The Hartbees River Thrust Belt (HRTS) is a 40-60 km wide, southwest-vergent zone of complex structure, lithostratigraphy and high-grade metamorphism in the northeastern part of the mid-Proterozoic Namaqua Tectonic Province. The HRTS comprises the boundary zone separating the Bushmanland and Gordonia Subprovinces of the Namaqua Province. A knowledge of the movement histories of major ductile shear zones within the HRTS is fundamental to understanding the tectonic development of the belt, and Namaqua tectogenesis as a whole. In spite of this, no detailed microstructural kinematic studies have been attempted and the movement histories and age relationships of these shear zones have not been described in detail. This thesis represents a detailed microstructural kinematic study of a representative suite of orientated samples of mylonitic rocks, collected from five ductile shear zones within the HRTS. These shear zones include the Neusspruit Lineament, the Kakamas shear zone (KSZ), the Hugosput shear system (HSS), the Rozynenbosch-Ganzenmond shear zone (RGSZ) and the Graafwater shear system (GSS). Accepted modern methods of microstructural kinematic analysis were applied to samples of mylonite from these shear zones, in order to determine the precise orientation of the kinematic vectors, and the sense and relative ages of movements on each of the shear zones. Shear sense criteria, including composite SoC planar fabrics and shear band foliations, asymmetrical porphyroclast systems, mica-fish, oblique grain-shape and subgrain fabrics, asymmetrical microfolds, and the displacement of fractured rigid grains, together with a well-developed mylonite elongation lineation, conclusively indicate that SSW-directed thrusting occurred along the HSS, RGSZ, GSS and possibly along the Neusspruit Lineament, while normal, top-to-NE movements occurred on the Neusspruit Lineament, KSZ and HSS. Rare transposition criteria, and textural and paragenetic contrasts between syn-kinematic fabrics, strongly suggest that the phase of normal, top-to-NE movement seen in the northeastern HRTS shear zones is younger than the more widespread top-to-SW thrusting event. On the basis of mesoscopic structural criteria, SSW-directed thrusting is correlated with the D₂ deformation event in the HRTS. The mylonite zones have been refolded by ENE-SSW trending F₃ crossfolds, whose demonstrated coaxial relationship to the mylonite elongation lineation precluded reorientation of primary kinematic vectors. In the southwestern HRTS, primary thrust vectors have been reoriented by right-lateral, strike-slip shearing adjacent to the Pofadder Lineament during D₄. Simple shear dispersion of mylonite lineations related to normal movement, suggests that they too have been modified by D₄ shearing, and this constrains the timing of extensional movements to post-D₂ and pre- or syn-D₄. Syn-kinematic mineral assemblages, rheological criteria and the annealing states of the mylonites, provide insight into the thermotectonic evolution of the shear zones. A model is proposed in which the movement histories of shear zones within the HRTS are explained in terms of a typical orogenic cycle, involving crustal thickening by thrusting during a compressional orogenic phase, followed by collapse of the thickened crust during an extensional taphrogenic phase.

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

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

M.Sc. / This thesis involves a study ofthe geology surrounding the —530 Ma to —519 Ma Venetia kimberlite pipes situated between AIldays and Messina (now renamed Musina) in the Beit Bridge Terrane of the Limpopo Belt, South Africa. The Limpopo Belt is an eastnortheast trending high grade metamorphic terrane thought until recently to be the result ofa collisional event between the Kaapv_aal and Zimbabwe Cratons between 2.7 and 2.65 Ga. However, recent studies have challenged this concept and suggest that the assembly was more complex and took place over an extended period of time ending at —2.04 Ga. This study involved surface mapping of the Farms Rugen (south) and Ostrolenca, providing additional information to help with mine planning, grade control and exploration. It forms a portion of a project initiated between Venetia Mine, the Venetia- Limpopo Nature Reserve and Professor Jay Barton of RAU to geologically map in detail the area around the pipes (scale < 1:10 000) and to study various aspects of the regional geology. The rock types into which the Venetia kimberlite pipes intruded belong to the Venetia klippe, an east-west trending synclinal structure with the axial plane dipping steeply northwards. Lithologically, the Venetia klippe comprises four layered units in which interlayered granitic or arkosic quartzofeldspathic gneisses, with and without biotite and garnet, and para and ortho-amphibolite, quartzite and meta-carbonate rocks (marble and limestone), banded iron formation and calc-silicate rock occur. Geochemical analysis (SEM and electron microprobe) of the meta-carbonates (re-crystallised magnesian limestone, coarse-grained marble and fine-grained foliated marble), indicate the precursors to be magnesian limestone, dolomite and limestone. Several events have been identified during the structural evolution of the area. They include: formation of gneissic metamorphic layering, tectonic suturing between different lithologies, formation of a syncline and east-west strike-slip faulting, north-south trending folds and northeast-southwest dextral strike-slip faulting, tourmaline bearing pegmatite emplacement, dolerite intrusion, tourmaline absent pegmatite emplacement, kimberlite emplacement and reactivation of pre-existing structures. Depositional structures only in the fine-grained foliated marble are preserved, e.g. graded bedding, cross-bedding, rip-up clasts and channels. These structures suggest deposition of the carbonates in two main depositional environments; peritidal (channels and rip-up clasts) and subtidal shelf (graded bedding and cross-bedding). A study of pegmatites in the area shows two main pegmatite types: tourmaline bearing and tormaline absent, each locally displaying a zonation. Mineralogically, the pegmaties are rich in quartz and albite and lack K-feldspar so they are classified as sodic-rich or plagio-pegmatites. Step heating 40Ar/39Ar analyses of muscovite from undeformed pegmatite yields an age of —2.0 Ga, which is interpreted to represent the time of pegmatite emplacement into the Venetia klippe rocks. Structurally, the pegmatites are sheet-like bodies cross-cutting compositional layering, joints, faults, folds and the dolerite, except for the older tourmaline bearing pegmatite that has intruded along east-west faults, but not northeast-southwest trending faults. By applying the principles of a dike propagation model, the source of the Venetia pegmatites should be greater than 5X5X5 km in volume and a maximum of 10km away. An appropriate granitic source has been recognized on the farm Gotha to the south of the mine by Martina Barnett. Leucocratic granodiorite, tonalite and granite with minor xenoliths of amphibolite, quartzite and magnetite quartzite define the Gotha Granitic Complex and pegmatite decreases in abundance away from it to the north and east. Deposition of Unit 3 lithologies into a rifted basin and an ancient epeiric sea is possible. However, there is more evidence (peritidal and shelf environments of the metacarbonates) and clean mature quartzites to suggest deposition into a passive continental margin or epeiric sea similar to the Malmani dolomites of the Transvaal Supergroup.

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

Thesis submitted for the degree MAGISTER SCIENTIAE to the Faculty of Science, Department of Geology, University of the Witwatersrand, Johannesburg / The Koperberg Suite intrusion at Jubilee, Namaqualand varies in composition from anorthosite, through mica diorite to pyroxene leucodiorite and pyroxene diorite. Detailed mapping and petrological studies of these rocks indicate that they were sequentially emplaced into the Concordia Granite country rocks, and that each of the rock types represent discrete magmatic events. The sequence of intrusion is from more acidic to more basic. Whole-rock geochemical analyses indicate that these rocks represent cumulates involving variable proportions of plagioclase, orthopyroxene, mica, quartz, oxides and immiscible sulphides. These cumulate phases intruded into the Concordia Granite at the time of peak of metamorphism and deformation in the Okiep Copper District, i.e, about 1030Ma ago, At the time of intrusion, the country rocks were under going partial melting under high grade (granulite facies) metamorphic conditions. and granitic anatects were present in the crust. Hybridisation of basic magma and granitic melts occurred within the shear zones along which the basic magmas ascended. The En content of orthopyroxene in the Koperberg Suite exceeds the An content of plagioclase. This is atypical of basic intrusions and is a consequence of this mixing. Mixing calculations based on the initial 87Sr/86Srratio (Ru) of the Jubilee samples at 1030Ma, imply high levels of assimilation (as much as 80% assimilation in the case of anorthositic rocks) between a granitic component, similar in composition to the Nababeep Gneiss and a mantle-derived basic magma. Sulphide mineralisation was initiated by the assimilation process, which caused the separation of immiscible sulphides from the hybridised magma. Subsequent oxidation of the original sulphide assemblage produced bornite, chalcopyrite and Ti-poor magnetite. / Andrew Chakane 2019

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016. / The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion.

