Publications

Application of Surface-Wave Analysis for Mineral Exploration: A Case Study from Central Sweden
Papadopoulou, M., Da Col, F., Socco, L.V., Bäckström, E., Schön, M., Marsden, P., Malehmir, A.

 

ABSTRACT

Near-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. Surfacewave 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.

The paper is available here.

Deep Targeting Iron-Oxide Mineralization Using Reflection Seismic Method: A Case Study from the Ludvika Mines Of Sweden
Markovic, M., Maries, G., Bäckström, E., Schön, M., Jakobsson, J., Marsden, P.,

 

ABSTRACT

Blötberget, 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.

 

The paper is available here.

High-Resolution Near-Surface Velocity Model for Depth Imaging of Mineral Deposits in the Ludvika Mining Area, Sweden
Schreiter, L., Buske, S., Malehmir, A., Bäckström, E., Schön, M., Marsden, P.,

ABSTRACT

Within the H2020-funded Smart Exploration project existing legacy seismic data acquired in the Ludvika Mines are analysed in order to delineate the deposits in depth. Here we present a velocity model derived using first-break traveltime tomography, which represent the near-surface materials at high resolution and can be directly used for refraction static calculations or incorporation and for depth imaging algorithm. Our results are consistent with derived velocities from downhole logging data and show a strong vertical velocity gradient in the upper first hundred meters. In mineral exploration clear images of the subsurface and an improved characterization of mineral deposits are required to reduce the risk before drilling. Especially in prestack depth imaging workflows, which are successfully applied to hardrock seismic data, a reliable velocity model is required that represents the lateral and vertical variations in lithology and assures the robustness of the velocity model within the application of depth migration routines at the same time. A special focus of this work lies on the derivation of a detailed near-surface velocity model, which accounts for strong scattering effects due to lateral inhomogeneities as well as for topographic effects on the reflections.

The paper is available here.

Improved Subsurface Imaging through Re-processing of Legacy 2D Seismic Data - A Case Study from a Deep South African Gold Mine
Manzi, M., Malehmir, A., Durrheim, R.J.

ABSTRACT

Over 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.

The paper is available here.

Potential of Legacy 2D Seismic Data for Deep-Targeting and Structural Imaging at the Neves-Corvo Mining Site, Portugal
Donoso, J.A., Malehmir, A., Pacheco, N., Araujo, V.,Penney, M., Carvalho, J., Beach, S., Spicer, B.

ABSTRACT

Volcanogenic-hosted massive sulphide (VMS) deposits show a strong seismic contrast (mainly due to their density) against almost all lithological host rocks therefore justifying their direct targeting using seismic methods (Salisbury et al., 2000; Malehmir et al., 2012 and references therein; Malehmir et al., 2013) when there is adequate signal-to-noise (S/N) ratio and suitable geometry. While there are earlier published accounts illustrating the use of seismic methods for direct targeting of deep-seated VMS deposits elsewhere (Matthew, 2002; Malehmir and Bellefleur, 2009), a number of attempts were done in Europe during the early 90s for this purpose and these have been overlooked for unknown reasons.

The paper is available here.

Preparation Study Based on Borehole Data for Delphi- Distomon Mining Area to Better Design Geophysical Works
Orfanos, C., Leontakaris, K., Apostolopoulos, G., Athanassas, K., Kofakis, P.

ABSTRACT

Europe is in need of fresh aluminum for its vast variety of developments and Greece has the potential to deliver. Delphi Distomon S.A is one of the largest bauxite producers in Greece and is interested to explore new deposits in new unexploited areas. Logistics, accessibility, environmental issues and high cost are key obstacles in the application of a high-definition 3D active seismic survey. Hence, an alternative integrated method of exploration will be carried out based on gravity, magnetotelluric and passive seismic methods. As a preliminary step for an optimized acquisition scheme, a dynamical approach is followed that utilizes a lithology model created by available drilling data, its transformation to a density one, the forward modelling and the comparison of the synthetic data with a previous gravity study in the area. The preliminary results of the analysis gave the chance to identify the vulnerabilities of the lithology and the equivalent geophysical model. As it was observed, they should be enriched during the survey with additional geological information and in situ observations. The emerged models can contribute remarkable to the stage of the processing of the different geophysical methods as well as the final stage of the integrated interpretation.

