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MONTHLY TALKS
If anyone has ideas for speakers/talks, please contact a council member
SAGA TALK – FRIDAY 210th Feb 2012 Venue: CSIR Carlow Road A new generation of low-noise EM sensors James Macnae (RMIT University) With funding from Abitibi Geophysique of Val Dor, Quebec, Chung and Macnae at RMIT University in Melbourne, Australia designed and tested compact magnetic B and dB/dt sensors suitable for geophysical operation, named ARMIT sensors. The sensors monitor the current and voltage induced in a “perfect” test conductor within the sensor. ARMIT sensors use a coil with a nano-engineered magnetic core materials to increase inductance L and proprietary resistance-reduction methods to engineer a very low resistance R and hence an arbitrarily large sensor time constant t = L/R. Prototype models have been designed with t in the 0.1 to 1 sec range. As long as t is comparable to, or preferably greater than any target time constant of interest, the sensor quantitatively measures the target decay, with a mathematically exact and known low-frequency roll-off. However, when data is stacked into a continuous time series, as in the Smartem 24 instrument for example, the response can trivially be deconvolved to recover the B or dB/dt field response free of sensor distortion. The ARMIT sensors were based on improvements to the design of a specific medical B field sensor, and have lower noise levels than published results for High Temperature Squids over the bandwidth of interest. Laboratory and field tests confirm that a 50 cm long sensor of mass less than 1 kg can be constructed with noise levels between 1 pT and 10 fT per √Hertz over the 10 Hz to 100 kHz bandwidth respectively. The sensors are robust, and a rigid 3-component mounting box with accelerometer orientation permits rapid field deployment without the need for levelling. Research continues to adapt the sensors for airborne and borehole environments, and to act as NMR sensors in hydrogeophysical applications. SAGA TALK – FRIDAY 29 JULY 2011 Venue: CSIR Carlow Road On Newton, Caverns and Wild Canines Presented by Gavin Selfe is a free-lance consulting geophysicist based in South
Africa who works all over Africa for mining and exploration companies.
In the past he worked for Anglo American and De Beers, and has 23 years
experience in the exploration game, travelling as far afield as Oman,
Russia, Brazil and Australia. His passions are Africa’s wild places and
her wildlife, with an eclectic mix of photography, mountain biking and
fly-fishing thrown into the fray. He is also currently vice-president of
SAGA and editor of SAGA’s 6-monthly newsletter. Abstract Gavin Selfe presents an informal and (hopefully) entertaining talk on two large scale gravity surveys for buried caverns in the remote Drotsky’s caves area of NW Botswana, at the behest of the Botswana government. Having faced visits from wild dogs and hyenas whilst on survey, torrential rain and flooding, blistering heat, burst radiators and dust storms destroying their camp, Gavin takes us through the technical and non-technical aspects of the surveys, and presents the surprising interpretation and results. The subsequent and exciting discoveries of pristine and beautiful caverns beneath the semi-desert dunes, never before seen by human eyes, will almost surely result in a new tourist attraction for 4x4 enthusiasts in the years to come. Roger Ellis, the leader of the team of intrepid cavers that has explored the new caves, will also be present at the talk, and will use the last 15-20 minutes to show an interesting set of slides of how the caves were entered and of course, the first mouth-watering snaps of some of the caverns.
FRIDAY 25 MARCH 2011 Recent advances in the role of Vertical Seismic Profiles (VSP’s) in exploration, mine planning and development. Presented by Charles Pretorius from Anglo American Venue: CSIR Carlow Road Time: 17H00 Abstract Vertical Seismic Profiles (VSP’s) have a significant role to play in mineral exploration, mine planning and development, particularly where high-resolution structural imaging is required in close proximity to drillholes: VSP’s utilise a surface source and sub-surface receivers deployed down a drillhole. This means that seismic energy only goes through the near-surface weathered layers once during the recording process and there is less attenuation of high frequencies compared to surface seismic surveys. Hence structural resolution can be improved. By deploying 3-component downhole receivers, both compressional (P) and shear (S) wave energy can be efficiently recorded and the S-wave images offer further improvements in structural resolution. Anglo Platinum, in collaboration with Anglo American and CGG Veritas, have conducted extensive 2D and 3D VSP imaging in the Bushveld Complex . They have found the VSP technique to be a useful complement to surface 3D seismics in the structural sterilisation of new shaft sites, prior to shaft sinking. P wave VSP data offers up to a 30% improvement in vertical resolution close to the deployment drillhole, compared to surface seismics, while improvements of up to 80% can be achieved with mode-converted shear waves. By conducting VSP surveys in multi-client batches it is possible to reduce per-borehole costs by up to 50%. A sustainable, commercial VSP service would probably require such multi-client collaboration, at least during the launch phase. The technical and economic benefits should justify the additional organisational effort. Local Magnitude Scale (ML ) for South Africa using data from tectonic earthquakes recorded by the South African National Seismograph Network during the period 2006 to 2009 By Ian Saunders, Seismic Network Manager, Seismology Unit, Council for Geoscience Email: ians@geoscience.org.za An equation to determine local magnitude (ML) based on the original Richter definition was empirically derived from synthetic Wood-Anderson seismograms recorded by the South African National Seismograph Network. In total, 196 earthquakes in the distance range 30 to 1000 km were considered to derive an attenuation equation appropriate for South Africa through inversion. Additionally, station corrections were determined for 29 stations through regression analysis resulting in values ranging from between -0.44 and 0.19 for stations operated under unfavorable conditions. The stations considered (66% of all available stations) have corrections between –0.1 and 0.1. The most appropriate ML scale for South Africa from this study satisfies this equation: ML=log10(A) + 1.075 log10 (R) + 0.00061R – 1.89+S with A the maximum amplitude determined from instrument corrected synthetic Wood-Anderson seismograms at a hypocentral distance R. S is the station correction term. The anelastic attenuation term derived from this study indicates that ground motion attenuation is significantly different from southern California but comparable with other intraplate regions. A distance correction term is added to anchor the equation to the definition of Richter (1935) for southern California. Links between basement configuration and orogene collapse as revealed by gravity and magnetics - Examples from Norway - By Jörg Ebbing
Venue:
Fugro Airborne, 22 Packard St, Woodmead Analysis of gravity and magnetic data are used to study the architecture and evolution of the Norwegian margin. Extrapolating onshore structures to the offshore realm, it can be deduced that NE-SW trending (i.e. orogen-parallel) late Caledonian gravity collapse played an important role in shaping the margin architecture. Magnetic anomalies link detachment zones onshore to structural highs offshore. Of particular interest is the recognition of the structurally denuded basement culminations onshore Norway, which are bound by the detachments. These structural highs contain high-density and highly magnetised rocks of assumed lower crustal origin, which can be interpreted to represent reactivated core complexes. By 3D modelling integrating a wealth of geophysical data (e.g. seismic profiles, petrophysical sampling and gravity and aeromagnetic data), the distribution and thickness of basement domains (e.g. Caledonian and Precambrian basement) can be resolved in detail, and it is shown that the crust is thinned from `normal´ or moderately reduced thickness down to 10 km or less over significant parts of the margin. The high-velocity, high-density lower crust on the margin is another feature of ongoing discussion and whether it reflects magmatic underplating, serpentinization or eclogitization of Caledonian lower crust. This lower crust tapers out below the onshore mountains, but is an important contribution to the isostatic state of the entire passive margin system and relates to the missing root of the present-day Scandes mountain chain. Biography Jörg Ebbing has a Master from University of Kiel (1999) and a PhD from the Freie Universität Berlin (2002). After the PhD he joined the Geological Survey of Norway (NGU), where he now is assistant team leader of the Continental Shelf Geophysics team, which is responsible for the gravity and magnetic data onshore and offshore Norway. He holds additionally an adjunct professorship at the Norwegian University of Science and Technology (NTNU), Trondheim, where he teaches courses on gravity and magnetics. In all the research projects interdisciplinary approaches with special emphasis on potential fields and integration with deep seismic results and geological studies are applied. He is currently active in research projects studying the lithospheric structure of the Norwegian continental margin and Africa, as well in projects on joint inversion of multiple geophysical data sets.
SAGA TALK – SEG Honorary Lecture
2009 Middle East & Africa Honorary Lecturer (SEG) Sponsored by Shell Multi-azimuth Seismic in the Nile Delta, Egypt Presented by Samir Abdelmoaty BP Egypt
The Nile Delta has emerged as a world-class hydrocarbon basin owing to significant gas and condensate discoveries. Early exploration relied on the use of direct hydrocarbon indicators (DHIs) and proved very successful in the shallow Pliocene section. More recently, significant pre-Messinian- (Miocene and Oligocene) aged discoveries have been made, opening these deeper high pressure, high temperature (HPHT) play fairways. However, detailed planning is needed to manage the cost and to mitigate the operational risks of drilling these wells, as well as the successful appraisal and development of the discovered resources.
