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11th SAGA Biennial Technical Meeting and Exhibition
- Conference date: 16 Sep 2009 - 18 Sep 2009
- Location: Swaziland, South Africa
- Published: 16 September 2009
41 - 60 of 157 results
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Architecture of the Onverwacht Suite, Barberton Mountain Land, South Africa: New Stratigraphic Nomenclature and Revised Models
More LessSynthesis of new and existing data identifies at least seven major shear zones and a major unconformity that separate the rocks of the southern Barberton greenstone belt into seven complexes with different complex geologic histories. The stratigraphic nomenclature presently applied to these sequences (e.g. formations) cannot incorporate these complexities. This requires changing the status of the traditional ‘Formations’ of the Onverwacht Group of the Barberton greenstone belt into ‘complexes’. The complexes are referred to collectively as the Onverwacht Suite. The total age range and thickness of the suite is about 120 million years and 15 km, respectively, but the precise age ranges of each complex and their original thicknesses remain unknown. All the complexes include significant volumes of intrusions into their volcanic and volcanoclastic host rocks. The ages of the intrusions of the different complexes are different. In some complexes the intrusions and volcanic rocks have similar if not identical geochemistry, and are co-magmatic. Others provide ‘stiching’ ages between complexes. Six of the complexes have ophiolite-like affinities that suggest the complexes formed predominantly in oceanic spreading- and intraoceanic arc- environments with water depths of 2-4km. The complexes are tectonically stacked and the original spatial relationships between them can only be inferred in most cases. At least one complex was uplifted by 2-4 km between about 3470 and 3460 Ma, giving a minimum uplift rate of some 2-4 mm/yr, similar to that in modern subduction zones and during emplacement of Phanerozoic oceanic crust as ophiolite complexes. Overlying coarse clastic sediments overlap in age with about 15 myrs of felsic-intermediate igneous activity dated between 3460 to 3445 Ma, that, in turn, relate in age to the intrusion of the tonalite-trondjemite plutons to the south of the greenstone belt. These sediments may therefore represent a sequence deposited in a tectonic basin associated with subduction and obduction processes. The emergence of the deep water complex above sealevel and the onset of subaerial clastic sedimentation (> 3455 Ma) probably best represents the start of obduction of the lowermost Onverwacht complexes across the older complexes (>3.5 Ga) that are now only preserved as remnants in the surrounding granitoid terranes. Timing of a second major episode of subduction/accretion, dominated by folding, thrusting and exhumation of the Barberton greenstone belt, occurred between 3.230 -3.140 Ma. Early minimum cooling rates during more than 18 km unroofing were in the order of 1.5-5 mm/yr, similar to those recorded in modern orogenic belts. Oblique convergence ended in collision and strike-slip displacements around 3.1 Ga. The deposition of the Moodies Group sandstones and conglomerates has been linked to this period of deformation, again at rates comparable to those measured in modern orogenic belts and transcurrent plate boundaries. Thus within all crustal regimes for which reasonably robust rates of tectonic processes can be determined, these rates are similar to within an order of magnitude as those encountered today. By 3.0 Ga the region was part of a rigid peneplained continent.
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Imaging Techniques for Full Tensor Gravity Gradiometry Data
Authors Jade L. Dickinson, J.R. Brewster, J.W. Robinson and C.A. MurphyFull Tensor Gravity Gradiometry has previously been demonstrated to be an effective tool in both the minerals and oil and gas industries. Full tensor data is a richer source of information than standard single tensor gravity. This extra information can be used by tensor imaging techniques to enhance target anomaly definition.
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Gravity Gradiometry – Today and Tomorrow
Authors Dan DiFrancesco, Thomas Meyer, Asbjorn Christensen and Desmond FitzGeraldGravity gradiometry is coming of age as a standard exploration process. The acceptance and scope of airborne surveys is on the rise, with success stories published and documented. A renewed interest in marine surveys for hydrocarbons is also occurring. New sensor and system developments are nearing a point where they may be ready for field tests and commercial deployment. It is accurate to say that the state of gravity gradiometry is healthy in today’s commercial marketplace. As good as this is, there remain a number of challenges and opportunities for full utilization of gravity gradiometry as a tool for the explorationist. A number of questions and concerns need to be addressed ranging from sensor performance to operational efficiency to data handling to educating users. While these challenges might seem daunting, the future looks bright for gradiometry as innovation and acceptance continue to grow. In fact, the time seems right to ask some thought-provoking “What if” questions: Is the era of gradiometry just beginning to dawn? How will the future unfold for this capability? What is the optimal exploration system? What if multiple gravity components could be measured at the same time (i.e. scalar gravity, 2nd order tensors, and 3rd order tensors)? Are the physical limits of measurement already being met? What if data were available without limits throughout the world?
