Masters Degrees (Geology)

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The mineralogy and related geology of the Albert Silver Mine, Bronkhorstspruit, Transvaal
(1970) Champion, Alfred Timothy.
The Albert Silver mine is situated on the farm Roodepoortjie, 32 kilometres north of Brorikhorstspruit in the Transvaal. The deposit forms the largest of a number of sub-parallel quartzhematite lodes accompanied by sulphide mineralization and is accompanied by an extensive alteration zone along its northern flank.
Stratigraphy and sedimentology of the Molteno formation in the Elliot and Indwe area, Cape Province.
(1981) Christie, Angus David Mackay.; Tavener-Smith, Ronald.
Abstract in PDF file.
The lithostratigraphy and petrogenesis of the Nsuze group northwest of Nkandla, Natal.
(1984) Groenewald, Peter Bruce.
The volcanic and sedimentary Nsuze Group constitutes the lower part of the
The geology of the Ngoye granite gneiss formation.
(1985) Scogings, Andrew John.
The Ngoye Granite Gneiss Formation is located in the Natal sector of the Proterozoic Namaqua-Natal Mobile Belt, about 10 km southwest of Empangeni. It forms a prominent east-west trending elongate whalebacked massif some 30 km in length, within amphibolitic gneisses and schists of the Tugela Group. A suite of twelve different, gneissic granitoids has been-recognised within the Ngoye Formation on the basis of field relationships, mineralogy and supportive geochemistry. They range in composition from peraluminous syenite to peralkaline granite. Peraluminous varieties are typically muscovite and garnet-bearing whereas metaluminous granites in the formation contain olivegreen biotite and/or hornblende and sphene. Riebeckite, aegerine and yellow-brown biotite, with accessory fluorite and zircon are characteristic of the peralkaline granites. Geochemically, the samples analysed display a range in SiO₂ from 63,79 - 78,47∞, are extremely depleted in CaO and MgO, while being enriched in Na₂O and K₂O. Depletion of CaO relative to alkalis is shown by an alkali-lime index of only 36, suggestive of an alkalic character. The agpaitic index (A. I. = mole Na₂O + K₂O/AL₂O₃) of the peralkaline samples ranges between 1,02 and 1,16; which classifies them as granites of comenditic affinity. Various chemical classification schemes have been tested and evaluated, of which the RI - R2 multicationic diagram provides results most similar to modally-derived terminology. Accordingly, the Ngoye granitoids are shown to range from minor syenites and alkali granites to predominant monzo - and syeno-granites. Trace element data indicate that the peralkaline granites are enriched in Nb, Zr and Zn relative to the other, non-peralkaline, granites in the formation. In addition, radioactive, magnetite-bearing quartz-rich rocks associated with the peralkaline granites, have extremely enhanced contents of Nb, Zr, Y, Zn, U, Th and to a lesser extent Sn and W. Peraluminous and near-peraluminous granites have the highst Rb/Sr and Rb/Ba ratios of all samples analysed, as well as enhanced Sn, U and Th contents while Zr is notably depleted. Small, muscovite-rich pods associated with muscovite-bearing granites are highly enriched in Sn. The application of certain discriminants based on modal and geochemical parameters has shown the Ngoye Formation to comprise typical "A" - type granites. "A" - type granites are characteristically intruded as ring complexes into anorogenic or post-orogenic tectonic settings in attenuated or epiorogenically-domed continental crust. Comparison of the Ngoye Formation wi th the well-known "younger granite" complexes of Nigeria and Saudi Arabia reveals marked similarities. The inference is therefore that the Ngoye Formation represents a metamorphosed "postorogenic" granite complex with most of the hallmarks of "A" type or "within-plate" magmatism. Four phases of deformation (D₁ to D₄) are recognised within the area mapped. Evidence of D₁ deformation is rare, but rootless folds within the transposed layering in the amphibolitic country rocks reflect the intensity of this prograde metamorphic event, M₁, during which upper amphibolite grades were achieved. Field evidence shows that the Ngoye granites were intruded after the D₁ event and prior to D₂. This latter event caused widespread folding about east-west F₂ axes, with the development of a pervasive S₂ planar fabric within the antiformally folded Ngoye Formation. S₂ is locally developed in the amphibolitic country rocks. The D₂ event culminated in the development of northward-directed overthrusting and retrogressive ,M₂, metamorphism of mylonitic thrust planes. Lateral shearing characterizes D₃, with development of macroscopic mylonites and mesoscopic conjugate shear zones. This was in response to a sinistral sense of movement, as indicated by prominent sub-horizontal extension lineations (L₃) and microscopic asymmetric augen structures. D₄ is deduced from stereograms and is indicated as cross-folding of F₃ fold axes.
The petrology, geochemistry and classification of the Bien Venue massive sulphide deposit, Barberton mountain land.
(1990) Murphy, Philip William.; Harwood, Anthony.; Kerr, Alan.
The Bien Venue massive sulphide deposit is associated with a felsic volcanic succession developed in the north-eastern part of the Barberton Greenstone Belt, Eastern Transvaal. The deposit is situated 8km east-north-east of Louw's Creek between the Lily Syncline to the south and the Stentor Pluton to the north. The stratigraphy of the Onverwacht, Fig Tree and Moodies Groups in the vicinity of the deposit is poorly documented, and the exact stratigraphic position of the host felsic volcanics is not known. They are tentatively correlated with the felsic volcanics from the Theespruit Formation, Onverwacht Group. The felsic volcanics have undergone low-grade greenschist facies metamorphism and occur as quartz-sericite schists. Detailed petrography enables sub-division of the volcanic succession into distinct units. A lapilli metatuff unit hosts the base metal and precious metal mineralisation. The sulphides are best developed in the upper part of this unit, together with intercalated barite-rich horizons and cherts. A series of structural events have modified the attitude of the lithological units and disrupted the continuity of the orebody. The orebody comprises stratabound lenses of massive to semi-massive and often banded sulphides, as well as disseminated sulphide mineralisation. The dominant base metal mineralogy consists of pyrite, sphalerite, chalcopyrite, galena and tennantite. Native silver and various copper-silver sulphides are also associated with the base metal sulphides. A vertical zonation of the mineralisation exists, from pyrite-chalcopyrite-rich ore in the footwall, to pyrite - chalcopyrite-sphalerite-galena-barite-rich ore towards the hanging wall. Geochemical studies indicate that the Bien Venue lithologies are rhyolitic to rhyodacitic in composition and show a calc-alkaline affinity. The mobility of some elements at Bien Venue has been clearly demonstrated. This is believed to be associated with hydrothermal alteration that has led to SiO2 and MgO enrichment, as well as K2O depletion, in the wall rocks of the deposit. The geological setting and nature of the mineralisation at Bien Venue suggest that it is an example of a volcanogenic exhalative sulphide deposit. In terms of the classification scheme suggested by Hutchinson (1973, 1980), Bien Venue would best be described as a Primitive type deposit that contains barite.
