2023 Student Abstracts
Researcher: Steve Jason Chingwaru (PhD, Stellenbosch University)
Supervisor: Dr Bjorn von der Heyden
Title: Gold deportment and ore characterisation of the historical Witwatersrand
tailings dams with emphasis placed on the sulphides
Abstract
The Witwatersrand Basin, discovered in 1881, has yielded over 53,000 tons of native gold hosted in quartz pebble conglomerates. Present gold extraction methods involve comminution and direct cyanidation, resulting in the retention of 5-10 % of residual gold in tailings. Re-mining primarily targets native gold recovery, achieving an average of 30-50 % gold recovery through direct cyanidation. This implies that the remaining 50-70 % of unrecovered gold, along with approximately 30 million tons of residual sulphide waste, is re-dumped to the tailing stream. The Witwatersrand tailings significantly contribute to South Africa’s pollution, causing acid mine drainage and heavy metal effluent due to sulphide waste oxidation. The mineralogical distribution of unrecovered gold during tailings reprocessing is inadequately characterized and absent from existing literature. Furthermore, the current body of literature lacks a comprehensive environmental assessment specifically addressing the movement and dispersion of heavy metals during sulphide oxidation within the Witwatersrand tailings. This PhD research focuses on the ore characterization and mineralogical deportment of unrecovered gold within the Witwatersrand tailings from Klerksdorp, Carletonville, Evander, and Central Rand goldfields. Simultaneously, an environmental assessment explores heavy metal behaviour, retention, and release mechanisms during sulphide oxidation in Witwatersrand tailings dumps. The methodology utilized employs the multi-element, high-resolution, and low detection capabilities of laser ablation inductively coupled plasma mass spectrometry analysis, combined with an automated mineralogical technique to analyse bulk tailings samples and their operationally defined mineral fractions. Additional analytical methods include aqua regia digestion coupled with ICP-MS analysis, fire assay, and mineralogical analysis using optical microscopy, electron microscopy, and X-ray diffraction analysis.
Metallurgical test work, incorporating gravity separation, direct cyanidation, and diagnostic leaching, validates Witwatersrand tailings behaviour in processing scenarios. Results indicate cyanide amenable gold recovery at 14-61 %, primarily in the form of micron to nano-sized native gold particles. Non-cyanide amenable phases contributing to the refractory behaviour of gold include sulphides (mainly pyrite) and silicates at 4-38 % and 11-32 %, respectively. In situ pyrite analysis reveals ‘invisible’ gold within detrital arsenian pyrite and pyrite. These Archean detrital pyrites exhibit grades comparable to auriferous sulphides from surrounding Archean granite-greenstone gold ores on the Kaapvaal craton (up to 2700 ppm). Pyrite also hosts a substantial concentration of heavy metals, with Co, Au, and Pb strongly leached during pyrite oxidation. However, a significant proportion of As, Ni, Cu, and Zn is retained in the iron oxyhydroxide alteration rims through incorporation and absorption. The study underscores the necessity of addressing ‘invisible gold’ during beneficiation, proposing tailored leaching parameters and a pretreatment strategy to potentially recover up to 420 tons of gold, thereby contributing to the local economy. Furthermore, the recovery of heavy metals can not only reclaim valuable ‘sweetener’ by-product metals such as Cu, Co, and Ni but also directly mitigate issues related to heavy metal pollution and acid mine drainage associated with surface tailings dumps.
Researcher: Mangs Ayuba Danmangu (PhD, University of Johannesburg)
Supervisor: Professor Nicola Wagner
Title: The petrography, mineralogy and geochemistry of coal within the Benue Trough, Nigeria
Abstract
Nigeria has significant coal deposits that are not well documented. This study considers the petrography of coal confined in the Benue Trough, Nigeria. Petrographic analyses, supplemented by mineralogy, and geochemistry, with a view to infer the depositional conditions that controlled the formation. The Benue Trough is rift-rift-rift system (triple junction) that trends NE-SW directions from south of Chad Basin to north of Gulf of Guinea.
Twenty-nine (29) grab samples acquired in nineteen (19) coal areas from Lower Benue Trough (LBT), Middle Benue Trough (MBT), and Upper Benue Trough (UBT). The proximate data of the coals shows high volatile matter yield, and fixed carbon, low ash, and high calorific values (24.82 MJ/kg areal average). Sulphur values are usually low (areal average of 0.72%).
Vitrinite reflectance values show the coal rank from low to medium in the categories of lignite to subbituminous and bituminous coal. Coal displayed predominantly vitrinite, with variable content of inertinite and liptinite macerals composition. Microlithotype composition showed variation in the three sub-regions with MBT samples being predominantly vitrite and carbominerite (carbargillites/clays, carbosilicates /clays, with limited carbopyrite).
