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9th SAGA Biennial Technical Meeting and Exhibition
- Conference date: 14 Sep 2005 - 16 Sep 2005
- Location: Cape Town, South Africa
- Published: 14 September 2005
66 results
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Combined stochastic and deterministic modelling as an innovative approach to jointly interpret multi-method airborne geophysical data sets
By D.G. EberleWhilst deterministic modelling has become an undisputed tool of geophysical data interpretation, multivariate
stochastic methods have rarely been utilised routinely. During the past few years, the Council for Geoscience, in cooperation
with the Federal Institute for Geosciences and Natural Resources of Germany (BGR), has developed and
tested a strategy to combine the benefits of these two quite different conceptual procedures of information
extraction from geophysical data sets.
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Innovative data processing methods for gradient airborne geophysical datasets
By P. McInerneyIntrepid Geophysics has adapted its existing software to include a new series of objects that can be used when
processing gradient datasets. These have the purpose of hiding the details (abstraction) of exactly what components of a
field have been observed in a survey dataset. This avoids the problem of doing a general rewrite of processing software
from the ground up for each special case. Historically, codes have mostly been written to filter, level and grid “scalar”
line data (e.g. Total Magnetic Intensity), so Intrepid Geophysics latest software update is a dramatic shift to the world of
vectors & tensors.
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Creating realistic 3D Geology models rapidly, using geophysicsto test them
By P. McInerneyThe traditional method of recording and communicating an understanding of the geological structure of a region has
been to create a map of the geology. Today there is a growing trend to use three-dimensional models of geology. One
of the challenges with 3D geology modelling is that it is frequently difficult to incorporate new data, and revise the
model. The potential field geology modelling method described here automates the task of model building, and
computes a model directly from the data (the geology observations). The method has been implemented in the 3D
GeoModeller software.
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Multidisciplinary geophysical investigations applied to unconformity–associated uranium exploration, Athabasca Basin, Canadian Shield
By M.D. ThomasThe Mesoproterozoic Athabasca Basin provides approximately one-third of world uranium primary production from
deposits located at or near the sub-basin unconformity, and because they are buried, geophysics plays a key role in their
exploration. This role is examined using results of recent studies near the McArthur River deposit lying at a depth of
about 550 m.
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The establishment of AfricaArray and sustainable geophysics training
By P. DirksAfricaArray is a pan-African initiative to promote geophysical research and capacity building, and was launched as
a long-term (10 year) programme in July 2004 by the University of the Witwatersrand, the Council for Geoscience
and Penn State University, USA.
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The Initiation of the South Atlantic Ocean: The broad context, the local questions
By C. ReevesIdeas on plate tectonics started with the recognition of the remarkably similar shape of the coastlines of Africa and
South America. The elegance of the theory at global scale has to be matched eventually with evidence (both
geological and geophysical) at local scale.
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AfricaSpan" regional 2D seismic and potential field programs
By N. TaylorIn partnership with Africa National Oil Companies and Ministries GX Technology has acquired and processed long
offset 2D regional PSDM seismic and potential field data programs to provide clues to broad regional tectonics and
the evolution of basins to help introduce new plays and exploration opportunities.
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The value of long offset acquisition offshore Namibia
By S. ToothillThe purpose of this paper is to highlight the benefits associated with the use of long offset data and some of the
practical issues encountered during acquisition and processing. The use of long offsets in shallow water settings such as
the UK Central North Sea, have yielded valuable information in the context of identifying additional potential from
existing and new plays in this mature basin.
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On kimberlite detection in brown-field exploration:some challenges to geophysics
By M. DoucouréWith the relatively easy bodies having already been found, the discovery of kimberlites
and sterilization of ground in brown-field exploration is challenging due to increasing
subtlety of targets, geologic complications and need to complete work rapidly.