The petrology and geochemistry of the karoo sequence basaltic rocks in the Natal Drakensberg at Sani Pass.
(1992) Ramluckan, Vijay Rajlal.; Dunlevey, John N.; Mitchell, A. A.
The Sani Pass in the Natal Drakensberg is situated in the north-eastern sector of the Lesotho Highlands which forms a major Karoo-age basaltic massif in the Karoo Igneous Province. The volcanic section exposed in the pass is approximately 800m thick, and comprises a succession of regularly stratified, massive and amygdaloidallavas which were extruded mainly by fissure-type eruptions. Dolerite dykes, which now occupy thefissures,form a network ofpredominantly NE-SW and NW-SE trending topographic features. During post-eruption cooling hydrothermal solutions percolated through the volcanic succession and produced an amygdale zonation which was controlled predominantly by ambientpressure and temperature conditions. An original maximum thickness of 1 820m of the volcanic succession has therefore been estimated and an average fossil geothermal gradient of 111° C/km is conceived to have persisted during amygdale formation. New electron microprobe data are presented for the silicate phases in the Sani Pass basalts and dolerites. These data do not effectively separate the Sani Pass volcanic succession into different geochemical units. Microprobe analysesfor olivine, albeit limited, are in the forsterite range and indicate that a proportion of olivine in the high-MgO basalts is due to cumulus enrichment. The pyroxenes are predominantly augite and minor pigeonite, with some ofthe augites displaying a tholeiitic trend similar to that recognised at Skaergaard. Plagioclase is mainly in the labradorite to bytownite range, the phenocrysts being slightly enriched in anorthite compared to the groundmass. The use ofwhole-rock geochemistry for 67 basalts and 8 dolerites has permitted the recognition of five geochemically distinct magma types, namely, the Giant's Cup, Agate Vale, Sakeng, Mkhomazana and the Phinong. The Phinong basalts comprise the upper two-thirds ofthe volcanic succession and although are generally homogeneous, there is a slight tendency for the more evolved rocks to be found higher up in the stratigraphic sequence. The remaining magma types precede the Phinong succession and are generally enriched in silica and have higher Zr/Nb and lower PfZr ratios than the Phinong basalts. Within the pre-Phinong succession the Giant's Cup basalts are generally depleted in the compatible elements, while the overlying Agate Vale basalts are enriched in incompatible elements. Except for a marginally lower Na20 and Sr content, the chemistry ofthe Sakeng basalts is variable, generally overlapping with the other magma types. The Mkhomazana basalts are slightly enriched in MgO, Ni, Cr and Sc compared to all other pre-Phinong basalts. The dolerites in the area adjacent to the Sani Pass are geochemically similar to the Phinong basalts. The Phinong magma type is considered to be equivalent to the Lesotho magma type, based on their geochemical and stratigraphical similarities. In terms ofdiscriminant diagrams the Giant's Cup, Sakeng and Mkhomazana basalts generally show some compositional overlap with the Phinong, or plot in incoherentfields, but the Agate Vale basalts are distinctly different and might indicate a new magma type within the Karoo Central area. Broad compositional overlap between the Phinong basalts and those preserved at Kirwan and Heimefrontfjella, Antarctica, indicates juxtaposition of Antarctica along the southern African east coast in a reconstructed Gondwanaland. Petrogenesis of the Sani Pass basalts has been examined in terms of alteration, open and closed system fractional crystallization, partial melting procesess and a heterogeneous source. Although limited alteration and conduit contamination have occurred, the most feasible mechanism responsible for the geochemical variation lies in the existance ofinhomogeneities in the upper mantle at the time ofgeneration of the Sani Pass magmas.
Richards Bay zircon.
(1992) Pietersen, Kevin John.; Cornell, David H.
Zircon from the zircon concentrate of Richards Bay Minerals was investigated with a view to understanding the morphology and provenance. The obsevations were applied to the reduction of uranium, thorium and other trace elements in the heavy mineral placer deposits. It is evident from differences in morphology, optical characteristics, cathodoluminescence, inclusion types and trace element analyses that the zircon is derived from numerous parent rocks. Rare earth element modelling reveals several possible parent rocks including rhyolites, granites, syenites, pegmatites and carbonatites. Fission track U mapping of individual zircons indicated an enrichment of U in the rims and grain terminations. The U maps were used to devise and test several methods, including abrasion and partial dissolution, to reduce the combined U and Th concentration from 450-563ppm to below 400ppm. The effect of magnetic cleaning, density separation and size classification of the zircon concentrate on the U +Th concentration was found to be negligible. Air abrasion and HF acid dissolution successfully reduced the U +Th concentrations to between 332 and 383ppm. The contribution of trace elements from inclusions, surface pit fillings and coatings, and foreign minerals within the zircon concentrate were evaluated by by scanning electron microscope identification.
Zinc-lead mineralization at Pering Mine in the Griqualand West sub-basin : an isotopic study.
