13th SAGA Biennial Conference & Exhibition

Conventional geological mapping using aerial photo interpretation coupled with field visits is often handicapped in areas with tropical weathering or sand cover in arid regions. High resolution airborne geophysical data acquisition over large areas covered by overburden can augment geological mapping of these areas provided information extraction is done in an adequate, automated and objective way. We suggest that the integration of airborne geophysical data with space-borne remote sensing data suites using fuzzy partitioning clustering meets these criteria. The outcome of unsupervised clustering is a classified zonal map which, in combination with some field inspections, produces a high resolution lithology map, in this case 100 m by 100 m pixel size, which is by power of spatial resolution far superior to any conventional mapping and can therefore provide new incentive for geological understanding of the area, modelling or mineral exploration. Our new approach to map hard rock geology hidden beneath overburden has been applied to a portion of largely sand and sediment covered southern Namibia by integrating airborne magnetic, radiometric and Landsat 7 data suites. The classified zonal map obtained from these data was converted to a lithology map by attributing what is known from previous geological investigations of this area. Apart from the structural control of known mineral showings, the resultant map clearly displays an area requiring further grass-root exploration.

A 7 km diameter circular structure, called the Bateke Plateau Structure, has been identified on Landsat imagery of eastern Gabon, in a region dominated by Palaeogene to Neogene continental sedimentary rocks of the Bateke Plateau, which unconformably overlie cratonic Archaean basement. Processing of DEMs derived from SRTM radar imagery of the structure, using various radial shading algorithms, has demonstrated that the structure consists of two nested toroidal rings, with a ring-shaped depression between them. The outer toroid has a peak-to-peak diameter of 5.8 km, and a thickness of 1.3 km, yielding a maximum diameter of 7.1 km. It is separated by a deep moat from the inner toroid, which has a diameter of 1.4 km, and a thickness of 700 m. Such a structure is consistent with a complex impact structure containing a central peak-ring uplift, formed by meteorite or cometary impact. Other possibilities for forming such a ring structure are considered highly unlikely, given the setting of the structure in a thin continental sandstone sequence overlying an Archaean craton, and the absence of young igneous intrusions, diapiric structures, karst, or deformation features. The Bateke Plateau Structure is postulated as a post-Neogene (Quaternary) complex impact structure with a peak-ring central uplift, which, because of its degraded, eroded state, is likely to be Pleistocene rather than Holocene in age.

The critically important steps to get best value from your gravity gradiometry data, assuming your contractor has done his job well in designing and acquiring the data, is the preparation of the representation of the potential field gradients. The ~200m resolving power of existing gradiometer systems approaches what is necessary for minerals applications. In particular, beyond the aircraft, the topographic surface represents the largest and most proximal density contrast encountered in an airborne survey. Hence terrain effects can have significant impact on AGG data. The critical steps are:  Terrain correction and determining ‘best’ terrain density  Gridding, using all the measured gradients to constrain the interpolation  Smoothing/de-noising by using the 3rd order tensor constraints  Anti-alias filtering of the gradient signals so that wave lengths are properly represented in all directions  Transformation of the gradients by integration to estimate the gravity or magnetic field Terrain corrections are a necessary step in the processing of observed AGG data in rugged terrain, in order to highlight subsurface density variations with a minimal overprint from the terrain. We propose a simple and rapid AGG tensor-based method to estimate an optimum bulk terrain density for subsequent terrain-correction. Each of the currently deployed systems for acquiring gradiometry is evolving driven by competition and the users’ needs. Mining applications of the technology to directly detect ore-bodies that show up as anomalies can now be successful provided the dimensions are of the order of 200m or more. High resolution 3D geology models of operating mines can be used to calibrate gradiometry surveys.

Despite many years of work, a convincing evolutionary model for the Limpopo belt and its geometrical relation to the surrounding cratons is still elusive. This is partly due to the complex nature of the crust and upper mantle structure, the significance of anatectic events and multiple high-grade metamorphic overprints. We use deep probing magnetotelluric data acquired along three profiles crossing the Kaapvaal craton and the Limpopo belt to investigate the crust and upper mantle lithospheric structure between these two tectonic blocks. The 20-30 km wide composite Sunnyside-Palala-Tshipise-Shear zone is imaged in depth for the first time as a sub-vertical conductive structure that marks a fundamental tectonic divide interpreted here to represent a collisional suture between the Kaapvaal and Zimbabwe Cratons. The upper crust in the Kaapvaal Craton and the South Marginal Zone comprises resistive granitoids and granite-greenstone lithologies. Integrating the magnetotelluric, seismic and metamorphic data, we propose a new tectonic model that involves the collision of the Kaapvaal and Zimbabwe cratons circa 2.6 Ga, resulting in high-grade granulite Limpopo lithologies. This evolutionary path does not require a separate terrane status for each of the Limpopo zones, as has been previously suggested.

Understanding of processes related to the deformation and evolution of the South Atlantic margins and factors controlling the continental rifting and breakup of Gondwana 200 my ago are few objectives of the interdisciplinary SAMPLE project (South Atlantic Margin Processes and Links with onshore Evolution). In frame of this project we conducted an on- offshore magnetotelluric (MT) survey in the Kaoko Belt in Northern Namibia and the Walvis Ridge to image the subsurface electrical conductivity structure of the Southern African passive continental margin. With a conductivity model we aim to study the magmatic and tectonic activity in this area since the early Cretaceous and the influence of pre-existing neoproterozoic structures on the placement of magma and subsequent continental breakup.

The Council for Geoscience carried out ground based time domain electromagnetic sounding (TDEM) surveys on prospects in five countries in Southern Africa namely Democratic Republic of Congo (DRC), Mozambique, Rwanda, South Africa and Zimbabwe. The surveys were undertaken on mining, mineral exploration and engineering sites. The TEMFAST-48HPC and TSIKL-5 instruments were used for data acquisition. In addition, the Geonics Protem 47 and Zonge Nano-TEM systems are being used in South Africa for geology and groundwater investigations. The Interpretation of time domain electromagnetic data was performed using different programs namely ERA, TEM-RESEARCHER (TEM-RES-WIN), IRAF and Sτ Inversion. The parameters that were obtained from modelled data for three case studies comprised of resistivity, chargeability and magnetic susceptibility. Modelling of TDEM data collected in most parts of Southern Africa should take into consideration, the super-paramagnetic effect. In South Africa TDEM surveys were used to delineate mined-out and non-mined areas in the eMalahleni coal mining areas. Building materials and aggregates were mapped using the TDEM technique in the Democratic Republic of Congo (DRC). In Rwanda aeromagnetic interpretation targets were investigated using the TDEM method for potential mineralisation. The coal bearing and mined out areas were demarcated on the basis of resistivity contrasts for the South Africa case study. The thickness of building aggregates was estimated from resistivity data for the DRC site. Areas with high chargeability and low resistivity were identified as potential targets for mineral exploration for the Rwanda prospect. The TDEM method has proved to be an important non-invasive tool for carrying out groundwater, mineral and engineering investigations.

