Dissertations / Theses: 'Structural bushveld complex south africa'

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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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Everitt, Simon James. "Evolution of the UG2 unit, Bushveld Complex, South Africa : mineral composition and petrological evidence." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001573.

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Several disequilibrium textures are found to occur within the hanging wall and footwall of the UG2 chromitite layer of the Bushveld Complex, South Africa. These textures include plagioclase chadacrysts found included within orthopyroxene and clinopyroxene as well as the orthopyroxenes exhibiting round crystal boundaries that appear to be resorbed. Textures found within the UG2 stratigraphy such as linear boundaries and 120° triple junctions at interfaces of adjacent plagioclase or pyroxene grains also suggest that recrystallization has taken place. The presence of both disequilibrium textures and recrystallization textures would suggest that a complex emplacement history has occurred. Ideally, this would be expected to be manifested by minerals of the same type but which are texturally distinct showing different composition. However this has been found not to be the case; minerals that suggest disequilibrium textures show similar compositions to the minerals which appear to have formed in equilibrium. This is also the same for recrystallized crystals which show the same compositions as crystals that have not been recrystallized. For example tabular clinopyroxene, which has a compositional range of En 44.6 to En 50.5, is indistinguishable from clinopyroxene occuring as discontinuous rims, En 44.3-48.2, and as intergranular necking connecting primocrysts of orthopyroxene ( En 44.3-50.4). Similarly, plagioclase occurring as inclusions with An 66.3-76.0 is indistinguishable from plagioclase occurring as zoned or recrystallized interstitial grains ( An 69.0- An 77.4). Compositional variation has however, been found to be controlled to an extent by stratigraphy in that minerals show different compositions within one layer to the same minerals within another layer, consistent with an evolving magma composition. It is concluded therefore that while composition is not texturally controlled it is to an extent stratigraphy controlled and that the evidence collected within the study supports two models for the formation of chromite within the Bushveld complex. The evidence is consistent with a combination of the magma mixing model and magma injection model to account for the textures and compositional variations found within the study. The evidence may also show support for models involving late modification of minerals by magmatic fluids but not as prominently as for the models mentioned above
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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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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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Mooney, David G. "An evaluation of small scale open cast mining of UG2 in the Bushveld complex." Thesis, Rhodes University, 1997. http://hdl.handle.net/10962/d1005555.

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The current weak state of the platinum market, as well as the large inventory of platinum group metals held by Russia, necessitates that the South African platinum mining industry must carefully evaluate the benefits and disadvantage of small-scale mining of shallow, open castable ore resources. Until the late 1980's, these resources were ignored due to the metallurgical complexities of treating oxidized ore, as well as the mind set that existed within the South African mining industry which militated against open cast mining in the Bushveld. During the latter part of the 1980's and early 1990's, advances in the metallurgical treatment of oxidized ore, specifically the UG2, as well as operational problems, created the impetus to begin the exploitation of these resources. Small-scale open cast mining has become viable due to the development of suitable mining methods that facilitate mining practices acceptable to the Department of Mineral and Energy Affairs, in terms of environmental legislation. Metallurgical advances and growing experience, especially with respect to the UG2, enables reasonable platinum group metals recovery from oxidized ore. The problems experienced in doing this can, and are being overcome. With growing public awareness of environmental issues, particularly related to the mining industry, the requirement to ensure that the small-scale open cast mine site is well managed is paramount. A methodology for the evaluation is presented along with a case study of a small-scale UG2 open cast pit. Evidence is presented that shows that these small-scale open cast mining operations are extremely profitable and require minimal capital expenditure. However, caution is advised when evaluating Merensky Reef open cast operations because of the problems that they present.

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Teigler, Bernd. "Mineralogy, petrology and geochemistry of the lower and lower critical zones, Northwestern Bushveld Complex." Thesis, Rhodes University, 1991. http://hdl.handle.net/10962/d1005590.

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This study of the lower part of the Rustenburg Layered Suite in the Western Bushveld Complex is based mainly on drill core samples from three localities, which are approximately 130 km apart. The NG-sequence, situated in the northwestern sector of the complex (Union Section, R.P.M.) extends from the floor of the complex to the base of the upper Critical Zone. The sequence is ca. 1800 m thick and it comprises mainly ultramafic cumulates, namely pyroxenites, olivine pyroxenites, harzburgites and dunites. Norites and anorthos ites are present only in minor proportion. Within the upper half of the NG-sequence ten prominent chromitite layers are correlated with the LGI MG4-interval. Correlation is also established between published sequences and the two other sequences studied, located 8 km and 55 km, respectively, east of Rustenburg. Whole-rock chemical data (major and trace elements), microprobe and Sr isotope data are presented. Petrographic studies provide modal analyses and measurements of grain size. All petrographic, mineralogical and other geochemical data point to an origin of the cumulates of the NG-sequence by crystallization from liquids of the U-type lineage and derivatives thereof. No evidence is found for the involvement of parental liquids with a distinctly different composition or crystallization order (A-liquids). However, subtle compositional variations of the parental liquids are evident in slight changes of the Cr content in orthopyroxene or in variations of Sr isotope ratio. The NG-sequence is characterized by intervals with reversed fractionation trends caused by repeated influxes of pristine magma (during periods of high magmatic activity) resulting in a high degree of rejuvenation. These intervals are overlain by others with a normal fractionation trend, interpreted as cumulates formed in periods with low or no magmatic activity, in which fractional crystallization controlled bulk composition of the evolving liquid. The Lower Zone in the NG-sequence is dominated by a progressive shift towards more primitive compositions, while in the Critical Zone fractionation was the major operating process in the magma chamber. However, during deposition of the pyroxenitic lower Critical Zone several replenishment events occurred, during which fresh Cr-rich magma was emplaced. Massive chromitite layers were deposited after mixing between the newly emplaced magma and the resident residual liquid shifted bulk compositions into the primary field of chrome-spinel. Cumulus plagioclase crystallized after bulk composition of the residual liquid was driven to the orthopyroxene plagioclase cotectic by continued fractional crystallization; this occurred once in the Lower Zone, yielding a single, thin norite layer, and again in the upper Critical Zone of the NG-sequence. A facies model is proposed based on the stratigraphic and compositional variations along strike in the Western Bushveld Complex. This model explains the variations by means of the position of the sequence with regard to a feeder system. The olivine- and orthopyroxene-rich, but plagioclase-poor NG-sequence represents the proximal facies, while the SF-sequence (poor in ferromagnesian phases, but plagioclase-rich) is developed as a distal facies, close to the Brits graben.

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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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Mitchell, Andrew Alexander. "The petrology, mineralogy and geochemistry of the main zone of the Bushveld Complex at Rustenburg Platinum Mines, Union Section." Thesis, Rhodes University, 1988. http://hdl.handle.net/10962/d1001563.

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Union Section of Rustenburg Patinum Mines is situated in the northwestern part of the Bushveld Complex, some twenty kilometres north of the Pilanesberg Alkaline Complex. The mining lease area covers a roughly triangular segment of Lower, Critical and Main Zone rocks, transgressed to the north and south by magnetite-bearing ferrogabbro of the Upper Zone. The Main Zone at Union Section is the focus of this study. The prime source of sample material for the study is the deep exploration borehole SK2, but additional, supplementary samples were collected on surface and underground, as well as from a second surface exploration borehole, SK4. In line with the recommendations of SACS (1980), the top of the Critical Zone, and therefore the base of the Main Zone, is taken to be the top of the Bastard Cyclic Unit. Sharpe (1985) suggested that the succession from the base of the Main is an isotopically separate entity Zone up to the Pyroxenite Marker from the rest of the Bushveld layered succession. This is not strictly true, as there is evidence that more than one parental magma was involved in the formation of this interval. It is, however, true that there are fundamental differences, particularly in isotopic makeup, between the Main Zone rocks below the pyroxenite Marker and those above (the latter having been assigned by Molyneux (1970) to subzone C of the Main Zone). Kruger et al. (1986, in press) suggested that the Pyroxenite Marker marks the base of the Upper Zone, and this convention is adhered to here. The implication of this is that the rocks which formerly constituted subzone C of the Main Zone are now considered part of the Upper Zone. The Main Zone rocks below the pyroxenite Marker were originally subdivided by Molyneux (1970) into two subzones, A and B. The results of the present study indicate that this subdivision is not justified. Instead, eight units have been distinguished in the Main Zone on geochemical, petrological and mineralogical bases. Each of these units is characterized by a coherent set, or progression, of chemical and petrological characteristics. The specific assignment of genetic connotations to these units has been deliberately avoided , at least until further studies of the Main Zone prove this to be justified. The demarcation of the eight units is illustrated in the composite diagram (Fig. 34) in the back pocket of this work, and the reasons for the subdivisions are listed in Table 6 (at the end of chapter 7 of this thesis). Until the late 1970's, it was thought that most layered cumulates formed by crystal settling (Wager and Brown, 1968). More recently, there has been a fundamental conceptual change, and many workers now believe that most cumulate rocks formed by in situ crystallization at the floor and walls of the magma chamber (McBirney and Noyes, 1979, Irvine, 1980a; Campbell, 1987). There is, however, some evidence for the physical separation of phases undergoing cotectic crystallization, particularly in the Upper Critical Zone and lower part of the Main Zone (Eales et al., 1986). This process, which has been alluded to in the past by various authors (Ferguson and Botha, 1963; Vermaak, 1976) involves the flotation of early-formed plagioclase crystals due to their positive bouyancy in tholeiitic liquids. The result is an apparent decoupling of the chemistry of pyroxene and plagioclase, as in unit IV of the Main Zone, where plagioclase becomes more anorthitic upwards, whilst pyroxene becomes more iron-rich. There is some substantial evidence, particularly in reversals in the strontium isotope initial ratio and the orthopyroxene Mg/(Mg+Fe) ratio , for multiple intrusion in the Main Zone. Although the largest and most important magma influx in the Main Zone was a high-R₀ aluminous tholeiite, as suggested by Sharpe (1985), the intrusive history of the Main Zone is believed to be far more complex than Sharpe (op. cit.) suggested. Significantly, there is strong evidence for small influxes of Upper Zone-type (Fe-rich tholeiite) magma in the upper reaches of the Main Zone. These are believed to be precursors to the major influx of Upper Zone-type magma at the pyroxenite Marker (Kruger et al, 1986, in press). The fate of intercumulus liquids in cumulate rocks has recently recieved substantial attention (Sparks et al., 1985; Morse, 1986; Barnes, 1986: Campbell, 1987). It is believed that the migration, or at least redistribution, of intercumulus liquids has played a vital role in modifying fractionation trends in the Main Zone. More importantly, the accumulation of late-stage intercumulus liquids is believed to be responsible for the formation of the Fe-rich ultramafic pegmatite bodies that interrupt the layered cumulates in borehole SK2
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Koegelenberg, Corne. "Experimental evidence for sulphide magma percolation and evolution : relevant to the chromite bearing reefs of the Bushveld Complex." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20043.

