PhD.G (Environmental Geology) / Department of Mining and Environmental Geology

The Platreef is a platinum group element (PGE) and base metal enriched mafic/ultramafic layer situated along the base of the northern (Potgietersrus) limb of the Bushveld Complex. It represents an important resource of PGE which is only in its early stages of exploitation. The present study contains a detailed petrographic and geochemical investigation of a borehole core drilled on the farm Townlands. At this locality, the Platreef rests on metasedimentary rocks of the Silverton Formation of the Transvaal Supergroup, and is comprised of three medium grained units of gabbronorite/feldspathic pyroxenite that are separated by hornfels interlayers. I refer to the three platiniferous layers as the Lower, Middle and Upper Platreef. The Middle Platreef is the main mineralized layer, with total PGE contents up to 4 ppm. The Lower and Upper Platreefs are less well mineralized (up to 1.5 ppm). Trace element and S-isotope data show compositional breaks between the different platiniferous layers suggesting that they represent distinct sill-like intrusions. The study also reveals a reversed differentiation trend of more primitive rocks towards the top of the succession. For example, pyroxene shows an increase in Cr2 O3 with height couples with a decrease in TiO2 . Olivine from the Upper Platreef has Fo contents between 80-83 (averaging Fo81) and those from the Middle Platreef have Fo from 78-83 (averaging Fo79 ). The Upper and Lower Platreefs have <FONT FACE="SYMBOL">d</FONT> 34S values averaging 80/00 while the Middle Platreef has <FONT FACE="SYMBOL">d</FONT> 34S values averaging 4 0 /00. All three Platreef layers have elevated <FONT FACE="SYMBOL">d</FONT> 34S values, indicating addition of 34S-enriched crustal sulphur. The model of contamination is supported by elevated K, Ca, Zr and Y contents in the Platreef relative to Critical Zone rocks from elsewhere in the Bushveld Complex, and by high Zr/Y ratios. Well defined correlations between concentrations of the individual PGE, and between the PGE and S suggest that the concentration of the PGE was controlled by segregating sulphide melt. Alteration of the rocks, possibly due to infiltration by fluids derived from the floor rocks, caused localized redistribution of Cu and, to a lesser degree, the PGE. A model is proposed whereby the Platreef magma assimilated calcsilicate and hornfels from the country rocks. The hornfels and calcsilicate of the Silverton Formation that forms the floor rocks to the Platreef on the farm Townlands constitute a possible source of the crystal sulphur. Release of S from the floor rocks caused S-supersaturation in the magma, followed by segregation of an immiscible sulphide melt. The sulphide melt scavenged the PGE from the silicate magma. The sulphides and the xenoliths were entrained by successive, metal-undepleted magma flows, causing high metal tenors in the sulphides and undepleted Ni contents in associated olivine / Dissertation (MSc)--University of Pretoria, 2006. / Geology / unrestricted

M.Sc. / Please refer to full text to view abstract

MESMEG / Department of Mining and Environmental Geology / Literature indicated that several mineralogical identification studies have been carried out on clays but few have focused on the characterisation of geophagic materials from South Africa. Large quantities of earth materials are consumed daily in Mashau Village, however, their mineral content and geochemical compositions had not been determined. Moreover, though the consumption of geophagic materials is very common in the village, the associated health implications had not been addressed. Thus, the main aim of the research was to mineralogically and geochemically characterise geophagic materials commonly ingested in Mashau Village and infer on possible health implications that could result from their consumption. Questionnaires were administered to geophagists in the study area with the aim of generating data on the prevalence of geophagia and the motivations for the practice. Geophagic soils and their parent rocks (for determination of provenance) were sampled and analysed for mineralogical and geochemical content. Geophagic soil samples were subjected to the following physicochemical analyses: colour, particle size distribution, pH, cation exchange capacity (CEC) and electrical conductivity (EC). An x-ray diffractometer (XRD) was used for mineralogical analysis while major oxides and trace elements abundances were determined using x-ray fluorescence (XRF) spectrometry and laser ablation inductively coupled mass spectrometry (LA-ICP-MS), respectively. Furthermore, provenance of the geophagic materials was determined using data obtained from mineralogical and geochemical analysis. Inferred health implications were based on the physico-chemical, mineralogical and geochemical data obtained. Outcomes of the questionnaire survey revealed craving to be the motivation for geophagia in Mashau Village. Although the practice seemed to be prevalent in females of certain ages, it was certainly not limited to gender, age, educational level or socio-economic status. Out of the 20 geophagic samples, 3 samples were brown, 2 had a strong brown colour and another 2 had a light olive brown colour. Other soil colours were less common, as each colour was only observed in one sample. The sand fraction dominated the samples; the clay content was low, giving the samples a sandy clay loamy texture. The pH of the soil ranged from being slightly acidic (5.4) to