Contamination at a feedlot, enclosure of animals, in San Pedro, Argentina, was investigated using geophysical methods. Results of inversion of time domain electromagnetic (TEM) data resolved three layers at each point of investigation, namely, a surface layer of clayish soil, a second layer comprising partially water saturated clastic sediments and hydrogeological basement that was very conductive, possible clay bearing. Resistivity of sediments is very low, below 10.5 Ohm m. The three layers are characterized by different resistivity range of values. The first layer is very thin, and it is not clearly seen in the profiles. In the corral it is fully contaminated by manure. The resistivity of this layer decreases in corral up to less than 3 Ohm m (the thickness of soil is less than 3 m within the corral increasing to the test site). Resistivity of the second layer is about 9.5-10.5 Ohm m. The resistivity of clay considerably decreases beneath the corral. The identified geo-electrical layers may not always be identified with geological layers. The TEM results showed full agreement with previous results of frequency domain electromagnetic (FDEM) method and electrical resistivity tomography. It was demonstrated that electrical and electromagnetic methods are a very important tools for the evaluation of contamination.

The Magnetic Induced Polarization (MIP) method uses the measurement of magnetic fields to directly detect internal and external current flow from IP-generating targets, rather than the resultant surface currents as with conventional Electric Induced Polarization (EIP). Magnetometric Resistivity (MMR) measures the magnetic field produced by galvanic current flow to detect horizontal variations in resistivity. MIP/MMR is insensitive to horizontal layering, and is especially suitable for regions with highly conductive cover where EIP and resistivity responses are sharply attenuated. Magnetic fields easily propagate through such conditions; therefore MIP/MMR is minimally impacted by conductive cover. The other major advantage of MIP/MMR, over traditional electrical IP and resistivity, is that it completely eliminates the need for measurement electrodes. Hence, it is effective in difficult ground contact conditions such as dry sandy soils, frozen ground, and rocky scree slopes. For inversion purposes, MIP has an additional benefit that magnetic fields can be measured in all three axes simultaneously, which provides significantly more information about target position and attitude. By using SQUID technology and remote referencing, we are able to improve the data quality and extract useful three component MIP and MMR data. We present a number of field trials using both frequency and time domain methods to analyze the MIP and MMR responses from porphyry copper, and unconformity uranium ore bodies.

From 20th November – 21st December 2012, Anglo American conducted a geophysical test surveys over porphyry copper systems. The purpose of the Magnetic Induced Polarization (MIP) survey was to test the viability of the MIP method in known porphyry copper prospect. There is broad correlation between the known chargeability anomaly and the MIP results, in terms of percentage frequency effect. There is a need to further test the viability of collecting MIP data using inductive sources instead of galvanic sources. Preliminary indications are that SQUID sensors are most suitable for MIP data acquisition and can be applied and used for exploration of buried porphyry copper deposits. Success in measuring inductive MIP effects using SQUID sensors will constitute a major breakthrough in terms of finding and defining new buried porphyry copper resources.

ence Device) systems will most likely provide the mineral exploration industry with a new tool that provides significant benefits over current airborne magnetic systems. Full tensor measurement of the magnetic field allows the application of filtering, gridding and visualisation techniques that greatly improve the information and resolution relative to data acquired with standard sensors. Potential benefits to the mining industry include faster execution of exploration work programmes and a reduction in exploration costs. Remote sensing of magnetic remanence as a physical property through the use of SQUID magnetometers has not been used as an exploration tool before and the SQUID system’s ability to measure remanence indicators will add significant benefits to exploration programmes. In 2007 Anglo American and De Beers entered into an agreement with the Institute of Photonic Technology (IPHT) in Germany to develop and operationalise a full tensor airborne magnetic SQUID system. Final field tests with a helicopter tow-bird mounted system were successfully completed in February 2012. In December 2012 a test survey was flown for De Beers over an area near Finch in the Northern Cape. The survey produced excellent results with noise levels generally below 10 pT/m. Visualisation of the full tensor and filtered products showed significant detail and resolution in the final data and allowed for the extraction of a wealth of additional geological information from the data.

A comparative study of the variation in magnetic properties in eight boreholes situated across the Karoo Basin was performed. Four of these boreholes incepted one or more dolerite sills. The aim of this study is to determine the thermal impact of the magma intrusions on the surrounding sediments by using several magnetic experiments. The methods that will be discussed include low field anisotropy of magnetization (LFAMS), magneto-stratigraphy using the classic baked contact test, as well as the magnetic alteration index (A40). Re-magnetization due to the heating effect of the dolerite intrusions are limited to short distances within the contact aureole. Those boreholes that intersect dolerite sills indicate that the heating effect occurred no wider than half of the sill thicknesses. These results also suggest a widespread elevation in the geomagnetic temperatures of the Karoo stratigraphic sequence to temperatures above 150 °C that gradually increases from southwest to northeast across the Karoo Basin.

The first formation of the crust is a controversially discussed topic amongst geoscientists. Tectonics on the Early Earth might have been similar to the plate movement and their driving forces that we observe today. However, regarding that some fundamental conditions like the thermal setting were considerably different at this time other processes like vertical mass transport might have played the governing role in tectonics. Unfortunately, there are only few remnants, e.g. the Barberton Greenstone Belt (BGB) in South Africa, where Early Earth’s tectonics can be studied. In the framework of the research initiative Inkaba yeAfrica two high resolution magnetotelluric (MT) field experiments were carried out in 2009 and 2010 across the southern part of the BGB. Unlike the surface structure which is well known from a number of geological studies, there is only little information on its deeper architecture. Imaging the complex subsurface is therefore the major aim of this project. The MT method allows resolving the electrical conductivity distribution at least down to lithospheric depths. Against the surrounding more conductive geological units the BGB is outlined as a highly resistive body. Mapping tectonic features within the BGB like faults and sutures which can be electrically conductive due to mineralizations along shear planes could be the first step to better understand the evolution of the BGB. However, various electromagnetic noise sources, e.g. power lines and electric fences, hinder the analysis of the MT data. Applying advanced filtering methods is therefore mandatory to improve the data quality as much as possible. Based on the good areal coverage of the ~ 200 MT sites (Figure 1), 2D interpretations along the six profiles with lengths between 80 and 110 km and a 3D analysis of the whole data set are conducted. In 2D models, the faults appear as zones of high conductivity down to a depth of 5 to 10 km; however, it seems difficult to follow these structures across neighbouring profiles. Therefore 3D inversion is more appropriate to correctly image this part of the Barberton Greenstone Belt.

