Theses and Dissertations (Geology)

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A petrochemical investigation of the Spitskop Alkaline Complex, Eastern Transvaal
Nel, David. Jacobus (University of Pretoria, 1976-10)
This study comprises a petrographical and mineralogical description of the rocks of the Spitskop Complex. Data on the chemical composition of the rock types, as well as on some of the minerals, are presented. The complex consists of a pyroxenite pipe near the perimeter of which is situated a composite ring-dyke of foyaite. Ijolite is present as dykes and sills in the pyroxenite, and the carbonatite occurs as a plug intrusive into the pyroxenite. The complex is surrounded by an aureole of umptekite, and xenoliths of gabbroic rocks and magnetitite are present within the complex. A plug and sill of latite inside the complex, as well as dykes and cone sheets of latite and trachyte in the country rocks, were encountered. Profiles of eight core boreholes, drilled to depths between 30 and 40 metres into the complex, are presented, together with thirty-two rock analyses, fifteen mineral analyses, and variation diagrams showing the chemistry of the clinopyroxenes. The borehole profiles indicate that the ijolite is intrusive into the pyroxenite in the form of sills and dykes. This feature is further confirmed by the nature of the outcrops to the west of the carbonatite. The foyaite is subdivided into porphyritic, hypidiomorphic, and trachytoidal textural varieties, and the ijolite into hypidiomorphic and porphyritic varieties. The chemical variation diagrams indicate that the clinopyroxenes of the alkaline rocks follow differentiation trends typical of alkaline complexes, whereas those of the theralites show trends similar to those usually found in layered intrusions. From the geochemistry, the following order of emplacement may be derived: pyroxenite – ijolite – foyaite, in cases where a low CO₂ pressure prevailed in the magma; and pyroxenite – ijolite – carbonatite, in cases of a high CO₂ pressure. The Upper Zone of the layered sequence of the Bushveld Complex is postulated as the source of the theralites, which are here interpreted as xenoliths within the Spitskop Alkaline Complex. A vertical displacement of not more than a few hundred metres is suggested.
The upper zone of the Bushveld complex at Tauteshoogte
Boshoff, J.C. (University of Pretoria, 1942-01)
Mineralogy of the lower part of the upper zone, eastern Bushveld Complex : implications for ore-forming processes
Harney, Dirk M.W. (University of Pretoria, 1991)
English: The lower part of the upper zone in the eastern Bushveld Complex was subjected to a detailed mineralogical investigation, aimed at gaining a better understanding of processes that led to the formation of the main magnetite layer (MML), sulfide-enriched horizons and possible concentrations of platinum-group elements (PGE). The most prominent rock types in the investigated stratigraphic sequence are anorthosites, containing variable amounts of magnetite, which are interlayered with gabbronorites, leuco-gabbronorites and magnetite layers. Elevated sulfide concentrations are commonly associated with magnetite layers. The highest values were found in an anorthosite directly below the MML, and the sulfide assemblage typically contains pyrrhotite, chalcopyrite, cubanite and pentlandite in decreasing order of abundance. PGE are not enriched in specific stratigraphic horizons, as in those known from the critical zone. However, a local concentration of Pt and Pd has been encountered in the sulfide-bearing anorthositic footwall of lower magnetite layer 2. Several Pt-Pd-Bi-Te minerals were