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FVM results of the COGITO-MIN reflection seismic profile Line A (a-c) and Line B (d-f). The influence of Vibroseis (Line A: 121, Line B: 152 source points) and explosive sources (Line A: 98, Line B: 58 source points) to the final image of profiles A and B are separated in (b) and (c) as well as (e) and (f), respectively.
Source publication
![Figure 1. Layout of the COGITO-MIN profiles on a geological map [12]...](publication/332771307/figure/fig1/AS:753568218873857@1556676072446/Layout-of-the-COGITO-MIN-profiles-on-a-geological-map-12-and-on-the-aerial-photo-The_Q320.jpg)
We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3–4 source points per kilometer along a seismic profile. Our results encourage the use of 2D seismic reflection profiling as a reconnaissance tool for mineral exploration in areas wi...
Contexts in source publication
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... stacking the energy instead of the migrated phases, the stacking result is less affected by velocity errors avoiding destructive interference. The FVM results show steep reflectors within the upper 1 km of the seismic section, strong but discontinuous reflectivity underneath the known Kylylahti body, and prominent reflectors at 4-7 km depth (Figure 9). Additionally, some dipping reflectors are imaged at the edges of the Kylylahti body. ...
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... some dipping reflectors are imaged at the edges of the Kylylahti body. Figure 9 shows separate stacks for shot gathers acquired with Vibroseis and explosive Figure 8. Detail of the seismic section A using (a) 5400 m/s and (b) 9000 m/s constant velocity for NMO correction followed by PoSTM and (c) DMO followed by the PoSTM. Figure (d) shows the PreSTM result of the same location. ...
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... stacking the energy instead of the migrated phases, the stacking result is less affected by velocity errors avoiding destructive interference. The FVM results show steep reflectors within the upper 1 km of the seismic section, strong but discontinuous reflectivity underneath the known Kylylahti body, and prominent reflectors at 4-7 km depth (Figure 9). Additionally, some dipping reflectors are imaged at the edges of the Kylylahti body. ...
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... some dipping reflectors are imaged at the edges of the Kylylahti body. Figure 9 shows separate stacks for shot gathers acquired with Vibroseis and explosive sources. For both of the profiles, subsurface reflectivity characteristics are somewhat independent of the source type and distribution. ...
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... Figure 9, the contribution of the Vibroseis and explosive data to the FVM stack are shown. For line A, the explosive source points are more evenly distributed along the profile length than for The PreSTM results with a limited number of shot gathers could not image reflections when every 5th source gather was stacked, and these results are not discussed further. ...
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... Figure 9, the contribution of the Vibroseis and explosive data to the FVM stack are shown. For line A, the explosive source points are more evenly distributed along the profile length than for line B (Figure 1) and thus also the resulting stacks from only Vibroseis and only explosive source records are more similar than in the case of line B, where most of the explosive sources are located in the SE end of the profile. ...
Citations
... Seismic imaging technology, as a method to obtain information about underground geological structures by analyzing the propagation and reflection of seismic waves, plays a crucial role in geological exploration 1-3 , resource development [4][5][6] , underground water detection 7,8 , and other fields. This technology records the vibration signals of seismic waves propagating underground using seismic instruments and processes and interprets these data through mathematical algorithms and signal processing techniques to obtain the physical properties and structural characteristics of underground media. ...
Seismic imaging techniques play a crucial role in interpreting subsurface geological structures by analyzing the propagation and reflection of seismic waves. However, traditional methods face challenges in achieving high resolution due to theoretical constraints and computational costs. Leveraging recent advancements in deep learning, this study introduces a neural network framework that integrates Transformer and Convolutional Neural Network (CNN) architectures, enhanced through Adaptive Spatial Feature Fusion (ASFF), to achieve high-resolution seismic imaging. Our approach directly maps seismic data to reflection models, eliminating the need for post-processing low-resolution results. Through extensive numerical experiments, we demonstrate the outstanding ability of this method to accurately infer subsurface structures. Evaluation metrics including Root Mean Square Error (RMSE), Correlation Coefficient (CC), and Structural Similarity Index (SSIM) emphasize the model's capacity to faithfully reconstruct subsurface features. Furthermore, noise injection experiments showcase the reliability of this efficient seismic imaging method, further underscoring the potential of deep learning in seismic imaging.