Helicopter VTEM active source, ZTEM AFMAG passive source EM and aeromagnetic survey results are compared over the Nuqrah Sedex massive sulphide deposit in Western Arabian Shield of KSA. Field data and 1D-2D- inversions are used to show that all surveys map major controlling structures that host the Nuqrah deposits. VTEM directly detects more massive sulphide mineralized vent portions of Sedex orebodies; whereas ZTEM likely defining larger, less conductive and weakly mineralized distal portions of Sedex system. ZTEM also maps possible conductive down-dip extension of Nuqrah South Sedex below 750m depths.

African Nickel Ltd applied a number of geophysical methods from May 2011 to March 2013 with state of the art equipment at the Jacomynspan nickel-copper project in the Northern Cape in order to guide drilling and to detect the better mineralised parts of the deposit. The Ni-sulphide mineralisation is hosted in a 100m thick mafic to ultramafic sill that dips 650-750 south. A high resolution aeromagnetic survey was conducted covering the main target zone and the strike extent of historical drilling. The survey successfully delineated the sub-crop of the east-west trending ultramafic rocks. This information was used to plan ground electromagnetic (EM) surveys. Physical property measurements in the form of magnetic susceptibility and electrical conductivity were collected on historical drill core. The relative conductivity readings show the mineralised harzburgite to be more conductive than the gneissic host rock and the tremolite schist mineralisation. It was anticipated when planning the EM techniques, that the current would gather in massive sulphide stringer zones and the net-textured higher grade mineralised harzburgite. Therefore the EM plate model targets could potentially indicate these units rather than the lower grade tremolite schist mineralisation. A moving loop Time Domain Electromagnetic (TDEM) survey was carried out using a Low Temperature SQUID sensor over the main target zone to assess whether multiple stacked conductors exist, to map the best mineralised zones, and to explore for massive sulphide mineralisation. Downhole Electromagnetic (DHEM) surveys were also carried out in order to confirm whether off-hole mineralisation was present. To image both deep and near surface geological structure and mineralisation, vector Audio-frequency Magnetotellurics (AMT) was carried out on the main target zone. The results confirm that the intrusion is steeply dipping to the south and clearly mapped the higher grade harzburgite mineralisation down to 500m depth. The final 3D model was integrated into Micromine software with modelled geology and EM plates. This work confirms that AMT is applicable at Jacomynspan to rapidly and cost-effectively prospect for higher grade mineralisation.

Trial surveys have been carried out successfully with High Temperature SQUID (HTS) sensors for Time Domain EM applications in Africa where previously SQUID technology had been available only for LTS under exclusive rights to Anglo American. The HTS sensor coupled with a 24-bit SMARTem receiver proved a practical and cost effective field solution capable of acquiring much better low-noise TEM data than conventional coils and 16-bit receivers. A trial line of TDEM and MIP data over a Xade Complex target in Botswana is shown here to illustrate that effective penetration of severely conductive (100 Siemens) Kalahari and Karoo cover can be achieved. This means that the HTS technology now available has tremendous potential for exploring for sulphide or gold targets elsewhere in Africa below previously debilitating conductive cover with these geophysical methods.

INFLUINS is a German research program which investigates the movement of fluids (and associated gases) in the Thuringian sedimentary basin. The phrase "integrated fluid dynamics" in the project name highlights the interest in the relationship between near surface and deeper fluid and material flows. One major part of the program is to examine shallow and medium depth structures, for instance to understand fluid-fault interactions, using magnetic field measurements. The main tool is an instrument measuring the full tensor of the Earth’s magnetic field (FTMG) in airborne or ground based operation. The sensors are planar gradiometer of first order with a base line of 3.5 cm and a sensitivity of below 100 fT/(m*sqrt(Hz)) based on low temperature Superconducting Quantum Interference Devices so called SQUIDs. The gradiometers effectively suppress the Earth’s magnetic field by about four orders of magnitude and are well suited to map the gradient of the Earth’s magnetic field. A low sensitive reference magnetometer triplet is used in order to enhance the suppression by another three orders of magnitude. The system can be operated in a nonmagnetic bird towed by a helicopter at low altitude or on a nonmagnetic cart towed by a 4x4 car. Both operations allow the investigation of huge areas in short time and record the full tensor gradient of the magnetic field. Here, we introduce the new features of an airborne FTMG system which provides superior performance in fixed wing and helicopter based applications compared to conventional Caesium type magnetometers. First of all we could half the length of the liquid helium cryostat. This enabled to build a new tow fish with a much more aerodynamic shape. Additionally, we improved the performance of the inertial measurement unit which leads to a better transformation from the body to a georeferenced coordinate system. First results of the new system in a newly developed bird flown in three survey areas in the Thuringian basin are shown. Standard deviation of noise level is lower than 60pT/m throughout a whole survey area. Examples of 2D maps of tensor components with high spatial resolution are presented.

The composition of the lithosphere beneath Cameroon and the origin of the Cameroon Volcanic Line (CVL) are still debated by the Science Community. Although many studies based on regional or global observations provide good arguments for the setting of the CVL, none of them are strong enough to be considered as unique. In this work we used the joint inversion of Rayleigh wave group velocities and Rayleigh wave group velocities to provide shear wave velocity profiles of the lithosphere beneath Cameroon. Preliminary results show that lithosphere is, on average, faster beneath the Congo Craton than the Pan-African lithosphere beneath Cameroon. Due to the limited resolution of the dispersion curves, the maximum investigation depth was taken to be 200 km. The calculated velocity-depth profiles do not show any sharp discontinuity that could be interpreted as the lithosphere-asthenosphere transition. In addition there is no clear evidence of the existence of a low velocity zone beneath any geologic province within Cameroon. The smooth velocity contrasts observed on the velocity models are believed to be influenced by lateral mantle heterogeneities rather than vertical ones. The shear wave velocities for the uppermost mantle are in general greater than 4.3 km/s at all stations. This is higher than the values obtained in the Main Ethiopian Rift, and suggest that the lithosphere is not globally perturbed by thermal anomalies. This suggests that the source of volcanism along the CVL is from small scale convection in the asthenosphere and occucontrolled by lithospheric fractures that are probably driven by the cold (and fast) edge of the Congo Craton.

