 45 tailings storage facility (TSF) disasters worldwide, resulting in fatalities, serious environmental damage, and the destruction of entire ecosystems. These failures often stem from substandard design or operational practices. Many TSFs are constructed in regions associated with intrusive mafic rocks such as gabbro, norite, pyroxenite, and anorthosite, which are commonly found alongside platinum group metals in areas like the Bushveld Igneous Complex in South Africa and the Great Dyke in Zimbabwe. The stability of these structures can be significantly influenced by the residual soils present at the construction sites. Residual soils, both cohesive and non-cohesive, contain varying quantities of different minerals, which can impact the compaction characteristics and, consequently, the stability of the TSF foundations. Cohesive soils rich in clay minerals, such as kaolinite and smectite, exhibit properties that can hinder effective soil compaction. The expansive nature of smectite due to its ability to absorb large amounts of water and host free exchangeable cations, counteracts the compaction process, reducing soil stability. Soil compaction is a complex process influenced by several factors, including compaction effort, method, water content, particle size distribution, and mineralogy. This study aimed to analyse these factors using a series of laboratory tests, including foundation indicators, MOD AASHTO compaction testing, and X-ray diffraction analysis, on residual soils from two TSF construction sites. The findings revealed that soils with high clay content tend to retain more water and have a higher optimum water content, adversely affecting their compaction properties. This study highlights the critical need to consider the mineralogical composition and weathering effects of residual soils in the design and construction of TSFs. By improving our understanding of these factors, we can enhance the stability of TSF foundations, reducing the likelihood of future failures. The insights gained from this research highlight the importance of thorough geotechnical assessments in the successful design and maintenance of TSF’s.
The cyclic unit of the upper critical zone on maandagshoek 254 KT eastern Bushveld complex
(University of Pretoria, 1981) Von Gruenewaldt, G.; Gain, Stephen Bryant
The farm Maandagshoek 254 KT is situated in the eastern lobe of the Bushveld Complex. The investigated sequence forms part of the Winterveld Norite-Anorthosite of the critical zone and consists of the UGl, UG2, UG3 and UG3A cyclic units. These cyclic units consist of a basal chromitite with or without olivine, overlain successively by melanorite, norite, and leuconorite to an anorthosite layer above. The cyclic units are punctuated by sharp contacts and a remarkable persistence along strike and dip. The En content of orthopyroxene and the An content of plagioclase decrease and increase respectively upwards through the UGl and UG2 cyclic units. Breaks in this trend occur below the chromitite layers where the En content of bronzite increases and in the anorthosite layers at the top of the cyclic units where the An content of plagioclase increases. A trace element study showed Rb and Zr to increase upward in the UGl and UG2 cyclic units. Rb and Sr display a reasonable antipathetic relationship. The Cr and Ni content of the orthopyroxenes increases upwards irregularly in the cyclic layers, but the Ni content decreases where visible sulphides are present. Cu, Ni and the platinoid elements increase in the chromitite layers, especially the UG2 chromitite layer. Clinopyroxene is not commonly cumulus and is identified as chromi~_ferous augite. The equilibrium temperature of a coexisting orthopyroxene-clinopyroxene pair was calculated according to the Wood-Banno and Wells modifications to be 1179°c and 1097°c respectively. Cumulus olivine associated with the UG2 pegmatoid and the UG3A chromitite was identified as chrysolite. The compositions of 15 chromite samples were determined and showed similar chemistry to those reported by De Waal (1975). The crystallization temperatures of coexisting olivine and chromite pairs was determined using the Jackson (1969) and Roeder et al, (1979) geothermometers. The UG2 chromitite layer contains an average of 8,5 g/t PGE and Au over a width of 0,64 metres in 22 intersections in borehole and underground samples. A study of the distribution of Pt and Pd in the weathered and unweathered zones clearly shows that both, but especially Pd, are mobile and depleted in the surface environment. The sulphide liquid in the UG2 chromitite layer was calculated to have contained 925 ppm Pt and 934 ppm Pd which is 578 and 359 times respectively the calculated levels in early immiscible sulphide liquids (Naldrett and Cabri, 1976). A model is proposed in which the UG2 chromitite layer acted as a physico-chemical barrier to the upward migrating late deuteric fluids and volatiles charged with platinoids, Au, Sb, As and Te. The platinoids were collected by earlier sulphide droplets which separated from the magma during crystallization of the UG2 chromitite layer. Structures are sub-divided into Class I and Class II features. Class I features are related to viscosity and density contrasts of layers at the time of crystallization of the magma and may be seen as bifurcating and anastomosing layers, folding and slump features, rafting of chromitite blocks, minor faults and potholes. Class II features are associated with tectonic movement which postdates the consolidation of the layering and are sub-divided into three categories; faults, dolerite dykes and pipes. The pipes are pegmatoidal in character, zoned with ultramafic cores and pyroxenite rims, have sharp contacts and cause downwarping and attenuation of the layering towards the pipes to form marginal synclines. It is postulated that intercumulus material coalesced along structural weaknesses and moved upward until the lithostatic pressure impeded upward movement at which time lateral and outward intrusions occurred. The layers of the intruded rocks bent down to accommodate the outward flowing material and gave rise to the marginal synclines. The concept of a closed cell cyclic unit is introduced to account for the inherent characteristics and origin of the cyclic units of the upper chromitite group.
