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NSG2022 4th Conference on Geophysics for Mineral Exploration and Mining
- Conference date: September 18-22, 2022
- Location: Belgrade, Serbia & Online
- Published: 18 September 2022
1 - 20 of 41 results
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Constraining the Temporal Evolution of the Deep-Water Orange Basin Using High-Resolution 3D Seismic Reflection Data
More LessSummaryWe use high-resolution 3D reflection seismic data to constrain the strato-structural evolution of the transitional and compressional domains of a Late Cretaceous deep-water fold-and-thrust belt (DWFTB) system, and its influence on the overlying Cenozoic sediments in the Orange Basin, South Africa. Multiple shale detachment surfaces (SDSs) have given rise to a complex structural framework with progressive sedimentation. The compressional domain consists of large-scale, landward-dipping DWFTBs with faults mainly detaching the Turonian SDS. Thrust sheets are segmented along-strike by extensive oblique-slip faults extending from the transitional domain into the down-dip compressional domain. The transitional domain is a complex region containing listric normal, thrust, and oblique-slip faults that have been reactivated to detach the older Albian SDS. Multiple SDSs transferred stress and redistributed strain during gravitational sliding, forming smaller, localized DWFTBs at depth. Cenozoic erosion is confined above the transitional domain including a large, slope-perpendicular Oligocene submarine canyon formed by turbidity currents; and a smaller series of slope-parallel, sinusoidal channels in the Miocene formed by bottom currents. Together with a present-day seafloor slump scar above a buried Late Cretaceous syncline, this indicates how the stratigraphy and structural geometry of a buried DWFTB system controls fundamental sedimentary processes in overlying basin evolution.
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3D Ip Using a Distributed Array System
Authors C. Nind, C. Phaneuf, N. Veillette and P. ColesSummaryThe Induced Polarization / Resistivity technique is effective in exploration for disseminated and massive polarizable mineral occurrences such as base metal sulphides, barren sulphides associated with gold, porphyry copper systems, graphite, alteration zones and structural features controlling mineral deposition, oxides and some clay minerals. The Distributed Array survey using the IRIS full waver system allows us to increase the data density and is ideal for large systems such as porphyry or skarn hosted deposits. It can also be used as a hybrid solution of ground and borehole IP. Full Waver receivers are installed on the surface and the current is injected at the surface and in the available boreholes. This method maximizes the depth of investigation by using boreholes, while acquiring a large, systematic coverage of readings in a regular mesh on the surface, resulting in a more reliable 3D inversion.
Major and junior mining companies will always have the challenge to explore deeper, penetrate thick conductive overburden and extract more precise 3D structural information about the mineralization and host geology. In response, Abitibi Geophysics has introduced innovative IP configurations to enhance exploration effectiveness.
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Finding Blind Ore Bodies Using 3D Seismic: St Ives-Victory, Western Australia
Authors K. Jarvis, A.M. Foley, M. Falconer, G. Turner, J. Kinkela, R. Smith, S. Bright and S. ZiramovSummaryMining companies are increasingly using seismic data to image hard rock environments containing prospective mineral deposits. A seismic dataset samples the earth with more detail than any other geophysical dataset. To extract maximum value from the seismic requires a transformation into volumes that are easily understandable by mine site geologists and engineers. In this presentation we introduce a new way to look at seismic by transforming the seismic to a rock model and showing how this relates to gold mineralization.
To convert the seismic data into a rock model requires an understanding of which rocks are present and the impedance variability of those rocks. The insitu impedance measurements from wireline logging were combined with core observations to characterize the impedance variability in the different rock types. Geostatistical inversion technology is used to integrate the drillhole measurements and observations with the seismic data and output statistically probable rock models and rock properties. Data from the St Ives/Victory complex was selected for testing because it had a large set of deep borehole data, several sonically logged boreholes, and good quality 3D seismic reflection data.
