Editorial

3 pages, 150 KiB

Open AccessEditorial

Editorial for Special Issue “Seismic Methods in Mineral Exploration”

by Gilles Bellefleur, Michal Malinowski and Milovan Urosevic

Minerals 2019, 9(10), 630; https://doi.org/10.3390/min9100630 - 15 Oct 2019

Cited by 4 | Viewed by 2935

In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and on new exploration tools and techniques used to guide deep and costly boreholes to most suitable [...] Read more.

In many parts of the world, exploration for mineral deposits is moving progressively but persistently to greater depths, relying on knowledge gained from previous exploration campaigns and on new exploration tools and techniques used to guide deep and costly boreholes to most suitable targets [...] Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

Research

Jump to: Editorial

16 pages, 2779 KiB

Open AccessArticle

Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland

by Niina Junno, Emilia Koivisto, Ilmo Kukkonen, Alireza Malehmir and Markku Montonen

Minerals 2019, 9(9), 529; https://doi.org/10.3390/min9090529 - 30 Aug 2019

Cited by 5 | Viewed by 3254

Abstract

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive [...] Read more.

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. The interpretation of these reflections has been complicated by disparate borehole data, particularly because of the scarce amount of available sonic borehole logs and the varying practices in logging of borehole lithologies. SOM is an unsupervised data mining method based on vector quantization. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

23 pages, 5564 KiB

Open AccessArticle

Elucidating the Effects of Hydrothermal Alteration on Seismic Reflectivity in the Footwall of the Lalor Volcanogenic Massive Sulfide Deposit, Snow Lake, Manitoba, Canada

by Ernst Schetselaar, Gilles Bellefleur and Patricia Hunt

Minerals 2019, 9(6), 384; https://doi.org/10.3390/min9060384 - 25 Jun 2019

Cited by 5 | Viewed by 4147

Abstract

The integrated analysis of seismic rock properties, lithogeochemical data, and mineral compositional data, estimated via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), provides insight into the effects of hydrothermal alteration on seismic reflectivity in the footwall of the Lalor volcanogenic massive sulfide (VMS) [...] Read more.

The integrated analysis of seismic rock properties, lithogeochemical data, and mineral compositional data, estimated via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), provides insight into the effects of hydrothermal alteration on seismic reflectivity in the footwall of the Lalor volcanogenic massive sulfide (VMS) deposit, Manitoba, Canada. The effects of hydrothermal alteration on variations in acoustic impedance are secondary in magnitude and superimposed on the dominant acoustic impedance contrast between felsic and mafic volcanic protoliths. This secondary effect is due to an increase in P-wave velocity with increasing intensity of hydrothermal alteration, as measured by the Ishikawa and Carbonate-Chlorite-Pyrite alteration indices. Mixture modeling of the seismic rock properties and mineral percentages suggests that the increase in seismic velocity is due to an increase in abundance of cordierite, which is one of the diagnostic aluminum silicates for hydrothermally-altered volcanic rocks metamorphosed in the upper almandine amphibolite facies. The synthetic seismic data of a simple VMS model consisting of mafic-felsic host rock contacts, a sulfide ore lens, and a discordant hydrothermal conduit, consisting of the amphibolite-facies mineral assemblage (600 °C, 6 kbar) encountered at Lalor, show enhanced seismic reflections at conduit-host rock contacts, in comparison to its greenschist facies equivalent (350 °C, 2.5 kbar). This zone of enhanced seismic reflectivity in the footwall of the massive sulfide ore zone is also recognized on the Lalor seismic data suggesting that high-grade terrains hosting VMS deposits possess enhanced potential for the seismic detection of their footwall hydrothermal alteration zones. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

22 pages, 18862 KiB

Open AccessArticle

Sparse 3D Seismic Imaging in the Kylylahti Mine Area, Eastern Finland: Comparison of Time Versus Depth Approach

by Brij Singh, Michał Malinowski, Felix Hloušek, Emilia Koivisto, Suvi Heinonen, Olaf Hellwig, Stefan Buske, Michał Chamarczuk and Sanna Juurela

Minerals 2019, 9(5), 305; https://doi.org/10.3390/min9050305 - 17 May 2019

Cited by 23 | Viewed by 5304

Abstract

A 10.5 km² 3D seismic survey was acquired over the Kylylahti mine area (Outokumpu mineral district, eastern Finland) as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project, which aimed at the development of [...] Read more.