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Thesis (MSc)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Pt mineralization within the Bushveld Complex is strikingly focused on the chromitite reefs, despite these horizons being associated with low volumes of base metal sulphide relative to Pt grade. Partitioning of Pt (Dsil/sulp) from silicate magma into immiscible sulphide liquid appears unable to explain Pt concentrations in chromitite horizons, due to the mismatch that exists between very large R factor required and the relevant silicate rock volume. Consequently, in this experimental study we attempt to gain better insight into possible Pt grade enhancement processes that may occur with the Bushveld Complex (BC) sulphide magma. We investigate the wetting properties of sulphide melt relevant to chromite and silicate minerals, as this is a key parameter controlling sulphide liquid percolation through the cumulate pile. Additionally, we have investigated how fractionation of the sulphide liquid from mono-sulphide-solid-solution (Mss) crystals formed within the overlying melanorite might affect sulphide composition and Pt grades within the evolved sulphide melt. Two sets of experiments were conducted: Firstly, at 1 atm to investigate the phase relations between 900OC and 1150OC, within Pt-bearing sulphide magma relevant to the BC; Secondly, at 4 kbar, between 900OC to 1050OC, which investigated the downwards percolation of sulphide magma through several layers of silicate (melanorite) and chromitite. In addition, 1atm experiments were conducted within a chromite dominated chromite-sulphide mixture to test if interaction with chromite affects the sulphide system by ether adding or removing Fe2+. Primary observations are as follows: We found sulphide liquid to be extremely mobile, the median dihedral angles between sulphide melt and the minerals of chromitite and silicate layers are 11O and 33O respectively. This is far below the percolation threshold of 60O for natural geological systems. In silicate layers sulphide liquid forms vertical melt networks promoting percolation. In contrast, the extremely effective wetting of sulphide liquid in chromitites restricts sulphide percolation. Inter-granular capillary forces increase melt retention, thus chromitites serve as a reservoir for sulphide melt. Sulphide liquid preferentially leaches Fe2+ from chromite, increasing the Fe concentration of the sulphide liquid. The reacted chromite rims are enriched in spinel end-member. This addition of Fe2+ to the sulphide magma prompts crystallization Fe-rich Mss, decreasing the S-content of sulphide melt. This lowers Pt solubility and leads to the formation of Pt alloys within the chromitite layer. Eventually, Cu-rich sulphide melt escapes through the bottom of the chromitite layer. These observations appear directly applicable to the mineralized chromitite reefs of the Bushveld complex. We propose that sulphide magma, potentially injected from the mantle with new silicate magma injections, percolated through the silicate cumulate overlying the chromitite and crystallized a significant volume of Fe-Mss. Chromitite layers functioned as traps for percolating, evolved, Cu-, Ni- and Pt-rich sulphide liquids. This is supported by the common phenomenon that chromitites contain higher percentages of Ni, Cu and Pt relative to hanging wall silicate layers. When in contact with chromite, sulphide melt is forced to crystallize Mss as it leaches Fe2+ from the chromite, thereby further lowering the S-content of the melt. This results in precipitation, as Pt alloys, of a large proportion of the Pt dissolved in the sulphide melt. In combination, these processes explain why chromitite reefs in the Bushveld Complex have Pt/S ratios are up to an order of magnitude higher that adjacent melanorite layers.
AFRIKAANSE OPSOMMING: Pt mineralisasie in die Bosveld Kompleks is kenmerkend gefokus op die chromatiet riwwe, alhoewel die riwwe geassosieer is met lae volumes basismetaal sulfiedes relatief tot Pt graad. Verdeling van Pt (Dsil/sulp) vanaf silikaat magma in onmengbare sulfiedvloeistof is klaarblyklik onvoldoende om Pt konsentrasies in chromatiet lae te verduidelik, a.g.v. die wanverhouding wat bestaan tussen ‘n baie groot R-faktor wat benodig word en die relatiewe silikaat rots volumes. Gevolglik, in die eksperimentele studie probeer ons beter insig kry oor moontlike Pt graad verhogingsprosesse wat plaasvind in die BK sulfied magma. Ons ondersoek die benattingseienskappe van sulfied vloeistof relevant tot chromiet- en silikaat minerale, omdat dit die sleutel maatstaf is vir die beheer van sulfied vloeistof deursypeling deur die kumulaat opeenhoping. Addisioneel het ons ook ondersoek hoe die fraksionering van sulfied vloeistof vanaf MSS kristalle, gevorm binne die hangende melanoriet muur, moontlik die sulfied samestelling en Pt graad binne ontwikkelde sulfied smelt kan beïnvloed. Twee stelle van eksperimente is gedoen: Eerstens, by 1 atm om ondersoek in te stel oor fase verwantskappe tussen 900OC en 1150OC, binne ‘n Pt-verrykte sulfied magma samestelling relevant tot die BK; Tweedens, by 4 kbar, tussen 900OC tot 1050OC, wat die afwaartse deursypeling van sulfied magma deur veelvuldige lae van silikaat minerale en chromatiet. Addisionele 1 atm eksperimente is gedoen binne ‘n chromiet gedomineerde chromiet-sulfied mengsel, om te toets of interaksie met chromiet die sulfied sisteem affekteer deur Fe2+ te verwyder of by te dra. Primêre observasies is soos volg: Ons het bevind sulfiedsmelt is uiters mobiel, die mediaan dihedrale hoek tussen sulfiedsmelt en minerale van chromiet en silikaat lae is 11O en 33O onderskydelik. Dit is ver onder die deursypelings drumpel van 60O vir natuurlike geologiese stelsels. In silikaatlae vorm die sulfiedsmelt vertikale netwerke wat deursypeling bevorder. Inteendeel, uiters effektiewe benatting van sulfiedsmelt binne chromatiete vertraag sulfied deusypeling. Tussen kristal kapilêre kragte verhoog smelt retensie, dus dien chromatiete as ‘n opgaarmedium vir sulfiedsmelt. S oorversadigte sulfied vloeistof loogsif Fe2+ vanuit chromiet en veroorsaak ‘n verhoging in Fe-konsentraie. Die gereageerde chromiet buiterante is daarvolgens verryk in Cr-spinêl eind-ledemaat. Die addisionele byvoeging van Fe2+ aan sulfied magma veroorsaak die kristalisasie van Fe-ryke Mss en verlaag dus die S-konsentrasie van die sulfied smelt. Dit verlaag Pt oplosbaarheid en lei tot die formasie van Py allooie binne-in chromatiete. Ten einde, ontsnap Cu-ryke sulfied smelt deur die onderkant van die chromatiet lae. Die observasies is direk van toepassing op die gemineraliseerde chromatiet riwwe van die Bosveld Kompleks. Ons stel voor dat sulfied magma, potensiaal ingespuit vanuit die mantel saam nuwe inspuitings van silikaat magma, deur die hangende silikaat kumulaat bo chromatiet lae deurgesypel het en ‘n betekenisvolle volume Fe-Mss gekristalliseer het. Chromatiet lae het gefunksioneer as lokvalle vir afwaartsbewegende, ontwikkelde, Cu-, Ni-, en Pt-ryke sulfied vloeistowwe. Dit word ondersteun deur die algemene verskynsel dat chromatiete hoër persentasies van Ni, Cu en Pt relatief teenoor die hangende muur silikaat lae het. Wanneer sulfied smelt in kontak is met chromiet, word dit geforseer om Mss te kristalliseer soos Fe2+ geloogsif word, waarvolgens die smelt se S konsentrasie verder verlaag word. Dit veroorsaak die presipitasie, as Pt allooie, van groot proporsies opgeloste Pt vanuit sulfied smelt. Deur die prosesse te kombineer, kan dit moontlik verduidelik word hoekom chromatiet riwwe in die Bosveld Kompleks Pt/S verhoudings veel hoër is as aanrakende melanoriet lae.

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10

De, Klerk William Johan. "Petrogenesis of the upper critical zone in the Western Bushveld Complex with emphasis on the UG1 Footwall and Bastard units." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005598.

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This study is an account of the stratigraphic sequence, the petrography, mineralogy (microprobe investigations of orthopyroxene, clinopyroxene, olivine and plagioclase feldspar), and whole-rock major- and traceelement geochemistry of the silicate cumulates of the Upper Critical Zone in the western Bushveld Complex. Two parts of the study - an investigation of a 350m column incorporating the MG3 and UGI Footwall Units, and a comparison of two additional Upper Critical Zone profiles with a previously compiled profile between the UGI and Bastard Units - are focused on RPM Union Section in the northwestern sector of the Complex. The third part is a detailed vertical and lateral investigation of the Bastard Unit at the top of the Critical Zone, which draws on sampling and data compilation from seventeen profiles in the western limb of the Complex. The MG3 Unit (45m) is made up of a lower chromitite layer overlain by a norite-pyroxenite-anorthosite sequence while the UGlFW Unit (295m) is composed of a related series of lower chromitite layers (MG4) overlain by a pyroxenite-norite-anorthosite sequence capped by the UGI chromitite layer. These mafic cumulates display a distinctive pattern of oscillating cryptic variation in whole-rock Mg/(Mg+Fe), FeO/Ti0₂, Cr/Co and Ni/V ratios through the sequence. Sympathetic oscillations are recorded for compositions of orthopyroxene and plagioclase feldspar and eight subcycles are recognised through the UGlFW Unit. The entire sequence is characterised by the presence of small, spheroidal, embayed and irregularly shaped plagioclase grains which are poikilitically enclosed in cumulus orthopyroxene grains of both pyroxenites and norites. This texture is indicative of partial resorption of pre-existing feldspar primocrysts within the melt prior to their being incorporated into the host orthopyroxene grains. Textural, geochemical and isotopic data suggest that this sequence was built up by periodic additions of fresh, relatively primitive liquid into fractionated resident liquid, and subsequent mixing within the magma chamber. The Bastard Unit sequence, described in Chapter 4, is the last and most complete cyclic unit (c. 60m) of the Critical Zone, and its upper contact defines the boundary between the Critical and Main Zones of the Complex. This Unit can conveniently be sub-divided into a lower part, where orthopyroxene occurs as a cumulus phase, and the upper part which is composed entirely of anorthosite (Giant Mottled Anorthosite). The basal part of the Unit (≤ 18m) comprises a thin chromitite layer < O.5cm) overlain by a pyroxenite-melanorite-norite-leuconorite sequence. The basal pyroxenite is orthocumulate in character and rapidly gives way to norites and leuconorites. A distinct threefold subdivision emerges within the Giant Mottled Anorthosite which is predominantly an adcumulate which becomes orthocumulate in character at its top. Apart from minor deviations in thicknesses these lithologies are recorded over the entire strike-length covered in this study. Profiles of cryptic variation are compiled for orthopyroxene, plagioclase and whole-rock data and show that the Bastard Unit displays a characteristic pattern which is maintained throughout the western Bushveld Complex. A minor yet distinctive reversal in cryptic variation is revealed at a level which is stratigraphically variable within the lower Giant Mottled Anorthosite, and results in a double cuspate pattern. A remarkable feature of the basal Bastard pyroxenites is that although the modal proportion of mafic to felsic constituents varies systematically away from the northwestern sector, the Mg/(Mg+Fe) ratio of orthopyroxenes remains constant at 0.804 over a lateral strike distance of 171km. Within the upper part of the Unit the orthopyroxene is markedly Fe-rich and it is here that inverted primary pigeonite appears for the first time as a cumulus phase. In addition, K-feldspar, oscillatory zoned plagioclase grains and high levels of incompatible trace elements are noted at this level. On the basis of the data presented it is concluded that the Bastard Unit represents the crystallisation of a final, relatively large influx of hotter primitive liquid, with upper Critical Zone affinities, and subsequent mixing with a column of cooler (less dense) supernatant liquid which had in part hybridized with the overlying Main Zone magma. It is hypothesised that this new liquid was emplaced as a basal flow beneath supernatant liquid and that it initiated the deposition of mafic cumulates at its base. The supernatant liquid is interpreted as representing the fractionated residuum produced by crystallisation of earlier cyclic units, with plagioclase on the liquidus, and that it contained an abundance of small plagioclase primocrysts in suspension. Development of the Unit can be viewed as a two-stage process. In the lower half of the unit, chemical and physical parameters typical of the new magma dominated the crystallisation process, and resulted in cumulates very similar to other relatively complete Upper Critical Zone units. In the upper, leucocratic sequence, above a minor reversal, crystallisation was from a liquid which was the product of mixing of a minor pulse of primitive liquid with the reservoir of hybridized supernatant liquid. Although the Bastard Unit is not continuous around the entire Western limb of the Complex, it is concluded that it developed in a single, or connected, magma chamber and that its irruptive feeder zone was located in the proximal northwestern facies of the Complex.

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11

Doig, Heather Leslie. "Strike comparison of the compositional variations of the lower group and middle group chromitite seams of the critical zone, Western Bushveld complex." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005618.

