Academic literature on the topic 'Igneous rocks – South Africa – Bushveld Complex'
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Journal articles on the topic "Igneous rocks – South Africa – Bushveld Complex"
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Prevec, Stephen A. "Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms." Geoscience Canada 45, no. 3-4 (2019): 117–35. http://dx.doi.org/10.12789/geocanj.2018.45.138.
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SUMMARYThe Bushveld Complex has continued to serve as the basis for study into the fundamental nature of petrological processes for layered intrusion formation and for oxide and sulphide hosted Platinum Group Element (PGE)–Cu–Ni ore deposits. These studies have included discoveries in terms of the physical extent of Bushveld magmatism, both laterally and internally. Lateral variations in the mafic to ultramafic Rustenburg Layered Suite of the Northern Lobe of the complex have also revealed petrologically distinctive Upper Critical Zone equivalent rocks (the so-called Flatreef) with enhanced contamination and mineralization traits that reflect a transition between Eastern and Western Lobe equivalent stratigraphy and Platreef-style complexity. Traditional magma mixing models have been re-examined in light of radiogenic isotopic evidence for crustal involvement early in the chromite precipitation or formation process, combined with evidence for associated heterogeneous fluid contents, cryptic layering profiles, and textural evidence. A wide variety of alternative ore-genesis models have been proposed as a consequence. The fundamental mechanics of magma chamber processes and the existence of the magma chamber as an entity have been called into question through various lines of evidence which have promoted the concept of progressive emplacement of the complex as a stack of not-necessarily-quite-sequentially intruded sills (with or without significant quantities of transported phenocrysts), emplaced into variably crystallized and compacted crystal-liquid mush mixtures, modified by compaction-driven late magmatic fluid (silicate and aqueous) activity. Alternatively, petrological and geochemical observations have been used to discount these interpretations in favour of more conventional cooling and gravity-driven accumulation of silicate and ore minerals in a large, liquid-dominated system.RÉSUMÉLe complexe de Bushveld a demeuré à la base d’études sur la nature fondamentale des processus pétrologiques de formation d’intrusions litées et des gîtes des éléments du groupe platine (ÉGP)-Cu-Ni hébergés dans les oxydes et les sulfures. Ces études ont comporté des découvertes sur l’étendue physique, à la fois latérale et interne, du magmatisme de Bushveld. Les variations latérales de la suite stratifiée et mafique à ultramafique Rustenburg du lobe nord du complexe ont également révélé des roches équivalentes pétrologiquement distinctes de la zone critique supérieure (le communément désigné Flatreef) avec des traits de contamination et de minéralisation accrus qui reflètent une transition entre la stratigraphie équivalente des lobes est et ouest et la complexité de type Platreef. Les modèles traditionnels de mélanges magmatiques ont été réexaminés à la lumière de preuves isotopiques radiogéniques indiquant une implication de la croûte au début du processus de précipitation ou de formation de la chromite, combinées à des preuves de contenu fluide hétérogène associé, de profils de litage cryptique et de preuves texturales. Ainsi, une grande variété de modèles alternatifs de genèse de minerai a été proposée. La mécanique fondamentale des processus de la chambre magmatique et l'existence de la chambre magmatique en tant qu'entité ont été remises en question au moyen de divers éléments de preuve qui ont mis en avant le concept de mise en place progressive du complexe sous forme d'un empilement non-nécessairement séquentiel de sills injectés (avec ou sans quantités significatives de phénocristaux transportés) mis en place dans des mélanges de bouillie cristaux/liquide à cristallisation et compaction variable, modifiés par une activité tardive de fluide magmatique (silicaté et aqueux) induite par la compaction. Alternativement, des observations pétrologiques et géochimiques ont été utilisées pour écarter ces interprétations en faveur d'un processus plus conventionnel de refroidissement et d’accumulation de minérais silicatés et minéralisés induite par la gravité dans un vaste système à dominance liquide.
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Wieser, Penny E., Zoja Vukmanovic, Rüdiger Kilian, et al. "To sink, swim, twin, or nucleate: A critical appraisal of crystal aggregation processes." Geology 47, no. 10 (2019): 948–52. http://dx.doi.org/10.1130/g46660.1.
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Abstract Crystal aggregates in igneous rocks have been variously ascribed to growth processes (e.g., twinning, heterogeneous nucleation, epitaxial growth, dendritic growth), or dynamical processes (e.g., synneusis, accumulation during settling). We tested these hypotheses by quantifying the relative orientation of adjacent crystals using electron backscatter diffraction. Both olivine aggregates from Kīlauea volcano (Hawaiʻi, USA) and chromite aggregates from the Bushveld Complex (South Africa) show diverse attachment geometries inconsistent with growth processes. Near-random attachments in chromite aggregates are consistent with accumulation by settling of individual crystals. Attachment geometries and prominent geochemical differences across grain boundaries in olivine aggregates are indicative of synneusis.