(1992) Turner, Audrey Michelle.; Duane, M. J.; Kruger, Frans J.
Detailed studies, both chemical and physical, have been performed on various dolomites and vug-filling carbonates, to determine the pathways and extent of the mineralizing fluids associated with the Pering Zn-Pb deposit within the Griqualand West sub-basin. Three carbonate phases were identified within the vugs using cathodoluminescence microscopy. The first phase formed a reaction rim on the host dolomites during the deposition of sphalerite and oscillatory zoned carbonate. Finally calcite was deposited, which is associated with post-mineralizing fluids. The vug-filling carbonates have very radiogenic 87Sr/86Sr values (0.72-0.76) compared with the host dolomites (0.70-0.73). The gangue carbonate minerals deposited within the vugs have similar radiogenic 87Sr/86Sr values to the gangue minerals of the main Pering orebody, indicating that the vugs formed part of the aquifer system through which the mineralizing fluids migrated. Radiogenic 87Sr was not acquired from the surrounding host dolomite. The mineralizing fluids may have picked up radiogenic 87Sr when migrating through porous rocks such as the Makwassie Quartz Porphyry of the Ventersdorp Supergroup or felsic rocks forming the Kaapvaal Craton. In addition, radiogenic Sr may have been acquired from dewatering of the Lokammona shales within the area, or expelled from amphibolite and granulite rocks involved in the Kheis or Namaqua Tectonic events. Two models are proposed to explain the genesis of the main Pering deposit and the occurrence of sphalerite in the vug-filling carbonates surrounding the deposit: 1) Mixing Model; and 2) Single Fluid Model. The Single Fluid Model is preferred which involves a single fluid migration and interaction with the carbonate host rock and/or pore fluid. The metals were probably transported as chloride complexes together with reduced sulphur at temperatures greater than 2000 C. Deposition of the ore minerals resulted from either a dilution of the fluid, a pH increase or a temperature decrease. Both dolomites and vug-filling carbonates have a model Pb age between 2.0 and 2.7. Secondary 1Ga model ages indicate a minor Namaqua tectonic influence. Carbon and oxygen isotopes indicate that the fluids originated in a deep burial environment. Future exploration work using cathodoluminescence microscopy and staining techniques will be both useful and cost-effective. Isotopic work should concentrate on the Rb-Sr system as radiogenic 87Sr/86Sr values are the best indicators of the path of the mineralizing fluid, and the proximity to ore concentrations.
The geology and geochemistry of the volcanic rocks of the Pongola sequence in southern Swaziland.
(1993) Mabuza, Mbongeni Henry.; Wilson, Allan H.
The ~3.0 Ga Pongola Sequence, comprising a lower dominantly volcanic Nsuze Group and an upper largely sedimentary Mozaan Group, crops out in the Mahlangatsha and Kubuta areas of southern Swaziland. The Nsuze Group consists of basaltic, andesitic, dacitic and rhyolitic rocks with intercalations of ferruginous shale and pyrophyllitic schists. The Mozaan Group comprises quartzites, ferruginous shales, basalts and minor amounts of andalusite and sericitic schists. In the study area in southern Swaziland the Pongola Sequence is represented by a northerly striking lens of metavolcanic basaltic rocks extending southwards to the Ngwavuma River valley. These lavas comprise basalts, basaltic andesites and very minor rhyolites that are amygdaloidal and vesicular in places. Hunter (1952) tentatively correlated these metabasaltic rocks with the Nsuze Group but the geochemistry indicates that an upper Mozaan correlation is more likely. In the study area four stages of deformation have been deduced: a cleavage development (D1); low angle thrusting and bedding-parallel thrust faulting (D2); normal/oblique slip faulting (D3) and fracturing/jointing (D4). There has been duplication of strata by thrusting and normal faulting. Absence of marker beds prevents the determination of the degree of duplication. It is clear from the geochemical analysis that there are two broad groups of data from the suite, one from the Sigwe Hills in the north and the other from south of the Ngwavuma River. The samples from south of the Ngwavuma River are enriched in TiO2, AI2O3, CaO, Cr, Zr and Nb compared to the samples from Sigwe Hills. These volcanic rocks are tholeiitic in nature and indicate a within plate continental setting.
A two-dimensional hydrodynamic model for the St Lucia Estuary mouth.
(1993) Jaaback, Kathryn Margaret.; Mason, Tom R.; Hearne, John W.
The reduced fresh water input into the St Lucia Estuary combined with the increase of sediment in the St Lucia Lake System has necessitated the implementation of a dredging programme. To ensure the effectiveness of the dredging programme, the behaviour of the sediment under various flow and tidal conditions needs to be determined. To establish how sediment will move, it is necessary to understand the hydrodynamics of the estuary. To achieve this, a hydrodynamic model which can be linked to a sediment transport model needs to be developed. Various existing types of hydrodynamic and sediment transport models are reviewed, to determine their suitability for the above purpose. Results of the analysis indicate that a two-dimensional hydrodynamic model is required. The two-dimensional hydrodynamic model developed is based on the momentum and continuity equations for an unsteady, non-uniform, free-surface flow for an incompressible fluid. The two dimensions are in the horizontal plane and flow is averaged over the depth. The equations are non-linear and are not decoupled, thus a numerical technique was needed to solve them. An Alternating Direction Implicit technique has been used. Boundary conditions in the modelled region were specified as flow velocity at the upstream boundary, and water levels, relative to the Mean Lake Level, at the downstream boundary. Two short simulations using hypothetical data were run on a 80826 IBM compatible. Results of the simulation indicate two areas where irregularities in the model output are a consequence of the use of hypothetical data in defining the boundary conditions. Recommendations for the collection of data in order to improve and calibrate the model are discussed.
Mechanisms of sill and dyke intrusion.
(1994) Kattenhorn, Simon Allen.; Watkeys, Michael Keith.
