Geology

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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 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.
Characterisation of geotechnical, geochemical and metallurgical properties for mine-to-mill optimisation at Sandsloot open pit platinum mine, South Africa
(2008) Walker, Shonagh.
Sandsloot open pit mine extracts platinum, copper and nickel from the Platreef orebody in the Northern Limb of the Bushveld Complex. At present, it is the world's largest open pit platinum mine, but it is one of the smaller of six pits to be mined in this area by Potgietersrust Platinums Limited (PPRust). As mining progresses and the mine operations expand, sound knowledge of the subsurface ground, the orebody properties and their performance in the processing plant is imperative. An accurately characterised orebody, in terms of its geotechnical, geochemical and metallurgical properties, will facilitate the development of appropriate and cost effective mining practices and processing plant design. It will improve the prediction and performance of materials in each of the steps involved in converting the orebody rock mass into a concentrate /marketable product, which ultimately leads to mine-to-mill optimisation. This dissertation has focused on the geotechnical and metallurgical strength properties of the Platreef orebody at Sandsloot; the geochemical properties of the various lithologies and defined for each orebody rock type the associations and correlations within and between these properties. The petrography of the orebody material was studied to identify and classify the rock types. A rigorous testing programme was conducted and an extensive database of petrographic, geotechnical, geochemical and metallurgical information was assembled. The corresponding results within and across the different studies were grouped together and statistical analysis and interrogation of the data sets were performed. The research identified diverse rock types with contrasting physical properties in the Sandsloot open pit orebody. For each of the rock types the distinguishing characteristics and the variations in properties were identified. Significant differences and relationships between rock types for each property were assessed for predictability in mining. Statistical associations and correlations between the properties of each study were defined and models for predicting strength and rock type were developed.
The mineralogy, petrology and PGE geochemistry of the UG2 cyclic unit at Lebowa Platinum mine (ATOK), North-Eastern Bushveld complex.
(2008) Fitzhenry, Clifford.
This project is an investigation of the UG2 cyclic unit of the Upper Critical Zone at Lebowa (Atok)
A combined sedimentological-mineralogical study of sediment-hosted gold and uranium mineralization at Denny Dalton, Pongola Supergroup, South Africa.
(2009) Hicks, Nigel.; Hofmann, Axel.
The ~2.98 - 2.87 Ga Pongola Supergroup in South Africa is subdivided into the lower volcano-sedimentary Nsuze Group, and the upper sedimentary Mozaan Group, the latter comprising a several kilometres thick succession of fluvial to shallow marine sandstones and shales. Thin beds of gold and uranium-bearing conglomerates are locally present in the Mandeva Formation near the base of the Mozaan Group and have been mined at Denny Dalton in northern KwaZulu-Natal. The style of mineralization strongly resembles that of the Witwatersrand goldfields, however appears to be of low grade and limited tonnage. The ~1 m thick basal conglomerate, the “Mozaan Contact Reef” (MCR, herein referred to as CG 1), at Denny Dalton hosts erratic gold and uranium mineralization. The conglomerate is laterally discontinuous and occupies east-northeast trending scour channels. Polymict, matrix-supported conglomerates are common, while clast-supported conglomerates are rare. Well rounded, pebble to cobble-sized clasts of vein quartz and chert are hosted in a sandy matrix of quartz, pyrite and sericite. Where mineralized, the CG 1 hosts abundant rounded pyrite grains, interpreted as detrital in origin, with subordinate U-bearing minerals, such as brannerite and uraniferous leucoxene. Rounded detrital pyrite occurs in three phases, compact, porous and radial. Gold forms inclusions within massive pyrite grains, which are concentrated in shoots associated with the basal parts of the channel scours. SEM-EDX results, as well as the high reflectivity of the gold show a high Ag content, indicative of a primary origin for the gold within the pyrite grains. Uranium within CG 1 is hosted primarily as secondary inclusions of uranium within black chert pebbles within the basal cobble-sized regions of the conglomerate. Geochemical comparison of the chert pebbles at Denny Dalton with similar chert from the Nondweni Greenstone Belt indicates that the uranium is secondary in origin as no U anomalies occur in the Nondweni chert. Geochemical and SEM analysis of the uppermost conglomerate (CG 4) indicate the presence of uraninite and coffinite within the uppermost horizon as both fillings of voids within, and coatings on, detrital pyrite grains. Palaeocurrent data indicate a likely source terrain for the detrital material to the west of the inlier. This orientation, as well as differing mineralogical and sedimentological aspects between the Mandeva Formation and the correlative Sinqeni Formation within the main Pongola basin, indicate a separate and more proximal provenance for the auriferous conglomerates of the White Umfolozi Inlier. The Mandeva Formation is a fluvial to shallow marine sequence that has been affected by cyclic sea-level changes. The basal conglomerates of the Denny Dalton Member were deposited in a proximal braided alluvial plain environment. The conglomerates fine upwards into trough cross-bedded quartz arenites which appear to have been deposited as shallow marine sands in a shoreface environment. They are overlain with a sharp contact by a laterally extensive unit of polymictic conglomerate which represents a transgressive ravinement surface within the wave zone and marks the onset of a major marine transgression into the Pongola basin. The conglomerate is overlain by massive grits and coarse-grained quartz arenite. This unit is overlain with a sharp and locally sheared contact by shales and subordinate banded iron formation which can be traced into other parts of the Pongola basin and indicates continued rapid transgression onto large parts of the Kaapvaal Craton with deeper marine, sub-storm wave base sediments being deposited in quiet-water environments on a sediment-starved shelf. The heavy mineral assemblage as well as bulk geochemical data is consistent with a granitoid-greenstone source terrain for the conglomerates and sandstones. The geochemical composition of chert pebbles from the CG 1 is similar to the composition of cherts present in the Nondweni Greenstone Belt that is situated ~30 km west of the White Umfolozi Inlier. Multiple sulphur isotope (ä34S, ä33S) values for detrital pyrite from the MCR are consistent with an origin from mantle-like rocks, such as hydrothermal sulphide-quartz veins in a granitoid-greenstone setting. Palaeocurrent, mineralogical and geochemical data all point to a likely granitoid-greenstone provenance to the west of the White Umfolozi Inlier.