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Methane on the Move: Quantifying Natural Greenhouse Gas Emissions over Geological Time in the Orange Basin, South Africa
Authors Rolando di Primio, Brian Horsfield, Zahie Anka and Gesa KuhlmannIn the assessment of past, present and future global climate the contribution of natural greenhouse gas emissions has been largely disregarded. Our studies in the Orange Basin, South Africa indicate a highly variable rate of methane emission from the basin to the hydro- and atmosphere through geologic time. In order to understand the interactions between sedimentary basin evolution in time and space and Earth´s climate a global assessment of thermogenic methane emissions is required.
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Stress Patterns in the Cape Fold Belt
By R.N. DomoneyRocks outcropping north of the Worcester Fault near Worcester, South Africa, belong to the Malmesbury Group and the Peninsula Formation of the Table Mountain Group. These exposures were studied to get an idea of their structural evolution. Flattening strains produced the planar fabrics in the rocks, with flattening being the dominant deformation mechanism resulting from successive compressive events. This flattening was responsible for the preferred attitude of the rocks and the compressional crenulation cleavages. The compression direction varied from NE-SW to NW-SE during the formation of the composite foliations during the Saldanian Orogeny. These foliations were subsequently crenulated during the Cape Orogeny. In general, NW-SE directed compressional stresses produced the deformation in the Peninsula Formation, where σ1 is oriented NW-SE. Extension direction is perpendicular to this, i.e. NE-SW. For the Malmesbury Group of rocks, NW- directed compressive stresses produced the fabrics in these rocks, with the extension direction being approximately perpendicular to this compressive direction. In general, it would appear as if the regional stress field varied somewhat in its orientation, and the structures in the Malmesbury rocks developed as a relatively continuous sequence of events within a geologically short period of time. It is also very clear that the later Cape Orogeny had a profound effect on the Malmesbury basement rocks, with stress orientations of the former influencing those of the latter.
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Significantly Increasing TEM Survey Performance by Modifying Frequency Content of Transmitter Waveforms
More LessTEM surveys typically operate with a simple transmitter waveform, such as a 50% duty cycle alternating square wave. The frequency of transmission and the duration of measurement is decided before the survey or, frequently in the case of ground TEM surveys, adapted during the survey by the operator to suit the conditions. With some sensor types in particular, achieving good quality data throughout all parts of the decay is difficult. Additionally, all surveys can be complicated by the presence of external sources of interference such as power transmission lines. We argue that significant improvements can be made by optimising the frequency content of the transmitter waveform. Additionally, in the case of ground surveys, the duration of an individual reading can be controlled in order to achieve rapid production and desired data quality. Variables are the EM noise spectrum (a function of the sensor and environment) and the conductivity of terrain. These change along the TEM profile and best results are obtained by regular re-evaluation in light of the target sought. There are several options available to modify the effective frequency content of a TEM transmitter waveform. For a conventional square wave transmitter, an irregular pattern of polarity reversals can be transmitted. Another method is to use two or more base frequencies sequentially. The survey can be automated and data can be combined automatically into a single decay with optimal signal-to-noise ratio over the entire decay.
Examples will be presented to illustrate improvements in performance.
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Case Study: Dighem Survey for Non-magnetic Dyke Detection; Dorstfontein Colliery, Total Coal RSA
Authors S.J. du Plessis and R. JoubertA Dighem airborne geophysical survey (simultaneous acquisition of airborne magnetic and electromagnetic data) was carried out for Total Coal South Africa from September 14 to October 23, 2007. Three blocks in the Secunda area were flown, namely: Dorstfontein, Boschmanskop-Tumelo and Forzando West. This paper deals with the Dorstfontein colliery survey only. The Dorstfontein mining area is located immediately east of the town of Kriel in Mpumalanga, South Africa. The purpose of the survey was to detect both magnetic and non-magnetic dykes. The data quality from the Dighem survey is very good and much improved on previous similar surveys in the 1990s and in 2000. This is due to improvements in technology, especially electronics. The Dighem survey successfully delineated known magnetic and non-magnetic dykes in the Dorstfontein area, as well as probable and possible dykes. Some 60% of the known and probable and possible dykes were detected by the magnetic method and 40% of the probable and possible detected dykes were non-magnetic. Using two flight directions at right angles to each other proved to be important, since if only one flight direction was used, some of the dykes may not have been detected.
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The Physics of the Ground Loop
Authors Braam du Plooy and John BellA ground loop is often used both as a model to explain the basics of electromagnetic exploration and as a tool in the calibration of AEM systems. A thorough understanding of the underlying physics is essential. During the calibration procedure of an AEM system, the electrical current in the ground loop was measured and recorded. A mathematical model in the form of a differential equation was stated for the current in the ground loop. The solution of the differential equation was calculated allowing for the particular transmitter current wave shape. There is good qualitative conformity between the measured current and modelled current. Quantitative agreement of the current amplitude depends on an accurate knowledge of the geometries of the problem.
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AfricaArray: Aims, Achievements and Future Activities
Authors R.J. DurrheimPHGM Dirks, A.A. Nyblade, G. Graham and S.J. Webb and MQW JonesAfricaArray (www.africaarray.org) is a long-term programme to build geosciences capacity in Africa in support of the mineral, petroleum, groundwater and environmental sectors. It seeks to do this by establishing effective Africa-based education and research programmes and observational networks, initially focused on geophysics, but planned to include other geoscience disciplines. The seismic network comprises 37 broadband stations in 16 countries as well as three temporary networks. More than 20 papers reporting on research findings have been published or are in press. Five students have graduated with MSc or PhD degrees, and 26 are registered.
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Observational Study to Mitigate Seismic Risks in Mines:a New Japanese - South African Collaborative Project
Mining-induced earthquakes pose a hazard to workers in deep South African mines, while natural earthquakes pose a hazard to people living close to plate boundaries. We introduce a 5-year Japanese-South African collaborative project entitled "Observational study to mitigate seismic risks in mines". The principal investigators are H. Ogasawara (Japan) and RJ Durrheim (South Africa). The project, which seeks to develop human and instrumental capacity in South Africa, will build on previous studies carried out by Japanese and South African seismologists and rock engineers in deep gold mines. This knowledge will be used in efforts to upgrade seismic hazard assessment schemes and to mitigate the seismic risks in deep mines. The knowledge is also relevant to the study of the mechanisms that generate tectonic earthquakes. The project was conditionally approved in April 2009 by the Japan Science and Technology Agency (JST), an external agency of the Ministry of Education, Culture, Sports, Science and Technology, and the Japan International Cooperation Agency (JICA), an external agency of the Ministry of Foreign Affairs. It is anticipated that the agreement between the Japanese and South African governments will be concluded by the end of the 2009 financial year and that research work will commence in 2010.
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Inversion of Magnetic and Gravity Fields Applied to the Sub-Basalt Imaging Problem
Authors J. Ebbing, M. Aarset, R.F. Reynisson and T. VattekarThis study investigates the feasibility to use gravity and magnetic inversion to image basalts and sub-basalt structures in sedimentary basins affected by volcanism. A regional 3D model was constructed for the Møre margin, mid-Norway, based on a wealth of seismic and petrophysical information. Resolution of the regional 3D model prevents however detailed imaging of the basalts and sub-basaltic structures. While it is difficult to identify the lateral extend of the volcanic features (at depth of 6 km) in the gravity and magnetic data, as well as in Full Tensor Gravity (FTG) data, the sub-basaltic basement architecture can be identified. The gravity gradients provide valuable information on the vertical and lateral extent below the basalts, despite the small density contrast to the surrounding. Inversion of the gravity and magnetic residuals, after correction for the regional anomalies provided by the 3D model, gives a better insight into the extent and thickness of the basaltic and sub-basaltic layers. Especially, coupled inversion increases the depth resolution, but magnetic and gravity inversion must be weighted differently. Such inversion requires detailed pre-knowledge on the regional structures and shallow sedimentary layers, and can assist other sub-basalt imaging techniques.
