Please read the abstract in the section 00front of this document / Dissertation (MSc (Engineering and Environmental Geology))--University of Pretoria, 2006. / Geology / unrestricted

Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The Swartland region in the western Cape, South Africa, covers approximately 5000 km2 and forms part of the Pan-African Saldania Belt that represents the southernmost extremity of the Pan-African orogenic belts in southern Africa. Regional mapping of the Swartland area shows that lithologies can be classified using predominantly structural and to a lesser extent lithological criteria. This led to the proposal of a new classification, were rocks of the previous classification of the Malmesbury Group are divided into two new groups, namely the Swartland and Malmesbury groups. The Swartland group can be divided into the Berg River and Moorreesburg formations, a series of quartz-chlorite-muscovite-feldspar schists, quartz schists, graphitic schists and limestones; and the Bridgetown formation, a series of metavolcanic rocks with WPB-MORB affinities that possibly represent seafloor. Deposition of the sediments is suggested to have occurred concurrently with deformation in an accretionary prism/fore-arc and was initiated with the opening of the lapetus Ocean at ca. 600 Ma. This early deformation event, Dt (ca. 575 Ma), only affected the Swartland group and exhibits pervasive bedding transposition, thrusting and imbrication of units creating a tectonostratigraphic sequence. Where identified, kinematic indicators and fold vergence indicate a top-to-the-west transport direction during the early, low-angle Di deformation. The Malmesbury group overlies the Swartland group, being locally separated by an unconformity. The Malmesbury group is a succession of conglomerates, grits and shales (Piketberg Formation), grading into greywackes, shales, siltstones, sandstones and minor limestones of the Tygerberg and Porterville formations. Sedimentation probably commenced after ca. 575 Ma and lasted until shortly after 560 Ma. Both the Swartland and Malmesbury groups were then deformed by the deformation event, D2 (ca. 552-545 Ma), and were intruded by the 552 to 510 Ma Cape Granite Suite. The Franschhoek Formation, formally part of the Malmesbury Group is now classified, along with the inferred ca. 535-510 Ma Magrug and Populierbos Formations of the previous Klipheuwel Group. The redefined Klipheuwel group documents a change in depositional environment from the continental slope/ocean trench, marine and flyschoid deposits of the Malmesbury group to continental, fluvial half-graben and graben deposits. Exhumation, extensive erosion and the formation of a peneplain, was followed by the deposition of the Table Mountain Sandstone Group around 550-510 Ma. The Spitskop gold prospect, located 10 km south of Piketberg, represents the first identified occurrence of mesothermal gold mineralisation in the Saldania Belt. Metamorphic devolatilisation of the Swartland group during Di led to the scavenging and transportation of gold along shallow-dipping shear zones that are contained within the early, sub-horizontal So/Si tectonic fabric. Pervasive fluid movement in the Spitskop area led to elevated gold values compared to background values throughout the lithologies at Spitskop. The lack of any economic-grade gold mineralisation is probably related to the absence of suitably orientated structures, such as high-angle faults, that are commonly believed to represent the prerequisite for large fluid throughputs that could result in economic-grade gold deposits. The mineralisation at Spitskop, however, provides a genetic model for further exploration