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5th SAGA Biennial Conference and Exhibition
- Conference date: 29 Sep 1997 - 30 Sep 1997
- Location: Swakopmund, Namibia
- Published: 29 September 1997
41 - 52 of 52 results
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How To Find A Water Wellfield : Geophysical Mapping For A Platinum Mine Water Supply
More LessAt start-up in 1993, the PPRust Platinum Mine water supply of over 2 million
cubic metres per annum was entirely sourced from water wellfields located over
mafic Bushveld rocks up to 9km north of the mine. The aquifers supporting this
supply were mapped, drilled and evaluated in a geophysically-driven programme
compressed into a 5 month period during mid 1992.
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Application Of Image Processing Techniques To Airborne Gamma-Ray Spectrometric Data
By Henk CoetzeeAirborne gamma-ray data are commonly collected as an add-on in magnetic surveys,
at little additional cost. Data are presented in a similar format to magnetic data, and
processed from raw line data to finished maps and images using similar algorithms. A
gamma-ray spectrometric measurement is however fundamentally difficult to a
magnetic field measurement, and therefore requires different treatment and a different
approach. Image processing techniques commonly applied to remotely sensed visible
and infra-red reflection data may be more suitable for the enhancement of radiometric
anomalies.
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The Development Of A Gis System And Database For The Management Of Geophysical Data And Interpretations For The Geophysics Division Of The Council For Geoscience
More LessGeographic Information Systems (GIS) and
databases have played a vital role in the
management of various types of data throughout
industry and the world. In every area of life, there
is normally some form of information involved,
but at some point, the efficient management of
that information must be questioned. It is for this
purpose that GIS systems and databases play a
vital role. Not only is it necessary to be able to
store the data efficiently, but it is also necessary
to be able to retrieve the data in as short a period
of time as possible, while obtaining the maximum
amount of information about that data.
Geophysics is a field which is certainly no
exception to this fact.
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Fractal Convergence Properties Of Geophysical Inversion
More LessOne serious problem with most inversion schemes is that they are liable to
converge to local minima - that is they reach a set of model parameters that
provides a better fit to the data than the starting guess, but they do not reach the
set of parameters that would provide the best fit possible. The set of initial model
parameters that converge to a particular minima of the misfit surface for magnetic
data is studied, and found to be fractal. The principle is demonstrated for the
situation where there are two minima available for the model to converge to.
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The Use Of Wavelets In The Filtering Of Geophysical Data
Authors G.R.J. Cooper, M.Q.W. Jones and D. SeabrookWavelets have many advantages over conventional Fourier transforms when it
comes to the filtering of geophysical data. Wavelet transforms give information
about the energy present in a signal at different frequencies and at different
positions. This can be used to filter data effectively. In addition, the wavelet used
can be selected for the task required - a wavelet that is well localised in space can
be used for edge detection, for example. The applications of wavelet based
filtering to magnetic data are demonstrated.
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Structural Insights Gained From A Comparison Of Offshore Namibia Satellite Gravity Data With Onshore Magnetic And Gravity Data
More LessOffshore Namibia satellite gravity data are juxtaposed against the aeromagnetic
data and Bouguer gravity data of southern Africa in order to elucidate structural
and lithological features within the offshore magnetic basement. A large circular
gravity high) interpreted to be of similar origin to the Erongoberg, is seen some
50km southwest of Walvis Bay. The most striking result of this study is that the
interpreted Mesozoic age, narrow, coast-parallel intrusions, associated with
extension, have been faulted along the offshore continuations of early Palaeozoic -
late Proterozoic structures, suggesting that these structures were active until late
Mesozoic times. An important implication is that these structures provided
potential pathways for major drainage systems and hence the focus of major
offshore sedimentation.
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Dighem Resistivity Techniques Applied To The Detection Of Intrusive Dykes Within Coal Seams
More LessThe DIGHEMv airborne HEM system has been
widely used:
1 to aid geological mapping,
1 for groundwater exploration,
• for the detection of kimberlites,
• as an alteration mapping tool in gold
prospecting
• and also to find and delineate diamondiferous
gravels.