found, namely michenerite, moncheite, merenskyite and froodite, and textural as well as compositional evidence indicates that these platinum-group minerals are of hydrothermal origin. Post-magmatic hydrothermal processes also affected the mineralogy and composition of sulfides above the MML. Pentlandite, in particular, reflects such hydrothermal activity and displays varying, but considerably elevated, Co concentrations. Changes in the Sr content and the Sr/Al 2o3 ratio of plagioclase, the whole-rock PGE concentration pattern and possibly also the composition of pyroxene at the level of the MML show that the MML formed in response to a magma mixing event between the resident and a less differentiated magma. Magma mixing resulted either from a breakdown of density stratified liquid layers or an influx of a small volume of new magma (up to 30 % of the hybrid). In addition to the formation of the MML, magma mixing is also believed to have caused the segregation of sulfides associated with that layer. It is concluded that the evolution of the upper zone does not reflect simple differentiation, but that it was interrupted by magma mixing events which occurred at the level of the MML and possibly also at other levels during crystallization of the upper zone. Afrikaans: Die onderste gedeelte van die bosone in die oostelike Bosveldkom-pleks is mineralogies noukeurig ondersoek met die doel om 'n beter begrip te vorm van die prosesse wat aanleiding gegee het tot die ontstaan van die hoofmagnetietlaag (HML), sulfied-verrykte lae en konsentrasies van die platinum-groep elemente (PGE). Die mees algemene gesteente tipes in die stratigrafiese suksessiewat ondersoek is, is anortosiete met varierende hoeveelhede magnetiet, wat tussengelaagd is met gabbronoriet, leukogabbronoriet en magnetietlae. Verhoogde sulfiedkonsentrasies is meestal geassosieer met magnetietlae. Die hoogste konsentrasies kom in 'n anortosietlaag direk onderkant die HML voor. Die mees algemene sulfiedassosiasie bevat, in volgorde van afnemende hoeveelheid, pirrhotiet, chalkopiriet, kubaniet en pentlandiet. Die PGE is nie in enige van die sulfiedgemineraliseerde lae verryk nie. Lokale verryking van Pt en Pd is egter teegekom in die sulfied-draende anortosiet net onder die laer magnetietlaag 2. Verskeie Pt-Pd-Bi-Te minerale is teegekom, te wete micheneriet, moncheiet, merenskyiet en froodiet. Tekstuur en samestelling dui daarop dat hierdie platinumminerale van hidrotermale oorsprong is. Na-magmatiese hidrotermale prosesse het ook die sulfied-mineralogie en samestelling bokant die HML geaffekteer. Veral pentlandiet reflekteer sodanige hidrotermale aktiwiteit en toon varierende, maar aansienlik verhoogde, Co konsentrasies. Veranderings in die Sr-inhoud en die Sr/Al 2o3 verhouding van plagioklaas, die heelgesteente PGE konsentrasiepatroon en moontlik ook die samestelling van pirokseen by die posisie van die HML dui daarop dat hierdie laag moontlik ontstaan het as gevolg van magmavermenging tussen die kristalliserende magma en 'n minder gedifferensieerde een. Magmavermenging kan of die gevolg wees van die ineenstorting van digtheidsgestratifiseerde vloeistoflae, of die gevolg van die invloei van 'n klein volume nuwe magma (tot 30 % van die hibriede produk). Bykomstig tot die ontstaan van die HML, word magmavermenging ook beskou as die oorsaak te wees vir die segregasie van sulfiede geassosieer met die laag. Daar word tot die slotsom gekom dat die ontstaan van die bosone nie die gevolg van 'n eenvoudige differensiasie is nie, maar dat dit onderbreek was deur episodes van magmavermenging soos byvoorbeeld by die HML en moontlik ook op ander tye tydens kristallisasie van die bosone.
