Doctoral Degrees (Geology)

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Open Access
The relationship between mineralisation and structure in the Pilgrim's Rest - Sabie gold-field
(University of the Free State, 1967) Zietsman, Andries Louis
The area that was investigated, covers the metallogenetic province of the Sabie-Pilgrim's Rest Gold-field in the Eastern Transvaal. The geological formations include the Basement Granite, Godwan Formation, Wolkberg Formation, and the Transvaal System. Diabasic and pyroxenitic sills, pre-mineralisation in age, and probably genetically related to the Bushveld Complex, are present also. Three generations of dykes can be distinguished, one before, one contemporaneous with, and the other after the mineralisation. Three types of folding are present, i.e., tectonic folds that are due to magmatic intrusion. At least two periods of tectonic folding can be distinguished, the one superimposed upon the other. The axes of the earliest folds trend approximately east, while those of the later folds trend north and northeast. Both periods of folding are due to compressional forces which can be ascribed to the intrusion of the Bushveld Complex. Both tectonic and non-tectonic faults are encountered. The tectonic faults consist of low-angle thrust-faults, low-angle gravity-faults, and high-angle normal faults. The thrusts are probably due to the same compressional forces that were responsible for the nortn- and northeast-trending folds, i.e., they are probably related to the intrusion of the Bushveld Complex as well. Evidence of gravitational gliding-tectonics is provided by the presence of low-angle gravity-faults. These structures postdate the thrust-faults. The high-angle normal faults are due to tensional stresses and they are mostly post-mineralisation in age. A remarkable directional relationship between the linear structures and the folds is noticeable. The linear features, as well as the axes of the folds are orientated in three directions, namely, north, east and northeast. The gold-bearing reefs consist of interbedded as well as, transgressive, epigenetic ore-bodies. The interbedded reefs are represented by bedding-thrusts. The localisation and development of these reefs were controlled by the presence of favourable horizons and the intrusion of sills, folding, especially superimposed folding, as well as the formation of the bedding-thrusts. The conditions necessary for the emplacement of the transgressive reefs were the presence of early planes of weakness and/or dykes which are pre-reef in age. The low-angle gravity-faults resulted in the opening of pre-existing fractures such as early high-angle faults, joints and dyke-contacts. Two distinctly different periods of mineralisation are visualised, one preceding and the other postdating the bedding-thrusts. The first period is seen as a process of contact-metasomatism, caused by the intrusion of the basic sills. This process was probably localised and controlled by the folding. The second period of mineralisation was one of fissure-filling by solutions which were introduced during two phases: an early pyrite-rich phase, which was followed by a later copper- and bismuth-rich phase. The bedding-thrusts, as well as the low-angle gravity-faults, acted as channel-ways for the mineralising solutions. The second period of mineralisation, which produced ore-minerals that are typical of mesothermal deposits, is visualised as a metal-liferous front originating from the "root" of the Bushveld Complex. The ore-minerals, including gold, are considered to have been derived from the magma-chamber itself, as well as from the adjacent sedimentary rocks. The deposits of chrysotile in the area are considered to have been localised due to a similar structural control as to that which influenced the localisation of the interbedded reefs, i.e., folding.
Open Access
Aspects of the hydrogeochemistry of the Karoo sequence in the Great Fish River basin, Eastern Cape Province, with special reference to the groundwater quality
(University of the Free State, 1978-12) Tordiffe, Eric Arthur Wolferstan; Botha, B. J. V.
The aim of the study was to examine some of the major aspects responsible for the chemical quality of the groundwater in the Great Fish River Basin and its influence on the irrigation water. Approximately 18 000 ha of land are at present irrigated from several weirs down the river. The section of the Great Fish River Basin under discussion comprises an area of approximately 25 000 km² located between longitudes 25°E to 27°E and latitudes 31° 15'S to 33° 15'S. This area is divided into the following geomorphologic provinces: The Marginal Region (lower than 760m), the Great Escarpment (750 - 1070m), the Headbas (1070 - 1370m) and the Interior Plateau (higher than 1370m). Each of these provinces play an important part in controlling the movement and the chemical quality of groundwater in the area. Most of the annual precipitation (350 - 450 mm) occurs between February and March when evapotranspiration is at its highest. Runoff from the entire basin amounts to only 3 percent of the annual precipitation. The rest of the water either evaporates immediately because of the semi-arid climatic conditions, or is temporarily stored in the soil before it is lost to the atmosphere by means of evapotranspiration. It is also pointed out that apart from periods of extreme precipitation, the monthly evapotranspiration always exceeds the monthly precipitation. Such semi-arid climatic conditions, as well as the nature of the soils in the area prohibit a fast infiltration of meteoric water and it is therefore doubted whether as much as 5 percent of the annual precipitation over reaches the groundwater table. The area under discussion is underlain by sedimentary rocks of the Karoo Sequence beginning with the glacial deposits of the Dwyka Tillite Formation (680 m) at the bottom, followed by the marine deposits of the Ecca Group (2 340 m), the transitional deposits of the Koonap Formation (980 m) and the fluvial deposits of the Beaufort Group (4 540 m). Because the Koonap Formation represents the transition between the marine (deltaic) deposits of the Ecca Group and the fluvial deposits of the Beaufort Group, it is regarded as a separate formation not belonging to either group. The Beaufort Group on account of the environment in which the sediments were deposited, is subdivided into the Adelaide Subgroup (reducing environment) and the Tarkastad Subgroup (oxidizing environment). Red mudstone is regarded as indicative of an oxidizing environment and is present only in patches in the Middleton Formation, which forms the lower part of the Adelaide Subgroup. No red mudstone is present in the Balfour Formation, which forms the top half of this subgroup, but becomes very prominent in the Katberg and Burgersdorp Formations of the Tarkastad Subgroup. The Balfour Formation, on lithologic grounds, is subdivided into the Oudeberg Sandstone Member (180 m), The Daggaboersnek member (1 200 m), the Barberskrans Sandstone Member (190 mA) and the Elandsberg Member (320 m). It is suggested that the arenaccous units of the Beaufort Group, i.e. the Oudeberg Sandstone Member, the Barberskans Sandstone Member and the Katberg Formation represent periods of major tectonic activity in the provenance which was located to the south-east. During such activity vast amounts of coarse-grained material were transported and deposited at a relatively fast rate. Owing to the semi-arid climatic conditions, which prevail in the area, the soils tend to be rather alkaline with a high clay content and the poor development of an A-horizon. Calcrete or caliche occurs at or near the surface of most of the soils. Dolorite has intruded the sedimentary strata as concordant and conical sills, as well as near-vertical dykes. The dykes in the south of the area have