... Geophysical methods allow a three-dimensional perspective of the study area and its physical properties. Among the multiple existent geophysical methods, the magnetic, gravimetric, electromagnetic (EM), seismic and radiometric methods have had a relevant role in the study of metallic mineral deposits, contributing to characterize the different geological formations and lithological units, delimit hydrothermal alteration zones and gather information at depth on the geometry and properties of the mineralized bodies (e.g., Neroni and Hunt, 2022;Lü et al., 2013Lü et al., , 2021Yan et al., 2021;Heinonen et al., 2019;Andersson and Malehmir, 2018;Thomas et al., 2016;Xue et al., 2014). In the IPB Portuguese sector, gravimetric, EM and seismic methods have had a vital role in the last decades (e.g., Leca, 1990;Oliveira et al., 1997;Carvalho et al., 2011;Yavuz et al., 2015;Matos et al., 2020;Dias et al., 2021;Donoso et al., 2021;Marques et al., 2022). ...
... Moreover, terrain access, noisy mining infrastructure and logistics cause many seismic surveys to result in irregular/sparse 3D or crooked-line 2D coverage, which in turn brings imperfect illumination of the target. Recent case studies performed in such conditions suggest that pre-stack depth migration (PreSDM) can effectively deal with such challenges where the conventional time-domain approach fails [18][19][20][21][22]. ...
... However, in the context of mineral exploration, PreSDM application is very limited. The application of raybased methods is so far concentrated on Kirchhoff pre-stack depth migration (KPreSDM) and its advanced forms i.e., coherency migration (CM) [20,23], and Fresnel Volume Migration (FVM)-a refined version of beam-type migration [18,19,21,22]. For wave-equation-based methods, one-way wave-equation migration was successfully used both for imaging and velocity model building [24]. ...
... The pre-processing applied to the data before migration followed the same workflow as presented in [19] for processing the COGITO-MIN 2D data (Table 2). There was, however, a notable difference in how the refraction statics was handled. ...
Seismic imaging is now a well-established method in mineral exploration with many successful case studies. Seismic data are usually imaged in the time domain (post-stack or pre-stack time migration), but recently pre-stack depth imaging has shown clear advantages for irregular/sparse acquisitions and very complex targets. Here, we evaluate the effectiveness of both ray-based and wave-equation-based pre-stack depth imaging methodologies applied to crooked-line 2D seismic reflection profiles. Seismic data were acquired in the Kylylahti mining area in eastern Finland over severely folded, faulted and subvertical Kylylahti structure, and associated mineralization. We performed 3D ray-based imaging, i.e., industry-standard Kirchhoff migration and its improved version (coherency migration, CM), and wave-equation-based migration, i.e., reverse time migration (RTM) using a velocity model built from first-arrival traveltime tomography. Upon comparing the three different migrations against available geological data and models, it appeared that CM provided the least noisy and well-focused image, but failed to image the internal reflectivity of the Kylylahti formation. RTM was the only method that produced geologically plausible reflections inside the Kylylahti formation including a direct image of the previously known shallow massive sulfide mineralization.
... They retain a good resolution with depth and provide robust imaging results if carefully planned, acquired, and interpreted considering complexity of the geology being addressed. Originally developed for oil and gas industry, the method has now routinely been adapted for hardrock and crystalline rock settings (e.g., Bellefleur et al., 2004;Dehghannejad et al., 2010;Cheraghi et al., 2012;Koivisto et al., 2012;Malehmir et al., , 2014Manzi et al., 2012;Urosevic et al., 2013;Place et al., 2015;Heinonen et al., 2019). Given sometimes their criticality for the industry and improved living standards, several R&D programme worldwide and particularly within the EU have been initiated calling for innovative and effective solutions for sustainable exploration and exploitation of raw materials. ...