Characterisation of weathering propagation from joint surfaces in different rock types
Bruyns, Leandi (University of Pretoria, 2025-04)
The propagation of weathering into adjacent rock material from joint surfaces represents a significant gap in the Engineering Geology field, requiring further investigation and detailed analysis. The impact of weathering on the engineering properties of rocks stands as an indispensable consideration in geotechnical designs, as it intricately alters the quality of the rock mass across temporal scales. This also influences the engineering lifetime of structures (slopes or tunnels) and the appropriate design parameters for these structures. This study encompassed a thorough analysis of various properties, including the physical, mineralogical, and textural attributes of the rock. This investigation sought to reveal how these properties undergo transformation as the process of weathering from a joint surface extends into the adjacent parent material. Physical properties were assessed using the Schmidt hammer test to derive rebound numbers (R-values), while mineralogical and textural analyses were conducted through Polarized Light Microscopy, Scanning Electron Microscopy (SEM), X-Ray Fluorescence (XRF), and X-Ray Diffraction (XRD) techniques. Weathering indices, including the Chemical Index of Alteration (CIA), Mineralogical Index of Alteration (MIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA), were used to assess the degree of weathering across each sample. Indications of weathering were evident at the periphery and adjoining rock material of the samples. Fracturing was deemed as being one of the main drivers during the process of propagating weathering. The thin sections indicated that the process of weathering propagated further into the unexposed portion of the rock, unnoticeable to the naked eye. Weathering indices revealed granite as the least weathered rock sample, followed by quartz-diorite and shale. Samples with lower quartz content experienced a greater reduction in hardness (strength), indicating the role that mineralogy plays in the ability of a rock to resist the weakening effects of weathering. The chemical composition of a rock, as determined by X ray Fluorescence (XRF) analysis, provides valuable insights into both the degree of weathering the rock has experienced and its potential for future weathering. This relationship is primarily influenced by the mineralogical composition of the rock, as different minerals weather at varying rates. Igneous rock samples exhibited a linear correlation between weathering degree and visible weathering propagation depth. The relationship between the decrease in hardness (strength) and the depth of weathering propagation revealed that as the depth of weathering propagation increased, the greater the decrease in hardness of the rock material adjacent to the joint. The joint weathering classification scheme adaptation, in which the methods of Amin et al. (2000) and Barton et al. (1977) were combined and used as a basis for the adaptation proposed, indicated that the igneous rock samples classifies as intermediately weathered, whereas the sedimentary rock sample (shale) classifies as slightly to intermediate based on the percentage decrease in hardness (strength) from the unexposed regions of the samples to the exposed regions of the samples as well as the zoning and depth of discolouration observed within the material adjacent to the joint opening. Each rock type showed distinct joint zoning patterns resulting from weathering propagation. This indicated that each rock responded differently to the process of propagating weathering. This highlights the importance of recognising that not all rocks react to weathering in the same way and emphasises the inadequacy of a single classification system for diverse rock types.
Combined use of environmental and artificial tracers to characterise the anthropogenically altered vadose zone and groundwater system
Van Wyk, Yazeed (University of Pretoria, 2024-11)
Understanding groundwater flow and contaminant transport in fractured rock environments is critical for sustainable water resource management, particularly in regions impacted by mining activities. Open-pit quarries significantly alter the natural hydrogeological regime by modifying recharge pathways, introducing contaminants, and enhancing preferential flow through fractures. This research systematically investigates the transport mechanisms and pathways of environmental and artificial tracers within the anthropogenically altered fractured vadose zone of an open-pit quartzite and sandstone quarry located approximately 20 km east of Pretoria, South Africa. The study employs a combination of environmental tracers (δ¹⁸O, δ²H, ³H) and artificial tracers (uranine, rhodamine WT) to characterise both the vadose and saturated zones, quantify fluid dynamics, and explain important tracer transport processes. A hydrocensus assessment and hydrochemical analyses were conducted and revealed two distinct water types: shallow groundwater samples displayed a calcium-magnesium bicarbonate facies, indicating relatively fresh shallow groundwater with little chemical alteration from recharge to discharge, while pit water samples exhibited