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JORDAAN, MARIE, and ABRAHAM E. VAN WYK. "Gymnosporia sekhukhuniensis (Celastraceae), a new species from South Africa." Phytotaxa 408, no. 1 (2019): 69–76. http://dx.doi.org/10.11646/phytotaxa.408.1.5.
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Gymnosporia sekhukhuniensis, a new species from north-eastern South Africa, is described, illustrated, mapped, and compared with closely related species. It belongs to Gymnosporia sect. Buxifoliae, more specifically Group 1, the members of which are characterized by the capsules being (2)3(4)-valved, rugose or verrucose, and the seeds partially covered by the aril. The new species has a restricted distribution range and is near-endemic to the Sekhukhuneland Centre of Endemism. This biogeographical region rich in restricted-range plants is more or less congruent with surface outcrops of mafic and ultramafic igneous rocks belonging to the Rustenburg Layered Suite of the eastern Bushveld Complex. The range of the new species shows marginal intrusion into the far northern part of the nearby Wolkberg Centre of Endemism, where it is associated with dolomites of the Malmani Subgroup. Gymnosporia sekhukhuniensis is a suffrutex mainly associated with rocky outcrops in open savannah. Diagnostic characters include its dwarf habit (up to 1.6 m tall), capsules that are relatively small (5–8 mm long), woody, scaly-rugose, with hard pointed apices, and leaves that are very laxly arranged on the stems, with some often present on the thorns. Also included is a key to the 10 currently accepted species in G. sect. Buxifoliae Group 1. The taxonomic significance of capsule and seed characters for demarcating sections and species in the genus Gymnosporia is emphasized.
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Brandt, S., R. Klemd, K. M. Haase, M. L. Fassbender, and T. Vennemann. "Formation of the Vergenoeg F–Fe–REE Deposit (South Africa) by Accumulation from a Ferroan Silicic Magma." Journal of Petrology 60, no. 12 (2019): 2339–68. http://dx.doi.org/10.1093/petrology/egaa010.
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Abstract Situated in the centre of the Paleoproterozoic Bushveld Large Igneous Province (LIP) of South Africa the Vergenoeg F–Fe–REE deposit is one of the largest, but at the same time most unusual, fluorite deposits on Earth. In situ major and trace element analyses of fayalite, magnetite, ilmenite, fluorapatite, fluorite and allanite from fayalite-rich rocks are combined with oxygen isotope data for fayalite, magnetite and ilmenite to unravel the complex evolution of the deposit. Textural and compositional characterization of the fayalite-rich rocks supports a magmatic formation as cumulates and an intense late hydrothermal overprint. Fayalite accumulated together with minor Ti-rich magnetite, ilmenite, fluorapatite and allanite from a highly evolved, H2O-poor felsic melt at low oxygen fugacity. Chondrite-normalized rare earth element (REE) patterns of fayalite and the recalculated parental melts, using fayalite–rhyolite partition coefficients, exhibit positive trends with strong enrichment of the heavy REE (HREE) relative to the light REE (LREE). Apart from the LREE depletion the patterns are similar to those of highly fractionated high-silica REE rhyolites that often occur in siliceous LIPs. We attribute the LREE depletion to crystallization of accessory allanite, the main host of the LREE in the cumulates. Chondrite-normalized REE patterns of the parental melt prior to fayalite accumulation, recalculated using allanite–rhyolite partition coefficients, resemble the composition of the rhyolites of the Rooiberg Group and therefore document a petrogenetic link to the Bushveld LIP. High δ18O values of fayalite (up to ≈7·4 ‰) are consistent with its crystallization in a rhyolitic melt that has formed by extensive fractionation from basic melts of the Rustenburg Layer Suite, the mafic member of the Bushveld LIP. Primary fluorite crystallized together with rare quartz, and a second generation of fayalite, magnetite and ilmenite from rare intercumulus melt in interstices between cumulate fayalite. Textural and mineral compositional data, as well as the generally negative δ18O values of magnetite (–2·9 to 0 ‰), are in agreement with the main magnetite–fluorite ore formation in Vergenoeg being related to a hydrothermal overprint, which was responsible for further F and Fe enrichments of the rocks. Fluorine-rich fluids, released from the crystallizing granites of the felsic member of the Bushveld LIP (Lebowa Granite Suite), caused the extensive alteration of fayalite to bowlingite and its replacement by Ti-poor magnetite and quartz. The hydrothermal overprint was associated with the widespread formation of secondary fluorite and minor fluorapatite. Our new petrogenetic model for the Vergenoeg deposit, as constrained from the primary fayalite cumulates, implies that the formation of the Vergenoeg deposit was directly linked to the evolution of the Bushveld LIP.
