M.Sc. (Geology) / The Main Reef Complex (MRC) section is developed in the Zwartkoppie and Sheba Formations of the Onverwacht and Fig Tree Group respectively. The section is represented by three shear zones, associated with a prominent anticlinal structure, locally known as the Birthday No.2 anticline. This tight isoclinal structure is marked by a chert unit, with a core of green quartz-carbonate schist, and is overlain and surrounded by greywackes and shales of the Sheba Formation. At depth the main mineralized fracture occurs to the south of, and parallel to the Birthday No.2 chert bar. Above the crest of the anticlinal structure gold mineralization is associated with three shear zones (which transgress the bedding of the greywackes and shales) known as the No .. I, No. 2 and No. 3 Fractures. Pyrite and arsenopyrite are the main ore minerals, with minor amounts of chalcopyrite, sphalerite, tetrahedrite and pyrrhotite. Pyrite mineralization is ubiquitously developed along the shear zones, while arsenopyrite mineralization is restricted to certain areas. Assay data of the greywackes and shales show that there is a correlation between gold contents and the abundance of arsenopyrite. Gold has been observed in association with all the sulphide minerals present, and as inclusions within pyrite and arsenopyrite. Electron microprobe analyses have revealed significant levels of gold in arsenopyrite, probably as submicroscopic inclusions.