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 geological evolution of a part of the Pongola basin, southeastern Kaapvaal Craton.
(1993) Gold, Digby James Comrie.; Strydom, Dawie.; Von Veh, Mark.; Hunter, Donald Raymond.
A stratigraphic and structural study of the Archaean Pongola Sequence on the southeastern Kaapvaal Craton centred on the area around the Klipwal Gold Mine is described. The lower predominantly volcanic Nsuze Group is overlain with a gradational transition by the upper clastic Mozaan Group in which six formations are recognized. The Sinqeni, Ntombe, Thalu, Hlashana, Odwaleni and the Kulphiso Formations. The Sinqeni and Hlashana Formations are predominantly arenaceous while the Ntombe and Kulphiso Formations are mainly argillaceous. The Odwaleni Formation contains a diamictite which is interpreted as a tillite, and is therefore the oldest glacial rock on record. The stratigraphic position of the Kulphiso Formation is problematic. The Mozaan Group was deposited in a deepening epeiric sea which was invaded periodically by storm generated deposits. Dolerite and ultramafic dykes and sills of various ages are represented. Three phases of deformation are recognized in the Klipwal area. Early compression from the south-southeast initiated a major zone of bedding-parallel shear, the Izermijn shear zone, along the Nsuze-Mozaan contact and an oblique ramp, the Klipwal shear zone, at a higher stratigraphic level. An extensional phase caused reactivation of the Klipwal shear zone and the development of a major low-angle normal fault, the Gu'nsteling fault, above the Sinqeni Formation. The main phase of deformation, related to northeast-southwest compression is the most complex and most widely developed. Early northwest-trending subhorizontal upright folds were disrupted by contemporaneous north-striking dextral or dextral reverse shearing and northwest-striking sinistral or sinistral normal shearing. The obtuse relationship of these shear zones to the compression direction is probably the result of reactivation of basement structures with similar orientations. Northwest-trending folding continued during and after the shearing. The structural styles and orientations observed in the Klipwal area are recognized regionally in the main Pongola basin, highlighting the need for further detailed studies before basin-wide correlations are made.
On the engineering geology of granite saprolite and its significance to the construction of Injaka Dam, South Africa.
(2004) Haskins, David Rodney.; Bell, Frederic Gladstone.
The intention of this work is to provide a deeper understanding of the engineering geological behaviour of granite saprolite and how this affects the engineering of such material, with specific reference to the construction of Injaka Dam in the north eastern portion of South Africa Whilst extensive investigation of weathered granites has been carried out internationally, very little detailed research on the nature of this material is documented locally. The construction of Injaka Dam afforded the opportunity to investigate the saprolite in detail. This study was initially submitted to the Department of Geology and Applied Geology at the University of Natal, Durban (renamed the University of KwaZulu-Natal in 2004) to fulfill the requirement of a Master of Science degree in 200 I. Following this submission, and supported by recommendations made by the external examiners and the project supervisor, it was agreed to upgrade the work and submit this thesis for the degree of Doctor of Philosophy. Intensive chemical weathering of granite at Injaka Dam site has resulted in the formation of thick saprolitic deposits overlying the weathered bedrock. The granite forms part of the 3 075 Ma Nelspruit Suite which has been intersected by the African erosion surface. The extensive, multicyclic period of weathering and erosion that formed this surface has resulted in deep (up to 35 m) chemical weathering of the underlying bedrock in this area. The construction of Injaka Dam on this material necessitated a thorough engineering geological investigation to understand the nature of the weathering and the possible influences it exerts on the engineering behaviour of the saprolite. This was accomplished by analysing the weathering of the granite and relating the effects of these weathering processes and changes to the engineering behaviour of the material. By applying various chemical and mineralogical indices to the weathered granite, the intensity of weathering and related changes could be quantified and compared with the engineering behaviour of the material. This was achieved by applying a series of engineering indices to the material and relating these to the quantified weathering changes. In this way tentative extrapolation of the engineering behaviour of the material could be gained and used to predict engineering performance. The resultant effects of the engineering behaviour of the material on the design and construction of the dam are also discussed.
Mineralogy and geochemistry of detrital rutile from the Sibaya Foundation, KwaZulu-Natal.
(2002) Bramdeo, Siksha.; Dunlevey, John N.
