School of Geosciences (ETDs)

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    Taphonomy and palaeoecology of a monospecific microvertebrate bonebed: behavioural implications for the late Permian (Lopingian) parareptiles
    (University of the Witwatersrand, Johannesburg, 2024-06) Mukwevho, Lutendo; Choiniere, Jonah; Smith, Roger
    Sociality in the vertebrate fossil record is a dynamic and fast-expanding area of research. Natural history observations of living animals are crucial for understanding and categorizing sociality, but these observations are not feasible for extinct species. Monotaxic bonebeds provide unique opportunities to conceptualize the social behaviours of these extinct animals. An unusual bonebed (SAM-PK-K11289) discovered in the uppermost Permian strata of the Balfour Formation, Karoo Supergroup, in the Eastern Cape presents a window into the sociality of Late Permian reptiles. The use of propagation phase-contrast synchrotron X-ray microcomputed tomography permitted the 3D reconstruction of skeletal elements in SAMPK-K11289, allowing the taxonomic identification of the individuals in the bonebed as most likely belonging to Owenetta. This is the largest aggregation of Owenetta individuals known to date, with a minimum number of 31, which are all very similar in body size. The ontogenetic profile of SAM-PK-K11289 was interpreted by analysing the size distribution of duplicate elements and by making comparisons with other Owenetta and procolophonid specimens. The specimens in the bonebed are all osteologically immature, indicating that they are juveniles. The bonebed occurs in a pedogenically modified ripple cross-laminated siltstone suggesting that a low-energy fluvial sedimentation likely contributed to the modification, disturbance and disarticulation of elements before the bonebed was buried at or very close to the death site. This bonebed provides novel information that directly challenges the popular belief that reptiles and their ancestors are non-social or asocial. Considering the overall circumstances of the bonebed, I hypothesize that Owenetta rubidgei juveniles were socially gregarious and this behaviour may have been induced or influenced by environmental changes during the early extinction phase of the end Permian mass extinction in the Karoo Basin.
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    The Taxonomy and Phylogeny of Varanopidae from the Middle Permian of outh Africa
    (University of the Witwatersrand, Johannesburg, 2024-08) Sibiya, Zoleka; Rubidge, Bruce; Benoit, Julien
    Varanopidae are the only pelycosaur-grade tetrapods from the Abrahamskraal Formation of the Beaufort Group. Although four varanopid species are described from the middle Permian of South Africa (SA), their validity has been questionable. Moreover, Ford and Benson recently proposed that varanopids belong to the Diapsida rather than Synapsida. Given this taxonomic and phylogenetic turmoil, this study i) describes two newly discovered and well-preserved varanopid specimens from the middle Permian of SA using CT scanning and ii) re-assesses the validity of the four species from the Karoo Basin in the light of new data from these specimens. The phylogeny of the group is addressed by updating two pre-existing cladistics matrices. The two new specimens exhibit a mosaic of features that overlap the diagnoses of several species of SA varanopids. In addition, some diagnostic traits of the four SA varanopid genera and species are found to be variable across ontogeny. For instance, dorsal osteoderms and the extent of ornamentation on the angular bone co-vary with size. It is therefore proposed that all varanopid specimens currently described from the middle Permian of South Africa belong to a single valid species, Heleosaurus scholtzi, with differences between specimens being accounted for by ontogenetic changes. The phylogenetic analysis supports Ford and Benson’s hypothesis but contra the prediction of this hypothesis, no differences in cranial fenestration during ontogeny are observed. Morphological characters preserved in the manus of the newly discovered specimen BP/1/8499 suggest that Heleosaurus was arboreal.
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    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.
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    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.
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    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.
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    The Equidae from Gladysvale, a Hominin locality in the Cradle of Humankind, South Africa
    (University of the Witwatersrand, Johannesburg, 2023-10) Van der Merwe, Daniel Jean; Badenhorst, Shaw
    The later Pleistocene compared to modern census data indicated that Equidae are represented lower than comparably sized bovids (BOV III & IV). The reason for this may be due to numerous factors that have been previously investigated such as, landscape usage, carnivore and prey relationships and accumulation factors. However, a largely unexplored factor that may also have played a vital role in their lower representation may have been the difference and effectiveness of predator avoidance behaviours utilized by Equidae. The Equidae remains from the external and internal deposits of Gladysvale (730 to 580 Kya and 257 to 195 Kya) in the Cradle of Humankind, may provide insight into the predatory avoidance behaviours of two different Equidae species, Equus capensis and Equus quagga. This study aimed to create and renew an understanding of the role of these animals within larger faunal communities in the Cradle of Humankind. Equidae fossil material mostly from Gladysvale along with supporting material from Sterkfontein, Kromdraai and Coopers were examined, measured and photographed, in an attempt to broaden the understanding of Equidae relations within the Cradle of Humankind. Furthermore, to also elaborate on the potential differences between Equus capensis and Equus quagga. Past research has usually assigned Equus capensis to the larger version of Equus quagga during the later Pleistocene, with other studies based on DNA analysis suggesting the two species have very little intraspecific diversity. However as seen in this study it would appear that there is a notable difference in size between the two Equidae species, but also a difference in overall representation within the Cradle of Humankind. This could imply that not only are the two species different in size but that they also employed different predatory avoidance behaviours.