From the abstract: In the layered sequence of the Bushveld Complex a number of distinct, but possibly genetically related groups of transgressive, postcumulus, ultramafic and mafic rock are recognised. The main part of this thesis investigates a suite of postcumulus rocks for which the name iron-rich ultramafic pegmatite is proposed. The majority of iron-rich ultramafic pegmatite bodies examined are from the upper critical zone of the layered sequence at Rustenburg Platinum Mines Amandelbult Section, in the northern sector of the western Bushveld Complex. Field relationships imply that the iron-rich ultramafic pegmatites should be considered as an integral feature of the layered sequence, even though they transgress the cumulates. Consequently, this thesis also includes a study of the cumulate sequence at Amandelbult. A second group of postcumulus, ultramafic rocks which is investigated comprises latiniferous ultramafic pipes; the Driekop pipe has been selected as a case­ study. This thesis is presented in four sections, namely, an introduction and verview, and studies on the Driekop pipe, the cumulate sequence at mandelbult and the iron-rich ultramafic pegmatite suite. A new classification scheme of discordant bodies of postcumulus, ultramafic rock in he Bushveld Complex is proposed (see also Viljoen & Scoon, in press). In he scheme presented here, two main varieties of postcumulus, ultramafic rock re recognised, namely, non-platiniferous magnesian dunites and iron-rich ltramafic pegmatites.

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

The Namaqua Province of southwestern Africa is comprised of a number of distinct tectonostratigraphic subprovinces and terranes, which have in common a 1100-1200Ma structural and metamorphic imprint. In the western Bushmanland Subprovince, E-Wtrending belts of supracrustal gneisses are intruded by and infolded with granitic gneisses of varying ages. A central zone of rocks metamorphosed in the granulite facies is bordered to the north and south by amphibolite facies rocks. A portion of the Garies-Platbakkies supracrustal gneiss belt has been mapped on a 1:15 000 scale. The supracrustal succession was deposited on an unconfirmed basement. It is structurally juxtaposed and infolded with three different granitic augen gneisses. Large bodies of orthopyroxene-bearing granite are syntectonically emplaced in the succession. A wide variety of anatectic granites crop out as sills, dykes and pods varying in size between a few metres and a few hundred metres. These bodies commonly truncate pre-existing foliations. The metamorphosed supracrustal succession contains gneissic equivalents of felsic, mafic and intermediate volanics; pelitic, semi-pelitic, magnesian and granitic composition sediments; feldspathic quartzites; and subordinate quartzites, banded iron formation and calc-silicates. The mineral assemblages of all the rocks indicate metamorphism in the granulite facies. A variety of field evidence exists which suggests that the metamorphic peak was responsible for generating significant quantities of partial melt. The rocks of the study area contain an early Dl fabric. This is refolded in tight, E-plunging D2 crenulation folds. D2 mineral fabrics pre-date the metamorphic peak. D3 open, asymmetric folds are N-vergent and fold the crystalline products partial melting. The southern limbs of D3-folds are attenuated in 04 shear zones. The whole belt is cut by steep, N-S-trending faults. A wide variety of thermobarometers are tested for their applicability to mineral assemblages in the supracrustal rocks. The results of this application suggest that the metamorphic peak occurred at 780 ± 30°C and 5.0 ± 0.4 kbar. Assemblages in shear zones indicate an isobaric retrograde cooling path. The phase relations of melting near the solidus are reviewed with reference to common assemblages in the leucosomes of rocks with granitic and peraluminous bulk compositions. Isobaric T-a(H₂O) sections are constructed from available experimental and thermochemical data. Biotite dehydration and dehydration melting reactions are balanced using natural mineral compositions. The predicted results are compared with the modal abundances of natural product assemblages. The results suggest that dehydration melting was responsible for migmatization, and the consequent reduction of water activity. The amount of melt produced was controlled by the amount of water available from the dehydration of biotite. There is no evidence for the control of water activity by an external fluid reservoir. Limited amounts of water-undersaturated melts were extracted from their sites of generation. This process was responsible for the depletion of some leucosome assemblages with respect to K₂O, H₂O and in peraluminous rocks Na₂O. The partial melts were emplaced locally in developing shear zones.