The discovery of igneous xenoliths in the Upper Zone of the Bushveld Igneous Complex and its implications on the model of emplacement of Upper Zone magmas
(University of Pretoria, 2023-10-31) Roberts, R.J. (James); alberts.adriana@gmail.com; Alberts, Adriana
The Upper Zone is the uppermost portion of the Rustenburg Layered Suite of the Bushveld Igneous Complex and has long been interpreted to have formed from the differentiation of a single magma pulse through closed-system fractionation. This is in contrast to theories proposed for the formation of the lower portions of the Bushveld, which state that multiple cycles of new magma injections occurred. In this study, the discovery of rocks believed to be igneous xenoliths in Subzone C of the Upper Zone in the Eastern Limb of the Bushveld Complex is investigated. The study area has not been extensively investigated in the past and the outcrops referred to in this study will be properly described for the first time. The xenoliths feature remnant trellis ilmenite exsolution textures that have not been observed elsewhere before. Extensive field work was conducted, as well as petrographical and geochemical analyses, that led to the conclusion that these foreign blocks were xenoliths of igneous origin. Furthermore, when geochemical and SEM data are analysed, the xenoliths show strong evidence of hydrothermal alteration and contain highly altered minerals, which the host rock does not, further solidifying the idea that these samples are, in fact, xenoliths. The presence of remnant ilmenite suggest that the xenoliths originated from magnetite bearing units, and since the only magnetite-bearing units in the Bushveld Complex are found in the Upper Zone itself, this implies that the xenoliths originated from elsewhere in the Upper Zone. Therefore, it was concluded that they could be further classified as being autoliths. This directly challenges the single magma theory, since the presence of autoliths from the Upper Zone in subzone C suggests that at least one other magma pulse contributed to the formation of the Upper Zone, and thus the Upper Zone did not form in a closed system.
Geological characterisation of the Bamboesberg Member within the Molteno-Indwe coalfield, Eastern Cape Province, South Africa
(University of Pretoria, 2024-01-02) Lenhardt, Nils; Hancox, John; mbreakfast@geoscience.org.za; Breakfast, Mzoli
The Bamboesberg Member forms the basal member of the Late Triassic Molteno Formation. It hosts the two economically significant coal seams in the Molteno-Indwe coalfield, namely the Guba and Indwe seams. The Molteno-Indwe coalfield is located mainly in the northern region of the Eastern Cape Province in South Africa. The Council for Geoscience (CGS) drilled thirteen vertical boreholes within the Molteno-Indwe coalfield between 1984 and 1986. These cores were retrieved from the National Borehole Core Depository in order to characterise the sandstones of the Bamboesberg Member. To achieve this objective, the cores were logged in detail and scanned using a hyperspectral imaging scanner. Additionally, sandstone samples were collected for physio-chemical analysis. The Bamboesberg Member consists of fining-upwards cycles of sandstones, interbedded with argillaceous units and, in certain areas, coal. The coal seams typically occur on top of the argillaceous successions. These sandstones are classified as sub-litharenite and are sourced from the recycled orogenic provenance. Through SEM-EDX analysis it was observed that the sandstones contain large euhedral detrital garnets and sub-rounded zircons. The coal samples from the Bamboesberg Member were assessed for their rare earth element potential. Most samples displayed a rare earth element concentration ranging from 100 to 200 ppm, while five samples exhibited a higher concentration of over 350 ppm. The minerals hosting the rare earth element were observed to be monazite, parisite, and xenotime. Three-dimensional (3D) modelling revealed that the Bamboesberg Member has a concave shape at its centre and the maximum thickness observed is 120 meters. It tapers off to the north, pinching out to 20 m north of Aliwal North. The Bamboesberg Member is more exposed in the western and central parts of the Molteno-Indwe coalfield. Consequently, the western and central portions of the coalfield have potential for further coal prospecting within the Molteno-Indwe coalfield.
