School of Geosciences (ETDs)

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3D seismic constraints on the strato-structural evolution of the deep-water Orange Basin, South Africa
(University of the Witwatersrand, Johannesburg, 2023) Maduna, Nombuso Gladys; Jinna, Zubair; Manzi, Musa
This research utilizes seismic attributes and advanced machine learning methodologies to analyse high-resolution 3D reflection seismic data from the deep-water Orange Basin, located offshore western South Africa. The primary goal is to gain valuable insights into the basin's tectonic setting, depositional environment, and hydrocarbon potential. Significant features are delineated within the basin including (1) a gravitational collapse system in the Mesozoic Late Cretaceous, (2) mass flow features in the Cenozoic, (3) natural gas and fluid escape structures, (4) a large slope-perpendicular submarine canyon cutting Oligocene strata, and (5) multiple slope-parallel, sinusoidal channel features in the Miocene. The Late Cretaceous succession exhibits a gravitational collapse system with a translational and compressional domain detaching on seaward-dipping Turonian shales. Gravitational collapse during margin uplift formed fold-and-thrust belts along the slope characterizing the compressional domain. As they are commonly linked to hydrocarbons, the compressional domain of these systems has been extensively studied, while the translational domain has been poorly constrained due to its structural complexity. In this research, the translational domain is shown to contain a mixture of extensional tectonics (normal faults) up-dip and compressional tectonics (thrusts) down-dip, with extensive oblique-slip faults cutting thrusts perpendicularly during the translation of sediment. Variance and chaos, conventional seismic attributes, were used to manually pick and interpret the >500 regional-scale faults arising from the gravitational collapse system. Fault-net, a convolutional neural network (CNN), was compared with these edge-enhancing seismic attributes for extracting faults from the seismic volume. The CNN offers several notable advantages over conventional seismic attributes, such as automation, accelerated analysis, and improved time-efficiency on large datasets. Analysing the distribution, type, and geometry of faults within the basin gave valuable insights into the potential hydrocarbon system at work. Numerous natural gas and fluid escape features are identified in the seismic volume including an elongated mud volcano, pockmarked surfaces, and polygonal faults. The stability of the evolving margin is influenced by the underlying structure of a Late Cretaceous gravitational collapse system, also referred to as a deep-water fold and thrust belt (DWFTB) system. The fault framework within provides primary migration pathways for hydrocarbons. Major seafloor slumping occurs directly above a syncline of the Late Cretaceous DWFTB system. This slumping surrounds a structurally controlled, 4.2 km long elongated mud volcano situated between the translational and compressional domains of the underlying DWFTB system. The late Campanian has the largest accumulation of hydrocarbons evidenced by (1) an anticline with a positive high amplitude anomaly situated at the intersection of the two domains, and (2) >950 pockmarks preserved on the palaeo-surface compared to the 85 pockmarks observed on the seafloor. In addition to tectonics, the onset of stratified oceanographic circulation patterns and climate played a large role in changing depositional trends since the mid-Cenozoic. The Oligocene is characterized by a ~2.3 km wide, >13 km long, slope-perpendicular canyon formed at ~30 Ma during a major sea-level fall by a turbidity current. The Miocene is characterized by a ~14 km wide zone of slope-parallel, sinusoidal channels between water depths of 1 200–1 500 m. The formation and preservation of these features during the Miocene are attributed to the erosive interaction between two distinct water currents: (1) the Antarctic Intermediate Water flowing northwards, and (2) the deep North Atlantic Deep Water bottom currents flowing southwards; and the effects of the Benguela Upwelling System and a dry climate prevailing in southwest Africa all intensifying around 11 Ma. While pre-Miocene hydrocarbons originate from Turonian and Aptian source rocks, the origin of hydrocarbons on the seafloor is likely biogenic, arising from organic-rich sediment in the Miocene
A Review of Mineral Exploration at the Karingarab Carbonatite, Southern Namibia
(University of the Witwatersrand, Johannesburg, 2023) Nehoya, Jennifer Ndapanda; Nex, Paul
This research report reviews the Karingarab Carbonatite, which is one of several alkaline and carbonatite occurrences in Namibia targeted for rare earth element (REE) potential which are used in medical, renewable energy, technology and military applications. Several exploration campaigns have occurred at the Karingarab Carbonatite since 1977 and all indicate positive concentrations of REEs at the deposit. The Karingarab Carbonatite (68 Ma) is one of 41 alkaline and carbonatite occurrences in Namibia which is documented in this report and is very similar in terms of composition, age and emplacement to the Dicker Willem (49 Ma) and the Gross Brukkaros carbonatites (77 Ma) all located along south-west to north-east trending structures on the west coast of southern Namibia. The Karingarab Carbonatite lies in the center of a 2.5 km diameter circular vent raise 300 m above sea level, the edges of the vent are brecciated extrusive phonolites and other alkali silicate rocks with country rock fragments of phyllites and schists of the Oranjemund group, crosscut with late stage dykes of varying compositions in the alkaline and carbonatite series. Four main lithology types are identified through their distinct geochemical signatures with varying degrees of weathering and alteration. The target and main lithology is a layered extrusive carbonatite with lapilli of various shapes and sizes diluted in parts with mostly phonolites, schists and phyllites. The second more common lithology is extrusive phonolites which are mostly brecciated with cross cutting carbonatite dykes. The third lithology type is formed by clay rich autoclastic volcanic breccias which are a mixture of all the proximal and local rock types of the Oranjemund group, lastly the fourth lithology is formed by overburden