an orientation of approximately 290°, coinciding with the Cape Fold Belt, whilst farther north, a prominent northerly trend with a weaker easterly trend is observed. In the extreme north, where the sedimentary strata is at its thickest, an almost random orientation is present. Various types of dolerite are encountered in the area and of particular interest is the occurrence of quartz dolorite which has intruded a sill of normal dolorite near Speelmanskop. This leucocratic body is probably the result of magmatic differentiation lower down in the cust, whilst limited differentiation whithin the body itself, both from floor to roof and in an "up-dip" direction, must have occurred. The intrusion of the dolerite is of particular importace because of the fracture zones it causes in the adjacent sedimentary rocks. Such zones are normally open to circulating groundwater. Where the dolerite itself is not fractured it may act as an impervious barrier when crossing the regional flow path of the groundwater. In such cases groundwater compartments are developed. Weathering of the provenance and of the various rock-types in the area, diagenetic processes which proceeded the deposition of the sediments in the Karoo Basin and the adsorption and ion exchange during the interaction of the surface and groundwater with the surrounding rocks, are considered to be the main geochemical factors responsible for the changes in the chemical quality of the groundwater in the area. During the chemical weathering of the rock-forming minerals cations such as Na+, K+, Mg++ are released to solution in the groundwater, whilst compounds such as SiO2O3 regroup to form residual clay minerals such as montmorillonite. Weathering of the sedimentary rocks is, however, limited because of the fact that the primary minerals which constitute such rocks have already withstood at least one cycle of weathering in the provenance. In areas where leaching is vigorous, K+ is, however, removed from illite in the mudstone with the result that this clay mineral adopts swelling features similar to montmorillonite, thus causing the rock to crumble. Dolerite in turn, because of its igneous origin, is more prone to chemical weathering. As a result of compaction the porosity and permeability of the sediments in the Karoo Basin was reduced to extremely low values. The chemistry of the interstitial waters was also altered by this process because of the diagenetic alteration of montmorillonite to illite during which K+ is removed from the water, whilst SiO2, H2O, Na+, Ca++, Mg++ and Fe++ are added to the water. During the compaction process, C1- was accumulated in the remaining water in the lower strata as result of ultra-filtration as the formation water was squeezed through clay-rich mudstone layers. Because of its small ionic radius and high electrical charge, Ca++ is adsorbed by the clay minerals in the mudrock of the area to a far greater extent than any of the other cations present. The maximum concentration of adsorbed Ca++ is observed in the Oudeberg Sandstone Member, which suggests that this unit represents a geochemical marker. A gradual increase in the CEC of the mudrock from the lower strata to this unit is furthermore observed. Sodium concentrations increase toward the south of the study area, therefore suggesting an influence of the palaeomarine environment on the adsorbed cations. Groundwater in the Great Fish River Basin is restricted mainly to joints in the sedimentary rocks and to fracture zones caused by the intrusion of dolerite. The water levels in most of the bore-holes therefore represent a pressure or piezometric surface rather than an actual water table. Such levels, however, regionally represent a surface which closely resembles the surface topography, whilst the flow of groundwater is down the regional slope and the rivers act as effluent drainage canals for the groundwater. Although the groundwater is recharged in the higher lying areas by circulating meteoric water, there appears to be no direct relationship between the seasonal precipitation and the groundwater levels. As far as the origin of the major ions in the groundwater is concerned, the cations are derived mainly from the weathering of primary rock-forming minerals, whilst the anions accumulate from non-lithologic sources. Generally, the groundwater in the areas of recharge, i.e. the higher lying areas, has a pronounced Ca++ and HCO-3-character, whilst in the stagnant low-lying areas Na+ and C1- are the predominant ions. In between the two extremes, groundwater with a prominent Mg++ and SC=4-character is encountered. This trend corresponds well with the normal metamorphism of natural waters and appears to be controlled largely by the topography of the area. Groundwater with a distinctly high Na+ and C1- -concentration also has a high salinity concentration. The pH in turn is highest in the areas of high Ca++ and HCO-3-concentrations and lowest in the areas of high Na+ and C1- -concentrations. All the water of the area is, however, oversaturated in relation to CaCO3 and, where conditions are suitable, calcrete is precipitated. Chloride is the dominant anion in the lower strata of the Karoo Sequence and is attributed mainly to the retention of this ion during the migration of the formation waters through the argillaceous material. High salinities, as a result of high Na+ and C1- -concentrations, prevail in the groundwater up to the Daggaboersnek Member. From the Barberskrans Sandstone Member upward, the concentration of these ions decrease sharply. The cation percentages in the groundwater of the upper strata, however very considerably, thus indicating the influence of chemical weathering. There is more SO=4 in the groundwater of the lower strata, which was deposited under reducing conditions, than in the upper strata, which was deposited under oxidizing conditions. This is attributed to the formation of pyrite under reducing conditions, which can later oxidize to release SO=4 to the water. During the periods of extreme precipitation a considerable amount of meteoric water infiltrates down to the groundwater level, dissolving precipitated salts on its way down. This naturally causes an increase in the salinity of the groundwater and is a result of an increase in Na+ and C1-. Seepage water in the Great Fish River contains Na+ as the main cation and increases gradually in concentration farther downstream. To the north of Cradock HCO-3 is the dominant anion but it decreases rapidly farther downstream, with a concurrent sharp increase in the C1- -concentration. The increase in the Na= and C1- -concentration coincides with an increase in the total salt load farther downstream. A similar trend is observed in the change in groundwater quality down the Great Fish River. This is conclusive proof of the influence of groundwater on the seepage water in the river. The groundwater compartments caused by dolerite intrusions also have a marked influence on the quality of the seepage water. During a single irrigation lead from Grassridge Dam the initial irrigation water reaching the consecutive weirs along the river possessed an extremely high salinity load as a result of the solution of precipitated salts in the river bed as well as the flushing of saline water from stagnant pools. The duration of the saline head increased at each consecutive weir downstream. Such conditions present a serious threat to the irrigable land along the Great Fish River and therefore measures will have to be taken to either prevent such contamination of the irrigation water or to limit the application of such contaminated water by allowing the saline head to pass the various weirs.
Open Access
The geology of the acid phase of the Bushveld complex, north of Pretoria: a geochemical/statistical approach
(University of the Free State, 1980-12) Bruiyn, Hendrik; Deringer, G. J.