Coal facies studies can be used to decode paleoenvironmental settings under which organic matter is accumulated. Indices that are usually considered in paleoenvironmental studies includes the following: gelification index (GI), tissue preservation index (TPI), ground water index (GWI), vegetation index (VI), and wood index (WI). MBT samples generally reported a high gelification index which is indicative of a wet environment. Relating the displayed facies models applied in this study, MBT differ from UBT and LBT, in agreement with coal quality differences. UBT and LBT samples were clustered in upper deltaic to drier piedmont plain setting, while MBT coals in lower deltaic marsh to wet forest swamp setting. All the samples plot was cluttered in ombrotrophic paleomire condition. An assessment of the equations visa-vice model facies used shows that, interpreting depositional environments from just a single model is not good enough for a conclusive decision.
The analysis plots show depletion in the major elements, trace, and rare earth elements, which could be linked to the source of the sediments from weathered basement rocks transported into the Benue Trough with mineral composition dominated by kaolinite, quartz, pyrite, and compounds like germanium. Dominant oxides in the coal samples are: Al2O3, SiO2, Fe2O3 with variations in others (BaO, CaO, Cr2O3, K2O, MgO, MnO, Na2O, NiO, P2O5, SO3, TiO2, & V2O5), with carriers being quartz, clay minerals and pyrite. Major oxides and trace elements studies are used to interpret paleo-setting and paleo redox conditions of peat swamp. V/Ni, U/Th, V/Cr, Sr/Ba, Ni/Co ratios reveal a new (fresh) aquatic setting of predominantly humid climate.
Gross calorific value (GCV) and combustion profiles show that the coals could be subjugated for power generation. Other applications such as energy in cement manufacture, block manufacturing works, foundries, washings, battery manufacture, and fuelwood in local cookery (smokeless coal briquettes) are also possible.
Researcher: Godfrey Shoriwa Chagondah (PhD, University of Johannesburg)
Supervisor: Associate Professor Axel Hofmann
Title: Petrogenesis and Metallogenesis of Granitic Rare-Metal Pegmatites along the Southern Margin of the Zimbabwe Craton: Implications to Exploration
The Archaean Zimbabwe craton of southern Africa is a classic granite-gneiss-greenstone terrain. World-class Lithium-Cesium-Tantalum (LCT) pegmatites and emerald deposits occur along the southern margin of the craton hosted within greenstone belts. The Bikita field is hosted in the Masvingo belt, whereas the Mweza field occurs in the Mweza-Buhwa belt. Research into the origin and nature of rare-element granitic pegmatites has been ongoing for more than a century. The occurrence of rare-element pegmatites in the Bikita and Mweza pegmatite fields, which are spatially associated with syn- to late-tectonic Chilimanzi and Razi granite suites, offer an excellent platform to test the hypotheses of pegmatite origin and contribute knowledge in resolving the controversy. This research project employed an integrated approach embracing desktop studies, fieldwork, mineralogical and petrographic observations, geochemical and geochronological techniques to investigate the granite-pegmatite relationships in the study areas.
The study findings are that the Chilimanzi and Razi suites are metaluminous, I-type granites with different degrees of magmatic fractionation. Broadly, the Chilimanzi Suite is more fractionated relative to the Razi Suite. The granite suites that surround the Bikita field are more evolved, altered, and exhibit elevated trace element contents including Li, Cs, Ta, Rb, Tl, Nb, W, Ga, Th, and U and simultaneous depletions in Sr, Ba and Hf and were thus more likely to spawn rare-element pegmatites relative to the plutons that envelope the Mweza field. Across both fields, the pegmatites are distributed in deformed and greenschist to upper amphibolite grade host rocks. In the Bikita field, the pegmatites were intruded into a system of regional faults and the intrusions truncate regional fabrics associated with the c. 2.63 Ga Limpopo orogeny. Pegmatites on the SW part of the Mweza field are syn-tectonic and were emplaced into shear zones, whereas pegmatites on the NE part of the field are post-tectonic. There is a narrow time window between pegmatites and granite suites magmatism with the former emplaced at c. 2630-2616 Ma, whereas the latter were intruded at c. 2635-2625 Ma. Petrographic, whole-rock, and mineral chemistry data reveal the complimentary role of magmatic and magmatic-hydrothermal transition in the petrogenesis and metallogenesis of the studied pegmatites and granites. The study established a petrographic, geochemical, and geochronological coherence which renders it conceivable for the pegmatites to be late-stage differentiates of the surrounding plutons. The main exploration implications of this study are that highly fractionated, syn-post-tectonic, I-type granites may be potential sources of LCT pegmatites, which could be explored in the rocks such as greenstones peripheral to the plutons using integrated exploration techniques.