Mechanisms of sill and dyke intrusion require an understanding of fracture growth,stress distributions and intensities, dilation,intrusion rates, hydraulic pressure,host-rock effects,en echelon fracture arrays,and flow direction. The methods of previous studies have been applied to natural sill and dyke examples of the Karoo Igneous Province in northern Natal . An en echelon array of Jurassic dolerite sills occurs within Permian Ecca sediments along the Mhlatuze River, west of Empangeni. Dolerite emplacement occurred as two intrusive phases. The first phase resulted in thick, . coarse-grained dolerite sills. The second phase produced relatively thinner, fme-grained sills. The intrusion of fmegrained dolerite into older sills is demonstrated by abrupt variations in the whole-rock and mineral geochemistry profiles across the sills. Syn-crystallisation effects such as crystal settling and fractionation, and post-crystallisation hydrothermal activity is also manifested in the mineralogical and geochemical changes across the sills. The fine grained doleriteis associated with xenolithic dolerite which represents a contaminated magma propagation front of the fine-grained dolerite. The higher viscosity of the xenolithic dolerite hindered propagation, and was thus overtaken and engulfedby the mainmagmapulse. Consistent sinistral off setting of sill segments is interpreted to be the result of a fingered sill periphery intruding an en echelon fracture array. Dilation of individual segments, or fingers, occurred simultaneously. Subsequent interaction of near-tip stresses induced inwardly propagating curvature of adjacent segmentsin the array.Resultant linkage has produced a stepped-sill geometry; sill propagation and flow directions were orthogonal to the plane of linkage. The flow direction is confirmed by shape preferred-orientations of acicular mineral grains within the chilled margins of the sills, indicating the direction of flow to be perpendicular to the plane of the en echelon array, and parallel to strike directions of offset surfaces that link adjacent sill segments. Multiple dyke intrusion is examinedat an outcrop of the Rooi Rand Dyke Swarm, along the Pongola River. Individual intrusive episodes are identifiable on the basis of chill-zone relationships. The pattern along the Pongola River suggests that younger intrusive episodes frequently intrude through the centres of older dykes. A three dimensional analysis of en echelon dyke let segments allows a re-construction of the dilation history,and provides an explanation for the development of blunt-ended intrusion segments. Mineral geochemistry anomalies around dyke tips suggests possible facilitation of incipient fracture via decreases in mineral strengths manifested by geochemical changes. A statistical digital analysis of micro-phenocryst orientations within chilled dyke margins is shown to provide a viable method to ascertain magma flow directions within dykes, and may thus be a useful tool for future investigations.
Assessment of the permeability of Vryheid formation sediments.
(1994) Venter, Bernardus Jacobus.; Jermy, Colin A.
Permeability is that physical property of a porous medium that controls the flow of fluids through that medium. The flow of methane and water may be induced by the excavation of a mine opening in methane-bearing strata. Methane flow into a mine opening constitutes one of the biggest hazards in the coal mining industry. It is poisonous to humans and can ignite at concentrations as low as 5 % per volume and create explosions in the presence of coal dust from mining. If the flow of methane and/or water into the mine opening becomes blocked by an impervious layer, excessive pressures may develop, particularly in the roof strata of the mined seam, which can lead to roof falls. In order to characterize the flow of methane and water into and around the openings in a mine, that was plagued by roof falls suspected of being the result of excessive fluid pressure build-up, a large scale laboratory investigation of the permeability of the roof sediments of the working coal seam in the area was undertaken. The permeability was measured under atmospheric conditions by means of a modified Ohle permeameter, and under triaxial conditions with the aid of a modified Hoek cell. The permeability of the sediments towards methane and water was measured. Nitrogen was used as a control because it is much less reactive than methane towards the sediments used in this project. It was found that the permeability decreases with increasing gas pressure, in the case of gas being the permeating fluid, and increased with increasing water pressure, in the case of water being the permeating fluid. In some instances anomalous plots of permeability versus reciprocal mean gas pressure were obtained. These were attributed to the effects of methane adsorption or the Klinkenberg effect, and a possible method to determine which of the two processes is dominant is discussed. To characterize the flow in the roof strata of the coal seam being mined, the permeability was correlated to fades type. The different fades types were numbered from 1 to 14 with increasing grain size for ease of correlation. Due to the variable nature of the sediments, even in a fades type, no single permeability could be obtained for a fades type. Instead permeability ranges were obtained for each fades type. The definition of the lower and upper limits for each range were found to be dependant on the number of tests done on samples for that fades type. Nonetheless a relationship of increasing permeability with increasing grain size was found in the coarser grained fades (facies type 8 and higher). For the fIner grained fades types the permeability was found to decrease with increase in grain size. A graph could be constructed for use in predicting possible hazardous zones by identifying the fades type and then reading the permeability range that can be expected off the graph. Due to the variable nature of the sediments, the graph is, at this time, only applicable to the areas where the samples were obtained. A permeability prediction graph for all localities would be an ideal but is beyond the scope of this project. Such a graph, and the methods discussed have a wide range of applications in the coal mining and methane gas exploitation industries.
The stratigraphy of the Natal Group.
(1994) Marshall, C. G. A.; Von Brunn, Victor.