being slightly alkaline. The CEC values were very high ranging from 17 t0 109 meq/100 g. vii The EC values were also high (ranging from 11.2 to 245 μS/cm) indicating a high amount of soluble salts. Mineralogical analysis of geophagic soils identified quartz, microcline, plagioclase, hornblende, dolomite, muscovite, kaolinite, smectite, talc, anatase, hematite, ilmenite, chlorite and epidote with quartz and kaolinite being the dominant minerals. Actinolite, augite, chlorite, epidote, forsterite, magnetite, muscovite, plagioclase, quartz, sepiolite and microcline were the minerals identified in rock samples. Geochemical analysis for major oxides content (SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5 and Cr2O3) indicated that both geophagic soils and parent rocks were mainly composed of silica and alumina. Trace elements geochemistry showed a depletion of LREEs and an enrichment of HREEs in geophagic soils. The results also revealed that the REEs were enriched in the bulk fraction than in the clay fraction. Relative to the Upper Continental Crust (UCC) compositions, the concentrations of trace elements in geophagic soils were generally low. Provenance determination results showed that geophagic soils in Mashau were derived from basalts and sandstones. Majority of the samples were formed as a result of intense weathering while some were as a result of intermediate weathering. The negative health implications of the studied materials could include perforation of the colon, damage of the dental enamel and anaemia. However, geophagic materials could also be a good source of mineral nutrients and beneficial for reduction of nausea during pregnancy. / NRF

MENVSC / Department of Ecology and Resource Management / Historically, mining activities have generated vast quantities of abandoned tailings dumps in several regions of South Africa and throughout the world. The management and disposal of huge volumes of tailings dumps has constituted a major challenge to the environment. The current study aims to establish the physicochemical properties and mineralogical characterization of the old copper tailings dump in Musina, to reveal the mobility patterns and attenuation dynamics of potentially toxic or heavy metal species as a function of depth, with a view of assessing their potential environmental impact with respect to surface and ground water systems. This information is crucial in the beneficial utilization of copper tailings in the development of sustainable construction materials as part of reuse approach management system. About twelve tailings samples were collected into polyethylene plastic bags from three established tailings profiles drilled by a hand auger. The collected tailings samples were characterized using standard analytical procedures i.e., X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS). The transfer of potentially toxic or heavy metal species from tailings to water was evaluated using the standardized batch leaching test (EN 12457) and speciation-equilibrium calculations on the aqueous extracts performed by MINTEQA2. The leachate concentration of cations in the collected tailings samples was determined by inductively coupled mass spectrometry (ICP-MS) and the leachate concentration of anions was determined by ion chromatography (IC). A modified sequential extraction scheme was applied on the selected tailings samples of the drilled tailings profiles to further understand the mode of occurrence, the geochemical partitioning and distribution, real mobility, and environmental bioavailability of potentially toxic or heavy metal species in the tailings and tailings-soil interface. The extracted fractions or phases from sequential scheme were as follows: (F1) water-soluble fraction, (F2) exchangeable fraction, (F3) carbonate fraction, (F4) iron and manganese hydroxide associated fraction, (F5) organic matter and secondary sulphide associated fraction, (F6) primary sulphide bound fraction, and (F7) residual or silicate fraction. The results obtained from the seven steps sequential extraction scheme were validated by the determination vi of percentage recoveries from pseudo-total digestion or total metal content of the original sample. The distribution of major elements and potentially toxic or heavy metal species in different leachate fractions obtained after each step of sequential extraction of the selected tailings samples was determined by inductively coupled plasma mass spectrometry (ICP-MS). The appraised data was used to reveal the impact of atmospheric oxygen and infiltrating rain-water on the chemistry of copper tailings dump by depth profiles. Macroscopic properties revealed that the abandoned Musina copper tailings are fine to medium coarse grained, and range in color from light/dark gray at the upper or shallow depth of the tailings, to dark reddish-brown at the deeper zone where the tailings are mixed with the underlying soil or soil-interface. The drilled respective tailings profiles were uniform and slightly varied in both mineralogical and bulk chemical compositions with tailings depth. Mineralogical analysis showed the following order of mineralogical composition within the respective tailings profiles: quartz> epidote> chlorite> muscovite> calcite> hematite. Chalcopyrite was the only sulphide mineral observed by optical microscopy, although not identified or quantified by XRD and SEM-EDS analysis. The observed discrete chalcopyrite grains were attributed to the primary mined ore (i.e., chalcopyrite, chalcocite and bornite) during past copper mining