To our knowledge, this system has not previously
been applied for the detection of dykes
transecting coal seams.
The DIGEMv system has been used at the Avmin
- Forzando Coal mine in order to detect non
magnetically susceptible dykes. The survey was
carried out by Geodass Pty Ltd in conjunction
with DIGHEM/ CGG.
The Forzando Coal mine is located in the Bethal
district in Mpumalanga.
Dykes intruding into coal cause major mining
problems and can also reduce the coal reserves by
burning of the coal seams in the vicinity of the
dyke.
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The Bushveld In A Single Pulse?
By A. RiceComputational modelling of freezing magma chambers bas suggested that
inclusion of the effect of suspended crystal bad (which increases the effective
density) serves to split the magma chamber up into a number of stratifications,
each stratification a layer of magma of significant depth, but each layer varying
in composition. This suggestion has been verified by reviewing the experience of
other disciplines (e.g., industry, limnology, etc) whose own efforts indicate the
size of these layers are amenable to quantitative estimates.
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The Use Of Geophysical Techniques To Site High Yielding Water Supply Boreholes
Authors Peter Rosewarne and Ted MillsGeological and climatic conditions in South
Africa are not generally conducive to the
formation of large scale aquifers capable of
sustaining high yielding boreholes. Over 80% of
the country is underlain by old consolidated rocks
with negligible primary porosity and 75% of the
country receives <250 mm/a of rainfall. With this
information as background it is not surprising
that, although groundwater is found almost
everywhere in the country, most boreholes have
sustainable yields of «51/s. It is also not
surprising that groundwater supplies only about
13% of the total water consumption in South
Africa, the remainder coming from surface water
sources. This ratio is reversed in many European
countries.
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An Assessment Of The Current Radio Tomography Imaging Capabilties - Results Of A 2-D Computer Simulation Study
Authors A.M. van Schoor, E.C. WedepohL and D.R. VogtIn this computer simulation study, the current RT technology as developed at CSIR,
Miningtek, is benchmarked. The basic principles, strengths and weaknesses of the
technique are highlighted and its applicability to the mapping of small-scale features
that disrupt the mining of ore bodies is assessed. It is found that RT can potentially
solve some of the typical problems encountered in South African gold, platinum and
base metal mines. In addition, areas where the current RT technology needs to be
improved are identified. Also, ways in which to reduce RT survey time and cost are
investigated.
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Geophysical High Grade Won Ore Exploration In The Postmasburg District, Nothern Cape
Authors R. Vonk and G. WepenerGeophysical surveys were conducted on several Iscor prospects in the
Postmasburg region with the objective to locate and delineate possible high grade
iron-ore deposits. The area is mainly covered by calcrete and the orebodies are
irregular shaped and confined to synclines and karst depressions in the
Campbellrand Subgroup. Several anomalies were located that could represent iron
ore deposits. These anomalies were interpreted and modelled to determine the
physical dimensions of the potential ore deposits. The project is currently in the
drilling phase to establish ore grade and reserves.
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Broadband Seismological Studies On The Kaapvaal Craton Data Acquisition And Research Objectives
Authors C. Wright, S.J. Webb and T.K. NguuriA network of 54 broadband seismometers that forms part of the international Kaapvaal
Craton project was deployed across southern Africa at the end of April 1997, and will
operate for two years. Data are digitally recorded continuously and collected from each
site every month, and then transferred to master tapes at four processing centres for
shipment to the U.S.A. for collation and formatting. The seismology group at the
University of the Witwatersrand is developing new research initiatives and training
programmes for postgraduate students that will complement the research programmes
of the American participants. The South African group is using teleseismic, regional
and mining-induced earthquakes to improve understanding of the structure of the crust
and upper mantle beneath the craton. Emphasis will be on quantifying anisotropy and
lateral variations in both P and S wave velocities, and in defining frequency
dependence of velocity models. The distribution of seismicity with respect to southern
Africa is also ideal for studying the structure of the lowermost mantle or D” region.
Further work on the structure of this region will focus on possible anisotropy, lateral
variations, and the sharpness and depth of the velocity discontinuity that exists at the
top of D” in some parts of the earth.
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