Research for this project involved the first systematic field and laboratory investigation over the entire known portion of the Natal Group depositional basin, from just north of Hlabisa in the north, to Hibberdene in the south, and, on a reconnaissance basis, as far south as the Mtamvuna River near Port Edward. The development of a stratigraphy for the Natal Group is traced through the work of previous researchers, who worked in specific areas. The SACS compilation was inadequate, and this unsatisfactory situation was addressed in presenting the first workable stratigraphic subdivision of the Natal Group for the whole of the basin. There are two proposed formations, each representing a cycle of sedimentation - a lower Durban Formation and an upper Mariannhill Formation. These are subdivided into the Ulundi, Eshowe, Kranskloof, Situndu and Dassenhoek Members, and the Tulini, Newspaper and Westville Members, respectively. They are generally greyish red in colour, and consist of conglomerates, sandstones, siltstones and shales. The generally accepted correlation between the Natal Group in KwaZulu-Natal and what was hitherto considered as its time-equivalent in Pondoland has been disproved. Consequently, the supposed interdigitation/transition between these two assemblages, along with the hypothesis that the Kranskloof and Dassenhoek quartz-arenite Members were littoral deposits formed during a marine transgression/regression cycle, is no longer accepted. A provenance to the northeast is proposed, based on palaeocurrent data. Pan-African mountain-building in what is now Mozambique provided molasse sediments which were laid down in an elongate (NE - SW) foreland graben basin. The age of this was determined as 490 Ma, from 4°Ar;J9Ar step-heating on micas extracted from argillaceous samples. Contemporaneous volcanism, as reflected in the presence of volcanic glass (sericitised) shards, is reported. The Natal Group is a molasse deposit, derived some 490 Ma ago from a Pan African orogenic event in southern Mozambique, and deposited in a foreland graben, the Natal Trough, during continued subsidence. Activity of this trough is seen to have continued from Pan African to Permian times. This assemblage rests on the basement, and is overlain by the Dwyka Group. Only part of the basin survives on the African continent, the unknown portion being removed during the fragmentation of Gondwana. The southern limit of the Natal Group is at the Dweshula High, near Port Shepstone, which, together with basin tilting, is seen to have been instrumental in causing the deposition of this assemblage. It is suggested that fluvial activity and debris flow processes led to the deposition of the conglomerates of the Ulundi, Tulini and Westville Members, whereas braided rivers of the Platte and Bijou Creek types deposited the arenaceous and argillaceous sediments which now constitute the other members. The climate was probably semi arid, with ephemeral streams. Shape parameters of the conglomerate clasts point to a fluvial environment. The dividing-line between monomict (quartz) Facies A to the south, and polymict Facies B to the north, of the Tulini Member, was found to coincide with the edge of the craton in this area. The common occurrence of pressure solution phenomena is described. The tensile strength of fractured quartzite clasts in the Ulundi Member is used to estimate a minimum thickness for the Natal Group of 1300 to 2600 m - considerably greater than the present thickness. This estimate supports the hypothesis that much of the Natal Group was removed by erosion during the 200 million year period between the cessation of Natal Group deposition and the onset of Dwyka glaciation, and indeed, by the glaciation itself. The Westville. Member is thus seen as the basal unit of a third cycle of sedimentation, all of which, except the remnants of the Westville Member, have been eroded away.
The petrology and geochemistry of the Merensky reef in the Rustenburg area.
(1994) Brown, Raylan Talbot.; Lee, C. A.; Wilson, Allan H.
Four Merensky reef underground exposures of different reef thickness, representative of the lithological variations exposed in mining, have been drilled and mapped. The relationship of the Merensky reef to the underlying rocks is paraconformable, and a broad-based definition of the highly variable Merensky reef, on the basis of detailed mine-wide mapping, is presented. Fifty two whole-rock samples from one drill intersection were analysed for major and trace elements by X-Ray Fluorescence spectrometry, and for platinum-group elements (PGE) by Neutron Activation analysis. The remaining three drill intersections were analysed for trace elements, and for PGE in one instance. Orthopyroxene and plagioclase mineral separates from one intersection were analysed for major elements by XRF, and the mineral compositions determined. The results of the whole-rock and silicate mineral chemistry are presented and discussed. Whole-rock geochemistry is controlled by modal composition, as are most trace elements. Incompatible elements such as Nb, Zr, Ba, Y and Rb occur in elevated abundances in the feldspathic pyroxenites and show systematic low-correlation relationships with Cu, Ni, Sand the PGE. These patterns are ascribed to the pore space competition between incompatible element enriched silicate melt and sulphide melt. The PGE are systematically associated with the base metal sulphide elements, with some localised decoupling, with Pd and Au showing the greatest chalcophile nature. The other PGE are highly correlated. Deviations in the geochemistry relative to the mode are analysed and discussed. Orthopyroxene and plagioclase mineral compositions consistently define three-way lithological associations, demonstrating limited geochemical relationship between the lithologies. These lithologies represent the footwall and hangingwall norites/anorthosites and the Merensky reef/Merensky pyroxenite sequence. The Merensky reef pegmatoid and the overlying Merensky pyroxenite have more evolved Mg# and Ca# than the norite or anorthosite. Ni in orthopyroxene correlates with whole-rock Ni, providing evidence of re-equilibration. A systematic relationship exists between plagioclase and orthopyroxene mineral compositions, with Ti in both phases defining primary and re-equilibrated trends. Apart from the elevated PGE abundances in the Merensky reef, the Merensky reef and overlying Merensky pyroxenite are geochemically indistinguishable. Certain evolved element distribution patterns coincide with the zone of elevated PGE, Cu and Ni abundances. Abundant geochemical evidence is consistent with late-stage in situ hydromagmatic alteration and modification to the Merensky reef, and in part, the Merensky pyroxenite. In contrast, the texturally similar footwall and hangingwall norites show very little evidence of hydromagmatic effects, where magmatic and submagmatic processes are well preserved. The whole-rock and mineral geochemistry defines and characterises the Merensky succession and provides certain constraints for petrogenetic modelling. A multi-stage process is envisaged for the petrogenesis and evolution of the Merensky succession, involving, 1) a magmatic stage, 2) a submagmatic stage, and 3) a hydromagmatic stage.
The geology and geochemistry of the Rooi Rand Dyke Swarm.
(1996) Meth, Deanna Lorrine.; Watkeys, Michael Keith.