which includes wind-blown dune sands and calcrete. The extrusive carbonatite lapilli is the dominant ore type, with deeper, fresh and unaltered carbonatites still mineralized and carrying lower grades while the shallower, weathered and altered carbonatite shows supergene enrichment and extremely high grades. This enrichment was upgraded by events in the early Paleogene which included deep erosion and surface weathering events along with a regional surface silcretization event capping and trapping mineralization. Preliminary findings following the first two drilling campaigns indicate a potential to produce from the carbonatite, 181 million tonnes of ore with 3.5 million tonnes of total rare earth oxides (REOs) at an average grade of 1.9% total REEs. The deposit remains partly open at depth, with satellite concealed volcanic occurrences still to be explored. Should the target become an operational mine, responsible sourcing will need to be considered particularly how to extract, refine, transport and process REEs in a manner which satisfies environmental, social and governance requirements (ESG) while ensuring the mineral value chain and potential industry spill-over is managed sustainably. Major risks to the target involve the criticality of supply which may be managed through monitoring geopolitics in supply, and technology improvements in substitution and recycling for the REEs and their products. Apart from these economic interests, the observations and studies on the subsurface lithologies at Karingarab will be invaluable to academia through improved literature on carbonatites, REE deposit genesis and the regional geology where much is covered by sand
Accessory REE mineralization of the Nokeng fluorite deposit as distal facies of the adjacent Vergenoeg pipe, Bushveld Complex, South Africa
(University of the Witwatersrand, Johannesburg, 2024-10) Makhema, Relebohile Edward; Yudovskaya, Marina; Madlakana, Nonkuselo
The Nokeng Plattekop deposit forms part of the Paleoproterozoic Bushveld Complex and it is located near Rust de Winter, approximately 80 km northeast of Pretoria. This deposit belongs to the Vergenoeg Igneous Complex, which is associated with a violent gas-vapour-rich rhyolitic eruption. The complex comprises the Vergenoeg discordant breccia pipe and a pyroclastic rock suite. Within the breccia pipe and associated pyroclastic rocks, rare earth element (REE) mineralization is observed in minerals like allanite, apatite, bastnasite, monazite, and xenotime. The Plattekop fluorite deposit, which lies 1000 m south of the breccia pipe, is postulated to represent spill-over remnants of the Vergenoeg volcanic edifice. This study performed a comprehensive petrographic and geochemical analysis of ore and pyroclastic breccia of the Nokeng Plattekop deposit, utilizing various analytical techniques, including optical microscopy, XRF, ICP-MS, and SEM. The aim is to characterise the style of accessory REE mineralization at Nokeng as a provisional distal facies of the Vergenoeg volcanic field. The findings of this study suggest that the Nokeng Plattekop deposit comprises a hematite-fluorite unit overlying an ignimbrite unit. Hematite-fluorite ores of the upper unit resemble the Vergenoeg ore, exhibiting elevated CaO concentrations and reduced SiO2 content attributed to high fluorite and hematite proportions. Conversely, the ignimbrite unit displays reduced CaO and elevated SiO2 concentrations, corresponding to lower fluorite content and higher rhyolitic lava fragments. The basal ignimbrite is proposed to have formed during the early stages of rhyolitic volcanism, while Nokeng and Vergenoeg ores formed during later stages dominated by Ca- and F-rich ferruginous magma. Petrographic evidence suggests hematite pseudomorphs after magnetite, indicating mineral assemblage evolution. REE mineralization in the Plattekop fluorite deposit is represented by bastnasite, monazite and xenotime, mostly associated with quartz, goethite, aegirine, hematite and fluorite. The highest REE + Y content (~ 5 890 ppm) is associated with Plattekop hematite-fluorite ores. Comparative analysis of REE distribution patterns suggests similar styles of mineralization between Vergenoeg and Nokeng, indicating both deposits as potential sources of REEs as by-product.
An investigation into high gear and low gear propulsion in human gait and its relation to metatarsal diaphyseal geometric cross-sectional properties
(University of the Witwatersrand, Johannesburg, 2023-06) Reyneker, Mark Brenden; Carlson, Kristian J.; Zipfel, Bernhard
This study investigates the relationship between metatarsal bone form, as quantified by cross-sectional geometric properties, and its relationship to high (medial forefoot loading) versus low gear (lateral forefoot loading) push-off during the propulsion phase of the gait cycle. The objective being to assess whether forefoot loading may be variable or whether high gear loading occurs in higher frequencies, as depicted in theoretical foot function models. The study sample (n=53), made up of three broad groups, include Later Stone Age southern Africans, post-industrial individuals from South Africa, and the Jomon of Japan. Metatarsals 1-5 cross-sectional geometric properties (CSA, Ix, Iy, Imin, Imax, Zx, Zy, Zp, Zmin, Zmax) taken from CT scans at 25%, 35%, 50% and 65% metatarsal diaphyseal biomechanical lengths are grouped into high gear (metatarsal 1-2) and low gear (metatarsal 2-5) for comparison. The combined population analysis reveals that the high gear metatarsal diaphysis exhibit significantly higher strength and rigidity driven mainly by the post-industrial individuals from South Africa and the Later Stone Age southern Africans. In contrast, the Jomon of Japan, exhibit no significant differences between high and low gear metatarsals except for CSA, Imax, and Zmax. Furthermore, metatarsal 1 and 5 differ far less in cross-sectional geometric properties in the Jomon of Japan compared to the other populations except for medial-lateral strength (Zy) and torsional and average bending strength (Zp) where metatarsal 5 is significantly higher. The study findings indicate that forefoot loading demonstrates variability during the propulsion phase of gait, while also suggesting a higher frequency of occurrence for high gear push-off. This challenges current theoretical models of foot function that emphasise high gear push-off as typical and normal for striding bipedalism.