Tectonic constraints from thin granitoid sheets in H.U. Sverdrupfjella, Western Dronning Maud Land, Antarctica
(University of Pretoria, 2024) Roberts, R.J. (James); Grantham, Geoffrey H.; emuburger@gmail.com; Burger, Erasmus Petrus
This work is a study of granitoid sheets in H.U. Sverdrupfjella. The objectives were to measure the orientations and take samples of the granitoid sheets to produce orientation, geochronological and geochemical data from the granitoids. This data is intended to reveal the nature and timing of emplacement for the granitoid sheets and to provide constraints regarding the tectonic history of the study area. This work identified three suites of granitoid sheets, namely the Pre-existing Granitoids, Salknappen Pegmatites and Dalmatian Granites: 1) The oldest of these suites is the Pre-existing Granitoids, as is evident from field relationships. Pre-existing Granitoids were only seen at a handful of outcrops at the Rootshorga nunatak, which limited the extent of study possible. 2) Salknappen Pegmatites are weakly deformed, very coarse grained and white in colour. From cross-cutting relationships, Salknappen Pegmatites are older than Dalmatian Granite. SHRIMP geochronology gives ages of 517 ± 3.5 Ma, 507 ± 3.1 Ma and 513 ± 3.7 Ma for the three samples which were dated. Geochemically, Salknappen Pegmatites have two distinct groups, one characterised by positive Eu anomalies (+Eu Salknappen Pegmatites), and another characterised by negative Eu anomalies (-Eu Salknappen Pegmatites). These rocks have a flat REE profile with LREE enrichment. Isotope geochemistry gives a younger model age and higher 143Nd/144Nd than Dalmatian Granites and show a similarity to the Rootshorga Complex country rock. 3) Dalmatian Granites crosscut the granitoid suites described above and structural features in the country rock. No deformation is evident in competent country rocks. In the field Dalmatian Granite can be identified by course to very coarse-grained texture and pink colour. SHRIMP dating gives ages of 492 ± 2.1 Ma, 483 ± 2.8 Ma and 483 ± 3.1 Ma for the three samples analysed. The geochemistry of Dalmatian Granite is consistent with an upper crustal source. The granitoids are interpreted to record the earlier stages of orogeny (Salknappen Pegmatites) followed by the late to post-orogenic stage (Dalmatian Granites). Owing to the ~30 m.y. gap between the emplacements of the two suites, a model involving a diachronous metamorphic event is favoured.
Principal component analysis of trace element data from the Upper Zone of the Bushveld Complex : constraints on possible tectonic provenance
(University of Pretoria, 2023) Roberts, R.J. (James); sebolaselby@gmail.com; Sebola, Selby
The Kaapvaal Craton in South Africa is characterised by ultramafic to mafic complexes, and several mafic intrusions are associated closely with different sections of the craton. The focus of this research is the Transvaal basin in the Kaapvaal Craton that hosts the Bushveld Complex. This complex is the most extensive mafic layered intrusion on Earth, with the magmas ranging from Fe-rich to Si-rich. The extensive body of research on this area is a good foundation for the current study, which focuses on the Upper Zone and upper Main Zone (UUMZ) of the complex. The Bushveld Complex is endowed with rich mineral deposits, lending it robust economic significance, allowing substantial contributions to the global economy through various avenues relating to mineral processing and distribution. Objectively, this research project seeks to provide tectonic constraints on the origin of the magma emplaced in the UUMZ through geochemical analyses of trace elements and rare earth element (REE) data from Bierkraal boreholes (western limb) and Magnetite Layer 21 (eastern limb), respectively. In this research approach, the geochemistry of basaltic rocks is considered a predictive indicator in determining the likely tectonic setting in which the parental magma originated. A global database of basaltic rock data was employed for this project, namely the GEOROC database, which was subdivided according to tectonic settings (convergent plate margin, oceanic island, submarine ridge, and oceanic plateau) for comparing the geochemical signatures against that of the Bushveld Complex. The overall data were analysed following a multidisciplinary approach, i.e. combining geostatistics and programming. Principal component analysis (PCA) was conducted of the Bierkraal trace element data (sampled in the western limb of the complex) by employing various software applications to generate a probability distribution function of the variables, i.e. the trace elements in this context. Initially, PCA identifies the elements that impart the most significant variation to the dataset. These elements function as indicators and identifiers of specific geological and chemical processes. Overall, the geochemical data from the Bierkraal area and those from Layer 21 are crucial for narrowing down the potential tectonic settings exhibiting similar signatures. The settings and locations most synonymous to those of the Bushveld appear to be those of the Kaula and Nihau islands of Hawaii. In addition, Hawaii data exhibit more depletions in elements such as Nb and Y relative to those of the UUMZ of the Bushveld Complex. The same data show overlaps with data from the Fiji and Tonga islands. These oceanic island-island arc settings are influenced primarily by mantle hotspots/plumes. On the other hand, the REE apatite data show a more generalised overlap with most identified tectonic settings within arc-related settings. The geochemical signatures showing the most similarity are those from the lower 300 m segment of the Upper Zone, characterised by multiple magnetite layers, and those from the East Scotia Ridge spreading centre, located approximately 1 288 km to the east of the tip of South America. This ridge is a back-arc tectonic environment associated with diverging plate motions and subsequent rifting, allowing molten rock to push upward and build new crust. Both geochemical signatures from the Bierkraal trace element data and REE apatite data can be related to an enriched magmatic source (i.e. E-MORB). Conventionally, an enriched geochemical signature is associated with magma derived from the lower parts of the mantle. However, taking the geological location and age of the Bushveld complex into consideration, the E-MORB geochemical signature identified in the Upper Zone could be created by the melting of Archaean crust during the upwelling of depleted (N-MORB) magma.