The Jurassic Rooi Rand dolerite dyke swarm was emplaced sub-parallel to the Lebombo Monocline during the initial stages of Gondwana breakup. The dykes extend northwards from the southern Lebombo region in northern KwaZulu-Natal, into central Swaziland, spanning a distance of approximately 200 kilometres with a width between 10 and 22 kilometres. Detailed mapping of a 600m-Iong section on the Pongolo River, established at least eleven phases of intrusion. Each dyke age was systematically sampled and analysed for whole-rock major, trace and rare earth element composition, as well as mineral chemistry. Selected samples were analysed for stable isotopes. In addition to notable intra-dyke chemical variations, there is also a high degree of inter-dyke mineralogical and geochemical variation, each dyke age bearing distinct geochemical characteristics. The apparent geochemical trend is not one of simple fractionation with time. Dyke chemistries are closely linked to magma genesis and magma volumes with time. Evolution of the magmas may be described in terms of varying degrees of partial melting and fractional crystallization, with a small degree of crustal contamination. Major, trace and rare earth element data indicate a lithospheric mantle source for the majority of dyke phases, and an asthenospheric source for only two of the eleven ages. Contrary to this, isotopic data (oxygen and radiogenic) indicate an enriched asthenospheric source for all the dolerites. This suggests that all ages may have originally been derived from the asthenosphere, with the majority of ages being intruded into the lithospheric mantle to later undergo partial melting and fractional crystallization, with some contamination. Previous studies assumed an asthenospheric source with depleted MORB-like rare earth element profiles to be representative for the majority of Rooi Rand dolerites. The Rooi Rand dolerites appear to display a geochemical link with the southern Sabie River Basalt Formation, as well as the Lebombo rhyolites. Magmatic evolution of the dykes was intimately linked to the initial rifting processes of lithospheric stretching and asthenospheric upwelling, which in this case concluded in a classic failed rift situation.
Palaeoenvironments of the Estcourt formation (Beaufort Group), KwaZulu-Natal.
(1997) Green, Dawn.; Watkeys, Michael Keith.; Smith, R.
At present the Karoo Basin covers approximately 20 000 km2. It is a large intracratonic basin which, from Carboniferous to Jurassic times, was infilled with a succession of sediments ranging from glacial deposits to those deposited in warm, equable conditions. The Beaufort Group forms part of this succession, and was deposited in a terrestrial, river dominated environment. The dominant lithologies exposed in the Estcourt region in the KwaZulu-Natal Midlands belong to the lower and middle Beaufort divided by the PermoTriassic boundary. The Permo-Triassic palaeoenvironment in this region is reconstructed using sedimentary profiles combined with the study of the fossil remains discovered in the area, including plant, body, and trace fossils. The lower Beaufort sediments in this region belong to the Estcourt Formation, and the Middle Beaufort sediments to the Belmont Formation. The Estcourt Formation is dominated by a succession of alternating sandstones, siltstones and mudstones, which are interpreted as representing sediments deposited in a fluvial-floodplain environment, which can be divided into two sub-environments. The first is dominated by sediments that were deposited by meandering rivers on a semi-arid floodplain, and the second sub-environment is represented by those sediments deposited in lacustrine environments. Both of these subenvironments are closely linked and alternate in the rock record indicating many episodes of transgressive-regressive lacustrine episodes. The Estcourt Formation can be closely correlated with the lower Beaufort sediments mapped in other regions of the Karoo Basin, indicating similar climatic and environmental controls throughout the Karoo Basin of southern Africa. The Estcourt Formation also contains a wide variety of body and trace fossils. The PermoTriassic boundary can be traced along the western border of Estcourt by using the distribution pattern of the two mammal-like reptiles Dicynodon and Lystrosaurus. There is evidence of an overlap in the distribution between these to mammal-like reptiles, which together with palaeoflora evidence, indicates that Lystrosaurus evolved during the Late Permian and not Early Triassic as previously thought. The first Triassic sediments are represented in the Estcourt region by a series of maroon shales which can be correlated with the Palingkloof Member.
Seismic stratigraphy of the northern KwaZulu-Natal upper continental margin.
(1998) Shaw, Michael John.; Mason, Tom R.; Watkeys, Michael Keith.; Ramsay, Peter John.
This study presents the interpretation of Edo-Western and Sparker seismic geophysical data acquired on the northern KwaZulu-Natal upper continental margin by various organisations since 1981. Five seismic sequences are recognised and these are traceable across the entire length of the study area. The oldest is interpreted as a late Cretaceous marine sequence (Sequence A), probably the offshore equivalent of the St. Lucia Formation exposed onshore. This sequence is overlain by a progradational, probable late Tertiary shelf sequence (Sequence B) onlapping in places against the underlying marine sequence. The outer portion of this sequence on the upper continental slope is characterised by complicated reflection termination patterns indicating the possible presence of discreet sequences within this shelf and slope unit. These shelf and slope sediments are overlain by a thin (less than 20m) reworked and eroded Pleistocene shelf unit (Sequence C), itself overlain by linear Pleistocene aeolianites (Sequence D) in places. The youngest sequence observed is the Holocene unconsolidated sediment wedge (Sequence E) on the inner shelf, attaining thicknesses of greater than 20m in places. The various sequences were mapped out and sediment isopach maps were produced (wherever possible) as well as an overall geological subcrop map of the study area. 150 kilometres of shallow penetration Edo Western seismic records acquired off the Sodwana Bay continental shelf were interpreted. Two sediment types are recognised, namely consolidated beach rock/aeolianite and unconsolidated Quaternary shelf sand/bioclastic reef derived sediment. In places, accumulations of bioclastic sediment in subaqueous dune troughs which have been subsequently buried by migrating bedforms manifest themselves on seismic records as dark semi-continuous reflectors beneath the migrating bedform. Close inshore, seismic records show prominent reflectors interpreted as consolidated sediment beneath varying thicknesses of unconsolidated sediment. Close to the shelf break (occurring at approximately -60m), seismic interpretation indicates that thin beach rock developments perch directly upon unconsolidated shelf sand, with the beach rock having been eroded through in places to expose unconsolidated sediment beneath. A sediment thickness map for this area was compiled from the seismic data. The limited penetration of the Pinger system necessitated "greater-than" values being used in many