activities in Musina. The tailings profiles were characterized by a medium alkaline pH (7.97-8.37) that corresponds very well with the tailings leachates or pore-water pH (8.36-8.46). This pH was constant and slightly varied with tailings depth in the respective tailings profiles. The high abundance of alumino-silicate minerals and traces of carbonates as calcite coupled with low sulphide mineral content, suggested a high neutralization capacity of the tailings which was in common agreement with an alkaline nature of the copper tailings dump. The chemical composition of major elements within the respective tailings profiles followed the order: Si>Al>Fe>Ca>Mg>K>Na, and corresponds very well with the mineralogical composition of the tailings, whereby alumino-silicates were the most abundant minerals in the tailings samples. Nevertheless, the solid-phase concentration of metals decreases with increasing tailings depth as Cu>Sr>Zr>Ni>Zn and was incongruent with the mineralogical composition within the respective tailings profiles. The main secondary minerals were calcite and hematite, and their proportion increased with increasing tailings vii depth. In addition, hematite formed coatings on the rims and corners of chlorite as observed from optical microscopy, and retained relatively high amounts of potentially toxic or heavy metals (up to 862 ppm of Cu, up to 36 ppm of Ni, and up to 25 ppm of Zn) at the upper and shallow depth of the respective tailings profiles, where bulk density was high and low porosity. Based on batch leaching tests, the amounts of potentially toxic or heavy metal species released into solution were low (0.27-0.34 μg/L Pb, 0.54-0.72 μg/L Ni, 0.88-1.80 μg/L Zn, and 20.21-47.9 μg/L Cu) and decreases with increasing tailings depth, indicating that, presently, the tailings have a minor impact on heavy metals load transported to the receiving surface and groundwater systems. The low concentration of potentially toxic or heavy metal species in solution is primarily due to their retention by secondary Fe oxide phases (i.e., hematite) and the prevailing medium alkaline pH condition of the tailings leachate or pore-water. The observations are consistent with MINTEQA2 speciation calculations, which predicted the precipitation of secondary phase cuprite (Cu2O) as the main solubility-controlling mineral phase for Cu, Zn, and Ni. Primary factors influencing aqueous chemistry at the site are neutralization and dissolution reactions as a function of pH, precipitation, and sorption into hydrous oxides (hematite and cuprite). Based on sequential extraction results, the leachable concentration of potentially toxic or heavy metal species in the water-soluble, exchangeable and carbonate fractions of the respective tailings profiles was relatively low, except for Cu and Mn. For instance, the leachable concentration of Cu and Mn reached 10.84 mg/kg and 321.7 mg/kg at the tailings-soil interface (3 m) in tailings profile C, respectively. The low concentration of potentially toxic or heavy metal species (Cr, Co, Ni, Zn, Cd, and Pb) in these fractions could be due to the low solubility of minerals bearing these trace elements caused by variations in pore-water pH in the respective tailings profiles. The high concentration of Cu and Mn in these fractions suggests their high mobility and therefore most available for uptake in the environment. Except for Cu>Mn>Cr, the contents of potentially toxic or heavy metal species in the Fe and Mn oxides and organic matter or sulphides bound fractions was low, due to the low viii quantity of these fractions in the tailings, despite their high affinity and sorption capacity for potentially toxic or heavy metal species. Likewise, the residual fraction of the respective tailings profiles contained the highest proportion of potentially toxic or heavy metal species. Although the highest potentially toxic or heavy metal species content was in fractions with limited mobility, care must be taken since any geochemical change or shift in the tailings pH or acidic conditions may cause them to be displaced to more mobile fractions, thereby increasing their mobility and environmental bioavailability. Therefore, physicochemical properties of the tailings including pH and mineralogical composition of the tailings samples were the main substrate controlling the geochemical partitioning and distribution, potential mobility, and environmental bioavailability of potentially toxic or heavy metal species by tailings depth. The knowledge of mobility and eco-toxicological significance of tailings is needed when considering tailings dump disposal or reuse in the environment. The addition of copper tailings at 3 and 28 days successfully improved the compressive strength of cement mortar mixtures incorporating tailings at C5 (5%) and C10 (10%) respectively, although with small margin relative to the control mixture (C0). The maximum strength was 31.15 Mpa attained after 28 curing days, and slightly varied when compared with other compressive strength on copper blended cement mortars mixtures in other countries, used for the development of sustainable construction materials. The chemical composition, physical properties and improved compressive strength on cement mortars mixtures incorporating copper tailings, implies that copper tailings are suitable for the development of sustainable construction materials, thereby ensuring job creation, availability of land for development usage, and the reduction of environmental pollution induced by the abandoned copper tailings dumps.