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Some thoughts on the crustal structure of the Mauritanides as revealed by geophysical data
By E. StettlerThe Mauritanides in the western part of Mauritania form a north-south striking assembly of metamorphosed rocks
from meta-sedimentary to ultra-basic and ophiolitic origin with interspaced calc-alkaline granite. Morphologically
they form a belt of low lying hills. Geologically they stand out because they contain a large number of small
copper-rich base metal deposits and a few Cr showings.
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A magnetic survey over the amphibolite-granulite transition in the basement rocks of the Vredefort dome, South Africa; preliminary results.
By M. MuundjuaThe Vredefort dome exhibits unique geological and geophysical features compared with other known impact
craters, and one of these is a negative magnetic anomaly over the basement rocks near the centre of the crater. In
this study we conducted a magnetic survey across the amphibolite-granulite transition.
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New palaeomagnetic data from the main and upper zones of the Bushveld Complex
By S. LettsThe Bushveld Complex (BC) has been the subject of many palaeomagnetic investigations since 1959. Despite these
studies, systematic inconstancies have been found between the palaeomagnetic findings and well constrained ages
determined for the Bushveld Complex.
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Smarter depth information: using geology in geophysical inversions
By C. WijnsWhile geophysical inversion software continues to become more sophisticated and easier to use, the challenge
remains to extract the most meaningful depth information from the data. Numerical inversion of geophysical data
does not normally require user interaction apart from the selection of initial inversion parameters, and most
programs provide default parameters that end up driving the bulk of solutions throughout the exploration industry.
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Implications of palaeogeotherms for the thermal history of the Witwatersrand Basin, South Africa
By M. JonesRegional greenschist facies metamorphism (350±50°C, ca 2.5 kbar) of sediments in the Witwatersrand Basin
implies that crustal temperatures were significantly elevated at some time in the Late Archaean and
Palaeoproterozoic relative to present day temperatures.
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Comparison of seismic location methods on a South African gold mine
By B. YoungThis paper explores two seismic location methods. One was a simplex method based on the Nelder-Mead simplex
method (Nelder and mead, 1965). The other is a double difference method developed by Spottiswoode and Milev
(1998). The two methods were compared using data obtained from Elandsrand gold mine. An initial area on the
mine was chosen (15 line) and the mine locations and the relocations using the simplex method and the hybrid
method were examined. The velocity model used was that given by the mine dataset.
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Witbank coalfield Aeromagnetic Merge Project-A Coaltech-2020 initiative
More LessA Coaltech-2020 Geological and Geophysical Steering Committee task was initiated in 2003 to source existing
airborne magnetic datasets over the Witbank coalfield and to collate these into a single map. The main project
benefit is to provide Coaltech-2020 participants with a more global perspective by being able to trace magnetically
susceptible dykes cross-cutting the coalfield, from beyond their individual mining leases, thereby potentially
identifying previously unknown dykes in their own areas. Potential savings to mining operations generated by
access to such additional information may be worth millions of rands.
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Enhancing extended Euler deconvolution
By G. CooperEuler deconvolution is a semi-automatic interpretation technique that is widely used to provide initial estimates of
source locations from aeromagnetic data. Mushayandebvu et al (2001) developed an extended Euler deconvolution
that estimated both the dip and susceptibility of thin dyke and contact models.
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Testing of geodetic and geophysical parameters on potential sites for space geodesy observatory
By S. MadisengThe techniques used in space geodesy are Very Long Baseline Interferometry (VLBI), Global Positioning System
(GPS), Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR). VLBI uses the precise timing of radio
signals from distant quasars arriving at different points on earth. SLR and LLR are based on the round-trip time
required by light from ground-based laser stations to bounce off satellites or the moon (in the case of LLR) and
return to the station. GPS methods measure the travel time of radio signals between satellites and receivers on the
ground.
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Development of an environmental geophysics test site
By S. FourieGeophysical test sites are developed to test situations that would most probably occur in real environmental surveys. These
test sites can be in laboratories [1],[2],[3],[5], or it can be real [4]. Environmental test sites are the easiest to develop and it
does not need to be large. This planned test site will be developed to test responses of shallow buried objects. All the
artifacts that will be buried at this test site, could have an environmental inclination.