A petrographical and geochemical study of the acid phase of the Bushveld Complex, north of Pretoria, was undertaken with the aim to identify the different rock units, to determine their interrelationships and to classify the rocks as well as describing their geochemistry. The oldest geological formation in the area is the Rooiberg Group which is subdivided into two units, namely the Kwaggasnek (lower) and Schrikkloof (upper) Formations. Petrographical, mineralogical and geochemical data are submitted for the different units. From the data it can be deduced that these units formed as products of a single parental magma, while statistical manipulation of the geochemical data indicates that these formations differ significantly from the Damwal Formation farther to the east. The gradational contact relationships between the felsites and underlying granophyre are described and explained in the text. The various granophyre occurrences of .the Rashoop Granophyre Suite are classifiedand described. The mineralogical, petrographical and geochemical data indicate a limited differentiation trend from the felsites into the granophyre. This may indicate that the granophyre in part resulted from . the rapid crystallization of the parental magma of the Rooiberg Group. A model for the origin and formation of the Rashoop Granophyre Suite, based on petrographical and-qeochernical evidence, is proposed. The granites are subdivided according to age and field relationships, as well as mineralogical, petrographical and geochemical characteristics into the Sekhukhuni, Verena, Makhutso, Klipvoor and Klipkloof granites. The mode of intrusion as well as the mineralogical, petrological and geochemical composition of each type are discussed. A petrochemical investigation of the granites indicate that the various granites, with the exception of the Klipkloof granite, represent the differentiation products of a single parental magma. A similar study on the Makhutso and.Verena granites indicates that leptite assimilation influenced the final differentiation trend in these granites, causing enrichment in certain elements and depletion in others.
Open Access
The seismo-deformation of Karoo aquifers induced by the pumping of a borehole
(University of the Free State, 2003-09) Dzanga, Panganai; Botha, J. F.; Cloot, A. H. J.
The research unequivocally showed that pump-induced seismo-deformations exist, especially in boreholes equipped with electric and diesel pumps. Central to seismo-deformations are the mechano- and the geo-acoustic effects on both the borehole water and the aquifer. These aspects of the pump instigate the proposed diaphragmatic deformation hypothesis. In an aquifer the pump vibrations manifest as Rayleigh waves. By virtue of the driving source, the waves are harmonic (White, 1965). To be effective in engineering the proposed diaphragmatic deformation on a hydrostratigraphic unit situated several metres below the ground surface, the waves propagate along the borehole. The component of the Rayleigh wave orthogonal to the unit instigates the deformation and thus oscillations are generated in drawdown curves. Oscillations are a common feature in pumping test data and the masking effect of abstraction makes them inconspicuous. However, the derivative technique when applied to the signal enhances the phenomenon. The technique suppresses the abstraction effect in the data leaving the time-dependent oscillations. The spikes obtained in some of the derivatives of the pumping test data may suggest a one-sided deformation, probably the upper lip to a hydrostratigraphic unit. Coupled with the effects of Rayleigh waves is the pressure variation on the water level caused by the sound. The humming sound of a pump in operation is capable of subjecting borehole water to constant pressure variations thus leading to inherent oscillations in the pumping test data. The conspicuousness of oscillations in the raw pumping test data (Figure 1.2) can be attributed to the high resolution of the equipment used and interferences of different wave forms existing in the system. For a borehole that is continuously in operation, the impact of seismo-deformations on the physical integrity of an aquifer can be detrimental. In hard-rock fractured Karoo aquifers, the induced seismo-deformations can be of astronomical severity. The fact that successful boreholes are drilled in the Karoo within a short distance of a failed or "dried up" borehole is a clear evidence of structural failure. Bedding fractures in particular are very susceptible (Rasmussen, 1998). The radial extent of failure depends on the strength of the vibrations which are habitually intense close to the borehole and decay exponentially-like with distance. The ultimate failure of hydrostratigraphic units after prolonged pumping, which is common in the Karoo, may be due to the evolution history of deformation that accumulates as residual strains and stresses (Botha and Cloot, 2002). The research also revealed that ground displacements are smaller when discharging than when not. According to the hypothesis, this is due to the decreasing hydrostatic pressure essential in opposing the normal stress from a pump. It is in this view that groundwater should be considered as a hydroskelatal component of an aquifer and the rationale of lowering the discharge rate should not only be seen as a process to prevent dewatering but as a mechanism for preserving the dynamic equilibrium between the normal stress emanating from a pump and the hydrostatic force offered by water. Offsetting the equilibrium can lead to irreversible plastic deformation and aquifer subsidence (Botha and Cloot, 2002). The failure of numerical models to simulate the oscillations completely indicates that the wave that triggers the proposed diaphragmatic deformation of a fracture is more complicated than the simple harmonic waveform caused by pump vibrations. The wave should be a convolution of the vibrations, sound and the natural ground roll. Besides, the pump vibrations on reaching a geological feature of interest in a multi-stratigraphic geologic terrain would have undergone multiple reflections and transmissions with the ultimate waveform being a distortion of the primary signal. The research conducted showed that pump-induced seismo-deformations should have the same status as the discharge rate in aquifer management. It is clear that the introduction of measures aimed at reducing the transmission of seismic waves to an aquifer should be a priority in order to deter the pump-induced seismo-deformations. This includes preventing the pump and the borehole casing from coming into direct contact; incorporating gadgets to tone down the frequency of the mains; and installing shock absorbers between the pump and the ground. The selection of pumps should be based on the seismological properties of the aquifer that is to be used and its hydrogeological properties.
Open Access
Geological conditions and environmental impact of the Mohale Dam, Lesotho Highlands Water Project
(University of the Free State, 2004) Letlatsa, Gerard Molatoli; Praekelt, Hermann J.; Van Tonder, Gerrit J.
Abstract not available
Open Access
A proposed method to implement a groundwater resource information project (GRIP) in rural communities, South Africa
(University of the Free State, 2005-07) Botha, Frederik Stefanus; Dennis, Ingrid
English: Groundwater forms an essential part of water supply in the Limpopo Province, South Africa. However, at planning level this message seems to be skewed and misinterpreted. Although a vast number of water supply schemes are developed using groundwater as a resource, these schemes are reported to fail and the resources are not considered sustainable. Therefore mistrust in groundwater has developed, planners effectively eliminate groundwater from integrated water resource planning and groundwater continues to be seen only as an ad hoc or emergency supply. The Groundwater Resource Information Project (GRIP) was introduced to compare available information with verified field information and it presents the information to planners and engineers in a format that is sensible and easy to incorporate, therefore presenting groundwater as an integrated sustainable and strategic resource. The work implemented during this project describes a hydrocensus - an information capturing and presentation protocol that can be introduced anywhere at any scale to give planners the opportunity to consider already developed groundwater infrastructure and incorporate it into the overarching planning. The methodology was developed to describe to the user how he/she should go about when conducting a hydrocensus to serve both the needs of water services and water resource managers. The development of groundwater in South Africa is discussed to provide a perspective on how groundwater was dealt with in the past and is looked upon now. Issues concerning groundwater resource mapping as attempted by the Department of Water Affairs and Forestry (DWAF) and the Water Research Commission (WRC) are discussed and commented on. Also discussed is the availability and format of groundwater data when creating maps and how the data are captured in the different databases. All the maps however are derived from questionable and unverified field data. The legal perspective on groundwater in terms of the National Water Act (NWA), the Water Services Act (WSA) and the Environmental Conservation Act (ECA) is also briefly discussed. The different uses of water are mentioned where groundwater may have a significant contribution. Shortcomings in the Act are also discussed. The proposed methodology spells out the so-called Groundwater Resource Information Project (GRIP) and with marketing in the 21st century becoming more important in science, the slogan “Get a GRIP on groundwater” was adopted. The methodology highlights the importance of an integrated team with various responsibilities and deliverables, the importance of field and office procedures and the involvement of the community. It describes various verification stages where a quality control officer checks field data through ad hoc site visits and where historically disadvantage individuals previously not involved with a project of this nature, can learn from more experience individuals. Information gathered clearly illustrates that vast amounts of money are spent on groundwater development and that the majority of villages in Limpopo already have boreholes in close proximity. The raw data can be used for immediate planning, operation and management purposes. The core of GRIP is, however, dissemination of information and much time was spent to develop an interface where data is captured, validated and placed on a database accessible through the World Wide Web. The data can be downloaded through various methods available on the web page and exported as an Excel spreadsheet. The data can then be imported in a GIS tool and manipulated to develop a series of planning maps, develop site -specific water supply business plans or help planning engineers with day- to-day requests. Prior to GRIP, it was difficult and time consuming for planners in Limpopo to get access to reports compiled by specialists for municipalities or consulting engineers, but through the means developed in GRIP, planning engineers are enabled to stand up in meetings and with hard evidence in hand support future groundwater development and planning, making it truly part of integrated water resource management (IWRM). This study lasted from the beginning of 2002 up to the middle of 2004. Further implementation of GRIP continues in Limpopo and the Eastern Cape and there is a strong possibility that is might be implemented in Kwazulu/Natal and the Free State. The GRIP website, other technology and legislation may change with further implementation of GRIP.