PhDENV / Department of Ecology and Resource Management / Kaolin dominated soils are common in the tropical and subtropical regions. People depend on kaolin-rich soils for agricultural production of food and fiber. The most popular of all South African soils is the Hutton form which accounts for the marvelous redness of the landscape across the Country. The apedal (structureless) soils in the group are characterised by a relatively low CEC (< 11 cmolc kg-1) reflecting oxidic mineralogy with predominantly kaolinitic assemblage. The geochemical and mineralogical composition of soil kaolin has significant implications on soil fertility, geochemical exploration and engineering properties. Despite the dominance of kaolin in these soils, little is known of their properties in the medium. The nature of kaolin minerals in soils varies with parent material, degree of weathering and pedogenic environment. Most studies conducted in South Africa on kaolins are limited to reference kaolins with little or no publication on soil kaolins, hence, this study. This research involved the evaluation of mineralogical and geochemical characteristics of oxidic soils and soil kaolins developed from four (4) selected parent rocks which were basalt, granite, arkosic sandstone, and gneiss. Soils developed from quartzite were selected as control. Representative soil samples collected from profiles developed from the different parent rocks were analysed for physico-chemical, mineralogical, and geochemical data. The mineralogical and geochemical data obtained by x-ray diffractometry (XRD), x-ray fluorescence (XRF), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) were used in unraveling the influence of the provenance and degree of weathering on the soil characteristics. The mineralogical and geochemical data for soil kaolins were determined through XRD, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and differential scanning calorimetry, XRF, and LA-ICPMS to establish their mineralogical and geochemical properties with respect to their parent rocks. Comparison between the soil kaolins and selected reference kaolins were also conducted. The phosphorus (P) sorption data acquired photometrically were employed to evaluate the relationship between the P sorption capacities of the soils and soil kaolins. The influence of soil properties on the fertility of the soils were assessed based on the physico-chemical (pH, particle size distribution, and electrical conductivity (EC)) and chemical (organic matter (OM) content, cation exchange capacity (CEC), available P, exchangeable cations (Ca, K, Mg, Na, and Al), and P sorption) data. The mineralogical and geochemical data for the parent rocks were obtained by XRD, optical microscopy, XRF, and LA-ICPMS. Multivariate statistical analyses were also conducted. Results showed that the dominant colour in the studied bulk soils was dusky red (31 %) followed by brown (23 %), reddish brown, yellowish red, and yellowish brown (23 %) as well as strong brown, dark brown, reddish grey, very dark greyish brown, and dark red. Soil textures were clayey to sandy loamy with OM contents between 0.41 and 4.76 %. The pH, EC, CEC, exchangeable cations, and available P values generally ranged from 5.22 to 8.38, 10.25 to 114.40 μS/cm, 2.93 to 18.30 cmol/kg, 0.03 to 13.92 cmol/kg, and <0.01 to 54.99 mg/kg, respectively. Kaolinite and quartz were the dominant phases for soils developed from basalt whereas, quartz and plagioclase were the dominant mineral phases in soils developed from granite, arkosic sandstone, and gneiss, respectively. Other minerals present in the soils were microcline, muscovite, hematite, goethite, montmorrillonite, anatase, gibbsite, chlorite, and actinolite. Geochemical compositions of the bulk soils show relative enrichment of Fe2O3, TiO2, CaO, K2O, MgO, MnO, and Na2O (except for CaO, K2O, MgO, MnO, and Na2O in soils developed from basalt). Chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) values varied between 54.92 and 99.81 % which suggest low to high degree of chemical weathering. The ACN-K and A-CNK-FM diagrams for the different soils also support these observations. Trace elements were generally enriched in soils developed from basalt and gneiss (except for Rb, Sr, and Ba in soils developed from basalt), but were depleted in soils developed from granite and arkosic sandstone (except for Cr and Ta). The principal factors responsible for the mineralogical and geochemical characteristics of the soils were the parent rocks and