Application of integrated methods to assess and characterise the hydrogeology of coastal aquifers in parts of Lagos, Southwest, Nigeria
(2020) Yusuf, Mumeen Adebayo
The scope of this Thesis was to apply integrated methods to characterise the groundwater systems of the Lagos Coastal Basin. Like every coastal area in the world, saline intrusion has been the major challenge threatening the fresh groundwater aquifers of the study area over the last couple of decades, and thus, necessitating its assessment. Environmental isotopes, being a reliable and standard tool in hydrological investigation, was employed in combination with geophysical and hydrogeochemical methods to study the coastal aquifer systems. Geophysical probing of the subsurface revealed an alternating sequence of clay and sand, constituting the major lithological units in the study area. The basin aquifers are hosted essentially by sands and clayey sand, while the modes of aquifer occurrences are unconfined to semi-confined and confined for shallow and deep aquifers, respectively. Hydrochemical interpretation identified a surficial thin layer of fresh groundwater overlying the main zone of saline intrusion, which essentially comprises Ca-HCO3 and Ca-Mg-HCO3, Ca-Mg-HCO3 and Ca-Mg-Cl-SO4 hydrochemical facies for both dry and wet seasons, whereas the surface waters are characterised by Mg-Cl and Na-Cl water types for the lagoon and the ocean, respectively. The evaluation of the chemical processes revealed the dominance of carbonate weathering in the shallow aquifer. Hydrochemical, statistical and geochemical model analyses identified that the groundwater chemistry is significantly controlled by water–rock interaction and ion exchange processes as well as anthropogenic activities. Stable isotopes revealed precipitation as the main source of recharge into the basin aquifer systems. Analyses of the 3 H and 14 C activities were in agreement, revealing an interesting fact about the increase in the groundwater residence time from the surface through deeper depths deducible from 3H values range between 0.1 TU and 2.8TU; 0.0 TU and 0.3 TU; and 14 C age range from 4350±10 to 1050±10 years and between 12030±69 and 7400±50 years for the shallow and deep aquifers, respectively. The mean residence time was supported by the aquifer systems‟ recharge which took place in Holocene for the shallow aquifer and Late Pleistocene–early Holocene for the deep aquifers evident from the calculated ambient temperature, 18 O and 14 C plots. The hydrogeological conceptual models showed that saline incursion severely impacted the second aquifer from a depth ≥20m to 170m in the western and central parts of the study. However, the observed local saline occurrence in places <20m was attributed to groundwater overexploitation. Conclusively, the hydrological systems of the Lagos coastal basin is continually being modified by both anthropogenic and natural activities that constitute not only a major threat to the groundwater sustainability of the Lagos coastal basin but can also consume the entire study area
Assessing aquifer vulnerability to landfill pollution using drastic method in Gauteng, South Africa
(University of the Witwatersrand, Johannesburg, 2023) Mphaphuli, Idah; Abiye, Tamiru
This study integrated the DRASTIC method and field investigations into mapping the degree of vulnerability of aquifers to landfill pollution in the Gauteng Province, which is one of the most populated provinces in South Africa. In order to investigate the aquifer vulnerability of Gauteng's heterogeneous and complex geology, the DRASTIC method was used to generate intrinsic and specific vulnerability maps. Three vulnerability classes were generated from the DRASTIC index, namely, low vulnerability, moderate vulnerability and high vulnerability, which covered 46%, 37% and 17% of the study area, respectively. The highly-vulnerable areas were associated with the karst aquifer of Malmani dolomite, permeable vadose zone, high hydraulic conductivity and loamy sand/sandy loam soil type, whilst moderately-vulnerable areas were associated with fractured/weathered aquifers, high recharge and low topography. The intrinsic vulnerability was validated using average NO3+NO2-N (nitrate + nitrite as nitrogen) and the results of water samples from field investigations conducted in Marie Louise and Robinson landfill sites. Elevated NO3+NO2-N concentration (9.85-16.03 mg/l) was observed in the highly-vulnerable areas. Water samples were collected, in order to analyse the water chemistry, stable isotopes and radioactive isotopes (tritium). Gibbs and Piper diagrams were used to evaluate the main mechanism controlling the groundwater chemistry and the dominant major ions that influence it. Pollution by leachate was detected in the Marie Louise landfill site, where the groundwater showed high tritium and ammonia concentration. The main hydrochemical facies detected in Marie Louise were Mg SO4, Ca-SO4, Na-SO4 and Na-Cl. The hydrochemical facies detected in Robinson were Na-SO4, Ca-HCO3, Na-Cl and Ca-Cl. The DRASTIC method was shown to be effective in assessing groundwater vulnerability on a regional scale, provided that there is adequate input data.
Baseline Hydrogeology of Dolerite Dykes in Lesotho, Mafeteng District as a Case Study
(University of the Witwatersrand, Johannesburg, 2024-06-10) Monyane, Napo Shadrack; Shakhane, Teboho; Abiye, Tamiru
Groundwater is a vital alternative resource due to the increasing demand for water supply in Lesotho’s rural and urban areas as surface water faces threats from population growth and climate variability. For instance, groundwater serves the demands of Lesotho's growing textile industry and agricultural sectors. The 3D form of the dolerite dykes widespread throughout the Karoo rocks in Lesotho may have an impact on the groundwater occurrence, flow, and yield characteristics of the region. However, specific research on their hydrogeology has not been extensively undertaken. This study aimed at characterising the hydrogeology of the dolerite dykes in the lowlands of Lesotho using selected places namely, Boluma-Tau, Ha Lumisi, Ha Mofota, Ha Maoela, Ha Mofo, Malumeng, Qalabane, Matlapaneng, Thabana Mohlomi, Ha Mohlehli, Malimong, Tsoeneng and Ha Lenonyane as case studies for the research. This research adopted the desktop and walkover survey in developing information on the region’s broad geological and hydrogeological setting within the Karoo lithologies. Included also was the use of ground magnetics in ascertaining the existence and determining the geometry of the dykes, using the D-8 algorithm for flow directions, and drilling and pumping tests for aquifer analysis. The dykes dominating the focal area in the Mafeteng District generally trend NE-SW, NNE-SSW and NW-SE. The magnetic results outlined negative anomalies along the dyke’s contact with the country rocks as surveyed from Qalabane, Mafeteng Lesotho, these magnetic lows imply fracture gaps along the strike of the dyke. A generalised dip, width, and depth could not be easily inferred due to inconsistent magnetic anomaly shapes, but forward modelling indicated a thin (10 m wide) shallow (10°) dyke trending NE-SW intruding both the Burgersdorp and Molteno Formations at Qalabane, Mafeteng. As per the D-8 results, the dolerite dykes in Mafeteng are distributed in the intermediate basin flow values due to a gentle hydraulic gradient. Certain dyke sites exhibit a groundwater flow direction towards the north, whilst others display a radial groundwater flow direction. The derivative analysis revealed the boreholes were drilled in a fractured dyke system, also the dominant radial flow regime and double porosity dip at different pumping durations, and the possible recharge boundary were revealed in some drilled dyke sites. Further analysis from the drawdown versus time curves resulted in average yields of 0.1 – 1.25 l/s with transmissivities ranging from 1 – 14 m2/day, insinuating that a limited extraction of the local water supply is suggested from the dolerite dyke lithologies in the lowlands of Mafeteng Lesotho, given the groundwater yielding capacity and magnitude of the transmissivities. Even though the drilled boreholes from the dyke sites indicated a fractured dyke setting, estimated transmissivity values are variable and low, this is indicative of the inconsistent apertures and lack of interconnectivity of the available secondary hydrogeological features in the lowlands of Lesotho.