areas. Greatest sediment thicknesses occur in subaqueous dune fields where unconsolidated sediment thickness is at least 11 m. In inshore areas absent of subaqueous dune fields, sediment thicknesses are typically low, varying between 1 and 3m. A prominent submerged dune ridge close inshore limits substantial unconsolidated sediment build-up to landward of this feature. On the seaward side substantial build-up is limited by the action of the Agulhas Current which is actively transporting sediment into the head of submarine canyons which incise the continental shelf at Sodwana Bay. This study shows that on the northern KwaZulu-Natal continental shelf where there is a dearth of unconsolidated Quaternary sediment, the Edo Western seismic system is a useful tool for discerning thin veneers of unconsolidated sediment less than 4m thick. When considering the overall low volumes of unconsolidated sediment present on the shelf, this hitherto unconsidered volume of sediment constitutes an important part of the shelf sediment budget. Submarine landslide features observed on sparker seismic records are described and discussed. Submarine landslides are present which affect a) Sequences A and B, b) Sequence B only and c) Sequence A only, ages of these sediment failures can thus be inferred as being either post- Late Cretaceous or post- Late Tertiary. Offshore Kosi Bay, submarine landslide features affecting Sequence A are buried by unaffected Sequence B sediments, indicating a post- Late Cretaceous to pre- Late Tertiary age of occurrence. Style of failure tends towards mass flow in those submarine landslides in which Sequence B only sediments are affected, while those in which Sequence A is affected exhibit some slide features indicating a greater degree of internal coherency of these sediments compared to Sequence B. Slope stability analysis of a submarine landslide feature offshore St. Lucia Estuary Mouth indicates the failed sediment mass would have been stable under static conditions and that external dynamic forces such as storm waves or seismic activity would have been necessary to induce failure. It is demonstrated that the Zululand earthquake of 1932 would have exceeded the intensity necessary to induce sediment failure and this event should therefore be considered as a possible cause. Seismic evidence of fluvial incision/subaerial exposure at the boundaries between Sequences A and B and C and E are further evidence of lowered sea-levels probably during the Oligocene and Late Pleistocene. The position of the incision into Sequence C relative the present course of the Mkuze River indicates the possibility that this incision could represent the palaeo-outlet of this river. Seismic expression of 3 submarine canyons in the study area indicate that they are currently undergoing active headward erosion, independent of any direct modern fluvial influence. In the case of Ntabende Canyon, a nearby continental shelf incision postulated to be the palaeo-Mkuze outlet indicates that provision of terrigenous material to this portion of the continental shelf could well have accelerated mass wasting processes within the canyon itself. This submarine canyon could therefore have progressed more rapidly to a relatively mature phase of development. Subsurface structure indicates the lack of any post- Late Tertiary fault features beneath the canyons, thus excluding faults active in post- Late Tertiary times as a developmental factor. It is shown that the overall, external morphology of the KwaZulu-Natal upper continental margin is strongly influenced by seismic stratigraphic relationships, with the main influencing factors being outcrop position of the various sequences and depositional angle of sediments of which a sequence is comprised. External morphology has also been greatly modified in places by mass-wasting processes. It is demonstrated also that relating the observed seismic stratigraphy to onshore geological cross sections is problematic due to the distances involved and lack of confident offshore dates for the seismic sequences observed. Seismic relationships observed contribute to an understanding of relative sea-level movements since the Late Cretaceous and the overall geological evolution of the northern KwaZulu-Natal upper continental margin, details of which are discussed.
The assessment of groundwater quality in rural communities : two case studies from KwaZulu-Natal.
(1998) Sherman, Heidi Michelle.
The health and life expectancy of populations in developing countries is largely determined by the availability of good quality drinking water. Boreholes and springs generally provide water of better microbiological and physical quality than surface water sources, however, they may cause health and aesthetic problems due to chemical constituents dissolved out of the host rock. As part of a pilot study to assess the health-related quality of community water supplies, samples were taken from two Quaternary catchment areas in KwaZulu-Natal. The Umkomazi catchment area is located inland from Amanzimtoti, while the Umfolozi catchment area is located north-east of Ulundi. The geology in these areas is significantly different. The Umkomazi area is predominantly underlain by basement rocks of the Natal Structural and Metamorphic Province, while the Umfolozi area is underlain by sedimentary rocks of the Karoo Supergroup. Geographical information systems (GIS) were used to examine the influence of lithology, rainfall and landuse activities on groundwater quality. Major ion analysis of groundwater samples from the Umkomazi area revealed a linear relationship between borehole and spring concentrations. Dwyka Tillite was found to produce water with the highest concentrations of major ions, while Karoo dolerite produced water with the lowest concentrations of major ions. Samples from basement rocks and Natal Group contained intermediate concentrations of major ions. In the Umfolozi area Karoo dolerite samples showed the lowest concentrations of major ions, while the Vryheid Formation and Dwyka Tillite produced the highest borehole and spring concentrations, respectively. High salinity levels in sedimentary rocks may be due to marine influence during deposition. Piper diagrams show relative enrichment of major cations and anions and Stiff diagrams showed characteristic patterns. Fluoride is associated with siliceous basement rocks and related to calcium concentrations through the solubility of calcium fluoride. The trace metals, manganese, iron and zinc were found to cause significant aesthetic problems and possibly health problems in sensitive individuals. These constituents are derived from weathering of bedrock and possibly from the corrosion of metal pipes. There is an inverse relationship between mean annual rainfall (MAR) and electrical conductivity (EC), except near the coast where windblown salinity increases with rainfall. Nitrate, ammonium and E. Coli contamination are linked to landuse activities such as occurrence of human and animal excreta near the water source and the proximity of pit latrines. It is recommended that rural communities be educated about the nature and importance of groundwater quality.
The bathymetry, sedimentology and seismic stratigraphy of Lake Sibaya- Northern KwaZulu-Natal.
(1998) Miller, Warwick Richard.; Mason, Tom R.; Watkeys, Michael Keith.
