Dissertations / Theses on the topic 'Bushveld Igneous Complex'

Philosophiae Doctor - PhD<br>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.<br>NRF Inkaba ye Africa Iphakade<br>2020-08-31

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.

The presence of trace transition metal species in the atmosphere can be attributed to the emission of particulate matter into the atmosphere by anthropogenic activities, as well as from natural sources. Trace metals emitted into the atmosphere can cause adverse health–related and environmental problems. At present, limited data exists for trace metal concentrations in South Africa. In this investigation, the general aim was to determine the concentrations of trace metals in atmospheric aerosols in the industrialised western Bushveld Igneous Complex, as well as to link the presence of these species in the atmosphere to possible sources in the region. The measurement site was placed in Marikana, a small rural town situated 35 km east from Rustenburg in the North West Province of South Africa. It is surrounded by numerous industrial and metallurgical operations. MiniVolumeTM samplers and Teflon® filters (2 ;m pores) were utilised to collect PM2.5 and PM10 particulate samples. The MiniVolumeTM samplers were programmed to filter 5 litres of air per minute for 12 hours per day, over a six–day period. The starting time for sampling was altered every six days, in order to obtain both day and night samples. Sampling was performed for a period of one year. The collected samples were chemically analysed with inductively coupled plasma mass spectroscopy (ICP–MS). Surface analysis of the sampled filters was performed with a scanning electron microscope (SEM) in conjunction with energy–dispersive spectroscopy (EDS). The dataset was also subjected to factor analysis in an attempt to identify possible sources of trace metal species in the atmosphere. The concentrations of 27 trace metals (Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Pd, Cd, Ba, Pt, Au, Hg, Tl, Pb, U) were determined. Pd, Hg, Tl, U, Ca, Co, As, Cd, Ba and Au were above the detection limit 25% or less of the time during the sampling period. With the exception of Ni, none of the trace metals measured at Marikana during the sampling period exceeded local and international standards. Higher Ni levels were possibly due to base metal refining in the region. Pb, which is the only metal species that has a standard prescribed by the South African Department of Environmental Affairs (DEA), did not exceed any of the standards. It is also significant to refer to Hg that was below the detection limit of the analytical instrument for the entire sampling period. The impact of meteorological conditions revealed that wet removal of atmospheric PM10 trace metals was more significant than the wind generation thereof. During the dry months, the total trace metal concentrations in the PM10 fraction peaked, while PM10 particles were mostly washed out during the wet season. Wind speed showed an unexpected inverse pattern compared to wet deposition. A less significant seasonal trend was observed for the trace metal concentrations in the PM2.5 fraction, which was attributed to a faster replenishment of smaller particles into the atmosphere after rain events. Separation of trace metal concentrations into PM10–2.5 and PM2.5 fractions indicated that 79% of the total trace metal levels that were measured were in the PM2.5 fraction, which indicated a strong influence of industrial and/or combustion sources. Fractionalisation of each of the trace metal species detected showed that for each metal species, 40% and more of a specific metal was in the PM2.5 fraction, with Cr, V, Ni, Zn and Mn occurring almost completely in the PM2.5 fraction. Surface analysis with SEM supported results from the chemical analysis, which indicated that a large fraction of the particles was likely to originate from anthropogenic activities and from wind–blown dust. SEM–EDS also detected nonmetallic S that is usually associated with the Pt pyrometallurgical industry that is present in the western Bushveld Igneous Complex. Correlations between Cr, V, Ni, Zn and Mn revealed that the main sources of these species were pyrometallurgical industries. Explorative factor analysis of the unprocessed and Box–Cox transformed data for all 27 metals detected, resolved four meaningful emission sources, i.e. crustal, vanadium related, base metal related and chromium related. Comparison of trace metal species to other parameters measured (e.g. CO, BC) also indicated pyrometallurgical activities and wind–blown dust to be the main sources of trace metals in this region.<br>Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.

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.

>Magister Scientiae - MSc<br>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.<br>National Research Foundation

>Magister Scientiae - MSc<br>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.