 

The paper is available here.

Smart Exploration: Innovative ways of exploring for the raw materials in the EU
Malhemir, A., Holmes, P., Gisselø, P., Socco, L.V., Carvalho, J., Mardsen, P., Verboon, A.O., Loska, M.

ABSTRACT

Europe has a favourable geology for a wide variety of commodities necessary for improving our modern life sustainably and environmentally friendly. The Smart Exploration initiative answered one of the seven societal challenges offered by the European Innovation Partnership on Raw Materials on new solutions for sustainable production of raw materials – new sensitive exploration technologies. The project involves 27 partners from nine European countries comprising of 11 research institutions, 11 small and medium enterprises and 5 stakeholders. It primarily focuses on developing cost-effective, environmentally friendly tools and methods for geophysical exploration in highly challenging brownfield areas to meet the ever-increasing community (social acceptance) and environmental issues, as well as reduce the return time (from exploration to production). The aim is to not only generate new technological and methodological markets, but also to create results that will also allow for improved exploration in the EU countries and beyond. Planned prototypes and their potential to impact the market as well as methodological developments will be introduced. Furthermore, the value of legacy data through the use of both traditional and innovative approaches, reviving these datasets and illustrating their potential for deep (+500 m) targeting of mineralized bodies will be discussed.

The paper is available here.

Surface Wave Analysis from Mineral Exploration: a 3D Example from Eastern Finland
Da Col, F., Karimpour, M., Papadopoulou, M., Socco, L.V., Koivisto, E., Salo, A., Sito, Ł., Malehmir, A., Savoilanen, M.

ABSTRACT

We present a feasibility study for surface wave tomography for mineral exploration. We apply a typical seismological approach, the Two Station Method to a hard-rock site, at exploration scale. Even with this method, we are able to separate the two propagation modes typical of these sites. After windowing the traces by picking one propagation mode in the group velocity matrix, we pick the phase velocity dispersion curve in the cross-multiplication matrix. We finally propose a plot consisting of slices of tomographic pseudo volumes, which allows us to understand the penetration depth we can have. Furthermore, it gives us a first indication of the velocity anomalies in the area.

The paper is available here.

The Value of Seismics in Mineral Exploration and Mine Safety
Manzi, M., Malehmir, A., Durrheim, R.

ABSTRACT

The word “seismics” in the geoscience community is often used synonymously with “oil and gas”, despite its successes in other applications, for example, in mineral exploration, engineering application, mine planning and safety.Over the past few decades, the method has been developed and successfully used for mineral exploration, mine planning, and safety in “hard rock” metallogenic provinces worldwide (e.g., Australia, Europe, Canada, and South Africa), leading to the discovery of giant minerals and metal deposits.However, despite these successes, the method’s capabilities in mining still remains less-known to many geoscientists and some mining companies are still reluctant to use it for “hard rock” exploration and mining.The purpose of this paper is to demonstrate how the reflection seismic method has been successfully used to explore and discover some of the world’s largest mineral and metal deposits that are located deep underground – where exploration drilling is more costly and risky. A wide range of case studies from hard rock environments are covered, for example, from South Africa and Canada.

The paper is available here.

Young Professional Aspects of the Smart Exploration Project: Career Management, Marketing and Sustainability
Markovic, M., Malehmir, A., Socco, V., Holmes, P.

ABSTRACT

Without doubt for a successful and long-lasting career, it is important to understand how to balance and promote personal and professional teamwork achievements. The modern age has brought many useful communication tools, making it easier to network and reach beyond conventional academic journals. This study, through a survey and statistical analysis of the results, shows how the young professionals pursuing their temporary position within the H2020-funded Smart Exploration project predict their future career, communicate their work with the outside world and envisage a positive work/research environment for their success. Smart Exploration has provided an opportunity to bridge the gap among universities, mineral exploration industry and small and medium enterprises by employing over 15 young professionals. It provides hands-on field experience using modern equipment and methods, as well as showing them how a collaborative and integrated team is tackling mineral exploration challenges within the EU. The project focuses on research and innovation, thereby tasks and activities have been designed with a great emphasis on young professionals, diversifying their activities across engineering and geosciences. This multidisciplinary environment has led to a much more secure feeling to promote their research and development, and a probability for a sustainable career.

