The 2.9 Ga old Usushwana Complex in the Piet Retief-Amsterdam area (south-eastern Transvaal) represents an exposed segment of a layered intrusion. It has the form of a dyke-like body elongated in a northwesterly direction, and extends to an estimated depth of 3000 -5500 m. Lithologically, the Complex consists of a cumulate succession of mafic rocks capped by granitoids and has intruded along the contact between the basement and the supracrustal sequences of the Kaapvaal Craton. Differentiation of an already contaminated gabbroic magma resulted in an ordered stratigraphic sequence comprising progressively more evolved lithotypes, with at least two imperfect cyclic units developed over a stratigraphic thickness of about 700 metres (Hlelo River Section). Meso- to orthocumulate textured gabbros and quartz gabbros grade upwards into magnetite- and apatite-bearing quartz gabbros, interlayered with discontinuous magnetitite horizons. The gabbros in turn grade into hornblende-rich, granophyric granodiorites. The differentiation process is regarded as having been considerably enhanced by the assimilation of acidic material, derived by partial melting of the felsic country rocks at the roof of the magma chamber. Recrystallisation of these rocks gave rise to the microgranites that locally overlie the granodiorites. Mineralogical, textural and geochemical features indicate a relatively advanced fractionation stage, suggesting that the exposed sequence of the Usushwana Complex in the study area represents the upper portion of the intrusion. No significant mineralised occurrences were identified. However, on the basis of similarities between the Usushwana Complex and other mafic layered intrusions which host significant ore deposits, it is suggested that economic concentrations of base metal(Cu-Ni) sulphides, PGE and chromitites are likely to be developed at lower stratigraphic levels.

The Cretaceous (133Ma) Kroonstad Group II Kimberlite Cluster is located approximately 200km south west of Johannesburg on the Kaapvaal Craton. The cluster is made up of six kimberlite pipes and numerous other intrusive dike/sill bodies. Three of the pipes are analysed in this study, which includes the: Voorspoed, Lace (Crown) and Besterskraal North pipes. These pipes were emplaced at surface into the Karoo Supergroup, which is comprised of older sedimentary rocks (300-185Ma) overlain by flood basalts (185Ma). At depth the pipes have intruded the Transvaal (2100-2600Ma) and Ventersdorp (2700Ma) Supergroups, which are comprised dominantly of carbonates and various volcanic units respectively. The pipes have typical morphology of South African pipes with circular to sub-circular plan views and steep 82o pipe margins. The Voorspoed pipe is 12ha in size and is characterised by the presence of a large block of Karoo basalt approximately 6ha in size at the current land surface. This large basalt block extends to a maximum of 300m below the current land surface. The main Lace pipe is 2ha is size with a smaller (<0.5ha) satellite pipe approximately 50m to the west. No information is available on the morphology of the Besterskraal North pipe as it is sub-economic and no mining has occurred. Samples from the Besterskraal North pipe were collected from the De Beers archives. The Kroonstad Cluster has been subjected to approximately 1750m of erosion post-emplacement, which has been calculated by the analysis of the crustal xenoliths with the pipe infill. The hypabyssal kimberlite from the three pipes shows a gradational evolution in magma compositions, indicated by the mineralogy and geochemistry. The Lace pipe is the least evolved and has characteristics more similar to Group I kimberlites. The Voorspoed and Besterskraal North kimberlite are intermediately and highly evolved respectively. The gradational evolution is marked by an increase in SiO2 and Na2O contents. Furthermore the occurrence of abundant primary diopside, aegirine, sanidine, K-richterite and leucite indicates evolution of the magma. The root zones of the pipes are characterised by globular segregationary transitional kimberlite, which is interpreted to be hypabyssal and not the result of pyroclastic welding/agglutination. The hypabyssal transitional kimberlite (HKt) is characterised by incipient globular segregationary textures only and the typical tuffisitic transitional kimberlite (TKt) end member (Hetman et al. 2004) is not observed. The HKt contact with the overlying volcaniclastic kimberlite (VK) infill is sharp and not gradational. The presence of HKt in the satellite blind pipe at Lace further indicates that the distinct kimberlite rock type must be forming sub-volcanically. The HKt is distinctly different at the Voorspoed and Lace pipes, which is likely a result of differing compositions of the late stage magmatic liquid. Microlitic clinopyroxene is only observed at the Lace HKt and is interpreted to form as a result of both crustal xenolith contamination and CO2 degassing. Furthermore the HKt is intimately associated with contact breccias in the sidewall. The root zones of the Kroonstad pipes are interpreted to form through the development of a sub-volcanic embryonic pipe. The volcaniclastic kimberlite (VK) infill of the Kroonstad pipes is not typical of South African tuffisitic Class 1 kimberlite pipes. The VK at Voorspoed is characterised by numerous horizontally layered massive volcaniclastic kimberlite (MVK) units, which are interpreted to have formed in a deep open vent through primary pyroclastic deposition. MVK is the dominant rock type infilling the Voorspoed pipe, however numerous other minor units occur. Normally graded units are interpreted to form through gravitational collapse of the tuff ring. MVK units rich in Karoo basalt and/or Karoo sandstone are interpreted to form through gravitational sidewall failure deep within an open vent. Magmaclasts are interpreted to form in the HKt during the development of an embryonic pipe and therefore the term autolith or nucleated autolith may be applied. Debate on the validity of the term nucleated autolith is beyond this study and therefore the term nucleated magmaclast is used to refer to spherical magmaclasts in the VK. The emplacement of the Kroonstad pipes is particularly complex and is not similar to typical Class 1 tuffisitic kimberlites. However the initial stage of pipe emplacement is similar to typical South African kimberlites and is interpreted to be through the development of an embryonic pipe as described by Clement (1982). The vent clearing eruption is interpreted to be from the bottom up through the exsolution of juvenile volatiles and the pipe shape is controlled by the depth of the eruption (+/-2km) (Skinner, 2008). The initial embryonic pipe development and explosive eruption is similar to other South African kimberlites, however the vent is cleared and left open, which is typical of Class 2 Prairies type and Class 3 Lac de Gras type pipes. The latter vent infilling processes are similar to Class 3 kimberlites from Lac de Gras and are dominated at the current level by primary pyroclastic deposition.