Rutile, although not a major component of detrital heavy mineral deposits, is a valuable source of titanium oxide. Theoretically rutile is pure titanium dioxide (TiO2) and should form white or colourless tetragonal crystals with a density of 4.25gm/ml. However, natural rutile although tetragonal, displays a variety of colours ranging from red through brown to black, yellow or blue, variable density between 4.23 to 5.50g/ml as well as a range in the magnetic susceptibility and electrical conductivity. In addition to these variations exhibited by natural rutile, samples from detrital heavy mineral deposits normally contain, in addition to homogenous grains, composite grains, in which rutile is intergrown with one or more mineral species, commonly quartz, feldspar and ilmenite. The Sibaya Formation, like most detrital heavy mineral deposits, has a polymictic source, and as such contains rutile grains formed in many different chemical environments. Homogenous rutile grains display a chemical variation with a preference for the select few elements, which are compatible with the rutile cyrstallographic structure. The ions that substitute for titanium (Ti4+) in the crystal lattice are a reflection of chemical environment in which the crystal formed. The size and charge of the Ti4 + ion greatly restricts the species that may enter the rutile crystal lattice, with Sb3 +, V3 +, Fe3 +, Cr3 +, Sn4 +, M04+, W4+, Mn4+, 8i5+, Nb5+, Ta5 +, Sb5 +, V5 +, being theoretically compatible with the size and charge of the Ti4+ ion. Electron microprobe analysis of detrital rutile grains from the Sibaya Formation, KwaZulu-Natal show that elements, Nb5 +, Ta5+, A13+, Zr4+, Si4+, Fe3+, Cr3 +, and V5 +, commonly substitute for the Ti4 + ion. However, Sb3+, Sn4+, M04+, W4 + and 8i5 + were not present at detectable levels implying that the provenance area is not enriched in these elements. Although the high Fe3+ values were expected in the rutile grains, as Fe3 + is common in many rocks, the high Si4+ values encountered were not expected, as Si4 + is not normally compatible with Ti4 + ion, as noted by their distinct separation in rutilated quartz. The anomalous Si4 + content of certain grains suggests that within the provenance area rutile bearing rocks formed under unusual conditions, such as high pressure, temperature and silicon activity where the high charge density of the Si4 + ion would favour the inclusion of Si4 + into the rutile lattice. The chemical variation of the rutile grains causes significant variation in the magnetic susceptibility and electrical conductivity, and thus has marked effects on mineral processing, which relies heavily on magnetic and electrostatic separation techniques. The data presented indicates that individual homogenous rutile grains displays significant range of chemical composition, commonly containing other oxides from a fraction of a weight percent to well over 10wt%. Data plots of TiO2, FeO and 'other' oxides (Nb2O5, Ta2O5, A12O3, ZrO2, SiO2, Cr2O3 and V2O3), showed that many of the more magnetic rutile grains appeared to be FeO enriched and contained a higher proportion of 'other' oxides. However, some grains that just had higher proportions of 'other' oxides and a lower FeO content were also magnetic. Thus magnetic susceptibility although strongly influenced by the presence of FeO, can also be enhanced by the substitutions of other oxides. The vast majority of rutile grains from the electrostatic fractions were relatively TiO2 pure, and contained low concentrations of 'other' oxides. However, some grains did have slightly enhanced SiO2 and V2O3 concentrations, which appear to enhance the conductivity of the grains. Four main colour groups were differentiated from the population of rutile grains from the Sibaya Formation, these being, reddish brown, black, blue and yellow. No single oxide seemed solely responsible for the colour of rutile grains. However, the red rutile grains had a slightly but significantly higher Cr2O3 and Nb2O5 content, whereas black rutile grains appeared to be V2O3 and Nb2O5 enriched. The blue colour of rutile grains appears to be influenced by a combination of SiO2, Al2O3 and Nb2O5 substitutions. The yellow rutile grains had slightly enhanced FeO and Nb2O5 concentrations. Although these differences are very small, trace quantities of certain elements and different combinations of elements can have a strong effect on colour. Apart from Fe3+, no single element; appears to be solely responsible for variations noted in the physical characteristics (magnetic susceptibility, electrostatic conductivity and colour) of homogenous rutile grains from the Sibaya Formation. However a combination of substituting elements appears to influence magnetic susceptibility and electrical conductivity. An enhanced Fe3+ content normally increases the magnetic susceptibility although combinations of other elements may have the same effect on Fe3+ poor grains. In general terms, the purer the rutile grain, the more likely it is, to be non-magnetic and conductive. Substitutions of 'other' oxides appear to decrease the conductivity of rutile grains. The relationship between grain colour and chemistry is also not very clear, verifying the widely held view that grain colour is often the result of more than just mineral chemistry.
The Ahlmannryggen group, western Dronning Maud Land, Antarctica.
(2001) Perritt, Samantha.; Watkeys, Michael Keith.