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Near-Surface Imaging in the Caspian Sea: Comparison of High-Resolution Towed-Streamer, Obn Multiple Migration, and Nfh Imaging
More LessSummaryShallow hazard assessment is crucial in the south Caspian Sea, which is known for shallow channels, gas, mud volcanoes, and structural uncertainty of faults and folds. Acquisition of an OBN survey with Near-Field Hydrophones (NFH) in the same area as a 3D High-Resolution Towed-Streamer (HR-TS) survey provides an opportunity to compare results from a near-surface perspective. We compare images from modern processing of the HR-TS data, OBN data (with multiple migration), and NFH data. The temporal resolution, evaluated in section view, is highest for the HR-TS dataset (processed at 1 ms). The OBN multiple migration (processed at 2 ms) is only slightly lower in final temporal resolution, however. Although the NFH has a higher bandwidth (processed at 0.5 ms), the result is not comparable to the other two in terms of resolution. The lateral resolution of the OBN image is significantly better than the HR-TS image, attributed to its wide-azimuth character. Residual acquisition footprint in both results is weak and not strong enough to interfere with interpretation. Given the high spatial resolution and adequate temporal resolution of the OBN multiple migration, the extra effort of a dedicated HR-TS survey may not be necessary for shallow hazard assessment in this case.
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Ten Years of Mineral Exploration Innovation in Central Sweden
By A. MalehmirSummaryBergslagen mineral endowed district in central Sweden hosts a variety of mineral deposits including massive sulphides and iron-oxides. Iron-oxide deposits are historically the most significant ones as their mining and technologies developed to process them contributed to the Swedish wealth and high-tech industry. The district is rich in mineral occurrences and can still yield significant new resources. New technologies can also be tested and experimented for this purpose given its proximity to several tech companies in the region. In this study, an overview of ten years of mineral exploration innovation from seismic, to UAV-based surveys is presented and showcased how various methods and solutions helped to provide additional geological information on the depth and lateral extension of the deposits and their host structures.
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Complex Electrical Conductivity of Kimberlites: A Case of North-Eastern Angola
Authors V. Emelianov, V. Abramov, K. Titov and A. RevilSummaryIn this paper, we present new data about complex conductivity of kimberlite. Six samples of different facies were taken within Alto Cuilo field in Angola: two hard (porphyric) kimberlites, three kimberlite breccia and one tuff-sandstone with kimberlite material. We also measured the specific surface area and the cation exchange capacity. Based on multi-salinity complex conductivity measurements we obtained the formation factor and the real part of the surface conductivity. We found medium–to–high values of the imaginary conductivity (Induced Polarization, IP) especially for the breccia samples. All studied samples contain ore minerals in minor quantity, so the IP effect can be attributed to both ore mineral or clayey matrix. We found a good correlation between the cation exchange capacity and both the quadrature conductivity and the real surface conductivity, which proves that the IP effect is related to the clayey matrix. We also found a satisfactory correlation between the imaginary conductivity and the surface conductivity. The respective slope (0.015) is typical of clayey sandstones. Considering also the surface conductivity values in the range from 0.013 to 0.16 S/m, we state that the values of electrical properties are typical rater of soils or clayey sandstones than of ingenious rocks.
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Monitoring for Microseismicity Induced by Goaf Collapse at Coal Mine
More LessSummaryWe took a detection experiment for the microseismicity induced by goaf collapse (GC) in a coal mine across about 4 months, using our vector scanning (VS) for microseismic monitoring. Through the experiment we tried to understand: What are the magnitude range of the seismic events induced by GC? If most of them belong to the microseismic, what is the detection ability of our microseismic network on the surface at coal mine? Is it possible to monitor both microseismicities induced by tunnel roof stimulation and GC using VS at the same time? What are the space-time characteristics of the microseismicity induced by GC? Is it possible to predict possible disaster by microseismicity instead of waiting the small quakes, at that time the real disaster may have happened? etc.