The Bushveld Igneous Complex (BIC) is the largest layered mafic intrusion in the world and contains the largest known deposits of vanadium, chromium and Platinum group elements on the planet, as well as large deposits of iron, nickel, copper, tin and fluorite. To aid and improve our understanding of the tectonics that prevailed during the emplacement of the Bushveld Complex relevant data can still be extracted from the metamorphic aureole of the Complex, not the least among which are accurate determinations of pressure conditions during peak metamorphism. A relatively large number of geothermobarometric investigations have been performed on the Bushveld Complex aureole. The summation of all the thermobarometric studies on the Bushveld Complex aureole produces a dataset with largely divergent pressure-estimates, ranging from 1.5 kbar to 5.5 kbar. This study’s main aim was to produce new thermobarometric data for the Eastern Bushveld Complex aureole. To this ends metapelites from the aureole were sampled between Lydenburg and somewhat northwest of Penge. Polished thin-sections were produced for a number of samples and studied under microscope. After XRF analyses were performed on a refined number of samples, pseudosections for these samples were produced using Perplex. Electron microprobe analyses were used to analyze mineral chemistries of five samples and the resultant data used to construct isopleths for these samples in Perplex. The isopleth data was then used to scrutinize and, where possible, refine PT-estimates. The principal results obtained from mineral equilibrium modeling were the pseudosections and isopleths of samples DY09-54 and DY09-56. These samples’ cumulate results suggest that the metapelites of their sampling locality, which lies roughly ~36 km northwest of Penge, reached 530-565 ºC and 2230-2960 bar during peak metamorphism. Modelled isopleths of MnO/(MnO+CaO+FeO+MgO) suggest that these estimates be refined to 550 ± 5 ºC and 2650 ± 20 bar. These pressure estimates agree well with the majority of barometric studies in the literature that post-date the nineteen-eighties. The pressure estimates of 2230-2960 bar suggest that DY09-54 and DY09-56 were at a crustal depth of 7.9-10.4 km during peak metamorphism, assuming that a roughly 1.5 km thick load of rock, mainly of the Rooiberg Group and/or the Lebowa Granite Suite, were situated above the Rustenburg Layered Suite and at the top of the pile that overlay the samples. In such a case the Rustenburg Layered Suite’s contribution to the load would have represented a 4.2-6.7 km thick pile of these mafic rocks and, assuming that the load of Pretoria Group strata in the floor to the Complex had a thickness of 2350 m, the base of the Rustenburg Layered Suite would have been at a crustal depth of 5.6-8.0 km during peak metamorphism and directly above samples DY09-54 and DY09-56. Modelled palaeogeotherms together with the peak-metamorphic crustal depths estimated for samples DY09-54 and DY09-56 suggest that at peak metamorphism the samples’ temperatures had been elevated by no less than 320-355 °C, assuming that no thermal metamorphic effect was active on the samples just prior to the intrusion of the Bushveld Complex. Copyright<br>Dissertation (MSc)--University of Pretoria, 2012.<br>Geology<br>unrestricted

A project report submitted to th~ Faculty of Engineering, University of the Witwatersrand, Johannt:')sburg, in par'cia1 fulfilment of the requirements fOl~ t.he degree of Master of Soience in Engineering (Mining). Roodepoort, 1991.<br>The Mines and Works Regulations allow the undermining of surface structures under conditions which are Itniformly applied in both the Central Witwatersrand and Bushveld Igneous Complex regions. which are different to There are, the Central however, factors Witwatersrand and Bushveld Igneous Complax and which affect the undermining of surface structures. Although the determination of the underground area affected by the restriction to mine under or near sut"face structures ("restricted area") is based on acoepted engineering principles t the determination of support requiremen'':.sfor the protection of the surfaoe is based on an extraction ratio or the conscruc+Lcn of waste packs and do not consider geotechnical differences. These requirements may re~ult in over- or underdesigned pillars, in spans bl'ilt.weenpillars either. being under- or overdesigned and in the lo-:::king up of valuable minerals. The depth cut-off of 240 m bel,ow surface at which the conditions are applied, Ls valld. There are similarities between the mining practices in the two environments based on the geometries of the orebodies and the strengths Of the oVerlying strata. However, pillar design and calcula'!:.ionof the mine spans between pillars differ fundamentally, as the strata immediately overlyin~ the Bushveld Ign~oue Complex on-reef exoavations are generally weaker than the rock masses in the Wi'l:.watel:'sranTdh.e pyroxenites oVerlying the UG2 re!llfare intersected by closely joints and to a depth spaced and moderately dipping of about 70 m the effects of weathering can be substantial. As a result the pyroxenites need to be partially or totally supported as a deadweight. The presence of geotechnical structures such nS dykes and faults further weakens the strata weathering along jointed zones on their margins 1S Severe and can extend to depths of 100 m. The de'.~erminationof safe mine spans depend on the competency of the norite/anorthosite series overlying the Merensky and UG2 reefs. Graphs based or; the Mohr-Coulomb failure index have been designed from which safe mine spans can be read off. The design of pillars is based on strength of material criteria and the orientation of the major jointing. The l1\iningon the Witwatersrand L. the area and depth range of interest has reSUlted in mainly supercriti(:lal mine spans, especially on the South reef horizon resulting in the subsidence of the overlying strata. Formulae have been designed to calculate the theoretical height Of caving in both the South and Main reef workings which, in conjunction with the graphs from which safe mine spans can be read off, can be used to determine maximum span widths.