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The variations in the composition, specifically the Cr20 S content and the Cr:Fe ratio, and the morphology of the Lower Group (LG) and Middle Group (MG) chromitite seams of the Critical Zone (CZ) across the western Bushveld Complex, including the Ruighoek and Brits sections, is investigated by means of whole-rock chemical data, both major and trace elements analysis, XRD and electron microprobe data. As a result ofthe paucity of exposed or developed LG1 - LG5 chromitite seams in the western Bushveld Complex, this study is confined to the investigation of the compositional variations of the LG6 to MG4 chromitite seams. In only one section, the Ruighoek section, was the entire succession of chromitite seams, from the LG1 - MG4, exposed. The silicate host rocks from the LG6 pyroxenite footwall to the collar of the CC2 drillcore (lower uCZ) in the Rustenburg section were sampled. This study reviews the compositional trends of the silicate host rocks, as the compositional variations of the chromitite seams reflect the chemical evolution of the host cumulate environment and, to a lesser degree, the composition onhe interstitial mineral phases in the chromitite seams. The compositional variations of the LG and MG chromitite seams are attributed to the compositional contrast between the replenishing magma and the resident magma. The chemical trends of the LG and MG chromitite layers and the host cumUlate rOCKS do not support the existence of two compositionalfy dissimilar magmas in the CZ, rather the cyclic layering of the CZ and the chemical variations of the chromitite seams are attributed to the mixing of primitive magma with the resident magma, both of which have essentially similar compositions. The compositional variations of the LG and MG chromitite seams along strike away from the supposed feeder site (Union section) to the distal facies (Brits section) are attributed to the advanced compositional contrast between the resident magma and the replenishing primitive magma pulses. The CZ is characterized by reversals in fractionation trends and this is attributed to the compositional evolution of the parental magma and not to the replenishment of the resident magma by influxes of grossly dissimilar magma compositions. The Cr20 S content and the Cr:Fe ratio of the MG chromitite layers increase from the Ruighoek (near proximal) section to the Brits section (distal facies). This is attributed to the advanced compositional contrasts between the resident magma and the replenishing primitive magma. In contrast, the Cr20 3 content and Cr:Fe ratios ofthe LG6 and LG8a chromitite seams decreases eastwards from the Ruighoek section. The average Cr:Fe ratio for the western Bushveld Complex is between 1.5 and\2.0, nonetheless, a progressively lower Cr:Fe ratio is noted from the LG1 chromitite up through to the MG4 chromitite seam in the Ruighoek section. tn the LG2 - LG4 chromitite interval a deviation to higher.lratios is encountered. A progressive substitution of Cr by AT and Fe in the Cr-spinel crystal lattice characterizes the chromitite succession from the LG1 seam up through the chromitite succession to MG4. The petrogeneSiS of the chromitite seams of the CZ is attributed to magma mixing and fractional crystallization of a single magma type.

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12

Mavimbela, Philane Knowledge. "Metamorphism in the contact aureole of the eastern limb of the Bushveld complex, South Africa." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/41190.

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The 2.06 to 2.054 Ga Bushveld Igneous Complex intruded into the sedimentary rocks of the Transvaal Supergroup and generated an extensive contact metamorphic aureole mainly developed in the upper Pretoria group. The studied samples represent the Silverton Daspoort and Timeball Hill formations and are divisible into garnet bearing hornfels (DY918, DY954 and DY956) and garnet-free staurolite-bearing metapelites (DY916, DY982 and DY987). The garnet-bearing hornfelses marks the garnet zone within the aureole and the garnet formation is controlled by different reactions forming from 490 to 630 0C. On the other hand, the garnet free staurolite-bearing Fe-Al rich metapelites define the staurolite zone restricted to the Timeball Hill formation. The recorded P-T conditions in G0 and G1 garnets of the DY954 hornfels imply that the two garnets formed under different conditions indicating two stages of metamorphism. However, the Lu-Hf isotope systematics of these garnets records a 2061 Ma age for all garnet porphyroblasts in both the DY918 and DY954 hornfelses, which support co-genetic garnet growth regardless of their stratigraphic positions. Therefore, the 2061 Ma garnet age denote the emplacement age of the Lower Zone and Critical Zone magmas which was synchronous with the extrusion of the Rooiberg Group volcanics. The fact that all analysed garnets do not record the 2059 – 2054 intrusion of the Main Zone and Upper Zone magmas probably means that the crystallisation temperatures of the later magma pulse was not significant enough to shift the Lu-Hf isotopic signatures. Euhedral staurolites are widespread within the Fe-Al rich metapelites with grain sizes of up 4mm; texturally the majority of them have been altered or overgrown by biotite and chloritoid. The alteration or of these staurolite porphyroblasts is due to isobaric cooling during uplift, and the St-Bt assemblage represent the peak equilibrium conditions and marks the upper stability limit of the Chl-Ctd assemblage.
Dissertation (MSc)--University of Pretoria, 2013.
gm2014
Geology
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13

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.

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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
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14

Smith, Jennifer Williamina. "The nature and origin of PGE mineralization in the Rooipoort area, northern Bushveld Complex, South Africa." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/31995.

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The Grasvally Norite-Pyroxenite-Anorthosite (GNPA) member within the northern limb of the Bushveld Complex is a PGE-Ni-Cu mineralized, layered package of mafic cumulates. This magmatic sulfide deposit is developed at the equivalent stratigraphic position to the Platreef, being overlain by Main Zone gabbronorites and in places resting unconformably on metasediments from the Transvaal Supergroup. Parental magmas to the GNPA member were of a ‘hybrid’ composition containing both B1 and B2/B3 type magma components which were strongly crustally contaminated and S saturated at the time of emplacement. At depth, the assimilation of crustal S was crucial for ore genesis. Although parental magma(s) experienced a second localised contamination event, interaction with the local footwall at the time of emplacement, did not have any control on the genesis of sulfide mineralization. A single primary sulfide liquid, enriched in PGE, Ni, Cu and semi-metals was distributed throughout the succession during multiphase emplacement of the GNPA member. The distribution and mineralogy of platinum-group and chalcophile elements results from the complex behaviour of these elements during both sulfide fractionation and hydrothermal processes. The primary assemblage is characterised by IPGE-rich pyrrhotite, IPGE-, Rh, and Pd-rich pentlandite, chalcopyrite, and associated Pt-As and Pd-Bi-Te minerals. Secondary assemblages in addition contain Pd- and Rh-rich pyrite and millerite, and discrete minerals including Pd antimonides and arsenides. Whilst correlations between the GNPA/Platreef and Upper Critical Zone remain relatively speculative, the northern limb deposits are thought to have formed from compositionally similar or related magmas, which were poorer in Mg, richer in Ca and Fe and Pd dominant relative to the magma(s) that formed the Upper Critical Zone. It is proposed that with depth the Platreef may progressively transform into a layered succession that is exposed south of the Ysterberg-Planknek Fault and represented by the GNPA member. The Platreef can therefore possible be viewed as a marginal facies of the GNPA member, and sulfide-rich magma which escaped up the margins of the northern limb chamber.

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15

Letsoele, Christopher Sbusiso. "The occurrences of ultramafic pegmatites at Dwarsrivier Mine, Lower Critical Zone, Eastern Bushveld Complex, South Africa." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/63298.

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This study presents a detailed petrological and geochemical investigation of the concordant ultramafic pegmatites of the Lower Critical Zone at Dwarsrivier Mine, in the eastern Bushveld Complex. The pegmatites are coarse-grained and of variable size and mineralogy. They occur within the LG-6 chromitite layer as well as in the silicate rocks of the Rustenburg Layered Suite. Field observations into their occurrence, and their association with the LG-6 chromitite layer, suggest that the pegmatites intrude, deform and disrupt the LG-6 chromitite. The mineralogy of the pegmatites is similar as the surrounding pyroxenite rocks, although they are texturally different from the surrounding pyroxenite host rocks. They comprise variable amounts of clinopyroxene, orthopyroxene, olivine, plagioclase, biotite and accessory amphiboles. Based on dominant mineralogy, the pegmatites can be grouped into clinopyroxene-, orthopyroxene- and olivine-rich pegmatites. The major and trace element composition of the pegmatites is different from the surrounding pyroxenite host rocks. The whole rock geochemistry of the pegmatites indicate that the pegmatites have a slightly higher concentration of incompatible trace elements compared to the pyroxenite host rocks, although compositional overlaps exist. Whole rock Mg# and trace element ratios suggests that the pegmatites are the products of less fractionated liquid(s) than their surrounding pyroxenite rocks. When the whole rock geochemical data of the pegmatites are compared to other similar concordant pegmatites in the eastern Bushveld Complex, as well as the discordant pegmatites from the western Bushveld Complex, it is established that the pegmatites at Dwarsrivier mine are not genetically related to the discordant, intrusive iron-rich pegmatites. They are also different from the concordant pegmatites found elsewhere in the eastern Bushveld Complex. The pegmatites are interpreted as the products of a volatile-rich melt which promoted the recrystallization or sub-solidus enlargement of the pyroxenes. The occurrence of cumulus olivine at the stratigraphic position of the Lower Critical Zone is exceptional. Olivine crystalized as a result of continuous phase shifts within the pegmatite melt. Some of the pegmatites are serpentinised by late hydrothermal fluids. The olivine-rich pegmatites display the most prominent serpentinisation, and are composed of a mineral assemblage dominated by serpentine and magnetite.
Dissertation (MSc)--University of Pretoria, 2017.
Assmang Dwarsrivier Mine
Geology
MSc
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16

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.

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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
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17

Twala, Mthokozisi Nkosingiphile. "Use of multispectral remote sensing data to map magnetite bodies in the Bushveld Complex, South Africa : a case study of Roossenekal, Limpopo." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/75756.

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Mineral detection and geological mapping through conventional ground survey methods based on field observation and other geological techniques are tedious, time-consuming and expensive. Hence, the use of remote sensing in mineral detection and lithological mapping has become a generally accepted augmentative tool in exploration. With the advent of multispectral sensors (e.g. ASTER, Landsat and PlanetScope) having suitable wavelength coverage and bands in the Shortwave Infrared (SWIR) and Thermal Infrared (TIR) regions, multispectral sensors, along with common and advanced algorithms, have become efficient tools for routine lithological discrimination and mineral potential mapping. It is with this paradigm in mind that this project sought to evaluate and discuss the detection and mapping of magnetite on the Eastern Limb of the Bushveld Complex, using specialized common traditional and machine learning algorithms. Given the wide distribution of magnetite, its economic importance, and its potential as an indicator of many important geological processes, the delineation of magnetite is warranted. Before this study, few studies had looked at the detection and exploration of magnetite using remote sensing, although remote sensing tools have been regularly applied to diverse aspects of geosciences. Maximum Likelihood, Minimum Distance to Means, Artificial Neural Networks, Support Vector Machine classification algorithms were assessed for their respective ability to detect and map magnetite using the PlanetScope Analytic Ortho Tiles in ENVI, QGIS, and Python. For each classification algorithm, a thematic landcover map was attained and an error matrix, depicting the user's and producer's accuracies, as well as kappa statistics, was derived, which was used as a comparative measure of the accuracy of the four classification algorithms. The Maximum Likelihood Classifier significantly outperformed the other techniques, achieving an overall classification accuracy of 84.58% and an overall kappa value of 0.79. Magnetite was accurately discriminated from the other thematic landcover classes with a user’s accuracy of 76.41% and a producer’s accuracy of 88.66%. Despite the Maximum Likelihood classification algorithm illustrating better class categorization, a large proportion of the mining activity pixels were erroneously classified as magnetite. However, this observation was not merely limited to the Maximum Likelihood classification algorithm, but all image classifications algorithms. The overall results of this study illustrated that remote sensing techniques are effective instruments for geological mapping and mineral investigation, especially in iron oxide mineralization in the Eastern Limb of Bushveld Complex.
Dissertation (MSc)--University of Pretoria, 2019.
Geology
MSc
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18

Botha, Pieter W. S. K. "The mineralogy and geochemistry of the Rooikoppies iron-rich ultramafic pegmatite body, Karee Mine, Bushveld Complex, South Africa [electronic resource] /." Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-01272009-172307/.