Open Access
A new perspective on the geohydrological and surface processes controlling the depositional environment at the Florisbad archaeozoological site
(University of the Free State, 2009-04) Douglas, Rodney Malcolm; Tredoux, M.; Holmes, P. J.
English: The Florisbad Quaternary Research Station and archaeozoological site is located 45 km north-west of Bloemfontein, Free State Province, South Africa (28° 46` 05.4”S, 26° 04` 10.7”E), and is sited around a series of highly saline, warm water spring vents. The site is partially covered by a large sand dune. The site is significant for three important reasons. Firstly, the discovery of the Florisbad skull (Homo helmei) in 1932 by Prof. T. Dreyer, secondly, a collection of faunal fossil remains representing at least 31 taxa, including extinct and extant species, and referred to as the Old Collection and, thirdly, a Middle Stone Age (MSA) human occupation horizon representing a temporary butchering site with evidence of a hearth, butchering tools, and faunal fossil remains. Spring- and excavation pit water samples were taken and analysed in 1988 during a high rainfall period, and in 1999 during an average rainfall period. In relation to the spring water, the results show that the total dissolved solids (TDS) of the excavation pit water were, in relation to the spring water, higher during the high rainfall period and lower during the average rainfall period. This was contrary to the norm, where it is expected that high rainfall periods should produce a decrease in TDS due to a dilution effect. The TDS of the spring-water remained stable throughout both high and average rainfall periods. Further analysis showed considerable TDS increases between the excavation pit waters, and between the pit waters and the spring-water. It is concluded that the pit waters were not directly related to the spring water and that the two water bodies were separate entities with the pit water being recognized as groundwater. An analysis of rainfall in relation to the TDS of the spring- and groundwater indicated that short-term rainfall affected the quality of the groundwater, but not the quality of the spring-water, while long-term rainfall had little effect on the quality of the spring-water. The question arose as to why the TDS of the groundwater was so much higher than that of the spring-water, and what factors were causing these differences? Organic-clay (peat) samples from the walls of the excavation pits as well as the walls of the open excavation area were analysed. The results of the analyses, and an examination of the stratigraphy, strongly suggested that minerals had accumulated in the organic-clay layers due to organic matter having a similar colloidal organization to that of clay, with the ability to adsorb large quantities of minerals on their outer surfaces. A comparison of the groundwater and organic-clay analyses results showed that the TDS of the decomposed Peat II organic-clay layer was considerably higher than that of the groundwater, with the same being true for the far less decomposed Peat IV organic-clay layer. By analysing and combing the water and organic-clay layer results with the many factors, mechanisms, and processes involved, it is concluded that the salinization of the organic-clay layers, and the flushing of ions from the organic-clay layers by percolating water during rainfall periods, is responsible for the increased mineralization of the groundwater. Other factors, mechanisms, and processes, such as rainfall, aeolian deposition, evaporation, capillarity, wind, temperature, matrix-suction, pH, Eh, PCO2, PO2, DOC, and biomineralization, all of which support the accumulation of free salts in a semi-arid environment such as Florisbad, were also investigated. Of primary importance was the question as to whether the spring-water was actually responsible for fossilization of the faunal remains, and could fossilization have taken place within the environs of the spring vents, or in the spring vents themselves? Previous research has suggested that the spring-water was calcium-carbonate rich, with evidence of calcium-carbonate deposition further suggesting that faunal remains of the Old Collection must have been in contact with the spring-water in spring vents for some time. An analysis of the spring-water analysed over the past 84 years indicated that there had never been sufficient Ca (under-saturation) in the spring-water for fossilization to occur, and this is confirmed by the current analyses. The contemporary lack of Ca in the springwater, combined with other environmental factors within the environs of spring vents, such as the lack of organic matter and clay, combined with a high Eh environment, also strongly indicated that, historically, fossilization could not have taken place within the environs of the springs. Contrary to earlier hypotheses, it is concluded that the spring water and spring flow would directly assist in the de-mineralization of faunal remains. A detailed investigation of the site, along with an analysis of the stratigraphy and sedimentation, revealed that previous theories on the formation of the site did not sufficiently accommodate the current stratigraphy in the context of the organic-clay layers, the salinization process, and fossilization. From this deduction all the existing and pre-existing evidence was revisited in an attempt to provide a hypothesis which would accommodate the existing morphology of the site, sedimentation, and fossilization. It is hypothesised that the spring site formed around a large drainage-impeded pan which was largely covered by a sand dune that had migrated from the area of the extensive salt pan to the north and north-west (Soutpan). The arms of the dune eventually came to rest up against the windward slope of a dune belt located just south of the spring site, and a dam began to form. High rainfall periods produced organic-clay layers, while sandy layers were produced during drier windy periods. This led to the formation of alternating horizontal layers of organic-clay and sand, eventually building up to almost the top of the sand dune on the leeward face. When the water level in the dam reached the top of the arms of the sand dune, it broke through the eastern arm. The dam water and sediments then evacuated the dam in a flash flood. This flash flood eroded the area to the east of the site to such an extent that the drainage was diverted, and a wide flat-bottomed vlei was formed where much of the dam sediments were deposited. This hypothesis provides an alternative for the formation of the spring site, accommodating all aspects of sedimentation, salinization, and fossilization. The dating of the Florisbad deposits and fossils has been subject to an ongoing debate since the first 14C dating was carried out in 1954. The ages and depths of recently published profiles did not appear to correspond to the assumption of greater compaction with depth and time. In an attempt to resolve this issue, linear, exponential, and logarithmic mathematical trend lines were then experimentally applied to the published profiles of electron spin resonance (ESR) and optical stimulated luminescence (OSL) dates in order to test the theory of compaction, and to validate the results. The hypothetical effect of manipulating ages on trend lines was also tested. A discussion on some possible shortfalls regarding the dating methods used is undertaken. A best logarithmic fit to data was obtained by holding the ESR Middle Stone Age Human Occupation Horizon (MSA) age at 127 ka, and advancing the lower deposit age from 250 ka to 420 ka. The next best fit to data occurred by regressing the ESR MSA age from 127 ka to 78 ka, and holding the lower deposit age at 250 ka. The application of exponential and linear trend lines produced poor fits to data. A suggested compaction trend line was also introduced which produced an ESR MSA age of 75 ka and a lower deposit age of 384 ka. In the final analysis, trend line results suggested an MSA age of 92 ±12 kyr and a basal deposit age of 400 ±20 ka. The logarithmic and suggested compaction trend line ages for the lower deposits both produced ages similar to the suggested Florisain – Cornelian faunal boundary of c. 400 ka. The exercise confirmed that the ages in the published profiles were disjunct and that this disjunction may be related to a number of different physical forces.