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Integration of Geophysical and Satellite Imagery Data From the Alto de Ligonha Pegmatite Fields, Northern Moçambique: Implications for the Control of Mineralisation
Authors Detlef Eberle, Abera Tessema, Elônio A Muiuane, Elias X Daudi and Alfredo M. PontavidaMajor parts of Mocambique were flown a few years ago to acquire high resolution magnetic and radiometric data. It has been since then the intent of the National Geology Directorate of Moçambique to interpret these data generating value-added maps that are easier to use by the exploration and mining industries than mere airborne geophysical grid data and maps. The National Geology Directorate of Moçambique and the Council for Geoscience have joined with the financial support of the National Research Foundation of South Africa to conduct an example study case in the Alto de Ligonha pegmatite fields, northern Moçambique, with a special view to support the small scale-mining sector of the region. Analysis of the airborne geophysical, satellite imagery and geology data, in combination with ground geophysical data acquired over specific mineral showings, reveals that the occurrence of pegmatites is mostly confined to amphibolitic gneiss, which is part of the meso-Proterozoic Namama Thrust Belt. Generation of the respective value-added map was achieved using crisp exploratory K-means clustering of the airborne geophysical data. The map is the result of clustering 850,000 four-element samples (Th- and K-surface concentration, apparent magnetic susceptibility and the vertical magnetic gradient) into a number of classes. It clearly enhances the outcrop area of the amphibolitic gneiss where the occurrence of mineralised pegmatites is the most probable. The automated integration of airborne geophysical data using the well known K-means algorithm proved to be a fast, objective and effective tool to generate a value-added integrated map. The experience made in the Alto de Ligonha pegmatite fields encourages the adoption of this methodology over other parts of the Moçambique Fold Belt. This makes it an integral part of geological mapping ongoing in the country.
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An Evaluation of the Educational Impact of the EarthWise Teacher Training Project
Authors Mariette Erwee, Marian Tredoux and Huibrie JoubertThe EarthWISE geoscience project has dual objectives: To host workshops for science educators, and to offer concurrent road shows for science learners and the community. The workshops are specifically meant to provide training in the section of the National Curriculum Statement, called “The Planet Earth and Beyond”, which includes knowledge in the fields of astronomy, geography and geology. Workshops are presented by knowledgeable individuals in these fields to ensure quality training. The road shows include interactive exhibitions of various scientific fields to increase science awareness among the learners and the community as a whole, and to provide information of possible career opportunities as motivation for their performance in science at school. The main focus of the project is on rural areas, although workshops are also offered in the major cities. In 2006, the EarthWise office was moved to the University of the Free State. In 2008, funds were made available from the Inkaba phase 2 budget to partially finance a part-time manager for the project, and at least one training workshop, with road show, per year. The 2008 activity was presented in Prieska, in the Northern Cape Province, and was attended by 18 educators. The road show attracted 225 visitors. General consensus of the education department involved, as well as the Prieska community, is that it was a very successful event. The study that will be reported on was instigated to investigate in a more rigorous way the educational impact of these workshops held in rural areas. To determine whether the project has been beneficial to the community, some aspects needs to be evaluated, including the increase of the teachers’ subject knowledge and the change of attitude of the learners and the teachers towards science. This is done by means of pre- and post-tests, discussion groups, questionnaires and personal interviews. Both the response of the teachers concerning their experience of the workshops and the results of the evaluations were positive. This is evidence of the necessity of training programs like the EarthWise project. Some very enlightening comments and ideas were also obtained and will be implemented to improve the quality of future workshops.
