Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2009. / Geology / unrestricted

At the Karee Mine of the Lonplats mining company in the Bushveld Complex, South Africa, the Rooikoppies iron-rich ultramafic pegmatite (IRUP), which covers the stratigraphy from below the UG2 chromitite layer up to the Main Zone, replaces cumulus anorthosite and pyroxenite. The Rooikoppies IRUP was studied using transmitted and reflected light microscopy, X-ray fluorescence, X-ray diffraction, and electron microprobe techniques. Two visually different varieties of IRUP were observed: a) a relatively smaller grained greyish variety and b) a relatively coarser grained greenish variety. In drill core, the IRUP body was observed to be in contact with the host cumulate rocks either by means of gradual or sharp contacts. Bulk rock compositions indicate that the Rooikoppies IRUP is enriched in Fe2O3, MgO, and CaO (relative to the cumulate host rocks) while having lower concentrations of Al2O3. Chemical differences between cumulus host rocks and IRUP are accompanied by changes in mineral assemblage and mineral chemistry. Spatially related IRUP samples revealed areas with potentially more pronounced increases in iron and magnesium contents relative to the host cumulate rocks. Element ratios indicate that aluminium acted as an immobile element during the formation of the IRUP body and that the addition of iron, magnesium, and calcium, through the action of hydrothermal fluids, diluted the already existing cumulus feldspar, resulting in the low concentrations of Al2O3 in the IRUP samples. The addition of iron, magnesium, and calcium also resulted in the crystallization of large proportions of clinopyroxene and olivine, and resulted in changes in the mineral assemblage and mineral chemistry, relative to the host cumulate rocks. The Rooikoppies IRUP body can be classified as a silicate rich variety (Viljoen and Scoon, 1985), consisting of clinopyroxene, olivine, plagioclase, secondary magnetite and ilmenite. It is suggested that the formation of the Rooikoppies IRUP is not due to a single event, but rather that the IRUP body formed through multiple replacement events, resulting in a network of chemically different zones within one large IRUP body. / Dissertation (MSc)--University of Pretoria, 2009. / Geology / unrestricted

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 / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2007. / Geology / MSc / Unrestricted

>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

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 1985. / Geology / unrestricted

A sequence of 3250 m of the Rustenburg Layered Suite and its associated mineralization south of Potgietersrus was investigated. Four episodes of faulting have deformed the area. This resulted in very early differentiates, not seen elsewhere in the Bushveld Complex, to outcrop together with economic concentrations of the best metallurgical grade chromite presently being mined in the Republic. The Mg:Fe:Ca ratio of theCa-poor pyroxenes varies from 89,5:8,8:1,6 in the lower zone to 44,2:52,3:3,37 in the upper zone. The latter composition demarcates the Fe-rich end of the two pyroxene limit. Textural evidence implies that there is a peritectic reaction between the ironrich Ca-poor pyroxene and the melt and that this may account for the termination of the two pyroxene field. A significantly higher mean Ko~~~F~p; for the study area (0,822) than for the other sectors of the Bushveld Complex (0,782) suggests that the pyroxenes of similar composition crystallized at higher temperatures in the Potgietersrus limb. Examination of the Al :Si ratio in Ca-rich pyroxenes from a variety of magmatic environments confirms that this variable can be used to monitor relative changes in the a ~~~t. Chemical data of the Ca-rich pyroxenes suggest that this phase define~ an Fe enrichment - Ca depletion trend during differentiation uhlike that for most other tholeiitic intrusions. The V205 content of the main magnetitite layer and the cr203 and the Cr/Fe2++Fe3+ values in the upper and lower chromitite layers in the study area are the highest encountered in the Bushveld Complex. Textural evidence in these layers show that they have been up-graded to dense monomineralic layers by postcumulus sintering. Calculated intensive parameters for the Potgietersrus magma suggest that it crystallized over a temperature interval from 1276°C in the lower zone to 1022°C in the basal portion of the upper zone. Oxygen fugacity conditions for the lower zone ranged from 10-6,21 to 10-4,98 atm whereas lower values of 1o-11 to 1o-9 atm were operative in the upper zone. The study area contains abundant concentrations of sulfides at several levels in the sequence. The separation of the sulfide liquid is related in most cases to new influxes of metal-rich magma and mixing with the residual magma in the chamber. Several definite sulfide facies occur in the layered sequence. Sulfur isotope investigations indicate that all the sulfur in the study area is mantle derived and that the isotopic composition of the sulfur was controlled by the prevailing fo2, which in turn controlled the partitioning of S02 and HzS between sulfide melt and magma. / Thesis (PhD)--University of Pretoria, 1983. / gm2014 / Materials Science and Metallurgical Engineering / Unrestricted

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M.Sc. / Please refer to full text to view abstract

Student Number : 9210081T - MSc dissertation - School of Geosciences - Faculty of Science / The occurrence of large, massive iron oxide deposits throughout the Bushveld Complex, South Africa, and its associated roof-rocks is well known. The style of mineralisation and the associated alteration exhibits many characteristics of iron oxide-copper-gold (IOCG) type deposits. The contained mineralisation is dominated by iron oxide and fluorite and is accompanied by a diverse polymetallic association, with anomalous fluorite, copper, gold, barite, uranium and LREE. The Ruigtepoort orebody, located in the western Bushveld Complex, is such an example and is surrounded by some 20 smaller occurrences in the upper stratigraphic portions of the Bushveld Complex, all displaying strong structural control. These IOCG bodies occur as narrow veins, hydrothermal breccias, subhorizontal sheets, or as pipe-like intrusions usually utilising pre-existing structures. Set in red Nebo granite, the mineralised core consists of severely chloritised rock that is haloed by progressively less-altered granite. The alteration passes from the chlorite core to more hematite-phyllosilicate-dominated alteration, to sericite-illite-dominated alteration; followed by the relatively fresh country granite. These alteration haloes dissipate rapidly away from the body over only a few metres. Sodic-calcic alteration described in other IOCG is not locally observed. Extensive zones of barren feldspar-destructive alteration exist, including K-metasomatism, sericitisation and silicification. Multiple alteration episodes appear to have occurred, resulting in extensive overprinting and a very complex paragenesis. The primary mineral assemblage consists of Fe-chlorite, fluorite, quartz, hematite, and specularite, with accessory pyrite and chalcopyrite. Multiple generations of hematite, quartz, fluorite and chlorite are also observed. At other localities, the assemblage is dominated by magnetite-actinolite-britholite. Significantly enriched concentrations of Au (2 g/t), Cu (0,45 wt%), Ba, Y and LREE are encountered in the small, mineralised core. A fluid mixing model is proposed characterised by an initial highly-saline, sulphur-poor magmatic fluid which mixed with a lower temperature oxidised, surficial fluid. Structure was probably a significant factor in determining the initial distribution of hydrothermal centres and the overall morphology of the entire system. Subsequently, continuous brecciation, alteration, mineral precipitation and fault activity helped develop the hydrothermal centres into a complex array of variably mineralised, lenticular, pipe-like and irregularly shaped breccia bodies.