The Mesoproterozoic Ritscherflya Supergroup forms an extensive volcano-sedimentary cover succession on the Archaean Grunehogna Province of western Dromring Maud Land, Antarctica. The oldest:, predominantly sedimentary deposits of this cover succession are exposed across the Borgmassivet and southern Ahlmannryggen mountain ranges, and are collectively assigned to the Ahlmannryggen Group. A revised lithostratigraphy places exposures from these two regions in separate subdivisions, with three formations being recognised in the Ahlmannryggen (Pyramiden, Schumacherfjellet and Grunehogna Formations) and four formations being defined for the Borgmassivet (Veten, Framryggen, HogfOlma and Brapiggen Formations). Deposition of these successions occurred in a combination of fluvial braid-plain and braid-delta plain environments, with exposures in the Ahlmannryggen and Borgmassivet regions representing contemporaneous sedimentation in different portions of the same basin, under similar conditions. The development of the Ahlmannryggen Group basin is attributed to flexing associated with continental collision during the assembly of Rodinia. Collision and accretion of a continental island arc terrain (the Maudheim Province) along the southern margin of the Grunehogna Province is considered responsible for flexural snbsidence and the development of a peripheral foreland basin. The Ahlmannryggen Group represents 'molasse' stage infilling of this basin, with sedimentation being dominated by a combination of transverse and longitudinal drainage systems entering a depo-centre located to the east/southeast of the presently exposed succession. SAMANTIIA PERRlTT Detritus entering the basin was sourced either directly or indirectly from at least seven different terrains, aged ca. 1135Ma, ca. 1335Ma, ca. 1600-1700Ma, ca. 2000-2100, ca. 2645Ma, ca. 2400-2900Ma and ca 2900-3300Ma, according to UlPb detrital zircon SHRIMP analysis. The source terrains included the Maudheim Province, basement granites of the Grunehogna Province, an older sedimentary terrain dominated by a banded ironstone association, at least two further magmatic provinces and two metamorphic terrains. Of these source terrains, only the Maudheim Province and Grunehogna Province basement granites are presently exposed in western Dromring Maud Land The subsequent development of large-scale buckle folds and extensive brittle deformation within the Grunehogna Province cover rocks is attributed to the formation of a regionally extensive sinistral strike-slip system during NNW-SSE Pan-African compression, and can be correlated to structures exposed in the Maudheim Province and northern Mozambique. It is proposed that this strike-slip system developed in response to escape tectonics operating during a late stage of Gondwana amalgamation, as a result of the Ross Orogeny, and the suturing of East and West Antarctica
Rock mass rating and slope stability analysis of quarry faces within the dywka [i.e. dwyka] tillite of KwaZulu-Natal.
(2002) Kujawa, Thomas.; Jermy, Colin A.
Dwyka tillite quarries in the Province of KwaZulu-Natal have shown remarkable stable slopes faces even though some of them were quarried over 30 years ago. This can be attributed to their resistance to weathering, the high degree of joint surface roughness, the general lack of any joint infill and the limonitic staining found on most weathered joint surfaces. The latter appears to increase joint roughness. The high percentages of joints terminating within the rock mass or against other discontinuities as well as their low persistence results in a high degree of joint interlocking. These are shown to be very important factors contributing to the overall slope stability. Detailed discontinuity surveys were carried out at five different quarries located throughout the KwaZulu-Natal region. Only three of these quarries are presently being quarried. This allowed the study and comparison of joint and slope stability characteristics for both the older, more weathered rock faces and those of the recently quarried, and thus fairly unweathered rock faces. Joint orientation data from the various sites show that two to three sets of high angle joints and one low angle joint set are common. The potential of wedge and planar failure is therefore very high. The steeply dipping discontinuities also promote the potential for flexural toppling failure and this was noted in several of the quarry faces. Recognised geotechnical techniques and computer models were used to establish potential modes of failure and to estimate factors of safety. Wedge failure, at partially saturated and saturated conditions, was identified as being the main source of potential slope instability on the quarry rock faces. The quality of the rock mass of each slope was also classified according to various rock mass classification systems. The rock mass quality generally was rated as being 'fair' to 'good', meaning that slopes are partially stable to stable. The results of each rating system were also compared.
The geology and rock mass quality of the Cenozoic Kalahari Group, Nchwaning Mine Northern Cape.
(2002) Puchner, Richard A.; Watkeys, Michael Keith.; Jermy, Colin A.; Maud, Rodney.
With the extension of the Nchwaning Mine shaft complex in the Northern Cape Province, various geological and geotechnical complications needed to be identified in order to ensure correct use of tunnelling methods and support techniques. An understanding of the geological history of the area and the resulting geotechnical nature was important in defining the rock mass quality ahead of shaft development. A total of 12 geotechnical boreholes were drilled, and an additional 18 old boreholes revisited to accurately detennine the stratigraphy, geological structure and associated weathering effects. Various soils and rock testing helped quantify the materials encountered. Sands of the Gordonia Fonnation form the surface cover of this area, and together with the weathered calcrete, calc-arenite, conglomerate and clay, they form part of the Cenozoic Kalahari Group. The 30m thick basal unit of red clay is common throughout this region. This silty clay material is problematic in that it is expansive and hygroscopic. The clay unit rests unconformably on folded, faulted and highly weathered shale of the Proterozoic Lucknow and Mapedi Formations of the Olifantshoek Supergroup. Unconformably below this sequence lies the manganiferous ore deposits of the Hotazel Member, which is contained within the Voelwater Formation of the Griqualand West Supergroup. For the development of the decline shaft through the Gordonia Formation a box cut was excavated to a depth of 25m. The anticipated poor geotechnical conditions for a further 125m below the Gordonia sands called for high quality permanent tunnel support in the upper weathered horizons. Barton's Q-analysis was adopted as a recognized tunnelling quality index to predict and quantify the rock mass characteristics ahead of the shaft. The highly variable and generally low Q-values from borehole core analysis indicated that precast tunnel lining be used for 800m (at 11.5°) through the entire weathered Cenozoic sequence and into the weathered shales immediately below the Red Clay.
The development and application of a 3D geotechnical model for mining optimisation Sandsloot open pit platinum mine South Africa.
(2003) Bye, Alan Russell.; Jermy, Colin A.; Bell, Frederic Gladstone.; Stacey, Thomas Richard.
