Field work and mapping with the aid of aerial photographs have shown the north Gap Dyke to be a vertical intrusion 93½ miles long . It extends from a point about 4½ miles south of Cathcart to the coast where it enters the sea about 100 yards north of the Ngadla R lver mouth. It is composed of several rock types including dolerite pegmatite, granophyric dolerite, subophitic dolerite, and it has a more or less central core of mobilized sediment at the western end. The essential minerals of the dolerite types include zoned plagioclase, which is described in some detail, and augite. Less important are hornblende and micropegmatite. Accessories include apatite, ilmenite, magnetite, quartz, actinolite, prehnite, calcite and epidote. Iddingsite (?), saussurite and chlorite occur as alteration products. The mode of origin of the Gap Dyke magma remains an open question: it may have arisen as a result of normal crystal fractionation or as the result of hybridization in depth followed by differentiation.

D.Phil. Geology) / This study presents detailed petrographic, mineral-chemical and geochemical characteristics ofmafic intrusions from three iron oremining areas - Thabazimbi, Sishen and Hotazel - in southern Africa In addition, as themafic intrusions at the Thabazimbi, Sishen and Hotazel mines occur in close spatial association with iron and manganese ore, this study addresses the aspect of whether these intrusions have a bearing on the localization of these ores. Precise geochronologic data of these previously undated mafic dykes and sills is presented to classify them into a regional context. particularly in considering whether these dykes and sills are part of known Large Igneous Provinces (LIPs) in sonthem Africa. The Thabazimbi dykes are coarse grained dolerites while the sills are diabases. The dykes are younger than the sills. Composition wise, sills are dominantly basaltic andesites, while the dykes are dominantly hasaltic. Different to the sills, the dykes are characterized byrestriction of olivine, higher HFSE and LREE as well as less prominent negative Bu" anomaly. Geochemical and isotope chemical characteristics of the Thabazimhi dykes and sills are explained in terms of a combined partial melting, followed by fractional crystallization and crustal contamination with differentiation model. with the dykes showing greater crustal assimilation. The petrogenetic characteristics of the Sishen dolerite dykes in many ways resemble both the Colombia River Basalts and the typical Umkondo dolerites, and point to significant crustal contamination, typical of continental tholeiites. Geochemical characteristics of the Sishen dolerites is acconnted by the partial melting followed by fractional crystallization and crustal contamination, but unlike the Thabazimbi dykes and sills crustal assimilation is significant. At Hotazel, the petrographyand geochemistry of 'bostonites' bas been used to define their true composition while at the same time highlighting the presence of a -2 - 3 m thick iron ore unit associated with banded iron formation and manganese ore. Geochemically, the Hotazel 'bostonites' are "basaltic andesites' while textnra1ly, the Hotazel <bostonites' are essentially diabases. Regarding the iron ores that occurs in the Hotazel Formation at the base of the Pre-Mapedi nnconformity, they are composed of various forms of hematite with variable minor chlorite. quartz and carbonates. Iron ore genesis is attributed to supergene processes similar to those that have affected Sishentype iron ore below the Gamagara unconformity on the Maremane Dome. A U-Pb 2046.6±3.4 Ma age has been obtained for the crystallization of a Thabazimbi sill by dating titanite. This is interpreted to indicate that while the mafic/ultramafic component ofthe Bushveld Complex may have been emplaced over a short period, there was later magmatic activity at 2046 Ma, represented by the Thabazimbi sill and other late Bushveld Complex related intrusions such as the Uitkomst Complex at 2044 Ma. The 1044.3±7.5 Ma age obtained for the Sishen dolerites has resulted into two major interpretations. Firstly. the age is interpreted to be the minimum age for Umkondo LIP. The age shows that while large sections of the Umkondo LIP may have been emplaced within a short time interval, emplacement of end members ofthis LIP was in progress at least - 50 Ma later. Secondly. the age of these dolerites shows that they were emplaced subsequent to major iron ore genesis at Sishen. The new age. coupled with the limited extent ofthese intrusions shows that they played a no part in the origin ofthe bulk ofthe iron ore at the mine.