Researcher: Mpofana Sihoyiya (PhD, University of the Witwatersrand)
Supervisor: Professor Musa Manzi
Title: Cost-effective and novel seismic methods for mineral and coal exploration: examples from Witwatersrand goldfields and Bushveld Complex
Abstract
The reflection seismic method has its origin from oil and gas exploration in the land and offshore sedimentary soft rock environment. Since the inception of the reflection seismic technology in hardrock environment, more advanced processing methods such as migration algorithms have been established to revamp the quality of hardrock seismic data for deep mineral targeting. This study shows the value of recovering and reprocessing legacy reflection seismic data using advanced processing techniques that were not available at the time of acquisition. This is achieved through different novel processing workflows that incorporate iterative static corrections, Kirchhoff pre-stack depth migration (KPreSDM), Kirchhoff pre-stack time migration (KPreSTM), and the newly developed Fresnel-volume (FV) and coherency migration (CM) techniques. This research also shows the value of novel processing of the seismic data acquired in-mine challenging environments.
The legacy data from the Kaapvaal Craton in South Africa have been processed to improve the delineation of the deep-seated mineral deposits such as the gold-bearing horizons (termed reefs) in the Witwatersrand Basin and Platinum Group Element (PGE) horizons in the Bushveld Complex. Furthermore, the shallow coal seams and associated geological structures of the Karoo Supergroup in the Evander Basin, an arcuate basin characterized by the Witwatersrand Basin towards the south and the Bushveld Complex towards the north, have been delineated for future mine planning and designs.
To better image and understand the geometry of the gold-bearing reefs and crosscutting geological structures in the South Rand goldfield, an 18 km long legacy two-dimensional (2D) reflection seismic line was reprocessed using today’s standard processing workflow which employed iterative static corrections. Improved structural imaging of the steeply dipping faults (mostly normal and reverse), as well as dolerite intrusions, was mostly achieved by using KPreSTM and KPreSDM, with KPreSDM providing better structural imaging than other techniques. Moreover, reprocessing of this profile using an improved velocity model and numerical simulations assisted in delineating near surface stratigraphic units and deep-seated (> 1 km depth) geological structures that are associated with the gold-bearing reef but missed by the legacy post-stack time migrated section.
In the Bushveld Complex, the PGE deposits (known as platinum reefs) are delineated using a newly developed depth migration technique called coherency migration. Imaging through CM workflow shows evidence of the complex structural architecture that controls the platinum deposits in the study area. The 50 km long legacy 2D profile traverses towards the center of the complex and provides a better understanding of the tectonic evolution in the region. Additionally, magnetic data were utilised to constrain seismic interpretation and delineate the highly magnetic major geological structures such as the Chaneng structure and strongly magnetized rocks of the Rustenburg Layered Suite. The Chaneng structure, in particular, was poorly defined by the seismic data due to its steeply dipping nature.
In 2020, in-mine seismic experiments were conducted to delineate the PGE-bearing horizons such as the Upper Group-2 (UG2) and Merensky Reef. Three reflection seismic profiles from these experiments were cautiously processed to attenuate the infrastructure-generated noise. The experiments were successful and delineated the Merensky Reef and UG2 mineralisations at depths between 55 m and 124 m beneath the developmental tunnel (~550 m below the surface).
Six legacy 2D reflection seismic profiles acquired for gold exploration in 1986 in the Evander Basin are processed for imaging both the Witwatersrand Basin and the Bushveld Complex, as well as the coal seams of the Highveld and Witbank coalfields. The profiles were acquired perpendicular to each other providing pseudo-three-dimensional (3D) imaging of the subsurface and better delineation of the geological structures. The degree of faulting and folding that affect the mineralisation observed on the processed profiles in all sites would not have been achieved if advanced processing workflows were not implemented. Processing of the legacy data provides a more cost‐effective way to explore the mineral deposits than reacquiring new data, which could be costly and limited by surface conditions. The processing approaches used in this thesis can be used in other brownfield mining regions where the legacy data exist, and they can also be used to revamp the quality of the data acquired in noisy mining environments.
Researcher: Dillan Fitton (MSc, University of Johannesburg)
Supervisor: Associate Professor Bertus Smith
Title: A detailed stratigraphic, mineralogical and geochemical assessment of the Hotazel Formation at Middelplaats, Kalahari Mn Field, Northern Cape Province, South Africa
Abstract
The Kalahari Manganese Field situated in the Northern Cape Province of South Africa is the largest known land-based Mn deposit on Earth. It is hosted by the Fe- and Mn-rich chemical sedimentary succession of the approximately 2.4 Ga Hotazel Formation. The Hotazel Formation forms part of the Postmasburg Group in the Griqualand West region of the Transvaal Supergroup. It is conformably underlain by the Ongeluk Formation volcanics and capped by the carbonates of the Mooidraai Formation. The Hotazel Formation is composed of four banded iron formation (BIF) units separated by three Mn formation (MnF) units with hematite-lutite transitions between the units. This study is based on a single drill core MP72 drilled on the Middelplaats farm (Northern Cape Province) located south of Hotazel. Drill core MP72 intersects the entire Hotazel Formation and is pristine with no evidence of alteration. This study investigated all the BIF and MnF units in the Hotazel Formation in drill core MP72. The results are used to produce depositional models and gain further understanding of the paleoenvironmental conditions during deposition of the Hotazel Formation.