Open Access
A geochemical study of the Middle Group chromitites, Helena mine, Bushveld complex, South Africa
(University of the Free State, 2011) Kottke-Levin, Janine; Tredoux, Marian; Gauert, Christoph
The study in hand reports on compositional variations in mineral and whole-rock geochemistry of the chromitite and silicate layers occurring in the Middle Group of the eastern Bushveld Complex. Special attention is paid to the platinum-group element (PGE) content and mineralization as well as the nature of platinum-group minerals (PGM) within the MG sequence. A general progressive evolution of the MG chromitite layers can be deduced from chromite composition showing decreasing Mg# and enrichment of Fe and Al relative to Cr as well as from the decreasing whole-rock Mg#. At the LCZ/UCZ transition no marked change in mineral and whole-rock geochemistry can be observed, indicating that the MG sequence derives from a continuously progressive evolving melt. The presence of one parental magma for the formation of the MG is further substantiated by the chondrite-normalized PGE patterns of the MG chromitite layers, which resemble each other. They further resemble that of the UG2, which suggests that they derive from the same magma and a similar style of mineralisation applied. One marked reset to compositions even more primitive than the MG1 chromitite layer is present at the level of the MG4A chromitite layer, which is illustrated by a low Mg#chr, low whole-rock Mg#, low mineral and whole-rock Cr3+/(Cr3++Fe3+) ratios and increasing mineral and whole-rock Cr3+/(Cr3++Al3+) ratios and TiO2 contents. It strongly suggests the addition of hot and primitive magma at this level of the MG stratigraphy. Whole-rock geochemistry of the silicate layers is strongly governed by mutual influence of co-precipitating minerals competing for major elements like Mg, Fe, Al or Cr, and hence a statement to general trend with respect to evolution from bottom to top of the stratigraphic column of the MG sequence can’t be made. Nevertheless, a strong decrease in whole-rock Mg# and low whole-rock Al2O3 concentrations at the level of the MG4A pyroxenite is illustrated, which can be ascribed to the same event of addition of primitive magma concluded for the MG4A chromitite layer. The existence of Na-rich silicate inclusions occurring in chromite of all the MG chromitite layers most likely proves chromitite formation by mixing of primitive melt with a siliceous melt. Hence, the general process for the formation of the chromitite layers and their corresponding silicate layers in the MG seems to be mixing of a primitive (mafic-ultramafic) parental melt with siliceous roof-rock melt deriving from the granophyric Rooiberg felsites. Although Cu deriving from the base metal sulphides (BMS) seems to migrate away from the chromitite layers, local Cu enrichment in the chromitite layers to concentrations up to >6000 ppm can be observed. This excess Cu most likely derives from an external source e.g. country rocks, which could have ‘generated’ metal-loaded hydrothermal fluids. Excess S occurring in the silicate layers may result from limited, probably hydrothermal, dissolution of BMS from the respective chromitite layer below. Chromitite samples have been investigated with the mineral liberation analyzer (MLA) for their PGM. The study focused on the mineral association of the PGM, i.e. whether they occur liberated, locked or attached to gangue or the BMS, since the mineral association is important to conclude on PGE mineralization and PGM formation. The majority of the PGM occurring in the chromitite layers of the MG sequence are Pt- Rh -sulfides (26.2%), followed by laurite (25%), Pt-Pd -sulfides (24.3%) and Pt -sulfides (13.8%). The remaining 10.7% comprise PGE –sulphoarsenides and PGE- arsenides, Pt - and Pd –alloys and Pt - and Pd –tellurides. Except laurite, which is commonly locked in chromite (66%), the PGM are dominantly associated with silicate minerals, and to a lesser extend with the BMS only. According to this discrepancy in the PGM association, PGE mineralization of the MG chromitite layers most likely can’t be modelled in terms of the R-factor and therefore PGE concentration by the cluster model is favoured by the author. Alteration of the primary silicate minerals in the MG chromitite layers to amphibole, chlorite, talc, mica and quartz can be observed locally. Since the primary BMS assemblage (chalcopyrite, pyrite and pentlandite) shows losses of Fe, Cu and S, and millerite, a Ni-rich sulphide of secondary origin, occurs, the influence of hydrothermal fluids on the chromitite layers was concluded. Besides affecting the BMS, the fluid most likely also redistributed the PGE occurring in solid solution in the BMS, i.e. Pt and Pd, as especially the negative slope from Pt to Pd in the chondrite normalized PGE patterns of the MG chromitite layers suggests. Enrichment of the high-temperature PGE (HT-PGE) over the low-temperature PGE (LT-PGE) is depicted in the chondrite normalized PGE patterns of the MG chromitite and silicate layers. The fact that the HT-PGE are enriched relative to the LT-PGE in the lowermost MG chromitite layers as well as in the MG4A suggests that temperature could play a role in PGE fractionation. Temperature control on PGE fractionation has also been concluded from changing Pt/Ir ratio in dependence of the whole-rock Al2O3 content from bottom to top of the MG sequence, with increasing Al2O3 concentrations considered to point to decreasing temperature. Hence, Al-depletion, i.e. decreasing Al2O3 content, of chromite relative to Cr may result in enrichment of the HT-PGE relative to the LT-PGE. The LT-PGE are preferentially concentrated by increasing amounts of plagioclase within the chromitite layers.