A major obstacle to exploiting these resources is seismic data quality. In large areas of the offshore Nile Delta, a thin but complex Messinian-aged interval, consisting of anhydrite and interbedded sands and shales, lies immediately above the deep reservoirs. This interval often generates wavefield distortion, attenuation, and the generation of complex multiple diffractions which degrade the underlying seismic image. To overcome this challenge, an innovative acquisition solution was developed and implemented: multi-azimuth seismic (MAZ). Simply put, MAZ is a program in which multiple passes of seismic data are shot over the same subsurface point but at varying azimuths to one another. The resulting data can then be stacked to produce an image with superior noise and imaging characteristics. In addition to the image quality improvements, recent studies have shown that MAZ data may also offer a unique opportunity to further characterize the subsurface by exploiting the multiple independent measures of the overburden and reservoir. The higher cost of MAZ has been offset by delivering a significant reduction in the risk and expense of deep HPHT drilling operations. MAZ has also proved to be an excellent front-end loading tool to optimize the appraisal and development program and reduce the risk and cost of major projects. Biography Samir Abdelmoaty, received his B.Sc. degree in physics and geology from Cairo University in 1971, followed by a Diploma and M.Sc. in geophysics. Recently, Samir attended The Management Program at Rice University and the International Management Program at Texas A&M. In 1972, Samir began his career with the Academy of Scientific Research before joining GUPCO in 1976. He was seconded to BG Egypt as the chief geophysicist in 1989. Returning to GUPCO, he progressed through several positions ending as the Geophysics general manager. In 1993, Samir become the president of PGS Tensor Middle East. In 1995, he joined BP Egypt (then Amoco) and currently, he is the deputy Exploration Performance Unit leader. Samir is a Life Member of SEG, member of EAGE, AAPG, and the president of the Egyptian Geophysical Society. Contributions to this lecture by BP colleagues Brian Barley, Walter Rietveld, Bob Marten, and Jim Keggin are gratefully acknowledged. When: Thursday 22 October 2009 at 17h00. Where: CSIR – Mining (Auditorium) Corner of Rustenburg and Carlow Roads, Auckland Park, Johannesburg 3D Inversion, Integration, and Visualization of Regional-Scale Gravity, Magnetic, and Electromagnetic Data for Mineral Exploration Speaker: John McGaughey (President of Mira Geoscience and the Advanced Geophysical Interpretation Centre) Abstract: The Mira Geoscience Advanced Geophysical Interpretation Centre has completed 3D inversion modelling, integration, and visualization of airborne gravity, magnetic, and electromagnetic data for the regional “QUEST” project area, BC, Canada. This was undertaken for Geoscience BC as follow-up analysis of QUEST project geoscience data. The objective of this work is to provide useful 3D physical property products that can be directly employed in regional exploration to target prospective ground based on different exploration criteria. This work considers all airborne gravity, magnetic and electromagnetic data available for the QUEST project area. The inversions were performed using the UBC-GIF GRAV3D, MAG3D, and EM1DTM, suite of algorithms for the gravity, magnetic, and AEM data respectively. The products are 3D inversion models of density contrast, magnetic susceptibility, and electrical conductivity, and integrated products combining the individual physical property models. These are provided for each of the five regions of the project area (A, B, C, D, and NT). The gravity and magnetic data were modelled in 3D using several smaller tiles after separation of regional signal. The tiles were combined to construct a detailed model over the whole area. The conductivity data were inverted for 1D (layered earth) models using a laterally parameterized method and subsequently interpolated in 3D. A late-time, background conductivity map has also been produced for the survey area. An estimate of the depth of penetration has been provided for the AEM conductivity models. The resulting models provide guidance to the regional structure and prospective geology and location of alteration and mineralization. Final density contrast, magnetic susceptibility, conductivity models have been integrated into a Common Earth Model ready for 3D GIS analysis, interpretation, and integration with geologic, drill-hole, and other geophysical information. The extensive set of digital deliverable products that accompany this report include: physical property cut-off iso-surfaces, observed and predicted data, and the inversion models in several different, commonly used formats. A suite of 3D PDF scenes have been produced to aid in visualization and communication. The resulting physical property models can be used to guide regional targeting and help design more detailed, follow-up data acquisition. The inclusion of geologic or physical property information in the inversion from maps, drill-holes, and samples was not within the scope of this project, although it is expected that the integration of these data would improve the resulting models, especially at the local scale.
FRIDAY 5 JUNE 2009 VENUE: FUGRO AIRBORNE SURVEYS, 22 Packard St, Woodmead TIME: 17H00 TOPIC: "Determining the focal mechanism of mine tremors - SA's contribution to the detection of clandestine tests of nuclear bombs" by Dr Ray Durrheim (CSIR) The talk describes work, funded by the US National Nuclear Safety Program, that Wits and CSIR is doing in collaboration with Penn State University and the Lawrence Livermore National Laboratories in the USA. BRIEF CV Ray started his career as an exploration geophysicist with Gencor. He was involved in gold, coal and base metal projects, gaining field and interpretation experience in ground and airborne magnetics, gravity, resistivity, CSAMT, IP, ground and airborne EM. Ray was appointed a lecturer in the Geophysics Department, Witwatersrand University in 1983, where his research activities included investigations of the crust and upper mantle using both explosive and mine tremor energy sources, and the application of the reflection seismic method to gold and platinum exploration. Ray joined CSIR in 1993, where he is a Fellow in the CSIR Natural Resources and the Environment Unit. While at CSIR he has conducted mine seismology research, managed the DeepMine and FutureMine Collaborative Research Programs, was seconded to the Mining and Mineral Sciences Laboratories of Natural Resources Canada in Ottawa during 2003, and is now the leader of the project “Minimising the Rockburst Risk”, sponsored by the Mine Health and Safety Council. Ray was appointed to the Wits/CSIR South African Research Chair in Exploration, Earthquake and Mining Seismology in April 2007. Ray is a registered Professional Natural Scientist; a member of the South African Geophysical Association (SAGA), Society of Exploration Geophysicists (SEG), the American Geophysical Union (AGU), the South African National Institute of Rock Engineering (SANIRE); and a Fellow of the South African Institute of Mining and Metallurgy (SAIMM). The honours he has received include the Salamon Prize (1998) for the best rock engineering paper authored by a member of SANIRE, the CSIR Outstanding Achiever Award (1999), and the SAIMM Silver Medal (2003) for the paper (co-authored by Fernando Vieira) entitled "Probabilistic mine design methods to reduce rockburst risk" SEG Distinguished Lecturer 2009 Download PDF Flyer (40kB) Date: Mon 18 May 2009 2009 Spring Distinguished Lecturer Integrating Seismic Acquisition and Processing Presented by Jack Bouska BP Corporation, Muscat, Oman Years of seismic specialization among practicing geophysicists have segregated acquisition, processing, and interpretation into separate functions, which makes it difficult for any individual to treat the whole seismic process as a single integrated system. From experience, I have developed a sometimes elegant, occasionally cumbersome, but always effective methodology which assimilates the tasks of acquisition design, seismic processing, and interpretation into one coordinated procedure. Decisions regarding acquisition parameters, survey geometry, and processing flow must be driven by interpretation requirements. These choices are guided by analysis of acquisition and processing tests applied to existing data sets rather than the more common practice of simply replicating the parameters used on previous surveys. This lecture will impart a concise but comprehensive introduction to the art of seismic design, data processing, and imaging with the overall goal of forging a unified system for the sole purpose of producing optimized products for pre- and poststack interpretation and attribute extraction. The lecture format will present cutting-edge case histories exposing both the philosophy underlying the whole process, as well as the specific strategy and tactical implementation of design and processing techniques used to achieve the interpretation goals. Biography Jack Bouska graduated with a geophysics degree from the University of Alberta (1980. He joined Seiscom Delta as a processing geophysicist in 1981, and moved to Western Geophysical’s computing science department in 1983. Joining Dome Petroleum in 1985, he remained through the merger with Amoco in 1988, and again through the merger with BP a decade later. During his tenure with Dome, Amoco, and BP, Bouska tackled a variety of roles including seismic processing and acquisition specialist duties in various incarnations of the geophysical technology groups, as well as performing seismic interpretation in Western Canada. In 1998, he moved to London and spent nearly a decade with BP’s Exploration and Production technical team in Sunbury (U.K.) During this