The Hotazel Formation, as studied from drill core MP72, displays three distinct BIF mineralogical facies. The bottom of the formation is dominated by oxide facies BIF, the middle of the formation by silicate facies BIF and the top by carbonate facies BIF. The MnF units are very fine grained with evidence of ovoids and lenticles and are fairly uniform. The mineralogy of the MnF units is dominated by braunite and kutnohorite. The BIF units are coarser grained with inclusions of sandy lenses and sedimentary structures such as cross lamination which indicates deposition might have occurred above wave base in the depositional basin. The transitional units (T) and MnF units show no dynamic sedimentary structures and were likely deposited deeper in the basin. Therefore, the BIF units were deposited source proximal in shallow water whereas the MnF units were deposited source distal in a deeper setting.
The geochemical analysis depicts the nature of the Hotazel Formation with a high Fe content in the BIF units (up to 61.297 wt%) and a high Mn content in the MnF units (up to 46.090 wt%) which clearly outlines the alternating layering of BIF and MnF units. The trace elemental analysis shows that deposition occurred in a marine environment as the REY patterns are similar to those of modern sea water, which is common for many Paleoproterozoic BIFs. The lack of Al and Ti shows that the formation was starved of clastic input which indicates that the REY patterns observed are a result chemical deposition and not clastic input. The REY shows two distinct features, the first being the lack of a positive Eu anomaly which indicates that the fluids that sourced the Fe and Mn were low temperature (>250°C). The negative Ce anomaly sheds new light on the Hotazel Formation as the full stratigraphic sample set shows that it occurs throughout the formation and is restricted mainly to the MnF and transitional units. The direct relationship between Fe and Ce and the inverse relationship between Mn and Ce suggests that the formation of the negative Ce anomaly was mostly like due to an in-situ oxidation process. During this process Fe oxidation buffers cerium oxidation, with cerium oxidation occurring after Fe depletion and prior to Mn oxidation. The progressive oxidation of Fe to cerium to Mn would have required the presence of free oxygen in the water body. The deposition of Fe and Mn was mediated by Fe- and Mn-oxidizing bacteria based on previously published δ13CPDB values (-9.5 to -3.40/00) and the volume of Fe and Mn found in the Hotazel Formation. The Mn-oxidizing bacteria would have required free oxygen.
Based on the data represented in this study and in previous literature three possible depositional models are considered: 1) dynamic hydrothermal plume and sea level model, which depicts a back-arc basin which hosts a waxing and waning hydrothermal plume; 2) static depleting plume model, which depicts a static basin which is invaded hydrothermal plume pulses; and 3) continentally derived model, which depicts a continental source of Fe and Mn which enters a marine environment via dissolved continental run-off. All the models have aspects supported by, but also contradicted by the data presented in this study, with the dynamic hydrothermal plume and sea level model seeming most likely. There are limitations to creating a depositional model based on one drill core as the features found in this drill core cannot always be extrapolated to the whole basin. However, insights from the drill core allows important paleoenvironmental conditions aspects to be better understood.
All the considered depositional models require the presence of free oxygen in the marine environment during the deposition of the Hotazel Formation. Recent age determinations place the age of the Hotazel Formation just prior to or at the onset of the Great Oxidation Event (GOE), with the latter marking the first emergence of Earth’s ozone layer. This indicates that the GOE was preceded or marked at its onset by increases of free oxygen in marine
environments.
Researcher: Fatima Zonke Chitlango (MSc, University of Johannesburg)
Supervisor: Professor Nicola Wagner
Title: Rare Earth Elements in South African Coals: Concentration and mode of occurrence in density fractionated samples from the Waterberg Coalfield
Abstract
In recent years, the demand for rare earth elements (in this study, REE refers to the sum of lanthanides, REY refers to lanthanides plus yttrium, and REY+Sc represents lanthanides as well as yttrium and scandium) has increased for use in technology, health care, renewable energy, oil refining, and electronics due to global supply shortages. This demand has led to increased interest and research in coal deposits being considered an alternative source for these critical raw materials. Several countries, including South Africa, are considering coal and its by-products for the extraction of REEs. However, it is essential to understand the concentration of REEs in the host rock before extraction. South Africa has extensive coal resources, but the understanding of the concentration, mode of occurrence, and distribution of REEs in the coals and associated sediments is limited. The Waterberg Coalfield is estimated to contain 40 to 50 % of South Africa’s coal resources, but this coalfield is underexplored, and there is currently no information available pertaining to REE concentrations. The recovery methods for critical elements (including REEs) include preconcentration, activation, extraction, enrichment, and purification. Among these recovery methods, preconcentration has a direct effect on extraction efficiency and energy consumption. Density fractionation of coal is considered a preconcentration method.