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19

Maier, Wolfgang Derek. "Geochemical and petrological trends in the UG2-Merensky unit interval of the upper critical zone in the Western Bushveld Complex." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005563.

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One of the most remarkable features of the layered sequence of the Bushveld Complex is its lateral consistency in lithology. This work has established a geochemical and lithological correlation along 170 km of strike of the interval between the UG2 chromitite and the Merensky Reef within the Upper Critical zone of the western limb of the Bushveld Complex. The correlation is based on geochemical investigations of 10 borehole intersections and lithological comparisons of more than 20 borehole intersections around the western lobe of the complex. The basic data presented include 123 whole-rock analyses for major and 12 trace elements, 97 analyses for ' 12 trace elements, and ca. 5500 microprobe analyses of all major phases. Patterns of cryptic variation are established. Some layers (the UG2 chromitite and pyroxenite) show considerable consistency with regard to geochemistry and lithology. Others can be traced along most of the investigated strike length, such as the Lone Chrome Seam, the Footwall Marker anorthosite and the immediate anorthosite footwall to the Merensky Unit. Most of the distinguishable members within the study section, however, show great variation along strike (i.e., the Lower and Upper Pseudoreef Markers, the central noritic sequence in the southern arm of the western limb and parts of the immediate Merensky Reef footwall succession). Several models have been evaluated to interpret the geochemical and lithological data. The author comes to the conclusion that the degree of lithological consistency depends on the variability of magmatic parameters within different parts of the chamber. The most important of these parameters are: (i) the size of fresh primitive influxes and consequently the heat flux, (ii) the composition of the residual liquid, and (iii) the frequency of the influxes. Fresh influxes of more or less similar composition thus spread out along the floor if the residual liquid was less dense than the fresh primitive liquid, but intruded the chamber as a plume where plagioclase had crystallized for some time and the residual liquid had become relatively dense. The size of the influx may be regarded as a measure of the amount of heat flux from the feeder into the chamber. A large influx created uniform physicochemical conditions in the chamber whereas a smaller influx created a strong lateral gradient of physicochemical parameters in the chamber, with subsequent differences in viscosity, density, convection currents, yield strength and thus different mixing behaviour of different liquids. Furthermore, a persistent heat flux from the feeder may have delayed crystallization of successive phases in those parts of the chamber proximal to the feeder . Therefore, new influxes would have been deposited on a footwall of varying thickness and lithology in response to different degrees of crystallization and accumulation along strike. The development of a normal cyclic unit (chromititeharzburgite-pyroxenite-norite (+anorthosite?)) may thus have been interrupted at various stages in different parts of the chamber. The ability to correlate anorthosites over great strike distances implies that their formation did not follow entirely random processes but was dependent on specific magmatic conditions which prevailed over laterally extensive portions of the chamber at certain stages during the evolution of the crystallizing liquid.

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20

Holwell, David. "Roles of magmatism, contamination and hydrothermal processes in the development of Platreef mineralization, Bushveld Complex, South Africa." Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/56160/.

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The Platreef is a highly complex, pyroxenite-hosted Ni-Cu-PGE deposit. It is located at the base of the northern limb of the Bushveld Complex, South Africa, in direct contact with a variety of country rock sediments and Archaean basement. The interaction of the Platreef magma with these diverse country rock lithologies during emplacement had a profound effect on the style and distribution of the mineralization on both regional and local scales. Geometrically, the Platreef was emplaced as a thin, sill-like intrusion, with pre-formed PGE- rich sulfide droplets entrained within the magma. Sulfur saturation is likely to have occurred in a deep staging chamber or conduit prior to emplacement, and where immiscible sulfide droplets became enriched in PGE, base metals and semi metals. After emplacement, the PGE and semi-metal rich sulfide liquid cooled to form 'primary' assemblages of IPGE-rich pyrrhotite, IPGE-, Rh- and Pd-rich pentlandite, chalcopyrite, Pt and Pd tellurides and bismuthides and electrum within the feldspathic pyroxenites of the Platreef. Assimilation and metamorphism of some sedimentary footwall rocks, particularly the dolomites of the Malmani Subgroup, released large volumes of volatiles into the Platreef magma. This hydrothermal activity redistributed PGE and base metal sulfides (BMS) into the footwall rocks, and in places overprinted the 'primary' assemblages, and occasionally decoupled PGE from BMS, with the petrology of the reef and footwall, and the mineralogy of the platinum-group minerals, significantly affected. Each locality along the strike of the Platreef with a different footwall lithology has its own unique hydrothermal history directly related to the nature of the local floor rocks. For example, where the floor is composed of anhydrous basement gneiss, volatile activity was relatively insignificant, and partial melting of the floor allowed the percolation of PGE-rich sulfide liquid to penetrate the footwall. The nature of the floor rocks also controls the type and amount of contamination in the Platreef. Sulfides in country rock shales, for example, are assimilated into the Platreef magma and locally upgrade the S content at such localities, although this did not trigger S saturation. Footwall sulfates, such as anhydrite, cannot be assimilated, but can interact with the Platreef sulfides through hydrothermal leaching when sufficient fluids had been released during assimilation. After emplacement of the Platreef, a significant period of cooling occurred, such that the Platreef was almost completely crystallized, during which time some ductile deformation occurred. The gabbronoritic hangingwall magma was then emplaced, forming a magmatic unconformity over the Platreef, occasionally exploiting shear zones to intrude finger-like bodies down into the Platreef. Where the hangingwall magma assimilated mineralized Platreef thin zones of PGE mineralization developed at its base. The magmatic intrusion of the Platreef can be considered to be distinct from that of other magmatic units in the northern limb of the Complex. Its Ni-Cu-PGE sulfide mineralization is orthomagmatic in origin however, complex interaction with a variety of country rock lithologies has locally altered the style and distribution of the mineralization, to form unique mineralogical associations and assemblages along strike. The understanding of local country rock control on features such as the mineralogy of the ores and the extent of remobilization into the footwall is critical in optimizing exploration, mining and mineral processing techniques.

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21

Fischer, Lennart Alexander [Verfasser]. "The Upper Zone of the Bushveld Complex, South Africa: Parental Magma and Crystallization Processes / Lennart Alexander Fischer." Hannover, 2018. http://d-nb.info/1160378800/34.

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22

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.

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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
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23

Fischer, Lennart A. [Verfasser]. "The Upper Zone of the Bushveld Complex, South Africa: Parental Magma and Crystallization Processes / Lennart Alexander Fischer." Hannover, 2018. http://d-nb.info/1160378800/34.

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24

Viljoen, Willemien. "Phase relations in the system Cu-Fe-Ni-S and their application to the slow cooling of PGE matte." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-10132005-100921/.

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25

Manyeruke, Tawanda Darlington. "The petrography and geochemistry of the Platreef on the farm Townlands near Potgietersrus, northern Bushveld Complex." Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-04282005-110052/.

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26

Armitage, Paul Edward Blake. "Development of the Platreef in the northern limb of the Bushveld Complex at Sandsloot, Mokopane District, South Africa." Thesis, University of Greenwich, 2011. http://gala.gre.ac.uk/9079/.

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The Platreef is a Ni-Cu-PGE mineralised tabular body at the base of the Rustenburg Layered Suite in the northern limb of the Bushveld Complex. The reef lies unconformably on a footwall (floor) sequence of Transvaal Supergroup sedimentary rocks and Archaean granite/gneiss basement, and is overlain by a hangingwall (roof) of Main Zone gabbronorites. Structural relationships suggest that the Platreef was emplaced as a broadly horizontal sill-like sheet into the Transvaal Supergroup, but local variations in its thickness and path of intrusion were caused by pre-existing structures in the country rocks. As the Platreef cooled and was nearly crystallised, ductile deformation occurred, possibly as an episode in a longer event. Main Zone magma was emplaced above the deformed, nearly consolidated Platreef and eroded the uppermost portion, locally assimilating mineralised reef. The Main Zone magma also intruded into shear zones as thin dykes down through the Platreef and metasedimentary floor. Structural patterns around a prominent dome in the floor rocks suggest that regional deformation may still have been active when the earliest Main Zone layers were developing, but ceased by Upper Main Zone time. Other studies of the Platreef beyond Sandsloot have shown that its earliest Ni-Cu-PGE mineralisation was orthomagmatic, largely preserved where the floor rocks are unreactive basement granite/gneiss. However, interaction between he Platreef magma and surrounding sedimentary rocks has produced different mineralogical associations and assemblages that were influenced by the local floor and roof rocks along the strike of the reef. At Sandsloot, the floor rocks are represented by reactive siliceous dolomites of the Malmani Subgroup. The Platreef magma caused contact metamorphism and metasomatism of the dolomites, releasing volatiles that entered the reef. These hydrothermal fluids stripped PGE from primary sulphides and redistributed the PGE within the reef and into the metasedimentary country rocks. In places, primary platinum group minerals were overprinted by lower-temperature species.

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27

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.

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28

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 - PhD
The 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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29

Field, Matthew. "The petrology and geochemistry of the upper critical zone of the Bushveld complex at the Amandelbult section of Rustenberg Platinum Mines Limited, Northwestern Transvaal, South Africa." Thesis, Rhodes University, 1987. http://hdl.handle.net/10962/d1007499.

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A study of petrological and geochemical variations through the upper Critical Zone of the Bushveld Complex at Amandelbult section of R.P,M. was undertaken. The sequence at this locality may be divided into seven "units" two of which appear to be complete, possessing the sequence harzburgite-pyroxenite-norite-anorthosite. The other five Units lack basal, intermediate or upper members. Considerable lateral variations are apparent in this sequence, but these are restricted to the Lower Pseudo Reef-Merensky Reef interval, tne same portion of the succession which is affected by pothole structures. The single most important petrographic feature of genetic significance is the occurrence of annealed, recrystallized anorthosite immediately underlying ulstramafic layers. This, together with the undulatory nature of the contact between the two rock layers, suggests that the ultramafic layer was emplaced as a hot liquid over a pre-existing, crystalline anorthosite floor, and that some remelting of this layer occurred. Variations in the chemical make-up of constituent silicate minerals reveal a number of significant processes which may have been operative in the magma chamber prior to crystallization, Olivine grains, for instance, exhibit extremely wide chemical variations both within single layers and from one layer to the next. These variations are best explained by re-equilibration processes with spinel and base metal sulphides, rather than by wide variations in original liquidus compositions. It appears that the compositions of the initial liquids from which each basal olivine-bearing layer crystallized, were approximately similar. Variations in the iron-magnesium ratio of ortho-pyroxenes indicate well defined continuous fractionation trends in units which are considered to be complete. Magnesian compositions are recorded in ultramfic members, while increasingly iron-enriched values are recorded upwards through the sequence pyroxenite-norite-antorthosite. Plagioclase grains exhibit less well defined fractionation trends, but it is clear that an upward increase in An is encountered through indivitual Units. This is in direct contrast to the trend exhibited by orthopyroxene. A further feature of plagioclase grains is the considerable degree of chemical zonation exhibited by them. In cumulus grains this is commonly manifested as strongly reversed rims, while in intercululus grains normal zoning is ubiquitous. Whole-rock chemical variations through the succession indicate that cyclical variations occur through successive Units, but that these merely reflect changes in modal mineralogy and not liquid fractionation trends. Such trends can be shown for selected element ratios, where these elements are known to partition into a single mineral phase. Rations of pyroxene components such as the nickel/scandium ratio, exhibit a saw tooth pattern through successive Units, while ratios of plagioclase components such as the strontium/alumina ratio have unique, fairly constant values for each individual Unit but different values for successive Units. The latter type of cyclicity is not always strictly confined to lithologically recognized boundaries between Units, and a slight overlap into overlying ultramafic layers is apparent. An investigation of variations in trace element levels in a single layer in five widely separated boreholes revealed that there is some evidence for a lateral fractionation trend from the southwest (more primitive) to the northeast (more evolved), although the small number of data points available preclude definite conclusions. There exists in the data some evidence that the Giant Mottled Anorthosite differs chemically from the other anorthosites in the study section, and that it more closely resembles rocks of the Main Zone. This evidence is particularly apparent in variations of the chromium/aluminium ratio of orthoyroxene grains, and in the An content of plagioclase grains, both of whose trends exhibit distinct inflections at the base of this member. The features of the succession at Amandelbult are best explained by the model of Eales et al. (in press, a), which visualizes the input of a number of pulses of new, hot liquid into a magma chamber containing the fractionated residua of previous influxes. At a critical point in time, just prior to the mafic Merensky Reef input, a large input of gabboic liquid was intruded at high levels in the chamber. The lower portions of this liquid mixed with the residua of earlier mafic inputs, which in turn mixed with new inputs of mafic, typical Critical Zone liquids. Thus the lower portions of the study section represent mixtures of new Critical Zone liquids with the residua of previous such influxes, while the upper portions have the added complication of mixture with a Main Zone-type liquid. The unique chemical character of the Giant Mottled Anorthosite appears to be a direct manifestation of the influence of the Main Zone liquid.
KMBT_363
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30

Scoon, Roger N. "Discordant bodies of postcumulis, ultramafic rock in the upper critical zone of the Bushveld complex : iron-rich ultramafic pegmatite bodies at Amandelbult and the Driekop platiniferous ultramafic pipe." Thesis, Rhodes University, 1986. http://hdl.handle.net/10962/d1004912.