A number of ilmenite-rich heavy mineral deposits occur along the northern margin of the intracratonic Karoo basin, and are hosted by the fluvio-deltaic Middle Ecca Group. Coastal reworking of delta front sands within a regressive, microtidal shoreline may be considered as a depositional model for the development of the heavy mineral deposits. An economic analysis of titanium suggests long term positive demand, and sustained high prices for this commodity. An evaluation of the Dwarsfontein ilmenite-rich heavy mineral deposit, using available data, indicates how important it is for deposits of this type to be situated close to an upgrading plant or export harbour.

This study is an extensive lithological, petrographical, mineralogical and geochemical description of fresh Collingham Formation core samples collected from borehole SFT 2, located on the farm Slangfontein, south of Jansenville in the Eastern Cape, South Africa. The borehole, drilled to 295 m on the northerly limb of a shallow westerly plunging syncline, intersected the lower Ecca Group rocks of the Ripon, Collingham, Whitehill and Prince Albert Formations and terminated in the upper Dwyka Group. A comprehensive log and stratigraphic column were compiled for the Collingham Formation and fresh core samples were analysed using X-Ray Diffraction (“XRD”), X-Ray Fluorescence (“XRF”), mercury porosimetry, and Total Organic Carbon (“TOC”). Thin section microscopy and Scanning Electron Microscopy (“SEM”) analyses were carried out on selected samples of core from borehole SFT 2. The matrix supported, massive to laminated lithological units of the Collingham Formation are interpreted as detrital, terrigenous sediments. These sediments are composed of intercalated fine-grained, poorly sorted, non-fissile mudstone; fine- to very fine-grained, predominantly pyroclastic airfall tephra; and less common fine-grained sandstones. Sediments of the Collingham Formation are considered to be immature, composed primarily of clay and aluminosilicates. The predominance of a clay fraction and aluminosilicates in mudstone samples is indicated by elevated K2O/Al2O3 ratio values, and the relationship of Zr, Al2O3 and TiO2. The presence of glauconite within the Collingham Formation indicates deposition in a mildly alkaline, slightly reducing marine environment. Rb/K ratio values (1.9 – 2.3 x 10-3) indicate brackish to slightly marine conditions, while low Zr/Rb ratio values indicate a low hydro-energy environment, with stable bottom water conditions. Hf and Nb concentrations indicate that detrital input was greatest during the deposition of tuffaceous units; while stable mineral assemblages and a low Fe2O3/K2O ratio values indicate deposition close to the source. A variation in Si/Ca values indicate times when sediments were affected by turbidity, interspersed with times of relative quiescence. The predominance of K2O over Na2O indicates that the Collingham Formation is alkali-rich, while SiO2/Al2O3 ratio values and the relationship of Zr, Al2O3 and TiO2 indicate that sediments are immature. In the lower portion of the formation, non-sulphidic, anoxic conditions are indicated by Mn/Al, V/(V+Ni), V/Cr ratio values, the Fe-Mn- V content, and the correlation between V and TOC. The upper portion of the formation is considered dysoxic, due to the presence and distribution of pyrite framboids, which indicate a fluctuating O2 level, likely indicating deposition at the interface between anoxic and slightly more oxic conditions. V/Cr ratio values indicate that the O2 regime was lowest during the deposition of the mudstones. The Chemical Index of Alteration (“CIA”) indicates a consistent weathering regime throughout the deposition of the Collingham Formation, associated with a temperate climate on the interface between glacial and tropical conditions. Although an anoxic and low hydro-energy environment is generally favourable for hydrocarbon accumulation, the Collingham Formation contains low levels of Total Organic Carbon (well below 0.9 per cent) and low porosities (ranging from 0.35 per cent to a maximum of 2.22 per cent), both of which are characteristic of a poor source for gas accumulation. Due to the laminate nature, permeability and fracturability of the Collingham Formation, there is the potential that the formation may form a good sealing sequence to the potentially gas-rich Whitehill Formation below. The metamorphic impact related to the Cape Orogeny (± 250 Ma), and reflected in the textures of the minerals making up the sediments of the Collingham Formation, suggests the enhancement in the sealing efficiency of this formation.