Mineral exploration has in recent years moved its focus to greater depths than ever before, particularly in brown fields. Exploring new deposits at depth, if economical, would not only expand the life of mine but also provide minimal environmental impacts. It allows the existing mining infrastructures to be used for a longer period. Exploration at depth, however, is challenging and requires a multidisciplinary team and methods, and innovative thinking for generating new targets and effective exploration expenditure. The application of seismic methods for mineral exploration has increasingly been conducted over the past 20 years because they provide high-resolution subsurface images, and retain good resolution with depth as compared with other geophysical methods. Nevertheless, and despite challenges in hardrock settings, only limited attention has been given to seismic interpretations, often performed subjectively. With the growing application of machine-learning solutions, hardrock seismic data can benefit these for improved interpretations and target generations.
This thesis showcases different workflows developed for deep-targeting metallic mineral deposits, starting from high-fold 2D, through sparse 3D reflection imaging and the implementation of deep-learning algorithms for diffraction pattern recognitions. Three different deposits were studied from Sweden and Canada. The Blötberget iron-oxide mineralization in central Sweden was first targeted in 2D, followed-up, a sparse 3D dataset was acquired enabling to image the mineralization both laterally and with depth, providing good knowledge on subsurface structures controlling the geometry of the deposits. In Canada, Halfmile Lake and Matagami mining sites were studied due to the accessibility to 3D seismic datasets, which contained diffraction signals as deposit responses. Deeplearning algorithms were utilized for the proof-of-concept and at the same time helped to generate new potential targets from other diffraction signals that were not obvious to an interpreter’s eye due to their incomplete tails originated outside of the seismic volume. The studies in this thesis show the effectiveness of seismic methods for mineral exploration at depth, especially in 3D, as they provide, among others, structural interpretation for future mineplanning purposes. Deep-learning solutions provide improved results for diffraction delineation and denoising and have great potential for hardrock seismics.
... Low impedance contrasts, scattering and incoherent reflections all represent major challenges to building a velocity model using methods such as reflection tomography or migration velocity analysis (Singh et al., 2019). Adjusting the PSDM algorithm with some innovative approaches (e.g., Fresnel volume migration) has provided promising results for a wide range of seismic applications (Buske et al., 2009) and recently also for mineral exploration (Bräunig et al., 2020;Heinonen et al., 2019). ...
Established 2D seismic data processing methods such as Kirchhoff pre‐stack time migration and Kirchhoff pre‐stack depth migration function relatively well for regular acquisition geometries and well‐constrained velocity models. Recently developed focusing pre‐stack depth migration methods have the potential to enhance image quality in the case of sparse and non‐regular source‐receiver distribution. We have tested the performance of the coherency migration method as one of these focusing migration approaches in comparison to standard dip‐moveout and Kirchhoff pre‐stack time migration techniques by applying them to the Swayze East seismic profile acquired in the Abitibi greenstone belt of Canada This seismic profile represents a crooked‐line survey that intersects several metal‐bearing deformation zones, providing good target geometries to examine various pre‐stack migration methods. Analysis of the seismic data indicates reflectivity associated with shallowly dipping reflections appear relatively well preserved over the entire 0–6 km offset range for the frequency range between 20 to 90 Hz. Although most reflections are visible already in either the dip‐moveout or the Kirchhoff pre‐stack time migration results, coherency migration method delivers the most improved image showing all reflective structures inferred for this area. The comparisons suggest the coherency migration method can be considered as superior in terms of resulting seismic image quality compared to conventional approaches for this type of crooked‐line seismic survey in such a complex geological setting. This article is protected by copyright. All rights reserved
... Reflection seismic methods have become one of the most used techniques for imaging the subsurface because they can provide high-resolution images of geological structures and lithological boundaries. Over the last few decades, reflection seismic methods have been developed and improved for mineral exploration and mine planning, mainly 2D seismic surveys, due to their lower cost and footprints compared to 3D surveys (Wright et al., 1994;Milkereit et al., 1996;Eaton et al., 2003a,b;Chen et al., 2004;Malehmir and Bellefleur, 2009;Dehghannejad et al., 2010;Cheraghi et al., 2011Cheraghi et al., , 2013Koivisto et al., 2012;Ahmadi et al., 2013;Malehmir et al., 2014Malehmir et al., , 2017aDonoso et al., 2019;Heinonen et al., 2019;Bräunig et al., 2020;Gil et al., 2021). Recently, however, there has been an increased use of 3D seismic surveys for this purpose in Canada (Adam et al., 2003;Cheraghi et al., 2015;Bellefleur et al., 2015), South Africa (Manzi et al., 2012a(Manzi et al., , 2013(Manzi et al., , 2019, Australia (Urosovic et al., 2012), Finland 2018;Singh et al., 2019), and Sweden . ...