Petrography and geochemistry of hydrothermal breccias hosted in the Schrikkloof Formation (Rooiberg Group), north of Modimolle, South Africa
(University of Pretoria, 2023) Lenhardt, Nils; Robb, Laurence; luzuko.chiya@gmail.com; Chiya, Luzuko
The Schrikkloof Formation, composed of rhyolites, tuffs and hydrothermal breccias, is the youngest rhyolitic volcanic sequence of the Rooiberg Group of the Bushveld Igneous Complex and is known to host polymetallic Sn-F-REE. The aim and objective of this research is to understand whether the hydrothermal brecciation in the upper Schrikkloof Formation is associated with ore forming processes or not. The study area is located approximately 20 km north of Modimolle and a total of 30 rock samples (7 rhyolites, 10 tuffs, 12 hydrothermal breccias and 1 vein) was collected from outcrops. These samples were sent for petrography, XRF (major element analysis), ICPMS (trace element analysis), SEM-EDX analysis (ore mineralogy). Geochemical results (REE diagram and Rb vs Nb+Y) suggest that the Schrikkloof Formation was derived from melting of the continental crust and was emplaced in an intra-cratonic (within-plate) tectonic setting. The sparsely porphyritic and glassy textures of both rhyolites and tuffs, respectively, in the Schrikkloof Formation indicate a subaerial environment. The hydrothermal breccias are particularly hosted within tuffs rather than in rhyolites, perhaps because of competency contrast. Hand-specimen and petrography observations suggested that both tuffs and rhyolites underwent varying degrees of hematitisation and sericitisation alterations. In addition, results also indicated that hydrothermal breccias are predominantly characterised by silica-rich (SiO2 > 70%) clasts cemented by Fe-rich veins (Fe2O3 > 80%). The clasts are mainly composed of quartz and K-feldspar, whereas the cement consists of hematite associated with anglesite (PbSO4) and monazite ((Ce,Nd,La)PO4). The Gresens’ and Grant’s mass balance approach results suggest that the hematitisation process is associated with the overall gain of Pb-Zn-Ce-Nd-La in hydrothermal breccia and hematitised tuffs. In conclusion, hydrothermal breccias are associated with Pb-Zn mineralisation and this may suggest that there is a concealed Pb deposit.
A parametric investigation on the shear strength and bearing capacity of Cenozoic Berea Red Sand with geosynthetic reinforcements
(University of Pretoria, 2021) Van Rooy, J.L. (Jan Louis); Angath, Ellisha
The use of Berea Red sands can be seen extensively among civil infrastructure particularly along the eastern coast of South Africa. These cohesive soils vary in colour, composition, and strength. Despite the understanding of limited works being published on the geotechnical properties on Berea Red sands as well as the implementation of reinforcing agents to improve it, this study was undertaken to investigate the bearing capacity and shear strength of Berea Red sands with and without reinforcing agents. In addition, the concept of reinforcing materials was investigated with the probability of improving the Berea Red sands regarding the abovementioned properties, thereby displaying the novelty of this study. Deformation behaviour under an increasing compressive load of 100kPa, 200kPa and 300kPa was implemented through a suite of consolidated undrained triaxial tests. The triaxial tests provided an appropriate technique to study the effects of stress and strain correlation as well as in obtaining the parameters needed to calculate bearing capacity and shear strength. The triaxial tests compared the behaviour of Berea Red sands under reinforced and unreinforced conditions. The implementation of two different reinforcing parameters were investigated and compared with each other as well as with the original unreinforced test results. The two reinforcing agents used resembled that of a diamond mesh and a mosquito net. Different configurations and layers of reinforcement were implemented in the triaxial tests to better study its contribution and influence on the bearing capacity and shear strength of Berea Red sands. The Berea Red sand properties of bearing capacity, shear strength and strength ratio increased by the implementation of reinforcing agents as well as the increase in reinforcing layers with the 4 layer diamond mesh exhibited the best strength properties when compared to unreinforced samples and 2 layer reinforced samples, across all confining pressures (100kPa, 200kPa and 300kPa).