The Beattie Magnetic Anomaly is the world’s longest terrestrial magnetic anomaly with a strike length of over 1000 km and a wavelength in excess of 100 km. Collinear with this is a large belt of elevated crustal conductivities called the Southern Cape Conductive Belt. Historical crustal interpretations proposed a common source of serpentinized ophiolite as an explanation for both the anomalous crustal magnetic susceptibility and electrical conductivities. Spreading between the Western and Eastern Cape of South Africa the mid- to lower crust that hosts these anomalies is obscured by the overlying Cape and Karoo Supergroups. Between 2003 and 2006, three high resolution geophysical experiments were completed across the surface maximum of the Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB). These included a magnetotelluric (MT) survey and near vertical reflection and wide angle refraction seismic profiles. Within the MT inversion model the SCCB appeared as a composite anomaly, which included a mid-crustal conductor which is spatially associated with the BMA and a laterally continuous upper crustal conductor which is located at depths equivalent to the lower Karoo Supergroup. Subsequently; the upper crustal conductor was identified in northern and eastern extensions of the magnetotelluric profile; a distance in excess of 400 km. Historical magnetometer and Schlumberger Sounding experiments have previously identified elevated conductivities in the Karoo sequences which were attributed to the Whitehill and Prince Albert formations. These carboniferous, transgressive sediments are known to be conductive from borehole conductivity surveys and direct measurements at surface. In order to constrain the conductive properties of these sediments, impedance spectroscopy (IS) experiments were completed on core samples collected from a historical borehole drilled near to the MT profile. Part One of this thesis presents the results of these experiments, which support the proposition that the Whitehill and Prince Albert Formations are responsible for the laterally continuous, sub-horizontal, upper crustal conductor visible in the MT inversion model. Vitrinite reflectance studies were performed on the same samples by the Montanuniversität, in Leoben, these results corroborate the proposition that elevated organic carbon, of meta-anthracite rank, is the primary conductive phase for the Whitehill and Prince Albert formations. Part two of this thesis completed forward modelling exercises using historical aeromagnetic data previously collected across the Beattie Magnetic Anomaly. Preliminary models were unable to fit the geometry of any single magnetic model with conductors present in the MT inversion model discounting the proposition that the SCCB and BMA arise from a single crustal unit. Two constrained models were arrived at through an iterative process that sought a best fit between the measured data and the NVR crustal interpretations. The first model, proposes a largely resistive unit which incorporates portions of elevated crustal conductivity; these conductors are spatially correlated to crustal portions also characterised by high seismic reflectivity. The size of this modelled body suggest the likely host of the BMA is an intermediate plutonic terrane, analogous with the Natal sector of the Namaqua Natal Mobile Belt as well as the Heimefrontfjella in Dronning Maud Land, Antarctica, with magnetite hosted within shear zones. This is in agreement with previous studies. The second model proposes a lower crustal sliver imaged in the NVR data at depths proximal to the Curie Isotherm for magnetite and hematite as the source of the BMA. At these depths geomagnetic properties such as burial magnetisation or thermo-viscous remanent magnetism (TVRM) can potentially be linked to regional scale tectonic processes and can theoretically elevate a body’s net magnetic susceptibility. TVRM has been proposed for long wavelength crustal anomalies elsewhere.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirement for the degree of Master of Science. 2016. / An important feature of the Merensky Cyclic Unit in the Bushveld Complex is the association of platinum group metals with narrow chromitite layers. The appearance and removal of chromitite layers in this unit has been used to define facies types. This study explores the hypothesis that individual chromitite layers within the Merensky Cyclic Unit at Marikana have distinguishing major element concentrations or ratios which could assist in tracing the continuity of the chromitite layers between facies types which is characterized by single or multiple layers. The examination of field relationships of the chromitite layers at the transition between facies types will be useful to improve understanding of lithological continuity. This study has two approaches; the first being the examination of underground exposures and petrographic analysis, and secondly by chemical analysis of chromite grains within the chromitite layers. No chromite mineral compositional trends or similarities were observed for grains in chromitite layers hosted by the same silicate mineral. The mineral chemistry evidence suggests that post cumulus processes are considered to have changed the primary chromite compositions and that reequilibration has occurred due to reaction with trapped intercumulus liquid. Little to no reaction with the host silicates of plagioclase and pyroxene is envisaged. The slow cooling of the Bushveld Complex has allowed intercumulus liquid a greater opportunity to equilibrate with the early minerals, destroying the early magmatic history by reaction and recrystallization. The cumulate deposition model envisaged to have formed the Merensky Cyclic unit at Marikana is by the emplacement of several pulses of superheated magma, supported by the occurrence of several chromitite layers within the sequence. / LG2017