Open Access
Investigation into alternative wheat aphid control strategies for emerging farmers
(University of the Free State, 2011) Richter, Johannes Mattheus; Prinsloo, G. J.; Van der Linde, T. C. de K.
In the Qwa-Qwa and Thaba N’chu regions of the Free State Province, South Africa, resource limited farmers that produce wheat are mainly situated in temporary crop environments. They are drastically affected by crop losses that occur during years of serious Russian wheat aphid (Diuraphis noxia) (Kurdjumov) and oat aphid (Rhopalosiphum padi) (Linnaeus) infestations. Therefore the main objective of this study was to identify simple alternate control methods to be used by small-scale farmers for the control of these aphids. The focus was on minimizing the numbers of the immigrating individuals. That must happen before they arrive in the crop habitat and decrease the possibility of the pest population reaching damaging levels when the crop is still in its susceptible phase for insect damage. Plant derived semiochemicals, which could modify insect behaviour, were considered as an option to be used since this could be extracted from plants, and were demonstrated to be successful in other countries. These semiochemicals are also known to attract natural enemies of these insects. It was therefore decided to test two types of extracts (an aqueous and a light mineral oil) which could be easily prepared from four plant species, namely Wild wormwood Artemisia afra (Jacq. ex Willd.), Big thorn apple Datura stramonium (Linnaeus), Khaki bush Tagetes minuta (Linnaeus) and Wild garlic Tulbachia violacea (Harv.). The plants were chosen due to their availability in the wheat production regions and their possible insect repelling properties known from other species in the same genera. The behavioural response of alate aphids D. noxia and R. padi and two parasitoids, Aphelinus hordei (Kurdjumov) and Diaeretiella rapae (McIntosh) to these extracts was tested in olfactometer trials in the laboratory. The aphid D. noxia showed the highest repellence to the aqueous extract of A. afra and the oil extract of T. violacea. Aphid R. padi was also best repelled by the aqueous extract of A. afra and the oil extract of D. stramonium. The parasitoid A. hordei was strongly attracted to the aqueous extracts of A. afra and T. minuta. Diaeretiella rapae on the other hand, was also highly attracted to the aqueous extract of T. minuta, but T. violacea oil extract had a very strong effect on the parasitoid and would be recommended to farmers. Artemisia afra and T. violacea are perennials and available as green material for extraction purposes in the winter when wheat is planted. The other two plants are annuals and not available in winter. The A. afra aqueous extract will repel both aphid species when sprayed early in the wheat growing season when wheat is still small and aphids are flying into the wheat. This extract will also attract A. hordei and this could enhance the biological control of D. noxia. The T. violacea oil extract could also be used to repel D. noxia. It could also be used to attract the parasitoid D. rapae later in the season and enhance the biological control of both aphid species. Thus there are potential alternate simple aphid control methods available for small-scale farmers. These methods should be refined and farmers trained to use them effectively.
Open Access
Composition and evolution of the proterozoic Vioolsdrif batholith (including the Orange River group), Northern Cape province, South Africa
(University of the Free State, 2011-12) Minnaar, Hendrik; Schoch, A. E.
English: The Vioolsdrif Suite and Orange River Group represent genetically related calcalkaline plutonic and volcano-sedimentary assemblages of Palaeoproterozoic age formed during the Orange River orogeny. Together they occupy the largest part of the Richtersveld Subprovince – a unique tectono-stratigraphic terrane. Radiometric data indicate the period of formation roughly between 2.0-1.73 Ga. The subprovince has been vastly eroded and isolated from its original tectonic environment by subsequent tectonic processes, leaving a relatively small portion of its original extent for investigation. Previous studies have dealt with limited parts of the subprovince and although informal subdivisions of the Orange River Group and Vioolsdrif Suite are generally in use, some correlations and further subdivisions remained controversial. This study has two main aims, viz., to propose formal subdivisions of the two units and to investigate the magmatic processes and original tectonic environment of their formation. Geochemical evidence is presented here to support the proposed subdivisions, which were previously based entirely on field evidence. The subdivisions largely follow that of previous studies. The Orange River Group is subdivided into the Haib and De Hoop Subgroups. Geochemical evidence show that these two subgroups differ in the magmatic processes that led to their formation. The Haib Subgroup shows a genetic gradational relationship with the Vuurdood Subsuite, which is regarded as remnants of the primary magmas. The De Hoop Subgroup does not display this relationship with the Vuurdood Subsuite. The Vioolsdrif Suite is subdivided into the Vuurdood, Goodhouse and Ramansdrif Subsuites. Mafic-ultramafic bodies of the Vuurdood Subsuite are regarded as remnants of the primary magmas. This is based on multi-element variation diagram patterns and comparison to source magmas in modern island arcs (MORB). Previous studies have also shown that initial isotope ratios for the Vuurdood Subsuite are similar to those of the Goodhouse Subsuite and Orange River Group, relating them to a similar source. Dark mineral cumulate material are contained in the mafic-ultramafic bodies. The Goodhouse Subsuite is subdivided into the Khoromus Tonalite, Blockwerf Migmatite, Xaminxaip River Granodiorite, Gaarseep Granodiorite and Hoogoor Granite. The Khoromus Tonalite is identified as the oldest unit within the subsuite based on contact relationships as well as radiometric data, which continuously render older ages for the Khoromus Tonalite compared to the other units within the subsuite. Certain field and petrological observations in this unit may be interpreted as products of magma mixing processes. The Blockwerf Migmatite is distinguished from the other units by its migmatitic character and anomalous La/Yb ratios. The unit is identified as a possible remnant volcanic centre. The Xaminxaip River Granodiorite is interpreted as a subvolcanic unit and is characterised by the development of migmatite in places. This migmatite is attributed to metamorphic conditions which locally reached high grade in an orogenic geothermal regime. The Gaarseep Granodiorite represents the main phase of the Vioolsdrif Suite. Its compositional range includes all those represented by the other units individually from gabbro through diorite, tonalite and granodiorite to granite. Its development spans almost the entire evolutionary history of the Richtersveld Subprovince as a whole. The Hoogoor Granite is included in the Goodhouse Subsuite based on the geochemical variation patterns and available radiometric evidence. The Ramansdrif Subsuite is subdivided into the Ghaams and Sout Granites based on grain size variation and petrological evidence. The subsuite could have been formed by partial melting of the older plutonic phases of the Vioolsdrif Suite. The deformation associated with this partial melting event has not been identified. Previous studies have related the evolution of the Richtersveld Subprovince to modern subduction zone magmatism similar to that of the Andean volcanic arc. This is largely supported by the current study, however, a change in magmatic processes and the tectonic environment can be observed in the geochemical variation patterns. Multielement diagrams show patterns typical of subduction zone magmatism for both the Orange River Group and Vioolsdrif Suite. During the initial stages, primary magmas, now represented by the Vuurdood Subsuite, were derived from a depleted mantle reservoir. The first volcanic eruptions – those of the Haib Subgroup – represent fractional crystallization products off the primary magmas. With progressive development of the arc, newly formed crust was continuously recycled back into the mantle and crustal partial melting led to a change in magmatic processes with magma mixing and contamination becoming increasingly important. Tectonic discrimination diagrams suggest that the initial stages of the batholith development may be compared to a primitive continental arc, while the later stages may be be compared to a typical continental arc.