A thesis submitted in fulfilment of the requirements for the degree of PhD in Geology< University of the Witwatersrand.<br>Numerous small base-metal deposits occur in the acidic rocks of the Bushveld Complex, and modern exploration programs are currently re-examining this metallotect in an attempt to refine the current working hypothesis for mineralisation in these granites. The hypothesis proposed for the origin of mineralisation is multifaceted, encompassing both spatial and temporal relationships between at least three episodes of ore formation. The first episode of mineralisation (typified by the Zaaiplaats tin deposit) occurred at relatively high temperatures (>600'C to 4000' C), and resulted in the formation of orthomagmatic cassiterite, scheelite and an early generation of fluorite. At lower temperatures (200°C<T<400°C), where processes were essentially fluid dominated, a mesothermal Cu-Pb-Zn-As-Ag-Au assemblage was deposited (exemplified by the Spoedwel, Boschhoek and Albert copper and silver deposits). A third episode of mineralisation resulted in the formation of an Fe-U-F assemblage and is recognised at several, but not necessanly all, of the deposits examined (for example, the Albert silver deposit). The extended nature of this three-stage paragenetic sequence is considered to reflect widespread mixing between an early fluid derived by H20-saturation of the granitic magma and an external meteoric/connate fluid, circulation of which was stimulated by the long-lived high heat-productive capacity of the Bushveld granites, as well as exhumation of the metallotect; The early high-temperature Sn/W assemblage was precipitated while magmatic fluids dominated the system. With time, the pluton cooled and was subject to regional uplift. Fractures developed, acting as conduits for external fluids of meteoric and/or connate origin. The late magmatic fluids, enriched in incompatible metals (and volatiles), interacted with the latter fluid, resulting in the localised precipitation of a secondary, lower-temperature mineral assemblage (Cu-Pb-Zn) in the zone of fluid mixing. As the external fluid component became progressively more dominant, the paragenesis changed, forming the :final Fe-U-F assemblage. The formation of these three different, temporally separate assemblages is adequately explained in terms of a fluid mixing model, wherein the concentration ofmetaIs and localisation of ore deposits are controlled by lithology and structure.<br>Andrew Chakane 2018