a calcium-magnesium-sulphate facies, reflecting sulphide mineral dissolution and contamination from legacy waste disposal. Stable isotope analyses (δ¹⁸O:-5.40‰ to-1.20‰, δ²H:-32.0‰ to-5.80‰) highlighted diverse recharge sources and evaporation effects, with D-excess values (4.04‰ to 14.94‰) further differentiating groundwater and surface water interactions. Tritium concentrations ranged between 0.0 and 2.3 Tritium units(TU), with a mean of 0.9 TU. Groundwater samples exhibited tritium concentrations between 0.4 and 1.0 TU, suggesting relatively older water or a mix of old and young recharge. Quarry pit water samples displayed tritium values of 1.0 to 1.1 TU, indicating a more recent recharge isotopic signature, suggesting that the pit water is primarily influenced by recent precipitation, runoff, and groundwater seepage. These findings provide insights into the groundwater recharge dynamics and the influence of quarrying activities on flow systems. Tracer experiments revealed significant seasonal variations in transport dynamics. During the wet season, mean residence times ranged from 0.689 to 2.043 hours, with an average of 1.1–1.3 hours, reflecting slower transport under higher soil saturation. In contrast, the dry season showed faster tracer movement, with residence times between 0.106 and 0.184 hours (average 0.13–0.15 hours), aligning with the observed higher flow velocities (0.009 m/s) despite lower saturation. This suggests that increased flushing volume temporarily enhanced hydraulic gradients by increasing the volume and pressure of water moving through the system. The resulting higher flow velocities likely reflect a more pronounced hydraulic gradient, even under lower soil saturation. If there has been any anthropogenic disturbance of the aquifer, such as changes in permeability due to mining or excavation activities, this could also contribute to localised increases in hydraulic conductivity, further accelerating transport. This would also be consistent with the lower recovery rate of 10% due to greater flow divergence from the injection point. The distance from the tracer injection to the breakthrough point was 6.5 meters, further emphasising the observed variations in transport dynamics. The application of analytical models (MDMi and MDP-2RNE) effectively captured seasonal variations in flow velocities, dispersion, and fracture connectivity. Péclet numbers and mean transit times varied between seasons, with higher velocities and lower retardation factors during the wet season, reflecting enhanced connectivity under saturated conditions. A steady-state water balance analysis was conducted to quantify inflows and outflows within the quarry pit lake system. The results indicated a water balance deficit of -30.96 ML, suggesting that estimated inflows (74.88 ML/a) were significantly lower than outflows (105.84 ML/a). This discrepancy was attributed to unaccounted surface runoff, which was not explicitly incorporated into the initial balance calculations. Given the quarry’s inward-draining nature, with steep gradients directing water towards the pit, additional runoff contributions were estimated based on a mean annual runoff rate of 42.2 mm/a for the quaternary catchment. When incorporating this missing runoff component (MARunoff = 79.3 mm/a), the observed deficit was largely reconciled, reinforcing the importance of considering surface runoff in hydrogeological assessments of open-pit mining environments. The hydrogeologic conceptual site mode (CSM) was developed from the geology, borehole lithology, structural geology, groundwater and surface water features. The CSM was supported by modelling results, which successfully validated the tracer results and represented groundwater flow and contaminant transport pathways. This model highlighted the impact of fractures and human-induced changes on the vadose zone, accurately capturing the key flow and transport processes. Key findings demonstrate the effectiveness of combined tracer methods in characterising the vadose zone and emphasise its critical role in groundwater contamination assessments. This research provides innovative insights into flow and transport dynamics in fractured, unsaturated systems, contributing to mine water management and understanding contaminant behaviour in such environments. Furthermore, these findings have broader implications for contaminant transport in anthropogenically altered vadose zones beyond mining environments. For example, previous research on potential SARS-CoV-2 contamination of groundwater in cemeteries has highlighted the risks associated with sinkhole formation and enhanced infiltration in altered vadose zones, which share similar hydrogeological characteristics with open-pit quarries. This study, therefore, shows the importance of understanding fluid pathways and contaminant mobility in disrupted subsurface environments, informing sustainable water resource management in both mining and burial site contexts. By integrating empirical data with tracer based analytical techniques, this work further highlights the importance of understanding complex interactions within anthropogenically altered vadose zones, ultimately supporting sustainable water resource management in open-pit mining operations.