The study aimed to assess density fractionated coal samples from the Waterberg Coalfield to determine the concentration and mode of occurrence of REEs, and to establish the behavior of REEs during density fractionation. Thirty density-fractionated coal samples selected from zones 8H, 8I, 7B, 4B, and 3C, sampled from an exploration core, were characterized using proximate analysis, petrography, X-ray diffraction (XRD), and X-ray fluorescence (XRF). The concentration of REEs in the density fractionated coals was determined using ICP-MS (after microwave digestion). The mode of occurrence of REEs was determined using Pearson’s correlation (indirect) and Tescan Integrated Mineral Analyzer (TIMA) (direct). The coals are classified as medium-rank C bituminous coals. The dominant minerals detected by XRD are kaolinite and quartz. The REY concentrations range from 45.1 to 389.2 ppm. The values are higher than that of world coals, except for sample 8H F1.30 (REY concentration of 45.1 ppm) and generally higher than the average reported for Chinese coals. Float products obtained at 1.40 to 1.80 densities show a greater variation of light REY (LREY) compared to medium REY (MREY) and heavy REY (HREY). Density fractions F1.30 and sink 1.80 show no distinct type of REY enrichment, as the LREYs are variable between the different zones. The results suggest a relationship between the concentration of LREY with float densities of 1.40 to 1.80. Pearson’s correlation identified positive correlation coefficients of REY with both organic matter and mineral matter, suggesting that the REY in the density fractionated coal samples have a mixed organic and inorganic affinity (i.e., association). The TIMA image analysis revealed that REEs in these samples have organic, intimate organic, and inorganic associations particularly associated with phosphates, silicates, aluminosilicates, iron-bearing, and sulphur-bearing minerals. The REE occurring in these coal samples may be due to inputs of hydrothermal solutions and terrigenous sediment input from the Bushveld Igneous Complex. Preconcentration by density fractionation may not be the best REY concentration process for these coals. Further investigations are required to confirm the potential of the Waterberg Coalfield coal ash for economic viability for REE extraction.
Researcher: Jessica Schapira (MSc, University of the Witwatersrand)
Supervisor: Professor Robert Bohlar
Title: Siderophore-mediated bioremediation of iron-bearing asbestos fibres in Pseudomonas fluorescens- inoculated soil microcosms
Abstract
The risk associated with asbestos minerals is an enduring global concern, especially with regards to exposure at the sources. The risks connected to exposure in their natural contexts (i.e., derelict mine sites and naturally occurring asbestos) form the subject of this study. These sites are plentiful throughout Southern Africa (and Africa) and are considered as unconfined, thereby constituting large environmental and human health risks. Asbestos in these settings is not inherently hazardous unless dispersed from its sources into environmental systems, such as the atmosphere, where it may be inhaled. Compared to occupational asbestos exposure, environmental sources present unique challenges with respect to their potential risks. Literature focused on these sites is lacking and without extensive knowledge the risks remain greatly unknown, and thus asbestos site assessment frameworks are imperative. South Africa, with its geological richness, allows for all aspects of environmental asbestos to be studied in its natural context.
In this research, mineral fibres from derelict asbestos mine sites were characterised mineralogically and geochemically to identify and assess their human health hazard potential, to define the degree of toxicity and to determine the potential negative environmental effects. High concentrations of heavy metals, including copper, iron, magnesium, manganese and zinc detrimental to human health and environmental functioning were measured in these fibrous minerals using X-ray fluorescence (XRF). The chemical stability of four asbestos minerals was studied using batch isothermal dissolution tests in acidic solutions and their stability determined as follows: chrysotile < crocidolite < amosite < anthophyllite. Significant inferences can be made regarding the persistence of asbestos particles in their natural environments from dissolution kinetics mechanisms.
The mineralogical, geochemical, and microbiological characterisation of solid asbestos mine waste rock substrates indicate that their properties, such as low macro and micronutrients and lack of properties of true soils, strongly alkaline pH and low to zero microbial abundance and diversity present significant challenges to rehabilitation strategies. Such parameters are identified as important baseline conditions that need to be considered prior to rehabilitation implementation, if long-term, self-sustaining ecological restoration is to be achieved on these sites.
Researcher: Mphanama Thangeni (MSc, University of Venda)
Supervisor: Dr Humbulani Mundalamo
Title: Coal Occurrence and Quality at Mushithe Area, Soutpansberg Coalfield, South Africa
Abstract
South Africa is the 7th largest coal producer in the world and continues to rely on coal as its primary energy source, owing to its abundant availability and low cost. The Mushithe coal occurrence, located within the Pafuri basin of the Soutpansberg Coalfield, has been overlooked compared to other coal occurrences in the Tshikondeni area. The coal occurrence at Mushithe outcrops at Mbodi River. The study aims at establishing the geological setting, mode of occurrence, coal quality and economic value of the Mushithe coal occurrence. Geological mapping and sampling, petrography, and geochemical analysis were done on 14 host rock and 6 coal samples.