Sedimentology, palaeoenvironment and structural interpretation of the Cretaceous SW Anambra Basin, Nigeria
(University of Pretoria, 2022-08) Lenhardt, Nils; Bumby, Adam John; Yang, Renchao; u19390514@tuks.co.za; Omietimi, Erepamo Job
The Inland Anambra Basin of Nigeria, formed on the western segment of the Lower Benue Trough, represents the sag phase of the Trough. Its basin infill comprises shallow to marginal marine and freshwater sedimentary clastic deposits of the Cretaceous to Paleogene age. The basin forms part of the larger rift systems of sedimentary basins of the West and Central African Rift Systems (WCARS), a geological chain of faulted and rifted structures that are genetically related. An important part of this study is to investigate the paleosedimentary history of the basin, paleoclimatic implications, paleowater depth, subsurface structures, formation of source beds, petroleum potentials, and evidence for the genetic link between the Anambra Basin and the Benue Trough and other WCARS basins. In order to address this scientific contribution, an integration of multi-proxy tools involving sedimentary geochemistry, mineralogy, organic petrography, rock evaluation, and satellite gravity survey was used in this thesis to provide robust data and new insights. Satellite-derived gravity data based on the total horizontal derivative technique records anomalous Bouguer values ranging from -58 and +28 mGal in generic directions of NE-SW and NW-SE, and the CRUST 1.0 model reports a Moho depth of 37 km. Seven high-anomaly zones (HR1-HR7) and four low-anomaly areas were identified in the research area (HL1-HL4). Additionally, the sedimentary basin depth ranged from 3.5 to 5.0 km, indicating adequate depths for source rock formation and hydrocarbon accumulation. Furthermore, all Cretaceous and Paleogene Formations were influenced by the primary structural trends that dominated the basin's formation history. The transgressive units of the Nkporo, Mamu and Imo Formations in the western segment of the basin from subsurface data revealed dominantly warm, humid tropical paleoclimates with high rainfall in the Late Cretaceous-Paleogene epoch, which corresponds to geologic events in WCARS Cretaceous basins in West Africa. Thus, the geologic record in West Africa indicates intense precipitation and high temperatures during the Cretaceous. The paleoenvironment was reconstructed as predominantly brackish to shallow-marine with some freshwater incursions. Deposition under an oxic environment is detected using a combination of paleoredox markers. On the other hand, anoxic conditions only occurred infrequently in the study area. The presence of wavy laminations in the mudrocks reveals receding seawater and strong paleohydrodynamic conditions. In addition, poor to medium primary productivity was recorded due to terrestrial clastic influx and hydrodynamic settings. Ultimately, the southwestern Anambra Basin is characterized by shallow sea deposits influenced by strong hydroenergy circulation. Furthermore, a high-resolution petroleum investigation suggests that the source rocks have a high potential for conventional gaseous hydrocarbons. An integrated approach based on palynofacies, maceral data, and rock eval interpretations supports type III kerogen in a marginal thermal stress stage. The results of this study contrasted favorably with other Cretaceous WCARS basins and showed that type III kerogen predominated. The basin's northern portion shows good shale gas potential. Finally, shallow marine to marginal marine transgressive, maximum flooding surface, and highstand deposits were detected in this study. The Anambra Basin and the other WCARS basins are genetically linked, as evidenced by similarities in paleoweathering, paleoclimate, paleowater depth, paleosalinity, paleoredox conditions, palynofacies assemblage, and structural trends, despite differences in sediment origin, paleogeographic positions, and the exposure of some WCARS basins to thermal fracture and crustal upheaval.
The potential clogging and filter performance of selected geotextiles with different soil types under unidirectional flow conditions in sub-soil drainage applications
(University of Pretoria, 2022) Van Rooy, J.L. (Jan Louis); Dippenaar, Matthys Alois; Mukwevho, Fhulufhelo Vincent
Non-woven and woven geotextiles have long been used as a cost effective solution in different applications such as separation, reinforcement, protection, filtration and drainage. One of the most common use of geotextiles is as filters in sub-soil drainage systems. The main function of a filter is to retain particles of the base soil whilst maintaining a good flow of water through the system. There’s still a lot of uncertainties concerning the long term performance of geotextile filters in filtration and drainage applications. However, there’s a lot of ongoing research to better understand the performance of these products. The purpose of this study is to determine the range of problematic soils in the particle size distribution graph and soil-geotextile compatibility of the different soils with selected geotextiles. In order to achieve the ultimate objective of the study, analysis of the permeability, gradient ratio, coefficient of uniformity and clogging potential of the soil-geotextile systems was achieved through the filtration compatibility test (Long Term Gradient Ratio test) of five different geotextiles against 3 soil types. The soil-geotextile systems were subjected to a maximum waterhead of 1420 mm for a maximum of 1008 hours or until the system has reached equilibrium. The results have shown that soils with high clay/silt fractions tend cause blocking, blinding, and clogging which can close most of the geotextile filter pores. Larger sand/gravel sized particles tend to form a filter bridge that hold back finer soil particles. Sandy gravel with bidim A2 and sandy gravel with bidim A4 were the overall best performers with overall gradient ratios of less than 1 which represents a more open filter. The gradient ratios of the other soil-geotextile combinations were higher than 1 which represents clogging and reduction in permeability. However, no geotextile was completely clogged by the soils.
Geochemistry and spatial variation in dolerites of the Drakensberg Group, Karoo Supergroup, South Africa
(University of Pretoria, 2022-03-08) Roberts, R.J. (James); u04541686@tuks.co.za; Kotze, Arnoldus Daniel
The Karoo Large Igneous Province (KLIP) in South Africa comprises a spatially limited basalt suite (Drakensberg Group) and a spatially extensive dolerite suite. This study aims to establish a tectonic regime that could have facilitated the KLIP and the extent of geochemical variation in the dolerite suite. Principal component analysis (PCA) is used to identify trends as this multivariate statistical operation is particularly well suited to identifying possible petrological processes. Major and trace element chemistry is interpreted from data made available by GeoROC, a public geochemical data depository. This study observed 139 samples of which 49 were basalts and 90 were dolerites, sampled along a c. 1500 km E-W tract along the southern margins of the Karoo basin. Disassociations between the KLIP and surficial manifestations of mantle plumes are discussed. Transition metal chemistry is described using Co, Cr, Cu, Ni, V, and Zn; however, anomalies in the transition metal data resulted in only LILs (Ba, Sr, and Rb) and HFSEs (Nb and Zr, and the REEs Ce, La, Nd, and Y) being used to investigate spatial variation in the KLIP. Spatial variation could not be inferred with major element chemistry nor with trace element chemistry, and the data is remarkably compatible to the lower crust. Although it is suggested that gravity could have been a driving force behind the KLIP, further studies must be done to provide a better understanding of the relationships between the KLIP and its host geology.