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Source Rock Potential of the Lower Ecca Group, Tanqua Karoo Basin
Authors J. C. Ferreira and A. AkinluaThe increase in demand for hydrocarbons is motivating a new period in exploration for hydrocarbon resources in previously overlooked areas. This is supported by renewed exploration including feasibility studies, which are currently being conducted within the Karoo Basins of South Africa. The Lower Ecca Group of the Tanqua Karoo Basin is one of the many areas that are currently being re-evaluated and it consists of the Prince Albert Formation which was deposited under deep to shallow marine conditions, which is overlaid by the Whitehill Formation carbonaceous shale that was deposited under anoxic bottom conditions. The purpose of the research is to assess source characteristics of organic matter of the Prince Albert and Whitehill Formations of the Lower Ecca Group within the Tanqua Karoo Basin. Organic matter will be assessed on the basis of quantity, quality and maturity of the organic matter by means of Rock-Eval pyrolysis and organic petrography. Rock-Eval pyrolytic analyses will be undertaken, in addition vitrinite reflectance and maceral composition will be determined. Two very important techniques which can be applied for the rapid assessment of maturation and source characteristics of organic matter, which in turn is crucial in determining source-rock potential.
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Delineate 3D Iron Ore Geology and Resource Models using the Potential Field Method
Authors Des FitzGerald, Jean-Paul Chiles and Antonio GuillenMost 3D geological modelling tools were designed for the needs of the oil industry or detailed mine planning and are not suited to the variety of situations encountered in other application domains. Moreover, the usual modelling tools are not able to quantify the uncertainty of the geometric models generated. The potential field method was designed to build 3D geological models from data available in geology and mineral exploration, namely the geological map and a digital terrain model (DTM), structural data, borehole data, and interpretations of the geologist. This method considers a geological interface as a particular isosurface of a scalar field defined in the 3D space, called a potential field. The interpolation of that field, based on cokriging, provides surfaces that honour all the data. The 3D model and its parts are always consistent with the observations. New developments allow the covariance of the potential field to be identified from the structural data. This makes it possible to associate sensible cokriging standard deviations to the potential field estimates and to express the uncertainty of the geometric model. It also, for the first time, gives a statistically optimal, geologically sound way of interpolating geology, other than directly joining the dots as you do with CAD. Practical implementation issues for producing 3D geological models are presented: how to handle faults, how to honour borehole ends, how to take relationships between several interfaces into account, how to model thin beds over many kilometres, how to optimise lithological properties and how to integrate gravimetric and magnetic data. We describe all geology surfaces and volumes using implicit functions. These are then rendered onto the required sections, plans etc. The estimation of ore-body grades and tonnes, using an unbiased and optimal geostatistical technique, makes use of the stratigraphically bound 3D geology model. An application to the geological modelling of the Hamersley Iron Ore district, Australia, is briefly presented.
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Full Tensor Magnetic Gradiometry Processing and Interpretation Developments
Authors Des FitzGerald, Dominik Argast, Rod Paterson and Horst HolsteinIn recent years, Anglo/De Beers have championed the development of a Full Tensor Magnetic gradient (FTGM) signal instrument from IPHT. Multiple surveys of this quantity have been made in Southern Africa. With the advent of this new potential field full tensor gradient instrumentation, new methods have been developed to de-noise and process these curvature gradients. Traditional Fourier domain and minimum least squares residual of the linear differential tensor relationships have been adapted. This leads to levelling, gridding and grid filtering innovations. The result is a full tensor grid representation of the curvature gradients that is coherent and compliant with the physics at all points in the grid. All of the observed data is thus honoured in the Tensor grid. Isolating the signal and then refining it to be sure there are no distortions have dominated efforts to date. Superior anomaly interpretation regarding the full magnetic history and inferences can then be made. A survey from the Groblersdal Platinum mine is shown in the context of the structural geology interpretation. In particular, the dolerite dykes and faults are seen. The Hornfels footwall contact is very strong. The phase map traces the Platreef contact. The Upper Zone magnetites are more pervasive and fine layered structure is revealed there. None of the granites can be seen. A 3D geology model is in preparation. The observed FTG signal will be compared to the predicted thin-body responses from the model. There is more directly inferable structural geology in this tensor signal than can be found in a conventional TMI signal.
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Remote Sensing Heat Anomalies
More LessRemote sensing heat anomalies directly deserves more attention. Many methods and instruments exist but results from these are largely ignored in the geothermal community. A calibration range is advocated in one or more of the more prospective regions to fasten better use of geophysical methods. Clever software is also required to bridge the gap.