Les cherts archéens permettent de contraindre les environnements primitifs qui ont vu l’apparition de la vie sur Terre. Ces roches siliceuses se forment selon trois processus : les C-cherts (cherts primaires) se forment par précipitation chimique de silice océanique sur le plancher, sous la forme d’une boue siliceuse ou en tant que ciment dans les sédiments de surface; les F-cherts (cherts de fracture) précipitent dans les fractures de la crôute depuis les fluides circulant; les S-cherts (cherts secondaires) sont issus de la silicification de roches préexistantes lors de la percolation de fluides enrichis en silice. Ces processus sont largement acceptés mais des questions majeures subsistent : comment reconnaître ces différents types de chert ? Quelle est l’origine de la silice et sous quelle forme a-t-elle précipité ? Quel signal chimique est porté par les cherts et comment s’en servir pour les reconstructions paléo-environnementales ? Ces questions sont abordées à travers trois sites de la ceinture de roches vertes de Barberton, en Afrique du Sud. L’approche adoptée combine l’analyse des structures sédimentaires et de déformation, de la pétrologie et de la composition chimique et isotopique de ces unités. Dans ces sites, la formation des cherts est étroitement liée à l’environnement de mise en place. La sédimentation clastique (turbidites) est à l’origine des C-cherts de Komati River, déposés sous la forme d’une boue siliceuse par adsorption de silice sur les particules argileuses en suspension. En absence de contribution continentale, les alternances de cherts noirs et blancs de Buck Reef sont interprétées comme issues de variations climatiques à l’échelle saisonnières (chert noir), voire glaciaires/inter-glaciaires (chert blanc). Les cherts de fracture de Barite Valley sont liés à la précipitation de silice depuis une suspension colloïdale thixotrope remontant à travers la croûte. La composition chimique des cherts est contrôlée par leur environnement de mise en place, et représente un mélange entre une phase siliceuse et une phase contaminante, indépendamment des processus qui ont précipité la silice. Les cherts de Komati River et de Barite Valley sont enrichis en Al, K, Ti, HFSE et en REE, ce qui est attribué à la contamination de la matrice siliceuse par la présence de phyllosilicate. Une telle contribution clastique peut expliquer les larges gammes de δ30Si dans les cherts de Komati River (-0.69‰à +3.89‰), et la majorité des valeurs positives est probablement liée à la contribution de l’eau de mer. Dans les dykes de Barite Valley, les δ30Si très négatifs (-4.5‰ à +0.22‰) sont cohérents avec l’origine hydrothermale basse température des fluides initiaux. A Buck Reef, l’absence de contribution continentale s’exprime dans les cherts blancs par une minéralogie exclusivement microquartzitique et par des concentrations extrêmement faibles en éléments traces (i.e. ΣHFSE et ΣREE<1ppm). 2% de carbonates et 3-4% de matériel continental (e.g. argiles) suffisent à masquer le signal siliceux dans ces cherts purs. Nous ne pouvons conclure sur la présence d’un signal océanique dans ces cherts par manque de fiabilité des proxys océaniques modernes (appauvrissement en LREE, enrichissement en La et Y). Reconnus à la fois dans des quartz océaniques, hydrothermaux, magmatiques et pegmatitiques, ils ne permettent pas d’identifier un signal d’eau de mer dans les cherts archéens. Les δ 18O de ces cherts indiquent la présence de circulations fluides secondaires à moins de 100°C, et leurs δ 30Si négatifs ou positifs (-2.23‰ et +1.13‰ en moyenne) montrent la contribution de fluides différents au moment de leur formation. Le couplage des observations pétrologiques et de terrain est la seule approche fiable pour reconnaître le mode de mise en place des cherts. Leur composition chimique dépend plus des conditions environnementales que des caractéristiques du fluide initial. / Archean cherts potentially constrain the primitive environment in which life emerged and evolved. These siliceous rocks formed by three processes : C-cherts (primary cherts) formed by the chemical precipitation of oceanic silica, either as a siliceous ooze (or silica gel) on the seabed, or as cement within still soft sediments at the surface ; F-cherts (fracturefilling cherts) precipitated from circulating fluids in concordant or crosscutting veins in the shallow crust ; S-cherts (secondary cherts) are the result of the metasomatism (silicification) of preexisting rocks during the percolation of silica-rich fluids. These processes are generally accepted but major questions remain unsolved : how to recognize various chert types ? Where does the silica come from and how did it precipitate ? What chemical signal is hosted in cherts and how can it be used for paleo environmental reconstructions ? These questions are addressed here using three sites in the Barberton Greenstone Belt, South Africa, which contain a variety of cherts deposited in very different environments. The approach combines field description of sedimentary and deformation structures, the characterization of various chert petrologies, and the study of their chemical and isotopic composition. In these three sites, chert formation strongly depends on the environmental setting. Clastic sedimentation is directly linked to C-chert formation at Komati River, where the silica was deposited as a viscous, siliceous ooze by sorption process onto suspended clay particles. A continental contribution is absent at Buck Reef, and the black and white banded cherts (C-cherts) are interpreted to have formed by chemical precipitation of oceanic silica during seasonal (black chert) and maybe glacial/inter-glacial (white chert) climatic variations. The fracture-filling cherts from Barite Valley precipitated from a thixotropic colloidal suspension that migrated upward through the crust. The chemical compositions of cherts from these three sites are essentially controlled by the environment of deposition, and represent mixtures of a siliceous and contaminant phases, independent from the silica precipitation mode. Komati River C-cherts and Barite Valley F-cherts are both enriched in Al, K, Ti, HFSE and REE, which represents the contamination by phyllosilicates of the microquartzitic fabrics. Such a clastic contribution may account for the wide range of δ30Si in Komati River cherts (-0.69‰ to +3.89‰) although the majority of positive values is attributed to seawater involvement. In the dykes, δ30Si is strongly negative (-4.5‰to +0.22‰) and is consistent with the low-temperature hydrothermal nature of these fluids. At Buck Reef, the lack of continental contribution is expressed in the white cherts, by a mineralogy exclusively composed of microquartz, and by extremely low trace element contents, i.e. HFSE and REE below 1ppm. We calculate that 2% of carbonates and 3-4% of clastic particles (i.e. clay, feldspar) would be enough to mask the silica composition in these high purity cherts. A marine signature was not recognized in their geochemistry because of the unreliability of commonly used modern proxys (i.e. LREE depletion, La and Y enrichment). These features were identified in oceanic, hydrothermal, magmatic and pegmatitic quartz and thus do not reliably identify an oceanic signal in Archean cherts. Because the δ 18O values in these white cherts indicates secondary fluid circulations at <100°C, their negative or positive δ30Si values (-2.23‰ and +1.13‰ in average) most probably represent different fluid contributions at the time they formed. The combination of field and petrological observations appears to be the most reliable approach to classify cherts and to deduce their origin, and we show here that their chemical composition depends more on the environmental conditions than on the primary fluid characteristics.