Detailed geological knowledge is often a major unknown factor in open pit mining and design, and therefore poses a significant risk in the mining venture. As the knowledge of the geology improves so the risk of unforeseen conditions reduces and therefore safety and productivity can be increased. Historically, geotechnical methods and information have predominantly been used exclusively for pit slope optimisation. This research documents the procedures and developments undertaken to compile a comprehensive geotechnical database, and the application of the geotechnical data to open pit mining, beneficiation and planning. The utilisation of the geotechnical information has been enhanced through the novel development and application of a computerised, 3D geotechnical model. Sandsloot open pit was developed to extract the Platreef pyroxenite orebody, which is hosted within the Northern Limb of the Bushveld Complex. Sandsloot is currently the world's largest open pit exploiting Platinum Group Metals. Interaction of the basic magma with the footwall sediments of the Transvaal Supergroup and varying degrees of assimilation has resulted in a unique suite of hybrid rock types. These various rock types provide significant engineering geological challenges. Geology and the detailed understanding of its properties are fundamental to the optimal design and successful operation of any mine. Extensive fieldwork was conducted to collect geotechnical information, both from exploration boreholes and in-pit mining faces. Over a 5-year period, geotechnical data were collected from 29,213 m of exploration core and 6,873 m of exposed mining faces. Extensive field and laboratory testing was undertaken in order to define the complete set of geotechnical properties for each rock type in the Sandsloot mining area. The geotechnical information relating to each borehole and facemap was stored in the Datamine® software package. The information was collected in the form of rock mass rating (RMR), uniaxial compressive strength (DCS), fracture frequency (FF/m) and rock quality designation (RQD). The architecture of the database was developed along the principals used for generating an ore reserve model. One of the novel applications was the development of a computerized 3D, geotechnical model in Datamine®. The geotechnical parameters, namely RMR, DCS, FF/m and RQD, were modelled for each rock type, using geostatistics, to generate a 3D model. The data were interpolated between exploration boreholes and exposed mining faces and the modelling was constrained using wireframes separated by rock type. The result is a 3D model containing 15 m3 model blocks populated with interpolated geotechnical information. The dimensions of the model blocks are linked to the mining bench height of 15 m. The model can be queried to give predictions on rock mass conditions for any planned mining area, as is the case with the ore reserve model, which provides predictions on platinum grades. The crux of the innovative research is the practical application of the 3D geotechnical model. This was achieved through the development of both a fragmentation and a slope design model, which read the interpolated geotechnical information. These models provided an engineering tool to optimise mining and milling perfonnance. Rather than viewing the drill and blast department as an isolated cost centre and focussing on minimising drill and blast costs, the application of the model concentrated on the fragmentation requirements of the milling and mining business areas. Two hundred and thirty-eight blasts were assessed to detennine the optimum fragmentation requirements for ore and waste. Based on the study a mean fragmentation target of 150 mm was set for delivery to the crushing circuit and a mean fragmentation of 230 mm was set for waste loading from the pit. The mine operates autogenous mills, which are sensitive to the fragmentation profile delivered. The harder zones occurring in the ore zone have a major impact on the plant's perfonnance. The geotechnical parameters in the model were related to Lilly's Blastability Index, and in turn to required explosive volumes and the associated drill and blast costs. Having defmed the fragmentation targets, the Kuz-Ram equation was used in the fragmentation model to predict the explosive volumes required to ensure consistent mining and milling perfonnance. The geotechnical model is used to predict changes in geotechnical conditions and therefore the blasting parameters can be adjusted in advance to ensure the milling and mining fragmentation requirements are met. Through the application of the fragmentation model over an eighteen-month period the loading and milling efficiencies improved by 8.5% and 8.8% respectively, resulting in additional revenue ofR29 million for PPL. Based on the mining rock mass rating (MRMR) values within the geotechnical model a stable slope design model was created in order to calculate optimum inter-ramp angles. From a slope design perspective the model was used to target data-deficient zones and highlight potentially weak rock mass areas. As this can be viewed in 3D, the open pit slopes were designed to accommodate the poor quality areas before they are excavated. It also follows that competent geotechnical zones can be readily identified and the slope optimised accordingly. Due to the detailed geotechnical infonnation being available in three dimensions, the open pit slopes were designed based on a risk versus reward profile. As a significant geotechnical database was available, more accurate and reliable designs were generated resulting in the overall slope angle increasing by 3 degrees. This optimisation process will result in a revenue gain of R900 million over the life of the mine. The revenue and safety benefits associated with this design methodology are substantial and have potential application to all open pit mining operations. The research has enabled detailed geotechnical infonnation to be available in three dimensions. This information can be readily accessed and interpreted, thus providing a powerful planning and financial tool from which production optimisations, feasibility studies and planning initiatives can be implemented. The development and application of a 3D geotechnical model has added a new dimension to the constant strive for business improvement and reflects a novel and successful approach towards the application of engineering geology at the Sandsloot mining operation.
The physical volcanology and geochemistry of the Nsuze group, Pongola supergroup, of northern KwaZulu-Natal and southeastern Mpumalanga.
(2003) Grant, Claire Elizabeth.; Wilson, Allan H.