Characterisation of a geothermal resource at Kwako Hills in Zambia using magnetic and natural source audio magnetotelluric methods
(University of the Witwatersrand, Johannesburg, 2019) Chinamora, Blessing; Dr Jones, Mike; Prof Webb, Susan
The announcement by the Zambian government that geothermal energy will be recognized as an energy source in the 2013 national budget drew a lot of attention to investors and scientists. Since the 1950s reconnaissance geoscientific surveys have been carried out on geothermal targets in Zambia by the Geological Survey of Zambia (GSZ). The GSZ, together with an Italian company (DAL, SpA), studied various hot springs (Legg, 1974) and as a result, various prospects have been considered for development or exploration. In this research, the Kwako Hills prospect which is located near Mumbwa district, about 150 km northwest of Lusaka, hosts two hot springs which are good surface manifestations for geothermal energy potential was investigated for its geothermal energy reservoir potential using magnetic and natural source audio-magnetotelluric (NSAMT) geophysical methods. The focus of these surveys was on examining the structural controls that govern the occurrence of the hot springs and the outcropping Hook Batholith just to the north of the east-west trending alluvium filled valley. The northern branch of the alluvium valley has a northwest–southeast trend which is the same as the minor fault controlling the two hot springs. These structural controls increase the vertical permeability in the area causing the thermal waters to circulate to depths where they acquire their heat. Permeability is high at intersections of faults and fracture zones, intersection of major and minor faults or intersection of faults and sedimentary aquifers. Major ENE and NE trending faults were mapped along the Mwembeshi Shear Zone and the boundary between the Hook Batholith and the Katanga sediments respectively. The area is underlain by foliated basement granitic gneiss, Hook Batholith granites and Katanga metasediments that are broken into fractures along the foliation trends that control the occurrence and flow of rivers and streams. Overlying the basement rocks are the recent Karoo and Kundelungu sediments which are also permeable along the bedding or cleavage planes. The vegetation pattern, flow and occurrence of rivers or streams reflect trends of zones of weakness in the basement. Fractured zones developed along these foliations and were mapped at outcropping scale using Google Earth, aeromagnetic and ground magnetic data interpretation. Interpretation of aeromagnetic data confirmed the foliation trends that were suggested by Abell (1970) and Naydenov et al. (2014). One dimensional (1D) and two dimensional (2D) magnetotelluric (MT) resistivity models were created on the basis of a 120 MT sounding data set. A dimensionality and distortion analysis of the NSAMT data was carried out based on the approach of Groom and Bailey (1989) and it was concluded that the data were collected almost perpendicular to strike, which is also supported by the geological mapping. MT smooth inversion models showed the lateral and vertical extent of the potential geothermal reservoir. Different 2D MT inversion approaches were applied to investigate the lateral continuity of the conductive sedimentary layer of the Kundelungu unit (slate, siltstone and shale). In order to map the subsurface structure of the area, a magnetic model was then produced using the acquired ground magnetic data and constrained using magnetic susceptibility measurements, MT data and geology mapped on the surface. Magnetic data interpretation confirmed an NW-SE fault controlling the hot springs, which was mapped using the NSAMT inversion results. The research shows that there is a lateral conductive, water saturated zone (reservoir) present between 150 m and 550 m depth and deeply seated faults in the basin. Along the deeply seated faults the conductive zones are vertical and continue with depth. The information shows that the thermal waters of the hot springs appear to circulate to depths more than 2.5 km along deep seated faults and foliation fractures penetrating the foliated rocks of the Hook Batholith and basement rocks. This water is heated by the regional geothermal gradient of 23ºC/km. Further exploration can be carried out on the study area to prove its potential for a geothermal resource.
Constraints on the genesis of orbicular granites and sulphide mineralization in the Koperberg Suite, South Africa and the Diana’s Pool area, Zimbabwe
(University of the Witwatersrand, Johannesburg, 2024) Dumisa, Senamile Siyaya
This work tackles a long-standing problem in petrology, the formation of orbicular granitoids. These bodies occur as entire facies or as areas enriched in orbicules within distinct facies of plutons. Some European examples are highly prized for their decorative qualities. However, their origin is a matter of much debate going back to times when the origins of granitoids themselves were not obvious and are confused by topics such as ‘granitization’ and over-exaggeration of metasomatic effects. Here, poorly studied outcrops of orbicular rocks from the Matopos granite batholith in the Diana’s Pool area, Zimbabwe and the Koperberg Suite, South Africa are tackeld. Enzman (1953) and Garvie (1969; 1971) studied the Koperberg Suite and the Diana’s Pool orbicules, respectively and employed field observations and petrography to examine and characterize the genesis of these rocks. However, there is little evidence presented to confirm their theories on how these rocks formed as previous work lacks detailed geochemical, mineral chemistry and isotope data to support Enzman and Gravie’s conclusions on the genesis of these rocks. Furthermore, there is no connection between the metallogenesis of the sulphide mineralization and the origin of orbicular rocks, which is a unique characteristic of particular orbicule sites in the Koperberg Suite. This study focuses on four different orbicular bodies (Orbicule Koppie, Henderson South, Henderson North and Hoogkraal Lease) from the Koperberg Suite, hosted in lithologies ranging from diorite to pyroxenite compositions. The orbicules from different orbicular share similar characteristics. Coarse- grained felsic cores, fine-grained and alternating ferromagnesian and feldspathic shells, and coarse- grained to pegmatitic matrices characterize them. The orbicules are generally spherical to ellipsoidal in shape, however, some appear to be abraded and deformed (e.g., Orbicule Koppie). The compositions and grain sizes of cores and the matrix are comparable in all localities. Both the matrix and the cores are medium- to coarse-grained and dominated by plagioclase (the matrix probably in slightly lesser proportions), microcline (in variable proportions, and seemingly absent in some cores), quartz, biotite, magnetite and orthopyroxene (in the case of Hoogkraal Lese, Henderson North and Henderson South). Contrary to the cores and matrix, shells are fine-grained and exhibit polygonal textures. In addition to this, the shells are dominated by biotite and orthopyroxene. Plagioclase in the Henderson North and Henderson South orbicules is more calcic than plagioclase in Hoogkraal Lease and Orbicule Koppie orbicules. Biotite in the Henderson North and the Orbicule Koppie orbicules is more magnesian than those at Henderson South and Hoogkraal Lease orbicules. Plagioclase in the Henderson North orbicules are characterized by elevated and radiogenic initial 87Sr/86Sr ratios than the other orbicule localities. There is also a variation in 87Sr/86Sr ratios within the individual orbicular structures (cores, shells and matrices) in individual localities. The orbicules at Henderson South, Orbicule Koppie and the Jubilee Pit host a bornite-dominated sulphide assemblage where disseminated chalcopyrite and bornite grains are characterized by granular textures and chalcopyrite is replaced by magnetite and bornite. Bismuth, Ni and Se in these sulphides appear to partition into bornite while Ag, In, Cd, Sn, Mn, Ge and Co partition into chalcopyrite. Diana’s Pool orbicular samples exhibit closely packed orbicules in a granitic matrix characterized by different types of orbicules containing coarse-grained felsic cores, fine-grained and alternating ferromagnesian and feldspathic shells, and a coarse-grained to pegmatitic matrix. The orbicules are generally spherical to ellipsoidal in shape, however, some appear to be abraded and deformed. The compositions and grain sizes of cores and the matrix are comparable. Both the matrix and the cores are medium- to coarse-grained and dominated by plagioclase (the matrix probably in slightly lesser proportions), microcline (in variable proportions, and seemingly absent in some cores), quartz, biotite and accessory hornblende and magnetite. Contrary to the cores and matrix, shells are fine-grained and exhibit polygonal textures. In addition to this, the shells are dominated by biotite and magnetite; however, they do not contain