Evaluating hydraulic and mechanical properties of weathered intrusive and chemical sedimentary bedrock in South Africa
Swart, Duan (University of Pretoria, 2024-11)
Weathered rock profiles are frequently encountered during geological, engineering, hydrological, ecological and forestry projects in South Africa. The soil-end exists in the most decomposed portion of a weathering rock profile. This zone comprises residual soil and completely weathered rock, both of which can be excavated as a soil. In this study, completely weathered rock retains the parent rock fabric and macro-structure with secondary minerals forming in place of the primary rock-forming minerals. Residual soil forms through further intensive chemical weathering to the point where most parent rock structure and grain relations have been lost either through decomposition or volumetric strain or a combination of both. The study was conducted with the use of traditional geotechnical laboratory methods, of which the results were compared and analysed with advanced visual techniques. The laboratory testing included particle size analysis and Atterberg limits testing, chemical testing methods, compression testing in oedometers, and saturated permeabilities in a triaxial cell. The advanced visual testing comprised X-Ray Computed Tomography (XRCT) scan that allowed for the modelling of 2D and 3D porosity and density models. These models provide invaluable insight on the structural properties that govern the compression behaviour the completely weathered rock and residual soils. The soil texture of the completely weathered rock and residual soil can be determined from simple field tests that only require water and common stationery. These tests make use of well understood behaviour characteristic of fine-sand, silt, and clay at varying moisture to determine the plasticity of the material, and subsequently the soil texture. The process through which completely weathered rock and residual soil form is governed by the physical and chemical changes caused by chemical weathering. The degree of weathering decreases with an increase in depth into the ground profile. The state of weathering can be quantified with the use of chemical weathering indices. The close relationship between the chemical and physical states of completely weathered rock, allows for the determination of structural prominence, which characterises the degree to which the relict rock structure influences compression behaviour. The structural prominence decreases as weathering increases and, consequently, this increases the compressibility of the material, regardless of the material’s void ratio or dry density. The novel concept of structural prominence can be used to assist engineering geologists and geotechnical engineers to better understand the behaviour of completely weathered rock and residual soil and has been shown in this study to be a better predictor of soil compressibility than the dry density or void ratio.
A geochemical assessment of old slimes tailings from two South African kimberlite diamond mines : implications for mineral-carbonation resource estimation
Vele, Mpho (University of Pretoria, 2025-01)
The potential of mineral carbonation as a method for capturing anthropogenic CO₂ is still to be developed within the context of South Africa, a country with significant CO₂ mitigation opportunities through the utilisation of suitable current and historic mine tailings. Historical tailings can offer supplementary sequestration capacity, given their geochemical and physiochemical properties are conducive to CO₂ reactivity. Thus, the study focuses on utilising historic tailings from two prominent diamond mines, Cullinan and Finsch, owned and operated by Petra Diamond Limited, to quantify their geochemical and physiochemical suitability for mineral carbonation resource estimation. Geochemical investigations were conducted, and the major oxide composition analysis revealed SiO₂ as the dominant oxide in Cullinan (42%) and Finsch (38%) tailings. Cullinan tailings had a relatively higher MgO concentration of 23% compared to Finsch (20%), while CaO was significantly higher at 7% for Finsch than Cullinan (3%) tailings. Mineral identification highlighted the modal heterogeneous nature of these tailings, with talc occupying 53 % of Cullinan’s total mineral composition and phlogopite dominating Finsch samples at 28%. The particle size distribution measurements indicated coarser particles in Finsch (D(v,90) = 277 µm) compared to Cullinan (D(v,90) = 85.4 µm), highlighting the variability in particle size between the tailings from different sites. Density measurements were conducted to estimate the tonnage values of the tailings. Therefore, densities of 1.86 g/cm3 for Cullinan and 1.79 g/cm3 for Finsch were used to calculate these values. By employing Digital Elevation Models (DEM) and density measurements, the estimated tonnage of Finsch tailings was ~ 13 times greater than that of Cullinan, which was remotely calculated as 26 702 611 metric tons (Mt). Consequently, the relative CO₂ sequestration capacity for Finsch and Cullinan was estimated to be 434 kgCO₂/t and 428 kgCO₂/t, respectively. Therefore, Finsch possesses a substantial amount of material suitable for carbon dioxide removal (CDR). Simulations of a Direct Mineral Carbonation (DMC) process using talc as the reacting mineral indicated a suboptimal CO₂ capture efficiency of 9%. The economic evaluation of the DAC process highlighted high operational costs, resulting in a negative present value (NPV), and this was categorised as a high-risk conceptual scoping study following the South African Code for the Reporting of Exploration Results, Mineral Resources and Reserves (SAMREC). The study quantified and characterised historic tailings from Cullinan and Finsch diamond mines, ultimately shedding light on their potential to provide additional sequestration capacity as a mineral carbonation resource. It also underscores the need for a comprehensive techno-economic assessment (TEA) using more reactive mineral feedstock and better-suited carbonation technology. Lastly, it provides a baseline for estimating the economic value proposition of using mine tailings for CDR.