Les komatiites sont des roches volcaniques ultrabasiques caractéristiques de l'Archéen et du Protérozoïque. Nous présentons ici une étude de la pétrogénèse des komatiites de la ceinture de Barberton en Afrique du Sud. Celle-ci comprend un modèle de fusion original bâti à partir de la constatation expérimentale qu'à très forte profondeur (P>13GPa), les liquides komatiitiques sont plus denses que la péridotite solide et donc ne peuvent pas s'échapper de leur source. Nous proposons que la fusion des sources des komatiites de Barberton ait commencée à une pression supérieure à 13GPa dans le manteau mais que les liquides produits soient restés retenus dans les sources jusqu'à ce que celles-ci n'aient dépassé, au cours de leur remonté, la limite de densité à laquelle le liquide devient moins dense que le résidu solide (à ~13GPa). Alors, les liquides auraient commencé à quitter leur source, d'abord doucement, puis de plus en plus vite alors que la différence de densité entre le liquide et le résidu solide s'accroissait. Les komatiites appauvries en Al, qui sont les plus abondantes à Barberton, auraient été produites par les premiers liquides qui ont quitté la source peu après le franchissement de la limite de densité. Les liquides qui quittèrent ensuite cette même source à moins forte pression, auraient formé les komatiites enrichies en Al. Les komatiites non-appauvries en Al auraient été produites par le même mécanisme mais par des sources de température potentielle plus forte. Une étude parallèle des trois systèmes isotopiques Sm-Nd, Lu-Hf et Re-Os nous a permis de contraindre l'histoire chimique des sources de komatiites de Barberton. Les systèmes Sm-Nd et Lu-Hf indiquent des sources appauvries et le système Re-Os une source chondritique. Nous proposons que les sources des komatiites aient été appauvries par l'extraction de croûte, mais qu'ensuite, leur composition en Re et Os aient été ramenées à leur valeur chondritique par le dernier épisode massif d‟accrétion de la Terre : « le vernis tardif ». / Komatiites are ultrabasic volcanic rocks characteristic of the Archean and Proterozoic eras. In this study, we investigate the petrogenesis of the komatiites of the Barberton greenstone belt in South Africa. We present an original melting model developed on the experimental observation that, at great depths (P>13GPa), komatiitic liquids are denser than solid peridotite, and therefore cannot escape their source. We propose that the fusion of the sources of Barberton komatiites began at pressures greater than 13GPa in the mantle but that the liquids produced were retained in the sources until they crossed, during their ascent, the density limit at which the liquid becomes less dense than the residue (at ~13GPa). Then, the liquids would have started to escape their source, slowly at first, and faster and faster as the density contrast between liquid and solid residue increased. Al-depleted komatiites, which are the most common type in the Barberton belt, were produced as the first liquids that escaped the source soon after they crossed the density limit. The liquids that later escaped the same source at shallower depth, formed Al-enriched komatiites. Al-undepleted komatiites were produced by the same mechanism but from hotter sources. From complementary studies of the three isotopic systems Sm-Nd, Lu-Hf and Re-Os, we constrained the chemical history of the sources of Barberton komatiites. The Sm-Nd and Lu-Hf systems indicate depleted sources whereas the Re-Os system indicates a chondritic source. We propose that the sources of the komatiites had become depleted by the extraction of early crust, and that their compositions in Re and Os were then reset to their chondritic value by contamination by material from the last massive accretion stage of the Earth: “the late veneer”.

No description available.

Graduation date: 1985

<p> New U-Pb ages from the Barberton Mountain Land document an 800 m.y. period of Archean magmatism (ca. 3540 Ma to ca. 2740 Ma) that can be divided into five distinct episodes. Magmatic activity during Episode I includes tonalite-trondhjemite gneisses such as the Steynsdorp pluton (3509 +8/-7 Ma) and a tectonically interleaved sliver (3538 +4/-2 Ma) located at the base of the Onverwacht Group. Trondhjemitic magmatism of Episode II is synchronous with volcanism and inferred D1 thrusting of the Onverwacht Group and is represented by plutons such as the Doornhoek (3448 ± 4 Ma), Theespruit (3443 +4/-3 Ma), and Stolzburg (3459 +5/-4 Ma). A quartz-feldspar porphyry dyke, related to Episode II, intrudes the Komati Formation of the Onverwacht Group and yields an age of 3467 +12/-7 Ma. D2-related thrusting, volcanism, sedimentation, and tonalitic plutonism in the north-central part of the Barberton greenstone belt (BGB) occurred during Episode III and are recorded by an ignimbrite which was deposited between the Fig Tree and Moodies Groups during regional deformation (3227 ± 1 Ma), by pre- and post-tectonic porphyries (3227 Ma), and by the emplacement of the Kaap Valley tonalite (3227 ± 1 Ma). Episode IV is characterized by the intrusion of large sheet-like potassic batholiths to the north and south of the BGB and syenitic plutonism at ca. 3107 Ma, and by D3-related deformation at the northern margin of the BGB. Gold mineralization also appears to coincide in time with this episode. The last known period of Archean magmatic activity in the BGB is represented by late phase granite magmatism at ca. 2740 Ma (Episode V).</p> <p> Epsilon Nd values range from +1.3 to -0.7 in rocks varying in composition from gabbro to granodiorite that were emplaced during Episodes I to IV. A gabbro from the Komati Formation, with a baddeleyite age of 3352 +6/-5 Ma, has an ϵNd of +1.3, which is the only value to fall on a depleted mantle growth curve. This value is similar to ϵNd data obtained by others for ca. 3450 Ma basalts from the Onverwacht Group. Three Episode IV plutons have identical ϵNd values of -0.5, and a granite pluton from Episode V has an ϵNd of -4.3, indicating a source compatible with remelting of older crust.</p> <p> In summary, the protracted evolution of the Barberton Mountain Land occurred in a series of discrete events widely separated in time. Each event is characterized by a number of geological processes (magmatism, volcanism, sedimentation) that appear to coincide in time with thrust-related deformation as a result of compressional tectonics. The duration of the main period of crustal growth occurred over ≈365 m.y. from ca. 3470 Ma, with the formation of the main Onverwacht sequence and its associated tonalitic-trondhjemitic rocks through ca. 3230 Ma, with the intrusion of the Kaap Valley tonalite and D2 thrust-related deformation, to ca. 3105 Ma, with the widespread emplacement of sheet-like potassic batholiths bordering the Barberton greenstone belt.</p> / Thesis / Master of Science (MSc)