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Magnetization Vector 3D Inversions of Airborne Magnetic Data Flown Over Grib Kimberlite Pipe
Authors V. Kaminski, A. Davydenko, A. Frolov and I. ShalovenkovaSummaryThis study is describing mapping of Grib kimberlite pipe in Arhangelsk region, Russia using full magnetization vector parameters extracted from airborne magnetic data by means of 3D inversions. The inversion results were used to calculate corrected magnetic susceptibility, which is compared with the results of classical 3D magnetic susceptibility inversion. The corrected magnetic susceptibility allows to map Grib kimberlite pipe more efficiently. The full magnetization vector inversion was also supported by inversion of magnetic field on the basis of vector scanning with use of regularization via elastic net method for evaluation of Magnetic susceptibility and remanent magnetization. The final results are provided as case study and the described methodology can be further used for advanced kimberlite exploration.
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Research and Application of Crack Prediction Technology for Pre-Stack Seismic Data
More LessSummaryFractures are characterized by strong heterogeneity and complex formation mechanism, and their important role in the process of oil and gas accumulation and even development, determine that fractured reservoir prediction has always been an important topic in today’s oil and gas exploration. Therefore, the effective prediction of shale oil fracture development area, development direction, and strength plays a very important role in predicting shale oil sweet spots and improving the benefit development of shale oil. In this paper, AVA is used to predict the development orientation and density of fractures in work area A. Secondly, based on AVA, the amplitude envelope and instantaneous frequency are extracted from each pre-stack azimuth gather, and ellipse fitting is performed to predict fractures and predict fractures. The main direction of the fracture is consistent with the fracture direction revealed by regional geological data. The prestack seismic attributes are used to quantify the degree of fracture development, and the predicted fractures are in good agreement with the FMI logging and core interpretation results.
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Case Studies Showcasing New Developments With Your Existing Potential Fields Datasets
Authors D.J. Fitzgerald, J. Thurston and G. CottewSummaryNumerical differentiation of gravity and magnetic data is conventionally implemented as finite impulse response (FIR) filtering. This works best for first derivatives, but amounts to narrow-band filtering for higher orders. We introduce an approach for differentiation using holomorphic function theory. This process provides high-fidelity, high-order gradients.
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Blast Vibration Prediction
Authors B. Trabi and F. BleibinhausSummaryFor mining operators it is essential to predict peak ground velocity (PGV) to minimize the impact of vibrations to sensitive areas nearby. There are numerous empirical formulas for this purpose and one of these is the USBM Scaled Distance (SD) approach. We investigate this approach and explored other strategies to predict the PGV. The Data for that study was derived from a array of 81 acceleration sensors deployed over several months inside and next to the mine. The large array made it possible to calibrate the decay exponent b in common blast gathers. We also present a method where we sequentially invert for the charge exponent c and then for the decay exponent. Finally we introduce a joint inversion where we invert the whole dataset to constrain the global b and c values. With that measurements we were able to compare the approaches and make prediction tests. Based on the key performance indicators like the root mean square residual and coefficient of determination we came to the conclusion that the currently used USBM SD approach performed worst. We also gained insights in parameter distributions and data uncertainty of the measured PGV.
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Underwater Electrical Resistivity Tomography to Characterize Subaquatic Tailing Deposits in Portman Bay (Spain)
Authors P. Martínez-Pagán, L. Rivero, M. Canals, M. Martínez-Segura, A. Urruela, A. Sendrós, A. Baza, R. Lovera, M. Himi and A. CasasSummaryPortman Bay (SE Spain) has been affected by mining activity for more than 30 years. The mining waste disposal has produced changes in its morphology from being clean crescent-shaped in 1957 to being completely buried in 1990 by an estimated amount of 60 Mt of flotation procedure effluent. With the scope of characterising the tailing morphology in the shallow flooded zone, we have carried out an electrical resistivity tomography campaign using cables and electrodes designed for marine settings. The present research has allowed us to characterize the subaquatic tailing dimensions with high resolution in an area where the application of direct methods such as borehole o indirect methods such as reflection seismic might be difficult due to the limited water thickness.
