Department of Geology

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    Interpretation of regional geochemical data as an aid to exploration target generation in the North West province, South Africa
    (University of Fort Hare, 2009) Mapukule, Livhuwani Ernest
    This study involves the application, interpretation and utilization of regional geochemical data for target generation in the North West Province, South Africa. A regional soil geochemical survey programme has been carried out by the Council of Geoscience South Africa since 1973. A number of 1:250 000 sheet areas have been completed, but there are no interpretative maps which could aid in mineral exploration and other purposes. In order to utilize the valuable and expensive data, the project was motivated through data acquisition and interpretation to generate exploration targets. The study area is confined to Mafikeng, Vryburg, Kuruman and Christiana in the Northwest Province, where potential exploration and mining opportunities exist in areas of great geological interest. These include geological events such as the Bushveld Complex, the Kalahari manganese field and the Kraaipan greenstone belts. The aim of this project was to utilize geochemical data together with geophysical and geological information to verify and identification of possible obscured ore bodies or zones of mineralization, and to generate targets. Another objective was the author to be trained in the techniques of geochemical data processing, interpretation and integration of techniques such as geophysics, in the understanding of the geology and economic geology of the areas. Approximately 5 kg of surface soil was collected per 1 km2 by CGS from foot traversing. Pellets of the samples were prepared and analyzed for TiO2, MnO and Fe2O3, Sc, V, Cr, Ni, Co, Cu, Zn, As, Y, Ba, Nb, Rb, Th, W, Zr, Pb, Sr and U using the simultaneous wavelength dispersive X-ray fluorescence spectrometer technique at the Council for Geoscience, South Africa. For each element the mean +2 standard deviations were used as a threshold value to separate the negative from the positive anomalies. The integration of geological, geophysical and geochemical information was used to analyze and understand the areas of interest. A number of computer programmes were extensively used for data processing, manipulation, and presentation. These include Golden Software Surfer 8®, Arc-View 3.2a®, TNT-Mips®, JMP 8 ®, and Microsoft Excel®. Through geochemical data processing and interpretation, together with the low resolution aeromagnetic data, gravity data and geological data, seven (7) exploration target areas have been generated: These have been numbered A to G. It is concluded that there is good potential for Cr, PGMs, vanadium, nickel, iron, copper, manganese, uranium and niobium in the targets generated. The results provide some indication and guide for exploration in the target areas. In Target A, Cu, Cr, Fe, Ni and V anomalies from the lower chromitite zone of far western zone of the Bushveld Complex, which has be overlain buy the thick surface sand of the Gordonia Formation. Target B occurs over the diabase, norite, andesitic lava and andalusite muscovite hornfels of the Magaliesberg Formation. This target has the potential for Cu, Fe and Ni mineralization. The felsic rocks of the Kanye Formation and the Gaborone Granite in target C have shown some positive anomalies of niobium, uranium, yttrium and rubidium which give the area potential for Nb, REE and U exploration. Target D is located on the Allanridge Formation, and has significant potential for Ni-Cu mineralization, and is associated with the komatiitic lava at the base of the Allanridge Formation in the Christiana Area. The light green tholeiitic, calc-alkali basalt and andesitic rocks of the Rietgat Formation are characterized by a north-south trending yttrium anomaly with supporting Ba and Y anomalies (Target E). This makes the area a potential target for rare earth elements. Calcrete on the west of the Kuruman has a low b potential target for vanadium. It is believed that the area might be potential for potassium-uranium vanadate minerals, carnotite which is mostly found in calcrete deposits. This study has proved to be a useful and approach in utilizing the valuable geochemical data for exploration and future mining, generated by Council for Geoscience Science. It is recommended that further detailed soil, rock and geochemical surveys and ultimately diamond drilling be carried out in the exploration target areas generated by this study.
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    Lithostratigraphic correlation, mineralogy and geochemistry of the lower manganese orebody at the Kalagadi manganese mine in the Northern Cape province of South Africa.
    (University of Fort Hare, 2012) Rasmeni, Sonwabile
    The Kalagadi Manganese mine in the Kuruman area of the Northern Cape Province of South Africa contains reserves of Mn ore in excess of 100Mt. Mineralization in the mine lease area is restricted within the Hotazel Formation of the Voȅlwater Subgroup, belonging to the Postmasburg Group, the upper subdivision of the Transvaal Supergroup. Surface topography is characterized by flat lying, undulation with minimal faulting and the ore are slightly metarmophosed. This study investigates the general geology of the mine, lithostratigraphic subdivision and correlation of the economic Lower Manganese Orebody (LMO) of the Kalagadi Manganese Mine in order to guide mining plan and operations once the mine is fully commissioned. At the commencement of this study, Kalagadi Manganese mine was a project under exploration with no specific geology of the mine lease area and no lithostratigraphic subdivision. The study also aimed determining the extent of lithostratigraphic correlation between the LMO economic orebodies of the Kalagadi Manganese mine with that of underground Gloria and open-pit Mamatwan mines. Four methods including petrographic microscope, Scanning electron Microscope (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses were applied mainly for the mineral identification, chemical composition and ore characterization of the Lower Manganese Orebody (LMO) at Kalagadi Manganese mine. The results of this study indicates the following: (1) Eleven textural distinct zones with economic zones restricted to the middle while the lower grade zones are confined to the top and bottom of the LMO; (2) The economic zones, comprising of Y, M, C and N subzones attain an average thickness of 10 m and are graded at an average of 40% Mn while the Mn/Fe ratio varies from 6 to 9; (3) The most economic zones are M and N subzones which are mostly characterized by oxidized ovoids and laminae, a characteristic applicable even to other zones of economic interest; (4) Braunite is the main mineral of the manganese ore and is often integrown with kutnahorite and other minerals (hematite, hausmannite, Mg-calcite, calcite, jacobsite, serpentine and garnet) which are present in variable amounts; (5) The Mg-rich calcite (Ca, Mg)CO3 is the second dominant manganese carbonate mineral and it corresponds to elevated MgO concentration and is often associated with marine environment. The occurrence of the Mgcalcite is not common in the manganese ore of this area except for the Mn-calcite, which was not determined by XRD analyses in this study; (6) MnO is the most abundant major oxide in the manganese ore while other major oxides present in decreasing order of abundance are CaO, SiO2, Fe2O3, and MgO. The oxides TiO2, Na2O, K2O, Al2O3, and Cr2O3 are depleted and are mostly  0.01wt% and  0.001wt% respectively while P2O5 concentrations are low ranging from 0.02wt% to 0.3wt%. The trace element concentrations of Ba, Zn and Sr in most borehole samples are slightly elevated ranging from 100ppm to 3.9% (36000pm) while Co, Cu, Ni, Y, As, Zr, V and La rarely exceed 50ppm. The enrichments of Cu, Zn, Ni, Co and V that are commonly associated with volcanogenic hydrothermal input in chemicals may reach up to 70ppm; (7) The mineralogical and geochemical characteristics of the manganese ore in the Kalagadi Manganese mine lease area are similar to that of Low-Grade Mamatwan-Type ore. The cyclicity (Banded Iron Formation ↔ Hematite lutite ↔ braunite lutite) and alternation of manganese and iron formation have been confirmed; and (8) The oxygen δ18O isotope values (18‰ to 22‰) indicate a slight influence of metamorphism of the manganese ore. No positive correlation exists between δ13C vs δ18O values and Mn vs δ13C values. Such observations indicate minimal action of organic carbon during manganese precipitation where the organic matter was oxidized and manganese content reduced. On the other hand, the manganese carbonates (CaO) are positively correlated with carbon isotope, this indicates diagenetic alteration, and the involvement of biogenic carbonate during the formation of manganese carbonates. It is concluded that the lithostratigraphic subdivision at Kalagadi Manganese mine is best correlated physically, mineralogically and geochemically with that of Gloria mine operating in the Low Grade Mamatwan - Type ore while correlation with an open-pit Mamatwan mine is also valid.
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    Targeting and characterizing potentially high yield aquifers in the neotectonic zones in the Eastern Cape Province in South Africa.
    (University of Fort Hare, 2014) Madi, Kakaba; Zhao, B.; Gwavava,O.
    The Eastern Cape Province has, besides the three known neotectonic belts (southern, eastern and northern) a fourth zone, which is inactive. This inactive zone is located almost in its central part north of the southern neotectonic zone, and south of the northern neotectonic belt. The three above mentioned neotectonic belts (southern, eastern and northern) were chosen for this study, each one with its own characteristics. This study aims at characterizing and targeting potentially high yield aquifers in the neotectonic zones in the Eastern Cape Province. The methods used in this study include: 1) A comprehensive literature review on neotectonics in South Africa in general and in the Eastern Cape Province in particular; 2) Extraction of lineaments through remote sensing and examination of digital elevation models; 3) Examination of seismic data for the subsurface visualization onshore and offshore; 4) Study on the genesis of the Grahamstown kaolin deposits through the structural component; and 5) Acquisition and interpretation of magnetic, electromagnetic and radiometric data from three of the hot springs in the northern neotectonic belt. The results indicate the following: 1) Old map of seismic epicentres in South Africa need to be reviewed continually. The Eastern Cape was regarded as quiescent in terms of seismicity. However, the investigation from recent seismic epicenters downloadable from the IRIS website has shown that recent seismic events occurred in the Eastern Cape Province especially in the northern and southern neotectonic belts. The central part located north of the southern neotectonic belt and south of the northern neotectonic belt is inactive. This inactive zone can be considered for the storage of nuclear wastes. 2) The eastern neotectonic belt has, like the northern neotectonic belt, a higher density of lineaments oriented northwest-southeast, which makes it the second important neotectonic belt. These lineaments correlate with the normalized difference vegetation index indicative of a good circulation of groundwater. In the south, the Eastern Cape great lineament oriented east-west is now considered a neotectonic domain because many seismic epicentres occur therein. Its geomorphologic shape in graben type form is a favourable structure for groundwater catchment. The surface topography is not uniform and high elevations in the east are related to the uplift that took place in the Quaternary. Most vector gradients are oriented east-west, a fact to be reckon with in the study of surface water flow and aquifers characterization. 3) Offshore along the east coast, the subsurface is affected by neotectonic faults, which are probably splays of the Agulhas Falkland Fractured Zone (AFFZ). The folds that occur are related to the regional compressional stress known as the Wegener Stress Anomaly (WSM). On land, straight lines from seismic profiles indicate that weathering occurs in consolidated materials probably along faults or fractures, unconsolidated sediments always have wavy profiles. On the other hand, field observations in King Williams Town have clearly shown that a tectonic uplift took place on a dolerite sill overlain by mudstones and sandstones. The uplift is possibly related to the Amatole-Swaziland event that occurred in the last five millions years. The escarpment along this dolerite sill overlain by sedimentary rocks is a meso-scale fault with a dip-slip component. Healthy vegetation and a river flowing parallel to the cliff indicate groundwater flow in the zone of weakness. 4) In the southern neotectonic belt there is a clear northwest-southeast horizontal compression and a southwest-northeast vertical to sub-vertical extension. Enrichment of granitic breccias and feldspar in the Grahamstown Dwyka tillite is the source for the formation of kaolin deposits. The weathering starts in the granitic breccias through their extensional fractures and then extends in the matrix, which has micro-fractures that are only visible with the transmitted microscope. Combined extensional strike-slip and dip-slip faulting is responsible for the earthquakes in the region of Grahamstown where the kaolin is formed. There is also an unreported thermal (quartz veins) and neotectonic event identified in this region. 5) The hot springs in the northern neotectonic belt are connected by a regional neotectonic fault. The use of magnetic and electromagnetic methods helped to decipher the occurrence of faults, fractures, dolerite dykes, and variable degree of weathering. Uranium/potassium ratios derived from radiometric surveys show that areas around some hot springs are characterized by enrichment in uranium. High concentrations of thorium are related to its low capacity of being easily dissolved in water. It can be concluded that seismicity, hot springs and accordingly deep groundwater circulation, high density of lineaments, quaternary tectonic uplift, are the predominate characteristics of the three neotectonic zones. Furthermore, on the environmental point of view, thorium concentration is higher than that of either uranium or potassium. Although it is nonetheless below the world average threshold of 7.4 ppm according to United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), it may be a source of radiation hazard to humans and animals if they are subjected to prolonged exposure. All the neotectonic zones in the Eastern Cape Province present potentials to host good and important aquifers. It is suggested that the Eastern Cape great lineament in the southern neotectonic belt and the Kokstad-Koffiefontein seismic belt in the northern neotectonic belt, be monitored for future research regarding, neotectonics, seismic risk assessment and hydrogeology.
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    Stratigraphy and sedimentology of the Mzamba formation in the Eastern Cape, South Africa.
    (2014) Susela, Zamampondo
    This research project is aimed at providing new information to the stratigraphy, sedimentology, palaeontology and diagenesis of the Mzamba Formation. The study area is located at the south of Port Edward, Eastern Cape. The methodologies employed in this study include field geological investigation and sampling, stratigraphic measurement and logging, thin-section microscope study, powder samples of XRD analysis, and SEM-EDX analysis of rock textures and mineral compositions. The stratigraphy of the Mzamba Formation can be divided into three newly established members, i.e. the Lower Conglomerate Member, Middle Silt/Mudstone-Shell Bed Member and Upper Mudstone-Shell Bed Member with a total thickness of 31.26m in an inland borehole and 30.05m in the field measurement. The Lower Conglomerate Member is 2.65m thick and consists of pebbly conglomerate with coarse sandstone, shell fragments and silicified wood trunks, representing shallow marine nearshore deposits. The Middle Silt/Mudstone and Shell Bed Member is 9.5 m thick and consists of black mudstone and fine-grained siltstone alternated with medium grained pecten beds, which was deposited in a storm influenced deeper marine environment. The Upper Mudstone-Shell Bed Member is 17.9m thick and is made up of fine-mudstones with articulated pecten layers which were deposited in a deep and quiet marine environment. Petrology studies showed that the Mzamba Formation consists of mixed sediments of carbonate and siliciclastic rocks. Siliciclastic rocks include pebbly conglomerates, medium to coarse sandstones and fine-grained mudstones, whereas carbonate rocks include packstone, wackstone and grainstone (pecten beds). The formation shows cyclical pattern of a series fining-upward cyclicities, changing from bottom conglomerate to sandstone, then upward repeated series of cyclotherms from pecten bed to mudstone. Mineralogy of the Mzamba Formation consists of terrigenous minerals of quartz, orthoclase, plagioclase, muscovite and various igneous and metamorphic rock-lithics, clay minerals of smectite, illite and sericite, and carbonate minerals of calcite and dolomite; with minor diagenetic minerals of pyrite, glauconite, hematite, gypsum, albite and organic maceral of vitrinite. Heavy minerals of garnet, zircon and rutile are minor minerals in the strata, which were detrital in origin. Mzamba Formation is a fossiliferous sequence, and contains both fauna and flora fossils in the strata. The pecten beds host well-preserved bivalve, gastropod, brachiopoda, ammonite, and echinoderm; whereas trace fossils of coprolites, burrows and tracks, as well as plant fossils of silicified wood trunks were also found in the formation. Some new fossil species were collected and studied, which include Bivalve: Pteriaceae, Pinnacea and Ostreacea; Gastropod: Cerithiacea and Mesogastopoda; Echinoderm: Echinocystoidea and Crinoidea. The benthonic species predominate in the lower part in the succession, whilst the planktonic species are abundant in the upper part of the sequence, which points to increase in water depths of the depositional environment. Based on lithology, sedimentary structures, and stratum architecture, seven different facies have been distinguished. Facies A (Flat bedded pebbly conglomerate), Facie B (Cross-bedded coarse calcareous sandstone facies), Facies C (Burrowed sandstone facies), Facies D (Shell-fragmental fine-grained calcareous sandstone facies), Facies E (Horizontal bedded calcareous mudstone facies), Facies F (Calcareous patch reef), Facies G (Wash out reef facies). Wash out reef facies is rich in algae, bivalve shells, broken oysters, coral fragments and small pebbles. Four types of cements were found in the Mzamba Formation, including calcite, smectite, illite and quartz. Calcite cement can be further classified into two types, micrite calcite cement and sparite calcite cement. The clay cement consists of smectite and illite and mainly occurs as matrix. The isopachous rim calcite and bright isopachous rim of silica cements indicate diagenesis in a marine phreatic zone. Authigenic minerals which formed in early diagenetic stage include quartz, plagioclase, glauconite and organic maceral of vitrinite. Three stages of diagenesis have been recognised in the sequence, i.e. syndiagenesis, early and late diagenesis. Glauconite pellets and worm faecal pellets were formed in syndiagenetic stage; cementation and authigenic minerals were formed in early diagenetic stage; whereas clay mineral conversion of smectite to illite, quartz overgrowth, bioclast recrystallization and calcite replacement took place during late diagenetic stage. The pebbly conglomerate at the bottom of the Mzamba Formation represents high energy deposits in a shallow marine environment; the grain-size gradually becomes finer in the middle succession and finest mudstone facies at the top of the succession, which represents deep marine deposits. Meanwhile, benthonic fossils are dominant in the bottom succession while plankton fossils are more abundant in the top succession. These features indicate that the Mzamba Formation constitutes a perfect transgression sequence, and the depositional environments started from shallow marine near shore environment, and gradually shifted to a deep marine quiet water environment.
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    Stratigraphy, sedimentary facies and diagenesis of the Ecca Group, Karoo Supergroup in the Eastern Cape, South Africa.
    (University of Fort Hare, 2014) Nyathi, Nonhlanhla
    This is a MSc research project, and is aimed at the new insight on the stratigraphy, sedimentary facies, diagenesis and depositional environments of the Ecca Group, Karoo Supergroup in the Eastern Cape Province. Methodologies used in this research include field investigation, stratigraphic logging, thin-section microscope study, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses. The stratigraphy of the Ecca Group is divided into five formations, namely the Prince Albert Formation, Whitehill Formation, Collingham Formation, Rippon Formation and the Fort Brown Formation from bottom upward. Based on the field investigation and laboratory correlation, the Prince Albert, Whitehill, Collingham, and Fort Brown Formations can each be subdivided into two new members, i.e. lower member and upper member; whereas three new members have been proposed for the Rippon Formation, i.e. lower, middle and upper members. The Ecca Group sediments were accumulated in various depositional environments, from bottom of deep marine environment, passed through the middle of deltaic environment, and ended in a lacustrine environment. The Prince Albert Formation, Whitehill Formation and the Collingham Formation were all deposited in a deep marine basin, whilst the Rippon Formation was laid down in a deltaic environment. As the climate gradually became warmer and drier, the top Fort Brown Formation was lastly deposited in a lacustrine environment. The stratigraphic succession of the Ecca Group constitutes a perfect regression sequence, indicating that the marine water gradually retreated and the sea-level gradually dropped. The rocks in the Ecca Group are mainly terrigenous sandstone and mudstone with some coarse grain-sized siliciclastic rock of conglomerate. The sandstones are dominated by feldspathic graywackes with minor quartz-wackes, and there are no arenites in the Ecca Group. Whereas the mudstones are dominated by grayish mudrocks and black shales, purer claystone was found in the turbidite facies of the Collingham Formation, which probably has economic significance for the future since the reserve is quite large. Optical microscope, XRD and SEM analyses demonstrated that the minerals in the Ecca Group include detrital minerals of quartz, orthoclase, microcline, plagioclase, biotite, muscovite; and clay minerals (smectite, kaolinite, illite and sericite). These minerals constitute the rock framework grains and cements whereas; the authigenic minerals of calcite and hematite were formed during diagenesis. Accessory minerals such as rutile and zircon are the heavy minerals present in the strata, and occur only in a small amount. Based on the lithologies, sedimentary structures and sequence stacking patterns, ten sedimentary facies have been recognised, namely 1) Grayish laminated and thin bedded shale facies, 2) Grayish laminated shale and intercalated chert facies, 3) Grayish rhythmite facies (all the three facies above were deposited in deep marine water); 4) Flat and lenticular bedded graywacke facies, 5) Grayish alternating mudstone and sandstone facies, 6) Dark organic rich mudstone facies, 7) Fossil bearing mudstone facies, 8) Laminated and thin bedded black mudstone with lenticular siltstone facies, 9) Interbedded grayish sandstone and mudstone facies (above Facies 4-9 were deposited in deltaic environment and appeared in the Rippon Formation); and 10) Varved rhythmic mudstone facies, which occurs only in the Fort Brown Formation and represents lacustrine sediments. Four types of cements have been identified in the rocks of the Ecca Group, including quartz, smectite, calcite and feldspar cements. The first three cement types are the major cement types, whilst the feldspar cement is minor and occurs only locally. Recrystallisation in Ecca sediments includes quartz, feldspar, clay mineral recrystallisation and conversion from smectite and kaolinite to illite and then to sericite. Replacement involves calcite replacing quartz, feldspar and clay matrix; accompanied by albitization, i.e. albite replacing other feldspar minerals in a deep burial environment. Dissolution in the Ecca Group involved calcite and kaolinite dissolving and leaching, which created more pore-space and increased porosity. The sediments of the Ecca Group went through three stages of digenesis, namely the early stage, the late stage and the up lift stage which led the rocks being exposed on the Earth’s surface and being weathered. In each stage, some minerals became unstable, then replaced by a more stable mineral suitable for the new diagenetic environment. Precipitation of cements and formation of authigenic minerals mostly occurred in the early diagenetic stage, which led the soft sediments becoming a hard rock; whilst recrystallisation, replacement, and dissolution took place mostly in the later diagenetic stage due to increase of temperature and pressure resulting from increase of burial depth.
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    Basin analysis of the Soutpansberg and Tuli coalfields, Limpopo province of South Africa
    (University of Fort Hare, 2014) Malaza, Ntokozo
    The Soutpansberg and Tuli Coalfields are both hosted in the Karoo Basin, Limpopo Province of South Africa. The Soutpansberg Coalfield is situated north of the Soutpansberg Mountain Range and has a strike length of about 200 km and width of about 80 km which is fault controlled and extends from Waterpoort in the west to the Kruger National Park in the east. The Tuli Coalfield occurs in a small intracratonic, east-west trending fault-controlled sedimentary basin with a preserved width of 80 km and length of 120 km. The east to west trend of the Tuli Coalfield parallels that of the Soutpansberg Coalfield further east, and the two coalfields link up with the north-south trending Lebombo Basin. The Tuli Coalfield occurs in the Tuli Basin, while the Soutpansberg Coalfield occurs in the Soutpansberg Basin. The two basins preserve a heterogeneous succession of the Upper Paleozoic to Lower Mesozoic sedimentary and volcanic rocks of the Karoo Supergroup. Because the area is largely covered by the Quaternary Kalahari Group sands, the stratigraphy of the succession is not as well understood as the Main Karoo Basin in South Africa. This study deals with the intra-basinal stratigraphic correlation, facies and depositional environments, petrography, geochemistry, provenance, geophysics, structural geology, diagenesis of sandstone, subsidence history and coal quality in the Soutpansberg and Tuli Coalfields. Based on the field work and detailed sedimentological analyses of over 2000 borehole data, seven facies associations (FAs) comprising sixteen major lithofacies were identified. The facies associations are: Glacial diamictite and sandstone (FA 1), Clast supported conglomerate and sandstone (FA 2), Tabular cross-bedded sandstone (FA 3), Trough and planar cross-bedded sandstone (FA 4), Fine calcareous and micaceous siltstone and mudstone (FA 5), Sandy shale/mudstone (FA 6), Laminated or thin-bedded Carbonaceous shale/mudstone and coal (FA 7). The facies associations (FA 1 to FA 7) correspond to the lithostratigraphic sub-divisions of the Tshidzi, Madzaringwe and Mikambeni Formations. The Madzaringwe Formation in this study is informally sub-divided into the Lower, Middle and Upper Members while the Mikambeni Formation is informally sub-divided into the Lower and Upper Members. Sedimentological characteristics of the identified facies associations indicate the following depositional environments: Fluvioglacial (braided streams) depositional environment (FA 1, Tshidzi Diamictite Formation); Floodplain ponds, lakes, marshes and backswamps (FA 6 and FA 7, Lower Member of the Madzaringwe Formation); Meandering and braided channels, crevasse splays, levees and crevasse channels (FA 2, FA 3, FA 4 and FA 5, Middle Member of the Madzaringwe Formation); Floodplain ponds, lakes and backswamps (FA 6 and FA 7, Upper Member of the Madzaringwe Formation); Meandering and braided channels, crevasse splays, swamps and shallow lakes (FA 5, FA 6 and FA 7, Lower Member of the Mikambeni Formation) and lastly braided channels, meandering channels, levees and crevasse channels (FA 2, FA 3, FA 4 and FA 5, Upper Member of the Mikambeni Formation). Paleocurrent directions were measured using directional structures (cross-bedding and asymmetric ripple marks). The paleocurrent analysis shows that the direction of the channels was from south-west to north-east in both coalfields. Based on the structural study and geophysical interpretations, the structural and tectonic settings of the two coalfields have been revealed, both coalfields are normal fault-bounded. The geological evolution of the Karoo strata, at least since the Upper Carboniferous, essentially follows the type model for passive continental margin terrain. Paleostress inversion techniques have been employed to interpret the stress regime of the two coalfields. The Soutpansberg Basin is characterised by W-E to ENE-WSW extension and N-S to NNW-SSE compression. The Tuli Basin is characterised by N-S to NNW-SSE compression and W-E to ENE-WSE extension. This stress field reflects the established structural trend of the two shear belts (the Tshipise and Siloam shear zones) bounding the Central Zone of the Limpopo Mobile Belt. The geophysical interpretations were focused on outlining structures, contacts and on the delineation of gravity, magnetic and radiometric signatures in areas defined as anomalous. The magnetic, gravity and radiometric data showed low amplitudes in the sedimentary strata compared to the surrounding and basement geological bodies. The E-N-E fault system has a notable signature, defining two magnetic domains on both southern and northern sides of the Soutpansberg Coalfield. The intrusive emplacements are mainly fault controlled and they trend in the same direction as the two fault systems. Jurassic volcanics (Letaba and Jozini Formations) follow a SW-NE trend, outcropping in the east (Soutpansberg Basin), producing a strong magnetic response in this area, and partly buried in the west, where magnetic intensity tends to be reduced. Petrographic and geochemical analyses of the Soutpansberg sandstones revealed immature sub-litharenite, sub-arkose and minor arkosic arenites in nature, dominated by sub-angular to rounded detrital grains, sourced from recycled orogens, craton interior to transitional continental. The sandstones of the Tuli Coalfield are classified as sub-arkoses and minor sub-litharenites and sourced from the craton interior and recycled orogen provenances. Both petrographic and geochemical results suggest a passive continental margin source. Petrographic and geochemical results of the samples of the Soutpansberg Coalfield suggest uplifted basement source areas dominated by sedimentary rocks with minor granite-gneiss rocks. The petrography and geochemistry of the Tuli sandstones suggest source areas dominantly composed of plutonic (granites) and metamorphic (gneisses and schists) rocks with a component from a sedimentary (quartz-arenites, quartzites, shales, arkoses and meta-arkoses) rocks. Diagenetic features of Mikambeni and Madzaringwe sandstones are subdivided into early, middle and late stages. Time is relative with the earliest diagenetic event occurring shortly after deposition and the latest occurring up until present time. The main diagenetic processes that have affected the sandstones include mechanical compaction, cementation and the dissolution of framework grains and cements. Early diagenetic processes include mechanical compaction, silica and calcite cementation, clay minerals (pore lining and pore-filling kaolinite, illite and smectite), feldspar authigenesis and the formation of hematite cements and coatings. Late diagenesis includes quartz and feldspar overgrowths, seritisation, chlorite alteration, grain deformation, pressure-solution and fracturing and albitisation. The subsidence of the basins is believed to be initiated and thermally controlled by tectonics (i.e. faults of basements blocks) rather than sedimentary burial. The subsidence within the basins supports the primary graben system which must have been centered within the present basins, and later became a region of major faulting. This gave way to the Late Carboniferous rapid subsidence, with areas of greater extension subsiding more rapidly. The Early Permian (last phase) is characterised by a slow subsidence representing the post-rift thermal subsidence. The rift flanks were gradually uplifted and, and then generally subsided as a results of thermal contraction after the extension terminated. Based on the coal analysis, both coalfields are characterised by coking bituminous coal. The study has revealed that the eastern Soutpansberg Coalfield is likely to present better opportunities for identification of potentially exploitable coal deposits as compared to the Tuli Coalfield.
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    Stratigraphy and sedimentology of the Msikaba formation in Kwazulu Natal South Coast, South Africa.
    (University of Fort Hare, 2015) Busakwe, Nolukholo Sinovuyo; Liu, K,
    The Msikaba Formation is a Late Devonian fluvial and marine succession which outcrops from Hibberdene to Port Edward along the south coast of KwaZulu-Natal Province, South Africa. The Formation is composed of brownish conglomerate at the bottom and white-greyish quartz arenite sequence in the middle and mixed quartz-arenite with feldspathic sandstone in the upper sequence. Previous studies put more emphasis on the correlation of Msikaba Formation with the Natal Group and Cape Supergroup, whereas this study revised the stratigraphy, and also put new insight on the petrography, sedimentary facies, depositional environments and diagenesis of the Formation. The total stratigraphic section attains a thickness of 184 m at Margate area and 186 m at Port Edward area. The stratigraphy of Msikaba Formation is well exposed on the outcrops along the KwaZulu-Natal coastline. The stratigraphy is subdivided into 4 new members along Margate to Shelly beach section; namely Manaba Member, Uvongo Member, Mhlangeni Member and Shelly Beach Member from bottom upward. Twelve sedimentary facies were identified and the sedimentary facies were integrated into 4 facies association: Facies association 1 (Gmm+Sm) represents braided fluvial deposits, Facies association 2 (Gcm+St+Sp+Sl+Shb) represents tidal channel and tidal flat deposit, Facies association 3 (St+Sp+Sr+Sl) is result of shallow marine deposit and Facies association 4 (Sp+Sl+St+Sm) is a mixed marine and fluvial deposit. Each facies association represents a specific stratigraphic unit and were deposited in a specific sedimentary environment. Grain size analysis was conducted on seventeen thin sections and 500 grains were counted from each thin section. The sandstone grain size parameters of mean, sorting, skewness and kurtosis fell under the average of 0.75, 0.78, 0.4 and 1.2φ respectively. The results show that most of the grain size are coarse to medium grained throughout the study areas and sorting of the sandstones are moderate to poorly sorted. The cumulative frequency diagrams and bivariate plots show positive skewness and negative kurtosis, which indicate a high hydrodynamic environment. Modal composition analysis and petrography studies show that detrital components of the Msikaba Formation are dominated by monocrystalline quartz, feldspar (mostly K-feldspar) and lithic fragments of igneous and metamorphic rocks. The sandstones could be classified as quartz arenite, sub-arkosic sandstone and feldspathic litharenite; and the provenance analysis indicates that the sandstones were derived from craton interior, recycled or quartzose recycled sources which may derived from weathering and erosion of igneous and metamorphic rocks. Diagenetic processes of the Msikaba Formation have been passed through early, mid- and late diagenetic stages. Cementation, mineral conversion and compaction affect early diagenetic stage; authigenic minerals, quartz and feldspar overgrowth are presented in mid-diagenetic stage, whereas recrystallization, replacement, deformation and dissolution have been strongly affected late diagenetic stage. Microscopy, XRD and SEM-EDX studies have identified five types of cements including smectite clay, kaolinite, hematite, quartz and feldspar cements. Quartz cement, pore-filling and pore-lining clay are the major type of cements in the Msikaba Formation. Based on the lithology, sedimentary structure and facies variations, the Manaba Member was most probably deposited in a braided fluvial environment, the Uvongo Member was deposited in a tidal channel environment, the Mhlangeni Member was formed in shallow marine storm-influenced environment, whereas the Shelly Beach Member was represented mixed marine and fluvial environment. The sequence stratigraphy of Msikaba Formation constitutes a transgressive sequence from Manaba Member to Uvongo Member, whereas it ended as a regressive sequence from Mhlangeni Member to Shelly beach Member. The Msikaba Formation shows major differences with the Natal Group and Table Mountain Group (Cape Supergroup) in the lithology, stratigraphic sequence, sedimentary structures, facies system, palaeocurrent styles, fossil contents and depositional environments, which demonstrate that they are not the equivalent stratigraphic unit. Therefore, the Msikaba Formation is a separate, younger stratigraphic unit, and cannot correlate with the Natal Group and Table Mountain Group as suggested by previous researchers.