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Lenhardt, N., W. Altermann, F. Humbert, and M. de Kock. "Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa." South African Journal of Geology 123, no. 4 (2020): 655–68. http://dx.doi.org/10.25131/sajg.123.0043.
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Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.
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Holwell, D. A., I. McDonald, and P. E. B. Armitage. "Platinum-group mineral assemblages in the Platreef at the Sandsloot Mine, northern Bushveld Complex, South Africa." Mineralogical Magazine 70, no. 1 (2006): 83–101. http://dx.doi.org/10.1180/0026461067010315.
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AbstractPlatinum group mineral (PGM) assemblages in the Platreef at Sandsloot, northern Bushveld Complex, in a variety of lithologies reveal a complex multi-stage mineralization history. During crystallization of the Platreef pyroxenites, platinum group elements (PGE) and base-metal sulphides (BMS) were distributed thoughout the interstitial liquid forming a telluride-dominant assemblage devoid of PGE sulphides. Redistribution of PGE into the metamorphic footwall by hydrothermal fluids has formed arsenide-, alloy- and antimonide-dominant assemblages, indicating a significant volatile influence during crystallization. Serpentinization of the footwall has produced an antimonide-dominant PGM assemblage. Parts of the igneous reef were subjected to alteration by a late-stage, Fe-rich fluid, producing ultramafic zones where the telluride-dominant assemblage has been recrystallized to an alloy-dominant one, particularly rich in Pt-Fe and Pd-Pb alloys. A thin, small-volume zone of PGE-BMS mineralization along the base of the hangingwall contains a primary PGM assemblage that is locally altered to one dominated by Pt/Pd germanides. This is thought to have formed when the new pulse of Main Zone magma entered the chamber, and scavenged PGE from the underlying Platreef pyroxenites. That each major rock type at Sandsloot contains a distinctive PGM assemblage reflects the importance of syn- and post-emplacement fluid and magmatic processes on the development of Platreef mineralization.
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Vonopartis, Leonidas, Paul Nex, Judith Kinnaird, and Laurence Robb. "Evaluating the Changes from Endogranitic Magmatic to Magmatic-Hydrothermal Mineralization: The Zaaiplaats Tin Granites, Bushveld Igneous Complex, South Africa." Minerals 10, no. 4 (2020): 379. http://dx.doi.org/10.3390/min10040379.
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The stanniferous granites of the Zaaiplaats Tin Field are part of the A-Type Lebowa Granite Suite, within the greater Bushveld Igneous Complex of northeast South Africa. The tin field comprises three granites: (1) the Nebo, a leucocratic, equigranular biotite granite; (2) The brick-red hypidiomorphic Bobbejaankop granite, which is extensively microclinized with chloritized biotite and characteristic synneusis-textured quartz; and (3) The variably altered roof facies of the Bobbejaankop granite known as the Lease microgranite. The Bobbejaankop and Lease granites were both extensively mined for cassiterite until 1989. The cassiterite is hosted in disseminations, miarolitic cavities, and within large hydrothermal, tourmalinized, and greisenized pipes and lenticular ore-bodies. An extensive petrological and whole-rock XRF and ICP-MS geochemical study, has provided new insight into the magmatic and magmatic-hydrothermal mineralization processes in these granites. Trace elements and Rayleigh Fractionation modelling suggest the sequential fractionation of the Nebo granite magma to be the origin of the Bobbejaankop granite. Incompatible elemental ratios, such as Zr/Hf and Nb/Ta, record the influence of internally derived, F-rich, hydrothermal fluid accumulation within the roof of the Bobbejaankop granite. Thus, the Lease granite resulted from alteration of the partially crystallized Bobbejaankop granite, subsequent to fluid saturation, and the accumulation of a magmatic-hydrothermal, volatile-rich fluid in the granite cupola. The ratio of Nb/Ta, proved effective in distinguishing the magmatic and magmatic-hydrothermal transition within the Bobbejaankop granite. Elemental ratios reveal the differences between pre- and post-fluid saturation in the mineralizing regimes within the same pluton. Thus highlighting the effect that the location and degree of hydrothermal alteration have had on the distribution of endogranitic tin mineralization.
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Johnson, J. E., S. M. Webb, C. B. Condit, N. J. Beukes, and W. W. Fischer. "Effects of metamorphism and metasomatism on manganese mineralogy: Examples from the Transvaal Supergroup." South African Journal of Geology 122, no. 4 (2019): 489–504. http://dx.doi.org/10.25131/sajg.122.0034.