time he consulted on seismic acquisition and processing projects from around the globe and led the development and instruction of BP’s internal course on seismic acquisition. Bouska currently works and resides in Muscat, managing BP’s seismic acquisition and processing projects in Oman. Bouska's innovations in acquisition design and processing have been recognized by CSEG with the Best Theme Paper award in 1995 (Sparse 3D), and Best of Session papers during the 1997 and 1998 CSEG conventions. SEG recently awarded him the Best Paper in THE LEADING EDGE 2005, and Honorable Mention in Best Paper category, 2005 SEG Annual Meeting. Bouska also served as an EAGE seismic acquisition short course instructor for 2007 and an EAGE Distinguished Lecturer in 2007-2008. Jack is an active member of EAGE, SEG, CSEG, and APEGGA. TWO SAGA TALKS TALK1: Background Info: The talk will explore the various techniques that are undertaken with and within the data acquisition aircraft prior to flight production taking place. These techniques include, • A radar/laser altimeter test CV Joel is a Wits' postgraduate (2006) from the prestigious School of Geosciences where he studied geophysics. Whilst at Wits, his research centred on , "Processing of an aeromagnetic dataset from Polokwane", which was sponsored by the Rio Tinto Mining & Exploration (RTME). He is also a proud holder of a BSc (Hons) in Applied Physics from the National University of Science and Technology (Zim). Of recent, he has been involved with Fugro Airborne Surveys, processing their airborne geophysical data around the world, including being part of Fugro's team that handled high profile jobs with the European Union (EU) in Ghana and the World Bank in Nigeria. Joel is married and has unwavering interests in, Image processing, wavelets and the inverse theory and likes tormenting his mind by regularly participating in chess tournaments. TALK 2: ABSTRACT Seismic activity in deep underground mines is an inevitable consequence of the mining operations having adverse implications on safety and productivity. Therefore seismic hazard assessments are of importance and have been studied for main events. This study, however, assesses the hazard posed by aftershocks following larger seismic events (ML>=2.0). The study follows two approaches: (1) Statistical analysis, where the properties of stacked aftershock data are studied using empirical relations. The time taken for the seismic activity rate to decrease to background levels is determined. (2) Deterministic analysis, where the relationship between mining conditions (stress level, strain rate and proximity to geological features) and aftershock productivity is investigated. The findings of this study will provide guidelines governing re-entry to working areas following a seismic event. The presentation will focus on deterministic analysis. BIOGRAPHY Thabang Kgarume obtained his BSc (honours) Geophysics from the University of the Witwatersrand in 2006 and is currently pursuing an MSc degree in Mine Seismology, studying mine tremor aftershocks of deep gold mines and their implications on seismic hazard assessment.
Date: Friday 6 March 2009 Time: 16h00 Venue: Fugro Airborne, 22 Packard St, Woodmead SITE CHARACTERIZATION USING MULTICHANNEL ANALYSIS OF SURFACE WAVES SUMMARY The dispersive nature of surface waves can be used to extract near-surface elastic properties of the surface and the application of the technique has developed into a routine tool for shallow subsurface investigations. Surface waves can generally be generated with ease, making the technique robust and attractive to use. The primary objective of the technique is to extract shear wave velocities as a function of depth and distance, and shear wave velocity sections can be generated by using a roll-along approach similar to seismic reflection surveys. This also allows the technique to be used to map anomalous subsurface variations, and to map bedrock topography, mapping of faults, fracture, weak zones and voids. The MASW (Multi-Channel Analysis of Surface Waves) technique makes use of a multi-channel approach (similar to seismic reflection) to separate the different modes of vibration, and also to separate surface waves from body waves. The method has developed into active and passive applications, where the passive method uses cultural and natural noise to increase depth of penetration. Basic theory, data acquisition, data inversion and applications will be presented. Biography - Alten du Plessis Alten obtained an MSc in physics from the university of Stellenbosch. After completing his national service as a physics lecturer at the Military Academy, he was employed by the South African Government at both the Atomic Energy Corporation and the Department of Minerals and Energy. Here he worked on interesting and challenging projects such as the configuration of a prototype uranium enrichment laser system and the implementation of national energy efficiency policies. He was also part of the government team that worked on the bi-national energy agreement with the USA. In the end of 1996 he joined ISS Geophysics where, most notably, he participated in the Deepmine research projects and investigated the feasibility of underground use of borehole radar, seismic reflection and ultrasonic emissions to image geological features and determine hangingwall stability. He also developed a portable passive/active seismic monitoring system as well as the prototype software for analysis of surface waves. In 2001 he established Global Geophysical and currently provides geophysical consulting services in mining, environmental, engineering and geotechnical disciplines.
Venue: CSIR, corner of Rustenburg and Carlo rd, Mellville JHB Airborne magnetic and electromagnetic data map rock alteration, water content and ice thickness at Mount Adams, Mount Baker and Mount Rainier, Washington: Implications for lahar hazards and hydrothermal systems by Dr. Carol Finn, U.S. Geological Survey Abstract High resolution helicopter-borne magnetic and electromagnetic (HEM) data flown over the rugged, ice-covered, highly magnetic and mostly resistive volcanoes of Mount Rainier, Mount Adams and Mount Baker, along with rock property measurements, reveal the distribution of alteration, water and hydrothermal fluids that are essential to evaluating volcanic landslide hazards and understanding hydrothermal systems. Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows. In addition, the HEM data was used to determine the ice thickness over large areas on Mount Baker and Mount Adams, important for understanding the hydrologic potential of the volcanoes. CV:
Dr. Carol Finn is a senior research geophysicist at the U. S. Geological
Survey. Her research interests are quite broad, but currently focus on
the application of magnetic and gravity data worldwide, along with other
geophysical techniques, to identify the subsurface distribution of
Dr Branko Corner, a past President of SAGA, based in Namibia, and an
independent geophysical consultant for the past 15 years, will be giving
a SAGA talk, which is an upgrade of the Radon U Exploration case studies
he gave at the ASEG last year: In this study the implementation and refinement of the Radon-on-Activated-Charcoal (ROAC) technique, developed by the South African Atomic Energy Board in the 1970’s, is discussed. Case study results using this technique (here referred to as RadonX) are presented, from two areas in Namibia. Depth of detection is investigated as well as correlation with drilling results. Radon emanometry is based on the ability of radon, a gaseous daughter product of uranium contained in ground air, to migrate to surface through porous and permeable cover sediments, as a result of the pumping action of diurnal pressure variations. With the RadonX technique the radon is adsorbed onto activated charcoal contained within a cartridge, fitted into the base of an inverted cup, and buried in the ground. The technique differs from alpha-sensitive radon detection systems in that it measures the gamma radiation arising from the daughter products of the adsorbed radon, namely 214Bi and 214Pb. The case study data are derived firstly, from an orientation survey over a known buried palaeo-channel of duricrust-hosted uranium and, secondly, from an exploration area potentially hosting uraniferous granites where the sand cover varies in thickness from 30 to 100m. Time domain electromagnetic (TDEM) soundings provided cover thickness and conductivity (porosity) data. The surveys show:
CV: Dr Branko Corner Branko obtained a BSc degree in Geology and Physics from Wits in 1969, where he went on to complete his BSc Hons, MSc and PhD degrees in Geophysics. He has 39 years of experience in geophysical exploration, teaching and research. His expertise includes the interpretation of all types of ground and airborne geophysical data sets, specializing in the synergistic interpretation thereof with geology. Branko was an Associate Professor and Head of the Department of
Geophysics at Wits from 1982-1993. His additional 27 years of
industry-related work were, and still are, focussed on the exploration
for base and precious metals, nuclear fuels, diamonds and groundwater,
throughout Africa. He also played a major role in establishing the
National South African radiometric calibration facilities, and in
implementing the quantitative usage of field gamma spectrometry in
uranium exploration. Branko has provided applied geophysics coursework
to numerous exploration companies, and still provides annual courses to
the Geology and MSc Exploration Geology students at the Universities of
Namibia and Rhodes. Branko established a geophysical consulting practice
15 years ago, and is based in Namibia. He still publishes and is author
or co-author of 17 refereed publications and 31 Conference proceedings.
He is also a recipient of the Henno Martin Medal for his contributions
to furthering an understanding of Namibian geology.