M.Sc. (Geology) / Please refer to full text to view abstract

No abstract available. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2013.

The aim of the research focuses on characterizing heavy mineral assemblages and interpretation of the provenance of the Ecca Group of in the Eastern Cape Province, South Africa. In South Africa, the Ecca Group outcrops extensively in the Main Karoo Basin. Mudstone, siltstone, sandstone, minor conglomerate and coal are the major constituent lithologies within the group. For descriptive purposes, the Ecca is categorized into three different geographical areas: the southern area, the western and northwestern area and the northeastern area. Six of the sixteen geological formations, namely the Prince Albert, Whitehill, Collingham, Ripon, Fort Brown, Waterford and Koonap Formations are present in the study area and are best exposed in road cuttings. For purposes of comparison, the underlying Witteberg Group, the Dwyka (which has Formation status here), and the overlying Koonap Formation of the Beaufort Group, are included in the study. This study is motivated by the relatively little information that is available on the heavy minerals of the Ecca Group, and that research of this nature had not been undertaken in the study area before. Another contributing motivation was to determine whether heavy mineral assemblages could be used to identify formations of the Ecca Group and for correlating between different localities in accordance with studies done elsewhere. Additionally, diagnostic heavy mineral assemblages could aid with stratigraphic selection of future boreholes in the Ecca Group. Heavy minerals are natural provenance tracers because of their stable nature and hydrodynamic behaviour. They are both non-opaque and opaque, with apatite, epidote, garnet, rutile, staurolite, tourmaline and zircon being good examples of non-opaque grains while ilmenite and magnetite are the most common opaques. Heavies are either derived from stable minor accessory minerals or from abundant but unstable mafic components of the host rock. They are very useful in interpreting the provenance due to the fact that some minerals are diagnostic of certain source rocks. However, sediments are exposed to several factors (conditions) such as weathering, erosion, breakage due to abrasion, mixing and recycling during transportation from the source to the depositional area. This implies that there are parameters other than the parent lithology that determine their final composition.

A number of outcrops of the Witteberg Group and lowermost Karoo Supergroup rocks were studied in the area south of the Darlington Dam, Jansenville District, with the aim of documenting structural characteristics of the area. All lithologies are folded with fold styles varying from gentle to near isoclinal (based on interlimb angle). Fold axes are either sub-horizontal or plunging at gentle to moderate angles whereas axial planes dip gently to vertically (predominantly steep to sub-vertical). Folds verge predominantly towards the north but where southward verging they are associated with faulting or strongly folded areas. Folds plunge gently to the east-southeast and west-northwest. The area consists of a large anticlinorium with both first and second order folds occurring. Eastwest striking faults occur in the study area and are classified as normal, reverse and thrust faults. A study of the joint sets shows that there are four dominant joint directions, namely 18o, 33o, 97o and 107o (in order from least to most important). An interpretation of the tectonic history is presented in which the relationships between faults and folds show that faults formed during and after folding. Folding, and reverse and thrust faulting, occurred during the compressional events that formed the Cape Fold Belt, whereas the normal faults formed during the relaxation of these compressional forces or during the break-up of Gondwana.