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AbstractManganese-bearing minerals in ancient strata provide a particularly informative record of the redox potentials of ancient Earth surface environments due to the high specificity of species that can oxidize Mn(II). However, little is known about how this sedimentary archive might have been altered by processes occurring long after lithification, including the effects of metamorphism, fluid mobilization, and metasomatism. We investigated Mn mineralization across known metamorphic gradients in the Kaapvaal craton, South Africa, in Archean and early Paleoproterozoic age carbonate-, shale-, and iron formation-bearing marine strata. We sampled contemporaneous strata that record the drowning of the Campbellrand-Malmani carbonate platform and a transition to iron formation deposition in a range of localities, from two metamorphosed (greenschist and above, affected by the intrusion of the Bushveld igneous complex) and four better-preserved (sub-greenschist) deep subsurface drill cores. To evaluate the geochemistry and mineralization tied directly to petrographic textures and cross-cutting relationships, we combined bulk geochemistry with light and electron microscopy and synchrotron microprobe X-ray absorption spectroscopy and imaging to produce Mn speciation maps at the requisite micrometer length scales for these textures. Samples with lesser degrees of post-depositional transformation contained minor amounts of Mn(II) in early diagenetic marine carbonate cements and detrital carbonate grains, while metamorphosed samples typically contained Mn concentrated into a combination of coarse-grained and vein-filling carbonate phases (ankerite, siderite, and rhodochrosite), garnet and amphibole. Chemical imaging analyses of these more metamorphosed samples show that Mn is held by phases and textures that mineralized post-deposition and lithification, demonstrating that Mn was mobilized – at least locally – by metasomatic fluids, although it is difficult to distinguish whether this Mn was original to these strata or was introduced secondarily. Our results confirm that Mn can be mobilized and therefore caution should be applied when interpreting Mn enrichments in sedimentary rocks, especially when Mn enrichment is not geographically extensive and coincides with metamorphic processes.
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Bamisaiye, Oluwaseyi Adunola. "Geo-Spatial Mapping of the Western Bushveld Rustenburg Layered Suite (Rls) in South Africa." Journal of Geography and Geology 7, no. 4 (2015): 88. http://dx.doi.org/10.5539/jgg.v7n4p88.
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Trend surface analysis (TSA) was used to investigate the structure and thickness variation pattern and to resolve trend and residual component of the structure contours and isopach maps of the Rustenburg Layered Suite (RLS) across the Bushveld Igneous Complex (BIC). The TSA technique was also employed in extracting meter scale structures from the regional structural trends. This enables small-scale structures that could only be picked through field mapping to be observed and scrupulously investigated. Variation in the structure and thickness was used in timing the development of some of the delineated structural features. This has helped to unravel the progressive development of structures within the RLS. The results indicate that present day structures shows slight changes in both regional and local trends throughout the stratigraphic sequence from the base of the Main Zone to the top of the Achaean floor. Structures around the gap areas are also highlighted. This paper represents the third of a three-part article in Trend Surface analysis of the three major limbs of the Bushveld Igneous Complex (BIC). This first part focused on the Northern Bushveld Complex, while the second part focused on the Eastern Bushveld Limbs.
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Cawthorn, R. G., and N. McKenna. "The extension of the western limb, Bushveld Complex (South Africa), at Cullinan Diamond Mine." Mineralogical Magazine 70, no. 3 (2006): 241–56. http://dx.doi.org/10.1180/0026461067030328.
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AbstractMafic rocks of the Bushveld Complex at the southeastern end of the western limb, intersected in bore core from the Cullinan Diamond Mine, are described. A 260 m thick ultramafic body of orthopyroxene and chromite cumulate rocks, with mg# – 100*Mg/(Mg+Fe) – values from 77 to 84 and 0.25 to 0.5% Cr2O3 in the pyroxene, is considered to have affinity to the Critical Zone. Such an interpretation considerably extends the eastern limit of Critical Zone rocks of the western limb of the Bushveld Complex. The whole-rock composition of the lower, chilled basal contact of this body has 10% MgO and 500 ppm Cr, and is comparable to magmas considered parental to the Bushveld Complex. Due to intrusion of a younger sill, the upper contact is not preserved in the bore core. The cumulate rocks have higher interstitial component, inferred from incompatible trace element abundances (Zr, Ti and K), than normal Critical Zone rocks, interpreted to be a result of more rapid cooling due to proximity to the basal contact. The near-constancy of mg# in the pyroxene in the entire succession suggests that large volumes of magma flowed through this conduit, with only the liquidus phases of orthopyroxene and chromite being precipitated.Five generations of sills, intruded into the underlying metasedimentary rocks, are identified. The oldest is tholeiitic, and was metamorphosed prior to the emplacement of the Bushveld Complex. The second equates to the magma proposed as being parental to the Bushveld Complex (2060 Ma). The third represents the products of differentiation of that magma. The fourth is syenitic, and related to the Pienaars River Alkaline Complex (1430–1300 Ma). The fifth is tholeiitic (1150 Ma), and cuts the Cullinan kimberlite.