of gold in the Swartland group. / AFRIKAANSE OPSOMMING: Die Swartland streek in die Wes-Kaap, Suid-Afrika, beslaan ongeveer 5000 km2 en vorm deel van die Pan-Afrikaanse Saldania-gordel wat die mees suidelike deel van die Pan-Afrikaanse orogene gordels in suidelike Afrika verteenwoordig. Regionale kartering van die Swartland streek dui aan dat die gesteentes geklassifiseer kan word deur oorwegend strukturele, en tot 'n mindere mate litologiese kriteria te gebruik. Gevolglik word ‘n nuwe klassifikasie voorgestel, waar gesteentes volgens die vorige klassifikasie van die Malmesbury groep verdeel word in twee groepe, naamlik die Swartland en Malmesbury groepe. Die Swartland groep kan verdeel word in die Bergrivier en Moorreesburg formasies, ‘n reeks kwarts-chloriet-muskoviet-veldspaat skis, kwarts skis, grafitiese skis en kalksteen; en die Bridgetown formasie, ‘n reeks metavulkaniese gesteentes met WPB-MORB affiniteite wat moontlik oseaanvloer verteenwoordig. Daar word voorgestel dat afsetting van die sedimente gelyktydig plaasgevind het saam met vervorming in ‘n akkresionere prisma/voorboog, geinisieer deur die opening van die lapetus Oseaan (ca. 600 Ma). Hierdie vroee vervorming, Di (ca. 575 Ma), het slegs die Swartland groep geaffekteer en vertoon deurdringende verplasing van gelaagdheid, oorskuiwing en imbrikasie van eenhede en het ‘n tektonostratigrafiese opeenvolging gevorm. Waar identifiseer, dui kinematiese aanwysers en plooi kanteling op ‘n bokant-na-wes beweging gedurende die vroee, lae hoek Di vervorming. Die Malmesbury groep oordek die Swartland groep, plaaslik geskei deur ‘n diskordansie. The Malmesbury groep bestaan uit ‘n opeenvolging konglomeraat, grintsteen en skalie (Piketberg formasie), wat gradeer in grouwak, skalie, sliksteen, sandsteen en ondergeskikte kalksteen van die Tygerberg en Porterville formasies. Sedimentasie het waarskynlik begin na ca. 575 Ma en het voortgeduur tot kort na 560 Ma. Beide die Swartland en Malmesbury groepe is hierna vervorm deur D2, (ca. 552-545 Ma) en daaropvolgend ingedring deur die 552 tot 510 Ma Kaap Graniet Suite. Die Franschhoek Formasie, voorheen deel van die Malmesbury Groep, word nou geklassifiseer tesame met die afgeleide ca. 535-510 Ma Magrug en Populierbos formasies as deel van die voorheen geklassifiseerde Klipheuwel groep. Die hergedefinieerde Klipheuwel groep dui op 'n verandering in afsettingsomgewing vanaf die kontinentale glooiing/oseaantrog, mariene en flyschoiede afsettings van die Malmesbury groep na kontinentale, fluviale half-graben en graben afsettings. Herblootstelling, omvattende erosie en die vorming van ‘n skiervlakte is gevolg deur die afsetting van die Tafelberg Sandsteen Groep random 520-510 Ma. Die Spitskop goudvoorkoms, 10 km suid van Piketberg, verteenwoordig die eerste identifiseerde voorkoms van mesotermale goudmineralisasie in die Saldania Gordel. Metamorfe ontvlugtiging van die Swartland groep gedurende Dt het aanleiding gegee tot die roofuitruiling en vervoer van goud langs laaghellende skuifskeursones in die vroee, subhorisontale S0/Si tektoniese maaksel. Deurdringende vloeistofbeweging in die Spitskop omgewing het aanleiding gegee tot verhoogde goudwaardes in vergelyking met agtergrond waardes dwarsdeur die litologiee by Spitskop. Die gebrek aan ekonomiese graad goud mineralisasie is waarskynlik verwant aan die afwesigheid van geskikte georienteerde strukture, soos hoe hoek verskuiwings, wat oor die algemeen beskou word as ‘n voorvereiste vir die toevoer van groot hoeveelhede vloeistof wat kon aanleiding gegee het tot ekonomiese graad goudafsettings. Die mineralisasie by Spitskop verskaf egter 'n model vir verdere goud eksplorasie in die Swartland groep.

Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The southern portions of the Early- to Mid-Archaean Barberton granitoid-greenstone terrain of South Africa consists of a high-grade metamorphic granitoid-gneiss terrain that is juxtaposed against the low-grade metamorphic supracrustal sequence of the Barberton Greenstone Belt. The boundary of the two different crustal domains corresponds to the Theespruit Formation, an amphibolite-facies, highly tectonized mélange of metabasites, felsic volcanics and rare, aluminous clastic sediments that occurs along the granitoidgreenstone margins. Amphibolite-facies lithologies in the Theespruit Formation are characterized by strongly prolate mylonitic fabrics that formed in a constrictional tectonic regime. Away from the granitoid-greenstone margin and towards the central parts of the greenstone belt, these rocks grade to, and are overprinted by, greenschist-facies S-L mylonites that formed during non-coaxial deformation. Both peak and retrograde minerals define, and are aligned parallel to, the fabrics in these rocks, indicating that shearing was initiated under peak metamorphic conditions and continued during retrogression. S-C’ fabric relationships indicate that shearing occurred in an extensional tectonic regime and that, during deformation, the gneiss terrain was uplifted relative to the greenstone belt. Peak metamorphic assemblages of grt-st-bt-chl-pl-qtz and ky-st-btms- pl-qtz in metasediments and grt-ep-hbl-pl-qtz in amphibolite constrain peak metamorphic conditions of 7.4 ± 1.0 kbar and 560 ± 20 ºC that were attained during the main accretionary episode in the Barberton terrain at 3229 ± 25 Ma. Peak assemblages in all rocks are pre-tectonic and were deformed and re-equilibrated during retrogression, resulting in these being minimum estimates of peak metamorphic conditions. Petrographic evidence and retrograde pressure-temperature estimates indicate that retrogression involved near-isothermal decompression of ca. 4 kbar prior to cooling into the greenschist-facies. The style and timing of metamorphism in the Theespruit Formation is similar to that of the granitoid-gneiss terrain, suggesting that the Theespruit Formation shares a geological history with the gneiss terrain and that it is allochtonous to the greenstone belt. The main deformational and fabric-forming event exhibited in the Theespruit Formation occurred during the exhumation of the granitoid-gneiss terrain subsequent to peak metamorphism. Consequently, the juxtaposition of this terrain againstthe greenstone belt was achieved by tectonic underplating and core complex formation at ca. 3.23 Ga. The occurrence of high-grade constrictional mylonites that are overprinted by low-grade non-coaxial mylonites as well as extension in an overall compressional tectonic regime is consistent with exhumation by extensional orogenic collapse. Burial of the high-grade terrain to depths of 25 – 30 km is only possible in a relatively cold and rigid crustal environment, while the extremely low apparent geothermal gradients of ca. 20 ºC/km preserved in this terrain suggest that burial and exhumation occurred rapidly, within a time-span of ca. 15 – 20 Ma. These parameters strongly suggest that metamorphism occurred in response to a lateral plate tectonic process that was operational in the Barberton terrain at 3230 Ma. / AFRIKAANSE OPSOMMING: Die suidelike dele van die Vroeg- tot Middel-Argaïese Barberton graniet-groensteen terrein van Suid-Afrika bestaan uit ‘n hoë-graad metamorfe graniet-gneiss terrein wat die lae-graad metamorfe groenstene van die Barberton Groensteen Gordel begrens. Die grens tussen die twee verskillende kors-domeine hang saam met die Theespruit Formasie, ‘n amfiboliet-fasies, getektoniseerde melange van metabasiete, felsiese vulkaniese gesteentes en skaars, alumineuse klastiese sedimente wat langs die graniet-groensteen kontakte voorkom. Amfiboliet-fasies gesteentes in die Theespruit Formasie word gekenmerk deur sterk prolaat milonitiese maaksels wat in ‘n vernouende tektoniese omgewing gevorm het. Hierdie rotse word weg van die graniet-groensteen kontak en na die sentrale dele van die groensteen gordel oordruk en vervang deur groenskis-fasies S-L miloniete wat tydens nie-koaksiale vervorming gevorm het. Beide piek en retrograad minerale definieer, en is georienteer parallel aan, die maaksel in die rotse, wat daarop dui dat skuifskeur onder piek metamorfe toestande begin het en volgehou het tydens retrogressie. S-C’ maaksels dui daarop dat skuifskeur in ‘n verlengende tektoniese omgewing plaasgevind het en dat die gneiss terrein opgehef is relatief tot die groensteengordel tydens vervorming. Piek metamorfe versamelings van grt-st-bt-chl-plqtz en ky-st-bt-ms-pl-qtz in metasedimente en grt-ep-hbl-pl-qtz in amfiboliet bepaal