The Nsuze Group forms the lower, predominantly volcanic succession of the Pongola Supergroup. The 2.9Ga Nsuze Group outcrops in southeastern Mpumalanga, northern KwaZulu-Natal and Swaziland. The volcanic rocks of the Nsuze Group are basalts, basaltic andesites, andesites, dacites and rhyolites preserved as both lava and pyroclastic deposits. The oldest volcanic sequence of the Nsuze Group is the basaltic Wagondrift Formation. The younger Bivane Subgroup represents the main volcanic component of the Nsuze Group. The White River Section represents a complex volcanic history of magma storage, fractionation, and eruption, supplied by a multi-level system of magma chambers. The basaltic and basaltic andesite rocks of the White Mfolozi Inlier represent the steady and non-violent eruption of lavas from related volcanic centres. The Nsuze Group rocks have been metamorphosed by high heat flow burial metamorphism to lower greenschist facies. Geochemically, elements display well-defined fractionation trends, with evident sub-trends within each phase group of samples. These sub-trends are related to the fractionation of key minerals, in particular plagioclase. The REE patterns show that evolution of magma was largely controlled by the fractionation of plagioclase. All REE patterns show LREE enrichment relative to the HREE. The Wagondrift Formation was derived from a more depleted source than the younger Bivane Subgroup volcanic rocks and exhibits a within-plate tectonic signature. The volcanic rocks of the Bivane Subgroup in the White River Section and the White Mfolozi Inlier are geochemically similar. The volcanic rocks of the Bivane Subgroup of both the White River Section and the White Mfolozi Inlier have a subduction zone tectonic signature, in particular a Ta-Nb negative anomaly. Tectonic discrimination diagrams suggest an enriched source related to a continental-arc setting. The geochemistry suggests an eclogitic source for the Nsuze Group volcanic rocks. The formation of eclogite in the mantle requires subduction of basaltic material. Archaean models for subduction-like processes include decoupling of oceanic crust and subsequent underplating of the continental lithosphere, and low-angle subduction which minimises the effect of the mantle wedge. It is possible that a combination of these processes resulted in an enriched eclogitic source for the magmas of the Nsuze Group.
The structural, metamorphic and tectonic context of selected sub-economic veining in the Natal thrust front and Natal Nappe zone, Northern KwaZulu-Natal.
(2000) Basson, Ian James.
The eastern portion of the Namaqua-Natal Mobile Belt, the Natal Metamorphic Province is divided into four main tectonostratigraphic units. These units comprise two accreted island arcs: the Mzumbe and Margate Terranes; an imbricately thrust nappe zone consisting of four ophiolitic nappes in a hinterland-dipping duplex; and the highly deformed metavolcaniclastic/metagreywacke Mfongosi Group directly adjacent to the stable northern foreland of the Kaapvaal Craton. Theories of late-tectonic left-lateral movement in the southern island arcs are extrapolated northwards of the southern margin of the Kaapvaal Craton coincident with the Lilani-Matigulu Shear Zone. The relative timing and structural context of vein-hosted mineralization with respect to major recognized tectonic events is resolved in five separate areas, two in the Natal Nappe Zone and three in the Natal Thrust Front. The Madidima Nappe of the Natal Nappe Zone contains several north-northeast- to northeast-trending and northeast- to east-northeast trending quartzofeldspathic veined reefs considered to have formed in a late-tectonic left-lateral shear system (main shear and synthetic shear orientations, respectively). The northeast- to east-northeast-trending reef is duplicated due to infilling of normally-faulted steep structures in the semi-brittle, incremental normal faulting of the banded amphibolite component of the nappe. Later left-lateral movement has reactivated one of these steep structures along the southern margin of a regional F2-folded band of granite-gneiss in that a southwest extension of this structure may be responsible for sub-economic veining for a length of up to 9 km. The extensive flat-lying topography of the Mbongolwane Flats area, in which the reefs are situated, is accounted for by the accelerated weathering of rocks which underwent sustained late-tectonic metamorphism in the epidoteactinolite facies, accompanied by pervasive shearing and block rotation to the south of the southern limb of the regional F2 fold in the granite-gneiss. A large, kilometer-scale, open advective fluid system which provided fluid-mediated exchange between co-existing rocks existed at the time of vein formation. The fluid system was driven by early-tectonic intrusion of a granite gneiss and amphibole-rich granite. Two areas in the Mfongosi River valley, the northern and southern Mfongosi Valley areas, contain typical evidence of deformation at the leading edge of collision in a mobile belt. The southern Mfongosi Valley area, at the confluence of the Mfongosi and Tugela Rivers, contains veining which resulted from pressure solution of the host metavolcaniclastic/metagreywacke. Veining occupies predictable shear and tension fractures formed during the initial deformation of a foreland margin sequence, in addition to occupying those fractures formed by buckling on the layer-scale. The structural context of the northern Mfongosi Valley veining is defined by subsequent deformation and vein fragmentation such that the metavolcaniclastic/metagreywacke was reduced to a melange in which vein segments acted as competent clasts; a large-scale porphyroblast/matrix system. Formation of the Manyane Thrust to the south of the Mfongosi Group interrupted the normal retrograde metamorphism of the remainder of the Tugela Nappe and initiated a "hot iron effect" whereby a short-lived thermal pulse acted at the thrust plane, producing a reversed geothermal