Dissertations / Theses on the topic "Igneous rocks – South Africa – Bushveld Complex"
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Curl, Edward Alexander 1972. "Parental magmas of the Bushveld Complex, South Africa." Monash University, Dept. of Earth Sciences, 2001. http://arrow.monash.edu.au/hdl/1959.1/9080.
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Haikney, Susan Ann. "The nature of olivine-rich cumulate rocks of the lower critical and lower zones of the northwestern Bushveld Complex." Thesis, Rhodes University, 1993. http://hdl.handle.net/10962/d1005592.
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Boreholes NG1 and NG2 were drilled on the farm Nooitgedacht 406 KQ to intersect the lower Critical and lower Zones of the western Bushveld Complex. The aim of this study is to describe the textural features and chemical characteristics of the olivine-bearing rocks in the intersections, as determined by petrographic studies, XRF analysis and microprobe analysis. The olivine-bearing rocks are dunites, harzburgites and olivine pyroxenites. They comprise olivine and orthopyroxene, with minor chromite, clinopyroxene and plagioclase, and their textures vary between adcumulate, mesocumulate and poikilitic. The sequence intersected can be broadly correlated with that in the eastern Bushveld Complex. Of the whole-rock inter-element ratios, the MMF (MgO)/[MgO+FeO])ratio is the clearest indicator of cyclicity. The olivine-rich rocks are more primitive than the associated rocks, and seem to become more primitive with height in most intervals. The plagioclase in the olivine-bearing rocks is unusually sodic in corrposition, having a maximum Na₂0 content of 8.12%. A comparison of olivine and plagioclase compositions with those in other intrusions has revealed that the only other major intrusion with sodic plagioclase is the Kiglapait intrusion of Canada. In the Kiglapait intrusion the sodic plagioclase occurs in conjunction with fayalitic olivine as opposed to the forsteritic variety of this study. Chemical variations in the rocks sampled indicate that periodic replenishment of the magma from which the rocks crystallised must have occurred. In some of the olivine-bearing intervals where little fractionation is evident, replenishment seems to have been continuous. In other intervals fractionation appears to have continued uninterrupted for significant periods, prior to rejuvenation by fresh influxes of magma.
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Mwenze, Tshipeng. "The implications of Sr and Nd isotope data on the genesis of the Platreef and associated BMS and PGE mineralisation, Bushveld Igneous Complex, South Africa." University of the Western Cape, 2019. http://hdl.handle.net/11394/6922.
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Philosophiae Doctor - PhDThe Platreef is a platinum group elements (PGE) deposit located in the Northern limb of the Bushveld Igneous Complex (BIC). It is a series of mafic and ultramafic sills that are overlain by rocks from the Main Zone (MZ) of the BIC. In comparison to PGE deposits (i.e., Merensky Reef and the UG-2 chromitite) occurring in the Critical Zone (CZ) of the Eastern and Western Limbs of the BIC, which are less than 1 m in thickness, the Platreef is 10 to 400 m in thickness and is comprised of a variety of rocks. PGE mineralisation in the Platreef is not confined to a specific rock type, and its distribution and styles also vary with depth and along strike. Despite the numerous researches that have been conducted, the genesis of Platreef is still poorly understood. New major and trace elements in conjunction with Sr–Nd isotope data, generated from whole-rock analyses of different Platreef rocks, were collected from four drill cores along its strike. The data were examined to determine the source of the magmas and identify the processes involved in its genesis. The study also aimed at establishing whether a genetic link exists between the Platreef magmas and the magmas that formed the Lower Zone (LZ), CZ and MZ in the Rustenburg Layered Suite (RLS) of the BIC. The petrography revealed that the Platreef in the four drill cores consists of harzburgite, olivine pyroxenite, pyroxenite, feldspathic pyroxenite and norite. Based on the textural and modal mineralogy variations, feldspathic pyroxenite was subdivided into five types (I, II, III, IV and V). The variation in the average contents of MgO, LaN/YbN and ΣREE for the Platreef rocks are consistent with the modal mineralogy from the least to the most differentiated rocks. However, the Sr–Nd isotope data of the Platreef rocks have revealed two distinct groups of samples with decreasing ɛNd2060. Group 1 consists of pyroxenite and feldspathic pyroxenite II, III and V having ɛNd2060 values that range from –8.4 to –2.9, and 87Sr/86Sr2060 values from 0.707281 to 0.712106. The Platreef rocks of group 2 consist of olivine pyroxenite and feldspathic pyroxenite Type I with ɛNd2060 ranging from –12.6 to –10.8, and 87Sr/86Sr2060 ranging from 0.707545 to 0.710042. In comparison to the LZ, CZ and MZ rocks, which have ɛNd values ranging from –8.5 to –5.1, and 87Sr/86Sr ranging from 0.704400 to 0.709671, Platreef pyroxenite of group 1 have lower negative ɛNd2060 values (from –3.8 to –2.9) and higher 87Sr/86Sr2060 values from 0.709177 to 0.710492, whereas feldspathic pyroxenite of group 1 have overlapping ɛNd2060 values (from –8.4 to –4.9) but also higher 87Sr/86Sr2060 values (from 0.707281 to 0.712106). Instead, the Platreef olivine pyroxenite and feldspathic pyroxenite in group 2 highly negative ɛNd2060 values and overlapping 87Sr/86Sr2060 values. It is therefore suggested that the Platreef magmas derived from the partial melting of an heterogeneous mantle source comprising depleted mantle melts and both metasomatized slightly unradiogenic Nd enriched melts and highly unradiogenic Nd enriched melts from the subcontinental lithospheric mantle. These magmas ascended via the continental crust using different paths and interacted with rocks of different Sr–Nd isotopic compositions which resulted in the formation the hybrid magmas. The study speculates that sulphide saturation in the Platreef magmas was reached in the staging chambers at depth, and the varying styles of the PGE mineralisation in the Platreef rocks are the result of the varying degree of partial melting of the heterogeneous source for their magmas. In conlusion, this study suggests that the genesis of the Platreef is much more complex and should be considered very much independent from processes involved in the genesis of the RLS in the Eastern and Western Limbs of BIC in agreement with earlier studies.