Coal bearing rocks at Mushithe are occurring as a valley isolated from the Pafuri Basin. The outcropping seam at Mushithe is exposed along the Tshamatsha Fault. The coal measures contain four to seven seams, ranging from 0.35 m to 11.38 m in thickness. Pink and red quartzite, mudstone, basalt, quartz vein, sandstone, shale, carbonaceous shale, and calcrete were identified as associated rock types. The general strike is northeast, and the dip direction is northwest, with an average dip angle of 23°.
Mushithe coal is dominated by vitrinite (65.77%) and inertinite (34.23%), with no liptinite detected. The high presence of vitrinite suggests that the coal is formed in a wet swamp environment. Additionally, signs of weathering such as cracks, fissures, and oxidation rims were observed in the coal. Coal quality belongs to bituminous C on UNECE 1998 classification, being characterised by low sulphur content (0.23 to 0.38 wt %) and high moisture (6.07 to 10.94 wt %), ash yield (16.7 to 41.9 wt %), volatile matter (29.7 to 35.8 wt %), fixed carbon (25.25 to 50.49 wt %) and calorific value (12.97 MJ/kg to 23.35 MJ/kg). Mineral matter constitutes approximately 5.7 to 35.8 wt %, predominantly quartz with varying proportions of clay (kaolinite), as well as minor carbonates (siderite) and sulphides (pyrite). The geochemistry is characterised by high values of Al2O3 from 7.56 to 15.83 wt %, SiO2 (9.76 to 20.04 wt %), and MgO (0.26 to 2.80 wt %). The outcropping seam was found to be of economic value and suitable for use as thermal coal for electricity generation.
Keywords: Mushithe coal occurrence, coal stratigraphy, geological mapping, coal quality
Researcher: Khetani Tom Ramphabana (MSc, University of Venda)
Supervisor: Dr Humbulani Mundalamo
Title: Lithostratigraphic and Geochemical Characterisation of the Waterberg Coalfield: Implications to Acid Mine Drainage, Limpopo Province, South Africa
Abstract
The study conducted at Sekoko coal mine in the Waterberg coalfield of South Africa aimed to establish the quality of coal and its host rocks, as well as the potential for acid mine water generation.
A total of 18 samples were collected from a box-cut and analysed using various methods such as, Scanning electron microscopy, X-ray diffraction spectroscopy, X-ray fluorescence spectroscopy, proximate analysis, Modified Sobek Acid Base Accounting test as well as petrographic study. The major rock types identified in the study area included shale, sandstone and gritstone. Coal was overlain by these rocks.
The study revealed significant concentrations of framboidal pyrite in coal, which increases with depth as determined by X-ray Diffraction spectroscopy and scanning electron microscopy. Whole rock geochemistry indicates that Fe2O3 was higher in coal (1.18 wt%) than in host rocks (0.45 wt%) and increased with depth. Average mean of 1.23% a.d. for sulphur content was revealed thus, classifying the coal as medium sulphur coal. Sulphur occurred as pyritic, organic, and as sulphate, in that order of abundance. Using both proximate analysis and calorific value (with mean value of 21.2 Mj/kg) coal was classified as below grade D. From the vitrinite reflectance value (ranging between 0.6 to 0.7), coal was ranked as medium-grade bituminous C. Paste pH and EC results indicated that the Sekoko coal is already undergoing oxidation, and modified Sobek tests indicated that over 72% of the analysed samples have sufficient sulphur to generate long-term acid mine drainage. The potential for acid generation increases with depth (1.09 to 181 kg/t) and was high on the southern side (181 kg/t) than the western side (52 kg/t). Results indicate that there aren’t enough neutralization materials to counter the acid production potential as the neutralisation potential is negative for all samples.
The study concluded that the coal from Sekoko coal deposit is enriched with pyrite minerals, hence this causes an increase in the potential for acid mine water generation. Screening of coal prior to utilization is recommended to reduce the content of pyrite in coal.