Mineral exploration is facing greater challenges nowadays because of the increasing demand for raw materials and the lesser chance of finding large deposits at shallow depths. To be efficient and address new exploration challenges, high‐resolution and sensitive methods that are cost‐effective and environmentally friendly are required. In this work, we present results of a sparse 3D seismic survey that was conducted in the Zinkgruvan mining area, in the Bergslagen mineral district of central Sweden. The survey covers an area of 10.5 km2 for deep targeting of massive sulphides in a polyphasic tectonic setting. A total of 1311 receivers and 950 shot points in a fixed 3D geometry setup was employed in for the survey. Nine 2D profiles and a smaller 3D mesh were used. Shots were generated at every 10 m, and receivers were placed at every 10–20 m, along the 2D profiles, and 40–80 m in the mesh area. An analysis of the seismic fold coverage at depth was used to determine the potential resolving power of this sparse 3D setup. The data processing had to account for cultural noise from the operating mine and strong source‐generated surface‐waves, which were attenuated during both, pre‐ and post‐stack processing steps. The processing workflow employed a combination of 2D and 3D refraction static corrections, and post‐stack FK‐filters along inlines and crosslines. The resulting 3D seismic volume is correlated with downhole data (density and P‐wave, acoustic impedance, reflection coefficient), synthetic seismograms, surface geology and 3D model of mineral‐bearing horizons in order to suggest new exploration targets at depth. The overall geological architecture at Zinkgruvan is interpreted as two EW overturn folds, an antiform and a synform, affected by later NS‐trending folding. Two strong sets of shallow reflections, associated with the Zn‐Pb mineralization, are located at the hinge of an EW‐trending antiform, while a strong set of reflections, associated to the main mineralization, is located at the overturned apex of the EW synform. The NS Knalla fault that crosses the study area terminates the continuation of the mineral‐bearing deposits at depth towards the west, a conclusion solely based on the reflectivity character of the seismic volume. This study illustrates that sparse 3D data acquisition, while it has its own challenges, can be a suitable replacement for 2D profiles while line cutting, and environmental footprints can totally be avoided. This article is protected by copyright. All rights reserved
... Unfortunately, this approach can fail to address all of the imaging challenges. Unlike the oil and gas exploration, where prestack depth migration (PreSDM) is often the standard imaging method, it has been only recently applied to characterise the geologically complex hardrock environment in a mineral exploration context (Schmelzbach et al., 2008;Hloušek et al., 2015;Heinonen et al., 2019;Singh et al., 2019;Bräunig et al., 2020;Brodic et al., 2021). ...