The paper is available here.

Smart Exploration: from legacy data to state-of-the-art data acquisition and imaging

Malehmir, A.,  Donoso, G., Markovic, M., Maries, G., Dynesius, L., Brodic, B.,Pacheco, N., Marsden, P., Bäckström, E., Penney M., and Araujo, V.

ABSTRACT

During the last decade, and possibly in years to come, miner-al exploration geophysics has strongly pushed itself towards developing new instruments and hardware solutions capable of addressing the ever challenging near-mine and brownfield explo-ration issues. New data will be acquired but higher noise levels and restricted access due to mining activities and infrastructure increase the challenge of acquiring data of sufficient quality to answer key geologic questions and define additional resources. Companies that value their existing data and reassess them rigorously and continuously are likely to benefit. However, new generations of geophysicists and mineral explorationists tend to prefer modern data from new instruments than the so-called ‘legacy data’. Legacy data by definition are those that have been acquired in the past, but their revival requires a significant amount of time and money, and still it may not always be possible to yield rewarding results. These data often suffer from bad documentation, inaccurate co-ordinates, and are stored on devices (e.g., tapes or hard copies) that makes it difficult to access or they may have partly been corrupted. However, legacy data are still valuable, especially if they are from brownfield or near-mine exploration sites and can be revived and reworked. Legacy data have the advantage of: • being less contaminated by noise from mining activities and infrastructures, • being acquired in places that now might be inaccessible (i.e., logistical challenges), • being cheaper to reprocess and reinterpret than to collect new data as data acquisition often makes up the bulk of a survey’s cost. Legacy data can also provide a first assessment if new and advanced data acquisition would lead to new knowledge and discoveries. Smart Exploration, an H2020-funded project involving 27 partners from nine European countries and six exploration sites was launched in late 2017. Its goal is to address some of these challenges concerning legacy data, to develop new geophysical instruments for a wide range of applications and to generate new targets at the explo-ration sites while training new generations of young professionals for these purposes. Here, we focus on re-evaluating the potential of some of the legacy data available from the exploration sites and together with new instruments developed during the project present how in-mine and brownfield mineral exploration can advance utilizing existing mining infrastructure. For example, we show the importance of legacy data from a 1996 dataset enabling imaging of a world-class +150 Mt massive sulphide deposit at depth as well as another case study showing that additional iron-oxide resources may be present downdip and under the known mineralized bodies. The development of a GPS-time system and an E-vibrator helped to then acquire a semi-3D tunnel-surface seismic dataset utilizing exploration tunnels in the Neves-Corvo mine.

The paper is available here.

Giving the legacy seismic data the attention they deserve

Manzi, M., Malehmir, A., and Durrheim, R.