Friday 21 Nov 2008 "The Magnetic Stratification of Mafic Layered
Intrusions: Natural Examples and Numerical Model" Venue: Fugro Airborne, 22 Packard St, Woodmead Time: 17h00
Several recent investigations have been
conducted on borehole cores through the Insizwa sill (South Africa), the
Great Dyke (Zimbabwe), and the Bushveld Complex (South Africa). We
present an overview of magnetic results on these intrusions. All intrusions display distinct variations of their magnetic properties (magnetic susceptibility, degree of anisotropy, shape factor, magnetic remanence, magnetic saturation, high field magnetic susceptibility) across the layering. The significance of these magnetic zones varies depending on the nature of variations from zone to zone. For example, a drop in magnetic susceptibility does not necessarily correspond to a new magma batch, unless it is also associated with a change in magnetic anisotropy parameters. In the studied cases, all open systems, the magnetic susceptibility and the total iron content (estimated from high field measurements) increase towards the top of these intrusions suggesting a general pattern of ironenrichment. A numerical petrologic model for a tholeiitic
magma predicts magnetic susceptibility variations across a statically
differentiated, closed system intrusion (no convection). The effects of
sequential magma recharge and discrete magma extraction are investigated
from the magnetic properties point of view. Conversely, these models can
be used to interpret the magnetic stratification pattern in natural
examples and Friday 3 October 2008 "Recent Low Temperature SQUID (LTS) case studies" by Ockert Terblanche, Anglo American Exploration Division Venue: Fugro Airborne, 22 Packard St, Woodmead
Fri 1 Aug - 17h00 at Fugro, 22 Packard St, Woodmead Enhancing Potential Field Data by Gordon Cooper (School of Geoscience, University of the Witwatersrand) There are a wide range of filters available for squeezing information from potential field data, such as derivatives, the Tilt angle, Theta map, etc. This talk will compare most of the filters in common use and also introduce some new filters. This talk was given at the EAGE conference in Rome in June 2008.
Fri 4 July - 17h00 at Fugro, 22 Packard St, Woodmead by Dr Stoffel Fourie on his PhD research work A new geophysical method was developed to satisfy a need for in-situ density measurements. Various situations, such as a gravity dam wall requires that density measurements should be done without damage to the structure. The sample volume should also not be that large in order to be sensitive enough for variations. This method measures the in-situ density of the weathered layer and other man made structures, using seismic waves in three directions. The seismic waves utilized are P-waves and S-waves. It is however surface waves that are treated like body waves because they do not separate at this shallow depth. These waves are very sensitive to the attenuation factor, which is in turn sensitive to certain physical properties of the propagation medium. This factor is utilised when the multi layer problem is encountered. The maximum depth of exploration is 2-5m and depends solely on the seismic skin depth. This method utilises a large base plate. The source is a large sledge hammer and shots are done at each side of the base plate. Different dominant frequencies are identified and used to calculate the densities of the layers associated with that specific frequency. The velocities of the subsurface are determined by small seismic refraction surveys. The method will find application mainly in the civil and engineering geology fields. The main application will be to determine subsurface densities and small movement elasticity modulli for engineers to aid in obtaining adequate design parameters. Case studies on three different geologic environments are presented. The results indicate that this method will be useful, although certain modifications are recommended to make this method even faster and more user friendly. TUES 13 May 2008 - SEG Distinguished Lecturer, Tad Ulrych Abstract: The purpose of this presentation is to convince you that treating amplitude and phase with the equal dignity that each deserves can lead to some interesting and important results. Specifically, I will deal with only-phase reconstruction, by which I mean the inversion of information by using only the phase component without any a priori assumption concerning the amplitude (championed by Alan Oppenheim and colleagues in the early 1980's). I will also reintroduce, after a 35 year absence from this field and because of exciting new developments, cepstral processing and its application to the deconvolution of thin beds. Finally, I will foray into the dangerous territory of attributes. Dangerous because there are so many and dangerous because I know so little. However, my colleagues (Mauricio Sacchi, Mike Graul, and Tury Taner) and I have recently had some hopefully interesting thoughts and results which we would like to share. A picture is, of course, worth a 1000 mumblings and so here is one. Figure 1a shows an image, the ? is mine. Research group RFOA receives only the amplitude spectrum, combines it with their best guess at the phase spectrum (=0 for example) and reconstitutes the image as shown in Figure 1b. Their conclusion? The image is that of a cloudy sky. Research group RFOP combines the received phase spectrum with their best guess at the amplitude spectrum (=1, for example), reconstitutes the image as shown in Figure 1c and concludes that Tristan and Isolda are in love. This is an example not of only-phase, but of phase-only. The former produces results that are even more informative.
CV: He has been an Invited Professor at PPPG (now CPGG) at the Federal University of Bahia, the University of Kyoto and OPERA, University of Pau. He has consulted and given courses in various locations around the globe, and continues to do so in spite of mandatory retirement which earned him his present position of Professor Emeritus (office, graduate students, research projects, no salary but free parking). Tad's interests are signal processing, information and inverse theory, and a plethora of other topics that change bimonthly. He has supervised a few students, published some papers and coauthored a book with Mauricio Sacchi. His hobbies include visits to the Pyramids of Giza with his most cherished wife, via camel. MAGNETIC ILLUMINATION OF KIMBERLITES AT PROJECT ALTO CUILO by Wayne Pettit (BHPB) 17h00 Fri 01 Feb 2008 The Alto Cuilo Project straddles the boundary between the Lunda Norte and Lunda Sul provinces in north eastern Angola and is located about 80km southwest of the town of Saurimo. Kimberlite outcrops and alluvial diamonds exist in the concession. A number of kimberlite type magnetic anomalies were identified at Alto Cuilo in 1997 in a fixed wing magnetic and radiometric survey based on 250m spaced flight lines and 80m sensor height. Subsequent ground based follow up to position drill collars has been hampered by the risk of unexploded ordinance. A low level helicopter borne magnetic survey was commissioned to replace the ground magnetic surveys. In July 2005 Fugro Airborne Surveys acquired over 13,000 line kilometres of horizontal magnetic gradiometer data with their proprietary MIDASTM system. The survey was flown on north-south lines spaced 100m apart with an average terrain clearance of 20m. A 5km square area around the Mussunuige-Luangue Complex was filled in to 50m spacing. The survey covers the northern 40% of the Alto Cuilo concession where the Kalahari cover thickness is more permissive of mining, the sands being between 30-100m thick. The helicopter data provide a far greater resolution of the previously identified magnetic anomalies enabling optimal drill sites to be selected. The data also identify a number of large subtle anomalies either not detected or poorly defined by the earlier fixed wing survey. In addition noisy and mottled textures in the magnetic data may be indicating the presence of magnetic sediments derived from the kimberlites. In total 244 magnetic targets have been identified in the helicopter magnetic survey, including at least 16 possible alluvial targets. Amongst the kimberlite vent type targets there are 5 having a surface area greater than 100ha, 40 above 20ha and 63 above 12ha. The largest pipe-like anomalies are located in the Extended ML Complex and in the Mussunuige West Block, all within a 12km radius of the existing camp. The many targets have been grouped into blocks defined by the major north-south river systems which hamper east-west movement of machinery. The blocks are prioritized in terms of potential to host large volumes of kimberlite. The targets are then prioritised for testing based primarily on the surface area of the observed magnetic anomaly and secondly on the logistical challenges involved. All access routes will be cleared with an armoured bulldozer. Brief CV Wayne hails from Zambia, the son of a land surveyor on contract to the British Government. With the move to that country’s independence the family relocated to Pietermaritzburg in KwaZulu-Natal, South Africa. There he matriculated from Maritzburg College and went on to study geology and physics at the University of Natal, PMB. After a stint in the armed forces Wayne returned to his studies in the earth sciences and completed an honours degree in geophysics at WITS. Directly upon graduation in 1988, Wayne was hired as a junior geophysicist by General Mining Corporation. He has stayed with the company through the years of transformation and change. Today he is the geophysics leader in Africa for the Mineral Exploration Department of BHP Billiton. In 1990 Wayne married Lee-Anne Calitz, a girl from the East Rand gold and coal mining towns. The couple currently lives in Johannesburg with their four children. The family returned in 2005 from a two year assignment in South America, and since then Wayne has been actively exploring for kimberlites with BHPB and its partners in Angola. 17h00 Tuesday 27 November Ken Witherley from Condor consulting: "Mapping targets of high
conductance with the VTEM airborne EM system" The VTEM airborne EM system has been in commercial use since later 2002 and has been applied to a wide range of mineral exploration targets on a global basis. While designed to have a broad-band conductivity response, certain styles of deposits such as magmatic Ni-Cu can show conductances which exceed the measuring aperture of the VTEM system as first designed. In 2006, Geotech Ltd. introduced a modified VTEM system which allowed for the enhanced mapping of targets of high conductance. We will present results from a number of such situations showing the comparison of airborne and ground results.