An ORION 3D DC/IP survey was conducted over Blackthorn Resources’ Kitumba IOCG deposit in Zambia. The survey results provided 3D models that successfully delineated the known deposit, and provided an enhanced understanding of the three-dimensional geometry of the mineralization. With this improved understanding of their deposit, Blackthorn was able to refocus their ongoing drilling program to best target possible extensions of the existing mineralization.

The “VIGOR” project aims at assessing geothermal resources in 4 regions of Southern Italy. The SkyTEM survey is a part of the planned geophysical activities and has been chosen since it is able to collect resistivity data on wide areas, with great resolution and in short times. To date, the application of AEM methods to geothermal targets has been limited, due to the depth at which the target is usually found. Kirsh and Siemon (2008) suggested its application in low enthalpy study. In this project AEM is tested in an area of known geothermal activities, and where a wealth of ancillary data is also present, in western Sicily. The results are composed in a 3D model of the electrical resistivity of the subsurface, and then interpreted for geothermal potential, following 2 main paths. The first is to produce a model of heat exchange capacity. The second aims at identifying directly conductive anomalies that might be associated to locally shallow hydrothermal fluids. “Termini” area is covered by extensive geological surveys. Since geological conditions of Sicily, even at shallow depth, are very complex, this area provided a good place for defining the resistivity values of the main geological units outcropping in the region. The “Western Sicily” area covers the main thermal manifestations of Western Sicily. Based on near real time preliminary results from the more regional mapping at 1 km line spacing, three infill areas were selected as being the most promising to test the concept. The obtained resistivity volume has then been the base for a detailed lithological and geothermal interpretation. Lithological and geological maps were used to constrain surface condition and to understand the resistivity ranges of the different lithological units. On the base of AEM derived resistivity values, and of laboratory measurements of thermal and electrical conductivity on samples, it was possible to establish the main links between lithology, electrical resistivity and thermal conductivity. The work in progress aims at extending the correlation also at depth, producing a 3D model of thermal exchange capacity for the areas surveyed. This detailed interpretative modeling provides also the basis for detecting resistivity anomalies within carbonate units, which may possibly represent hydrogeological or hydrothermal bodies.

Archean cratons, and the stitching Proterozoic orogenic belts on their flanks, form an integral part of the Southern Africa tectonic landscape. Of these, virtually nothing is known of the position and thickness of the southern boundary of the composite Congo craton and the Neoproterozoic Pan African orogenic belt due to thick sedimentary cover. We present the first lithospheric-scale geophysical study of that cryptic boundary and define its geometry at depth. Our results are derived from two-dimensional (2D) and three-dimensional (3D) inversion of magnetotelluric data acquired along four semi-parallel profiles crossing the Kalahari craton across the Damara-Ghanzi-Chobe belts (DGC) and extending into the Congo craton. Two dimensional and three-dimensional electrical resistivity models show signifi cant lateral variation in the crust and upper mantle across strike from the younger DGC orogen to the older adjacent cratons. We find the Damara belt lithosphere to be more conductive and significantly thinner than that of the ad jacent Congo craton. The Congo craton is characterized by very thick (to depths of 250 km) and resistive (i.e. cold) lithosphere. Resistive upper crustal features are interpreted as caused by igneous intrusions emplaced during Pan-African magmatism. Graphite-bearing calcite marbles and sulphides are widespread in the Damara belt and account for the high crustal conductivity in the Cen tral Zone. The resistivity models provide new constraints on the southern extent of the greater Congo craton, and suggest that the current boundarydrawn on geological maps needs revision and that the craton should be extended further south.

The Mumbwa iron oxide copper-gold (IOCG) exploration project is located in west-central Zambia. A FALCON® airborne gravity gradiometer (AGG) survey, flown by Fugro Airborne Surveys in 2004, was the catalyst to advance IOCG exploration efforts in the Mumbwa area, leading to the Kitumba discovery. The FALCON AGG survey mapped several regional elements considered prerequisite for prospective IOCG terrains: post-tectonic igneous intrusions and intersection of district-scale fault structures, thus highlighting two prospects, Kitumba and Mutoya, as particularly amenable to IOCG mineralization. The FALCON AGG survey accurately delineated the spatial extents of the Kitumba and Mutoya prospects and identified significant uranium anomalism, upon which the Kitumba discovery hole S36-001 was sited. In 2007 AIM Resources (now Blackthorn Resources), in a joint venture with BHP Billiton, drilled the Kitumba discovery hole, S36-001, intersecting significant Cu mineralisation over a 655 m interval grading 0.46% Cu. In-fill drilling in 2011 intersected high-grade mineralisation in several drill holes, including drill hole S36-038 with the best drilled thickness intersections containing 223m at 4.67% Cu. In 2012, Blackthorn Resources reported the total JORC Inferred and Indicated Mineral Resource of the Kitumba prospect as 187Mt of 1.14% Cu and 0.04 g/t Au, using a 0.5% Cu cut off. The FALCON AGG survey also identified an 19km N-S striking, hitherto unknown, massive hematite-siderite IOCG system, Mushingashi, under 250m-350m sedimentary cover. Widely spaced reconnaissance drilling has intersected low tenor Cu anomalism in hematite-siderite breccia systems with large areas remaining untested. The understanding of the mineralization in the Mumbwa area remains patchy. This is primarily due to the sheer size of the IOCG footprints of the Kitumba, Mutoya and Mushingashi systems, but also due to extensive leaching and possible supergene processes at Kitumba. Ground based geophysics (3D IP/MT) and additional drilling has been undertaken at Kitumba and at the new FALCON AGG prospect, Kakozhi, to the west of Mutoya, to address this issue.

The benchmark geotechnical and structural mapping airborne electromagnetic technology, DIGHEM, is used to corroborate the newly developed GENESIS time-domain fixed wing electromagnetic system. Examples of these data are presented from a South African Permian age coal deposit. Both 2D and 3D products deliverable from the GENESIS system are shown; their value addition to the structural understanding of the coal deposit illustrated.

Aeromagnetic compensation plays an important role in airborne magnetometry, and in particular, in gradiometer systems. This paper provides a perspective on the range of performance levels achieved in the compensation of typical commercial gradiometer systems, in terms both of residual errors, and the robustness and stability of model solutions. For brevity, the analyses presented are limited to lateral gradients on fixed-wing platforms.