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From the abstract: In the layered sequence of the Bushveld Complex a number of distinct, but possibly genetically related groups of transgressive, postcumulus, ultramafic and mafic rock are recognised. The main part of this thesis investigates a suite of postcumulus rocks for which the name iron-rich ultramafic pegmatite is proposed. The majority of iron-rich ultramafic pegmatite bodies examined are from the upper critical zone of the layered sequence at Rustenburg Platinum Mines Amandelbult Section, in the northern sector of the western Bushveld Complex. Field relationships imply that the iron-rich ultramafic pegmatites should be considered as an integral feature of the layered sequence, even though they transgress the cumulates. Consequently, this thesis also includes a study of the cumulate sequence at Amandelbult. A second group of postcumulus, ultramafic rocks which is investigated comprises latiniferous ultramafic pipes; the Driekop pipe has been selected as a case study. This thesis is presented in four sections, namely, an introduction and verview, and studies on the Driekop pipe, the cumulate sequence at mandelbult and the iron-rich ultramafic pegmatite suite. A new classification scheme of discordant bodies of postcumulus, ultramafic rock in he Bushveld Complex is proposed (see also Viljoen & Scoon, in press). In he scheme presented here, two main varieties of postcumulus, ultramafic rock re recognised, namely, non-platiniferous magnesian dunites and iron-rich ltramafic pegmatites.

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31

Andrews, Marcelene. "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 Tweefontein and Sandsloot farms." University of the Western Cape, 2015. http://hdl.handle.net/11394/5229.

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>Magister Scientiae - MSc
The Platreef is known for its complexity and its heterogeneous lithologies, coupled with an unpredictable PGE and BMS mineralisation. The motivation behind this study was to aid mining geologists in targeting mineralisation irrespective of the farm. It is known that the Platreef generally overlies different footwall lithologies at individual farms. Thus, the aims of this study were firstly to investigate the potential of chemostratigraphy by delineating indices indicative of distinctive lithological layers. These indices were then tied to the second aim; which were to use geochemical vectoring, which is process-based, to target the PGEs at two different farms. This study included three drillcores: from the farms Sandsloot (SS339) and Tweefontein (TN754 and TN200). The footwall units at Tweefontein are shales of the Duitschland Formation and the Penge banded iron formation; and at Sandsloot it is the Malmani Subgroup dolomites. Samples included 121 quarter cores, used for petrographical and geochemical studies. The elemental rock composition was determined by XRF and ICP-OES analyses. The approach also included statistical and mass balance methods to understand the geological and geochemical controlling processes. Initially, the Platreef package at both farms was petrographically divided into three main layers: pyroxenite, and two distinctive feldspathic pyroxenites (FP-I and FP-II). However, the pyroxenites were also further separated as P-I and P-II, because of a higher notable difference in the degree of alteration within P-I. Progressive degrees of metasomatism were further observed in the lithologies, e.g. within the Platreef package, where feldspathisation was potentially the main metasomatic process. Many geochemical plots (corroborated by the petrographical and mass balance results) illustrated that the feldspathisation were linked to an increase in the content of Al₂O₃ and CaO, and coupled with a decrease in content of Fe₂O₃ and MgO. Together with other geochemical trends, geochemically distinct units of the Platreef package could be discriminated with a metasomatism index (MI; CaO + 10Na₂O / CaO + 10Na₂O + Fe₂O₃ + MgO). The ensuing MI is lowest for the P-II pyroxenite and shows a progressive increase through FP-I, P-I to the highest values in FP-II. Geochemical layering were also observed in the calcsilicates and hornfels; e.g. a progressive decrease in the content of Fe₂O₃, Al₂O₃, Ce, Co, Cu, Ni, Zn, Zr, Au, Pd and Pt from the hornfels subunits H-I, H-II to H-III and an increase in of SiO₂, Fe₂O₃, TiO₂, SO₃, Co, Cu, Ni, Rb, V and Zn content from CS-I, CS-II to CS-III. Correlating the pyroxenites and feldspathic pyroxenites spatially from one drillcore to another were hindered, hence, chemostratigraphy were not completed. In terms of vectoring, it was essential to establish a possible link between the metasomatism index and the nature and style of the PGE and/or BMS mineralisation. The Hornfels subunit H-I and calcsilicate subunit CS-III were the main carriers of BMS and PGE. The Platreef package were more complicated: P-I (low PGE, low BMS); P-II (low PGE, high BMS); FP-II (high PGE, low BMS); and FP-I (high PGE, high BMS). Element indices (e.g. Cu+Ni and Co+Zn) were developed to define a consistent gradient indicative of these ore subunits. A validation process to assess the metasomatism index (MI), base metal indices and PGE distribution within the individual drillcores (TN754, TN200 and SS339) were then undertaken. The results were that the MI ranges were similar in all drillcores, and discriminated the subunits of the Platreef package, gabbronorites and even the calcsilicates. The base metal ratios (e.g. Ni/Co and Cu/Co) were indicative of the PGE rich zones. Trends of the base metal ratios reflected a strong positive relationship with the MI within the Platreef package and the calcsilicates. However, the opposite trend is observed with the hornfels. In conclusion, the MI could potentially be a strong vector of high PGE and BMS mineralisation. It is also possible to discriminate lithologies within the Platreef package with the MI. However, it should be noted that the limitation of this study is that the results are based on three drillcores. The Platreef is heterogeneous at individual farms and extremely diverse across the northern limb. Therefore, future research could be undertaken to validate these findings, by using a bigger drillcore database.
National Research Foundation

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32

Manyeruke, Tawanda Darlington. "Compositional and lithological variation of the Platreef on the farm Nonnenwerth, northern lobe of the Bushveld Complex implications for the origin of platinum-group elements (PGE) mineralization /." Thesis, Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-01192009-164657/.

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33

Edwards, Hunter R. "A multi-isotopic geochemical investigation of the Lower Zone, Bushveld Complex, South Africa: implications for a crustal component for parental magmas." Master's thesis, Faculty of Science, 2020. http://hdl.handle.net/11427/32606.

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The current study focuses on the Lower Zone of the Bushveld Complex, South Africa using multiple geochemical and isotopic systems to determine the origin of crustal signatures, i.e. crustal assimilation or recycled crust in the mantle source, present throughout the Rustenburg Layered Suite (RLS) such as elevated  18O values. These geochemical and isotopic systems include major elements, trace elements, highly siderophile elements, oxygen isotopes, 87Sr/86Sr, 143Nd/144Nd, and Os-Os isotopes. Samples come from the Nooitgedacht Borehole 2 (NG2) at Union Section of the western limb of the Bushveld Complex, which sampled the Lower Zone. The 87Sr/86Sri (0.7043 – 0.7086) and Ndi values (-7.40 - -4.97) calculated in this study are in agreement with published data for the Bushveld. The majority of NG2 samples contain  18O greater than mantle peridotite (5.50‰) and MORB (5.70‰), in which NG2  18O ranges from 5.60 up to 8.00‰ for olivine, orthopyroxene, and clinopyroxene separates. These high  18O values suggests the Bushveld magmas sourced a crustal reservoir, either through crust assimilation or recycled crustal materials in the mantle source. This is the first study utilizing the Re-Os isotope system for the Lower Zone. The Osi values for the NG2 suite range from -4.37 to +35.9, which overlap with published data for the Critical Zone and the Platreef, the only previous Re-Os studies on the Bushveld. However, there are no previously reported negative Osi values for the Bushveld. The range in Osi values for the NG2 samples suggest mixing of at least two geochemical reservoirs. In addition to Lower Zone NG2 samples, sample NG2-773.65 is a chilled margin sample at the base of the NG2 borehole that contains high  18O ( 18O = 9.42 – 9.78‰) and radiogenic Osi (Osi = +62.5), in which the crust and/or recycled crust in the mantle source caused these high values. Sample NG2-734.64 contains the second lowest  18O ( 18O = 5.67‰) and most unradiogenic Osi (Osi = -4.37) values for the NG2 suite, evidence for a harzburgitic SCLM (H-SCLM) mantle source component. A lack of correlations for Osi values with  18O and 87Sr/86Sri values are indices for crustal assimilation processes. This lack in correlation may suggest a crustal component in the mantle is more likely than assimilation of the crust during ascent of the magmas toward the surface. The geochemical data presented in this study suggest the Lower Zone parent magma had a H-SCLM mantle source component in addition to the assimilation of the crust and/or the eclogitic SCLM (E-SCLM).

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34

Surtees, Grant Bradley. "The evolution of the Brosterlea Volcanic Complex, Eastern Cape, South Africa." Thesis, Rhodes University, 2000. http://hdl.handle.net/10962/d1005556.