ABSTRACT

Key minerals may soon be in short supply as shallow mineral deposits are mined-out; therefore exploration for economically feasible deep-seated deposits to sustain a long-term global growth is a great challenge. New deposits are likely to be found using reflection seismic surveys in combination with drilling, field geological mapping and other geophysical methods. Seismic methods have already have contributed significantly to the discovery of some of the world’s major mineral deposits (Milkereit et al., 1996; Pretorius et al., 2000; Trickett et al., 2004; Malehmir and Bellefleur, 2009; Malehmir et al., 2012). However, use of the method is not widespread because it is deemed to be expensive. Although improvements in computing capabilities have led to cost reductions, the costs are still beyond exploration budgets of many companies. Thus, mining companies have had little financial ability to acquire new reflection seismic data, and very little governmental support has been available to acquire research seismic surveys for mineral exploration. Over the last few years, there has been a proliferation of seismic solutions that employ various combinations of equip-ment, acquisition, and processing techniques, which can be applied in hard rock situations to improve the imaging resolution (Denis et al., 2013). The best acquisition solutions to date have come from the deployment of high-density receiver and source arrays which the extension of the seismic bandwidth to six octaves using broadband sources (Duval, 2012). Another area of seismic research has focused on surface seismic acquisition using three-component (3C) microelectro-mechanical (MEMS-based) seismic landstreamers (Brodic et al., 2015), coupled with wireless seismic recorders, and surface-tunnel-seismic surveys (Brodic et al., 2017). However, numerous difficulties have been encountered, even with these innovative acquisition seismic approaches. Seismic surveys acquired in the mining regions suffer from noise produced by the drilling, blasting and transport of rock and the crushing of ore. Furthermore, in some mining regions the acquisition of new data is not permitted due to new environmental regulations. In such a fast evolving seismic technological era, legacy reflection seismic data are often regarded by mining companies and geoscientists as inferior compared with the newly acquired data. This paper demonstrates that if the legacy data are properly retrieved, reprocessed, and interpreted using today’s standard techniques, they can be of significant value, particularly in the mining regions where no other data are available or the acqui-sition of new data is difficult and expensive. The development of multitudes of processing algorithms and seismic attributes, in particular, make it worthwhile to reprocess and interpret legacy data to enhance the detection of steeply dipping structures and geological features below the conventional seismic resolution limits (i.e., a quarter of the dominant wavelength), which was not possible with the tools that were available when the data were originally acquired and processed. The new information obtained from the legacy data may benefit future mine planning operations by discovering new ore deposits, providing a better estimation of the resources and information that will help to site and sink future shafts. Thus, any future mineral exploration project could also take the geological information obtained from the reprocessed and interpreted legacy seismic data into account when planning new advanced seismic surveys (Manzi et al., 2018). The latest seismic algorithms are particularly interesting to South Africa’s deep mining industry because South Africa has the world’s largest hard rock seismic database, which could benefit from new processing techniques and attributes analyses. These techniques could be applied to legacy seismic data to identify areas of interest, improve structural resolution and to locate deeper ore deposits. Seismic attributes, in particular, could be used to identify any subtle geological structures crosscutting these deposits ahead of the mining face that could affect mine planning and safety.

The full paper is available for reading and download here.

The role of land gravity data in the Neves- Corvo mine discovery and its use in present-day exploration and new target generation

Marques, F., Matos, J.X.,Sousa, P.,Represas, P., Araújo, V., Carvalho, J., Morais, I., Pacheco, N., Albardeiro L. and Gonçalves P.