NRF Inkaba ye Africa Iphakade
2020-08-31
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Gwatinetsa, Demand. "Distribution of iron-titanium oxides in the vanadiferous main magnetite seam of the upper zone : Northern limb, Bushveld complex." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013281.
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The main magnetite seam of the Upper Zone of the Rustenburg Layered Suite (SACS, 1980) on the Bushveld Complex is known to host the world‘s largest vanadium bearing titaniferous iron ores. The vanadiferous titanomagnetites, contain vanadium in sufficient concentrations (1.2 - 2.2 per cent V₂O₅) to be considered as resources and vanadium has been mined historically by a number of companies among them Anglo-American, Highveld Steel and Vanadium and VanMag Resources as well as currently by Evraz Highveld Steel and Vanadium Limited of South Africa. The titanomagnetites contain iron ore in the form of magnetite and titanium with concentrations averaging 50-75 per cent FeO and 12-21 per cent TiO₂. The titaniferous iron ores have been historically dismissed as a source of iron and titanium, due to the known difficulties of using iron ore with high titania content in blast furnaces. The economic potential for the extractability of the titaniferous magnetites lies in the capacity of the ores to be separated into iron rich and titanium rich concentrates usually through, crushing, grinding and magnetic separation. The separatability of iron oxides and titanium oxides, is dependent on the nature in which the titanium oxide occurs, with granular ilmenite being the most favourable since it can be separated from magnetite via magnetic separation. Titanium that occurs as finely exsolved lamellae or as iron-titanium oxides with low titania content such as ulvospinel render the potential recoverability of titanium poor. The Upper Zone vanadiferous titanomagnetites contain titanium in various forms varying from discrete granular ilmenite to finely exsolved lamellae as well as occurring as part of the minerals ulvospinel (Fe₂TiO₄) and titanomagnetite (a solid solution series between ulvospinel and magnetite) . Discrete ilmenite constitutes between 3-5 per cent by volume of the massive titanomagnetite ores, and between 5-10 per cent by volume of the magnetite-plagioclase cumulates with more than 50 per cent opaque oxide minerals. The purpose of this research was to investigate the mineralogical setting and distribution of the iron and titanium oxides within the magnetitite layers from top to bottom as well as spatially along a strike length of 2 000m to determine the potential for the titanium to be extracted from the titanomagnetite ores. The titanomagnetites of the Upper Zone of the Bushveld Complex with particular reference to the Northern Limb where this research was conducted contains titanium oxides as discrete ilmenite grains but in low concentrations whose potential for separate economic extraction will be challenging. The highest concentration of titanium in the magnetite ores is not contained in the granular ilmenite, but rather in ulvospinel and titanomagnetite as illustrated by the marked higher concentration of TiO₂ in the massive ores which contain less granular ilmenite in comparison to the disseminated ores which contain 3 to 8 percentage points higher granular ilmenite than the massive ores. On the scale of the main magnetite seam, the TiO₂ content increases with increasing stratigraphic height from being completely absent in the footwall anorthosite. The V₂2O₅ content also increases with stratigraphic height except for in one of the 3 boreholes where it drops with increasing height. The decrease or increase patterns are repeated in every seam. The titanomagnetites of the main magnetite seam display a variety of textures from coarse granular magnetite and ilmenite, to trellis ilmenite lamellae, intergranular ilmenite and magnesian spinels and fine exsolution lamellae of ulvospinel and ferro-magnesian spinels parallel to the magnetite cleavage. The bottom contact of the main magnetite seam is very sharp and there is no titanium or vanadium in the footwall barely 10cm below the contact. Chromium is present in the bottom of the 4 layers that constitute the main magnetite seam and it upwards decreases rapidly. In boreholes P21 and P55, there are slight reversals in the TiO₂ and V₂O₅ content towards the top of the magnetite seams.