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Detailed field mapping (Map, Appendix B) has been conducted in and around the boundaries of a 14x18km, volcanic complex 35km northeast of Molteno in the Eastern Cape Province, South Africa. The structure is interpreted as a subsidence structure, and is filled with two volcaniclastic breccias, numerous lava flows, a number of sedimentary facies, and lies on a base of Clarens Formation overlying Elliot Formation rocks. This is an important study because 'widespread, voluminous fields of basaltic breccias are very rare (see Hanson and Elliot, 1996) and this is the first time that this type of volcanic complex and its deposits have been described. Detailed analyses of the two volcaniclastic breccias revealed changes in colour, clast types, clast sizes, and degree of alteration over relatively short distances both vertically and laterally within a single breccia unit. The variation in clast sizes implies a lack of sorting of the breccias. The lower of the two volcaniclastic breccias fills the subsidence structure, and outcrops between the Stormberg sedimentary sequence and the overlying Drakensberg basalts and was produced from phreatomagmatic eruptions signalling the start of the break-up of Gondwanaland in the mid-Jurassic. The upper volcaniclastic breccia is interbedded with the flood basalts and is separated from the lower breccia by up to 100m of lava flows in places, it is finer-grained than the lower volcaniclastic breccia, and it extends over 10km south, and over 100km north from the volcanic complex. The upper breccia is inferred to have been transported from outside the study area, from a source presumably similar to the subsidence structure in the volcanic complex. The pyroclastic material forming the upper breccia was transported to the subsidence structure as a laharic debris flow, based on its poorly sorted, unwelded and matrix-supported appearance. However, both breccias are unlikely to have been derived from epiclastic reworking of lava flows as they contain glass shards which are atypical of those derived from the autoclastic component of lava flows. The breccias are therefore not "secondary" lahars. There is also no evidence of any palaeotopographic highs from which the breccias could have been derived as gravity-driven flows. Based on the occurrence of three, 1m thick lacustrine deposits, localised peperite, fluvial reworking of sandstone and breccia in an outcrop to the south of the subsidence structure, and channel-lags encountered only in the upper units of the Clarens Formation and only within the subsidence structure, the palaeoenvironment inferred for the subsidence structure is one of wet sediment, possibly a shallow lake, in a topographic depression fed by small streams. Magmatic intrusions below the subsidence structure heated the water-laden, partly consolidated Clarens Formation sandstones, causing the circulation of pore fluid which resulted in the precipitation of minerals forming pisoliths in the sandstones. Intruding magma mixed, nonexplosively, with the wet, unconsolidated sediments near the base of the Clarens Formation (at approximately 100m below the surface), forming fluidal peperite by a process of sediment fluidisation where magma replaces wet sediment and cools slowly enough to prevent the magma fracturing brittly. Formation of fluidal peperite may have been a precursor to the development of FCIs (Fuel Coolant Interactions) (Busby-Spera and White, 1987). The breccias may represent the products of FCIs and may be the erupted equivalents of the peperites, suggesting a possible genetic link between the two. The peperites may have given way to FCI eruptions due to a number of factors including the drying out of the sediments and/or an increase in the volume of intruded magma below the subsidence structure which may have resulted in a more explosive interaction between sediment and magma. Phreatic activity fragmented and erupted the Clarens Formation sandstone, and stream flows reworked the angular sandstone fragments, pisoliths and sand grains into channelised deposits. With an increase in magmatic activity below the subsidence structure, phreatic activity became phreatomagmatic. The wet, partly consolidated Clarens Formation, and underlying, fully consolidated Elliot Formation sediments were erupted and fragmented. Clasts and individual grains of these sediments were redeposited with juvenile and non-juvenile basaltic material probably by a combination of back fall, where clasts erupted into the air fell directly back into the structure, and backflow where material was erupted out of the structure, but immediately flowed back in as lahars. This material formed the lower volcaniclastic breccia. A fault plane is identified along the southwestern margin of the subsidence structure, and is believed to continue up the western margin to the northwestern corner. A large dolerite body has intruded along the inferred fault plane on the western margin of the structure, and may be related to the formation of the lower volcaniclastic breccia, either directly through fluidisation of wet sediment during its intrusion, or as a dyke extending upwards from a network of sill-like intrusions below the subsidence structure. Geochemical analysis of the Drakensberg basalt lava flows by Mitchell (1980) and Masokwane (1997) revealed four distinct basalt types; the Moshesh's Ford, the Tafelkop, the Roodehoek, and the Vaalkop basalts. Basalt clasts sampled from the lower volcaniclastic breccia were shown to belong to the Moshesh's Ford basalt type which does not outcrop in situ within the subsidence structure. This implies that the Moshesh's Ford basalts were emplaced prior to the formation of the lower volcaniclastic breccia, and may have acted as a "cap-rock" over the system, allowing pressure from the vaporised fluids, heated by intruding basalt, to build up. The Moshesh's Ford basalt type was erupted prior to the resultant phreatomagmatic events forming the lower volcaniclastic breccia.

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Ramushu, Adam Puleng. "Geochemical and Petrographic Characterization of the Transition Boundary between the MG2 package to MG3 package at Dwarsrivier Chrome Mine, Bushveld Complex, South Africa." University of the Western Cape, 2018. http://hdl.handle.net/11394/6407.

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Magister Scientiae - MSc (Earth Science)
This study area is situated within the Eastern Bushveld complex at Dwarsrivier chrome mine, which is approximately 30 km from Steelpoort and 60km from Lydenburg in the Mpumalanga province. The primary aim of the project is to identify the petrological and geochemical characteristics that can be used to distinguish the various rock types of feldspathic pyroxenites, chromitites, anorthosites and chromitite pyroxenites and determine whether the various rock types are from the MG2 package and MG3 package were formed from a single or multiple magma pulses. The geochemical and mineralogical variation studies were carried out using cores from borehole DWR74 and DWR172 located on the farm Dwarsrivier 372 KT. Using the combination of various multivariate statistical techniques (factor, cluster and discriminant analysis) multi element diagrams and trace element ratios, the outcome of the study demonstrated that each of the four rock types can be sub-divided into two groups.

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Mandende, Hakundwi. "Geochemical and petrographic characterization of platreef pyroxenite Package p1, p2, p3 and p4 units at the akanani prospect area, bushveld Complex, South Africa." University of the Western Cape, 2014. http://hdl.handle.net/11394/4350.

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>Magister Scientiae - MSc
This study is focused on the Akanani prospect area, approximately 25 km north-west of the town of Mokopane, Limpopo Province where exploration geologists at the study area have classified the ‘pyroxenitic’ units into P1, P2, P3 and P4 units upward in order of succession with height based on their textures, mineralogy and colour. The primary aim of this study is to distinguish the distinctive geochemical and mineralogical characteristics that can be used to identify each unit (P1 to P4) and in so doing create major geochemical, petrographic and mineralogical variables that will help or facilitate the exploration for and recovery of PGE and BMS mineralisation. Geochemical and mineralogical variation studies were carried out on the cores from ZF044, ZF045, ZF048, ZF057, ZF078, ZF082 and M0023, located in the Platreef at the Akanani Prospect area on the farms Moordkopje 813LR and Zwartfontein 814LR. Using a combination of various multivariate statistical techniques (factor, cluster and discriminant analysis) and mineralogical studies (CIPW norm, microprobe analysis, petrography), the outcomes of the study have demonstrated that the Platreef at Akanani comprise at least four lithological units i.e. the basal pyroxenite portion referred to as the P1 unit comprises chromitite, pyroxenites and feldspathic pyroxenites with associated Cr, TiO2, chromite, pyroxenes, hematite and Fe2O3, the mineralized section of the P2 unit is characterized by harzburgite, serpentinized harzburgite and in places orthopyroxenites are present consistent with high MgO and LOI contents, the feldspathic portion referred here as the P3 unit is characterized by a feldspathic pyroxenite containing higher Al2O3, Na2O, K2O, albite, hypersthene and SiO2 and the top most portion of the P4 unit comprising CaO, Diopside, ilmenite, anorthite, apatite and P2O5 that can be interpreted to have formed by three separate magma pulses. Considering the possibility that the P4 unit is a hybrid melt of assimilated Platreef that interacted with intruding Main Zone magma, this reduces the number of magma pulses to two. The classification of P1, P2, P3 and P4 units of the Platreef at Akanani shows that the criteria used by mining personnel to classify the four lithological units is not definitive and therefore are not highly reliable. Although various multivariate statistical techniques were employed relatively similar elemental associations were obtained highlighiting the importance of this approach. The strongly positive correlation between sulphides, PGEs and chromite at Akanani is consistent with an orthomagmatic deposit that had been disturbed by significant hydrothermal activity, while in places a good BMS-PGE relationship is commonly associated with the main chromitite stringers in P1. Mineral and whole rock compositions of silicate rocks highlight the strongly magnesian nature of the ultramafic P2 unit. Mineral chemistry studies of chromite, orthopyroxene, olivine, clinopyroxene and plagioclase are consistent with the multi- emplacement model. Convective exchange resulted in the enrichment of iron at the bottom of the stagnant chamber, while incompatible elements migrated upwards consistent with iron depletion with stratigraphic height. Injection of P1 magma and subsequent mixing with country rocks gave rise to the formation of chromitites and addition of plagioclase component to the intruding magma. A normal fractionation trend is suggested between P2 and P3 consistent with enrichment of MgO in P2 and enrichment of Al2O3, Na2O, SiO2 and K2O in P3. The An% of 84.4 of plagioclase coupled with CaO enrichment in P4 is suggestive of some Main Zone influence and can be interpreted as resulting from partial melting and recrystallization of P3 in response to the intrusion of the Main Zone magma is suggested for the formation of the P4 unit. There exists a good correlation between the modal mineralogy and mineral chemistry as determined optically, the norm as determined by the CIPW norm and the whole-rock geochemical results as determined by multivariate statistics and conventional methods.

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Mudanalwo, Ratshalingwa Patience. "Geochemical controls of platinum-group elements distribution patterns in the Patreef, bushveld complex, South Africa: a case study at Zwartfontein farm, Akanani prospect area." University of the Western Cape, 2020. http://hdl.handle.net/11394/7871.

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>Magister Scientiae - MSc
The Platreef, is a contact-type pyroxenitic reef in the Northern Limb of the Bushveld Complex, enriched in platinum group elements (PGE) and base metal sulfides (BMS). Relatively subdued mining in the Platreef, compared to RLS, has been attributed to limited knowledge regarding irregular distribution, complex style and genesis of PGE mineralisation in the Platreef. This study was, therefore, aimed at investigating the petrogenesis of the Platreef, particularly to evaluate whether the formation of the ore reefs resulted from a single or multiple sill-like magma intrusions. The study also sought to unveil the interplay of fractional crystallisation, hydrothermal fluid activities, floor rock and crustal contamination on the formation of Platreef types, PGE mineralisation and the magma source.

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Theron, Luhann Marlon. "Phase relations and Pt solubility in sulphide melt in the FE-NI-CU-S system at 1 ATM : implications for evulution of sulphide magma in the Merensky reef, Bushveld Complex, South Africa." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80358.

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Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: It is widely accepted that sulphide is the carrier and concentrator of PGEs during magmatic mineralization episodes in the Merensky Reef (MR). PGE concentration peaks and sulphide volume percent peaks are very closely correlated. Koegelenberg, (2011), showed in an experimental investigation that sulphide movement through a cumulate silicate and cumulate oxide pile behave in such a way that sulphide melt gets trapped in chromitite layers. When looking at the compositional distribution of sulphide within the MR it is noted that not only does the sulphide volume percent varies with MR stratigraphy but also the sulphide composition. Sulphide composition is more Cu-rich in the chromitite layers and more Fe and Ni dominated in the hanging wall to the chromitite layers. Until now the more Cu-rich assemblage of the chromitite layers are accepted to be of a sulphide melt composition compared to the Fe and Ni dominated Monosulphide Solid Solution or MSS composition in the hanging wall. In this study we used an experimental approach with a sulphide starting composition thought to exist as the parental sulphide composition of the MR to investigate the phase relations with changing temperature. It is found that the sulphide composition in the chromitite layers represent a sulphide melt composition at 1000 ± 50ºC. At 1000ºC, 50% of the sulphide system would exist as a melt. This Cu-rich melt would have segregated from the MSS and be trapped in the chromitite layer. Also at 1000ºC the partitioning of the Pt would have induced a secondary enrichment step of the Pt concentration in melt through the partitioning of Pt between a sulphide melt and a sulphide solid phase. The experimental evidence in this study points towards a possible source for the parental sulphide magma to the MR, which could have been a slightly Cu enriched mantle sulphide composition. Also, the secondary enrichment of Pt through sulphide melt fractionation at 1000ºC plays an important role in the shaping of the ore body.
AFRIKAANSE OPSOMMING: Dit word wydliks aanvaar dat die sulfied fraksie van die Merensky Rif (MR) die draer en die konsentrasie agent is vir Platinum Groep Elemente (PGE`s) gedurende mineralisasie episodes. PGE konsentrasie en sulfied volume persentasie is op `n hoogtepunt by gelyke stratigrafiese posisies in the MR. Koegelenberg, (2011), het deur middel van eksperimente bewys dat `n sulfied smelt deur `n voorafbestaande kumulaat laag kan beweeg en dat veranderende fisiese eienskappe tussen sulfied smelt en silikaat kristal en sulfied smelt en chromiet kristal, die sulfied smelt sal opsuig en verhoud om verder deur te suipel. Dit is egter oplettend dat nie net die sulfied volume persentasie varieer as `n funksie van die MR stratigrafie nie, maar ook die sulfied samestelling. Die meer Cu-ryke sulfied samestelling in die chromiet lae word aanvaar as `n sulfied smelt fraksie en die meer Fe en Ni dominerende sulfied samestelling in die oorhangende wandgesteentes verteenwoordig die Monosulfied Vaste Oplossing (MVO) soliede fase. In hierdie studie maak ons gebruik van eksperimentele petrologie tesame met `n begin samestelling verteenwoordigend van die oorsprong sulfied samestelling van die MR, om die fase verwantskappe van hierdie spesifieke samestelling te ondersoek. Dit word gevind dat die fraksionering tydens die vorming van die MR plaasgevind het by ongeveer 1000 ±50 C. By hierdie temperatuur is 50% van die sisteem teenwoordig as `n smelt fase. Hierdie Cu-verykte smelt was daartoe instaat om deur die silikaat laag te suipel, geskei te raak van die Fe en Ni dominerende MVO en vasgevang te word in die chromiet lae. Hierdie fraksionering van die sulfied smelt het ook `n sekondêre effek gehad op die verspreiding van Pt tussen sulfied smelt en sulfied soliede fases. Hierdie eksperimentele bewyse dui eerstens op die moontlikheid van `n sulfied smelt in die MR wat sy oorsprong vanuit `n effense Cu-verykte mantel bron kan hê, en tweedens op die belangrikheid van `n sekondêre proses vir Pt re-distribusie tydens die vorming van die MR.