hornblende. Plagioclase in cores, shells and matrices shows an almost complete overlap of An contents. Biotite composition in the shells is significantly less magnesian than in core and matrix, whose compositions overlap. Initial 87Sr/86Sr ratios from plagioclase in shells are slightly more radiogenic than in the matrix and cores. Formation of both the Koperberg Suite and Diana’s Pool orbicules has been attributed to metasomatic processes. However, modelling of the Koperberg Suite orbicules using the Magma Chamber Simulator and a variety of textural and geochemical constraints rules out a metasomatic origin. The quartz + biotite-dominated diorite (Orbicule Koppie) and the pyroxene-diorites (Hoogkraal Lease, Henderson South, Henderson North), together with more felsic anorthosite and the more mafic pyroxenites, are all produced by progressive AFC + recharge processes, where the magma was most likely anatectic melts of the country rocks that were at granulite grade. In both Diana’s Pool and the Koperberg Suite, cores are autoliths, which are plagioclase-rich, cumulate, or rim fragments reworked by new magma inputs or injections. Heterogeneous nucleation leading to the formation of orbicular shells around the cores is attributed to adiabatic decompression of magma pulses ascending in dykes leading to superheating and resorption of early solids, and volatile exsolution, inducing undercooling, supersaturation, and shell crystallization. An alternative process that triggered superheating is magma mixing (e.g., Henderson South and Henderson North). The coarse-grained matrix crystallized later, after the orbicules formed, creating the groundmass, and locking the orbicules in place. The deformation of shells and cores (e.g., Orbicule Koppie and Diana’s Pool) suggests that the orbicules continued to evolve in the presence of a melt (matrix material) until they were emplaced at their present setting. The in situ sulphide assemblages in the Koperberg Suite have been reassessed in view of recent research on sulphide behavior. The bornite-chalcopyrite assemblage is atypical of the intermediate solid solution (iss) assemblage (chalcopyrite and pyrrhotite) observed in most Cu-Ni magmatic sulphide deposits. The high concentrations of trace elements that are incompatible with monosulphide solid solution and the depletion of Ni and Co in the sulphides are consistent with the derivation of sulphides from a Cu-rich sulphide melt that separated from a Ni-rich sulphide melt prior to magma emplacement and orbicule formation. The oxidation and Cu-enrichment of a sulphide melt that formed the mineralization in the orbicules and Koperberg Suite more generally began prior to the emplacement of the silicate Koperberg Suite magmas that formed the orbicules, suggesting no link between orbicule genesis and sulphide metallogenesis.
Cost-effective and novel seismic methods for mineral and coal exploration: Examples from Witwatersrand goldfields and Bushveld Complex
(University of the Witwatersrand, Johannesburg, 2023) Sihoyiya, Mpofana; Manz, Musa S. D.
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 environment
Cranial orientation and the lateral semicircular canal in primates: implications for palaeobiological reconstructions and the evolution of locomotor repertoires
(University of the Witwatersrand, Johannesburg, 2023) Pestana, Christopher; Benoit, Julien; Beaudet, Amélie
The lateral semicircular canal and its predicted relation to head posture have been used in reconstructions of locomotion and posture of contemporary and extinct species, and in the evolution of bipedalism. Inferences of head posture in fossil species sometimes assume that the lateral semicircular canal is held near the earth’s horizontal when the head is at rest. Despite the physiological importance of the vestibular system, the relationship between head posture and lateral semicircular canal orientation in primates has not been explored on a statistically significant sample, using phylogenetically corrected methods. This study tests the hypothesised relationship between lateral semicircular canal orientation and head posture in primates, and investigates potential links to locomotor categories. This study finds that lateral canal orientation is not significantly correlated to positional repertoires. Significant differences in canal orientation are detected between terrestrial and arboreal species. Neutral head posture distinguishes several locomotor categories, and explains a moderate proportion of the variance in positional behaviour. Brain mass is found to correlate with positional behaviour when correcting for the effects of the phylogeny. The implications of the evolution of head posture in fossil species are discussed.
Exploration Geology of Structurally Controlled Sediment-Hosted Gold Mineralization at Kasenseli, Northwestern Zambia
(University of the Witwatersrand, Johannesburg, 2023-10) Mulenga, Kapalakasha; Kinnaird, Judith; Nex, Paul
Occurrences of economic quantities of gold within the Roan and Nguba groups of the Katanga sedimentary units are not a common phenomenon. This is a new area of exploration for gold, and very little exploration work has been done to act as a guide in such a geological environment. More common are post-Nguba unit or Kundelungu group related gold occurrences which respectively occur around the Kasempa and Mumbwa areas and these are related to the Hook granite as well as the major shear zones that traverse these areas. The study area lies within the Lufilian Arc Fold and Thrust Belt and is located on the western end of the external fold and thrust zone which is part of the western extension of the Zambian Copperbelt. The area covering Mwinilunga is subdivided into four terranes based on regional structural features and metamorphism. The four terranes are; the Kasai Shield, the Kabompo Dome, the Western Foreland and the Lufilian Arc. Four main units that are present within the study area include the Roan member shale unit, the arkosic sandstone and its related sub-units which occur as lenses within this main unit, the Grand Conglomerat marker unit (diamitite), and the Nguba member shale which is interbedded with siltstone in some zones. Based on the contact relationship of the units to Grand Conglomerat marker unit, the oldest unit within the study area is the Roan shale unit (which could be of Mwashya age or older), followed by the arkosic sandstone, the diamictite unit which is the Grand Conglomérat marker unit and finally the Nguba shale. Polished thin section and mineral liberation analysis was undertaken on most of these units. Among the notable features of the stratigraphy in the area is the presence of a redox boundary between the pinkish-grey coarser arkosic sandstone unit (oxidising facies) and the greenish-grey clast-poor diamictite (reducing facies) where richer pockets of gold mineralisation have been observed. Gold mineralisation has been mainly observed to be hosted in the clast-poor diamictite mostly in the alteration halo which forms around the arkosic sandstone-quartz vein-diamictite contact. Further away from this contact and away from other related structures such as faults, veins and folds, mineralisation gradually diminishes. Gold mineralisation in this area shows a strong correlation to copper with the high- grade zones having elevated copper mineralisation both in the mineralised zone and in the residual soils. On a district scale, the study area and its surroundings are extensively folded and faulted, and the area has undergone episodic deformation resulting in the development of various structures. Among the notable structures within the study which are relatable to the Lufilian Arc Fold and Thrust Belt (LAFTB) on district to regional scale include folding, shear faulting, normal faulting, and the development of joints. The structural aspect plays a critical role with regards to the location of mineralisation. Observed structural features which were critical as pathways and deposition site of uriferous/mineralised fluids include first order folding with a NNE – SW oriented axial trace as well as first order NE – SW oriented shear faults and shear zone, the second order NW – SE oriented faults and veins which are the structures that host the mineralisation, and the NW – SE oriented (axial trace) folding where saddle-reef hosted mineralisation has been observed within the study. The physiochemical redox boundary between the Nguba member diamictite (reducing facies) and pre-Nguba arkosic sandstone (oxidised facies) played a critical role in the location of the mineralisation in the area. One thousand six-hundred and fifty (1650) soil samples were collected from the entire study area which covers a surface area of about 13 square km. Analysis and interpretation of soil assays showed that only copper may reliably be used as pathfinder in the exploration for gold mineralisation and/or deposits particularly in Nguba group member units. In addition, based on stratigraphic correlation, the possibility of Kamoa-style copper mineralisation has been suggested.