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Mwenze, Tshipeng. "The use of chemostratigraphy and geochemical vectoring as an exploration tool for platinum group metals in the Platreef, Bushveld Igneous Complex, South Africa: a case study on the sandsloot & overysel farms." University of the Western Cape, 2014. http://hdl.handle.net/11394/4460.
Full textAbstract:
>Magister Scientiae - MScThe paucity of geochemical criteria for stratigraphic correlations and defining the styles of mineralisation pose serious problems in locating PGE-rich zones in the Platreef. This study is therefore aimed at identifying and appraising process-based mineralogical/geochemical criteria which may be useful in stratigraphic correlations and characterizing the nature and styles of PGE mineralisation. In addition, the work investigated the possible use of geochemical vectoring as a tool to locate the PGE-rich zones. Boreholes OY 482 and SS 330, drilled at the Overysel and Sandsloot farms respectively, were logged, and a total of 119 quarter cores were sampled for petrographic studies. The elemental contents in the rocks were determined by XRF and ICP-OES analyses and were evaluated using various statistical and mass balance techniques. In borehole OY 482, where the floor rock is Archaean granite, the Platreef consists of three feldspathic pyroxenite sills referred to as Lower, Middle and Upper Platreef units, from the bottom to the top, respectively. The results show that the Lower and Upper Platreef units have higher median values of Mg# (0.58 and 0.57) and Ni/Cu (0.68 and 0.75) when compared to the Middle Platreef (Mg#: 0.54 and Ni/Cu: 0.67) which may not be totally suggestive of two magmatic intrusive pulses. In borehole SS 330, where the floor rock is dolomite, the rocks consist of clinopyroxenites and olivine clinopyroxenites (variably serpentinised). These two units are intercalated with each other and are products resulting from the injection of Platreef magma sills within the dolomite floor rock. The hierarchical clustering and mass balance calculations show that when compared to the Platreef feldspathic pyroxenites, which have higher SiO2, Al2O3 and Fe2O3 median contents, the clinopyroxenites possess higher CaO median content whereas the olivine clinopyroxenites have higher MgO and LOI median contents. The PGE-rich zones (i.e. Pt+Pd) in clinopyroxenites are marked by low Ca/Mg median values, whereas in both, the olivine clinopyroxenites and the Platreef units, these zones are marked by high Mg/Fe median values. The suggested base metal index [(Cu/Zn) x (Ni/Co)] used to vector towards PGE-rich zones, which reflects the presence of the base metal sulphides (BMS), correlates with the Pt+Pd in the BMS-rich zones. This is not always the case in zones of low BMS contents which may reflect changes in the mineralogy of the BMS. In conclusion, the two boreholes studied show contrasting petrographic and geochemical attributes. This dissimilarity is mainly due to the fact that borehole OY 482 comprises Platreef magmatic rocks whereas borehole SS 330 intersected metamorphic/ metasomatic rocks.
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Sargeant, Fiona. "The seismic stratigraphy of the Bushveld Igneous Complex, South Africa." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250322.
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Otto, Tahnee. "Texture development in titaniferousmagnetites found in Layer 21 in the Bushveld Igneous Complex, South Africa." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/63292.
Full textAbstract:
Very limited studies have been conducted on titaniferous-magnetite exsolution textures and
the conditions needed for the formation of these textures. Published research surrounding
the exsolution textures consider only a particular element of the oxide, or a specific
condition. The Upper Zone of the Rustenburg Layered Suite in the Bushveld Igneous
Complex boasts 25 magnetite layers. The 21st layer counted from the Main Magnetite layer
is called Layer 21, which is the uppermost titaniferous-magnetite layer in the Upper Zone.
Uncommon exsolution textures in the titaniferous-magnetite grains were studied in order to
gain a greater understanding of the formation of oxide exsolution textures. The exsolution
texture presents itself as a three-dimensional framework of ulvöspinel-rich lamellae together
with magnetite prisms. This is called a cloth texture exsolution. The data collected for this
investigation included Scanning Electron Microscope (SEM) images, elemental weight
percentage data, and SEM line scans. Previous studies do not show exsolution textures that
are exactly similar to the exsolution textures seen in Layer 21, although the same basic type
of microtexture can be seen. This indicates that conditions such as temperature, pressure,
and oxygen fugacity, as well as the bulk mineral chemistry, plays a large role in the formation
of the exsolution texture. A rough model has been provided that considers all of the
information collected in previous studies in order to start the development of a complete
model. Another model has been provided explaining the physical appearance of the cloth
texture exsolution. The exsolution textures need to be investigated on a three-dimensional
basis in order to develop a more accurate understanding of why the titaniferous-magnetite
exsolution textures are different from location to location.Dissertation (MSc)--University of Pretoria, 2017.