Keywords: Waterberg Coalfield, Acid Mine Drainage, Acid Base Accounting, Coal Quality
Researcher: Rutger Alexander La Cock (MSc, Stellenbosch University)
Supervisor: Dr Bjorn von der Heyden
Title: Carbon-gold systematics in the Barberton Greenstone Belt
Abstract
The relationship between carbon and gold has been a subject of interest to scientists and geologists for over half a century. The deposits of Fairview mine lie within the Barberton Greenstone Belt (BGB) and provide a unique opportunity to study the relationship between carbon and gold in some of Earth’s oldest, well-preserved continental crust. Previous research has shown that mineralised shear zones at Fairview contain carbon in the form of carbonates and graphite. Scanning electron microscopy (SEM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are used in conjunction to reveal how ore fluids evolved over time. Major and minor element changes are best seen in variations in carbonate chemistry whilst changes in trace metal concentrations are captured by detailed mapping of zoned pyrite. A dominance of the dolomite-ankerite series of carbonates appear favourable when seeking higher gold grades as they form sites of replacement for auriferous pyrite. Based on analyses using Raman spectroscopy (RS), the graphite in shear zones is of nanocrystalline size and has a high degree of structural disorder. Graphite Raman geothermometry indicate that this graphite has been exposed to maximum temperatures averaging around 400 ⁰C. Carbon isotope analyses suggest that ore fluids were derived from carbonaceous shales of the Fig Tree Group, or from a similar lithology beyond the BGB. X-ray computed tomography (XCT) highlights the close spatial association between Au-bearing sulphides and graphite within the Fairview ore. Most of the graphite is interpreted as being deposited from fluids, with the graphite then later acting as a chemical trap during subsequent fluid flow events, where gold deposition took place via carbon reduction. Based on Re-Os geochronology, gold associated pyrite formed at 2913 ± 284 Ma (Re-Os isochron age) and this argues in favour of the younger ages generated in previous studies. The younger isochron age of 2652 ± 64.3 Ma is the result of resetting of Re-Os isotopes in pyrite during cratonic extension which initiated the Transvaal Supergroup sedimentation process. It is theorized that melting of a shallowly subducting slab beneath the continental crust of the Barberton terrane helped transport auriferous fluids to upper crustal levels, where gold was deposited in shear zones. This is based on the date of pyrite formation from Re-Os isochron ages and existing geochronology data. This research highlights the important role of carbon in forming large, high-grade gold deposits in Archaean greenstone belts.
Researcher: Tshifhiwa Rammela (MSc, University of Johannesburg)
Supervisor: Professor Michiel de Kock
Title: Geology of the Malmani Subgroup in the Vaal area South of Johannesburg: Implications for the future development of the GlenDouglas dolomite mine
Abstract
Glen Douglas Dolomite Mine, an operation located south of Johannesburg in the Vaal area is faced with a challenge of running out of metallurgical dolomite (i.e., principally the low silica Lyttelton Formation), which is the core commodity of the mine. The distribution of lithological units of the Malmani Subgroup at Glen Douglas Dolomite Mine are not clearly understood.
In order to understand the distribution of the lithological units of the Malmani Subgroup, a study of the lithofacies was conducted at Glen Douglas Dolomite Mine. This helped identify the different formations of the Malmani Subgroup. The stratigraphic and geochemical variation of the dolomite units is influenced by younger intrusions occurring in the pit.
Lithofacies of the Malmani Subgroup at Glen Douglas Dolomite Mine were documented, but this was limited by accessibility to the pit benches. Some areas were easily accessible, and some were not accessible at all. Based on this, there is little lithological grounds for the identification of the Monte Christo and Eccles Formations at Glen Douglas Dolomite Mine. All units encountered at Glen Douglas Dolomite Mine conform to descriptions of the Lyttelton Formation, but they exhibit varying Silica-content.
The lithofacies and geochemical data have to a large degree shown the prominence of the Lyttelton Formation to be on the western side of both B and C-pit, with little SiO2 contamination existing as a result of mafic intrusions, detrital inputs or chertification.
Old borehole data obtained from the mine were utilised to create a geological block model. The block model was constructed based on SiO2 values and shows very healthy reserves for both metallurgical and aggregate dolomite. It can be deduced that the uppermost part of the Monte Christo Formation only intersects the pit area on the lowermost part of the eastern bench profile.
Researcher: Thabo Stephen Kgarabjang (MSc, University of Limpopo)
Supervisor: Professor Napoleon Hammond
Title: Mineralogical characteristics and nature of ore-forming fluids associated with gold mineralization along the Antimony Line in the Murchison greenstone belt, South Africa
Abstract
The Antimony Line in the Murchison greenstone belt hosts several gold-antimony mineralisations within massive, fractured talcose and carbonate host rocks. Samples from three orebodies, Beta, Athens and Monarch at the Stibium Mopani Mine were studied to characterise the ore mineral assemblage and geochemical distribution of the mineralisation in the host rocks, and the source of the mineralising fluids. Predominant ore minerals identified in the deposits include ullmannite (Ni1.00 (Sb, As)1.02 S1.01), gersdorffite ((Ni, Fe, Co)1.02 (Sb, As)1.00 S1.02), arsenopyrite (Fe1.04 As1.00 S1.09), and stibnite (Sb1.00 S1.49). The composition of gersdorffite is predominantly Ni, As and S with minor amounts of Co, Fe and Sb. Ullmannite occurs as euhedral to irregular massive crystals which are replaced at the edges by stibnite and berthierite. The composition of ullmannite is primarily Ni, Sb and S, with minor amounts of As. Stibnite occurs in association with several other ore minerals such as pyrite, gersdorffite, ullmannite and gangue minerals such as carbonate and fuchsite. Stibnite forms the primary source of Sb in the host rocks. Microprobe analysis revealed no element impurities in arsenopyrite mineral chemistry, with Fe, As and S being the only compositions.
