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13th SAGA Biennial Conference & Exhibition
- Conference date: 06 Oct 2013 - 09 Oct 2013
- Location: Kruger National Park, South Africa
- Published: 06 October 2013
101 - 108 of 108 results
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Feasibility Of Using Seismic Reflection Surveys To Discover Iron Oxide Copper Gold Deposits In The Gawler Craton, South Australia
Authors E. Okan, A. Kepic and P. WilliamsIOCG deposits remain important sources of copper and gold in Australia especially since the discovery of the giant Olympic Dam deposits in 1975. They are considered to be metasomatic expressions of large crustal-scale alteration events driven by intrusive activity and are associated with felsic igneous rocks in most cases, commonly potassic igneous magmatism, with the deposits being commonly ~2.2 –1.5 Ga in age (Harrison, 2009). They tend to be enriched in Ca, Fe, Mn and P, with many deposits exhibiting an additional distinctive enrichment in Fe with economic levels of Cu, Au, Ag, Rare Earth Elements (REE), and U (Esdale, et al 1994). Such deposits have large net tonnages of economic minerals. Due to these distinguishing features, the IOCG class of deposits is a prime target for exploration by the mining industry. Although IOCG’s are largely classified by their geochemical characteristics many have significant petrophysical contrasts in magnetic susceptibility and/or density. Thus, potential field geophysical methods are typically used to detect both the major structures that lead to the location of prospective targets and the deposits themselves. Such methods have poor resolution at depth, and are limited to either directly detecting shallow targets or very large deposits with sufficient contrast in areas with significant cover, such as the Gawler Craton. Thus, the traditional approaches to exploration for IOCG deposits in the Gawler Craton are becoming less effective and more expensive; hence another method such as seismic reflection is proposed.
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Linking The Damara (namibia) And Lufilian/katangan (zambia) Belts Through Geophysical Interpretations
Authors W. Rankin, S.J. Webb, D. Kiyan, J.A. Kinnaird and R.L. EvansThe Damara Belt, (Namibia) and the Lufilian Arc/Katangan Belt, (Zambia) formed during the Pan-African orogeny (ca. 800 – 500 Ma) as a result of the collision of the composite Kalahari Craton, to the south, and the composite Congo Craton, to the north. Their connection is highly speculative due to Kalahari and Karoo cover and their extent holds both academic importance and economic interests as the Damara Belt is rich in Uranium (U) and the Lufilian Arc in Copper-cobalt (Cu-Co) mineralisation. Due to limited outcrops on the border of Namibia and Botswana, geophysical techniques have become the main approach in constraining the possible extent of these belts. This study involves the interpretation of aeromagnetic and gravity datasets supplied by Rio Tinto complemented by regional-scale magnetotelluric (MT) data from the South African MagneTotelluric Experiment (SAMTEX) project. Three 400 km long potential field profiles are being modelled in Oasis Montaj using GM-SYS. These profiles intend to show the folding style of the Ghanzi-Chobe Belt, extent of the Matchless Amphibolite Belt (MAB) and contribute to the understanding of the strong remanent negative feature seen in northern Namibia. Potential field data as well as complementary MT data from SAMTEX were used, augmented by recent MT data acquired as part of the NSF Incipient Rifting project. Three roughly N-S MT profiles were analysed and modelled; DMB, NEN, OKA-CAM, listed west to east. The geoelectric strike analysis of the MT data shows different strike results for the upper 5 km of the crust compared to the strike results for 5 – 15 km of the crust. The strike angle increases from approximately 47° in the west to 85° in the east. These data will contribute to a better understanding of the tectonic evolution of these mobile belts and cratons by their incorporation into an interpretative sub-Kalahari geological map of the Kalahari Desert area.
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A Report On Ground Geophysical Surveys Carried Out At Aliwal North, Badfontein And Kenegha Drift Hot Springs In The Eastern Cape Province, South Africa
Authors M.F.A Sekiba, P.K. Nyabeze, E. Madi and O. GwavavaThere are seven recorded occurrences of hot springs in the Eastern Cape Province of South Africa. , Geophysical surveys were carried out across three springs namely Aliwal North, Badfontein and Kenegha Drift. The geology at Aliwal north and Badfontein consists of brownish-red and grey mudstone and sandstone. The geology at Kenegha Drift consists of thick layers of coarse pebbly feldspathic sandstone, mudstone and shale. The aim of the study was to investigate groundwater bearing structures in the vicinity of hot springs. The study involved application of electromagnetic conductivity and magnetic techniques. A Geonics EM34-3 electrical conductivity unit used in the horizontal dipole configuration with 10 m, 20 m and 40 m dipoles. The maximum depths of investigation for the three dipoles are 7.5 m, 15 m and 30 m respectively. Magnetic data was recorded using Geometrics G859 and 856AX magnetometers. The station separation for magnetic and electromagnetic surveys was 2.5 m and 10 m respectively. The magnetic data was presented as profiles. Electrical conductivity data was modeled using EM4Soil inversion software to generate conductivity depth sections. The maximum electrical conductivity values that were measured using different coil separations at the three hot springs are presented in Table 1. The high conductivity peaks could be associated with water bearing fractures or faults.