Geology
MSc
Unrestricted
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Bamisaiye, Oluseyi Adunola. "Visualisation, 3D Modelling and Spatial Analysis of the Rustenburg Layered Suite, Bushveld Igneous Complex, South Africa." Thesis, University of Pretoria, 2015. http://hdl.handle.net/2263/65903.
Full textAbstract:
Adequate knowledge of the regional subsurface geometry depth relationship between the limbs and distribution of mineral zones within the Rustenburg Layered Suite (RLS) is required for better understanding of the emplacement geometry, distribution of economic mineral zones and structural evolutionary issues. This will lead to improved exploration prospects that could assist in less degradation mining activities and environmental hazard control and management. Incompleteness of surface outcrops and limited availability of seismic data has been a hindrance to this. This research focused on the determination from available borehole data, the geometry and depth relations to modern topography of the RLS. Extensive Geostatistical analysis of hundreds of borehole log data was carried out to better constrain the complex geologic structural framework and architecture of the RLS. This has helped to identify and visualize the subsurface stratigraphic units, their geometric forms and improved the understanding of the geology and structure of the RLS.Thesis (PhD)--University of Pretoria, 2015.
Geology
PhD
Unrestricted
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Fraser, Nicholas Tweedie. "A Metamorphic Study of Pretoria Group Sediments Found at the Dwarsrivier Pass, Bushveld Igneous Complex, South Africa." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/76009.
Full textAbstract:
The study takes place in the Dwarsrivier area which lies on the border between Mpumalanga and Limpopo, to the North-West of Lydenberg, at an exposed road cutting. Within the road cutting, there is a unique portion of exposed rock which is light in colour and identified as a calc-silicate. The calc-silicate material is present as a package of rock and is surrounded top and bottom by pyroxenite. The surrounding rock belongs to the Bushveld Igneous Complex (BIC), which is the largest known layered intrusion on the planet and is host to numerous mines. The sample area is within the Critical Zone of the BIC and the host rock consists of pyroxenite which is crystalline and mafic. The calc-silicate package originates from the Pretoria Group sediments, which hosts the BIC, and has undergone varying degrees of metamorphism and mineralisation. The metamorphism formed and allowed for the preservation of two rare minerals, namely wüstite and chlorospinel. Numerous tests were performed on the samples, including SEM point scans to identify these rare minerals and to better understand how the calc-silicate package was preserved in the BIC. A model was created to explain the occurrence of the calc-silicate slab and surrounding features. The previous model involved the slab rising up through the BIC, but the proposed model in this thesis is that the calc-silicate was part of the roof rock which then delaminated, and subducting into the ductile magma of the BIC.Dissertation (MSc)--University of Pretoria, 2019.
Geology
MSc
Unrestricted
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Van, Huyssteen Darryn Ashley. "Mineralogical variation in the basal Upper Zone, Bushveld Igneous Complex, South Africa: implications for ore genesis and mineral extraction." Thesis, Rhodes University, 2017. http://hdl.handle.net/10962/5060.
Full textBook chapters on the topic "Igneous rocks – South Africa – Bushveld Complex"
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Robb, L. J., L. A. Freeman, and R. A. Armstrong. "Nature and longevity of hydrothermal fluid flow and mineralisation in granites of the Bushveld Complex, South Africa." In The Fourth Hutton Symposium on the Origin of Granites and Related Rocks. Geological Society of America, 2000. http://dx.doi.org/10.1130/0-8137-2350-7.269.
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Longridge, Luke, Roger L. Gibson, and Paul A. M. Nex. "Structural controls on melt segregation and migration related to the formation of the diapiric Schwerin Fold in the contact aureole of the Bushveld Complex, South Africa." In Sixth Hutton Symposium on The Origin of Granites and Related Rocks: Proceedings of a Symposium held in Stellenbosch, South Africa, 2- 6 July 2007. Geological Society of America, 2010. http://dx.doi.org/10.1130/2010.2472(05).
Full textConference papers on the topic "Igneous rocks – South Africa – Bushveld Complex"
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Webb, S. J., G. R. J. Cooper, L. D. Ashwal, and M. W. Knoper. "The statistical and wavelet analysis of density and susceptibility measurements of the Bellevue drillcore, Northern Lobe, Bushveld Igneous Complex, South Africa." In 7th SAGA Biennial Technical Meeting and Exhibition. European Association of Geoscientists & Engineers, 2001. http://dx.doi.org/10.3997/2214-4609-pdb.143.p5.
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