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2nd Conference on Geophysics for Mineral Exploration and Mining
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
1 - 20 of 68 results
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Developed Correlations Between Sound Wave Velocity and Porosity, Permeability and Mechanical Properties of Sandstone Core Samples
More LessSummarypetrophysical properties such as porosity and permeability of the reservoir rocks and rock mechanical properties are affected by the relevant physical properties and such physical properties and mechanical properties affect the drilling programs and the development plans for a reservoir. It is more convenient to use homogenous rock samples with nearly constant initial permeability, obtaining such cores is very difficult. In this paper a simulated natural and homogeneous compacted sandstone rock with known physical and petrophysical properties were used. The physical properties include grain size, cementing material concentration, and compaction (confining) pressure. The effect of these properties on the petrophysical properties of Rock such as permeability and porosity were also known. For the same simulated natural sandstone rocks, Sound wave velocity was measured using an ultra sound tool. Good relationships have been developed between sound wave velocity and other rock properties; porosity, permeability, mechanical parameters namely Young, shear modulus and poison’s ratio. This study has been carried out on dry core samples and core samples with different saturations. The results of this study were presented as graphs of simulated lithification factors, porosity, permeability mechanical parameters versus sound wave (compressional and shear) velocity under different degree of water saturation.
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Geophysics, Petrophysics and Field Data Integration for Porphyry Delineation in the Canadian Cordillera – Some Caveats
Authors I. Lenauer, H. Ugalde, B. Milkereit and W. MorrisSummaryThis contribution presents an integrated interpretation of airborne geophysical and remote sensing data over the Central Cordillera in British Columbia, Canada. Data comes from the Search II survey, commissioned by the British Columbia Geological Survey in 2016. The study area is part of the Mesozoic volcanic arcs preserved as the Quesnel and Stikane terranes in Western Canada. Sedimentary and volcanic cover as well rugged terrain and difficult access make field mapping in this area quite challenging. The first part of the work consisted on interpreting the geophysical data to determine structures that could have a role on porphyry emplacement, and the extension of these under sedimentary cover, as well as zones of potassic alteration. Subsequent field mapping was focused on obtaining structural information as well as petrophysical and alteration data over exposed faults and intrusives. Field observations did not locate faults with similar strike to the ones interpreted from the airborne data but did find numerous secondary structures with different strikes that are however consistent with the main stress regime for the area. Magnetic susceptibility traverses indicate that not all alteration features create a decrease in magnetic susceptibility. These are important findings for field structural follow-up of airborne data interpretation.
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Keynote: Helicopter Airborne Gravity Gradiometry
More LessSummaryRotary-wing airborne gravity gradiometry provides both better signal-to-noise and better spatial resolution than is possible with a fixed-wing survey in the same terrain by virtue of the low altitude, low speed and close terrain following capabilities of a helicopter. In rugged terrain, these flight characteristics provide a significant advantage for the use of helicopters for gravity data acquisition. Comparing helicopter surveys over gentle terrain at Margaret Lake, Canada, and over rugged terrain at Mount Aso, Japan demonstrates that although there is some loss of spatial resolution in the more rugged terrain, the line spacing remains the limitation to resolution in these examples. The slightly higher altitudes forced by rugged terrain make the requirements for terrain correction easier than for gentle terrain. Transforming the curvature gradients measured by the Falcon gravity gradiometer into gravity and the complete set of tensor components without loss of resolution is done by a Fourier method over gentle terrain and an equivalent source method over rugged terrain. The Fourier method is perfectly stable and uses iterative padding to improve the accuracy of the longer wavelengths. The equivalent source method relies on a smooth inversion and the source distribution must be customized to suit the survey design.
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FDEM & Magnetic Data Integration for Kimberlite Exploration – Remanent magnetization and apparent susceptibility mapping
Authors H. Ugalde, W. Morris and B. MilkereitSummaryWe present a case of FDEM and Magnetic data integration for kimberlite exploration in the Northwest Territories, Canada. Data comes from six high resolution helicopter-borne surveys commissioned by the Northwest Territories Geological Survey (NTGS). Analysis starts with the calculation of an apparent magnetic susceptibility distribution from the FDEM data. This is then compared to magnetic susceptibility derived from the total field magnetic data. The differences allow to recognize areas of prominent remanent magnetization. Helbig analysis on the magnetic data over these areas gives an estimate of NRM intensity and direction. Integration of these results with the Apparent Polar Wander Path for the area of study, gives us a full understanding of the different components of the NRM (thermal and viscous).
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Borehole Magnetics - Mineral Deposit Mapping and Age Estimation of the Stratmat Deposit, Bathurst, New Brunswick
Authors W. Morris, H. Ugalde and S.-.L. UnderhaySummaryBorehole vector magnetics. Stratmat deposit, Bathurst Mining Camp, improved borehole navigation, ore deposit modeling, age estimation from magnetic remanence interpretation
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Using Magnetic Data for VMS Exploration in Vihanti, Western Finland
Authors H. Leväniemi, S. Heinonen and J. LuukasSummaryThe magnetic properties of two mineralisation in the Vihanti region, western Finland, are studied. The study area is part of the 1.92–1.93 Ga Vihanti-Pyhäsalmi Belt that contains the most important volcanogenic massive sulphide deposits in Finland. The two mineralisations presented in this study, Lampinsaari and Kuuhkamo, show on aeromagnetic maps as high-amplitude anomalies that are not fully explained by the observed drill core susceptibilities. Constrained magnetic modelling and inversion are used for determining the intensity and direction of the remanent component. The results indicate that the strong magnetic anomalies are dominantly caused by remanent magnetisation that is mainly, but not completely, aligned with the current Earth’s field direction. The information can be applied in generating more reliable magnetic models for the region to enhance data integration for mineral exploration.
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ZTEM in Deep Brownfield Exploration in Outokumpu
More LessSummaryGeological Survey of Finland (GTK) ordered a ZTEM (Z-Axis Tipper Electromagnetic) survey from Geotech Ltd. as a part of its Developing Mining Camp Exploration Concepts and Technologies – Brownfield Exploration Project. The project took place in Outokumpu Mining District in North Karelia in Eastern Finland and was conducted by the Geological Survey of Finland and the University of Helsinki together. The Outokumpu Cu-Co-Zn-Ni-Ag-Au ore belt is historical mining area where there has been exploration for over hundred years. The goal of the project was to develop new deep exploration concepts when working in previously explored and exploited mining area (brownfield) in crystalline bedrock areas. Among other geophysical surveys, ZTEM survey aimed at gathering information from the depth of several kilometers. The contractor also provided 2D and 3D inversions which combined with other data sets. In this abstract, the ZTEM data is compared to GTK’s own airborne electromagnetic data.
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Targeting Supergene Manganese in the Capricorn Orogen Using Airborne EM
Authors C. Soerensen, S. Spinks, R. Thorne and T. MundaySummaryWhile airborne electromagnetics (AEM) is routinely employed as an exploration tool for Mn mineral systems in Australian, the challenges of using the derived data to better delimit the extent of supergene Mn resources in regolith settings has received limited attention. This is particularly so for geological settings where the measured AEM response is strongly affected by IP effects. Here the question as to whether inverting for conductivity and IP can improve the definition of supergene Mn mineralisation in the subsurface, thereby helping determine the resources present is examined. The focus of this study was the Butcherbird/Yanneri Ridge deposits which occur in the Collier group in the eastern part of the Bangemall Basin in Western Australia. These deposits are highly conductive, and chargeable. A full non-linear 1D inversion of the helicopter (XTEM) time domain airborne EM data set effectively outlines the lateral and vertical extent of supergene Mn mineralisation defined in drilling, particularly when inverting for both conductivity and IP. This is not the case when just inverting for conductivity or when employing transforms on the data.