piek metamorfe toestande van 7.4 ± 1.0 kbar en 560 ± 20 ºC wat bereik is gedurende die hooffase van akkresie in die Barberton terrein teen 3229 ± 25 Ma. Die piek metamorfe versamelings in alle rotse is pre-tektonies en is vervorm en geherekwilibreer tydens retrogressie, wat maak dat die beramings minimum skattings van piek metamorfe toestande is. Petrografiese getuienis asook druk-temperatuur beramings dui daarop dat retrogressie gepaard gegaan het met byna-isotermiese drukverligting van naastenby 4 kbar voor afkoeling tot in die groenskis-fasies. Die styl en tydsberekening van metamorfose in die Theespruit Formasie is vergelykbaar met metamorfose in die granietgneiss terrein, wat daarop dui dat die Theespruit Formasie ‘n geologiese geskiedenis met die gneiss terrein deel en allochtoon is tot die groensteen gordel. Die hooffase van vervorming en maakselvorming in die Theespruit Formasie het plaasgevind gedurende die herontbloting van die graniet-gneiss terrein na piek metamorfose. Gevolglik is dieteenplasing van dié terrein teen die groensteen gordel vermag deur tektoniese onderplasing en kernkompleksvorming teen ongeveer 3.23 Ga. Die verskynsel van hoëgraadse vernoude miloniete wat oordruk word deur lae-graadse nie-koaksiale miloniete asook verlenging in ‘n algeheel saamdrukkende tektoniese omgewing dui daarop dat herontbloting plaasgevind het deur middel van verlengende orogenetiese ineenstorting. Die begrawing van die hoë-graadse terrein tot dieptes van 25 – 30 km is net moontlik in ‘n relatief koel en star kors-omgewing, terwyl die uitermate lae geotermiese gradiente van ongeveer 20 ºC/km wat in die terrein behoue gebly het daarop dui dat begrawing en herontbloting vinnig geskeid het, binne ‘n tydsverloop van ongeveer 15 – 20 Ma. Hierdie beperkings is ‘n sterk aanduiding dat metamorfose plaasgevind het as gevolg van ‘n laterale plaattektoniese proses wat werksaam was in die Barberton terrein teen 3230 Ma.

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.

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.

In the Upington region, there are three major- tectonic crustal provinces; namely the Kaapvaal Craton, Kheis and Namaqua tectonic provinces. The Eburnian-aged (early Proterozoic) Kheis Province developed along the western flank of the Archaean Kaapvaal Craton while the Kibaran-aged (middle Proterozoic) Namaqua Metamorphic Province, superimposed on the Eburnian-aged basement, developed to the east of the Kheis Province. The Namaqua Metamorphic Province is divided into the Gordonia and Bushmanland Subprovinces, the former being further subdivided into various tectonostratigraphic terranes. These are termed, from west to east, the Kakamas, Areachap, and Upington Terranes. The Upington Terrane includes fault bounded grabens with accompanied bimodal volcanism and sedimentation of the Wilgenhoutsdrif and Koras Groups. The Areachap Terrane consists predominantly of amphibolites generated in an island arc environment while the Kakamas Terrane is characterised by volcano-sedimentary sequences which have been extensively intruded by syn to late-tectonic predominantly I-type Keimoes Suite granitoids. The main styles of mineralisation correlate well with the various tectonostratigraphic terranes. Sedimentary exhalative massive sulphide deposits are characteristic of the Bushmanland Subprovince and are thought to be associated with the deposits at Aggeneys and Putsberg to the west of the area under investigation. These deposits are considered to have been deposited in an east-west-elongated intracontinental basin. The Kakamas Terrane is typified by granite-related mineralisation. In the eastern portion of the Kakamas Terrane, Sn-Wand base metal-bearing veins occur while pegmatites are developed in the western portion. These two styles of granite-related mineralisation is considered to reflect differing depths of formation due mainly to varying degrees of thrusting. The Areachap Terrane consists of volcanogenic massive sulphide deposits of the Besshi-type and is considered to have formed in a back-arc environment. In the Upington Terrane, the Wilgenhoutsdrif and Koras Groups consists essentially of minor Cu occurrences mainly disseminated within basalts and in structural trap sites. The possibility for sediment-hosted Cu deposits is not ruled out. More recent surface processes have led to uranium and gypsum deposits in pans, river beds and calcretes. Eburnian aged tectonic setting remains enigmatic. Kibaran-aged tectonics which best fits the metallogeny of the area under investigation is considered to be of a subduction zone from west to east formed by the collision of the Bushmanland "microcontinent" against the Kaapvaal Craton. Subduction fbrmed an island arc setting in which the massive sulphide deposits were formed in the Areachap Terrane while the Wilgenhoutsdrif Groups developed in a marginal basin. Further convergence led to collision of the two continents and underriding of the Bushmanland "microcontinent" which generated predominantly I-type granitoids represented by the Keimoes Suite. The level of emplacement of these granitoids is a reflection of the degree of foreland thrusting and produced shallower level Sn-W and base metal vein-type mineralisation closer to the suture zone and deeper level pegmatites further from the suture zone to the west. The final period of deformation is represented by northward lateral movement which created "pull apart" fault-bounded basins into which the Koras Group was deposited.