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A Comparison: Ert, Ip and Sp Methods in the Exploration of Graphite in the Lower Austria
Authors A. Preiner, D. Ottowitz, B. Jochum, M. Peresson and A. RömerSummaryThe demand for different mineral raw materials increases from one year to the next, and the same applies to graphite. Especially due to the increasing demand in the course of electromobility. In order to secure the supply for the next years, it is always evaluated whether former mining sites can be reactivated, which is also the case in the investigated measuring area in Amstall (Lower Austria). In the 1980s, Austria was one of the largest graphite exporters worldwide, especially in Lower Austria. Since graphite is very conductive, several geophysical exploration methods are suitable for this purpose. A comparison between the ERT, IP and SP was attempted and subsequently correlated. The SP anomalies were used as a guide to plan the ERT/IP profiles. The certain areas were further investigated based on the geoelectrical measurements by means of geochemical investigations. Based on the results of the measurement methods, different graphite occurrences could be confirmed.
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Remediation Monitoring Guided by 3D Time-Lapse Inversion of Dense Dc Borehole Data
Authors D. Domenzain, L. Liu, A.K. Kühl, I. Yélamos Vela and A.V. ChristiansenSummarySubsurface pollution can be remediated by injecting reactive agents in-situ. However, unknown subsurface pathways may complicate the three-dimensional spread of the remediation agent. In many cases, electrical conductivity is a good proxy for finding the remeadiaton agent at depth.
We present a time-lapse volume of DC conductivity that accuratelly locates the remediation plume in three-dimensional space. Our data were acquired on an uncontaminated controlled site equipped with boreholes having permanent electrodes. The data were collected with a novel multichannel DCIP instrument that has a fast acquisition rate. DC data were inverted using a novel 3D DC inversion algorithm that can efficiently handle sensitivity calculations of large datasets (10data-points), and it can do so on a fine mesh for both forward and inverse models (0.25m in voxel length).
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Mine Blast Source Time Functions
Authors F. Bleibinhaus and B. TrabiSummaryWe develop, calibrate, and test a method to simulate the waveforms of mine blasts. Our model allows for spatial and temporal delays of the blast array, and accounts for the impact of charge weight on amplitude and bandwidth. We verify the method using a large station array deployed at an ore mine. Although the waveform fit at specific stations is often limited, we can demonstrate a detailed match of resonance modes and side-lobes in mean amplitude spectra. Our goal is to use the STF for deconvolution in seismic imaging and for PGV prediction.
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Characterizing Volcanogenic Massive Sulphides Using Acoustic Impedance Inversion, Neves-Corvo, Southern Portugal
Authors G.A. Donoso, C. Bautista, A. Malehmir and V. AraujoSummaryThe Neves-Corvo mining area in southern Portugal has proven in the past decades to be a notable example for the use of seismic technologies for the detection and targeting of volcanogenic massive sulphide (VMS) deposits, in particular copper and zinc bearing Lombador and Semblana. Post-stack acoustic inversion was used having as input a 3D reflection seismic volume from the area together with sonic and density logs from a well intersecting the Semblana deposit. Resulting in a density attribute volume that matched the known Semblana deposit, and that also allowed to characterize the density body corresponding to the Lombador deposit. Additionally showing that a strong shallow reflection associated to a lithological contact did not represent a high-density feature, making a good case for the predictability of seismic inversion methods for mineral exploration in hardrock settings. This method would allow to predict and export a geobody of rock properties, in particular density, analogous to the VMS deposits in the Neves-Corvo area.