In 2010-2011, the Department of Geological Survey (DGS) acquired a new airborne magnetic Tie Line Survey over Botswana. It was flown on a 10 km by 50 km grid and totalled 70,176 line-km of data. The control lines were flown in single segments over a short time period to provide the most accurate levelled data set. Strategic deployment of magnetic base stations facilitated diurnal correction using a distance-weighting scheme. After compilation of the Tie Line Survey, some 70 higher resolution magnetic surveys were recompiled, most acquired by DGS supplemented by some from industry. They were then levelled to the magnetic datum provided by the Tie Line Survey, from which a new nationwide grid of total magnetic intensity at 50 m resolution was prepared. These data and enhanced nationwide magnetic grids were released by DGS in 2012.

The present work intends to contribute to the role of geophysical methods as a tool for groundwater exploration in a Basement Complex, geological transition zone and Sedimentary terrain. It will also enhance the understanding of the subsurface geology and establish possible variation in such geoelectrical parameters as we move from Basement Complex to Sedimentary terrain in the study areas. At present there is no available detailed geophysical and hydrogeological information on the study area and this could have been the main factor responsible for the failure of hand-dug wells and boreholes drilled in the area. The transition zone in the study area is defined between the exposed crystalline rocks in Akaka and some part of Ishara and the thick cover of sedimentary rocks most especially sandstones and very thick lateritic soil which overlie the Basement complex rocks in Ode-Remo, Ilara and Ishara.

This paper addresses the early contributions made by surface seismic surveys to an ongoing exploration programme over a shallow potash prospect. The latter is underlain by Lower Cretaceous evaporates hosting thin potash (sylvinite) beds near the top of the 100 m thick Upper Evaporite sequence, separated by a 30 m thick Bischofite unit from the 260 m thick Lower Evaporite Sequence. The Evaporate Sequences are capped by Upper Cretaceous anhydrites and carbonates which in turn are overlain by up to 200m of Triassic and Neogene-age sediments. In the complete absence of any information relating to formation “seismic properties, an ongoing borehole geophysical logging programme was extended to include density and sonic logging in order to provide essential information for use in the interpretation process, namely formation velocities and the location of significant reflection events modelled from synthetic seismograms.

ropy has identified a link between fracture density and orientation observed by well logs and the intensity and orientation of the observed anisotropy. Recent work has correlated these measurements to provide quantitative estimates of fracture density from 3D wide-azimuth seismic data for tight gas sands. The work highlights the impact of advanced seismic processing in successfully recovering reliable fracture estimates which correlate well with borehole observations. These kind of areal, quantitative estimates of fracture density provide a valuable tool to guide drilling and completion programs in tight reservoirs. . Pre-stack seismic data and azimuthal WAZ (wide azimuth) seismic processing can help in the identification of sweet spots in Shale resource plays through detailed reservoir-oriented gather conditioning followed by pre-stack seismic inversion and multi-attribute analysis. This analysis provides rock property estimates such Poisson’s ratio, and Young’s modulus, amongst others. These properties are in turn related to quantitative reservoir properties such as porosity and brittleness. In this presentation we show an integrated approach based on pre-stack azimuthal seismic data analysis and well log information to identify sweet spots, estimate geo-mechanical properties and in situ principal stresses.

The state-of-the-art in 3D modelling of the structurally complex orebody begins with (1) 3D seismic imaging, (2) horizon picking, (3) data conditioning, (4) fault detection, (5) fault-horizon projection, (6) data integration, and (7) statistical analysis. A variety of 3D seismic imaging and interpretation techniques have played an integral part in improving the quality of the orebody modelling for deep mineral mining industries. This paper presents the world-class model of the VCR orebody across KDC East gold mines (Witwatersrand Basin) as derived from the 3D seismic reflection data, underground geological mapping, and exploration boreholes. The re-processing of the 1994 seismic data using advanced seismic imaging algorithms, such as Kirchhoff prestack time migration (KPSTM), has increased the signal-to-noise (S/N) ratio of the data. The technique has proven to be effective in imaging the steeply horizons and structures (e.g., faults, dikes) in the areas characterized by major lateral velocity variations (such as the Witwatersrand Basin), compared to finite-difference poststack migration (PSDM). The seismic attributes such as dip, dip-azimuth and edge detection have been successfully applied in delineating complex structural architectures, such as multiple fault bifurcations, intersecting and cross-cutting faults that cannot be interpreted using conventional picking on seismic sections. Consequently, these complex structures and their geometries were modeled and projected to the VCR horizon using the advanced modelling techniques derived from Non-Uniform Rational B-spline (NURBS). The computed compartment maps from the integrated data have resolved orebody compartment sizes below the dominant seismic wavelength (~124 m). Using these different techniques, a geologically reasonable 3D structural orebody model was developed. The model could be used for future mine planning and designs.

The Richter or local magnitude scale (ML) has been used, with some modifications, to measure the size of earthquakes since 1935. It has long been recognised that this single-number representation of a multi-dimensional phenomenon is inadequate and cannot fully describe the energy released by an earthquake or the displacement caused by it. The high stresses encountered in deep South African gold mines induce numerous mining-related seismic events. Large databases of good quality data make it possible to identify and quantify the effect of various factors on estimates of the size of the events, principally source effects (various failure mechanisms), path effects (especially geological inhomogeneity), and the unequal radiation of energy with azimuth. We propose that three parameters that give insight into the damage potential should be routinely reported: (i) Area of the source (m2), which is easily derived from the relatively stable Moment parameter, (ii) Energy per unit area of the source (KJ/m2), derived from model-based source parameters, and (iii) Azimuth of strongest shaking (degrees).

Two underground sites in a deep level gold mine in South Africa were instrumented by the Council for Scientific and Industrial Research (CSIR) with tilt meters and seismic monitors. One of the sites was also instrumented by JApanese-German Underground Acoustic emission Research in South Africa (JAGUARS) with a small network, approx. 40 m span, of eight Acoustic Emission (AE) sensors. The rate of tilt and the seismic ground motion were analysed in order to understand the coseismic and aseismic deformation of the rocks. A good correspondence between the coseismic and the aseismic deformations was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events, the coseismic and aseismic tilt shows a rapid increase. Much of the aseismic deformation, however, occurs independently of the seismic events and blasting and was described as ‘slow’ or aseismic events. During the monitoring period a seismic event with MW 2.1 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emission network. More than 21,000 AE aftershocks were located in the first 150 hours after the main event. Using the distribution of the AE events the position of the rupture area was successfully delineated. The tilt changes associated with this event showed a well pronounced after-tilt. The distribution of the AE events following the main shock was related to after-tilt in order to quantify post-slip behaviour of the source. No evidence was found for coseismic expansion of the source after the main slip. Therefore the hypothesis of the post-seismic creep type behaviour of the source was proposed to explain the large amount of tilt following the main shock. Previous studies using numerical modelling and analytical tools show that for this specific event and rupture area, the amount of measured tilt is highly sensitive to seismic activity in specific regions, in particular, to the bottom corner of the source area. Thus, it is concluded that the post-seismic creep behaviour, if present, most probably occurred in the bottom corner of the rupture area, a region also characterised by large amounts of aftershock activity.