Thesis (MSc)--Stellenbosch University, 2013. / This study presents a facies outcrop characterization and petrographical analysis of Unit B of the Permian Laingsburg Formation. Unit B is interpreted as a base-ofslope system, which represents a strikingly sand-rich succession. The base-of-slope system is defined by a channel-levee complex. The study provides systematically a clear understanding and description on reservoir heterogeneities, in terms of facies distribution, physical processes and architectural elements. The dataset included detailed sedimentary logs, photomosaic interpretations, supplemented by a petrographical study to determine the textural and compositional attributes of the studied sandstones. Seven lithofacies was recognised within Unit B, based on detail observation and description on grain size and sedimentary structures. They mainly consist of 1) thick to massive bedded ‘structureless’ sandstone, 2) horizontal and ripple cross-laminated thin-medium bedded sandstone, 3) silty sandstone, 4) structureless siltstone, 5) hemipelagic mudstone, 6) muddy slump, and 7) sandy slump. Palaeocurrent analysis indicates that the mean sediment transport direction of Unit B was to the E and NE. Lithofacies 1 comprises thickly to massive bedded, frequently amalgamated, mostly very-fined grained sand, mixed grading, irregular to sharp upper contacts, structured upper bedding planes, large floating mudstone clasts and granules, rare groove and flute casts. Also, scour and fill features have been documented. Lithofacies 1 has been interpreted to result from channelized sandy debris flow currents. Lithofacies 2 composes of thin-medium bedded, very fine-grained sand, ungraded, sharp upper contacts, discrete units with traction bed forms, horizontal and cross-lamination, mud-draped ripples, internal erosional surfaces and preserved crests. Lithofacies 2 shows diagnostic sedimentary features for a deep-water bottom reworking current. Lithofacies 5 composes of very fine–grained mud, ‘structureless’ to finely horizontally laminated, fissile mudstone. Deposition resulted from suspension settling of mud fractions out of a low-energy buoyant plume. Lithofacies 6 composes of contorted and convoluted bedding, steeply dipping layers and irregular upper contacts. Deposition occurred via slumping on an unstable slope. Lithofacies 7 composes of fine–grained ‘structureless’ sandstone, amalgamated units, with dark floating mudstone granules. Lithofacies 7 has been interpreted to form from channelized flows evolving into slump deposition on an unstable slope. The petrographic data reveals that the reservoir quality of the sandstones is strongly controlled by depositional processes and diagenetic products. The sediments of the Karoo Basin appear to be diagenetically controlled as a function of burial depth. The major diagenetic products controlling the reservoir quality of the sandstones, includes compaction (mechanical and chemical), and authigenic porefilling constituents (quartz cement, feldspar dissolution and partial to complete replacement, calcite cement, chlorite and illite). Compaction played a major role in the evolution of the sediment, as compared to the effect of quartz cementation, and is considered here to have caused irreversible destruction of depositional porosity and permeability. The sediment has undergone intense mechanical compaction during early-stage diagenesis, low temperature and shallow depth of burial (probably the first 2 km). The high burial palaeotemperature (250 ± 500C) or more specifically the high geothermal gradient of the Karoo Basin consequently increased the number of diagenetic reactions. The high burial temperatures may have increased pressure dissolution and quartz cementation. With compaction been limited, quartz cementation and the authigenesis of chlorite and illite at deeper depths may have had a profound effect on the permeability distribution of the studied sandstones. After the completion of diagenesis, the pore systems of these sandstones were completely destroyed by low-grade regional burial metamorphism.