Comparison of the engineering geological properties of near surface and deep sedimentary rocks of the Karoo Supergroup, South Africa
(University of Pretoria, 2021) Van Rooy, J.L. (Jan Louis); humanhendre@gmail.com; Human, Hendrik Gert
The sedimentary rocks of the Karoo Supergroup cover approximately 75% of the surface area of South Africa. Major projects have been constructed on and in these rocks with a number of tunnelling projects such as the Lesotho Highlands Water Project and the Orange-Fish Tunnel. The mechanical properties of these rocks have been well studied and recorded through research and construction projects. During the exploration phase for shale gas, two deep boreholes were drilled in the southern part of the Main Karoo Basin, near Willowvale and Ceres. This provided the opportunity to access rock samples from deep formations. Various laboratory tests were done on selected cores to be able to determine the engineering properties and strength characteristics of the deep Karoo Supergroup rocks, and these engineering properties and strength characteristics are compared to the shallow or near surface rocks, which is presented in this dissertation. Five core samples from the Willowvale borehole (KWV-01) were retrieved for laboratory testing, which include samples of a dolerite sill, sandstone from the Pluto’s Vale Member, carbonaceous shale from the Whitehill Formation, massive shale from the Prince Albert Formation, and lastly, tillite from the Dwyka Group. Four core samples were retrieved from the Ceres borehole (KZF-01) and, included fine sandstone from the Tierberg Formation, carbonaceous shale from the Whitehill Formation, shale from the Prince Albert Formation and diamictite from the Dwyka Group. The density, porosity, water absorption, specific gravity, slake durability, free swelling and mineralogy of the different rock samples were determined and compared between the two boreholes (KZF-1 & KWV-1), as well as with those of the known properties of the near surface Karoo rocks published in literature, and also results from twelve surface samples collected during this research project. The Geodurability Classification system is used to classify the core samples, so as to determine its durability. The sandstone, shale and tillite show increased UCS, durability, density, and lower expansiveness when moving from surface deeper into the Main Karoo Basin rocks.
Geotechnical and risk analyses for the positioning of shafts at the Wesizwe Platinum project
(University of Pretoria, 2011) Handley, M.F. ; vcmostert@twp.co.za; Clark-Mostert, Vennessa
The Wesizwe main and ventilation shaft positions are sited within an almost square block formed by four faults. The shaft positions were not sited within the centre of gravity of the Wesizwe lease area. This is due to factors related to the local community and various environmental issues. It was decided to position the shaft in the current block as geological and rock engineering confidence was high in regard to the structures within the area, and the shaft position was falling within the allowable distance radius from the nearby community and river boundary. A seismic survey, conducted on the area, indicated a near vertical fault. The fault, which has a 30m throw, occurs approximately 50m north of the position at which the main shaft was site. It was suggested that this fault, which was a reinterpretation of the northern boundary fault, would have a negative effect on the rock mass behaviour in the shafts. Previously it was noted that the shaft level breakaways and geotechnical borehole information do not correlate. A 20m vertical discrepancy was observed between the planned Merensky breakaway and the Merensky position indicated by drilling. The logical interpretation was that this was due to faulting and a note was sent out to make the project team aware of this 20m discrepancy. This was again brought to the team’s attention upon the release of the seismic study interpretation indicating a 30m fault in this area. Geotechnical logging had already been done on the diamond drill holes sunk at the positions indicated for the Wesizwe Main and Vent Shafts. The rock mass ratings indicated that these positions were favourable and that the rock mass of the shafts can be referred to as “Good Rock”. To determine what the geotechnical character of the fault was, four boreholes (WF01, WF049, WF059 and WF090) were geotechnically logged at the predicted depths of the fault intersection. Two zones carrying less competent ground were identified near the fault intersection positions as was indicated by the seismic interpretation. By combining the zones into one area of less competent ground it was found that the affected area does not exceed a vertical influence of 58m, and has a minimum vertical influence of 25m. The rock mass in these affected areas are overall rated as “poor rock” to “exceptionally poor rock”. The rock quality designation (RQD) ratings for the affected area fall between 36 to 52 %. A decision needed to be reached as to whether the shafts would be developed at the positions indicated, or whether a new area needed to be selected for the main and ventilation shaft positions. This decision was reached by combining all available information and weighing the risks related to the options. From this study, a general approach to shaft positioning for platinum projects was formulated.