Fri 31 Aug 2007 - 17h00 at Fugro, 22 Packard St, Woodmead Some thoughts on the application of borehole wireline geophysical logs in rock mass geotechnics by Kazek Trofimczyk (Anglo American) Borehole geophysical logging has come a long way since the turn of last century. Applications in the mineral industry have tended to focus on mapping of lithology and lithological boundary contacts. More recently people have begun to see the value of acquiring in-situ physical property measurements for rock mass geotechnical applications. This talk highlights a few examples of where downhole geophysical logging can add value to rock engineering analyses. Brief CV: Kazek graduated from Wits University in 1992 and has been employed as an Anglo American geophysicist since 1994. He's had experience in all the major Anglo divisions, but in particular, De Beers (Kimberlite exploration), Anglo Coal, and Anglo Platinum. The focus of his work in the last 5 years or so has been in borehole geophysics, looking at wireline logging applications, borehole radar and borehole seismics (VSP).
Fri 27 July 2007
Speaker: Allan Place, Manager – Business Development, MDA
Geospatial Services (from Ontario, Canada)
MDA provides advanced information solutions that capture and process vast
amounts of data, produce essential information, and improve the decision
making and operational performance of business and government
organizations worldwide. MDA's Geospatial Services provides Earth
observation data, information products and services from aerial platforms
and the majority of commercially available radar and optical satellites.
These products and services are used globally for resource mapping,
environmental monitoring, offshore oil and gas exploration, ice
reconnaissance, maritime surveillance and disaster management. Fri 22nd June 2007
Speaker: Vic Simmonds - MD Crimesight (www.crimesight.co.za)
Fri 30th March 2007 @ CSIR (cnr Rustenburg & Carlow Rd, Emmarentia) - 17h00 Geological storage of carbon dioxide and the role that geophysics
can play by A brief introduction to the new field of storing carbon dioxide emissions in geological formations, followed by an overview of how geophysical methods are used. The talk will introduce the main storage methods : deep saline aquifers, CO2 flood enhanced oil recovery projects, storage in coals through CO2 enhanced coalbed methane production and storage in depleted oil and gas fields. Possibilities in South Africa and the role of geophysical methods in selecting sites and monitoring CO2 in the subsurface will be covered. Brief CV
Fri 24th Nov 2006 EULER DECONVOLUTION WITH IMPROVED ACCURACY AND MULTIPLE DIFFERENT STRUCTURAL INDICES by G.R.J. Cooper School of Geosciences, University of the Witwatersrand, Johannesburg Euler deconvolution is a semi-automatic interpretation method that is
frequently used with magnetic and gravity data. For a given source type,
which is specified by its structural index (SI), it provides an estimate
of the source location. It will be shown that by computing the solution
space of individual data points and selecting common source locations the
accuracy of the result can be improved. Furthermore, only a slight
modification of the method is necessary to allow solutions for any number
of different SI's to be obtained simultaneously.
Fri 20 Oct - CSIR (cnr Rustenburg & Carlow Rd, Emmarentia) - 17h00 We are privileged to have an SEG Distinguished Lecturer in SA for our next talk. As part of the SEG/AAPG 2006 Fall Distinguished Lecturer Tour, Bill Fahmy (Exxon Mobil Exploration Company) will be presenting the lecture:
DHI/AVO Best Practices Methodology and Application
The first example is from an exploration setting. The example shows how
applying best practices can help identify the risks correctly and set
expectations prior to drilling the first well in a frontier basin. By
using our best practice methodology the main risk identified here was low
gas saturation, even though no low gas saturated sands had previously been
encountered in the area. Subsequent drilling confirmed this prediction.
In summary, for each case history we will present our pre-drill analysis and predictions and share the learnings from the post well drilling results. Also, as an audit of the process, we will show the overall statistics of how the best practices have fared since its implementation.
Friday 28 July 2006 (VENUE: CSIR Miningtek in Melville ) Oil, Minerals, Geoinformation …and Africa’s future by Colin Reeves (Earthworks by Achterom 41A, 2611 PL Delft, The Netherlands) Africa is 22 per cent of the world's land area but attracts less than 1 per cent of the world's foreign investment. Its potential as a world supplier of oil, gas and solid minerals is enormous and, properly managed, these resources could really 'make poverty history' and sustain rapid economic development. But the continent's geology is still largely unexplored, presenting a challenge for sound geo-information management to underpin sound exploration …and a challenge for sound governance to underpin the most basic of human needs
May 05, 2006 The Future of Geophysical Technology: Revolution or Evolution? by Dr. Helmut Jakubowicz of Veritas Research "Come and learn about the exciting new techniques and technologies in geophysics" March 14, 2006 The Electric Earth: Understanding Earth processes from deep-probing
electromagnetic imaging by Prof. Alan Jones, Head of Geophysics,
Dublin Institute for Advanced Studies (Sponsored by: SAGA and Wits
Geosciences (AfricaArray) Abstract Examples will be shown of deep-probing EM studies conducted on cratons in Canada and southern Africa which are contributing to understanding Archean tectonic processes. Also, a region of the Canadian cordillera will be highlighted where by combining the EM results with geochemistry and with laboratory studies of candidate mineralogies representative of the mantle using various mixing laws we can define a maximum temperature for the region.
Friday, 27 January Exploring Yemen While the festive seasons break is still lingering in the back of our minds this first talk of 2006 is not intended as a technical expose but will touch slightly on the history, geology, tectonics, geophysics and of course the exquisite scenery and charm and traditions of this very mountainous country.
Friday, 2 December Semblance Analysis using Wavelets and The Tilt Angle – Theme and
Variations Semblance Analysis using Wavelets The Tilt Angle - Theme and Variations Fri 28 October Electroseismics: Promises, Limitations and Pitfalls The coupling of seismic and electromagnetic energies in fluid-saturated porous rocks has been studied since the early 20th century. However, an electroseismic (ES) theory that incorporates the full set of Maxwell's equations is a fairly recent development (Pride, 1994). This theory shows that two types of ES energy conversion can generally occur in fluid-saturated rock. In homogeneous regions the electric and magnetic fields are carried along with the seismic waves and no radiating EM waves are produced. These fields may therefore be labelled as co-seismic fields. However, when seismic waves traverse boundaries between dissimilar fluid-saturated media, EM waves with the same frequency content as the seismic waves are generated. These EM waves propagate independently from the seismic waves and may be labelled the interface response. Both the co-seismic field and the interface response show promise of yielding valuable information on the subsurface distribution of rock and fluid properties. Both are, however, limited in their application by different constraining factors. These factors, as well as a number of pitfalls in the study of electroseismics, will be discussed.
Fri 05 Aug Recent Developments in Remote Sensing by Andrew Terhorst (Satellite Applications Centre (SAC))
Fri 08 July 2005 - SAGA AGM Talk: "The galaxy, the universe, and everything" by Fabio Frescura
Fri 1 July 2005 The Development of Low Temperature SQUID Systems for the Geosciences Fri 27 May 2005 VENUE: CSIR Miningtek, cnr Carlow and Rustenburg Rds, Emmarentia The Stilfontein seismic event of March 2005 by Friedemann Essrich Friedemann, a seismologist based in Klerksdorp, has travelled around
Stilfontein recording the effects of the seismic event that occurred there
earlier this year. Fri 06 May 2005 Africa Array by Prof. Paul Dirks The Array itself is a network of broadband seismometers across the continent, but it is also a network of researchers and a network of ideas. Operating the array and analysing data that comes from it will provide a good background for many up and coming students on the continent. With the current critical shortage of young geophysicists in the training pipeline, both locally and internationally, this should be interesting to most of us. It will also have particular interest for those who are interested in geophysics at the larger scale.