A 10.5 km² 3D seismic survey was acquired over the Kylylahti mine area (Outokumpu mineral district, eastern Finland) as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project, which aimed at the development of cost-effective geophysical imaging methods for mineral exploration. The cost-effectiveness in our case was related to the fact that an active-source 3D seismic survey was accomplished by using the receiver spread originally designed for a 3D passive survey. The 3D array recorded Vibroseis and dynamite shots from an active-source 2D seismic survey, from a vertical seismic profiling experiment survey, as well as some additional “random” Vibroseis and dynamite shots made to complement the 3D source distribution. The resulting 3D survey was characterized by irregular shooting geometry and relatively large receiver intervals (50 m). Using this dataset, we evaluate the effectiveness of the standard time-imaging approach (post-stack and pre-stack time migration) compared to depth imaging (standard and specialized Kirchhoff pre-stack depth migration, KPreSDM). Standard time-domain processing and imaging failed to convincingly portray the first ~1500 m of the subsurface, which was the primary interest of the survey. With a standard KPreSDM, we managed to obtain a good image of the base of the Kylylahti formation bordering the extent of the mineralization-hosting Outokumpu assemblage rocks, but otherwise the image was very noisy in the shallower section. The specialized KPreSDM approach (i.e., coherency-based Fresnel volume migration) resulted in a much cleaner image of the shallow, steeply dipping events, as well as some additional deeper reflectors, possibly representing repetition of the contact between the Outokumpu assemblage and the surrounding Kalevian metasediments at depth. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

15 pages, 17005 KiB

Open AccessArticle

Cost-Effective Seismic Exploration: 2D Reflection Imaging at the Kylylahti Massive Sulfide Deposit, Finland

by Suvi Heinonen, Michal Malinowski, Felix Hloušek, Gardar Gislason, Stefan Buske, Emilia Koivisto and Marek Wojdyla

Minerals 2019, 9(5), 263; https://doi.org/10.3390/min9050263 - 30 Apr 2019

Cited by 19 | Viewed by 6431

Abstract

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 [...] Read more.

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 with limited access for active seismic surveys. We used the seismic data acquired within the COGITO-MIN project comprising two approximately 6 km long seismic reflection profiles at the polymetallic Kylylahti massive sulfide mine site in eastern Finland. The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. We discuss post-stack and pre-stack data processing and compare time and depth imaging techniques in this geologically complex Precambrian hardrock area. The seismic reflection profiles show prominent reflectors at 4.5–8 km depth utilizing different migration routines. In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

20 pages, 8099 KiB

Open AccessArticle

Simultaneous Inversion of Shallow Seismic Data for Imaging of Sulfurized Carbonates

by Kamil Cichostępski, Jerzy Dec and Anna Kwietniak

Minerals 2019, 9(4), 203; https://doi.org/10.3390/min9040203 - 28 Mar 2019

Cited by 11 | Viewed by 3819

Abstract

In this article, we present a high-resolution shallow seismic surveying method for imaging the inner structure of the Miocene evaporitic formation, where sulfur ore occurs. The survey was completed in the northern part of the Carpathian Foredeep (SE Poland) where sulfur deposits occur [...] Read more.

In this article, we present a high-resolution shallow seismic surveying method for imaging the inner structure of the Miocene evaporitic formation, where sulfur ore occurs. The survey was completed in the northern part of the Carpathian Foredeep (SE Poland) where sulfur deposits occur up to a depth of ca. 260 m. In this region, the sulfur ore is strata-bound and exists within a carbonate interval of a thickness of approximately 28 m. The average sulfur content reaches up to 30%. Five seismic profiles were acquired with a total length of 2450 m. The acquisition was designed to obtain high-resolution, long offsets and a satisfactory signal-to-noise ratio. In the field, we used 48 channels and variable end-on roll-along spread that allowed us to record offsets of up to 375 m. Data processing was aimed at preserving relative amplitudes (known as RAP, relative amplitude preservation processing), an approach that is necessary for seismic inversion application. With the utilization of well log data and results of simultaneous inversion, we were able to calculate the elastic properties of the deposit to evaluate sulfur ore content and changes in lithology. The sulfur content is strongly dependent on the carbonate reservoir’s porosity. To evaluate porosity changes and associated sulfur content, a simultaneous inversion procedure was used. This is a pioneering approach in which we applied pre-stack inversion methods to shallow carbonate sediments. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