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    Potential Source for the Alluvial Gold Deposit in the Kapoeta Area, Eastern Equatoria State, South Sudan
    (University of the Witwatersrand, Johannesburg, 2023-10) Bali, Francis Khamis Alex; Woldai, Tsehaie; Kinnaird, Judith A.
    This study concentrates on the integrated approach of applying geochemical, and remote sensing data combined with field investigation to understand the source of the alluvial gold deposit in the Kapoeta area. The use of an integrated technique approach proves effective in mapping and outlining areas of potential gold mineralisation in Kapoeta. Kapoeta has been known for its endowment of gold deposits for quite some time. Landsat-8 (OLI) and SRTM-DEM satellite images were employed during this study to map lithological units and highlight areas of hydrothermal alteration and structural trends in Kapoeta to understand the potential source for the widely distributed alluvial gold in the area. The several image-processing techniques employed were effective in mapping the lithological units and outlining the major structural trends in the area. Mapping the hydrothermal alteration zones was challenging because of the overburden that masks most parts of the Neoproterozoic juvenile metavolcano-sedimentary sequences. Secondly, the vegetation cover is another factor affecting the mapping of the lithological units around the Didinga Hills and Dongotona mountains. Structural mapping identified four main trends N-S, NNW-SSE, NW-SE, and NE-SW. The image interpretation, together with geochemical occurrence and anomaly map showing Cu, Co, Ni, and Cr, shows that N-S and NNW-SSE are the potential controls on mineralisation in the area. The whole-rock geochemical data plotted on the TAS discrimination diagrams shows that the rocks analysed are dominantly tholeiitic with minor calc-alkaline units. Trace elements normalised to the primitive mantle show low concentrations of Zr, Hf, Nb and Ta. The REE normalised chondrite values indicates general enrichment of LREE elements relative to HREE with a negative Eu anomaly. On the tectonic discrimination diagrams, the results indicate that the rocks of Greater Kapoeta belong in a marine environment related to a spreading centre, oceanic island, oceanic ridges, and floor. The distribution of Cu, Co, Cr and Ni and their high concentration suggest that these elements are the potential pathfinders for gold in the area. The study concludes the following: Based on the remote sensing, field observations and geochemical data indicates that the gold mineralisation of Kapoeta is orogenic in nature with a strong element of epigenetic characteristics, however, a syngenetic origin cannot be ruled out. The host lithologies may vary from quartz veins to schists, amphibolites, quartzo-feldspathic gneisses, and ultramafics and the marbles related to the N-S, NNS-W-SSE and NW-SE trending shear zones that limit the greenstone belt.
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    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.
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    Utilizing legacy seismics and non-seismic geophysical methods for deep mineral targeting and near-surface characterization: implications for mine development planning
    (University of the Witwatersrand, Johannesburg, 2023) Mutshafa, Ndamulelo; Manzi, Musa
    This thesis demonstrates through several case studies how the reprocessing of legacy reflection seismic data using advanced algorithms can be of value to mineral exploration and mine development, especially in hard-rock environments. The thesis also showcases how the integration of seismic and non-seismic geophysical datasets can assist in delineating near- surface geological structures (e.g., boulders and fractures) for mine planning and designs. Papers I and II demonstrate how the reprocessed legacy reflection seismic data have been used to delineate and image the world-class gold deposits such as the Black Reef (BLR) and Ventersdorp Contact Reef (VCR) of the Witwatersrand goldfields in South Africa. The two legacy reflection seismic profiles (Paper I) were acquired in 1988 for deep mineral exploration and mine planning over an area that is dominated by dolomitic outcrops that cause scattering of seismic energy at the near-surface, preventing energy propagation into the subsurface. Various migration approaches, namely, pre-stack time, pre-stack depth, and post-stack time migration were applied to test their capabilities in improving structural imaging. Reprocessing results from the pre-stack depth migration using the Kirchhoff algorithm provided the most improved subsurface images, especially the deeper targets due to its ability to honour complex lateral variations in the velocity field. In addition, Kirchhoff's pre-stack and post-stack time migration techniques improved the continuity of the near-surface reflections below the dolomitic rocks. Paper II presents the results from the recovered and processed 25.3 km long legacy seismic survey that was acquired in 1983 by the Gold Division of Anglo-American as part of the Witwatersrand goldfields exploration program. The reprocessing of the data improved the imaging of the gold-bearing horizon termed Ventersdorp Contact Reef (VCR), which is situated at depths between ~2400 and ~4100 m below the ground surface near the South Deep mine in Fochville, South Africa. The pre-stack time and phase-shift migration approaches were tested during processing, and both revealed a dipping reflection associated with the gold-bearing horizon and major steeply dipping faults that crosscut and displace the deposit. The interpretation of the results was constrained using borehole logs and surface geology. This is encouraging and motivates the use of legacy seismic data in the exploration of deep-seated targets. Papers III, IV and V present the results from the use of multi-geophysical methods (resistivity, magnetics, seismic, ground penetrating radar and multichannel analysis of surface waves) at Tharisa platinum mine to provide a comprehensive understanding of the subsurface geology by accurately delineating and locating boulders, mapping fractures and groundwater aquifers to improve Platinum Group Elements (PGEs) mining efficiency and reduce risks. The results from these integrated geophysical methods were successful in complementing each other in terms of providing a clear picture of the near-surface geological structures to help the mine plan better for future operations.
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    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.