As exploration for hydrocarbon resources moves to increasingly complex geological environments, the integration of multiple physical measurements is needed to build better Earth models. Seismic has enjoyed a long history as the geophysical workhorse in the oil & gas industry for imaging the subsurface and guiding exploration and development decisions. While this still holds true, it has now become clear that multiple physical measurements are needed to build improved earth models, particularly as exploration for hydrocarbon resources moves to increasingly complex geological environments. Examples of challenges are ultra-deep water exploration where drilling risks are high include sub-salt and sub-thrust exploration where seismic imaging faces significant problems.

Recent interest in the Karoo basin of South Africa has been sparked by the possibility of extensive shale gas reserves. Here we present an integrated study of historical reflection and refraction seismic (Soekor and academic), borehole, MT and regional gravity and magnetic data, with the goal of evaluating the shale gas potential. The reflection seismic data, constrained by 5 deep boreholes and MT data are used to map the contact between the base of the Karoo (Dwyka Group) and the underlying basement. This provides an immediate constraint on the thickness of the Karoo (~5.5 km). By constraining the gravity data with the structure known from the reflection seismic and density data from boreholes, this contact can be extended to regions where the seismic data are sparse and suggests that the basin in the region near 24° longitude is thinner than on either side. The flexure of the basin also suggests that at the time of deposition, the Kaapvaal Craton was stiff, preventing a deep basin from developing further northwards on craton. Additionally the magnetic and borehole data highlight pervasive dolerite sills and dykes. These sills and dykes can be highly fractured at surface, but at depth are possibly impermeable, providing seals and traps. They are also an important source of heat and need to be accounted for when evaluating the gas potential. The borehole data indicate sills can occur at any depth throughout the basin. The near surface sills are easily mapped with the coarse national magnetic data and single flight line modelling suggests that the edges of deeper sills can be delineated with higher resolution magnetic data. This approach indicates the importance of integrated studies to evaluating the shale gas potential in the Karoo.

As the most part of the world, India is also getting more and more dependency on groundwater resources and hence mapping and cautious management become imperative. Ministry of Water Resources of the Government of India has launched a flagship project to tackle this problem. AQUIM stands for pilot project on aquifer mapping and it is a great challenge, not merely because includes the acquisition, in less than one year, of 13,800 line-km of helicopter-borne transient electromagnetic (HTEM) data over six different areas across India (Figure 1), but also because its ultimate aim is to develop a cost-effective tool to locate, characterize, and, eventually, manage water resources. An accurate picture of groundwater through aquifer mapping allows water management plans at the appropriate scale to be effective for the protection of this invaluable resource, while it is becoming physically and economically scarcer and scarcer. This is a necessary prerequisite to achieve drinking water security, improve irrigation strategies and develop sustainability, especially in a country, like India, characterized by an impetuous economic and population growth. Depending on the outcomes, AQUIM is planned to be scaled across the entire country within the next decade. The original scientific plan of AQUIM starts with compiling of the existing database in the area and conceptualize the hydrogeological set up followed by SkyTEM survey, ground truthing and validation of the derived model by ground based data, joint inversion and data integration, deriving 2/3D hydrogeological model at 1:50,000 scale and demarcating the aquifer disposition precisely usable to village level up to 200 m in hard rock and 300 m depth in alluvial. CGWB will use the above information to carry out aquifer modeling for effective management and development of groundwater resources. CSIR - National Geophysical Research Institute and the HydroGeophysics Group (HGG) at Aarhus University signed an agreement concerning the acquisition, processing and inversion of the HTEM data from the six areas of the AQUIM project.

Ground electromagnetic and resistivity datasets were modelled using two different inversion methods. The main objective was to deduce accurate depth models that show variations in the subsurface geology. Groundwater bearing structures were investigated using geophysical methods consisting of electromagnetic induction (EI) and electrical resistivity tomography (ERT). An inversion program EM4Soil that models multi frequency electromagnetic data was used to generate 2-Dimensional depth models for shallow thermal spring aquifers. ERT data was modelled using Res2DINV software. The positive correlation of the inversion models showed that the two methods of inversion are complementary. The integrated geophysical survey approach proved to be an important tool for the rapid and cost effective determination of the geometry of shallow aquifers.

The Vaal Gamagara water supply scheme is a R300 Million intervention by the South African Department of Water Affairs and Forestry (DWAF) to interconnect the Vaal river water supply with the towns of Postmasburg, Kuruman, Hotazel , the surrounding mines as well as the cattle and game farms. Considerable savings in the project costs were achieved by prospecting and developing groundwater wells that deliver some 4 million litres per day into the scheme. Locating these zones permitted DWAF to extract a safe, secure water supply, and was accomplished from a combination of airborne magnetic and TDEM and ground gravity surveys combined with a fundamental understanding of the geology.

Self-demagnetisation can significantly reduce the amplitude and alter the orientation of magnetisation in highly magnetic bodies, thereby modifying the observed magnetic field, sometimes substantially. In tabular bodies, for example, the transverse magnetisation is reduced, with the result that the magnetisation vector rotates towards the plane of the body. Furthermore, when highly magnetic bodies are in close proximity, the assumption of uniform inducing field is violated. Highly magnetic bodies can modify the local magnetic field appreciably, with the result that the magnetisation induced in one susceptible body is affected by the magnetisations of all its neighbours. It is important to take such interactions between highly magnetic bodies into account. Potential field modelling and inversion software “VPmg” has been upgraded to account for self demagnetisation and interaction between magnetic bodies. The algorithm computes H-field perturbations at the model cell centres in two stages: initialisation and optimisation. During initialisation, a demagnetisation tensor is estimated for each cell, from which a first estimate for the H-field perturbation is derived. During optimisation, the H-field field estimate is refined iteratively via an inversion procedure. Remanence is taken into account as well as induced magnetisation. The algorithm has been validated for homogeneous spheres, spheroids, slabs, and cylinders. It has also reproduced magnetic interactions between two horizontal cylinders, previously published by Hjelt. Explicit verification for complex heterogeneous bodies requires a suitable independent algorithm for benchmarking. The application to inversion in a highly magnetic environment is illustrated in a field data example.