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Raising the Bar by Lowering AEM Base Frequency to 7.5 Hz with Helitem35C
Authors G. Konieczny, A. Smiarowski, G. Paleolog and P. MilesSummaryLowering the base frequency of AEM systems is important for increasing depth of exploration in conductive terrain, but is difficult because receiver coil motion noise dramatically increases noise levels. By re-designing the receiver coil and coil suspension, the receiver coil motion noise has been largely eliminated in the Helitem35C system. In this paper we compare survey data acquired at 30 Hz with 15 Hz and 7.5 Hz data. In order to generate appreciable ground signal at 7.5 Hz, a 50% duty cycle square pulse has been used. The survey data had signal well above noise levels to the 30 ms channel centre time possible with the 7.5 Hz, providing greater depth of exploration and better interpretation of conductors.
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Application of Airborne Magnetic Data to Gold Mines in Namuno, Mozambique
Authors C. Macuacua, T. Mogi, K. Ishitsuka and M. UtsugiSummaryThe availability of high-resolution aero-geophysical data was a monumental step toward the discovery of new gold and mineral deposits in very remote areas in Mozambique. However, many mineral occurrences and deposits were identified previously by either local prospectors or small-scale miners with limited structural and geological knowledge. Therefore, the exploitation of resources has proceeded chaotically, which is not beneficial for local communities or state revenues. To contribute to improving this circumstance, we studied the Namuno District, where there is high rate of small-scale gold mining but limited knowledge of the geological structures that host the gold mineralisation.
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Identification of Kimberlite Bodies in Brazil from a 3D Audio-Magnetotelluric Survey
Authors E. de Oliveira, P. Pastana De Lugão and B.F. KriegshäuserSummaryWe report on a successful identification of kimberlite bodies in Brazil through the use of the electromagnetic technique audio-magnetotelluric (AMT). Macnae (1979) writes that “In one large survey in South Africa, electromagnetic (EM) techniques have proven to be remarkably effective in detecting the presence of weathered clays or epiclastic kimberlite contained within the pipes.”
Full tensor AMT data were acquired at 65 stations in a 3D configuration with frequencies ranging from 10 kHz to 1Hz in the NW portion of the Mato Grosso state, Brazil, an area of thick jungle coverage. During the AMT survey, few outcrops were seen, because of the dense forest cover. Usually, the occurrences found were of sand deposits, indicating the occurrence of Fazenda Casa Branca and Utiariti Formations and gravel from Salto das Nuvens Formation, widely used in paving trails in this region. In the area of the survey, three main targets were identified and confirmed by the 3D resistivity model in depth obtained from inversion of the AMT data, helping the exploration in a region of difficult logistics due to the dense jungle cover and remote location.
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Combined Interpretation of ERT, SP and VLF-EM Data for the Identification of Manganese Deposits
Authors N. Kordatos, G. Vargemezis, P. Tsourlos, G.N. Tsokas and P. TsitsanisSummaryThe signature of a mineral deposit can vary to different geophysical methods, depending on its mineral concentration, size and depth. For this reason, a single geophysical method in several cases could be insufficient, if the expected geophysical response is weak or the interpretation is not unique.
Combined interpretation of different geophysical methods can contribute to this problem in two ways.
In the first place, the existence of a mineral deposit is verified by the fact that different geophysical methods point to a certain location. In addition, geophysical signatures can be related to the characteristics of the mineral deposit and contribute to its qualitative evaluation.
In this work we apply the Very Low Frequency electromagnetic (VLF-EM), Electrical Resistivity Tomography (ERT) with Direct Current (DC) and Induced Polarization (IP) data and Self-Potential (SP) geophysical methods over surficial manganese mineralization located in Piavitsa area (Chalkidiki, Northern Greece). For the final interpretation of geophysical data, information from geological maps and borehole data have also been used. Results over the same profile are presented, where each method has a very good response over the mineralization body. Moreover, the characteristics of the geophysical models are related to the properties of the mineralization.
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Multi-Parameter Visualization of Petrophysical and Geochemical Data for Base Metal Exploration
Authors C. Hebert, E. Veglio, S. Liu, L. Sun and B. MilkereitSummaryA large petrophysical and geochemical dataset has been obtained from archived drill core for a base metal exploration project located north of the Bathurst Mining camp (New Brunswick, Canada). The integration of this large, heterogeneous dataset presents a unique opportunity for statistical analysis of correlating and visualising multi-parameter behaviour in a bi-modal felsic/mafic geological setting. Large variation in parameter distribution enables questioning the linkage between petrophysical and geochemical parameters. To better characterize mineralization and alteration zones, a statistical approach has been developed for interactive visualization of the contribution of each parameter to the exploration model. The integration of geophysical and geochemical datasets produced robust results for imaging wide-spread alteration zones and associated base metal mineralization.
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Gravity and Magnetic Modeling of Polyhedron and Iterative SVD Applied to Regional-Residual Gravity Data Separation
Authors E. Amarante and E. SampaioSummaryWe have developed a method of forward modeling to determine the gravity and magnetic potential of a convex polyhedron and an iterative procedure of singular value decomposition (SVD) to filter and extract residual gravity anomalies in order to obtain useful information to improve geological mapping and the search of sulphide deposits. The forward modeling method is based on the fundamental work of Werner (1994) . It employs Green’s divergence theoremto change potential volume integrals into asumof surface integrals, with each face of the polyhedron divided into triangles. So, each surface integral consists of the contribution of a triangle calculated relative to its own coordinate system – z perpendicular to the face and x parallel to one of its sides – which is subsequently transformed into the global coordinate. The resulting potentials are derived to yield the analytical solutions of the gravity and magnetic anomalies.
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Interpretation of High Resolution Aeromagnetic (HRAM) Data over Chibok and Damboa Chad Basin, North Eastern Nigeria, Usi
Authors G.A. Bala and D.N. ObioraSummaryHere we present the interpretation of high resolution aeromagnetic (HRAM) data of Chibok and Damboa areas (sheets 112 and 134), north-eastern Nigeria, using forward and inverse modelling methods on Oasis montaj 6.4.2 software. Quantitative depths estimates obtained by employing SPI have shown minimum to maximum depth to anomalous source at 72.7m to 5026.8m.Oasis montaj 6.4.2 software. The estimated depths from the forward and inverse modelling methods for profiles 1–7 are 2749, 2201, 2088, 703, 521, 927 and 481 m respectively. The respective susceptibility values of 0.20407, 0.47779, 7.8043, 0.1349, 0.0889, 0.3083 and 0.4820 SI, which indicate the presence of sedimentary intrusions (basalt or limestone), few metamorphic rocks (schist) and minerals (magnetite).
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Locating Potential Field Sources Using Wavelet Analysis
More LessSummaryCooper (2006) introduced a particularly simple wavelet based semiautomatic interpretation method. When applied to magnetic data the wavelets were based on horizontal derivatives of the first order analytic signal amplitude of the response from different sources, such as dykes and contacts. The wavelets were not applied to the data itself, but to the horizontal derivatives of its first order analytic signal amplitude. While the method worked well, the use of second order derivatives made it sensitive to noise. This abstract introduces several improvements to the original methodology, with the aim of increasing its robustness to noise, namely
- Use wavelets based on derivatives of the zero order analytic signal amplitude
- Use wavelets based on the Hilbert transform of the analytic signal amplitude of different orders
- Application of a sharpening technique to improve the response of the transform
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Deep Targeting Iron-Oxide Mineralization Using Reflection Seismic Method: A Case Study from the Ludvika Mines Of Sweden
Authors M. Markovic, G. Maries, A. Malehmir, E. Bäckström, M. Schön, J. Jakobsson and P. MarsdenSummaryBlötberget, in the Ludvika Mines of Bergslagen mineral district of central Sweden, is well-known for its iron-oxide, sometimes apatite-rich, deposits. There is also a renewed interest in exploring and mining the deposits due to accessibility to the market and recent advancements made in the mining and metallurgical technologies. During two field campaigns (2015 and 2016), high-resolution reflection seismic data were acquired using both cabled-and wireless-recorders as well as a landstreamer system. In this study, we have merged the two datasets and process them together to provide deeper information on the extension of the mineralization and potential unknown resources at depth. We show how the merged dataset images the mineralization much better and deeper than known also potential reflections under the known ones that can be targeted through a drilling program. This study demonstrates reflection seismic method is a powerful tool for imaging iron-oxide mineralization at depth. We argue that they should be acquired more routinely at the site for mineral exploration purposes. It also paves the way for justifying a 3D seismic survey in the area.