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A High-Resolution Seismic Survey Across the Balmuccia Peridotite, Ivrea Zone, Italy – Project Dive
Authors D. Pasiecznik, A. Greenwood, F. Bleibinhaus and G. HetényiSummaryThe Ivrea Verbano Zone (IVZ) is one of the most complete crust–upper mantle geological references in the world, and the Drilling the Ivrea-Verbano zone project (DIVE) aims to resolve the uncertainties below this area. Geophysical anomalies detected across the IVZ indicate that dense, mantle-like rocks are located at depths ca. 1–3 km. One of the goals of this project is the drilling of a 4 km deep borehole that will penetrate the Balmuccia Peridotite (Val Sesia, Italy). The objective of this borehole is to approach, and possibly cross, the crust–mantle transition zone.
Two joint geophysical surveys were performed in October 2020 with the goal of obtaining a seismic characterization of the drill site: (1) a deep seismic survey entitled SEismic imaging of the Ivrea ZonE (SEIZE) and (2) a smaller seismic survey at the proposed drill site, entitled High-resolution SEismic imaging of the Ivrea ZonE (HiSEIZE). In this study, we focus on the HiSEIZE data.
This project will not only provide site characterization for the DIVE project, but also contribute to understanding the structure of the Balmuccia Peridotite, its changes in depth and its relationship with the crustal-mantle transition.
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Evaluation of Machine Learning Algorithms for the Classification of Lithology Using Geophysical Logs
Authors O. Atita, R. Durrheim and E. SaffouSummaryClassification of subsurface formation lithology from well log data is a significant task in geoscience, petroleum exploration and engineering. Presently, several machine learning algorithms have been implemented for lithology classification to improve the prediction accuracy. However, due to the complex geological conditions, such algorithms are hardly adopted for mineral deposits. In his paper, we evaluated three popular machine learning algorithms, such as the Support Vector Machine, Random Forest and Gradient Boosting Decision Tree. This study used the process of grid search and 10-fold cross-validation to optimize the hyperparameters of each model and avoid overfitting. The performance of each model is evaluated using metrics of accuracy, precision, recall and F1-score of predicted labels of lithology against the true labels. The results show that the Gradient Boosting Decision Tree model has better lithology classification performance, with a precision of 97.74%, recall of 98.67% and F1-score of 98.20% among other models. The interpretation of GBDT model shows that the order of features contributing to the lithology classification is VP >Density >Vs > natural gamma. The study reveals that GBDT model can provide significant information for further exploration targeting of deep mineral deposits.
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Rock Microstructure and Attenuation of Elastic Waves Influence on the Effective Parameters Selection in Porous-Fractured Media
Authors G. Damjanovic, I. Bayuk and M. KrasnovaSummaryAt present, to assess the microstructure of porous-fractured media, it is customary to use theoretical models of effective properties based on the theory of elasticity. However, when using these models, the effective elastic parameters often turn out to be overestimated. In this regard, it becomes necessary to switch to viscoelastic models, in which the elastic moduli are replaced by complex viscoelastic ones. This work is devoted to the construction of viscoelastic models of rocks of the Domanik Formation in order to assess the influence of the viscoelastic properties of the components that make up the rock and the parameters of its microstructure on the attenuation of elastic waves and velocity. Dolomite with an admixture of earth silicon, uniformly saturated with kerogen, was chosen as the object of study.
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Reappraisal of Legacy Reflection Seismic Data for Gold Exploration: Case Study From Witwatersrand Goldfields, South Africa
Authors N. Mutshafa, M. Manzi and M. WestgateSummaryReappraisal of legacy reflection seismic data has shown to deliver value, particularly in brownfield settings. The 25.3 km long seismic profile used in this study was acquired in 1983, by the Gold Division of Anglo American, as part of their Witwatersrand goldfields exploration program. In this work, we demonstrate how the reappraisal of legacy reflection seismic data can be advantageous in the mineral exploration industry by using the latest seismic processing tools to improve the imaging resolution. The purpose of this study is to improve the imaging of the Ventersdorp Contact Reef (VCR) gold orebody, situated at depths between 2400 and 3900 m below the Fochville gold mines surface, South Africa. The preliminary results of the reprocessed legacy seismic section reveal a dipping reflection associated with the VCR mineralization.
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