Application of spectrometric nuclear logging techniques for mining and exploration AUTHORS - Mark Berry, Craig Smith, Mihai Borsaru and Jacek Charbucinski There have been significant advances in the last ten years on the use of spectrometric nuclear techniques for borehole logging applications. At CSIRO, one area of research has focused on the application of prompt gamma neutron activation analysis (PGNAA). This technique can be used to estimate a range of elemental concentrations including Cu, Zn, Ni, Fe, S, Si and others. In addition the technique can be applied to automated lithological interpretation and other important rock property information such as ash content for coal, characterisation for prediction of acid mine drainage and salinity monitoring. This presentation will summarise CSIRO's research in this area and provide a range of case studies where the PGNAA technique has been applied to grade control and production monitoring at operating mine sites around the world. Thur 23 Sept 2004 Comparison of three current airborne systems designed to measure the
earth’s gravitational field and the impact of instrument sensitivity on
mining exploration (Download Extended Abstract - 200kB) Airborne gravity gradiometry is now being used by several companies worldwide for minerals exploration. Although gradient measurement techniques are not new in exploration, the availability of airborne systems represents a major breakthrough in the application of the technology. Several airborne systems are now available (e.g. Bell Geospace’s FTG, BHP Billiton’s Falcon system, ARKeX’s FTGeX) with others still in the development stage (e.g. ARKeX’s EGG, Gravitech’s vibrating string, Gedex’s instrument). As explorationists’ the geological objectives are generally well understood but which instrument is the most suitable and what other techniques are available (e.g. conventional airborne gravity, magnetic gradiometry)? A comparison of three airborne gravity gradient systems will be discussed and their respective impacts on mineral exploration. In particular, instrument sensitivity and the impact of instrument noise on acquired data will be reviewed. Fri 27 Aug 2004 Evaluation of a Full Tensor Gravity Gradiometer for Kimberlite
Exploration A test survey program of a full tensor (gravity) gradiometer (FTG) operated as the “Air-FTG” system was carried out in Botswana. The main purpose of this program was to evaluate the resolution of the system as well as the amplitude and spectral character of the noise. This information can be utilized to determine the effectiveness of the system for kimberlite exploration in other environments. High resolution ground gravity data had previously been collected over all three of the FTG test blocks. These data were upward-continued to the level of the airborne drape surface before a first vertical derivative transformation was applied. After re-sampling at the locations of the airborne survey observations, the resultant data were subtracted from the airborne vertical gravity gradient data. Assuming that the ground gravity data are accurate and measured with sufficient sampling density, the residual provides a post-processing estimate of the noise of the airborne system data. The RMS noise values obtained from the three separate tests carried out over a 10-month period progressively decreased from 15.4 Eö to 5.4 Eö as acquisition and processing methods were improved by the contractor. The airborne FTG data contain information for wavelengths down to approximately 400 m, which corresponds to a bandwidth of zero to 0.15 Hz given an average airspeed of 60 m/s. There is a significant amount of residual noise in the range of 300m to 900m with longer wavelength noise also present which is thought to be due to mis-leveling of traverse lines. The noise characteristics that were derived from the test surveys were used in a forward modeling exercise to determine the effectiveness of this system for kimberlite exploration. The results from modeling a range of kimberlite bodies of different sizes and depths of burial indicated that larger kimberlite bodies would be readily detected, but noise would limit the detection of smaller and more deeply buried bodies. The specifics of this result were, of course, contingent on the density contrasts assigned to the bodies and would need to be varied from one geological environment to another. The results of the modeling could be used as an input, along with line-km costs and a definition of the acceptable level of risk, to determine the optimal line spacing. A number of products were calculated from the tensor components in an attempt to enhance the signals due to kimberlites. The most useful operator was found to be the determinant (I2) of the gravity gradient tensor which is calculated from all of the tensor components. This rotational invariant will tend to better resolve kimberlite anomalies but at the expense of a decrease in the signal-to-noise ratio.
Fri 30 July 2004
AGM - Indaba Hotel
Fri 18 June 2004
Geophysical Signatures of Broken Hill Type Orebodies: Implications for
exploration and resource definition Fri 28 May 2004
Airborne Gravity: Review, advances, application
The greatest challenge in airborne gravity has been reducing the large
accelerations due to aircraft motion. These accelerations can be in excess
of 100 000 mgals while the response of the geological target is often only
a few mgals. Advances in GPS technology have enabled the measurement of
vertical accelerations to a high degree of accuracy, thus providing a
means of stripping out a major portion of the aircraft noise. Furthermore,
improved INSs have provided the platform stability necessary to allow
production in a far greater range of turbulence conditions.
Fri 23 April 2004
SLOPE STABILITY RADAR Slope stability is a critical safety and production issue for open cut mines. The ‘slope stability radar’ has been developed to remotely scan a rock slope to continuously measure the movement of the face. The system can detect and alert movements of a rough wall with sub-millimetre precision in near real-time, and with reliability and resolution. The advantage of the slope stability radar over other monitoring techniques is that it provides full area coverage without the need for mounted reflectors or equipment on the wall. In addition, the radar waves adequately penetrate through rain, dust and smoke to give reliable measurements, 24 hours a day. The measurement technique is tolerant of vibrations and overcomes the need for a highly stable footing required by traditional surveying systems, making it easy to move from one location to another. The system is self-powered and designed for minimal maintenance. Radar displacement images, co-registered with digital photography images, are transferred from the radar site in the pit to the mine office via a radio telemetry link. Custom-written software provides mine managers and geotechnical engineers with a complete picture of slope movements over defined time intervals. The time-history of the movement of any selected points or regions on the slope can also be displayed. Also provided is the ability to set movement thresholds that will trigger alarms at the radar site or mine office. The system is used at numerous coal and metalliferous mines in Australia, Indonesia and South Africa, and has provided real-time monitoring of slope stability during active mining operations. More than 40 rock wall and spoil failures have been captured by the system, and on every occasion adequate warning was provided to mine operators. The high level of movement precision and broad area coverage of the rock face provides a better understanding of the geodynamics, which leads to extra warning time. This technology enables a radical change in the management of risks in open cut mining operations.
Pictures from David Noon's talk on Slope Stability radar
Fri 27 Feb 2004 DATA-DRIVEN SIMULATION OF THE ROCK MASS RESPONSE TO MINING (PART 1): LABORATORY EXPERIMENTS USING NEPEAN SANDSTONE MODELS By : R J Durrheim, Division of Mining Technology, CSIR, South Africa & Denis Labrie, Mining and Mineral Sciences Laboratories, CANMET, Canada Many mining excavations are situated in overstressed regimes where the rock surrounding any void will fracture and fail, regardless of the rock-breaking method or shape of the excavation. Numerical modelling tools are widely used to determine which mining geometries and sequences will limit the extent of rock failure and to establish the optimum trade-off between the rock engineering ideal and various economic and practical considerations. This series of laboratory experiments seeks to advance efforts to simulate the deformation and failure of the rock mass during mining by integrating physical observations in the numerical modelling process. Simple models were carved from 25 cm sandstone cubes and triaxially loaded. Sensors and cameras were used to monitor the deformation, acoustic emission and the evolution of damage. The blocks were sliced after completing the tests and the fractures were mapped. Comprehensive data sets were gathered for use in the calibration, evaluation and improvement of numerical modelling codes.
Fri 30 Jan 2004
IMPROVED SEISIMIC EVENT LOCATIONS Earthquakes and mining-induced seismic events are characterised principally by the hypocentral location and by some measures of size, such as Magnitude. The hypocentral location is the “point” where the event started and is usually determined from inverting velocity-distance-time equations. I will discuss some of the problems inherent in this seemingly simple problem and show some of the solutions that have been used and are currently in development to improve the (hypocentral) locations. The following topics will be covered: § Why do we need good locations? § Selection of P- and S-wave arrivals § Choice of minimisation function § Avoiding local minima § Handling poor network configurations § Development of velocity models – use of calibration blasts § Absolute and relative locations § The hybrid location method § Use of development blasts for improving locations § Use of waveform similarity in automatic locations The last three points (in bold) are recent developments and are resulting in significant improvements in events locations. The talk will therefore focus on these developments.