Finite Element Analysis of Dinocephalian Skulls to Address Head-Butting Behaviour in Early Therapsids
(University of the Witwatersrand, Johannesburg, 2024-08) Bolton, Andrew; Benoit, Julien; Mangera, Taahirah
The origin of complex social behaviour in the mammalian lineage has been a long-standing enigma. Behaviours do not leave a rich fossil record; however, adaptations to highly specialised complex behaviour can be traced back in some lineages, such as the dinocephalians. Dinocephalians dominated carnivorous and herbivorous niches of terrestrial ecosystems in the Middle Permian (~273-259 million years ago). Species within this clade often have skulls with considerable pachyostosis (overly thickened bones) and cranial ornamentation (horns and bosses). This morphology has been interpreted as evidence for head-butting, but the evidence is circumstantial at best. For this project, I used three-dimensional models of the skulls of four dinocephalians and two outgroups to simulate and investigate the capabilities of these skulls to withstand different magnitudes of head-butting and flank-butting impacts with finite element analyses. Palaeopathological analyses vindicated the accuracy of FEA data, which indicates that dinocephalian skulls modelled here arguably reflect biological truth. As head-butting is a complex social behaviour, this would strongly suggest the presence of dominance hierarchies, territoriality, and gregariousness. This represents the earliest robust evidence of complex social behaviour in tetrapods, preceding all known examples of social interactions in dinosaurs and mammals by hundreds of millions of years.
Hydrogeological assessments and investigation of inflow sources at Lumwana Copper Mine, Zambia
(University of the Witwatersrand, Johannesburg, 2023) Mbilima, Mike; Abiye, Tamiru
This Research Report presents results of integrated field and desktop-based hydrogeological investigations at the Lumwana Mine, Zambia. Groundwater occurrence in the mine poses challenges with effective mining operations and slope stability. The primary aim of this study was to establish the sources of groundwater inflows and to establish the nature of surface water and groundwater interaction within the Lumwana Mine hydro-geotechnical units. The Lumwana hydrogeological investigation has been achieved through the integration of multi-disciplinary data types, which include geology, structures, hydrochemistry, meteorological data (rainfall, temperature, humidity and evapotranspiration), environmental isotopes, dewatering pumping records, groundwater level monitoring, water temperature, general hydrogeological data and surface hydrology. The investigation has confirmed the presence of hydraulic connections between different surface water bodies such as dams, diversion channels, streams and open pit excavation, and has proven to be a useful approach in tracing the source of mine inflows. Rainfall, groundwater and surface water samples have similar δ18O and δ2H isotopic signatures thus lamenting the existence of a hydraulic link between groundwater and surface water. Recharge estimation through Water Table Fluctuation method (WTF) determined 8% of mean annual precipitation (MAP). The dominant hydrochemical facies are Ca-Mg-HCO3 and Ca-Mg-SO4. The local geology and geochemistry of the tailings are the main controllers of groundwater chemistry through rock-water interaction. The geology of the study area consists of older metamorphosed gneisses, schists, migmatites, amphibolites and granitoids. Integrated assessment of the Lumwana hydrogeological environment has enabled the development of the Lumwana Mine hydrogeological conceptual model. In the shallow, highly to moderately weathered zones, groundwater flows from south towards low topographic regions in the northwest mimicking the general topography. The hydraulic test conducted at Lumwana Mine has revealed the saprock units have higher hydraulic conductivity by several orders compared to the saprolites and the fresh bedrock, where groundwater flow is mainly controlled by the occurrence and distribution of the fracture network.
Innovative surface, tunnel, and in-pit geophysical methods for mineral exploration and mine planning: case studies from the Bushveld Complex mines, South Africa
(University of the Witwatersrand, Johannesburg, 2023) Rapetsoa, Moyagabo Kenneth
Innovative geophysical methods were used to study the platinum group element mineralisation and their associated geological structures at Maseve and Tharisa mines, western Bushveld Complex. Four case studies are presented in this thesis that incorporate the use of in-mine or near mine geophysical methods for mineral exploration. The first one being in-mine seismic data acquired in 2020 at Maseve mine using cost-effective seismic source and sensors, followed by innovative seismic experiments acquired in 2022 at Maseve mine to evaluate the viability of using tunnel and surface experiments for mineral exploration in a noisy, logistically difficult mine environment. Thirdly, the 2021 integrated geophysical surveys conducted at Tharisa mine to image fractures that act as water pathways into the pit. Finally, integrated geophysical techniques are used to delineate boulders to enhance future mine planning and designs at Tharisa mine. The acquired geophysical data were processed using modern processing algorithms to enhance the target mineralization and complex geological structures in all the sites. In-mine reflection seismic datasets acquired in 2020 at Maseve mine proved useful as they provided optimum imaging of the economic Platinum Group Elements (PGEs) such as the Merensky Reef and Upper Group 2 chromitite layers (known as reefs). This is one of the few in-mine seismic experiments to have been conducted in South Africa for mineral exploration. In 2022, 2D reflection seismic profiles were acquired on surface above the Merensky Reef and Upper Group 2 chromitite, together with four 2D reflection seismic profiles acquired along the mine tunnel at ~ 550 m below the surface and tens of meters above known mineralisation: Merensky Reef and Upper Group 2 chromitite layer. Interpretation of the in-mine and surface seismic data were complemented by the use of 3D ray tracing numerical simulations to understand the distribution and out-of-plane reflectivity from the target mineralization. The 2022 Maseve reflection seismic data improved the imaging of geological structures and mineral deposits. The geophysical data acquired in 2021 at Tharisa mine demonstrated the importance of using near-surface integrated geophysical methods (magnetics, seismics, and electrical resistivity) with other datasets such as borehole logs and physical property measurements to understand the geophysical response of the mineral deposits. Ground magnetic data delineated a major dyke that was identified on the aeromagnetic data and geological mapping. Electrical resistivity tomography, on the other hand, identified linear low resistivity zones that differentiateiii fractured and undisturbed hard rock. Seismic methods were important for depth to bedrock imaging. Integration of geophysical methods was encouraged by the need to understand geological structures (e.g., faults, dykes, iron-rich ultramafic pegmatites, boulders) that can have impact on the efficiency, safety and costs of mining in South Africa. Moreover, this approach encourages the implementation of innovative geophysical surveys in brownfield sites for better mine design and planning, and to increase a life of mine (LoM)
Late Quaternary Palynological Studies at Lake St Lucia, KwaZulu-Natal
(University of the Witwatersrand, Johannesburg, 2023-08) Effiom, Angela Charles; Neumann, Frank; Bamford, Marion
Palynological studies were done on lacustrine sediments deposited during the last ~6300 and about ~2000 cal yrs BP in Mkhuze Swamp, which drains into the most northern part of Lake St Lucia located in the Indian Ocean Coastal Belt Biome of KwaZulu-Natal, eastern South Africa. The aim was to reconstruct the past vegetation and to infer past climate fluctuations as well as human disturbances to complement growing evidence from other disciplines about these questions in the area. Following standard palynological methods, samples from two cores Mkhuze River Delta (MKD-1, long core) and Mkhuze swamp (MK24-1, short core) were extracted and analyzed. Palynological results for both cores show a dominance of Poaceae (20-90%) suggesting a strong influence of grassy woodland savanna. Spirostachys pollen dominated the arboreal spectra of the pollen profile in MK24-1, but it dominated the arboreal pollen spectra for the last 2600 cal yrs BP in MKD-1 as Podocarpus pollen dominated the arboreal spectra from 6300-2600 cal yrs BP indicating a change from a forested environment to a more open woodland environment. The results also show that the mid Holocene was humid with high precipitation and high sea level while the late Holocene was warm, dry with Marine influence (more sea water flowing into the lake due to high evaporation and low fresh water supply caused by drought). Similar pollen fluctuations were observed in records from Lakes Eteza and Sibaya also located within the Indian Ocean Coastal Belt Biome. The presence of Pinus pollen at the top of the profiles suggests the onset of European settlement when pines were introduced for timber production. Other published pollen records from the region in the last ~7000 cal BP show a general trend from a mesic forested environment towards an open woodland environment with grasses which is due to climate change.
Late Triassic to Early Jurassic ecology: An insight into diet and trophic levels using non-traditional Ca isotopes
(University of the Witwatersrand, Johannesburg, 2023-07) Davechand, Priyanka; Bybee, Grant; Choiniere, Jonah
The diet and trophic structuring of organisms in deep time is poorly understood, making comparison of ancient and modern ecosystems challenging. Proxy data (e.g., dental morphology, jaw muscle reconstruction) remain the most common mode of palaeodietary inference, but the correlative strength of these proxies remains untested due to a lack of direct evidence and an incomplete sampling of palaeobiodiversity. These major challenges in palaeodietary reconstruction can be overcome using novel geochemical markers in fossilised tooth enamel, which provide direct evidence of palaeodiet and trophic relationships. Traditional stable isotopes of carbon, oxygen, and nitrogen have been used in the past to infer palaeodiets, but these elements are susceptible to diagenetic alteration during fossil preservation and require large sample amounts for assays. In contrast, non-traditional calcium (δ44/42Ca) isotopes are less susceptible to diagenesis and require significantly smaller sample amounts. This, together with the fractionation that Ca isotopes undergo as a bio-essential element, allows δ44/42Ca to be utilised on a broad range of palaeontological questions including assessing dietary range and trophic level. The diverse ecosystems of the Elliot Formation (Karoo Supergroup) in South Africa are represented by abundant fossils of a variety of reptilian and mammalian stem lineages that coexisted during the latest Triassic–earliest Jurassic interval (218–190 Ma). The broad range of body sizes, inferred dietary preferences, and phylogenetic positions make the Elliot palaeoecosystems an ideal natural laboratory in which to apply palaeodietary isotopic tools. This dissertation aims to assess the palaeotrophic divisions of the Elliot Formation vertebrates using non-traditional δ 44/42Ca isotopes. This research uses ion-exchange chromatography on vertebrate tooth enamel to assess the palaeodietary preferences of Elliot Formation reptilian and mammalian lineages. To obtain these data, existing techniques for sample preparation of non-traditional δ 44/42Ca isotopes were modified and optimised at the Wits Isotope Geoscience Laboratory (WIGL) at the University of the Witwatersrand. δ 44/42Ca analysis was conducted on a variety of specimens across a broad range of amniote lineages, ranging from: dinosaurs such as presumed herbivorous sauropodomorphs Massospondylus and Aardonyx, the presumed omnivorous ornithischian (Lesothosaurus and Heterodontosaurus), and the presumed carnivorous theropod Megapnosaurus; to cynodont therapsids (Tritylodon, Pachygenelus and Scalenodontoides); to pseudosuchians such as the crocodylomorphs Protosuchus and Orthosuchus and earlier branching taxa (‘rauisuchians’ and poposauroids). A leaching procedure was also tested to ensure that the results produced were not influenced by diagenetic biases. Once consistent and reproducible methods were finalised, column chemistry and Multicollector-Inductively Coupled Plasma Mass Spectrometery (MC-ICPMS) analysis was conducted on the different Karoo-aged specimens. There are various outcomes from this dissertation. One important outcome was the optimisation of time for Ca separation using ion-exchange chromatography. This allowed for a shorter chemical preparation time and increased the number of analyses completed per session. Another improvement of the method was that the leaching procedure can be used to control for any diagenetic biases by removing secondary calcite in samples as old as those from the Triassic–Jurassic period. Elliot taxa were then analysed, and significant differences were found between δ 44/42Ca values of large carnivorous pseudosuchians (‘rauisuchians’; -0.45 ‰ to -1.17 ‰) and co occurring herbivorous sauropodomorph genera (-0.26 ‰ to -0.69 ‰). These results indicated that non-traditional δ 44/42Ca isotopes can be used to understand trophic structures and palaeodiets in ecosystems at least 210 million years old. We also found that while some taxa had δ44/42Ca isotope values in-line with their presumed diets, other taxa had more diverse diets than initially presumed. δ 44/42Ca-enriched values in this study provide evidence for herbivory in crocodylomorph and the oldest theropod. There is also a possibility of an omnivorous diet for presumed herbivorous Lesothosaurus as the δ 44/42Ca values are relatively depleted to other herbivores. In addition to diet, calcium plays a major role in the formation of reptilian eggs and there are documented changes in δ 44/42Ca values during the reproductive cycle. To assess this in a living system, Crocodylus niloticus, was analysed to understand if δ 44/42Ca could be used to identify the difference in sex based on the δ 44/42Ca values. No isotopic differences were found between the juvenile male and female Crocodylus niloticus samples. Testing these important ecological principles in temporally constrained formations allows us to understand the historical nature of biodiversity changes, especially across periods when environments on Earth were experiencing extreme conditions. The ability to determine factors such as palaeodiet and palaeotrophic range will enable the development and improvement of palaeoecological analysis. This research presents the first ever δ 44/42Ca values on Karoo-aged vertebrate fossils and will have a large impact on how palaeoecological reconstruction is conducted in the future of palaeosciences.
Machine Learning Algorithms-Based Classification of Lithology using Geophysical Logs: ICDP DSeis Project Boreholes, South Africa
(University of the Witwatersrand, Johannesburg, 2024-09) Atita, Obehi Chapet; Durrheim, Raymond; Saffou, Eric
One of the most significant geosciences tasks is the accurate classification of lithologies for metal and mineral resources exploration, characterization of oil/gas reservoir(s), and the planning and management of mining operations. With the availability of abundant, huge and multidimensional datasets, machine learning-based data-driven methods have been widely adopted to assist in solving geoscientific problems such as the efficient evaluation and interpretation of large datasets. The adoption of machine learning-based methods aims to improve lithological identification accuracy and extract information required for accurate and objective decision-making with respect to activities such as exploration, drilling, mine planning and production. Practically, this helps to reduce working time and operating costs. We aim to evaluate the feasibility of machine learning-based algorithms application to geophysical log data for the automated classification of lithologies based on the stratigraphic unit at the formation level for the purpose of distinguishing and correlating the quartzites between boreholes, and mapping key radioactive zones within the mining horizon. This study implemented four different machine learning algorithms: gradient boosting decision trees, random forest, support vector machine, and K-means clustering models. Analyzed features and labelled datasets are multivariate downhole geophysical and lithology logs from the two ICDP DSeis project boreholes drilled in the Klerksdorp gold field, respectively. To mitigate misclassification error and avoid model overfitting/underfitting, the optimal combination sets and optimal values for each implemented supervised model’s hyperparameters were obtained using the Grid search and 10-fold cross-validation optimization methods. The input dataset was randomly split automatedly into training and testing subsets that made up 80% and 20% of the original dataset, respectively. The models were trained and cross-validated using the training subset, and their performances were assessed using the testing subset. The classification performance of each model was evaluated using F1 scores and visualized using confusion matrices. The best supervised classification model for our study area was selected based on the testing subset F1 scores and computational cost of training models. The testing subset results shows that Random Forest and Support Vector Machine classifier models performed much better relative to the Gradient Boosting Decision Trees classifier model, with F1 scores over 0.80 in borehole A and B. In borehole A and B, Random Forest classifier has the least computational training time of about 14- and 6- hours, respectively. The feature importance results demonstrate that the logging feature P-wave velocity (Vp) is the highest predicting feature to the lithology classification in both boreholes. We find that the quartzite classes at different stratigraphic positions in each borehole are similar and they are correlated between the DSeis boreholes. The K-means clustering revealed three clusters in this study area and effectively map the radioactive zones. This study illustrates that geophysical log data and machine learning-based algorithms can improve the task of data analysis in the geosciences with accurate, reproducible and automated prediction of lithologies, correlation and mapping of radioactive zones in gold mine. This study outputs can serve as quality control measures for future similar studies both in the academic and industry. We identified that availability of large data is the major factor to high accuracy performance of machine learning-based algorithms for classification problems.
Naturally occurring asbestos (NOA) and asbestos contamination of the environment: Implications for in-situ risk assessment and rehabilitation
(University of the Witwatersrand, Johannesburg, 2023-01) Schapira, Jessica Shaye; Bolhar, Robert; Master, Sharad; Rumbold, Karl
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. Present bio-solutions to ensure asbestos mine land rehabilitation success are discussed and the potential of using available agronomic bio-fertilisers (microbial strain Pseudomonas fluorescens) is examined. The growth-based assays indicate that this micro-organism is suitable for an environmental biotechnology applied to ecosystem restoration of asbestos-mining lands. Naturally Occurring Asbestos (NOA) occurrences are highly dependent upon the geological conditions, and understanding these in a large variety of settings may allow the development of predictive strategies necessary for in situ identification and hazard assessment required for health risk mitigation in the context of mining and other geologically disruptive activities. A variety of natural asbestos rock samples was examined, showing how geological databases relevant for predicting natural occurrences of asbestos provide baseline data required for mitigating asbestos exposure risks.
Near-surface geophysical investigation of the Far Western Limb of the Bushveld Complex, South Africa
(University of the Witwatersrand, Johannesburg, 2023-10) Nadan, Thiashen; Scheiber-Enslin, Stephanie; Manzi, Musa
Platinum Group Elements (PGE’s) and chromium are the main economic minerals that are found within the Bushveld Complex. In particular, the Far Western Limb of the Bushveld Complex has not been completely explored, as it is overlain by a thick Quaternary sedimentary deposit which masks the contacts between the different underlying lithological units. Chromium outcrops within the Far Western Limb have already been identified and mined. The study aims to assess the feasibility of extended geophysical surveys which will further identify the shallow subsurface lithologies and evaluate the future mining potential in the area. Results of this study show that the quaternary cover is approximately eighty meters thick, implying a shallow bedrock within the Far Western Limb. This was used to delineate a contact between the Transvaal Supergroup and the Rustenburg Layered Suite that was lost beneath the sedimentary cover. This shows that shallow geophysical investigations and drilling can prove useful in delineating the lithologies hosting the chromium ores.