A Dissertation Submitted to the Faculty of Science University of the Witwatersrand, Johannesburg for the Degree of Master of Science. / Beatrix Mine is located 35 km south of the city of Welkom in the Welkom Goldfield and as such forms the most southerly of the Witwatersrand-type gold mines. The Beatrix Reef overlies an angular unconformity at the base of the Turffontein Subgroup, Central Rand Group Significant, southerly truncation of over 600m of the Johannesburg Subgroup, and the lower formations of the Turffontein Subgroup, occur at this unconformity in the Beatrix area.. characteristics of the Beatrix Reef conglomerates such as the morphology, sorting and packing of clasts, and the arrangement. of the sediments in various sedimentary structures and facies/ sequences, suggest deposition within a braided fluvial environment on a coarse-grained braid-delta. Sedimentation occurred after the fluvial degradation of previously deposited units, and culminated in a marine/ lacustrine transgression. Low aggradation rates led to significant reworking and concentration of placer materials in a depositional model probably typical of ventral Rand Group placer formation. Heavy minerals (and gold) are concentrated in response to hydraulic conditions and show a close association with large and small scale sedimentary features. Transport directions deduced from the sedimentary structures suggest a north to south dispersal of sediment down the braid plain. Sedimentary structures in the finer rained units at the base of the Eldorado Formation are indicative of tidal influences and document the marine transgression as the culmination of the degradational events. The lithologys sedimentary structures and facies sequences of the coarser grained units of the Eldorado Formation well as the overall coarsening upward of these lithologies indicate sedimentation in a braided , fluvial system, on an alluvial fan prograding across the preyiously deposited units" Sedimentary ~tructures and lithologic variations confirm a continued north to south dispersal pattern. In the area south of the Sand over the period of fluvial degradation and transgression after the formation of the Beatrix: Reef was followed by more rapidly aggreding fluvial progradation due to a major change in base level in response to compressional tectonics and uplift along the Western Margin Structure. Only in post-Central Rand Group times did relaxation and extensional tectonics result in the outpourings of the Ventersdorp .supergroup lavas and the cessation of active Witwatersrand Supergroup sedimentation. / Andrew Chakane 2018

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

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Basin subsidence analysis, employing the backstripping method, indicates that fundamentally two different basin-generating mechanisms controlled Tanqua depocentre development in SW Karoo Basin. The subsidence curves display initial dominantly decelerating subsidence, suggesting an extensional and thermal control possibly in a strikeslip setting during the depocentre formation; on the other hand, subsequent accelerating subsidence with time suggests that the dominant control on the depocentre formation in SW Karoo was flexure of the lithosphere. Based on these observations on the subsidence curves, it is possible to infer that the first stage of positive inflexion (~ 290 Ma) is therefore recognised as the first stage of Tanqua depocentre formation. Petrographic study show that most of the studied sandstones of the Tanqua depocentre at depth of ~ 7.5 Km were subjected to high pressure due to the overlying sediments. They are tightly-packed as a result of grains adjustment made under such pressure which led also to the development of sutured