Fri 28 Nov Textural analysis is a powerful tool, but it is rarely applied to potential field data because the results are often noisy and ambiguous. In this talk an introduction to textural analysis will be presented, followed by some new texture filters which have been specifically designed for gravity and magnetic data. These filters are particularly useful for the detection of subtle Kimberlite pipe anomalies embedded in noisy backgrounds. Applications to both synthetic data and real data (from SA and Australia) will be shown. Fri 22 August 2003 Techniques will be discussed that demonstrate how downward continuation can be used to enhance detail within geophysical datasets whilst minimising the noise problems conventionally associated with this approach. Some of the techniques described can also be used to compute stable horizontal and vertical field gradients, thus allowing improved Euler deconvolution solutions, analytic signals, and cleaner sunshaded imagery. (This talk was given at the EAGE in Stavanger, Norway, in June 2003.) Fri 1 August 2003 Since shortly after the invention of the electronic magnetometer in the 1940s, airborne systems have been used to map variations in magnetic total field strength (F) over the Earth’s surface. From initial naïve ambitions of finding buried magnetite deposits of economic value, the technique has evolved into one of the most sophisticated (yet inexpensive) tools for rapidly mapping geology over large areas. Reconnaissance surveys of a technical standard achievable in the period until ~1990 cover over half the land area of the Earth and have been systematically compiled for many large (continent-sized) regions. But even the assembly of thousands of individual surveys on land and millions of km of shiptracks at sea, while giving a tantalizing new glimpse of the Precambrian mosaic of the continents, does not yet provide a complete global magnetic anomaly map. The elegant simplicity of the magnetic anomaly patterns over the ocean has, nevertheless, been seminal in the evolution of ideas on ocean-floor spreading and global tectonics. The global uniformity of coverage afforded by satellite magnetometry, meanwhile, is obviously highly attractive. Unfortunately, potential field theory predicts that the resolution of anomalies at satellite altitude will be no better than several hundred kilometers. And experience from Pogo and Magsat over 20 years ago shows that amplitudes of even the largest crustal anomalies are no more than 10-20 nT. Improved technology has overcome the problem of signal-to-noise ratio and hence anomaly reproducibility in the current generation of satellite-borne magnetometer systems. Improved resolution of detail can only be attempted as satellites descend into lower - ultimately fatal - orbit. The GFZ ‘Champ’ satellite mission has produced a stable picture of crustal magnetic anomalies and their reconciliation with crustal geology has commenced. One of the largest anomalies is coincident with an area of the Arctic Ocean that has a distinctive signature on the marine/aeromagnetic anomaly compilation – probably a large igneous province lying entirely below sea level. Three distinct anomalies, now situated above Early Cretaceous oceanic crust off South Africa, Antarctica and Argentina respectively, coalesce when ocean creation is reversed in computer animation, suggesting a common origin off the southern coast of Africa during the early stages of dispersal of the three continents, 120-140 million years ago. Several pairs of anomalies in the South Atlantic and Indian Oceans suggest a similar conjugate origin on now-opposing sides of their respective mid-ocean ridges. Anomalies over the continents at satellite altitude are less easily related to what is known of the Precambrian crust. Suggestions of ancient meteorite impacts are not easily verified from direct observation of the crustal geology, such as in the Bangui region of central Africa. FRIDAY 6 JUNE 2003 A DIGHEM airborne geophysical survey of the area north of Rosh Pinah, southern Namibia, covered an area of 138 km2. Approximately 70% of the surveyed area is sand covered, making surface geological mapping impossible. The airborne data included: Interpretation of the data yielded: • An upgraded geological map which combines the radiometric and
magnetic data, with the known geological information. This revealed areas
underlain by the Rosh Pinah Formation where it was previously not known. THURSDAY 24 APRIL 2003 GeoMole Slimline Borehole Radar was born in 1992 to map nickel sulphide shoots at Kambalda from 47mm boreholes. In 1994 it received the British Aerospace Award for Excellence in Engineering Design. Abstract Potholes and other geological structures disrupt UG2 and Merensky mining in certain sectors of the Bushveld, e.g. Lomberg et al., S. Afr. J. Geol., 1999, 102 (3), page 219. This problem is being addressed in a series of borehole radar trials from haulages, crosscuts & raises at mines belonging to Anglo Platinum's RPM: Rustenburg Section. The work started in July 2001, and is ongoing. Since then a number of borehole radars have been deployed ahead of mining at Bleskop and Brakspruit in 48mm boreholes with lengths up to 120 metres. The talk will be illustrated with slides. These will show that borehole radar, appropriately designed, can provide high resolution 3D surface contours of large tracts of UG2 reserve; and locate potholes, rolls and other geological features which are important in mine layout and production planning. GEOPHYSICAL PROSPECTING OF THE BUSHVELD: FROM TRAILING TO LEADING
EDGE By : Geoff Campbell, Consulting Geophysicist,
GAP Geophysics Airborne or ground gravity surveys allow for broad-brush mapping of
large Bushveld structures and floor perturbations along the outcrop
contact and at depth. Aeromagnetic surveys with terrain clearances and
flight line spacings as low as 20m and 12.5m respectively, map litho- and
loss-of-ground features with unprecedented detail (±5m) at outcrop or
subcrop. The depth continuity and truncation of these features are mapped
from 2D an 3D seismic surveys with a relative precision of around 10m to
20m. 3D surveys remain a de rigeur requirement for any producing mine but
2D surveys still have a role to play in the assessment of one-off,
structural problems and in greenfields prospecting. While aeromagnetic survey technology has recently advanced to a new maturity level, data interpretation continues to be hampered by the sparseness of rock palaeomagnetic information required for magnetic modelling purposes. In contrast, one major technological challenge still faces seismic surveying, the ultra-high (5m to 10m) mapping resolution required for cost effective mapping of shallow (50m to 300m) prospects has not been demonstrated in the field. Further experimentation with seismic energy sources (and arrays) is required before the problem is deemed intractable. Friday 22 November In 2001, De Beers discovered 38 kimberlites worldwide. In order to turn these occurrences into deposits, the company must cost effectively determine which of those have economic potential. The early stage evaluation of these kimberlites involves the analysis of mineral chemistry and microdiamonds, which can indicate if the intrusion has sampled diamond-bearing mantle. A second factor that is critically important to this evaluation process is to determine the size of the body with an acceptable confidence and to provide a first pass geologic model. Kimberlites commonly consist of multiple intrusions that can possess different physical properties. A magnetic susceptibility database complied by De Beers indicates a high degree of variability of magnetic properties, both between the different facies (crater, hypabyssal, diatreme) and also within the same facies measured for different bodies. In the past, magnetic modelling has been used as the prime determinant of kimberlite size. However, it has been found that this data provides only what should be considered to be a lower limit of size as some phases can be non-magnetic. The collection of complementary geophysical data sets, such as, gravity can help provide a more complete picture of the size and complexity of the body. As the potential of a kimberlite is further increased, depth-sounding techniques can be used to provide more information on the 3-D shape and help optimize the cost effectiveness of delineation drilling. In an environment that does not have thick conductive cover, the CSAMT technique can be particularly useful as kimberlites are often more conductive than surround rock. Construction of a robust 3-D geophysical model enables drill sites to be established that optimally investigate the contact of the body and sample the main components of the kimberlite. An example of the geophysical delineation of the Thankane body in Botswana and results of the subsequent drilling will be presented. Fri 18 Oct 2002 ABSTRACT: Extended Euler now involves use of the Hilbert transform of the
analytic signal. The availability of gradient & tensor data also has impacted on the
evaluation of these techniques. Talk will be an overview and practical short demonstration. Fri 27 Sept 2002 The International Continental Scientific Drilling Program,ICDP is a multinational program designed to promote and coordinate continental drilling projects with a variety of scientific targets at drill sites of global significance. The ICDP addresses fundamental scientific problems of global importance and societal relevance. A brief introduction to current and future projects as well as participation opportunities will be given HYBRID MOMENT TENSOR INVERSION by LINDSAY LINZER However, such an approach is often problematical due to limited access
to the site, poor exposures (if any) of the failure plane, not to mention
that fracture mapping is time consuming and requires a degree of
experience. An added difficulty is that planes of failure often do not
follow faults of geological origin, but are related to the geometry of EVALUATION OF INTERFERENCE EFFECTS IN A COAL 3D SEISMIC SURVEY
by MARK GIBSON A 1.7km2 3D seismic survey was acquired over a coal deposit under development, to determine what geological structures might lie within the proposed longwalls. The initial interpretation of this data by the acquisition company suggested that several normal and thrust faults might intersect the planned roadways. These results were of concern since the scale and geometry of the thrusts was not consistent with underground mappings and surface borehole logs. A more detailed interpretation was performed by a team consisting of an experienced interpreter and a site geologist. The re-interpretation demonstrated that the thrust structures are interference phenomena, caused by events associated with channels in the roof and floor of the target seam. It also demonstrated that these channel edges can be mapped by the 3D seismic method. Roadway development and control boreholes have not intersected any of the originally interpreted thrust faults, supporting the channel related interference interpretation. The influence of geology on groundwater modelling and management and