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Fast track reservoir characterisation of a subtle Paleocene deep marine turbidite field using a rock physics and seismic modelling led workflow
By H. MorrisThis paper presents a novel approach to identifying/tracking interlocking Palaeocene sand and shale filled
channels based on forward modelling, AVO classification and inversion of inversion techniques for an appraised
subtle Paleocene deep marine turbidite, Central North Sea.
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The applicability of various seismic offset reflectivity models
By G. SmithThe variation of the amplitudes of seismic reflection data as a function of angle of incidence or offset (AVO) is a
technique that is widely applied in exploration for hydrocarbons and the characterization of reservoirs. Many
approximations of the Zoeppritz equations have been proposed, and another one is added here to add to the general
confusion. A simple method of comparing them is used here to compare two approximations with the full solution.
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The fluid factor angle applied to the Sable oil field area (South Africa)
More LessThe study was aimed at exploring the robustness of seismic attribute displays and the application of different fluid
factor angles to delineate the differences between the E-BD channel complex and E-BD2 sandstone, in the region of
the Sable Oil field, Bredasdorp Basin, offshore South Africa. Seismic attribute slices generated from stacked
amplitudes, fluid factor, intercept AVO and gradient AVO were sliced at 13At1 and E-BD top horizons, which were
interpreted as the base and top of the E-BD sandstones respectively.
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The application of the continuous wavelet transform to potential field data
By G. CooperThe continuous wavelet transform (CWT) has been used with much success in the analysis of non-stationary time
series. It has been used much less frequently in the interpretation of magnetic or gravity data, although several
approaches have been tried. A simple method of obtaining location and depth estimates of potential field sources is
suggested here. For gravity data the method uses wavelets based on the integer-order horizontal derivatives of the
gravity anomaly from a point source.
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Processing of gravity data using gravity wavelets
By A. ChatuDuring the last decade, many new geophysical data processing methods have been developed. Gravity wavelet
is a new method in geophysical processing that is drawing attention of most potential field workers. It has
ample applications in processing and interpretation of potential field data.
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Three-dimensional gravity model of the Witwatersrand Basin and Vredefort impact Structure
By S. CoomberThe Archaean Witwatersrand basin is, economically, one of South Africa’s most important geological feature.
Approximately 40% of the gold ever mined globally comes from the Central Rand Group (contained in the
Witwatersrand Supergroup) making it a unique, mammoth resource. As a result, the Witwatersrand basin has become
the most extensively studied basin in the world.
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Ibhubesi Field, South Africa: is cross-plotting of AVO attributes a reliable / suitable technique to predict gas directly
By M. MbandeziThis project investigates the use of crossplot analysis for interpreting 3D seismic data to detect and map the distribution
of gas-sands in the iBhubesi gas field on the west coast of South Africa. Forest Oil international provided us with
stacked P R , P-wave reflectivity and S R , S-wave reflectivity, and inverted P and S wave 3-D seismic and borehole log
data, in 2003.
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Adding value to old seismic data through re-processing
By M. GibsonGold Fields has an extensive archive of 2D seismic lines acquired in the Witwatersrand Basin during the 1980’s, as
well as more recent 3D seismic surveys at the Oryx (1992), Driefontein (1995) and Leeudoorn (Kloof 7 shaft, 1994)
mines. Recent projects at Oryx and Kloof needed updated structural interpretations of borehole and seismic data.
At Oryx, a new 2D seismic acquisition was considered to tie new boreholes.
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Case studies on Kirchhoff and wave equation anisotropic PSDM
By S. Grion3D prestack depth migration (3D PSDM) is the tool of choice for accurate structural imaging. This paper addresses
the following key issues in 3D PSDM: (1) the relative merits of Kirchhoff and Wave Equation Migration (WEM)
schemes and (2) the use of anisotropy and the importance of well calibration.