Adjoint-state methods (ASMs) have proven successful for calculating the gradients of the functionals commonly found in geophysical inverse problems. The 3D ASM image-domain tomography (IDT) formulation of the seismic velocity estimation problem highlights imperfections in migrated image volumes and, using appropriate penalty functions (e.g., differential semblance), forms an objective function that can be minimized using standard optimization approaches. For time-lapse (4D) seismic scenarios, the 3D ASM-IDT approach can be extended to multiple datasets and offers high quality estimates of subsurface velocity change. I discuss two different 4D inversion strategies: absolute and relative. The absolute approach uses the difference of independent 3D inversions to estimate a 4D model perturbation. The relative approach inverts for the model perturbation that optimally matches the monitor image to the baseline image - even where migrated energy is imperfectly focused. Both approaches yield useful 4D slowness estimates; however, we assert that the relative approach is more robust given the ubiquitous presence of non-repeatable 4D seismic acquisition noise and imperfect model estimates.

Integrated geophysical imaging technique has been applied in the detailed investigation of foundation of buildings in order to identify the geologic formations and mechanisms of rocks and soils causative to the identified defects. The study was also aimed at the estimation of the dependent elastic constants of the subsurface formations which is useful to engineers. The study area is part of the Zaria Batholith which comprises series of granites that intruded the country rock gneisses. It falls within the Nigeria Basement Complex which is underlain by Precambrian rocks at the elevation of about 670 m above the mean sea level. It has a Tropical-continental climate with distinct wet and dry seasons. Structurally, the study area is characterized by deformations which are mainly due to NW-SE and NE-SW fracture patterns in the Nigerian basement complex caused by a trans-current movement. The study area precisely is located within 70 35’ 17’’E and 70 41’ 17’’E longitude, and 110 7’ 50’’N and 110 11’ 22’’N latitude on the Nigeria National grid. Three buildings affected by such defects were selected for investigation. Two of them were located at the Staff quarters of Ahmadu Bello University, Zaria, Nigeria and the other, at the students’ hostel of the same University. While the former were solely characterized by severe foundation-based cracks with unknown cause at sight of superstructure, the latter is a case of severe crack due to leaning having a relative rotational angle of about 5.50. Modern geophysical field equipment, namely; 24-Chanel Seismograph (Terraloc Model MK6) and Lund Imaging system (Terrameter Model SAS 4000/1000) with its electrode Selector (Model ES464) having 42 take-outs, were used for the data collection of the seismic refraction tomography and the electrical resistivity imaging respectively. Eight profile lines were laid parallel and close to each of the buildings during the investigation. While the geophone spacing of 5.0 m was used in the seismic refraction method, the take-out spacing for the electrodes ranged between 1.5 m and 5.0 m in the electrical resistivity method. The travel-time data for the p-wave velocity and Electrical Apparent Resistivity data were collected and processed with computer software namely; REFLEX-W version 3.0 and RES2DIV version 3.4 respectively. Both software were based on a high resolution inversion modelling techniques for data processing. Spearman’s formula for rank correlation analysis was applied on the pair of interpreted tomograms. The rank correlation results obtained from the two methods showed that there is positive correlation in the range of (0.3170 – 0.9883 0.0001) between the structural displays of their lithological stratification. The interpreted results from the seismic refraction tomography technique show that the compressibility of the soils within the foundation depths (0-5 0.1 m) ranges from 2.21797 x 10-09 to 1.45565 x 10-10 ( 0.08 x 10-09) Pa-1), while the estimated allowable total foundation bearing pressure ranges from about <4.5 x 108 Pa to < 1.31 x 1011 Pa ( 0.08 x 10-09) Pa). The depth range to the bedrock is 7 – 18 ( 0.1) m, while the overburden and the weathered basement thicknesses have been estimated to be in the range 3 – 26 0.1 m and 7 – 30 0.1 m respectively. The aquiferous zones based on the interpreted results, mostly occur both at the lower depths of the overburden and within the weathered basement. The integrated interpretations show that expansive soils such as clays, predominantly characterize the near-surface of the three sites. The clays usually undergo seasonal swells and shrinkages which have posed danger to the structures. Also based on the results, fractures, synclinal structures of shallow bedrocks, weakness of intact rocks, structural arrangement of the subsurface lithology, soil creep/crawl and to some extent, the growth of tree roots, have partly contributed to ground movements and differential settlements of most of the buildings in the area. These have resulted in the structural defects on the buildings. Conclusively it was observed that while two of the sites (sites 1 and 2) show low tendency of progressive structural failure, the other (site 3), poses a high tendency of a progressive structural failure.

This work presents the first results from an ongoing cooperation project between the Department of Geological Survey (DGS) in Botswana and the Geological Survey of Sweden (SGU). The purpose of the project is to find suitable rock to produce aggregate for concrete and roads in Botswana. We show in this paper how different geophysical methods can be used in this process. Airborne data together with the available bedrock information are used to find suitable areas for bedrock sampling and later strength testing. Measurements of the gamma radiation are crucial since rock material with very high natural gamma radiation should not be used as building material in houses. Where airborne gamma radiation data are available it should be used initially to identify certain areas with high gamma radiation. The airborne magnetic data together with ground magnetic measurements were used to define the lateral extent of certain rock types. Measurements of the magnetic susceptibility on outcrops are essential here in order to determine the cause of a magnetic anomaly. Our results from gamma radiation measurements on outcrops have revealed a syenitic rock with very high radiation that should not be used for building purposes. Also the Gaborone granite complex show high gamma radiation while mafic and sedimentary rock show low gamma radiation.

This study presents a semi-automatic sequential hydrogeophysical inversion method for the integration of resistivity data and lithological borehole information into groundwater models in sedimentary areas. Large scale airborne geophysical EM-surveys play an increasingly important part in the geological mapping of the subsurface especially in a hydrogeological context. Airborne EM surveys provide valuable information of the geological structures and the lateral heterogeneity than boreholes cannot reveal due to the spatial scarcity (Jørgensen et al., 2003). However, boreholes play a key role in linking the resistivity to the different lithological and hydrological classes. Today, geologists and hydrogeologists in most cases interpret AEM-derived electrical resistivity distributions manually along with borehole observations within the context of a given geological setting. Due to the discrepancy between hydrological and geophysical parameter spaces the challenge is to translate the electrical resistivity distribution into hydrogeological classes. Our results suggest that a competitive groundwater model can be constructed from densely sampled resistivity models from AEM surveys together with borehole information, using the procedure outlined below.