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Remote Sensing Reconnaissance of the Congo-Zambezi Watershed: Exploration of Palaeo-hydrological Patterns and Structural Controls on Biogeography
Authors T.J. Flϋgel, F.D. Eckardt and F.P.D. CotterillEarth’s land surface is ultimately related to (and highly affected by) the underlying geology. Landscapes are the interface between terrestrial, subaerial and climatic processes, and this is where hydrological processes hold a dominant role in determining the nature of landsurfaces. The understanding of large rivers with their associated tributaries and evolution is of fundamental importance when looking at landscape evolution. Yet, the origin of these drainage systems, especially in Africa, rarely receives deserved attention in contemporary geology and biology. Our current understanding of the Congo-Zambezi watershed often invokes data that is over 50 years old. A dearth of recent research into the Congo-Zambezi system largely reflects challenges of fieldwork across a vast area that remains difficult of access; fortunately, analyses of remotely sensed data reveals invaluable reconstructions of landforms. Although high resolution remotely-sensed data has been available since the late 1970’s, it was computationally challenging to derive sufficiently accurate river profiles from these data. The precise resolution of elevation data was significantly rectified by the 2003 Shuttle Radar Topographic Mission (SRTM). Surface elevation models (SEM) obtained from the SRTM along with Landsat 7 ETM + imagery now allows precise mapping of rivers and their profiles across the encompassing landscape. The presence of water falls and rapids (knickpoints) along river profiles reveal subtle geological structure. Integrated maps point to present and historical links (and barriers) across neighbouring drainage systems in relation to structural controls. Additional to the resolution they provide into the dynamic histories of fluvial systems, spatial contexts of knickpoints reveal valuable insights into potential barriers to dispersal of aquatic biota through fluvial systems. This poster presents the preliminary findings of selected river profiles in the study region.
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The Structure of the Karoo-age Ellisras Basin in Limpopo Province, South Africa in the Light of New Airborne Geophysical Data: a Preliminary Report
Authors C.J.S. Fourie, G. Henry and L.P. MarèThe Waterberg Coalfield is destined to become the major source of energy for South Africa in the future. In 2008, Coaltech Research Organisation funded an airborne magnetic and radiometric survey over the Karoo-age Ellisras Basin in which the coalfield is developed. Interpretation of the magnetic data has provided a novel half-graben model for the structure of this basin. The northern boundary is the block-faulted Melinda Fault Zone, with the southern, less-faulted part of the basin sloping gently to the north. The thickness of the Karoo Supergroup reaches 1 500m in the eastern part of the basin, and decreases to the west. The new geophysical data has contributed much to the understanding of the geological evolution of this important coalfield.
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Development of a Proposed Geo-science Train
Authors C.J.S. Fourie, M. De Coure and L. CroukampThe proposed Geo-Science Train (GST) facility will promote scientific research, science advancement, accumulation of scientific knowledge, service delivery of a geoscientific nature and training as its main objectives. It will attempt to reach South Africans from all walks of life strengthening the Public Understanding of Science Engineering and Technology (PUSET) program of the Department of Science and Technology (DST), but special attention will be given to rural areas and communities. The facility will be a mobile geological survey and science centre, strengthen the science awareness program of DST through the network of science centres, by hosting science exhibitions on board that will move with the train from town to town. More children and adults will be reached who would otherwise not have had the means or opportunity to view these science exhibitions. Training of students (to PhD level) through Research and Mapping of areas visited by the Geo-Science Train will contribute directly to education and economic development of the rural areas in South Africa. The Geo-Science Train will create an avenue for international research consortiums (e.g. Inkaba yeAfrica and SAMTEX) to make direct contributions towards the training of South Africans by promoting the understanding of the resources of South Africa. Services by the Geo-Science Train will be geared as training and service delivery. Day to day problems of rural communities and municipalities, such as clean drinking water, sources of suitable local building materials and the placement of waste sites and cemeteries will also be addressed from this facility. The train can provide access to a post box of the Department of Home Affairs, making it possible for persons in the rural areas to do applications for documents (I.D., birth certificates etc.). The contents of the post box will be delivered to the Department upon the return of the Geo-Science Train to Pretoria, approximately once every 3 months. Funding should be from government and industry.
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