A sparse 3D seismic survey was acquired over the Blötberget iron oxide deposits of the Ludvika Mines in south-central Sweden. The main aim of the survey was to delineate the deeper extension of the mineralisation and to better understand its 3D nature and associated fault systems for mine planning purposes. To obtain a high-quality seismic image in depth, we applied time-domain 3D acoustic full-waveform inversion (FWI) to build a high-resolution P-wave velocity model. This model was subsequently used for pre-stack depth imaging with reverse time migration (RTM) to produce the complementary reflectivity section. We developed a data preprocessing workflow and inversion strategy for the successful implementation of FWI in the hardrock environment. We obtained a high-fidelity velocity model using FWI and assessed its robustness. We extensively tested and optimised the parameters associated with the RTM method for subsequent depth imaging using different velocity models: a constant velocity model, a model built using first-arrival travel-time tomography and a velocity model derived by FWI. We compare our RTM results with a priori data available in the area. We conclude that, from all tested velocity models, the FWI velocity model in combination with the subsequent RTM step provided the most focussed image of the mineralisation and we successfully mapped its 3D geometrical nature. In particular, a major reflector interpreted as a cross-cutting fault, which is restricting the deeper extension of the mineralisation with depth, and several other fault structures which were earlier not imaged were also delineated. We believe that a thorough analysis of the depth images derived with the combined FWI–RTM approach that we present here can provide more details which will help with better estimation of areas with high mineralisation, better mine planning and safety measures.
... Hence, the slowness estimation (and therefore FVM) is completely data driven and needs no a priori in-formation on strike and dip directions of the expected structures. This ability to image arbitrary dips and strikes without a priori information makes FVM extremely robust for imaging in hard-rock environments, especially when the signalto-noise ratio is low, the coverage of the data is sparse and the impedance contrasts of the expected structures are small, as shown in Heinonen et al. (2019). Therefore, we used FVM as the preferred imaging technique for the 3D dataset here in this study. ...
We present pre-stack depth-imaging results for a case study of 3D reflection
seismic exploration at the Blötberget iron oxide mining site belonging
to the Bergslagen mineral district in central Sweden. The goal of the study
is to directly image the ore-bearing horizons and to delineate their
possible depth extension below depths known from existing boreholes. For
this purpose, we applied a tailored pre-processing workflow and two
different seismic imaging approaches, Kirchhoff pre-stack depth migration
(KPSDM) and Fresnel volume migration (FVM). Both imaging techniques deliver
a well-resolved 3D image of the deposit and its host rock, where the FVM
image yields a significantly better image quality compared to the KPSDM
image. We were able to unravel distinct horizons, which are linked to known
mineralization and provide insights on their possible lateral and depth
extent. Comparison of the known mineralization with the final FVM reflection
volume suggests a good agreement of the position and the shape of the imaged
reflectors caused by the mineralization. Furthermore, the images show
additional reflectors below the mineralization and reflectors with opposite
dips. One of these reflectors is interpreted to be a fault intersecting the
mineralization, which can be traced to the surface and linked to a fault
trace in the geological map. The depth-imaging results can serve as the
basis for further investigations, drilling, and follow-up mine planning at
the Blötberget mining site..
... The passive seismic experiment was performed in the Kylylahti mine area between early August and late September 2016 as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe; Koivisto et al., 2018) project. This project aimed for development of an efficient integrated exploration workflow ranging from regional-scale exploration to detailed resource delineation and mine planning including an active-source and passive seismic component. ...
For the first time, we apply a full-scale 3D seismic
virtual-source survey (VSS) for the purpose of near-mine mineral
exploration. The data were acquired directly above the Kylylahti underground
mine in Finland. Recorded ambient noise (AN) data are characterized using
power spectral density (PSD) and beamforming. Data have the most energy at
frequencies 25–90 Hz, and arrivals with velocities higher than 4 km s−1 have a
wide range of azimuths. Based on the PSD and beamforming results, we created
10 d subset of AN recordings that were dominated by multi-azimuth
high-velocity arrivals. We use an illumination diagnosis technique and
location procedure to show that the AN recordings associated with high
apparent velocities are related to body-wave events. Next, we produce 994
virtual-source gathers by applying seismic interferometry processing by
cross-correlating AN at all receivers, resulting in full 3D VSS. We apply
standard 3D time-domain reflection seismic data processing and imaging using
both a selectively stacked subset and full passive data, and we validate the
results against a pre-existing detailed geological information and 3D
active-source survey data processed in the same way as the passive data. The
resulting post-stack migrated sections show agreement of reflections between
the passive and active data and indicate that VSS provides images where the
active-source data are not available due to terrain restrictions. We
conclude that while the all-noise approach provides some higher-quality
reflections related to the inner geological contacts within the target
formation and the general dipping trend of the formation, the selected
subset is most efficient in resolving the base of formation.