Quasi-3D inversions of an extensive helicopter time-domain electromagnetic (HTEM) data set acquired across the Okavango Delta (OD; Figures 1 and 2) yield 3- to 4-layer electrical resistivity models that include (1) a shallow resistive layer of dry and fresh-water-saturated sands, (2) an intermediate-depth conductive layer of intercalated saline-water-saturated sands and clay, and (3) a relatively deep resistive layer of fresh-water-saturated sands/gravels and/or crystalline basement. The upper resistive layer clearly represents unconsolidated sediments in the current alluvial fan-like environment, whereas the intermediate conductive layer likely represents sediments deposited under earlier lacustrine conditions. The top part of the deeper resistive layer has an intriguing fan shape, centred about the entrance to the main part of the delta (Figures 2e and f). If the fan-shaped portion of the deeper resistive layer comprises fresh-water-saturated gravels/sands, it would be evidence for a paleo-alluvial fan, which we refer to as the Paleo-Okavango Delta in the following text.

Acidic mine water is generated in situ in the hanging and foot-walls of mines. In the gold mines of the Witwatersrand the oxidation of pyrite generates acid. This acid infiltrates groundwater and is and will continue to be a major environmental hazard specifically in and around the mines. Non-invasive geophysical techniques make it possible to map the extent and the flow pattern of acidic water. Induced polarisation (IP) in conjunction with direct current resistivity will be used to map the extent of acidic mine water at a bioremediation program near the Vaal River in the Northwest Province. Data will be collected where the survey can be repeated in order to monitor the time dependence of the phenomenon. Ways of separating the environmentally-associated IP signal from electromagnetic coupling and cultural noise will also be investigated.

Two-dimensional inversion results obtained using three electrode arrays, the Wenner, Schlumberger and dipole-dipole synthetic data sets were combined using Algorithm librarian of an image processing program PCI Geomatica widely used for remotely sensed data. The hybrid or combined images which were obtained using, the maximum, minimum, median and average values of the produced inverse models were compared. Image registration was applied in order to establish correspondence and integration between the images. All the images resolved and recovered the essential features of the true models. The images produced bear considerable likeness to the true models. An evaluation of the accuracy of the seven images for the four geologic models was assessed using four criteria via an error measure and the recovered mean resistivity values of the predicted blocks from the true blocks. The results show that the images of maximum approach give the least estimated mean absolute error. Also, the mean resistivity values of the blocks are closest to the true blocks for all the images of maximum method. Thus, it is corroborated that when inverse models are combined, most reliable and detailed information about the geologic models is than using individual inverse models.

Despite the many advances on magnetic surveying technology and semi-automated modelling and interpretation routines, topographic effects on the data are normally neglected; usually due to the assumption that magnetic data collected on a surface parallel to the ground will not suffer from terrain effects. However, on areas of substantial topographic relief like the Andes, large magnetic anomalies induced by the terrain can be common and of similar amplitude than the anomalies generated by the geological target of interest. These effects are mostly dependent on the orientation of the effective magnetic field versus the topographic slopes, and the large susceptibility contrast between air and the ground. We present a combined 3D forward and inverse modelling technique to reduce magnetic data from topographic effects. The algorithm is applied on a dataset at the Southern Andes, where topographic relief is in excess of 4000 m and the observed magnetic anomalies showed direct correlation with topography, but field mapping did not identify any major faults at the location of the magnetic lineaments. Although the computation could possibly be automated, it is recommended to apply it carefully on a case by case basis and with proper geological control.

ard continuation filter were grouped into NE-SW and NW-SE, respectively. The depth to the top of the deepest magnetic source is about 3.5 Km. The pattern of the high positive anomaly (47.788–86.331nT) shows that Ajase BIF is structurally controlled with approximately NE-SW trend. This mode of occurrence was ascertained by the result of Euler deconvolution using structural index of 1.0 that proves the confinement of Ajase iron ore mineralization to veins.

A helicopter-borne transient electromagnetic (HTEM) survey system is being designed with characteristics suitable to map glaciolacustrine overburden overlying Precambrian bedrock for the purpose of correcting airborne gravity measurements for lateral variations in overburden thickness. The HTEM system parameters such as transmitter power and waveform are optimized for overburden mapping, by using forward modelling and inversion. This paper will discuss some inversion results that test the capability of the system at resolving the thickness of an overburden under multi-layer geological scenarios.

The Slave “Diamond Corridor” is a north northwest trend that appears to have controlled the emplacement of the most significantly diamondiferous kimberlites of the Slave craton of northern Canada and any extension of the corridor is prime diamond exploration country. A northern extension of the corridor into the Lena West diamond area of the Northwest Territories that includes the diamondiferous Darnley Bay and Dharma kimberlites requires major left-lateral displacements (~350km) that are not generally recognised and are not identified in the surface geology. Major faults are recognised by Zolnai in the petroleum literature and there is geomorphological and geophysical evidence to support them. Euler deconvolution analysis of regional airborne magnetic surveys show little in the near surface platform rocks but strong linear breaks that coincide with other evidence of faulting in the deeper basement rocks Discovery of an economic diamond field in a corridor south of Darnley Bay striking parallel to the Slave “Diamond Corridor” will support continuity of the corridor and the need for a major displacement.

The quality factor Q has been estimated using spectral amplitudes of P and S waves from earthquakes recorded by the seismic network of Egyptian National Seismological Network (ENSN) in south Sinai and north Red Sea region. The earthquakes recorded at nine stations – DHA, NUB, TR1, TR2, KAT, SH2, GRB, HRG and SFG have been used. The spectral amplitude ratios have been calculated between 2 - 20 Hz and single station spectral ratio method has been applied for this purpose. The results show that the quality factors for both P and S waves (Qp and Qs) increase as a function of frequency according to law Q = Q0fn. By averaging the Q- Value obtained at all stations we calculated the average attenuation laws: Qp = (13.15± 0.76) f0.95± 0.19 and Qs = (20.05± 0.79) f1.03±0.04 for P and S waves respectively. The QS /QP ratio for KAT station at lower frequencies is less than 1, whereas at HRG and SH2 stations QS /QP ratio is are greater than 1. These relations are useful for the estimation of source parameters of earthquakes and simulation of earthquake strong ground motions.

Subsidence and collapse of unmapped shallow coal mine workings poses a risk to the public and hampers the development of valuable property. A high-resolution reflection seismic survey was conducted to determine whether it is possible to map the extent of the mine workings. Two 94 m profiles (tied to boreholes) were surveyed using a sledgehammer source. Processing was optimized to image the shallow reflections. The refraction seismic models and stacked time sections were compared and integrated with the borehole data to produce a 2-D geological model. It was concluded that high-resolution shallow reflection seismics could be successfully used to map the extent of the old mine workings provided adjustments are made to the acquisition and processing parameters.