Impact spherules are sand-sized spherical particles that have been interpreted to have formed by the cooling, crystallization, and quenching of melt droplets condensed from vapor plumes that are created during large meteor impacts. Spherules may be deposited globally as unique marker beds, such as at the K-Pg boundary. A minimum of 11 spherule beds have been identified in the Archean and Paleoproterozoic, and provide a record of impact events that predate any known craters. This study of 3.24 Ga impact spherules from the S3 spherule layer in the Barberton Greenstone Belt (BGB) in the Kaapvaal Craton of South Africa focuses on the heterogeneity of textures and geochemistry produced during the cooling and crystallization of spherules within a vapor plume. Type 4b spherules are layered phyllosilicate spherules with discrete differences in texture and composition between the inner and outer layer, even after alteration. Compositionally layered phyllosilicate spherules were analyzed using Energy Dispersive X-ray Spectroscopy (EDS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) to measure major, trace, and rare earth element (REE) concentrations. Backscatter Electron (BSE) images and elemental X-ray maps indicate a range of compositional differences between the inner and outer layers of type 4b spherules. The majority of REE plots have nearly flat patterns, with little to no light to heavy REE fractionation; however, the outer layers consistently have higher concentrations, averaging about 10x chondritic, whereas the interiors are at or below chondritic levels with a mid-REE enrichment. The trace and REE patterns of the type 4b spherules are consistent with a more mafic inner layer and a more intermediate outer layer. Mechanisms to produce this layered texture may include: (1) accretion of less mafic material from the plume onto existing melt droplets as the plume continues to fractionate, (2) collision of melt droplets of different viscosities, (3) by differentiation within the melt droplet prior to crystallization, or (4) by diagenetic effects. Based on textures, such as distinct boundaries between layers, and compositional patterns, such as an enrichment of Ti and REE in the outer layer, the data best fits the particle collision formation mechanism hypothesis, which has important implications for impact plume studies, such as plume density, turbulence, temperature, and opacity. / Geology