Textural analysis and plagioclase grain size distribution of the Rooiberg Group, Bushveld Igneous Complex, South Africa
Brown, Melissa (University of Pretoria, 2024-01)
The Rooiberg Group, occurring within the Kaapvaal craton at ~2,06 Ga, is a silicic large igneous province (SLIP), is a precursor to, and is synonymous with the Bushveld Igneous Province (BIC), the world’s largest mafic body. The Rooiberg Group’s volcanic successions, namely the Dullstroom, Damwal, Kwaggasnek, and Schrikkloof formations, were previously interpreted as largely consisting of lava flows, ranging from low- and high-Ti basalts to high- Mg rhyolites. Lenhardt et al. (2017) challenged the dominant lava-flow interpretations and proposed the Rooiberg Group is dominantly composed of highly welded, lava-like ignimbrites. In this study, petrographical and textural analysis was undertaken, and plagioclase grain size distributions studied throughout the Rooiberg Group formations to bring to light a clearer understanding of the Rooiberg Group’s eruptional and emplacement styles, as well as the palaeoenvironment and volcanic origins. The Dullstroom and lower Damwal formations consist of lava flow sequences, whereas the upper Damwal, Kwaggasnek and Schrikkloof formations almost exclusively consist of ignimbrites originating from highly explosive pyroclastic eruptions, aligned with the increasingly siliceous composition of these formations. The Damwal, Kwaggasnek and Schrikkloof ignimbrites have various degrees of welding, ranging from nonwelded ignimbrites displaying classic pyroclastic textures, to highly welded, lava-like and rheomorphic ignimbrites, that have often been misinterpreted as lava-flows due to the lava-like textures. The various degrees of welding reflect the welding continuum, where different degrees of welding may be found within a single pyroclastic flow cooling unit. The Rooiberg Group volcanics were emplaced in an alluvial to lacustrine palaeoenvironment, originating from caldera ring-fissure eruptions. Grain size distributions of the different formations possibly reveal that the remaining Rooiberg volcanic exposures are distal deposits, where the youngest formations (Kwaggasnek to Schrikkloof) reflect increasingly distal deposits. The Rooiberg Group occurs over an extensive area, where outcrops occur according to “fragments” or “packages”, including the Nylstroom Package, Rooiberg Fragment, and Bothasberg Package.
The engineering properties and road building characteristics of mudrocks, with special reference to Southern Africa
Venter, Jacobus Petrus (University of Pretoria, 1980-05)
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
Raible, Kirsten (University of Pretoria, 2024-05-16)
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
Tunnell, Jason (University of Pretoria, 2023-12-05)
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
Gain, Stephen Bryant (University of Pretoria, 1981)
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
Alberts, Adriana (University of Pretoria, 2023-10-31)
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
Breakfast, Mzoli (University of Pretoria, 2024-01-02)
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
Burger, Erasmus Petrus (University of Pretoria, 2024)
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
Sebola, Selby (University of Pretoria, 2023)
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
Chiya, Luzuko (University of Pretoria, 2023)
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
Angath, Ellisha (University of Pretoria, 2021)
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
Omietimi, Erepamo Job (University of Pretoria, 2022-08)
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
Mukwevho, Fhulufhelo Vincent (University of Pretoria, 2022)
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.

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