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science, 2020<br>The Bushveld Complex was emplaced by repeated injection of magma ranging in volume from small to large pulses (Eales and Cawthorn, 1996). It consists of five limbs, namely; northern limb, eastern limb, western limb, far western limb as well as south-eastern limb and is variably enriched with ores ranging from chromium and platinum group elements (PGE) to vanadium (Eales and Cawthorn, 1996). The Complex extends north of the Hout River Shear Zone (van der Merve, 1976; Vermark and van der Merve, 1986) that was recently proven at the Waterberg Project area (Huthmann et al., 2016; Kinnaird et al., 2017). This research was proposed to further prove the existence of the Bushveld Complex north of the Hout River Shear Zone. The task was to evaluate how the Non Parella sequence (NP1) correlates with the known northern limb (south of the Hout River Shear Zone), the Villa Nora fragment and the Waterberg sequence as well as its affiliation with the Bushveld Upper Zone. Furthermore, Huthmann et al(2017) stated that there is a lack of stratigraphic connection between rocks north and rocks south of the Hout River Shear Zone and this research aimed to evaluate this. The 2500 m deep NP1 borehole was drilled by Rand Mines Ltd in 1991 on the Non Parella farm located north of the Hout River Shear Zone and west of the Waterberg Project area. The entire core was logged as the Upper Zone by the Rand Mines exploration team. To further evaluate the NP1 sequence, core logging and sampling were carried out in April 2017 at the Council for Geoscience core library. Core logging was followed by the petrographic description of thin sections and whole rock XRF analysis undertaken at the University of the Witwatersrand in 2017. Sr isotopic analysis of fresh, unaltered plagioclase grains using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) was also performed at the University of Johannesburg in June 2018. The stratigraphy of the NP1 core is made up of Waterberg sedimentary rocks and dolerite sills from surface to a depth of 1312 m below surface. From 1312 m to 2158 m further below surface is the fine-grained to porphyritic gabbronorite package. The lower unit of the NP1 sequence from 2158 m to end of hole at 2500 m consists of magnetite and olivine-rich gabbroic rocks. These olivine-rich gabbroic rocks are olivine-bearing gabbro, plagioclase-phyric (plagio-phyric) olivine gabbro, and olivine gabbro to troctolite, and the section includes a 3.5 m interlayer of mottled anorthosite. The gabbronorite section includes a number of subvertical feldspar-quartz-magnetite veins and feldspar veins while the zone of the transitional contact between gabbronorite and olivine gabbro includes metasedimentary xenoliths. NP1 whole rock geochemistry does not reveal the upwards Si, Fe, and P enrichment expected for the Bushveld Upper Zone as identified by von Gruenewaldt (1973) in the eastern and western limbs and by Ashwal et al (2005) in the northern limb. It rather reveals an opposite trend consistent with the visible increase in magnetite, fayalitic olivine and apatite contents towards the lower part of the NP1 intersection within the gabbroic rocks. The trace and major element compositions of NP1 gabbronorite appeared to be sharing similar characteristics with the compositions of low and high Ti volcanic rocks of the Dullstroom Formation (Buchanan et al., 1999) indicating that the NP1 gabbronorite package could belong to the Dullstroom Formation and not the Upper Zone as it was initially logged by the Rand Mines exploration team. Sr isotope analysis of plagioclase in situ was carried out to verify the NP1 sequence affiliation with the Upper Zone. The initial Sr ratios of plagioclase from NP1 gabbronorite range from 0.7042 to 0.7066 and are not consistent with the Upper Zone signature of 0.7063 to 0.7079 in the northern limb (Mangwegape et al., 2016) and 0.7065 to 0.7075 at the Waterberg Project area (Huthmann et al., 2017). In contrast, the initial Sr isotope ratios of plagioclase from NP1 olivine-rich gabbroic rocks, ranging from0.7064 to 0.7073, are consistent with an origin from the Upper Zone melts. This interpretation is also supported by the elevated while variable abundances of apatite, magnetite, and olivine within the NP1 gabbroic rocks that is consistent with the Upper Zone rock compositions elsewhere in the northern limb and the rest of the Bushveld Complex. Field relations between the Bushveld Complex and Rooiberg Group whereby the unconformable emplacement of the Rustenburg Layered Suite (RLS)cross-cut the Rooiberg Group, specifically the Damwal and Dullstroom Formations, across the Bushveld Complex (Buchanan et al., 2004: Buchanan, 2006) provides more evidence that the NP1 gabbronorite package indeed belong to the Rooiberg Group. Dullstroom Formation rocks form the roof of the RLS in the NP1 sequence. The intrusive relationships between the RLS and its roof are supported by evidence of metamorphism within the NP1 gabbronorite section that include the presence of recrystallised sieve-texture porphyroblasts of clinopyroxene and phlogopite as well as granoblastic texture and metamorphic associations of hornfels. Considering the analytical results from this research and evidence from literature, the NP1 borehole intersected an earlier unseen top contact (at 2158 m) of the Upper Zone with the metamorphosed rocks of the Dullstroom Formation. This correlation is consistent with the similarities in the mineral assemblages, the similar whole rock geochemical compositions, the identical Sr isotope composition of plagioclase, evidence of metamorphism and the occurrence of sedimentary xenoliths in the up-section of the NP1 core. The NP1 sequence further confirms the existence of the Bushveld extensive magmatic basin north of the Hout River Shear Zone. The absence of magnetitite layers at the NP1 sequence favours a provisional stratigraphic connection rather with the Waterberg Project area (located north of the Hout River Shear Zone) than with the Villa Nora sequence and the northern limb (both located south of the Hout River Shear Zone) supporting an earlier hypothesis on a lack of stratigraphic continuity between RLS sequences north and south of the Hout River Shear Zone (Huthmann et al., 2017)<br>CK2021