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Angle gathers for wave equation pre stack depth migration
More LessIt is now recognized that shot-record wave-equation migration is the best method for imaging in complex media.
However, it is also recognized that producing one output image is not enough. Velocity analysis can only be done
when a gather is produced, as well as AVO analysis or multiple attenuation.
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Imaging deep geology using full tensor gravity gradiometry inversion: K-2, deepwater Gulf of Mexico
By P. HoughtonA common misunderstanding in the oil industry is that Full Tensor Gravity Gradient (FTG) data
is only of use when resolving shallow sections of the earth model. This paper will highlight the
ability of FTG to resolve deep as well as shallow geological targets by showing examples from
an imaging study of the pre-salt K-2 Field, Deep Water Gulf of Mexico. Combined Pre Stacked
Depth Migration (PreSDM) and gravity gradient inversion was used to resolve the base of salt at
a depth in excess of 7 ½ kms.
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Borehole radar EM wave simulation for mining applications using a parallel implementation of the 3-D FDTD algorithm
More LessA borehole radar is a high resolution electromagnetic (EM) sensor for detecting electrical discontinuities in
rock formations. Often the host rock medium through which the wave propagates as well as the target ore-body
have complex electromagnetic properties. Modelling EM wave propagation in 3-D can be used to better understand
the physics of observed responses. It can provide useful insight into the interpretation of real data sets, as well as
show the effects that drilling fluid (mud), water and air in the borehole will have on the coupling from the antenna
to the host rock medium.
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Improved interpretation of borehole radar data through interactive 3D forward modeling
By D. VogtBorehole radar is being applied to delineate tabular orebodies in South African gold and platinum mines. The radar
is omni-directional in azimuth, leading to an ambiguity in the direction to a reflector. One way of resolving the
directional ambiguity is through the use of a priori information. The regional dip and strike of the orebody are
known, and can be used as a first approximation for the position of the reflector. A program called Fresco has been
developed in which a candidate orebody can be manipulated, and its radar response can be modelled in real time.
The model can then be manipulated until the modelled response agrees with the measured response.
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Borehole radar delineation of the UG2 reef at Modikwa Platinum Mine
By P. du PisaniThe effectiveness of imaging the major platinum bearing reefs of the Bushveld Complex with borehole radar has
been proven under the PlatMine Research Collaborative. In this paper the technology was applied, at Modikwa
Platinum Mine, as a value adding exploration tool to assess two mining challenges on the UG2 reef.
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Application of the multi-electrode resistivity method to surface-water/ground-water interaction as applied to vegetation controls
By L. SoltauThe South African National Water Act of 1998 makes provision to have a groundwater reserve set aside to cater for
basic needs and ecologic use of water. Groundwater/surface water interaction is of import to define this groundwater
reserve. The distribution of vegetation around the Langebaan Lagoon is expected to be at least in part dependant on
groundwater conditions.
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Surface nuclear magnetic resonance (SNMR) sounding technique applied to primary aquifers in Southern Africa
By R. MeyerSurface Nuclear Magnetic Resonance sounding (SNMR) is the only geophysical method that allows the direct noninvasive
determination of both the volume of exploitable groundwater and its depth distribution. Furthermore, the
technique is unique in that it can discriminate between the sizes of the water bearing pores. Since 1999 a number of
exploratory SNMR surveys have been conducted in Botswana, Namibia and South Africa.
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Electro-kinetic soundings with a TDEM instrument
More LessIn 2003 the newly developed theory and an algorithm for the calculation of the EKE effect was presented at SAGA.
Since that time the progress in further developing the method of electrokinetic sounding was as follows:
1. New software for the mathematical modeling and interpretation of EKE in Matlab was written. It allows improved
visualization, more accurate and faster calculation of the EKE effect in a multilayered media.