Carbonaceous materials found in Archean rocks have been the source of study and controversy for the last two decades due to questions of the biogenecity of these particles. One of the key locations for these studies is the Barberton Greenstone Belt (BGB), in South Africa which contains some of the oldest known rocks on Earth, ranging in age from 3.5 to 3.2 billion years old. Preserved within the Onverwacht and Fig Tree Groups of the BGB are spherules that formed by the condensation of an impact-produced global vapor plume. The spherules are distal deposits that would have been deposited globally, but are only preserved at this location and in western parts of Australia. Like several other sediments in the BGB, there is evidence of minor amounts of carbonaceous particles contained within the spherule beds. Four individual impact events are preserved in distinct beds designated as S1, S2, S3, and S4. Due to the wide distribution of this bed in a variety of depositional settings, including both protected shallow and deep water depositional settings where there is little evidence of reworking, the S3 bed is an ideal choice for mineralogical, geochemical, and petrographic studies of impact spherules. This research examines samples from four different locations of the S3 spherule bed layer, the Barite Syncline, Maid-of-the-Mist, Sheba Mine, and Loop Road locations, in order to determine the origin of carbonaceous particles contained within the bed. Several geologic processes could account for the presence of the carbonaceous materials within the S3 spherule bed layer. These processes include: (1) Diagenetic processes, (2) Fisher-Tropsch Synthesis, (3) Microbial activity, and (4) Primary condensates from the impact plume. In order to distinguish between these processes, the spatial distribution of the carbonaceous matter was mapped, noting the mineral associations with these grains. Petrographic and electron microanalytical studies of the S3 samples reveal the presence of carbonaceous material in the sections with highly concentrated spherules, Barite Syncline, Loop Road, and Sheba Mine locations, but not in the samples from the Maid-of-the-Mist location, where there is a low concentration of spherules and abundant admixed volcanic detritus. Only Fischer-Tropsch Synthesis can be excluded as a process responsible for the origin of carbonaceous materials in the S3 beds. Though there is no direct evidence of the biogenecity of the observed carbonaceous materials, other textual observations within the S3 spherule bed are consistent with microbial activity, including Ambient Inclusion Trails and an unusual feature with a cyanobacteria-like morphology. While microbial activity cannot be ruled out as a process responsible for the origins of the carbonaceous materials, the findings of this study indicate that the carbon was mobilized from within the spherules during diagenesis. The location of carbon along spherule rims and microfractures within the spherules can also be attributed to diagenetic processes, such as fracture flow, dissolution, and replacement. A plausible explanation is that the carbon was a primary condensate from the impact plume, but has been diagenetically remobilized locally into microfractures and along the rims of the spherules. / Geology

Background: South Africa has a generalised HIV epidemic which is managed through free Antiretroviral Therapy (ART). Adherence to ART has emerged as a crucial issue in HIV/AIDS therapeutics. Purpose: The aim of the study was to explore determining factors for poor and excellent adherence to ART for HIV positive patients residing in Barberton, a mining town in Mpumalanga Province. Methodology: A generic qualitative research design was undertaken. Data was collected through in-depth qualitative interviews from a purposive sample of 13 ART patients. Qualitative interpretive analysis was employed. Findings: The study found that excellent adherence to ART is significantly associated with the availability, effectiveness and comprehensiveness of HIV services, psychological support and medical advances. Side effects of ART, opportunistic infections and alcohol and drug use hinder adherence. However, longer duration on ART enhanced self-efficacy and facilitated adherence. Successful ART is dependent on taking ARVs as prescribed and executing necessary lifestyle changes. / Health Studies / M.P.H.

Prison gangs are currently rife in South African correctional centres. Correctional officers and fellow offenders are frequently attacked by gang members, facilities are damaged and inmates are injured or killed in fights or during fires in correctional centres. Severe gang violence occurred at the Polls moor and Rustenburg correctional facilities at the end of 2016 and inexperienced correctional officers lacked the expertise to suppress the violence. This state of affairs necessitates further study into the management of prison gangs. Given the above background, this study aimed to examine how correctional facilities can suppress gang activity. The study provides an overview of the history of gangs in South Africa and shows how community gangs spread to prisons. This is followed by a meticulous documentation of the different elements of gang culture by means of observation in an effort to arm future correctional officers with knowledge regarding gangs. The findings of the observation revealed that gangs each have a unique way of greeting, using hand gestures, tattoos and verbal greetings. These communicative acts can be used as part of a strategy to prevent new offenders from becoming involved in gang activity. The observational research was confirmed by means of qualitative research. The experiences of gang members were examined by means of questionnaires to better understand the dynamic. The qualitative study was conducted at four correctional facilities, namely a maximum, medium A and medium B facility and a town youth facility. These different facilities ensured that all age groups were represented. Questionnaires were distributed to offenders who voluntarily consented to participating in the research. The literature study showed that South Africa has good legislature and policies in place, but that they have to be implemented more strictly and that the correctional officers have to be empowered by an increase in human resources and funding. In addition to capacity building, the strategic framework presented as part of the study suggests that supervision of gang members should be sharpened by for instance reconsidering the lay-out of correctional facilities. Gang members should be involved in rehabilitation programmes, which are frequently available, but not implemented. Correctional officers should be trained to manage gang members and legislation and policies should be revised frequently, as criminals tend to adjust their modus operandi continuously. The suggested framework can be of great value to the Department of Correctional Services, as managing gang activity in correctional centres can greatly change the efforts of the department to rehabilitate offenders. / Corrections Management / M. Tech. (Correctional Services Management)