Problems in parameter estimation in probabilistic seismic hazard analysis and some solutions
(University of Pretoria, 2020) Kijko, Andrzej; u28038020@tuks.co.za; Vermeulen, Petrus Johannes
Probabilistic Seismic Hazard Analysis (PSHA) is not a new study field — indeed, it dates from the late 1960s. However, the original and introductory study paid scant attention to a crucial aspect, namely the estimation of the model parameters. Consequently, over the ensuing five decades, Parameter Estimation in Probabilistic Seismic Hazard Analysis (PE-PSHA) has not gained due recognition as an independent field of study. A review of the relevant body of literature indicates that PE-PSHA is not yet regarded as an entity, a coherent body of literature, or a study field. This study aims to introduce PE-PSHA as a distinct field of study. In 1968, Cornell introduced what is known today as Probabilistic Seismic Hazard Analysis (PSHA). Although a landmark study, it is peculiar and even astonishing that Cornell (1968) simply ignored the crucial aspect of parameter estimation of models. This aspect and the implications of ignoring the importance of parameter estimation are discussed in detail in this thesis. Seismicity modelling in general and the classic Cornell–McGuire procedure are introduced, which provides the platform for the introduction of the parameters typically associated with it, usually referred to as seismicity parameters. Subsequently, each parameter is discussed in detail, clarifying the development of estimation techniques, as well as the problem areas that could be identified. In some instances, solutions are put forward, either as own research by the author or gleaned from the literature. A discussion is presented on the magnitude of completeness (𝑚𝑐) of seismic catalogues, along with a critical analysis of the estimation techniques currently employed. Concerns about some of these methods are discussed comprehensively and clarified by detailed argument. The two principal model parameters are discussed, namely the Gutenberg–Richter 𝑏-value and the rate of seismicity (RoS). A review of the estimation techniques of these parameters is presented, as well as the problems encountered. This review also serves as an overview of the historical development of the estimation of the two parameters. Various solutions have been put forward to some of the problems encountered; however, these solutions are not being employed. Subsequently, some estimators for the 𝑏-value for incomplete catalogues are compared. The maximum possible earthquake magnitude for a given area (𝑚𝑚𝑎𝑥) from the seismic catalogue data is discussed. A few procedures (or estimators) have been proposed, although only by a few researchers. The estimators are discussed in some detail and are analysed critically, among which are methods newly investigated by the author. The concept of seismic zones is discussed, as, although seismic zones are not parameters, the delineation of seismic sources is a modelling procedure that requires estimation from the catalogue data similar to estimating parameters (this can be regarded as a generalised part of parameter estimation). The practice of seismic zoning based largely on expert opinion is analysed critically, and a number of alternatives are discussed. In the conclusion to the study, the need for PE-PSHA to be regarded as an entity, or separate field of study, is highlighted. In addition, the discussed problems and solutions are reviewed, and recommendations are made. Finally, possible future research areas are pointed out.
Mechanical and hydraulic properties of residual dolomite and wad found in the Malmani Subgroup in South Africa
(University of Pretoria, 2019) Dippenaar, Matthys Alois; Van Rooy, J.L. (Jan Louis); u14312868@tuks.co.za; Swart, Duan
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.
Engineering geological mapping for urban development in low relief semi-arid regions (Outapi northern Namibia)
(University of Pretoria, 2019) Dippenaar, Matthys Alois; u15305083@tuks.co.za; Shaanika, Giesberta Naipopya
Considering the current lack of engineering geological mapping in urban developments in Namibia, it was necessary to pioneer the input of engineering geology in the planning of infrastructure. The benefits of engineering geological mapping in sustainable development were highlighted and present methodologies were explored, looking at their applicability to Namibia. The early activities of engineering geological mapping include terrain classification, which groups areas of terrain that have similar conditions. It applies the principle of homogeneity such that areas falling under one terrain class are treated the same during planning, as they are deemed to have the same impact on engineering structures. The traditional way of doing terrain classification places much reliance on topography features, such as valleys, streams, etc. However, this becomes fairly difficult to apply in flat lying areas where topographical features may not be readily visible from aerial photographs. Therefore, soil variability mapping using colour and texture, vegetation mapping, and damage distribution mapping or structural damage techniques were recommended to aid terrain classification in flat lying semi-arid environments. Employing these techniques, Outapi Town in northern Namibia was mapped, identifying four terrain classes. With subsequent testing methods, these were upgraded to just three engineering geological zones. The main geotechnical constraints identified include the possibility of collapse settlement given the aeolian nature of the Outapi soils, susceptibility to flooding attributed to the flat nature of the area with no properly defined pathways, potential for dispersion as the soils are rather fine and saline, and, to a lesser extent, the presence of potentially expansive soils.