2. The instrument TSICL-5, intended to the TDEM method was adjusted to allow for the additional measurement of the
EKE effect. Supplementary to the basic receiver an external amplifier with an input connection designed for a matched
impedance of the ground electrodes or porous pots for the electric signal was built and fitted to the instrument. An external
trigger device fitted to the receiver converts the geophone pulse to run the software. The software was also altered
to display the recorded seismo-kinetic event. The set up of the receiver is done automatically (calibration) before the
actual measurements take place.
3. Laboratory and fields testing of the instrument and software has showed not only a principal possibility of the registration
of EKE, but very stable and repeatable signals.
4. The EKE soundings were recorded along a profile (approximately 200 m in length) on the farm Horseback, close to
Cullinan. This profile was repeated twice. Along one part of the profile no considerable EKE signals were recorded but
the opposite end shows very strong EKE signals with amplitudes of the order of a few millivolts. This signal is very
well correlated from sounding to sounding. The strong signals coincide, according to the farmer to a local spring located
in this area. The interpretation of collected data was done using the newly developed software. Field result
showed that the EKE anomaly is associated with water saturated sediments located at a shallow depth of 3 -4m. The
predicted permeability of the water saturated layer is to be ~20-30 D.
The obtained results show that the EKE method can be successfully used for searching for groundwater at very
shallow depths. It is very important because most of the other geophysical methods cannot be used for this type of hydro
geological problem.
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In-mine electrical resistance tomography (ERT)
More LessIn-mine, tunnel-to-tunnel electrical resistance tomography (ERT) has, in recent years, been a topic of research at
CSIR Mining Technology. This novel and unconventional application of ERT is aimed at detecting and delineating
geological features that affect the continuity of the tabular platinum reefs of the Bushveld Complex ahead of
mining. In this paper, the contrast between conventional ERT and the in-mine approach is highlighted. Some of the
key challenges associated with in-mine ERT are discussed, together with how these challenges are overcome in an
effort to optimise the application for routine in-mine use. Two proof-of-concept case studies are also included.
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Development of a combined resistivity and induced polarization instrument for the laboratory environment
By L. MareAs part of the expansion of the physical properties database of the Council for Geoscience to include resistivity and
induced polarization (IP) data, a demonstration model of the Swedish built ABEM RIPS3 was obtained in September
1996. Right from the onset, using the ABEM RIPS3 produced several problems.
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Application of an improved S-layer differential transform on TDEM sounding data to delineate an iron ore deposit
By M. CombrinckThe S-layer differential transform, based on the late time approximation of a thin conductive sheet, was applied to
Time Domain Electromagnetic (TDEM) sounding data acquired in order to delineate an iron ore prospect.
Although giving very good results on synthetic data, the S-layer differential transform is extremely sensitive to
noise in real data. This is due to the fact that the method requires two successive numerical differentiations which is
an extremely unstable procedure.
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Numerical integration for reducing degree of generated noise
By S. LephotoInterpretation of TDEM sounding data is commonly done using the S-layer differential transform. This method is
based on the thin sheet model. In this method, the first and second time derivates of the magnetic field are solved
simultaneously for the conductance (S) and depth (d). Taking the derivatives of S to d then yields the conductivity
of an equivalent S-layer and depth d.
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Effects of uneven terrain on forward modeled TDEM data
By J. MahanyeleInterpretation of TDEM (Time Domain Electromagnetic) data (especially application of conductivity-depth transforms)
has been habitually done from a flat terrain approach. Interpretation of the acquired results therefore suffers the
imprecision introduced due to topographical variations. The effects of terrain unevenness were investigated using
Maxwell EM interpretation software.
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The development of low temperature SQUID systems for the geosciences
By T. le RouxSuper-conducting Quantum Interference Devices (SQUIDs) are tiny sensors that detect and measure very small
magnetic fields. As part of an ATD-GRG research project, the Institut für Physikalische Hochtechnologie (IPHT) in
Jena, Germany, have developed a Low Temperature SQUID (LTS) ground Transient ElectroMagnetic (TEM)
system for Anglo to further strengthen the company’s mineral exploration capabilities.
