Thesis (M.Sc.(Geology))--University of Pretoria, 2008. / Abstract in English. Includes bibliographical references (leaves 123-126).

This project is an investigation of the UG2 cyclic unit of the Upper Critical Zone at Lebowa (Atok) / Thesis (M. Sc.)-University of KwaZulu-Natal, Westville, 2008.

Thesis (M.Sc.(Geology))--University of Pretoria, 2007. / Abstract in English. Includes bibliographical references (leaves 208-235).

Thesis (M.Sc.(Geology))--University of Pretoria, 2003. / Summary in English. Includes bibliographical references.

Thesis (Ph.D.(Mineralogy))--University of Pretoria, 2001. / Summaries in English and Afrikaans. Includes bibliographical references.

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

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

M.Sc. / This study focuses on the Merensky Reef (MR) occurring within the Two Rivers Platinum mine property in the farm Dwarsriver 372 KT, on the Southern sector of the Eastern Limb of the Bushveld Complex. Five MR exploratory drill core intersections were obtained. Petrographic and mineral chemical characteristics of these drill core samples focused on the characterization of minerals like clinopyroxene, orthopyroxene, plagioclase, chromite and olivine. Data of the cryptic variation of orthopyroxene, plagioclase and chromite, from a 10 m interval (approximate thickness of the section studied); from footwall through the MR to the hangingwall lithologies at Dwarsriver are described in this study. Locally the vertical cryptic variation of these minerals is broadly consistent with regional trends of the RLS. The lateral variation (i.e. along strike) is less pronounced; however, locally these minerals appear to be chemically evolving moving to the south of the property. Footwall orthopyroxene compositions vary from a minimum of En66 and reach a maximum of En84. Those of the MR range from En71 to En85. Hangingwall orthopyroxene compositions range from En60 and reach a maximum of En80. Plagioclase compositions in the footwall units range from a minimum of An69 and reach a maximum of An85. Those of the MR range from a minimum of An35 to a maximum of An84. This wide range in plagioclase compositions is believed to be as a result of the increased presence of fluids within the MR interval. The hangingwall plagioclase compositions range from An64 to An84. By analogy of the Western Limb, where the lithologies of the Northwestern sector are believed to be proximal to the feeder of this limb; the local lateral variation in the present study suggests that the lithologies of either the Central or Western sectors are most probably proximal to the feeder for the Eastern Limb. PGM assemblages associated with and adjacent to the MR chromitite stringers were evaluated using an MLA. Data obtained from this technique is in broad agreement with regional studies of the MR. With the aid of wholerock PGE assays the MLA technique has proven to be a powerful tool in evaluating PGM assemblages relatively quickly, from a few carefully selected samples. The mineralogical associations of the PGM with the gangue and host minerals have shown three main associations. These are the associations of chromite, BMS and silicates with the PGM, of which the base metal sulfide (BMS) association is remarkable given that these have a relatively low modal abundance. The relatively high mineralogical association of the BMS with PGM has been explained by a model involving a base metal sulfide liquid which possibly scavenged chalcophile and siderophile elements. Chromite chemistry and modal analyses of MR secondary silicate phases, which peak adjacent to the chromitite stringers, suggests elevated fluid overprinting within and adjacent to the chromitite stringers. The upper chromitite stringers, however, have higher abundances of PGM phases that are believed to be secondary in origin relative to the basal chromitite stringers. Generally the PGM associated with the upper chromitite stringers are also bigger in size averaging 70 μm as opposed to 27 μm for those associated with the basal chromitite stringers. The increase in grain size of the PGM along with the higher modal abundance of secondary PGM phases associated with the upper stringers is believed to be as a result of fluids. These fluids although affecting both the upper and basal chromitite stringers, appear to have had a relatively higher influence on the upper chromitite stringers. The most common PGMs encountered in this study are isoferroplatinum, sperrylite, michenerite, maslovite, cooperite, laurite and braggite.

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.