the integration of geological information in groundwater models by
Koos Vivier, GeoCon. Friday 08 March Potential field gradients are a staple interpretation tool, both in Airborne Gravity and Magnetic Survey in the Volcan Auca Mahuida and
Senal Cerro Bayo Fields of the Neuquen Basin, Argentina in 2001 by
PATRICK HARBORD of the Aerogravity Division of Carson Services Inc, USA. An integrated geologically constrained interpretation was made from the data. This interpretation defined structural information and depth to structure calculations, which were verified to within 30 to 80 meters during drilling. The geology of the area was complicated with interlaying zones of basaltic material found at several levels. These basaltic layers were found at different depths and can be related to mineral ore bodies in the modeling software. In essence the survey, while for a petroleum prospect also defined very well potential mineral bodies. The total well depths were in the 3000 meters range. In this complex area where seismic procedures would not work, the Aerogravity data provided a fast and economical method to define the drilling prospects with a high degree of accuracy. Friday 21 Sep 2001 Abstract Borehole Radar in Witwatersrand Gold Mines by Declan
Vogt, CSIR MiningTek Abstract Inversion of Induced Polarization Data from Donlin Creek,
Alaska This is a dramatic result. It suggests that inversion processing can have a big impact on the cost effectiveness and the utility of IP surveys in mineral exploration. In order to do inversion processing high quality data must be collected. It is necessary to recognize and minimize sources of error in the survey procedure, and to record error estimates when data is collected. A set of data is included to show how IP errors relate to primary voltages; this illustrates the weakness of assigning errors arbitrarily. Historical "rules of thumb" suggest that the depth of penetration for an IP survey is about 2 dipoles. This case history shows that mineralization can be detected at a depth of four dipole lengths and in the presence of near surface IP sources. However, there is a fine line between the detection of a signal from deep targets and the generation of completely spurious targets that can be created by pushing the inversion too hard. The supervision of an experienced interpreter is necessary when using these methods. Resolving Hell -
In-Mine Seismic Profiling Traditionally, delineation of the reef has relied heavily on interpolation between widely spaced boreholes, with the operation tolerating the inevitable inaccuracies this approach produces. More recently, 2D and 3D surface seismic techniques have been successfully implemented in the Witwatersrand Basin. Although this technique provides invaluable information on a regional scale, resolution of the reef geometry is insufficient for local-scale mine planning. To this end, advance knowledge of disruptions to the reef, including faults, dykes, rolls and associated slopes and terraces, will facilitate the planning of more cost effective and safer mine layouts. During the course of a three-year DEEPMINE project the feasibility of mine seismic profiling (MSP) was investigated. The MSP technique is an adaptation of vertical seismic profiling to the underground environment. Over a two-year period a number of MSP surveys were conducted on ultra-deep South African gold mines. The field trials comprised an MSP survey at Driefontein Gold Mine and two surveys at Mponeng Mine. The target reflectors were the Ventersdorp Contact Reef (VCR) and the Carbon Leader Reef at Driefontein and the VCR at Mponeng. The presentation will include the following aspects of the MSP technique:
"Computer Modelling
Illustrates why High Resolution Magnetic Surveys are Needed for
Generation of Quality Drill Targets"
A comparative study of a medium-resolution
survey (400 metre line spacing, flying height 80 metres) and a coincident
high-resolution survey (80 metres line spacing, flying height 50 metres) is
used to investigate the significance of line spacing and flying height to
the recovery of source information from the magnetic data. Differences in
both single and multi-line inversions of the two data sets are established
for bodies of different size and orientation.
Determination of depth and dip of source bodies requires modelling, and no qualitative image interpretation is complete without calibration from modelling. Nor is modelling the ultimate authority. The residual ambiguity of even the best-constrained models leaves some uncertainty in the source magnetic parameters, which can only be dispelled by drilling. ADVANCES IN GEOPHYSICAL WIRELINE LOGGING OF
GEOTECHNICAL BOREHOLES IN THE MINE LEASE AREA by Marcus Chatfield (BPB) Given the high cost of shaft-sinking and raise-boring
operations in South Africa and, in particular, the high cost of failures,
there is a need to extract more information from cementation or pilot
boreholes. The application of wireline logging technology including
ACOUSTIC and OPTICAL TELEVIEWERS, FULL WAVEFORM SONICS and FLOWMETERS
provides an objective and quantitative analysis of ground conditions prior
to developing a mineshaft. The combination of LITHOLOGY, ROCK STRENGTH
PREDICTIONS from shear wave measurements and FRACTURE FREQUENCY data
allows a simple but effective ROCK MASS RATING log to be created. "EM Mapping in Kimberlite Exploration"
presented by Anton Wolmarans (De Beers) ABSTRACT "Airborne EM: Where
it's at and where it might go" presented by Andy
Green (CSIRO Exploration and Mining; Sydney, Australia) ABSTRACT
For an encore I will speculate on where the technology might be pulled and what the future applications are going to demand from it..... Environment vs Minerals. Accurate sounding vs deep targets. Helicopter vs fixed wing.......And the big one, dollars per line kilometer. Short Biography for Andy
Green With Jon Huntington he developed the use of Landsat and other remote sensing techniques to mineral exploration in Australia. The associated work on image processing techniques led naturally to its application to airborne geophysical data. Since then he has been increasingly involved with the acquisition, processing and analysis of airborne geophysics, especially airborne electromagnetics. He was the founding director of the Cooperative Research Centre for Australian Mineral Exploration Technologies which concentrated on the development of the Tempest AEM system, the EM-Flow interpretation software and major projects in AEM for environmental and geological mapping. A CRITICAL LOOK AT THE TECHNICAL AND ECONOMIC FEASIBILITY OF
ULTRALIGHT GEOPHYSICAL PLATFORMS by Edgar Stettler, Council for
Geoscience. ABSTRACT After collecting airborne geophysical data for 3 years with ultra light aircraft it is possible to stand back and evaluate the technical and economic feasibility of flying ultra light surveys. Part one of the presentation will deal with examples of magnetic, gamma-ray spectrometer, near infra red spectrometer and high detail terrain model data collected simultaneously over known geology that are shown to convince the audience that technically the ultra light platform collects very high quality data. The state of the time domain EM system still being developed will also be discussed. Part two will deal with the economic feasibility of flying ultra lights, ie considering the whole cost, influence of weather, size of survey area etc in relation to the type of ultra light aircraft used. Our process of obtaining an air service license specifically for ultra lights which is nearly complete will also be mentioned briefly. Fri 02 March 2001 Entrepreneur ( ahnt rep ren er) n. Person in effective control of commercial undertaking. (OED). Peter Annan, current vice-president of the SEG, writes, in the presidents page of the January 2001 edition of The Leading Edge some thought provoking ideas as to future tendencies in our profession. He contends that exploration geophysics is an applied science and: "Implicit with 'applied' activity is the economic driver; the business side brings a unique perspective beyond that of pure science. Within SEG this fact is recognized and scientific excellence move ahead side by side with commercial realities." Many geophysicist in South Africa have been isolated from the rewards and cruelties of the commercial world by working within a large mining organization or government department. As we move into the 21st century this comfort zone is fast disappearing. This presentations seek to demonstrate that there is a definite upside to this scenario. South Africans are doubly fortunate; they have not just a new century to explore but a new made country in which to do so. Implications for geophysical modeling and layering mechanisms based
on analysis of physical property data from the Bellevue borehole The Bellevue (BV-1) deep stratigraphic borehole represents an ideal target for detailed geophysical property measurements, which can be made in stratigraphic context for nearly 3000 m of Bushveld magmatic rocks. This drillcore, sited in the Northern (or Potgietersrus) Lobe and completed in 1991, starts in granitoid roof rocks, extends through the entire Upper Zone, and ends approximately in the middle of the Main Zone. A detailed core log is available online (Knoper & von Gruenewaldt, 1996). Recognizing the paucity of geophysical measurements for Bushveld rocks, especially in stratigraphic context, we are undertaking detailed measurements of density and magnetic susceptibility in the BV-1 borehole. The results will be relevant to establishing an improved understanding of magmatic processes in layered mafic intrusions, as well as to regional and local geophysical modeling. The most recent gravity modeling of a continuous Bushveld model incorporates these results and the latest receiver function results from the Kaapvaal seismic experiment support this configuration. September 22, 2000 August 11, 2000 March 3, 2000 November 19, 1999 August 23, 1999 July 17, 1998 AGM Friday, April 24, 1998 (I have as to be confirmed...) Friday, March 27, 1998 Friday, February 27, 1998 Friday, January 30, 1998 Friday, October 31, 1997 Friday, July 18, 1997 Friday, May 23, 1997 March 24, 1997 Friday, February 21, 1997 Friday, September 6, 1996 Friday, August 23, 1996 Friday, July 26, 1996 Monday, April 29, 1996 Monday, April 1, 1996 Friday, January 27, 1995 Friday, November 25, 1994 Tuesday, September 27, 1994 AGM Friday, November 26, 1993 Friday, September 4, 1992 (This talk may have been cancelled by Anglo,
I can't remember) Tuesday August 4, 1992 Friday June 26, 1992 Friday May 22, 1992 Friday April 10, 1992 Friday March 27, 1992 Friday February 28, 1992 Friday January 31, 1992 Friday October 25, 1991 Thursday, October 3, 1991 (SPECIAL TALK JOINTLY WITH GSSA Economic
Geology Division) Friday, June 28, 1991 <end of data>
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