gradient in the underlying Mfongosi group. This reversed gradient would have been counteracted by a steepened normal geothermal gradient in the Mfongosi Group caused by overloading of the Natal Thrust Front by the Natal Nappe Zone. These geothermal gradients partly account for the concentration of veining in the areas of the Mfongosi Group which are directly adjacent to the Manyane Thrust, and directly adjacent to the Kaapvaal Craton, in the lower portions of the thrust front Stable isotope studies indicate fractionation between vein and wall rock under a short-lived, mainly rock-buffered, layer-scale fluid-movement system. Also forming part of the Mfongosi Group of the Natal Thrust Front, the Ngubevu area contains an apparently enigmatic distribution of veining accompanied by gold and base metal mineralization. The structural evolution of the Ngubevu area occurred during consistent left-lateral transpression into which has intruded early-tectonic veins, formed by pressure solution and having the same structural format as the early-tectonic veining in the southern Mfongosi Valley area. Subsequent deformation of the system was accompanied by 1900 -trending tension gashes which were continually ptygmatically-folded, sheared and offset to form occasionally mineralized quartzofeldspathic "blows" and along-strike stringers in the epidote- actinolite schist. Where veining cross-cuts narrow calcite - graphite - sericite - quartz - albite - tourmaline ± chlorite schist layers, gold mineralization occurred. The late-tectonic tension gashes, antitaxially filled by quartz and amorphous calcite, cross-cut the entire range of lithologies. The fluid system during vein deposition varied: during infilling of early-tectonic fractures a short-lived fluid-flow system dominated, with the emplacement of re crystallized wallrock occurring in a closed, non-advective regime under the influence of diffusion caused by pressure solution. The fluid system changed to a more open, advective, greater than layer-scale rock-buffered one with a decreasing contribution of material from immediate host rocks. An internal fluid source is implied for the entire period of vein emplacement, derived from structural analyses which indicates negative dilation across the Mfongosi Group in this area and by comparison of vein:wallrock δ180 values which indicate a lack of igneous-derived fluids. The Phoenix Mine, in the central portion of the Tugela Nappe, and the Ayres Reef, hosted in Manyane amphibolite adjacent to the Manyane Thrust, are grouped together on the basis of their cross-cutting nature and timing with respect to metamorphism and deformation of the host rock, and also due to their similarity in isotopic plots. Both vein sets occur in approximately east-west to east-northeast-trending zones which show evidence of late-tectonic left-lateral movement. Phoenix Mine veining occurs in weakly-metamorphosed meta-gabbro/meta-norite of the Tugela Rand Complex. The Manyane amphibolite demonstrates the amphibolite facies of metamorphism due to the short-lived thermal pulse at the Manyane Thrust. Both sets of veining display slickenlines which are indicative of their emplacement prior to the late-tectonic left-lateral movement. The unusually thick quartz veins of both deposits are the results of late- to post-Tugela Rand Complex fluids or the tapping of late-tectonic metamorphic fluid reservoirs. This caused silica metasomatism and redeposition of material in post-thrusting collapse features. A highly channelized, single-pass fluid system is proposed in the absence of intrusion-derived fluids. Whole rock geochemical data allow a distinction to be made between the Natal Thrust Front and the Natal Nappe Zone: the Foremost nappe of the nappe zone consists primarily of N-type mid-ocean ridge basalts/ocean-floor to within-plate basalts which were intruded prior to nappe emplacement by metaluminous orogenic volcanic arc granitiods. The thrust front displays a lateral variation in metabasite/metasediment ratio, with the ratio increasing from east to west in this inlier. In the east, in the Nkandlha area, melanged metagreywackes dominate and there is a marked paucity of associated metabasites. In the central portions of the thrust front, in the vicinity of the Mfongosi area, active continental margin/continental arc magmatogenic greywackes and arkoses are interlayered with calk-alkaline volcanic arc basalts (volcaniclastics). The greywacke geochemistry indicates little to no mafic/ultramafic influences in sediment contribution and the source of sediment is inferred to be the southern portions of the Kaapvaal Craton. The Nkandlha and Mfongosi area Mfongosi Group segments are considered to be in-situ or para-autochthonous. The western-most Ngubevu area predominantly hosts metabasites. The geochemistry of the metabasites indicates that they are N-type mid-ocean ridge basalts/ocean floor basalts from a destructive plate margin setting. The metabasites are interbanded with metapelitic/metacalcsilicate layers produced in a shallow water oxic environment, here inferred as a spatially-restricted shallow, marginal basin. The metabasites in the Ngubevu area are notably similar to those of the Madidima Nappe, indicating a similar provenance and pre-collisional mode of formation. It is proposed that the variation in the Natal Thrust Front was due to a north-east/south-west distribution of lithological proportions or mixing, with greywackes dominating in the northeast (in proximity to the Kaapvaal Craton) and metabasites dominating in the southwest. Left-lateral transpressional movement within the Mfongosi Group of the Natal Thrust Front, and the Natal Nappe Zone, was continuous throughout plate collision and obduction.
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 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.
Aspects of the geology and geochemistry of the proterozoic rocks of the Valley of a Thousand Hills, KwaZulu-Natal.
(1999) Milne, George Charles.; Kerr, Alan.; Watkeys, Michael Keith.