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Iorga-Pavel, Adina. "Evolution of Fe-Ti-V oxides from the main magnetite layer, Upper Zone, Bushveld Complex, South Africa: a comparison across the Western, Northern and Eastern Lobes." Thesis, Rhodes University, 2017. http://hdl.handle.net/10962/7357.

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The Main Magnetite Layer (MML) from the Northern, Eastern and Western lobes of the Bushveld Complex shows significant differences in textures and in mineral chemistry. The MML in the Eastern and Western lobes is massive, with rare, small and altered pyroxene inclusions. By contrast, the MML in the Northern Lobe is more heterogeneous, and it is made of anastomosed and sometimes imbricated, thin layers of magnetitite, magnetite-rich and silicate-rich rocks, where the inclusions in Ti-magnetite are more numerous and consist of mainly altered subhedral and anhedral plagioclase. The comparison of the maximum values of the oxides shows that the MML in the Northern Lobe has the highest content of V2O3 (1.97 wt%), TiO2 (22.49 wt%) and MgO (2.92 wt%), while the MML in the Eastern Lobe has the highest content of Cr2O3 (2.92 wt%) and Al2O3 (9.80 wt%), but lowest V2O3 (0.52 wt%). The lower TiO2 content and higher V2O3 content in the MML of the Northern and Western Lobes suggest lower oxidising conditions during the crystallization of oxides. The MML in all three studied lobes consists of two layers of magnetitite, suggesting that MML was formed by two separate magma influxes, probably on a diverse and complex type of magma chamber floor. The high TiO2 content in magnetite, together with the negative correlation between TiO2 and V2O3 suggest that the maximum V content should represent a “less evolved” and less oxidized melt. In this respect, higher concentrations V2O3 in magnetite can be expected in magnetitite layers with lower TiO2. It can be inferred that the Ti-magetite in the MML from the Eastern Lobe was formed from a more evolved (TiO2 and FeO enriched) and more oxidized (lower V2O3) melt, compared with the MML from the Northern and Western lobes. These findings can be used to illustrate: a) that high fO2 can be responsible for the relatively low V content in magnetite from Fe-Ti oxide ores and b) the vanadium in magnetite decreases significantly in more evolved cumulates, due to a decreasing fO2 with differentiation. Compositional profiles of Ti- magnetite along the stratigraphic height of the MML in the Eastern Lobe (composed of two layers, separated in the outcrop by a parting plane) depicts a cryptic variation with depth in each of the two layers, where each layer can be divided into four sublayers, labelled upwards as A, B, C (with C1, C2, C3 and C4) and D based on Cr, Mg, Ti, Al and V variation. Small scale reversals of the mentioned elements and the repetition of A, B, C and D sub-layers in each layer suggest that MML formed from two successive influxes of magma (indicated by relatively elevated values of MgO), which evolved by crystallization and cooling in a similar manner, to produce the A to D variation. Based on these observations and theoretical considerations, this study dismisses several models for the genesis of the MML: the immiscibility, the increased oxygen fugacity, the relative increase of H2O content of the melt, pressure variation within the magma chamber, magma mixing, and crustal rock contamination. The model proposed here for MML genesis involves the crystallization of both Ti-magnetite and ilmenite from a Fe-Ti-Ca-Al-rich melt (ferro-diorite) along its line of descent, and gravitational settling of oxides in a dynamic regime. The factor which triggered the crystallization of magnetite is a critical saturation of melt in magnetite (attaining saturation of magnetite and ilmenite in the melt after some silicates crystallized). The difference between the nature of silicate inclusions in magnetite and the nature of the magnetite floor, suggest that the Fe-rich magma was not in equilibrium with the cumulates from the present floor, but rather it was emplaced laterally on long distances, the melt being disrupted from its own cumulates. The absence of correlation between the Cr2O3 in magnetite and co-existing ilmenite can indicate than no in-situ fractional crystallization took place at the moment of magnetite accumulation, but rather that magnetite and ilmenite gravitationally accumulated and the grains mechanically mixed from a flowing magma. The model presented herein proposes a five stage model of MML formation: Stage 1 is represented by the intrusion of a Fe-T-Ca-Al-rich magma which expands laterally within a flat and thin magma chamber. Oxides start to crystallize within a dynamic regime of the magma. Stage 2 is given by the accumulation of oxides at the bottom of the new floor. Some plagioclase starts to crystallize (e.g. subhedral plagioclase in the MML of the Northern Lobe). Stage 3 is a short living static regime, where both plagioclase and magnetite crystallized, without fractionation, forming the thin magnetite-anorthosite layer separating the MML into two layers. Stage 4 is represented by a new influx of Fe-Ti-Ca-Al-rich magma which is emplaced above the magnetite-bearing anorthosite, flushing out the liquid which was in equilibrium with the anorthosite. The oxides started crystallizing in a dynamic regime, as in Stage 1. In stage 5, the accumulation of oxides produced the upper layer of the MML. Our interpretation is that the flow of the magma was more dynamic (probably more turbulent on long distances) in the MML of the Northern Lobe, compared to the MML in the Western and Eastern lobes, producing highly heterogeneous and imbricated thin layers of magnetitite and silicates. The presence of olivine corona around orthopyroxene suggests the incongruent melting of orthopyroxene, which points out towards a local re-heating of existing silicate layers, this being a strong argument for multiple injections in generation of MML. Massive crystallization of oxides produced the sulphur saturation of the magma and caused the precipitation of the igneous sulphides, which nucleated on the existing oxides. Later hydrothermal fluids (and/or late magmatic volatiles?) percolated the MML, producing chloritization of the included silicates, remobilization of igneous sulphides and precipitation of hydrothermal sulphides.

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Zilibokwe, Nosibulelo Julie. "Characterization of the distribution of platinum group elements in sulphide ores within the Merensky Reef at Modikwa and Two Rivers Platinum Mines, Eastern Bushveld Complex, South Africa." Thesis, Rhodes University, 2017. http://hdl.handle.net/10962/7938.

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The distribution of the platinum group element (PGE), in the Merensky Reef was characterized by, first determining the occurrence of the platinum group minerals (PGM), then by establishing the PGE concentration in the base metal sulphides (BMS) associated with the PGE mineralization in the Merensky Reef from selected borehole intersections, at the Two Rivers (TRP) and Modikwa Platinum Mines in the Eastern Bushveld Complex. A mineral liberation analyser (MLA) was then used to identify the PGM phases; their silicate and base metal associations; and their grain size distribution. Electron microprobe quantitative analysis and mapping were then used to determine the compositional variation of the PGM and the PGE elemental distribution in the BMS, respectively. The study showed that the BMS including pyrrhotite, pentlandite, and chalcopyrite were the principal sulphides, where pyrrhotite was most prominent with minor quantities of pyrite. Orthopyroxene, clinopyroxene and plagioclase were the most abundant primary silicate minerals identified, while secondary silicates identified included talc, serpentine and amphibole. Platinum group minerals showed three distinct groups with respect to the mineralogical association with the PGE; (i) BMS association; (ii) chromite association; and (iii) silicate association. Of the BMS, chalcopyrite showed the most dominant association with the PGMs. All samples from both mines exhibited a wide range of PGMs, including maslovite, braggite, cooperate, laurite and PGE alloys such as ferroplatinum as well as other unidentified platinum and palladium sulphides, arsenides and bismuthides, while gold was present as electrum. The PGMs ranged in size from less than a micron to about 125 microns with an average of 20 microns. The close association of PGM with BMS along the margins of sulphides indicates that the PGMs were derived from the sulphide melt. PGE distribution in the sulphides at Modikwa showed pentlandite contained the highest concentrations of palladium (up to 379 ppm) and chalcopyrite hosting the highest rhodium concentrations (up to 793 ppm). Samples from Two Rivers revealed pentlandite as the principal host to both palladium and rhodium, with concentrations reaching up to 695 and 930 ppm, respectively. Magnetite at both Modikwa and Two Rivers showed significant rhodium content, reaching up to 982 and 930 ppm, respectively. The pyrrhotite compared to other sulphides contained all the elements found in the platinum group (PPGE), namely, platinum, palladium and rhodium, with all the platinum identified found in the pyrrhotite. The concentrations for the iridium group (IPGE) namely, iridium, osmium, and ruthenium were below the detection limit. The PGE mineralization in the stratigraphy varied within each mine. The mineralization revealed top loading in the central sector (Modikwa) and bottom loading in the southern sector (Two Rivers). The sequence of the Merensky Reef at the two sectors of the Eastern Bushveld Complex showed a remarkable similarity in their mineralogy suggesting that these two sectors were formed from the same liquid or formed simultaneously within a single magma chamber; however the PGE distribution within the stratigraphy may have been controlled by the presence of cumulate sulphides.

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Osbahr, Inga [Verfasser], and Reiner [Akademischer Betreuer] Klemd. "Platinum-group element distribution in base-metal sulfides of the Merensky Reef and UG2 from the eastern and western Bushveld Complex, South Africa / Inga Osbahr. Betreuer: Reiner Klemd." Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2012. http://d-nb.info/1026805929/34.

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Raines, Mark Douglas. "An assessment of equilibrium in the Merensky Reef : a textural, geochemical and Nd isotope study of coexisting plagioclase and orthopyroxene from Winnaarshoek in the eastern Bushveld Complex, RSA." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1015644.