contacts. It is clear the high compaction i.e. grain deformation and pressure solution occurred on the sediments; leading to total intergranular porosity reduction of the quartz-rich sediments and dissolution of the mineral grains at intergranular contacts under non-hydrostatic stress and subsequent re-precipitation in pore spaces. Furthermore, siliciclastic cover in the Tanqua depocentre expanded from minimal values in the early Triassic (Early to Late Anisian) and to a maximum in the middle Permian (Wordian -Roadian); thereby accompanying a global falling trend in eustatic sea-level and favoured by a compressional phase involving a regional shortening due to orogenic thrusting and positive inflexions (denoting foreland basin formation). The estimate of sediment volume obtained in this study for the Permian Period to a maximum in the middle Permian is therefore consistent with published eustatic sea-level and stress regime data. In addition, this new data are consistent with a diachronous cessation of marine incursion and closure of Tanqua depocentre, related to a compressional stress regime in Gondwana interior during the late Palaeozoic. / AFRIKAANSE OPSOMMING: Die ontleding van komversakking met behulp van die terugstropingsmetode bring aan die lig dat die ontwikkeling van die Tankwa-afsettingsentrum in die Suidwes-Karoo-kom hoofsaaklik deur twee verskillende komvormende meganismes bepaal is. Die versakkingskurwes toon aanvanklike, hoofsaaklik verlangsaamde versakking, wat daarop dui dat ekstensie- en termiese beheer gedurende die vorming van die afsettingsentrum plaasgevind het, waarskynlik in strekkingwaartse opset. Aan die ander kant toon daaropvolgende versnellende versakking wat mettertyd plaasgevind het dat die vorming van die afsettingsentrum in die Suidwes-Karoo eerder oorwegend deur kromming van die litosfeer beheer is. Op grond van hierdie waarnemings met betrekking tot die versakkingskurwes, kan mens aflei dat die eerste stadium van positiewe infleksie (~ 290 Ma) dus as die eerste stadium van die vorming van die Tankwa-afsettingsentrum beskou kan word. Petrografiese studie toon dat die meeste van die sandsteen wat van die Tankwaafsettingsentrum bestudeer is, op diepte van ~ 7,5 Km aan hoë druk onderwerp was weens die oorliggende sedimente. Die sandsteen is dig opmekaar as gevolg van die korrelaanpassing wat onder sulke hoë druk plaasvind, wat op sy beurt ook tot die ontwikkeling van kartelnaatkontakte aanleiding gegee het. Dit is duidelik dat die sediment aan hoë verdigting, dit wil sê korrelvervorming en drukoplossing, onderwerp was, wat gelei het tot algehele afname in interkorrelporeusheid by die kwartsryke sedimente; die ontbinding van die mineraalkorrels in interkorrelkontaksones onder niehidrostatiese spanning, en daaropvolgende herpresipitasie in poreuse ruimtes. Voorts het silisiklastiese dekking in die Tankwa-afsettingsentrum toegeneem van minimale waardes in die vroeë Triassiese tydperk (vroeë tot laat Anisiaanse tydperk) tot hoogtepunt in die mid-Permiaanse tydperk (Wordiaans–Roadiaans). Dié ontwikkeling het gepaardgegaan met algemene dalingstendens in die eustatiese seevlak, en is verder aangehelp deur saamdrukkingsfase wat gekenmerk is deur regionale verkorting weens orogeniese druk en positiewe infleksies (wat met voorlandkomvorming saamhang). Die geraamde sedimentvolume wat in hierdie studie vir die Permiaanse tydperk bepaal is, met die hoogtepunt in die middel van dié tydperk, is dus in pas met gepubliseerde data oor die eustatiese seevlak en spanningstoestand. Daarbenewens strook hierdie nuwe data met diachroniese staking van mariene instroming en die afsluiting van die Tankwaafsettingsentrum wat met spanningstoestand in die Gondwana-binneland gedurende die laat Paleosoïkum verband hou.