... Consequently, seismic methods, which can provide su cient depth penetration and superior image resolution, are becoming more attractive. Moreover, recent advancements in the acquisition, processing, and imaging have made modern seismic methods more cost-e ective, making them viable options for non-hydrocarbon exploration (Yavuz et al., 2015;Heinonen et al., 2019). ...
... Other techniques focus instead on poststack signal enhancement through attribute analysis (Górszczyk et al., 2015;Hajnal et al., 2015;Manzi et al., 2015). Furthermore, studies also show that Fresnel volume migration (FVM), as an advanced seismic imaging technique based on prestack depth migration, is particularly e ective in delivering high-resolution seismic images in hard-rock environments (e.g., Heinonen et al., 2019;Jusri et al., 2019;Hlouöek et al., 2015a). ...
... Advanced seismic processing and imaging techniques in hard-rock environments should be prioritized to allow the accuracy of the subsequent processes in QSI, which can lead to improving the feasibility of QSI in these environments. To this end, studies show that Fresnel volume migration (FVM) is an advanced seismic imaging technique that has proven e ective in hard-rock environments (e.g., Hlouöek et al., 2015b;Riedel et al., 2015;Heinonen et al., 2019;Jusri et al., 2019). The following two chapters of this dissertation will further discuss the application of FVM in a hard-rock environment and a method to perform FVM for AVA analysis. ...
Quantitative seismic interpretation (QSI) has been widely used in oil and gas exploration in sedimentary environments and has been shown to be effective for reservoir characterization, leading to an increase in oil and gas discoveries. Various studies show promising indications that QSI may also be feasible in hard-rock environments, especially for geothermal and mineral exploration. However, despite rapid improvements in seismic processing and imaging techniques in hard-rock environments in recent decades, little progress in QSI for hard-rock exploration has been reported. As a result, fundamental questions, such as whether implementing QSI in hard-rock environments is feasible and how to integrate QSI in a comprehensive hard-rock exploration workflow, remain unanswered. In order to address these questions, this dissertation presents a comprehensive discussion on determining the key aspects for reliable QSI in hard-rock environments. Specifically, this dissertation discusses the feasibility of QSI in terms of amplitude-versus-angle (AVA) analysis through Fresnel volume migration (FVM). The integration of FVM and QSI is expected to be a solution to improve quantitative characterization in hard-rock environments.
This dissertation is publication-based and comprises three main chapters. The first main chapter discusses two case studies utilizing QSI in sedimentary and hard-rock environments, using data from the New Jersey shelf and a metamorphic formation in Southern Tuscany. This chapter provides an analysis to determine the most important factors for reliable QSI, especially in hard-rock environments, i.e., optimal seismic processing and imaging. The second main chapter contains a publication showing an extensive case study where optimal seismic processing followed by FVM was successfully performed to reveal high-resolution seismic K-Horizon in metamorphic rocks below a geothermal field in Southern Tuscany. Finally, the third main chapter discusses a method for obtaining angle domain common-image gathers (ADCIGs) from FVM, which can be used to facilitate AVA analysis from the migration output. The synthetic test results suggest that this method can be effective for identifying AVA anomalies in qualitative AVA analysis. Overall, the outcomes of this dissertation can potentially improve the feasibility of QSI in hard-rock environments, which can lead to more progressive hard-rock characterization, especially for geothermal and mineral resource exploration.