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Evidence of mineral disequilibrium is presented for the Merensky Reef at Winnaarshoek in the eastern Bushveld Complex. Petrographic disequilibrium textures, disequilibrium in orthopyroxene, plagioclase and clinopyroxene mineral compositions as well as disequilibrium in Sm-Nd isotopic compositions of whole rock samples and coexisting plagioclase and orthopyroxene are presented. Disequilibrium textures presented include clinopyroxene exsolution lamellae in orthopyroxene; resorbed plagioclase in orthopyroxene or relict plagioclase; various inclusions such as orthopyroxene, plagioclase or clinopyroxene in larger oikocrysts of clinopyroxene or orthopyroxene; discontinuous rims of clinopyroxene surrounding orthopyroxene; resorbed orthopyroxene in clinopyroxene; and corona textures associated with olivine. These textures were used to derive a possible mineral crystallization sequence. At least two sequences of crystallization took place, both of which crystallized plagioclase first. One sequence then crystallized olivine which was then consumed to produce orthopyroxene which crystallized prior to late clinopyroxene. The other sequence indicates orthopyroxene crystallization after plagioclase crystallization, followed by crystallization of clinopyroxene. These sequences indicate at least two magmas were responsible for the genesis of the Merensky Reef and its hanging wall and footwall units. Compositionally, disequilibrium is evident in the range of compositions found in coexisting orthopyroxene, plagioclase and clinopyroxene with stratigraphic height, with particular reference to the change in mineral composition in each of the hanging wall, Reef and footwall units. Orthopyroxene compositions range in Mg numbers between 74.6 and 82.9 (77.4) in the hanging wall, 78.5 and 87.0 (avg. 81.1) in the Reef, and 77.9 and 84.1 (avg. 81.3) in the footwall. Plagioclase compositions range in An content between An64.9 and An82.3 (avg. An75.1) in the hanging wall, An56.8 to An70.8 (avg. An62.7) in the Reef, and An54.2 to An86.3 (avg. An73.2) in the footwall. In terms of Sm-Nd isotopic compositions, disequilibrium is evident between both whole rock samples and coexisting plagioclase and orthopyroxenes. Bulk rock Sm-Nd isotopic compositions show a range in ԐNd values between ԐNd (2.06 Ga) = -4.8 to -6.4 in the hangingwall, ԐNd (2.06 Ga) = -6.3 to -8.5 in the Reef, and ԐNd (2.06 Ga) = -4.5 to -6.3 in the footwall. Similar ԐNd values are present in the hanging wall and footwall units, with a clear “spike” in the Merensky Reef. ԐNd values in plagioclase are between ԐNd (2.06 Ga) = -5.8 and -7.8, while orthopyroxene isotopic Sm-Nd values are between ԐNd (2.06 Ga = -7.1 and -9.1. The mineral disequilibrium features presented within this study help elucidate the crystallization sequence of the magma as well as to constrain the contamination of the magma upon ascension and emplacement of the Merensky Reef. The results of this study favour a model where a mantle plume resulted in the ascent of a new magma which was contaminated by the assimilation of old, lower crust. Contamination took place prior to the possible lateral emplacement of the Merensky reef as a density current. 5-10% contamination of depleted mantle or a B2-“like” source by Archaean TTGs is modeled to achieve the contamination “spike” of ԐNd = -8.5 in the Merensky Reef.

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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.

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>Magister Scientiae - MSc
The 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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Coetzee, Hendrik. "The tectono-chronological evolution of the Bushveld complex." Thesis, 1995. http://hdl.handle.net/10539/22842.

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A dissertation submitted to the Faculty of Science of the University of the Witwatersrand for the degree of Master of Science
Detailed high precision geochronological studies have been performed on the 2054 Ma old Bushveld Complex, in an attempt to unravel its tectonic and thermal evolution in the period immediately following intrusion and crystallisation. The geochronological techniques used have been specifically chosen to sample specific temperature episodes in the cooling of the Complex, rather than to necessarily provide an accurate emplacement age, The Bushveld Complex is seen in this study as part of the Bushveld Magmatic Province, rather than as an isolated intrusion, The geochronological data are therefore interpreted in the context of the current understanding of the Proterozoic tectonic and thermal history of the Kaapvaal Craton. The development of clean chemical methods and accurate geochronological methods are essential to this type of study. The reduction of laboratory blanks, especially for lead and the development of laboratory techniques for the analysis of small samples therefore played an important part in this study. It has been possible to lower analytical blanks, especially lead blanks to levels where the analysis of small samples is possible. In addition, the zircon evaporation technique was attempted. Phlogopite micas from the Critical Zone of the Bushveld Complex give a wlde range of Rb-Sr model ages, some almost 100Ma older than the preferred age. This indicates a period of hydrothermal alteration of considerable duration at the same time as the intrusion. The slightly young Rb-Sr age recorded for all the mica and whole rock data collected for this study indicates the alteration of the micas which is evident from petrographic and electron microprobe studies. U-Pb and Pb-Pb zircon ages are also Significantly younger than the preferred age, indicating a degree of alteration. This is also seen in the discordance of the zircons seen in the U-Pb data.
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Greyvensteyn, Renee May. "A GIS-based structural analysis of the Bushveld Complex and surrounding areas." Diss., 2001. http://hdl.handle.net/2263/26417.

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Sepato, Obone. "Statistical and wavelet analysis of density and magnetic susceptibility data from the Bushveld Complex, South Africa." Thesis, 2015. http://hdl.handle.net/10539/18528.

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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2015
The Bushveld Complex (BC) is the largest known layered intrusion. This suite of rock crop out in northern South Africa to form the Western, Eastern and Northern Limbs. Most research carried out focuses on the mineralized horizons in the Rustenburg Layered Suite (RLS) of the BC. This study presents a large database of wireline geophysical logs across a substantive part of the stratigraphy of the RLS. These consist of density and magnetic susceptibility datasets sampled at 1 cm. The major lithologies of the RLS intersected in the boreholes presented are gabbro, gabbronorite, norite and anorthosite whose density histograms reveal that they are predominantly normally distributed, with density averages of 2.86-2.91 g/cm3. The lithologies consist of mainly two minerals, pyroxene and plagioclase. In general, the average density increases with an increase in pyroxene. The distribution of the magnetic susceptibility for these lithologies has a large variation from SI to 13.2 SI, which is typical of layered intrusions. Susceptibility distributions are also multi-modal, asymmetric and not normally distributed, which makes the average magnetic susceptibilities less representative of the lithologies. Cross-correlation plots between density and magnetic susceptibility for several boreholes show that the above-mentioned lithologies form clusters (circular to elliptical), which typically overlap. This has been further investigated using k-means classification, to automatically detect these clusters in the cross-correlation plots and to compare these with those created by lithologies. The comparison shows some degree of correlation, implying that physical properties can be used to identify lithologies. This is particularly true for the Eastern Limb. However the classification has not been effective in all of the boreholes and often becomes complicated and an inaccurate representation of lithology log. This occurs in boreholes in which there is an overlap in the physical properties of the abovementioned lithologies. Analysis on the density and magnetic susceptibility data has also been carried out using wavelet analysis at individual locations across the BC. This has revealed multi-scale cyclicity in all of the boreholes studied, which is attributed to subtle layering created by variations in modal proportions between plagioclase and pyroxene. In addition to this, since layering is generally ubiquitous across layered intrusions, this cyclicity can be assumed to be present across the entire BC. This technique may become increasingly important should the cyclicity in physical property data correlate with reversals in fractionation trends since this may suggest zones of magma addition, whose thickness or III volumes can be quantified using wavelet analysis. This could be an important contribution since the current perspective on magma addition in the RLS is that four major additions have formed this 8 km thick suite of rocks, as opposed to smaller periodic influxes of magma. Wavelet-based semblance analysis has been used to compare the wavelengths at which the cyclicity occurs across boreholes. A comparison of wavelengths of this cyclicity shows that boreholes in the northern Western Limb show positive correlation in the density data at wavelengths >160 m and 20-60 m, while those further south show correlations at wavelengths of 120-200 m and 60-80 m. Boreholes of the Eastern Limb show positive correlation in the density and magnetic susceptibility data at wavelengths of 10-20 m, 20-30 m and 5m. These positive correlations across boreholes in density and magnetic susceptibility respectively, may imply that cyclicity may be produced by a chamber-wide process for several kilometres of the BC.

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"A mineralogical and petrographic study of prematoids and layered rocks of the upper critical zone of the western Bushveld Complex, South Africa." Thesis, 2015. http://hdl.handle.net/10210/14325.

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D.Phil.
This study which describes rocks of the Upper Critical Zone of the Bushveld Complex is subdivided into three parts. The main rock type of the Upper Critical Zone, the noriteanorthosite, is the subject of the first part. Inclusions in chromite and plagioclase were studied. The inclusions' in chromite were observed at different stages of their formation. The chromite crystals usually overgrow plagioclase, pyroxene and hydrous minerals (biotite, amphibole and clinozoisite) trapping them at grain boundaries or triple junctions of chromite host grains. With 'continuous growth of the host minerals the inclusion starts changing its shape from elongated to circular and the hydrous mineral proportion of the inclusion increases. Simultaneously amphibole changes its composition from pargasitic to tremolitic...

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Wabo, Hervé. "Paleomagnetism of post-Transvaal sill complexes, selected dykes and the Uitkomst Complex - relation to the Bushveld Complex." Thesis, 2014. http://hdl.handle.net/10210/8790.

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Ph.D. (Geology)
The Paleoproterozoic (i.e. 2500 Ma to 1600 Ma) apparent polar wander path (APWP) for the Kaapvaal craton (KC) is not well constrained, due to the lack of reliable paleopoles and absence of numerical ages for existing poles. In addition, the duration of emplacement, and timing of remanence acquisition of the Rustenburg Layered Suite (RLS) and other units of the Bushveld Large Igneous Province (LIP) are still unclear. During the present paleomagnetic study, samples were collected from the small intrusions that occur around the RLS and that are believed to be related to the Bushveld LIP for the establishment of new paleomagnetic and virtual geomagnetic poles. In addition, samples from post-Transvaal sills and dykes were targeted for U-Pb dating and geochemical analyses. Geochronological and geochemical data helped to constrain the timing of the newly defined paleopoles. These paleopoles were used in conjunction with previously published ones from KC to evaluate the APWP for this craton during the Paleoproterozoic. Two of the studied post-Transvaal sills in the eastern KC revealed U-Pb ages that are identical to the age recently reported from the Marginal Zone of the RLS. Geochemical signatures of sill samples were in very good agreement with the newly obtained ages. New ages and geochemical data provided constraints on the magnetic components recorded by the sills. The results confirm the existence of B1 Bushveld magma-related sills on KC as well as pre and post-Bushveld sills as previously suggested. Particularly, dataset from the B1 Bushveld magma-related sills allowed for understanding the magnetic history of the RLS at the early stages (Marginal Zone) of its formation. Paleomagnetic sampling of the Uitkomst Complex provided constraints on the remanence acquisition of this complex and also helped to understand the timing of the Bushveld magmatism outside of the main complex. Paleomagnetic data from a post-Transvaal dolerite dyke swarm near Lydenburg revealed a complex magnetic history. Characteristic magnetic components constrained by geochemical analyses were not similar to the RLS, but indicate probable relationship to other units of the Bushveld LIP. The new ages generated in this study coupled to those previously obtained from the upper layers of the RLS suggested that this suite emplaced within a time period of at least 4 million years. Paleomagnetic results from the B1 Bushveld magma-related sills and available data from the upper layers of the RLS reveal that during the RLS emplacement, the Earth’s magnetic field reversed at least eight times. These results, together with data from the Lydenburg dykes, further indicate a minimum of nine changes in polarity of the Earth’s magnetic field during the formation of the Bushveld LIP. During the present study, new pole positions of different reliability were added to the existing paleomagnetic database for the KC. Paleopoles from the Paleoproterozoic database of the KC (including those generated in the present study) were used to propose a new APWP for this craton from ~2200 Ma to ~1800 Ma. Particularly, poles from the B1 Bushveld magma-related sills and Uitkomst Complex provide the information to identify striking features in the APWP of the Paleoproterozoic KC.

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Courtnage, Paul Michael. "Post-Transvaal deformation between the Johannesburg dome and the Bushveld complex." Thesis, 1995. https://hdl.handle.net/10539/24288.

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A dissertation submitted to the Faculty of Science, University or the Witwatersrand, for the degree of Master of Science.
The study of an area north of the Johannesburg Dome has revealed that the rocks of the Transvaal Supergroup have been affected by widespread deformation, as well as metamorphism to the greenschist facies. Thermal modelling suggests that the metamorphism, and hence porphyroblast growth, can probably be attrIbuted to the thermal effect of the Bushveld Complex. Thus, textural relationships between porphyroblasts and cleavage microstructure in slates could be utilized to establish the relative timing of ductile deformation events in the area. (Abbreviation abstract)
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Shelembe, Refilwe Pamela. "The Merensky Unit, Lonplats' Mines, western Bushveld Complex." Thesis, 2008. http://hdl.handle.net/10539/5910.

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