D.Phil. (Geology) / The structural history and mechanisms of bedding-parallel faulting associated with the Ventersdorp Contact Reef (VCR) on the Kloof Gold Mine are discussed. Pre-VCR deformation is determined by folding of the Booysens Shale Formation and the Turffontein Subgroup. Extension of Ventersdorp age (± 2700 Ma) probably took place by the simultaneous operation of normal, strike-slip and oblique slip faults (mixed-mode extension). Because the strikeslip and oblique-slip faults were extensional, they could be utilised as conduits for dykes, forming "Fault and Dyke Zones". Northwestward directed thrusting, which postdates the normal faulting, resulted in positive inversion. The thrust faults have a ramp-flat symmetry with ramps forming in the VCR horizon and the overlying Alberton Formation and flats forming in the underlying Booysens Shale Formation and along the contact between the VCR and the Alberton Formation. The thrust faults follow complex deformation paths, indicated by out-of-sequence thrusting, simultaneous folding and thrusting, underthrusting and compressed boudins. Hanging-wall ripouts, which can be related to this thrust event, are introduced as a shear sense indicator. No northwestward verging thrust faults of post-Transvaal age (post 2430 Ma) could be identified, indicating that this compressional event occurred prior to the deposition of the Black Reef Quartzite Formation. The minimum amount of shortening due to northwestward directed thrusting was estimated as 37 % with the help of restored sections. However, due to the out-of-sequence propagation of thrust faults, a control of the strain estimation was possible and true shortening probably exceeded the calculated amount of shortening considerably. The restoration of sections with out-of sequence thrusts is discussed in detail. Sheath fold-like structures in pseudotachylyte can be related to northwestward directed thrusting and are introduced as a new shear sense indicator.

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

Ph.D. (Geology) / The Paleoproterozoic (i.e. 2500 Ma to 1600 Ma) apparent polar wander path (APWP) for the Kaapvaal craton (KC) is not well constrained, due to the lack of reliable paleopoles and absence of numerical ages for existing poles. In addition, the duration of emplacement, and timing of remanence acquisition of the Rustenburg Layered Suite (RLS) and other units of the Bushveld Large Igneous Province (LIP) are still unclear. During the present paleomagnetic study, samples were collected from the small intrusions that occur around the RLS and that are believed to be related to the Bushveld LIP for the establishment of new paleomagnetic and virtual geomagnetic poles. In addition, samples from post-Transvaal sills and dykes were targeted for U-Pb dating and geochemical analyses. Geochronological and geochemical data helped to constrain the timing of the newly defined paleopoles. These paleopoles were used in conjunction with previously published ones from KC to evaluate the APWP for this craton during the Paleoproterozoic. Two of the studied post-Transvaal sills in the eastern KC revealed U-Pb ages that are identical to the age recently reported from the Marginal Zone of the RLS. Geochemical signatures of sill samples were in very good agreement with the newly obtained ages. New ages and geochemical data provided constraints on the magnetic components recorded by the sills. The results confirm the existence of B1 Bushveld magma-related sills on KC as well as pre and post-Bushveld sills as previously suggested. Particularly, dataset from the B1 Bushveld magma-related sills allowed for understanding the magnetic history of the RLS at the early stages (Marginal Zone) of its formation. Paleomagnetic sampling of the Uitkomst Complex provided constraints on the remanence acquisition of this complex and also helped to understand the timing of the Bushveld magmatism outside of the main complex. Paleomagnetic data from a post-Transvaal dolerite dyke swarm near Lydenburg revealed a complex magnetic history. Characteristic magnetic components constrained by geochemical analyses were not similar to the RLS, but indicate probable relationship to other units of the Bushveld LIP. The new ages generated in this study coupled to those previously obtained from the upper layers of the RLS suggested that this suite emplaced within a time period of at least 4 million years. Paleomagnetic results from the B1 Bushveld magma-related sills and available data from the upper layers of the RLS reveal that during the RLS emplacement, the Earth’s magnetic field reversed at least eight times. These results, together with data from the Lydenburg dykes, further indicate a minimum of nine changes in polarity of the Earth’s magnetic field during the formation of the Bushveld LIP. During the present study, new pole positions of different reliability were added to the existing paleomagnetic database for the KC. Paleopoles from the Paleoproterozoic database of the KC (including those generated in the present study) were used to propose a new APWP for this craton from ~2200 Ma to ~1800 Ma. Particularly, poles from the B1 Bushveld magma-related sills and Uitkomst Complex provide the information to identify striking features in the APWP of the Paleoproterozoic KC.