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Seismic Interferometry for Mineral Exploration: Passive Seismic Experiment over Kylylahti Mine Area, Finland
Authors M. Chamarczuk, M. Malinowski, D. Draganov, E. Koivisto, S. Heinonen and S. JuurelaSummaryWe present the results of adapting seismic interferometry (SI) for reflection imaging in mineral exploration. We use a unique dataset of one-month ambient-noise recordings acquired with large-N array (~1000 receivers) deployed in a regular grid (50 m receiver interval, 200 m line interval) directly above the known mineralisation and underground mine infrastructure at the Kylylahti polymetallic mine located in Eastern Finland. Ambient-noise in the study area is dominated by the road traffic and mine activities (both surface and underground) providing quasi omni-directional distribution and broad freqeuncy spectrum of the noise sources. We start from the simple 2D forward modelling using existing geological model. Results of the SI applied to field data from selected receiver lines exhibit reflections related to the bottom of the ore body as well as the reflection from the target area confirmed by synthetics. Finally, we develop robust mineral exploration SI workflow (MESI) tailored for reflection imaging and apply it to our 3D ambient-noise dataset. Migrated sections obtained from the MESI-processed data exhibit high reflectivity, compatible with the active-source seismics and directly related to the known geological structures.
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Application of Surface-Wave Analysis for Mineral Exploration: A Case Study from Central Sweden
Authors M. Papadopoulou, F. Da Col, L.V. Socco, E. Bäckström, M. Schön, P. Marsden and A. MalehmirSummaryNear-surface velocity models are important for deep imaging of mineral deposits with seismic exploration. The near-surface can be quite complex from loose, highly heterogeneous materials to stiff, fractured rocks. Surface-wave analysis can be an effective method to image the shallow subsurface of such challenging environments. Here, we propose a workflow that includes several processing and inversion steps. Initially, for the optimization of the processing parameters, we assess the presence of sharp lateral variations with a method based on the measured energy of Rayleigh waves. Then, using a moving window of receivers, we extract Rayleigh-wave dispersion curves along the acquisition line as the maxima of the f-k spectrum. Finally, the dispersion curves are inverted using a laterally constrained inversion scheme. The proposed methodology has been tested on legacy data from a mining field.
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Improved Subsurface Imaging through Re-processing of Legacy 2D Seismic Data - A Case Study from a Deep South African Gold Mine
Authors M. Manzi, A. Malehmir and R.J. DurrheimSummaryOver the last few years, there has been a proliferation of seismic solutions, which employ specific combinations of equipment, acquisition, and processing techniques that can be applied in hard rock situations to improve the imaging resolution. The latest developments in seismic processing, in particular, make it worthwhile to re-process the legacy data to enhance the resolution of the data. This is particularly important in the mining regions where no new data are available or the acquisition of new data is expensive or not allowed due to new environmental regulations. In this work we demonstrate, through a case study from one of the world’s deepest gold mines in South Africa, how revisiting, recovering and re-processing of the seismic data acquired decades ago can significantly improve the quality of the interpretations. The information can benefit future mine planning operations by providing a better estimation of the resources and inform in the siting of the sinking of future shafts. Thus, any future mineral exploration plans could take the information obtained from the re-processed legacy seismic data into account when planning either 2D or 3D seismic surveys.
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