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Borehole orientation surveys: Results from a benchmark study
By A. WolmaransDetermining the orientation or trajectory of any geological borehole is every bit as important as the core or other
information that may be extracted from the borehole. Uncertainties in the location of geological contacts, structures,
etcetera, which propagate into uncertainties in resource volume calculations, increase the risk associated with resource
evaluation projects and may even lead to resource discounting factors being introduced.
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The effect of magnetometer and accelerometer errors on the predicted trajectories of boreholes surveyed by EMS instruments
More LessA wide range of borehole surveying instruments is available. They provide data (such as borehole direction and dip,
and the components of the local magnetic and gravitational field) at pre-determined downhole stations. A number of
algorithms are used to convert these data to 3D coordinates in the relevant reference systems (Orpen, 2005). Electronic
Multi-Shot (EMS) type borehole navigators are used extensively within the hard rock mining environment to determine
the trajectories of boreholes, especially as the alternatives (optical deflection and inertial navigation based systems, e.g.
gyros) are seen as being either too expensive, or don’t fit the smaller diameter boreholes.
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Recommendations for wire-line calipers
By R. van BurenDuring the first quarter of 2005, a due diligence study on caliper techniques, was conducted at a De Beers
operation. The purpose of the study was to determine the accuracy and precision of a newly acquired GeoVista 4
arm caliper for down-hole measurements. The survey was conducted in one of the large diameter drill holes (LDD)
drilled as part of the Resource Extension Project currently underway at the operation. These holes are being used for
resource evaluation, with the grade analysis performed on samples in the range of 1 tonne. The reason for acquiring
the caliper was to obtain more accurate estimations of down-hole sample volumes, which has the effect of
increasing confidence in grade values.
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Electromagnetic measurement of coal roof-beam thickness
By L. CandyIn underground coal mines where coal is left in the roof or floor after mining, it is often necessary to measure the
thickness of the remaining coal. Radar and radar-like techniques have been attempted in the past but have met with
limited success. By taking advantage of the resistive contrast between the coal and the surrounding rock
electromagnetic sounding (EM) has been proposed as a feasible technique to achieve non-intrusive coal thickness
measurements.
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Comparison of the capabilities of neutron tomography with X-ray tomography on geological samples
By F. de BeerNondestructive testing (NDT) methods have been recognized as powerful tools for investigating mechanical
properties in geotechnical engineering and have recently been applied to earth science materials (de Beer, 2003) In
this study experiments were conducted on several rock samples to investigate the abilities of non-destructive
techniques (NDT) on geological samples.
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Application of high-resolution 3D seismic to mine planning in platinum shallow mines
By E. GillotOver the last decade 3D reflection seismic has been applied for platinum mining in South Africa. 3D seismic surveys
have almost exclusively been conducted in the Western Bushveld where ore extraction depths range between 500 and
2000m. The ore is mined mainly via vertical shafts and also some decline shafts. In the Eastern Bushveld, the mining
targets are at shallower depths of less than 400m.
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Geophysical investigation at Namakwa Sands - Are we out of our Depths?
More LessAnglo Base’s Namakwa Sands heavy mineral sands operation is located on the West Coast of South Africa. Heavy
minerals are extracted from paleo-beach sands, but in certain areas of the deposit relative hard calcretised or
silcretised horizons occur. Although this material is mineralised, it is discarded to waste as the current plants are
not equipped to liberate mineral from the hard layers. It has become essential to determine the amount of hard
material in the ore body to justify the construction of a new plant for treating the hard material.
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Comparison of the electromagnetic structure of Archean cratons
By A. JonesArchean cratons contain the cryptic signatures of lithospheric formation processes dominant during the first half of
the Earth’s existence. One of the main debated topics in the geosciences is whether these tectonic processes are
similar to those occurring today, particularly plate tectonics, or whether other non-plate tectonic processes, such as
mantle plumes and sagduction, were more important.