Geochemical data from the host rocks along the Antimony Line show several characteristics distinctive to schists of basaltic origin, but exhibiting some degree of differentiation from andesitic to alkaline basalt. Hydrothermal alteration is pervasive along the Antimony Line and is characterised by carbonatisation, potassic, and sulphidation alterations. Carbonatisation is the most common alteration type in the host rock samples and is characterised by the alteration of chlorite and biotite to form carbonates. Sulphidation in the host rocks is characterised by the presence of several sulphide minerals including stibnite, ullmannite and gersdorffite. There are Sr-Ca and Mg-Ca substitutions in the carbonates and Rb-K substitution occurs in the K-bearing minerals such as biotite and muscovite during potassic alteration. Co-Ni substitution is associated with sulphidation alteration along the Antimony Line.
Mass-balance studies of the hydrothermally altered assemblage indicated a variable degree of enrichment of the trace and pathfinder elements (Au, As, Sb and Ag) in the deposits. In particular, Au enrichment is highest at Monarch with an average enrichment of 9761% (0.91 ppm), while antimony recorded the highest enrichment at Beta with 7167% (221.40 ppm). Antimony generally shows an increasing trend of enrichment from Monarch to Beta, while gold enrichment increases from Beta to Monarch. The As distribution pattern in the orebodies is the same as that of Au, suggesting a close association with Au mineralisation. A combination of arsenopyrite geothermometry and oxygen isotope quartz-dolomite pair from mineralising quartz-carbonate vein indicated temperatures of the ore formation ranging from 242°C in Athens to peak temperatures of 420°C at Monarch.
The carbon (13C) isotope ratios of carbonates from the Athens, Beta and Monarch deposits have a wide range (13Ccarbonates= -6.26 to -3.79‰), suggesting different sources for the ore fluids. The isotopic composition of the mineralising fluids indicate δ18Owater range from +2.54 to +8.27‰ (Athens: δ18Owater range from +2.54 to +2.96‰, Beta: δ18Owater range from +5.15 to +5.68‰ and Monarch: δ18Owater range from +7.32 to +8.27‰). This range is consistent with fluids of crustal origin, typically magmatic and metamorphic hydrothermal fluids that may be evolving from a unique fluid source during ore fluid migration, or discrete fluid regimes associated with each of the deposits. The brittle-ductile Antimony Line has acted as a conduit for the fluid flow which initiated the mineralisation of the major deposits.
Researcher: Rethabile Tau (MSc, University of the Witwatersrand)
Supervisor: Dr Stephanie Enslin
Title: The tectonic evolution of the Bredasdorp Basin and its implications for oil and gas formation
Abstract
The Bredasdorp Basin is an offshore rift basin located in the southernmost tip of Africa, within the larger Outeniqua Basin. Previous studies have indicated the presence of hydrocarbons, as well as structures or evidence that allude to the presence of hydrocarbons, where the basin has not yet been extensively drilled or explored. In this study, seismic attributes applied to high resolution pre-stack time migrated 3D seismic data are analyzed, in conjunction with well logs, specifically the gamma ray logs.
By employing these methods, the study aims to delineate the presence of hydrocarbons and their
migration, as well as deduce the evolution of the basin based on the structures observed. Using artificial neural network (ANN) to predict the lithologies and analyzing the patterns in the gamma ray logs, the stratigraphic results show that the basin begins with a marine dominated environment from the Valanginian age to Aptian age. From the Aptian to Albian age, there are consistent changes in sea level and sedimentation, caused by thermal sag and uplift. Past the Albian age to present age, the deposition environment is dominated by sandstones and coarse sediments. This is due to the evolving basin moving from a distal to a proximal environment of deposition. Using seismic attributes such as envelope attribute, edge detection and variance attribute, structures such as paleo pockmarks and fluid escape structures are identified. These identified paleo pockmarks have diameters ranging from 400m to 900m. In addition to these structures, erosive features were observed which could be classified as submarine channels or slump structures, with the dominating channel having depths of up to 1585 m. Using variance and ant-tracking, the fault structures observed of the study areas revealed two dominating phases of rifting. The first phase has horsts and grabens bounded by normal faults trending E-W, with implications that the rifting propagated N-S in this phase of rifting. This phase of rifting ends during the Aptian age. The next phase of rifting begins during the Santonian age, with the fault bound horsts and grabens