ABSTRACT

Several blind massive sulphide deposits associated with the Iberian Pyrite Belt (IPB) Volcano-Sedimentary Complex (VSC) (Figure 1) were discovered in SW Iberia using joint interpretation of geo-logical and geophysical models, such as Neves-Corvo (Albouy et al., 1981; Leca et al., 1983) and Lagoa Salgada (Oliveira et al., 1998) in Portugal, and Valverde and Las Cruces in Spain. In the IPB Portuguese sector, the former government agencies Serviço de Fomento Mineiro (SFM) and Instituto Geológico e Mineiro (IGM), as well as LNEG, fostered the acquisition of systematic geophysical surveys, in particular gravimetry, in the region during the second half of the 20th century. Since the 1960s, the former SFM carried out detailed ground surveys over N-S for E-W grids with distances between survey stations of 200, 100 and 50 m grid size (Oliveira et al., 1998). This enabled the identification of several potential targets which attracted the interest of important international investors and led to a continuous investment in geophysical research, based on ground and airborne surveys (Matos et al., 2019). The discovery of several massive sulphide deposits, includ-ing the world-classNeves-Corvo Cu-Zn-Sn deposit in 1977 (see location in Figure 1, Albouy et al., 1981; Carvalho et al., 1996; Carvalho et al., 1999; Oliveira et al., 2013) was a direct result of joint efforts of mining companies (a consortium formed by the Soc. Mineira e Metalúrgica de Peñarroya Portuguesa, Soc. Mineira de Santiago/Emp. Mineira e Metalúrgica do Alentejo and Societé d’Études de Recherches et d’Exploitations Minières), and former SFM exploration surveys (Albouy et al., 1981; Leca et al., 1983; Carvalho et al., 1999; Matos et al., 2019). The consortium invested significantly in exploration (Albouy, et al., 1981), namely: processing of the SFM-acquired gravity data (covering an area of 300 km2), collection of new gravity surveys (190 km2), more than 200 km of electric resistivity and magnetic profiles, as well as very-low-frequency (VLF) studies on several drill holes. The Neves-Corvo deposits occur along a NW trend, with seven deposits dispersed in a large complex antiform structure (Carvalho et al., 1996; Araújo and Castelo Branco, 2010; Oliveira et al., 2013). Understanding the geometry of subsurface orebodies requires accurate geological mapping based on surface surveys and/or borehole logging (Matos et al., 2019). The accuracy of the conceived model for geology and ore deposit at Neves Corvo, however, is limited by the sparse geologic outcrops and a biased distribution of drill holes. This has driven an impetus towards acquisition of geophysical data which can be more uniformly sampled and is typically less expensive to collect. Among the different geophysical methods employed, a strong response is expressed within the gravity data. This is the result of the large physical property contrast between high density, massive sulphide deposits and the volcano-sedimentary host rock lithologies (Neves, Corvo, Graça and Zambujal). The uppermost lenses are located in the NE flank of a gently dipping structure (10º-40º NE), at depths between 230 m (Corvo) and 350 m (Neves) (Albouy et al., 1981; Carvalho et al. 1996; Matos et al., 2019). These were therefore the first four orebodies to be discovered, while the gravitational response of the deeper Neves-Corvo mas-sive sulphide lenses were weaker and more difficult to recognize. With less obvious gravitational anomalies to guide exploration at such depths, rock density studies become a key issue in the geophysical characterization of Neves Corvo. In the case of the Semblana deposit (2010, ~800 m depth), ground electromagnetic surveys and extrapolation of favourable geology down dip from the Zambujal area were utilized for exploration in addition to the gravity data (Araujo and Castelo Branco, 2010). The use of gravity for direct detection of massive sulphides in the IPB has limitations. In areas covered by thick Flysch sediments (locally >1 km) where the VSC occurs at greater depths, the gravitational response is weak and more so a function of regional geologic elements. Localized variations in density, such as those caused by high density basic rocks or black shales with dissem-inated pyrite, are common within the VSC sequences. Intense rock weathering, low density siliceous shales or volcanogenic sandstones also contribute to a complex and multi-layered gravity profile. The elevated copper grades of the Neves-Corvo deposits justified more investment in exploration. The possibility of new discoveries with high metal content warranted an extension of exploration research, to explore deeper structures in the area (>>500 m depth). Considerable efforts were exerted in areas such as the Neves-Corvo-Corte Gafo, a 600 km2 polygon located NE of the mine site (Carvalho et al., 1996; Matos et al., 2019). With technical support of the former SFM gravity team, Somincor/Lundin implemented a multidisciplinary programme of gravity and magnetic surveys (9015 points covering an area of 314.5 km2, as well several profiles of transient electromagnetics (TEM, 215.5 km), magne-totellurics (27.0 km) and reflection seismic data (24.0 km). At a regional scale, a multitude of geophysical methods were deployed to characterize specific exploration targets throughout the IPB. These included: deep seismic reflection, electrical resistivity induced polarization, electromagnetic EM 37, pulse electromagnetic, transient electromagnetic, vertical transient elec-tromagnetic, vertical electrical soundings and magnetotellurics. In structurally complex zones, such as the Semblana area (Araujo and Castelo Branco, 2010), down-hole electromagnetic surveys were essential in the identification and delineation of the primary mineralized trends. In the Neves-Corvo region, seismic profiles were used by Lundin/Somincor to define key tectonic structures (Araújo and Castelo Branco, 2010; Inverno et al., 2015; Matos et al., 2019).

 

The paper is available for reading and download here.

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Smart Exploration has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No.775971