Open Access
The geology of the Springbok Flats
(University of the Free State, 2012) Nel, Leon; Van der Westhuizen, W. A.
The Springbok Flats constitutes an extensive tract of generally flat country extending from south of Bela Bela north-eastwards to Zebediela Location. This area is located within 28˚00´ and 29˚30´ east and 24˚15´ and 25˚30´ south with a total areal extent of approximately 8 000 km2. A comprehensive exploration programme commenced in 1976 and was completed in 1982. During the exploration programme 3 000 boreholes were drilled. These borehole data was re-interpreted in conjunction with downhole geophysical surveys in order to create a sedimentological database suitable for the reconstruction of palaeo-environments of the Karoo-aged strata in the Springbok Flats Karoo Basin (SFKB). Structurally the SFKB comprises two elongated basins i.e. Roedtan Basin (north) and Settlers-Tuinplaats Basin (south). These two basins are bordered by pre-Karoo aged tectonic features i.e. Thabazimbi-Murchison lineament (northern boundary of the Roedtan Basin) and the Droogekloof Fault Zone (northern boundary of the Settlers-Tuinplaats Basin). These tectonic features were continuously active after the deposition of the Karoo strata in the SFKB resulting that the existing SFKB is considered to be a preserved Karoo-aged basin. Stratigraphically the SFKB was subdivided into 7 distinctive lithostratigraphic units. Lithostratigraphic Unit 1 comprises glacier derived sediments and is correlated with the Dwyka Group of the Main Karoo Basin. Lithostratigraphic Unit 2 is a mega upward coarsening cycle resembling a deltaic deposit. This deltaic deposit is overlain by a cyclothem consisting of Lithostratigraphic Units 3 and 4 respectively. Lithostratigraphic Unit 3 is a composite coal zone. Based on selected seam horizons a coal zone resource of 3492 mt was demarcated. In areas adjacent to palaeotopographical highs uranium is associated with the coal zone and a resource of 363.0 mt with an average grade of 0.40 kg/t U3O8 was calculated. A prominent regionally developed disconformity marks the commencement of Lithostratigraphic Unit 5. A continuum of fluvial environments including alluvial fans, braided rivers, meandering river systems and anastomosed river systems was postulated as depositional environments for Lithostratigraphic Unit 5. A lithostratigraphic unit, comprising basal calcrete conglomerates followed by intensely bioturbated siltstone and a lesser bioturbated sandstone respectively, constitutes Lithostratigraphic Unit 6. The texture and sedimentary structures of Lithostratigraphic Unit 7 which overlies Lithostratigraphic Unit 6 is compatible with a typical aeolian deposit. The termination of the Karoo-aged strata in the SFKB is marked by the presence of amygdaloidal basaltic lavas.
Open Access
Geochemical and mineralogical characterization of the lithological units of the geodehoop colliery in the Witbank coalfield to fathom the source and the receptor of metals in the riet-olifants catchment, South Africa
(University of the Free State, 2022) Netshitungulwana, Khashane Robert Tshishonga; Gauert, C.; Vermeulen, D.; Yibas, B.
The study aims to understand the element deportment's geochemical characteristics from the source, pathway and receptor realm in the Riet-Olifants catchment (ROC) drainage system. The ROC is part of the Olifants primary catchment (OPC) area that extends over the border between South Africa and Mozambique and covers a total area of approximately 87000 km2. The ROC is the area most influenced by coal mining activities surrounding the major towns of Emalahleni (formerly Witbank) and Middleburg. The geological units of the Vryheid Formation, Ecca Group of the Karoo Supergroup dominate the area, with the Witbank coalfield being the primary resource for coal. The focus herein is directed on identifying the geochemical characteristics of the source rocks, the pathways of mobilization and transport and the receiving environment. The key to this study is to identify the mobile elements in minerals occurring in different sedimentary units of the source rock geological units, with the assessment of its contribution to the elevated metal concentrations in the receiving environment of the drainage area. The results are also tested in determining the geogenic element entry of naturally occurring source rocks from an anthropogenic source. In recent years, the area has been under regulatory verification over high pollution levels through coal mine drainage (MD). Previous studies show that although the land use of industrial and agricultural activities is also essential, the contribution to water and sediment contamination from the mining activities within the catchment is significant and yet needs to be fully understood.
Open Access
An investigation of the iron-cyanide mineralization in gold mine dumps
(University of the Free State, 2022) Welman-Purchase, M. D.; Hansen, R. N.