Physico-chemical properties of South African shales and siltstones in the context of geological CO2 storage
(University of Pretoria, 2020) Altermann, Wladyslaw, 1954-; Van der Merwe, Liesel Laura; Doucet, Frédéric J.; nnxokwana@geoscience.org.za; Nxokwana, Ngqondi Songezo
Shale is normally impermeable and has a low porosity; it was therefore not considered by the project on geological storage of CO2 in South Africa (the “Atlas” project) as a potential storage reservoir. However, research in other parts of the world such as the United States of America (USA) on carbonaceous shales similar to those of the Central Karoo Basin of South Africa has proved that shales store significant amounts of CO2 in an adsorbed state within their organic matter, also known as kerogen. The paucity of conventional storage reservoirs for the geo-sequestration of CO2 in the interior of South Africa, where most sources of the anthropogenic CO2 are situated, has prompted this study, which focuses on the carbonaceous shales and siltstones of the Karoo Basin of South Africa and their potential for CO2 adsorption. Six samples from five old Soekor boreholes were selected for the study and their physico-chemical properties were studied through parameters such as petrography, mineralogy, elemental composition, bulk density, maturity (vitrinite reflectance), kerogen, total organic content (TOC), low pressure adsorption and high pressure adsorption. In terms of TOC, which is one of the important parameters for gas adsorption onto shales, the studied carbonaceous shale samples compare quite favourably to those from other parts of the world that have been found to successfully store significant amounts of CO2. These include the Barnett Shale of the USA which measures 4.00 wt.% of TOC and the famous Marcellus shale (USA) with 1–10 wt.%. The Irati and the Rio Bonito formations of Brazil have the highest TOC values found in the literature, measuring 2.3–26.30 wt.% and 1.7–43.90 wt.%, respectively. The Whitehill Formation of the Karoo Basin of South Africa has values of 0.5–14.70 wt.% TOC as described in the literature. In this study a sample from the Whitehill Formation from borehole G39974 gave a measured value of 4.52 wt.%, while a sample from the underlying Prince Albert Formation, from borehole KL 1-65, measured a value of 1.17 wt.% TOC. In the north-eastern part of the Karoo Basin, two samples from the Pietermaritzburg Formation, a north-eastern stratigraphic equivalent of the Whitehill Formation which pinches out in this part of the basin intersected by boreholes SW 1-67 and LA 1-68, measured 2.50 wt.% and 0.77 wt.% TOC, respectively. Sample 1124.5 from the Volksrust Formation intersected by borehole BE 1-67 measured 0.21 wt.% TOC. For maturity studies, all the six samples measured reflectance values above 1.4%Ro and are therefore classified as overmature. A plot on the HI vs Ol index plot revealed that these samples plot predominantly below the gas prone Type III kerogen curve. The samples exhibit a specific surface area of 17.40–21.88 m2/g, with an average of 19.66 m2/g. This compares quite favourably with the gas-bearing Silurian shales in the Sichuan Basin (China) which exhibit a specific surface area of 17.83–29.49 m2/g, with an average of 22.18 m2/g. There is also a trend of increasing surface area with TOC content, affirming the influence of organic matter on the surface area. The high pressure adsorption experiments on the samples exhibited anomalous behaviour which affected the credibility of the results. Most experiments showed an unprecedented increase in pressure instead of the expected decrease due to the CO2 being adsorbed onto the shale samples. The samples are from the old Soekor drill cores which have been exposed to the atmosphere for over 40 years and have undergone severe weathering during that period. The weathering and the degree of oxidation and break-down of pyrite are strongly suspected to be the cause of the anomalous behaviour. Based on the content of organic matter and kerogen, these samples have potential to store CO2. However, maturity studies have revealed that these shales and siltstones are in fact overmature and at this stage are likely to have less gas generating capacity and thus less affinity to adsorb CO2. This could be argued also in favour of storage capacity as the gas does not disturb contact of CO2 to rock, however, the high tightness as a consequence of over-maturity will have a higher negative effect on adsorption potential. Further studies on freshly drilled core samples are recommended to ascertain these findings given the limitations posed by the condition of the current samples, especially in studying the adsorption behaviour. Only then can we conclusively deduce whether or not the shales and siltstones of the Karoo Supergroup have a role to play in South Africa’s anthropogenic CO2 geo-sequestration endeavours.
Use of tritium and stable water isotopes to assess contaminant transport at a burial site in Middelburg, Mpumalanga
(University of Pretoria, 2020) Diamond, Dr. Roger; Lorentz, S.A. (Simon A.); Dippenaar, Matthys Alois; u28498021@tuks.co.za; Mahlangu, Sarah Ndazi
When different water resource components coexist in nature, they usually have an impact on each other. Studies of how they impact each other in terms of water quantities, flow dynamics, quality and contamination are therefore necessary to ensure an appropriate water and environmental management is conducted. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large-scale burials. A literature review conducted has enabled familiarisation with similar studies that have been conducted around the subject. Reliable methodologies have therefore been adopted from the published literature and applied on the current research. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways of near-surface and groundwater from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the cemetery. Water samples collected were analysed for inorganic constituents, tritium, and stable water isotopes. The tritium and stable water isotope results – revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation in the vadose zone due to reduced conditions and the wetland acting as a filter to improve the water quality of the shallow interflow on reaching the stream. Since isotope data indicated to be a useful tool in studying water resource interactions, the methodology should form part of site investigations for cemetery development or on existing cemeteries to study the current impact and/or predict future impacts that the cemetery may have on the water resources. The methodology best applies in areas with multiple water resources, where there may be an interconnection between them. The isotope studies can also be used to estimate recharge and thus contaminant transport rate of the cemetery leachate.

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