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Electrical anisotropy across southern Africa derived from MT studies and compared with seismic anisotropy results
By M. HamiltonData from part of the Southern African Magnetotelluric Experiment (SAMTEX) have been analysed using an
impedance tensor decomposition method in order to gain a better understanding of geoelectric directionality and
dimensionality and its variation with depth, and the electrical anisotropy properties of the region. The SW-NE transect
from Sutherland to Messina, South Africa, is coincident with part of the Kaapvaal Craton Project’s Southern Africa
Seismic Experiment (SASE) deployment. Shear-wave splitting analyses on the SASE data, reported in the literature,
showed that splitting delay times appear to exhibit geological control, with the Late-Archean regions showing generally
greater anisotropy.
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Titan-24: the application of distributed array technology to geological mapping and target definition
By S.J. BateThe Titan-24 distributed array system has been used in a wide variety of geological environments for mineral,
geothermal and oil and gas exploration. The technology has also been used in a slightly different configuration to
produce regional MT sections to kilometers depth for geological research purposes.
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Acoustic / Chirp surveys applied on Coal (A world first?)
More LessTypical problems on coal mines include determining the thickness of coal left in the floor by historic mining
(potentially a large reserve of coal that can still be extracted), and identification and determination of the thickness
of sandstone partings located within coal seams. An additional problem encountered at Anglo Coal’s Bank Colliery
was determining the risk to planned underground workings beneath a dam- critical information required being the
bathymetry of the dam and the amount of sludge in the dam.
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Electric and electromagnetic methods: an opportunity to enhance the seismic reflection tool
By C. BoulangerAfter the 1950’s, seismic reflection soon became recognised as the best method for deep underground investigations
and replaced potential methods such as electric or EM methods, for exploring deep targets.
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Simultaneous inversion of pre-stack seismic data
By B. RussellWe present a new approach to the simultaneous pre-stack
inversion of PP and, optionally, PS angle gathers for the
estimation of P-impedance, S-impedance and density. Our
algorithm is based on three assumptions. The first is that
the linearized approximation for reflectivity holds. The
second is that PP and PS reflectivity as a function of angle
can be given by the Aki-Richards equations (Aki and
Richards, 2002).
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Contributions to the gravity field of Southern Africa from crustal thickness variations and mantle seismic velocity variations
By S. WebbAs a result of the Kaapvaal Project we now have unprecedented coverage of the crustal thickness and details of the
seismic velocity variations in the tectosphere beneath southern Africa. By using these data and reasonable density
relationships we can calculate the contribution of each of these components to the overall gravity field of southern
Africa.
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Visibility filtering of potential field data
By G. CooperThe viewshed of a topographic dataset is the region around a given observation point that is visible from that
location. It has many uses, such as in urban environment planning, or in siting television and radio transmitters. The
viewshed is used here as a data enhancement tool to aid in the interpretation of geophysical potential field data. The
fraction of the area of a moving window visible from each point on the dataset (considered as if it were topography)
is computed. Since this area changes if the observer is raised above the surface, its vertical derivative can also be
computed. This derivative was found to be a useful method of enhancing subtle features, and is demonstrated on
aeromagnetic and gravity datasets from South Africa.
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A New Gravity Isostatic Anomaly Map of South Africa
Authors C.J.S. Fourie, R.H. Stettler and L. CroukampAll over the world, Geophysical test sites are developed to test situations that would most probably occur in surveys.
These test sites can be in laboratories [1],[2],[3],[5], or physical [4]. Environmental test sites are the the easiest to
develop. The planned test site will be developed to test the responses of shallow buried objects. All the artifacts that
will be buried at this test site, could have an environmental inclination.