Cyanide, in the form of NaCN/KCN, is still widely used world-wide in the gold extraction process. Success of this extraction is owed to the high affinity that cyanide has for gold. Post extraction, waste material is added to tailings dam facilities in the form of a slurry. This slurry is likely to contain cyanide, which is hazardous if it is not managed. Another element that cyanide has a high affinity for, is iron. Iron-cyanide compounds (such as Prussian and Turnbull’s blue) are CNSAD (strong acid dissociable cyanide), meaning that they are stable compounds that only dissociate at pH conditions that are very low (<1). UV-radiation also dissociates these compounds. The potential determination of iron-cyanide compounds to form in the environment and their subsequent dissociation, is an area that requires more investigation. The main aims of the study include the modelling of Prussian/Turnbull’s blue in the goldmine tailings environment. To determine in a lab investigation whether or not iron-cyanide are able to form in different samples associated with such environments. Different analysis of the different samples and the analysis of a blue sample found on a tailings dam close to Welkom. Further modelling the affects that pH and the presence of other complexes has on the production of Prussian blue. The last aim was to determine if there are bacteria present that are able to degrade cyanide. The research approach consisted of two branches, namely modelling and the analysis of samples. Modelling was preformed using PHREEQC. The samples mentioned in this research consist of two branches, namely the laboratory study of adding cyanide to different samples and analysing them, and analysing tailings samples. Methods used in the laborarory study include XRD, FT-IR, XPS and total cyanide analysis. 9 samples were collected from a tailings dam close to Welkom, which forms apart of the Free State goldfields. XRF, ICP-OES, total cyanide, CNS analyzer (LECO) and metagenome analysis were performed on these samples. The main findings show that Prussian and Turnbull’s blue are able to form in such tailings environments. Prussian blue forms in an oxic environment and Turnbull’s blue forms in both an oxic and anoxic environment. The main variables that affect the formation of these iron-cyanide compounds is oxygen, the pH and concentrations of cyanide and iron available in solution. A NaCN solution was added to a pyrite sample, a Witwatersrand reference material and a tailings sample, where pyrite and the Witwatersrand reference material produced a blue substance. The analysis of these two samples and a blue sample from a tailings dam were analysed with FT-IR, revealing the presence of an iron-cyanide bond. The cyanide concentrations of the 9 tailings samples ranged from 0.6 – 10 ppm, where the highest concentration was found in a sample containing a blue substance (2.1) and the lowest is deeper into the tailings below the blue sample (2.3), suggesting that iron-cyanide compounds/complexes immobilize cyanide. The metagenome analysis revealed that the naturally occurring bacteria in the tailings are able to degrade or assimilate cyanide in the oligotrophic tailings environment. Cyanide is a source of carbon for the bacteria and an energy source. In conclusion, iron-cyanide compounds/complexes are able to form in the goldmine tailings environment, where a blue sample from a tailings dam was analysed and determined to be an iron-cyanide compound. It was also determined that these compounds/complexes immobilize cyanide, which are naturally degraded by the bacteria on the tailings dam. Ultimately, geochemical risk assessments for mining projects may benefit from including a microbiological aspect, which has not previously been considered. It is recommended that the following options be followed for remediation of cyanide: 1) The addition of an iron-source for iron-cyanide formation, immobilizing the cyanide 2) Burial of the material, possible burial in a mine void (anoxic environments result in higher pH conditions and zero UV radiation) or the addition of a pH buffer e.g., dolomite 3) Determine which microbes are present in the environment 4) Nurture the bacteria colonies, if found to be necessary
Open Access
Geochemical evolution in defunct gold mine tailings and modelling of seepage water quality: an investigation of a typical tailings storage facility in the East Rand, Johannesburg, South Africa
(University of the Free State, 2022) Fourie, Petrus Johannes; Usher, B.; Hansen,R. N.
The geochemical evolution in a defunct tailings dam was investigated in the East Rand Basin of the Witwatersrand. The research aimed to geochemically characterise the tailings, quantify oxygen infiltration into the tailings dam and develop a numerical geochemical model to simulate the geochemical evolution within the dam over the past 60 years. Two holes (3.4 and 6 m deep, respectively) were hand-augured into the tailings dam to geochemically characterize the tailings. Tailings samples were collected at roughly 15 cm intervals. On selected samples from the 6 m hole, the whole-rock elemental composition (using X-ray Fluorescence and a Leco Element Analyser) was performed, as well as acid-base testing, X-ray diffraction and Scanning Electron Microscope. Field measurements of pH, Electrical Conductivity (EC) and Oxidation-reduction Potential (ORP) were performed on drilled-out samples of the 3.4 m hole. The oxygen concentration in the tailings gas phase was measured to correlate the oxygen ingress with the other measured geochemical parameters and for later use in the geochemical model. Air chambers were installed in the 6 m hand-augered hole. Each air chamber comprised a perforated 7 cm high plastic container wrapped in a geotextile that is then connected with an 8 mm silicon pipe. Air collection chambers were installed at depths of 0.5 m, 1 m, 1.5 m, 2 m, 2.5 m, 3 m, 4 m, 5 m, and 6 m. Based on the oxygen concentration in the gas phase, the top of the tailings dam was subdivided into three geochemical environments, namely the Oxic Zone (0-2 m), the Transition Zone (2-4 m), and the Anoxic Zone (>4 m). The data shows that oxygen penetrates slightly deeper during the winter than in the summer months. The seasonal effect could be attributed to the higher rainfall in the summer than in winter. A conceptual model of the geochemical evolution within the tailings dam was developed. The aim was to outline the major mechanisms that influence the geochemical evolution in the dam to include them in the numerical model. Batch reactor testing was performed at three different pH's (pH ~3, pH ~5 and pH ~7) to back-calculate the effective surface area of the pyrite in a tailings sample based upon its reaction during the experiment. The experiments were performed over about 14 days. Except for the last few days, samples were collected twice a day. The sulphate production was the lowest in the pH ~3 experiment and the highest in the pH ~7 experiment. This is because pyrite oxidation by oxygen is inversely proportional to hydrogen activity. The modelled pyrite reaction rate fitted the results for all three experiments. The optimal surface area was determined at 1046.26 g/cm². A numerical geochemical model was performed to simulate the geochemical evolution within the dam over the past 60 years. The primary objective of the modelling was to improve the understanding of the mechanisms that control the geochemical reactions and dispersion of chemicals. A secondary objective of the model was to match the model results with the observations 60 years after closure.
Open Access
A multi-isotope (S-Sr-Nd) investigation of the Flatreef, Northern Limb, Bushveld Complex: Petrogenetic implications and comparison with the Merensky Reef
(University of the Free State, 2022) Keet, Jarlen Jocelyn; Roelofse, Frederick; Gauert, Christoph
Historically, research on the Bushveld Complex (BC) in the northern limb mainly focused on the near surface Platreef. The Platreef is well-known for being complicated and erratic due to significant degrees of country rock assimilation and contamination along strike. A correlation of the disrupted magmatic stratigraphy of the Platreef to the Upper Critical Zone of the western and eastern limbs has thus proven difficult. The discovery of the Flatreef, the down-dip, sub-horizontal extension of the Platreef, on the farms Turfspruit and Macalacaskop, opened new avenues for enquiry. The proportion of assimilated country rock within the Flatreef is significantly less than in the near surface Platreef, with a stratigraphy that is less disrupted and affected by footwall interaction than the Platreef, such that Bastard Reef and Merensky Reef correlates may be identified in the Flatreef stratigraphy. In this study Sr, Nd and S isotopic compositions across the stratigraphic units of the Flatreef as intersected by drill hole UMT-393 on the farm Macalacaskop, and to a lesser extent, drill hole UMT-276 on the farm Turfspruit is reported. The initial ⁸⁷Sr/⁸⁶Sr ratio (Sri) (also indicated as ⁸⁷Sr/⁸⁶Sri) results show a significant shift from about 0.706 to 0.707 in the immediate footwall, to values > 0.709 near the top of the Main Reef. This isotopic shift matches the isotopic shift described for the Merensky Reef of the eastern and western BC. The mineralized units of the Flatreef, namely the Main Reef and Upper Reef, have 𝛿³‏⁴S values ranging between -0.2 to 1.5‰ (with the exception of three outliers), and 0.52% and 11.2‰ in UMT-393, respectively. The S-isotope data for UMT-276 are lighter with 𝛿³‏⁴S values ranging between -0.96 and 2.24‰ for the Main Reef and 3.19‰ was recorded for an Upper Reef sample. These near-mantle 𝛿³‏⁴S values fall within the range of about 0 to 3‰ reported for the Merensky Reef in the eastern and western BC.

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