degree of weathering. In the soil kaolins, the dominant clay mineral was kaolinite accounting for 23 to 85 wt % followed by montmorrillonite, chlorite, and gibbsite. The non-clay minerals like quartz, plagioclase, muscovite, microcline, anatase, goethite, hematite, and actinolite accounted for the remaining percentages. The soil kaolins were characterised by thin platy kaolinite particles with partially to poorly-ordered structural order. The platy kaolinite crystals have their longest dimension sizes between 0.06 and 0.25 μm. The dehydroxylation temperatures for the studied soil kaolins ranged from 425 to 475 ˚C. The SiO2/Al2O3 ratio was lowest in soil kaolins developed from basalt and higher in soils developed from granite, arkosic sandstone, and gneiss which is consistent with their mineralogy since the former have more kaolinite. Higher Fe2O3 and CEC values were obtained relative to reference kaolins which could be attributed to the presence of more structural iron in the soil kaolins as well as their smaller crystal sizes. The presence of weatherable and accessory minerals accounted for the enrichment of Co, Ni, Cu, Zn, and Pb in the soil kaolins. The kaolinite in the soils were formed by leaching and desilication of the primary minerals in the parent rocks under suboxic conditions. H-type P adsorption isotherms obtained for both the soils and soil kaolins indicated their high affinity for phosphorus by chemisorption. The average maximum P adsorption values were in decreasing order of soils developed from basalt > granite > arkosic sandstone > quartzite (control) > gneiss, respectively whereas, for soil kaolins is basalt > granite > quartzite (control) > arkosic sandstone > gneiss, respectively. Relative to other soils developed from different parent rocks, soils developed from basalt (with more clay content) had higher capacity and buffer power for P adsorption. The standard P requirements for the soils ranged from 7.78 to 92.91 mgP/kg and were classified as low based on the Langmuir model. Significant correlation between the P adsorption parameters for the soils and soil kaolins indicated that the later could be taken as a good predictor for P sorption dynamics in the soils. Electrical conductivity of the soils were taken to be negligible in interfering with plant growth. The available P values were generally below the critical level of 12 – 15 mg/kg for soils developed from basalt, gneiss, and quartzite (control) but higher in soils developed from granite and arkosic sandstone. All the soil evaluation factor (SEF) average values estimated were greater than five indicating that they are not of poor soil fertility. The correlation results between the soil properties and P sorption parameters suggest that several variables can influence the P sorption dynamics of the soil. Regression analyses further indicated that CEC, pH, OM, and clay content in the soils account for 99 % bounding P energy variation whereas, Fe2O3 accounts for 76 % P sorption maximum variation in the soils. In addition, variations in Fe2O3 and sand contents in the soils account for 96 % and 95 % maximum buffering capacity and external P requirement (EPR) variations, respectively. Models to advance the interplay between the various soil properties and P sorption parameters in the soils were developed. Mineralogical and geochemical characteristics of the soils were principally controlled by the parent rocks and degree of weathering. The soil kaolins displayed significant differences relative to reference kaolins. Langmuir model is most suited for describing P sorption in soils and soil kaolins developed from different parent rocks within the studied area. P sorption parameters for the soils can readily be obtained from the P sorption parameters of the kaolins present in them. EPR obtained and models for predicting P sorption parameters from selected soil properties developed for the various soils will improve the efficiency of routine P fertilizer applications. Iron oxide (Fe2O3) played the most crucial role in explaining the P sorption dynamics of the soils. The major contributions from this study have been: better understanding of the influence of parent rock characteristics and degree of weathering on the soil characteristics, the nature of soil kaolins and its influence on soil properties as well as P sorption dynamics in soils have been better established, and improvement of the understanding on the relationship between soil properties and P sorption dynamics in the soils. / NRF