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3D seismic tomography for subsurface tunnel preliminary studies in Barcelona
Authors R.C. Bertran, E. Gillot, D.M. Linares, T.A. Marco and R.M. MartinezDrilling galleries with tunnelers is subjected to strict technical requirements. The anticipation of
obstacles in advance of the tunnelling is essential to the operations and the in-site day-by-day safety.
The recognition of the fractured zones and the circulation of water are the objectives of this
methodology combining high-resolution seismic and 3D tomography.
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Pole Reduction with Variable Geomagnetic Field Parameters
Authors G.R.J. Cooper and D.R. CowanBecause of the dipolar nature of the geomagnetic field, magnetic anomalies located anywhere other than at the
magnetic poles are asymmetric even when the magnetic source distribution is symmetrical. Pole reduction takes the
anomaly and transforms it into that which would have been measured if the body had lain at the magnetic pole. The
algorithm is usually applied in the frequency domain which has the disadvantage of restricting the application of the
algorithm to regions possessed of constant geomagnetic inclination and declination. A simple algorithm for pole
reduction is suggested here that employs a Taylor series expansion in the space domain. The algorithm is
demonstrated both on synthetic data and on aeromagnetic data from the Northern Territories, Australia.
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Interpretation of a 3D Ultra-High Resolution Chirp Seismic Dataset Acquired by an Autonomous Underwater Vehicle (AUV)
Authors I. Stevenson, L. Martin and G. NgaisiueDe Beers Marine (DBM) have been routinely operating an Autonomous Underwater Vehicle (AUV) as its principle
ultra-high resolution geophysical survey platform since 2001. This platform routinely collects Swathe Bathymetry,
Side Scan Sonar and Chirp Sub-Bottom profiler data in support of DBM’s mining activities for diamondiferous
gravels, offshore the west coast of Southern Africa.
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Deep-Crustal Electrical Imaging Beneath the Vredefort Impact Structure, South Africa, Using Broadband Magnetotellurics
Authors M.R. Muller, S.J. Webb, A.G. Jones, W.H.B. Steenkamp, P. Kowalczyk, R.L. Evans, C.J.S. Fourie, C. Smith, A. Mountford and the SAMTEX teamMagnetotelluric (MT) data have been recorded along a 200 km-long profile across the auriferous Archaean
Witwatersrand Basin, South Africa, (Fig. 1) as part of the broader, multi-institutional Southern African MT
Experiment (SAMTEX).
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The Calibration of CSAMT Data in a Strong Magnetic Background
Authors O. Terblanche and J.J. van der WaltCSAMT has become an important tool for De Beers in areas with sedimentary cover for the delineation of
kimberlites and surrounding country-rock geology. This method provides high-resolution conductivity sections
from which geologic horizons can be interpreted and combined with other datasets to generate 3-D geologic
models. However, confirmation drilling in some environments has demonstrated a constant depth exaggeration. An
average exaggeration of 30% was observed.
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Fractal analysis of African River basins, Paleo-Drainage Reconstruction and Related Ecological Economics
Authors J. Stankiewicz and M. de WitRiver systems are often referred to as a type-example of fractal geometry in Nature.
We test this for major river basins across Africa and investigate deviations from
perfect fractals to test for geologic and climatic variables, and determine thresholds
relevant to future surface water supplies.
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Hydrogeological Effects on Superconducting Gravimeter Measurements at Metsahovi in Finland
Authors T. Hokkanen, K. Korhonen, H. Virtanen and M. PirttivaaraThe purpose of this study is to gain a better knowledge of superconducting gravimeter (SG) data at the
Metsähovi Gravity Station in Southern Finland. SG data have a high accuracy (1 ngal) and are very sensitive
to various environmental and hydrogeological effects. So, before we are able to investigate their effects on
data we must isolate them and analyze their characteristics.
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Processing of Multicomponent Seismic Data Acquired on Transects in Barents-Kara Region
More LessThe main purpose of this project is to find a way of estimating porosity using 3D-seismic data. Here the development of
a method for processing and interpretation of multicomponent seismic data is presented.
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