A regional field and geochemical study has allowed the identification of three primary units within the Proterozoic basement of the Valley of a Thousand Hills. The Nagle Dam Formation incorporates several chemically distinct orthogneiss series, characterised by limited intragroup fractionation, and derived from discrete sources. Intrusive into the gneisses are the megacrystic A-type granites of the Mgeni batholith, comprising the biotite granites of the Ximba Suite; the hornblende granites and charnockite of the Mlahlanja Suite; and the medium grained leucogranite of the Nqwadolo Suite. Petrogenetic modelling indicates that these are predominately cumulates. A general model for the A-type granites suggests that they were derived through variable MASH processes on an original within plate type basalt. Enclaves within the Mgeni batholith form a distinct series, the Valley Trust Formation, comprising a nongenetic orthogneiss association of amphibolite and crustal sourced quartzo-feldspathic gneiss and locally derived paragneisses. Interaction between the biotite granite and the pelitic enclaves generated a biotite garnet granite. Geothermobarometry suggests temperatures of metamorphism to a maximum of 770°c for the Nagle Dam Formation and c.850°C at a pressure of 6 kb for the Valley Trust Formation. Potential magmatic temperatures of c.760°C at 5 kb are derived for the Mgeni batholith. High Mn garnets within late veins indicate subsequent intrusion at higher levels. Derivation of a tectonic model for the Valley of a Thousand Hills is assisted by a revaluation of the chemical tectonic discrimination plots as source or initiator discriminators. These indicate an origin for the Nagle Dam Formation in an arc environment, while the bimodal orthogneiss association of the Valley Trust Formation and the A-type character of the Mgeni batholith suggests their evolution during extensional events. Geothermobarometry defines an isothermal decompression path, possibly generated during a collision event, superimposed on which is a potential midcrustal heating event, resultant on the intrusion of the Mgeni batholith. These data can be integrated with revised lithotectonic data from the southern portion of the Natal Province to derive a regional model. This comprises: the collision of a number of arcs with associated splitting to form backarcs, sedimentation, and failed rift systems; syn-collisional S-type magmatism, contemporaneous with isothermal decompression of the region; and a series of pulses of post-orogenic granites.
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.
The geology and structure of the Bushveld Complex metamorphic aureole in the Olifants River area.
(1998) Uken, Ronald.; Watkeys, Michael Keith.
The contact metamorphic aureole of the Rustenburg Layered Suite of the Bushveld Complex extends to a depth of over 5 km into the underlying mainly argillaceous Pretoria Group. When compared to other parts of the metamorphic aureole, the Olifants River area is unique in that it is characterised by a high degree of syn-Bushveld Complex deformation and very coarse grained pelitic assemblages. This is believed to have resulted from a combination of greater magma thickness, a deeper emplacement depth and a high degree of subsidence related deformation that was focused along the Thabazimbi-Murchison Lineament. This area also contains a laterally extensive and deformed quartz-feldspar porphyry sill, the Roodekrans Complex that is shown to represent a hypabyssal equivalent of the volcanic Rooiberg Group. There are three main metamorphic zones. A wide andalusite zone dominated by staurolite, garnet and cordierite assemblages. This is followed by a narrow fibrolite zone without staurolite, and a wide inner aureole of migmatite. The migmatite zone is characterised by garnet-cordierite-aluminosilicate assemblages with corundum, spinel and orthopyroxene assemblages at the highest grades. Metamorphic pressure and temperature estimates indicate pressures of between 3 kb and 4 kb in the lower part of the andalusite zone at temperatures of approximately 550°C. Porphyroblast-matrix relationships reveal a close link between deformation and metamorphism resulting in a spectrum of textural relationships developed as a result of inhomogeneous strain. Porphyroblasts in low strain domains preserve textures of “static type" growth whereas syntectonic textures are found in foliated rocks. Pre-tectonic porphyroblasts in many foliated domains indicate that deformation outlasted porphyroblast growth and increased in intensity and extent with time. Retrograde porphyroblasts are post-tectonic. Evidence is presented for both rotation and non-rotation of porphyroblasts in relation to geographical coordinates during extensional top-to-south, down-dip shear in the floor. The unique structural setting in this area triggered the growth of large diapiric structures in the floor of the Rustenburg Layered Suite that are preserved as periclinal folds on the margin and within the northeastern Bushveld Complex. Extreme gravitational loading and heating of the floor by a thickness of up to 8 km of mafic magma resulted in the generation of evenly spaced, up to 7 km diameter wall-rock diapirs that penetrated the overlying magma chamber. Diapiric deformation is restricted to rocks above a decollement zone that is developed along competency contrasts and corresponds approximately with the 550 °C peak metamorphic isotherm. Strongly lineated, boudinaged and foliated rocks are developed in the interpericlinal domains between adjacent periclines. Migmatites in these domains are characterised by conjugate extensional ductile shears and associated asymmetrical boudinage suggesting bulk deformation by pure shear processes. The extension lineation was produced by lateral extension along flow lines directed toward dome culminations. Each of the four diapiric periclines is cut by a different erosional section enabling reconstruction of a typical diapir geometry. At the highest structural levels, periclines have bulbous shapes with overturned limb geometries forming overhangs. The surrounding layered igneous rocks are locally deformed into a series of outward verging folds that define a broad rim syncline. Deformation within the pericline cores is represented by constrictional deformation that produced radial curtain-type folds with steeply plunging lineations and concentrically orientated folds in the outer shell. Diapirism is closely linked to magma emplacement mechanisms. Floor folds in the country rocks were initiated in the interfinger areas of a fingered intrusion. With further magma additions and the coalescence of intrusion fingers into a single sheet, interfinger folds matured into large diapiric periclines which rose to the upper levels of the magma chamber. Strain rates estimated from strain analyses, pericline geometry and model cooling calculations are in the order of 10-14 S-1, corresponding to diapiric uplift rates of 0.6 cm/yr. Diapirism is broadly compatible with a N-S extension in the Olifants River area during emplacement of the Rustenburg Layered Suite. On a regional scale, this is indicated by existence of a major EW dyke swarm that coincides with the long axis of the Bushveld Complex. The accommodation of the Bushveld Complex into the Kaapvaal Craton was facilitated by a combination of craton-wide extension that accompanied plume related magmatic underplating, and loading of the Bushveld Complex. Isostatic adjustment in response to Bushveld Complex subsidence resulted in further development of large basement domes around the perimeter of the Bushveld Complex.

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