The morphology of Lake Sibaya is a product of an ancient fluvial system that drained a coastal landscape dominated by aeolian processes. The sedimentary processes within the lake are driven by wind generated currents. The dominant sedimentary process is one of lake segmentation, whereby prograding bedforms isolate the lake into smaller water bodies. The prograding bedforms include cuspate forelands and sand spits. The size and mobility of these bedforms is a function of sediment availability and current regime. The bathymetry of Lake Sibaya is discussed, with emphasis on geomorphic features derived from the ancient aeolian landscape as well as features related to modern sedimentary processes. The presence of underwater knickpoints and terraces indicate that lake level fluctuations have been common in Lake Sibaya. It is during lake highstands that large volumes of sand are eroded from aeolian dunes which surround the lake and made available for shoreline progradation. Ancient dune topography is preserved to depths of 20 m below water-level within the lake. Surface sediment distribution maps were compiled from 515 grab samples and thirteen core samples. Fine grained, well sorted, coarse skewed quartz sand comprises the majority of the surface area of the lake floor. Gyttja is the other dominant sediment type and accumulates in palaeovalleys and depressions on the lake floor. Sediment distribution in Lake Sibaya is discussed in terms of modern lacustrine processes as well as inherited sedimentary characteristics. The stratigraphy of the sediments underlying Lake Sibaya was investigated using a Uni-Boom seismic profiling system. Seismic profiles were compiled by identifying acoustically reflective surfaces that show regional development. Thirteen seismic overlays were prepared, and are illustrated as west - east and north - south seismic profiles. Five sequences ranging in age from late Cretaceous to Holocene were identified from the seismic profiles, and are described in terms of sequence stratigraphic principles. The seismic sequences were interpreted within a lithostratigraphic framework and are presented as a series of idealised geological sections. Thirteen sediment cores were collected from the Lake Sibaya area in order to ascertain the accuracy of the stratigraphic interpretation of the seismic records, to investigate reflective horizons identified from seismic records and to collect dateable material. Interpretation of the sediment cores reveals that a proto Lake Sibaya existed on drowned dune topography, during the period ± 43500 BP to ± 25500 BP prior to the Last Glacial Maximum. During the early to mid Holocene the Lake Sibaya site was occupied by a saline lagoon which underwent isolation from the sea ± 5030 BP. Since the mid-Holocene the lake has evolved to totally freshwater conditions and has undergone little sedimentation. The geological evolution of the Lake Sibaya area is discussed in terms of the geometry of the identified seismic sequences, the sedimentary characteristics of these sequences and the radiocarbon dates provided from the sediment cores. Palaeo-environmental conditions during the accumulation of the sedimentary sequences is discussed where fossil remains permit.
Sedimentology, stratigraphy and geological history of part of the northern KwaZulu-Natal coastal dune cordon, South Africa.
(1999) Sudan, Pascal.; Whitmore, Gregory P.; Uken, Ronald.
The northern KwaZulu-Natal coast is backed by a continuous aeolian dune cordon that rises in places, to a height of more than 100 metres and a width of 2 kilometres. This MSc thesis documents the geomorphology of the area, as well as the mineralogical, geochemical and textural variation of nine boreholes within a small part of the coastal dune cordon between Lake Nhlabane and Cape St.-Lucia. The results provide useful constraints on the identification of individual beach and aeolian dune systems, their age relationships and spatial distribution. Aeolian dunes within the coastal dune cordon were studied using aerial photographs and grouped into five dune classes that reflect their relative age. These comprise 1) a system of highly weathered dunes inland of the present coastal dune cordon, that are thought to represent older dune cordons; 2) a system of weathered and reworked dunes located on the most inland portion of the coastal dune cordon; 3) a less altered, large field of linear parallel dunes located in the northern part of the study area; 4) a system of large scale parabolic dunes; and 5) a system of coastal, relatively unweathered small parabolic dunes. Mineralogy, geochemistry, texture and SEM analysis of borehole samples revealed a complex internal structure within the present coastal dune cordon. In the most inland part of the dune cordon, a basal light grey unit (Unit K) presents similar characteristics to the Kosi Bay Formation. This is overlain by Unit A, comprising beach and dune systems, characterised by a very high heavy mineral content. Unit A also forms the basal unit of the central and coastal portions of the dune cordon. Unit B contains a mixture of reworked sediments from Unit A and younger sediments. Aeolian Units D and E form the upper part of the dune cordon. Units D and E were derived from beach - foredune systems and contain a high carbonate bioclast content. All units are interpreted to be derived from immature sediment from the Tugela River and mature sediment from the continental shelf. In the southern part of the study area, an additional unit (Unit C) with unique characteristics has been interpreted as an aeolian deposit reworked from local fluvial sediments. The units identified from their sedimentological characteristics can be directly correlated to the regional dune classes identified from the geomorphology. Luminescence dating of two calcareous dunes was undertaken, revealing that only the sediment of the small coastal parabolic dunes (Dune Class 5, Unit E2) is of Holocene age. The deposition of the large field of linear dunes (Dune Class 3, Unit D2) took place between 15 000 and 11 000 BP, during the marine transgression following the last glaciation. Luminescence dating also indicated that both dunes were subject to at least one major reworking event. A study on the weathering characteristics of the dunes can be used to attribute a relative age to the nine sedimentological units. With the help of sea level curves and the two luminescence dates, the nine units were attributed an approximate absolute age and regrouped into four sediment packages thought to broadly represent four interglacial periods. The three younger packages are attributed to the penultimate interglacial (lower part of Unit A), last interglacial (upper part of Unit A, Units B and C) and "Holocene" interglacial (Units D and E). Hence the northern KwaZulu-Natal coastal dune cordon under study represents a complex stacking of three generations of coastal dune cordons, and appears to be constituted of sediments with age ranging from at least two hundred thousand years ago to present. The oldest sediment package (Unit K), interpreted as the Kosi Bay Formation, and the older dune cordons (Dune Class I) must be older than 200 000 years, which is older than considered by previous studies. The "Holocene" dune cordon (Units D and E) is interpreted as the Sibayi Formation.

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