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A Report On Borehole Siting At Tshivhilwi Village In Limpopo Province, South Africa
Authors M. Sethobya, P.K. Nyabeze and S. PhalanndwaThere is scarcity of portable drinking water in Tshivhilwi Village located in the northern Limpopo Province of South Africa. A site was investigated for groundwater potential. Previously drilled boreholes (BH1 and BH2) had low groundwater yields, there were drilled into weathered meta-volcanic dykes. Geophysical surveys were carried out at the site for groundwater exploration. The surveys were conducted in order to locate a sustainable groundwater source for the site. The geophysical methods that were applied included magnetic, electromagnetic (EM) and electrical resistivity tomography (ERT) techniques. These methods were used to map possible fracture or fault zones that could have groundwater potential. Equipment that was used for measuring magnetic, electromagnetic and resistivity data comprised Geometrics G856 magnetometers, Geonics EM34-3 conductivity meter and an Iris Syscal Pro switch 72 channel resistivity meter respectively. The station spacing for magnetic and electromagnetic surveys was 5 m, this was chosen in order to map subtle variations in the subsurface geology. ERT Resistivity surveys were carried out using a 5 m and 10 m dipole-dipole and Schlumberger arrays. ERT traverses were carried out along lines EF and EG. EM profiling was done along lines AB, CD and EH. The average line separation for the magnetic survey was 25 m. Geological contact zones were inferred from magnetic survey data, low resistivity zones with corresponding high electromagnetic conductivity values were identified as possible targets. Borehole targets S1 and S2 were recommended. A groundwater yielding borehole was drilled a few meters south for target S2. The surveys showed that geophysical methods are effective tools for investigating the occurrence of shallow groundwater aquifers.
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Aem Discrete Conductor Inversion
Authors M.A. Vallée, J. Lemieux and T. KimuraDiscrete object modelling has been used since the beginning of airborne electromagnetic exploration. A recent effort of integrating existing modelling and inversion tools with airborne data shows that simple models are still quite useful for exploration. They can provide simple parameters of a model with minimum a priori and still provide adequate data fitting. Approximations allow using models with reasonable computer resources. Plate models have been popular and inversion programs have been developed around them. Another inversion approach is based on approximation of sphere or plate response in free-space. Finally, a recent development is an analytic solution for a conductive sphere in a layered earth. We present some applications of this methodology.
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Investigating Airborne Low Frequency Gpr Antenna-ground Coupling Through Modelling
Authors D. Vogt and M. Van SchoorGround Penetrating Radar (GPR) is often a good tool for detecting near surface structure, as it is cheap, fast and has high resolution. At lower frequencies, it is an excellent tool for detecting voids such as sinkholes, old excavations or rat-holes that pose a risk to surface infrastructure. However, in some situations, the potential risk from the voids prevents the use of GPR on the surface, and airborne application needs to be considered. While GPR has been successfully applied from the air, the applications have usually been over ice, which is a particularly radar transparent medium. In this case, information is required about sub-surface structure in a moderately conductive environment. In order to better understand the performance of GPR, a typical resistively loaded dipole antenna with a design frequency of around 50 MHz has been modelled at various heights above the ground. The modelling was conducted using a Finite-Difference Time-Domain code that incorporates a dispersive lossy medium model. The results show that coupling of energy into the ground is not adversely affected by raising the antenna. The antenna characteristics change, with slightly less energy being emitted at lower frequencies, but the coupling into the ground does not change. There is some change in the spreading pattern of signals in the earth that will result in small changes in the shape of the diffraction hyperbolas that are usually seen. The modelling supports testing of an airborne system to determine whether it is capable of producing meaningful results.
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Wavelet-based Semblance Analysis Of Density Data From The Western Limb Of The Bushveld Complex
Authors O. Sepato, S.J. Webb and G.R.J CooperThe Bushveld Complex is a 2.06 Ga layered suite of mafic and ultramafic rocks. These rocks are believed to have formed from several magma pulses covering an estimated 65 000 km2. Wireline geophysical logs of density and magnetic susceptibility data have previously been studied using wavelet analysis. This analysis has revealed cyclicity in the physical property data, which has been attributed to magmatic pulses which resulted in layer growth, analogous to sedimentation in a sedimentary basin environment. These studies were carried out in the Northern Limb of the Bushveld Complex. This study expands on previous work, making use of three boreholes from the Western Limb. Results once again show cyclicity in density data, with strong correlations at a wavelength of 150 m, which is similar to the wavelength of the cyclicity discovered previously in the Northern Limb. Analysis is currently being done on data from the Eastern Limb of the Bushveld Complex.
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Airborne Ground Penetrating Radar: Practical Field Experiments
Authors M. Van Schoor and D. VogtThe performance of ground penetrating radar (GPR) under conditions where the ground coupling of the antenna is potentially compromised is investigated. Of particular interest is the effect of increasing the distance between the antennae and the ground. In this paper, a field trial approach is used and the study is intended to complement a related theoretical model study. Preliminary results suggest that, in the case of moderately conductive survey conditions, it is possible to conduct meaningful GPR surveys with an antenna raised up to 2-3 wavelengths off the ground. Advanced GPR and imaging processing could possibly be used to extend this height even further. The findings of this study lend support to the concept of deploying GPR systems on mobile platforms, including low-altitude airborne vehicles.
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