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    Geological and geophysical investigation of the South Eastern Karoo basin, South Africa
    (University of Fort Hare, 2015) Baiyegunhi, Christopher
    Geological and geophysical methods were used to investigate the south eastern Karoo Basin of South Africa in an area extending from longitudes 24 o E to 29o E and latitudes 32o S to 35o S. This was undertaken in order to reveal geologic structures, isochore thicknesses of the geologic sequence and their variations across the study area, proffer the possible provenance of the sediments and assess the potential of oil and gas accumulation. The methodology used includes field investigation, rock sampling, preparation of thin sections, petrographic studies, X-ray diffraction analysis, density measurements, porosity calculations, extraction of elevation data from Google Earth, 2½ D gravity profile modelling, generating of isochore (true vertical) thicknesses and depositional surfaces maps from the models, PetroMod 1D modelling and qualitative interpretation of magnetic, gravity and radiometric maps. Petrographic study was carried out on twenty six thin sections of rocks from the eleven geologic formations that cover the study area. Petrographic studies on the diamictite of the Dwyka Group shows abundance of monocrystalline quartz, granite and quartzite components in the breccias which possibly indicate the existence of granitic and metamorphic rocks in the source areas. The sandstones of the Ecca and Beaufort Groups are immature, greywacke and the heavy mineral assemblages signify that the minerals are of granitic, volcanic and metamorphic origin. The magnetic maps show two main magnetic anomalies, a major one trending in a northeast to southwest direction which is part of the Beattie magnetic anomaly and another that is a “bean-shaped” anomaly. The radially averaged power spectrum shows two depths to magnetic sources. The first depth is about 0.6 km which is the average depth to the top of the shallow sources, while the average depth to the top of the deep sources is about 15 km. The shallow sources are connected to magnetic minerals within the Beaufort Group while deep magnetic sources were inferred to be in the basement. The gamma ray spectrometric map shows areas with relatively high gamma radiation count. The high radiation count is possibly due to the uranium and thorium in the detrital materials, as well as the enrichment of radioelements in the feldspars (k-feldspar), calcite, quartz, zircon and clay minerals in the fluvial channel sandstones of the Beaufort Group. A total of two hundred and fifty-eight (258) rock samples were collected in the field and densities (dry, wet and grain densities) and porosities were determined in the laboratory. The Karoo Supergroup density values range from 2.526 – 2.828 g/cm3. The average porosities range from 0. 49 – 3.31 %. The dry densities and porosities of all the formations are inversely correlated with correlation coefficient values (R) that range from 0.9491 - 0.9982. The density of the dolerite intrusions (mostly sill) ranges from 2.700 – 2.837 g/cm3 whilst the porosity range from 0.1118 – 0.3868 %. The Bouguer anomaly map shows an increase in gravity values from -140.7 mGal in inland to about 60.1 mGal in coastal areas. This dominant gravity variation is inferred to be due to a deeper basement and/or Moho that get shallower from inland towards the coast. The Moho is at about 45 km depth inland and shallows to about 42 km at the coast. The 2½ D gravity modelling was done for fourteen (14) profiles with each profile having three (3) models corresponding to minimum, average and maximum densities to obtain the thicknesses of the geologic sequence. The current isochore thicknesses extracted from the gravity models show that the Beaufort Group is the thickest of all the groups that make up the Karoo Supergroup with maximum vertical thickness of up to 634 m, followed by the Ecca and Dwyka Groups with maximum vertical thicknesses of about 3207 m and 727 m, respectively. The maximum elevation for the Dwyka, Ecca and Beaufort sediments are about 500 m, 400 m and 285 m, respectively, whilst the maximum depth below sea level are around 8500 m, 7000 m and 5500 m, respectively. The PetroMod1D model result yield average vitrinite reflectance and temperature values of about 6 % and 500 ℃ respectively for the lower Ecca Group which belong to the dry gas window based on classification by several authors. Thus the rocks of the lower Ecca Group are thermally matured for hydrocarbon (shale gas) generation that can merit gas exploration in the Karoo Basin.