14 pages, 9988 KiB

Open AccessArticle

Acquisition and Processing of Wider Bandwidth Seismic Data in Crystalline Crust: Progress with the Metal Earth Project

by Mostafa Naghizadeh, David Snyder, Saeid Cheraghi, Steven Foster, Samo Cilensek, Elvis Floreani and Jeff Mackie

Minerals 2019, 9(3), 145; https://doi.org/10.3390/min9030145 - 28 Feb 2019

Cited by 29 | Viewed by 8052

Abstract

The Metal Earth project acquired 927 km of deep seismic reflection profiles from August to November of 2017. Seismic data acquired in this early stage of the Metal Earth project benefited greatly from recent advances in the petroleum sector as well as those [...] Read more.

The Metal Earth project acquired 927 km of deep seismic reflection profiles from August to November of 2017. Seismic data acquired in this early stage of the Metal Earth project benefited greatly from recent advances in the petroleum sector as well as those in mineral exploration. Vibroseis acquisition with receivers having a 5 Hz response (10 dB down) generated records from a sweep signal starting at 2 Hz, sweeping up to 150 Hz or 200 Hz. Not only does this broadband signal enhance reflections from the deepest to the shallowest crust, but it also helps the use of full waveform inversion (e.g., to mitigate cycle-skipping) and related techniques. Metal Earth regional-scale transects using over 5000 active sensors target mineralizing fluid pathways throughout the crust, whereas higher spatial-resolution reflection and full-waveform surveys target structures at mine camp scales. Because Metal Earth was proposed to map and compare entire Archean ore and geologically similar non-ore systems, regional sections cover the entire crust to the Moho in the Abitibi and Wabigoon greenstone belts of the Superior craton in central Canada. Where the new sections overlap with previous Lithoprobe surveys, a clear improvement in reflector detection and definition is observed. Improvements are here attributed to the increased bandwidth of the signal, better estimates of refraction and reflection velocities used in processing, and especially the pre-stack time migration of the data. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

21 pages, 45558 KiB

Open AccessEditor’s ChoiceArticle

Underground Vertical Seismic Profiling with Conventional and Fiber-Optic Systems for Exploration in the Kylylahti Polymetallic Mine, Eastern Finland

by Marko Riedel, Calin Cosma, Nicoleta Enescu, Emilia Koivisto, Kari Komminaho, Katri Vaittinen and Michał Malinowski

Minerals 2018, 8(11), 538; https://doi.org/10.3390/min8110538 - 20 Nov 2018

Cited by 18 | Viewed by 5985

Abstract

Seismic reflection methods have been used for the exploration of mineral resources for several decades. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Instead, mining and exploration companies have traditionally [...] Read more.

Seismic reflection methods have been used for the exploration of mineral resources for several decades. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Instead, mining and exploration companies have traditionally focused more on the use of potential field, electric and electromagnetic methods. In this context, we present a case study of an underground Vertical Seismic Profiling (VSP) experiment, which was designed to image a (semi-)massive sulfide deposit located in the Kylylahti polymetallic mine in eastern Finland. For the measurement, we used a conventional VSP with three-component geophones and a novel fiber-optic Distributed Acoustic Sensing (DAS) system. Both systems were deployed in boreholes located nearby the target sulfide deposit, and used in combination with an active seismic source that was fired from within the underground tunnels. With this setup, we successfully recorded seismic reflections from the deposit and its nearby geological contrasts. The recording systems provided data with a good signal-to-noise ratio and high spatial resolution. In addition to the measurements, we generated a realistic synthetic dataset based on a detailed geological model derived from extensive drilling data and petrophysical laboratory analysis. Specific processing and imaging of the acquired and synthetic datasets yielded high-resolution reflectivity images. Joint analysis of these images and cross-validation with lithological logging data from 135 nearby boreholes led to successful interpretation of key geological contacts including the target sulfide mineralization. In conclusion, our experiment demonstrates the value of in-mine VSP measurements for detailed resource delineation in a complex geological setting. In particular, we emphasize the potential benefit of using fiber-optic DAS systems, which provide reflection data at sufficient quality with less logistical effort and a higher acquisition rate. This amounts to a lower total acquisition cost, which makes DAS a valuable tool for future mineral exploration activities. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Seismic Methods in Mineral Exploration

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (8 papers)

Editorial

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI