Includes bibliographical references. / Ten Gough Island primary magma compositions were calculated for use in constrained forward modelling. The primary magma compositions were calculated by the addition of 14-28% clinopyroxene and equilibrium olivine, in equal proportions, back into the primitive lava compositions in 1 % increments until an Mg# of 69 was reached. Constrained forward modelling methods were used in determining the chemical and mineralogical nature of the mantle source region as well as the required melting parameters required in producing the Gough Island suite of lavas. The models indicate that the full compositional range, as well as the crossing REE patterns at Dy, can be produced through ~5-8% equilibrium melting of a mantle source region composed of garnet lherzolite or ~30-50% melting of a garnet pyroxenite source.

Includes bibliographical references (leaves 185-193). / Small scale diver-assisted diamond mining has taken place since 1990 in the shallow marin (<30 m water depth) portions of Mining Licence 45 (Elizabeth Bay) between Halifax Island and Elizabeth Bay along the southwestern coast of Namibia. These operations in the northern part off the coast of the Sperrgebiet have produced almost 400,000 carats over a period of 17 years. Although sparse records remain from the early days, sufficient data from various sources were collected, collated and summarised to make meaningful observations. From historic and current diamond diving records, 4 submarine areas which have yielded high returns were described in terms of their geomorphology, sedimentology and diamond occurrence. Using detailed geophysical survey data (Sidescan Sonar and Multi-beam Bathymetry), the deposition of diamonds at these sites were modelled in GIS-based reconstructions. The diamond size frequency distribution (SFO) of the Shallow Marine (0 to -30 m) deposits in the study area is similar to the proximal aeolian deposit mined on land at Elizabeth Bay and the deeper Midwater (-30 to -70 m depth) deposits situated southwest of the study area.

Includes bibliography. / The Kaapvaal Craton is one of the best preserved of all Archean cratons. It is partially covered by the supracrustal sequences of the Witwatersrand, Ventersdorp and Transvaal Basin (and correlated Griqualand West Basin), which span almost a billion years (~3.1 to 2.2 Ga). This thesis describes and interprets eight newly available seismic reflection profiles, acquired by the vibroseis method to 6 seconds TWT, and totaling ~720 km in length. New stratigraphic and structural features are identified across three main regions: the Kaapvaal Craton's western margin, the northern margin or Bushveld lines (flanking the Thabazimbi-Murchison Lineament and across the western extremity of the Bushveld Igneous Complex) and the Kaapvaal Craton interior. The seismic data was interpreted using Charisma seismic interpretation software, Geoframe version 3.6 (developed by Geoquest, Schlumberger) on a UNIX, SUN workstation.

South Africa is an energy intensive economy which primarily relies on the burning of fossil fuel such as coal. The South African coal energy sector accounts for approximately 420 million metric tonnes of carbon dioxide emitted per annum. With present alarming concerns with regards to the ever-increasing atmospheric carbon dioxide concentrations resulting in global warming and climate change, several mitigation strategies have to be implemented. A majority of Carbon Capture and Storage (CCS) technologies require monitoring from potential leakages, making the process expensive. However, a benign technology exists to permanently store away anthropogenic CO₂ with products obtained instantaneously. This CCS technology is known as Mineral Carbonation. The fundamental procedure is a reaction between (magnesium - calcium - iron) silicates and CO₂ to form carbonates. The products of from the reaction require no monitoring and the fear of leakage of CO₂ is eliminated. Moreover, the carbonates from this technology are useful in the road, agriculture and building industries. The CO₂ storage capacity in mineral carbonation exceeds other CCS techniques. The South African mineral industry annually produce immense tonnages of ultramafic mine tailings. Due to the generally fine nature of the tailings, no further cost would be incurred in grinding the material. The platinum group metal (PGM), nickel and copper companies are examples of industries that produce massive tonnages of which could serve as potential feedstock for the purposes of mineral carbonation. Recent studies have shown that, the potential feedstock could sequester close of 70% of the annual CO₂ produced at Secunda, South Africa. A mineralogical investigation into the mineral carbonation potential of mine tailings was conducted using samples from seven mining companies. Four of the mining operations considered (Impala, Rustenburg, Amandelbult and Mogalakwena) are PGM operations mining the Merensky, Upper Group 2 (UG-2) and Platreef. Nkomati was another operation selected for the study, with samples collected from the Main Mineralised Zone (MMZ) and Chromititic Peridotite Mineralized Zone (PCMZ). Tailings material from the dormant O'okiep operation was the seventh, chosen for the study. To determine the suitability of these tailings for mineral carbonation, the particle size, surface area and mineral for each individual operation was accounted using Malvern, BET analysis, XRF, QXRD and QEMSCAN respectively. The overall fine-grained nature of the mine tailings was manifested in the particle size distribution results were sizes ranged from d(0.5) = 33.67 (Nkomati) to d(0.5) = 231.45 (Impala). The range in surface area was 1.45 m²/g (Amandelbult) to 5.89 m²/g (Nkomati). A theoretical carbonation capacity ranking scheme was developed where the seven mining companies selected for this study were graded based on their suitability for mineral carbonation. Three distinct factors made up the classification criteria of the ranking scheme. The first was the carbonation capacity. This was determined by the mineralogy, the Rco2 value and the tonnage of mine waste produced annually. The second major factor was the reactivity (ignoring kinetics) of the tailings. In this case, the particle size distribution and surface area of the respective mine tailings were considered. Thirdly, the distance from the CO₂ (Secunda) source was taken into account as the cost of transporting CO₂ to the mineral carbonation facility should be weighed up. In using these principles, Nkomati was unquestionably ranked first while O'okiep was rated last priority among the seven operations. The motive behind was to improve upon the theoretical carbonation capacity ranking scheme and in turn examining a variety of South African mine tailings for the purposes of detailed mineral carbonation studies in South Africa.

Includes bibliographical references (leaves 142-160). / The Cullinan kimberlite is a Group I kimberlite and is located in the northeastern region of the Kaapvaal Craton, South Africa. The kimberlite pipe has been dated at 1180 ± 30 Ma and intrudes the Bushveld Igneous Complex (2.05 Ga). This study explores the geochemistry of a suite of one hundred selected diamonds and their associated mineral inclusions. The majority of the diamonds described here are peridotitic (94%) and the remainder are eclogitic. The peridotic inclusions may be further subdivided into harzburgitic and lherzolitic parageneses.

Includes abstract. / An O, H, Sr and Nd isotope study was carried out on the ~ 2059 Ma Bushveld granites and granophyres. A small number of Rooiberg Group felsites were also studied.

Includes bibliographical references (leaves 97-115). / A suite of sulphide-bearing diamonds recovered from the Ellendale 4 and 9 pipes in the Ellendale diamond province of lamproite intrusions in north-western Australia have been investigated for their nitrogen aggregation state and the Re-Os isotope geochemistry of the sulphide inclusions. The Ellendale lamproites, dated at ca. 20 Ma (Allsopp et at., 1985) intrude the King Leopold Mobile Belt just south of the Kimberley craton and are thus an atypical, off-craton diamondiferous locality. The diamonds contain roughly equal proportions of peridotitic and eclogitic inclusions (Hall & Smith, 1984; Griffin et at., 1988; Jaques et at., 1989). The diamonds in this study range in size from 0.26 to 0.92 carats and are dominated, with the exception of one octahedron, by highly resorbed tetrahexahedroida.

This is a study of Phanerozoic carbonatites and related alkaline silicate rocks from Zandkopsdrift in Namaqualand, South Africa (55 Ma), and Marinkas Quellen (529 Ma), and Dicker Willem (49 Ma) in southern Namibia, all emplaced within the Proterozoic Namaqua Natal province. The aims of this thesis are to characterise their mantle source region, including the timing and nature of the metasomatism that affected their sources, and to constrain their petrogenesis, particularly the relationships between the carbonatites and associated silicate igneous rocks. These associated silicate igneous rocks include olivine melilitite, aillikite and alkaline lamrophyre at Zandkopsdrift, nepheline syenite and trachyte at Marinkas Quellen, and ijolite and trachyte at Dicker Willem. At both Marinkas Quellen and Dicker Willem, the trachytes appear to be derived primarily from fenitised country rock. The major and trace element characteristics, enrichment in LREE and other incompatible elements, large Zr-Hf-Ti depletions and high Zr/Hf ratios all appear to have been inherited from a metasomatised mantle source region rather than being the result of residual source mineralogy. The δ18O and δ13C values of carbonate in the study locations vary significantly. The δ13C values (-3.9 to -8.8 ‰) are within the range of mantlederived carbonatites, whereas the δ18O values are often significantly higher (+8.64 to +22.22 ‰, versus SMOW) for “mantle-derived” carbonatites. The higher δ18O values observed are most likely attributable to low-temperature, post-emplacement alteration by hydrous fluids. O-isotope thermometry of the silicate mineral pairs (clinopyroxene, amphibole, and biotite) gives close to magmatic temperatures (≈800 oC), whereas the equilibration temperature of calcite-silicate mineral pairs is lower. The carbonatite and associated igneous rock samples contain unradiogenic Sr and mildly radiogenic Nd isotope compositions below and above Bulk Earth/CHUR values respectively. This suggests that carbonatite magmas were generated from sources with long-lived Rb/Sr lower than, and Sm/Nd higher than, the primitive mantle. In ƐHf(t)-ƐNd(t) space, the carbonatites and associated silicate rocks plot as much as 8 ƐHf units below the terrestrial ƐNd-ƐHf array, indicating mixing of a source with moderate ƐNd and exceptionally unradiogenic Hf isotope compositions. The radiogenic Pb isotope composition of the carbonatites (206Pb/204Pbi ratios from 18.06 to 22.38), is consistent with a source having high U/Pb, akin to the HIMU mantle end member. The radiogenic isotopes of the carbonatites and the alkaline silicate rocks seem most consistent with a dominantly asthenospheric source, with minor contributions from lithospheric sources. There is little evidence supporting the derivation of carbonatites at the three complexes from parental hybrid carbonate-silicate magmas. Rather, the evidence seems most consistent with deriving the carbonatites directly from very low-degree mantle melts, which subsequently become variably differentiated, first by melt-rock interaction in the mantle and subsequently by fractional crystallization. The associated silica undersaturated silicate igneous rocks appear most likely to represent relatively primitive (melilitites) to differentiated (nepheline syenites) melts of metasomatic wehrlites that were formed by carbonatite-peridotite melt-rock interaction.

The Southern Marginal Zone (SMZ) of the Damara Belt, exposed in the Gaub Canyon in central Namibia, consists of fourteen lithotectonic units of high strain amphiholite facies rock with pelagic, hemi-pelagic and clastic sedimentary protoliths. These rocks are intercalated With lenses of metabasite. Regional high-pressure - low-temperature metamorphic conditions (~1O kbar and ~600°C) dominate the Southern and Southern Marginal Zones of the Damara Belt, leading to the interpretation that these tectonostratigraphic terranes formed in an accretionary prism along an ancient subduction margin. The structures in the SMZ are the result of progressive deformation, inferred to have initiated under low-grade metamorphic conditions (D₁) and evolved through prograde to peak metamorphism (D₂), ending in relatively low-temperature retrograde conditions (D₃). Each of the deformation phases is characterised by a foliation. D₁ is associated With pure shear dominated layer-parallel extension characterised by disrupted lithological layering and hedding-parallel foliation S₀+₁. D₃ is defined as deformation related to the formation of an axial-planar S₂ caused by folding of S₀+₁ around F₂ hinge lines. Widespread isoclinal recumbent folding resulted in transposition of these fahrics and the general foliation is thus termed S₀+₁+₂. This composite foliation contains a down-dip stretching lineation L₂. Folding was contemporaneous With top-to-the-SE directed thrusting in D₂ faults and shear zones that are seen to displace D₁ fabric. Fold hinge lines parallel to L₂ suggest D₂ is characterised by non-ideal simple shear. D₃ is defined by a crenulation cleavage S₃, at near right angles to S₀+₁+₂ foliation resulting from NW-SE pure shear shortening. This phase of deformation is also associated with retrograde, reverse faulting that is localised along some of the D₂ shear zones.

Includes abstract. / Includes bibliographical references (leaves 93-97). / This study is aimed at developing a workflow, and ultimately a model, for quantitative interpretation of sonic and seismic data. Measured data collected at the point of logging can be fraught with errors that can lead to wrong interpretation. One of such data is the shear wave velocity which in most cases is collected with the compressional wave velocity. The measured shear wave velocity log may contain errors that are due to drilling conditions, mud invasion etc. It may also contain cycle skips and might contain a lot of missing data and information. It is because of the poor quality of this type of log that has often made well log analysis companies and log interpreters neglect the measured shear wave log and subsequently generate or create an estimated shear wave log which they use for interpretation and modelling to check how the amplitudes vary with increasing offsets, among other uses.The workflow presented in this study considers the effect of working with the measured data, a reprocessed shear wave log and a locally estimated shear wave log. Specific correction procedures for invasion of the logs was done and synthetic seismograms were created for each type after correction for comparison to a 3D seismic data. The results of this study suggest that oil based mud invasion can cause significant problems to sonic logs especially the shear wave log. It also suggests that, if a shear wave log is of low or bad quality, a reprocessed shear wave log would be better for interpretation and modeling rather than a locally calibrated shear wave log or an estimated shear wave log using global predictions. The conclusion is evident from the synthetics generated using the measured shear wave data and the estimated shear wave data.