Accepted Presentation Abstracts
Permitting for the Parkdale Quarry: Interplay Between Geology and Engineering, and Environmental and Social Concerns
Bieber, David, Martin Marietta - West Division, U.S.A., david.bieber@martinmarietta.com
Responsible permitting of accessible mineral reserves is critical for the development of the green economy. One key to gaining access to critical mineral resources is to acknowledge the interplay between geology and engineering, and environmental and social concerns. Addressing environmental and social concerns as an afterthought in mine planning contributes to the public's negative perception of mining. Permitting for the Parkdale Quarry in Fremont County, Colorado offers a case study for an effective strategy for addressing environmental and social concerns up front. The Parkdale Quarry is adjacent to the Arkansas River and U.S. Highway 50 scenic corridor. Front Range Aggregates permitted a significant expansion of the quarry with no opposition voiced at the local level, and minimal comments on the project Environmental Impact Statement. A key to the success of the permitting process was early, open, and on-going communication with potentially interested parties, including those likely to oppose the project. Major concerns included visual impacts, impacts to tourism, water quality, and impacts to wildlife. The early dialog gave Front Range Aggregates an understanding of concerns and provided an upfront opportunity for those concerns to be addressed in the mine plan. The resulting changes included integrating wildlife-friendly features into the reclamation plan; the implementation of concurrent reclamation to minimize disturbed acreage; configuring the mine plan so that mining was screened from view by topography; and an integrated monitoring program to anticipate potential water issues.
Bore Design for a Mine Environment
Bolton, Hugo, SMEC, hugo.Bolton@smec.com
Mine environments can be some of the most challenging particularly when it comes to bore design. Bore design involves more than just drilling the borehole and installation. For a successful pump bore one needs to consider a number of factors. Some can be measured while other factors are based on judgement and experience.
This presentation will provide an understanding of the science (i.e. what you can measure) and the art (i.e. those factors that are more related to the bigger picture).
This presentation will cover:
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Understanding the bigger picture
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Type of screens
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Natural pack vs gravel pack designs and fractured rock designs
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Potential available data
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Importance of screen placement
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Sand grading analysis and gravel pack design
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Screen aperture
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Screen velocity and flow estimate
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Things to watch out for
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Project examples
New insights from multisource datasets into the deep structure of the Louta phosphatic deposit (Gantour basin, Morocco): Mining implications
Mohammed Anas Charbaoui, Polytechnic University UM6P, Geology & Sustainable Mining Institute GSMI, Ben Guerir, Morocco, anas.CHARBAOUI@um6p.ma; Azzouz Kchikach, Mohammed Jaffal, Yazami Oussama Khadiri, Mourad Guernouche, Es-Said Jourani
The structure of Deep sedimentary basins can be studied using geophysical methods and geological investigations. These investigations help acquire a variety of geoscientific data that can be used in mining and hydrogeological resources exploration. This study is based on the combined analysis of this information. It concerns the Gantour Phosphatic Basin (GPB), which hosts an important part of Morocco’s phosphate reserves. The main objective is to provide a better understanding of the deep structure of the phosphatic series in the Louta deposit located in the central part of this basin. We started by developing a geological model of Louta deposit based on borehole data using Datamine Studio RM software. This allowed to understand the deep phosphatic series’s structure. Then, we developed an accurate and updated piezometric map that allowed for a better understanding of the groundwater flow in the study area. Electrical Resistivity Tomography (ERT) profiles were acquired, which highlighted and enhanced the main features controlling the deepening of the phosphate series. The superimposition of the piezometric map with the geological model shows the importance of the volume of phosphate below the groundwater level. The elaborated geological and geoelectrical models correlate perfectly and show that the phosphatic series in this deposit has a monoclonal south-dipping structure under the Plio-Quaternary cover. Such information can allow the mining engineers to develop the approach for extracting phosphates in this geological and hydrogeological context.
Seabed Mining: At What Environmental Cost for Renewable Energy Technology
Godwin, William, Consulting Geologist, U.S.A., godwinbillh@gmail.com
With the push to find rare earth and other metals necessary for battery storage and renewable technologies are we losing perspective of environmental consequences of our mining activities needed to extract these products? From my perspective as a geologist, the earth contains all the necessary raw products to allow humankind to enjoy life comfortably, have modest growth potential and still have resources available for generations to come. The earth however is not a limitless source and there are repercussions. Efforts have begun to mine polymetallic nodules from the seafloor of the northern Pacific Ocean. These nodules are rock concretions that contain minerals like manganese, nickel, cobalt and copper. There is huge market for these minerals to support technology, in particular in the manufacturing of batteries and storage devices. While deep-sea mining has not started in any part of the world, 16 international mining companies have contracts to explore the seabed for minerals within the Clarion Clipperton Zone (CCZ) in the Eastern Pacific Ocean, and other companies have contracts to explore for nodules in the Indian Ocean and Western Pacific Ocean. Several articles and peer-reviewed papers have been written recently on this subject, which provide a basis towards both education for future mining and environmental concerns.
Using Machine Learning to Evaluate Coal Geochemical Data with Respect to Dynamic Failures in U.S. Coal Seams
Hanson, David, NIOSH, U.S.A., bug4@cdc.gov, Heather Lawson, bug4@cdc.gov
The question of whether a model could be constructed that could predict the probability of dynamic failure occurrence based on geochemical data was assessed using a random forest analysis, cluster analysis and dimension reduction. Overall, the objective was to search for similarities and differences between coal bed samples, determine why they might exist, and how they relate to the ground truth of dynamic failure occurrence. A random forest analysis performed on data from the Pennsylvania Coal Sample Databank cross-referenced with accident data from the Mining Safety and Health Administration (MSHA) determined that 7 parameters of the 18 examined exerted the most influence on results. These parameters were weight percent pyritic sulfur, weight percent organic sulfur, weight percent oxygen, weight percent volatile matter (moisture-free-basis), Van Krevelen ratio ((H/C)/(O/C)), weight percent moisture (as received), and vitrinite reflectance. A comparison was made for random forest classifiers where a default threshold of 0.5 and a tuned threshold were applied. The random forest classifier achieved a precision of 96.7 % in the tuned threshold case. A non-linear (t-SNE) dimensionality reduction operations was applied to the data. The top 7 features determined from the random forest classifiers were used. Application of t-SNE to the dataset provided good separation of the dynamic failure and control data in two dimensions. Cluster analysis on t-SNE processed data resulted in HDBscan finding 4 clusters, with one relatively distinct dynamic failure cluster, and 3 clusters consisting mostly of control group members but with a small number of dynamic failure members. Ultimately, however, as accident data are derived from in situ cases of failure, direct association between geochemical parameters and coal behavior requires validation through laboratory testing in a controlled environment.
Monitoring Pit Slopes, Mine Tailings and Dams Using Ambient Seismic Noise Interferometry: Detecting Subsurface Changes before Surface Expressions
Hollis, Dan, Sisprobe SAS, dan.hollis@sisprobe.com; Nick Arndt, nick.arndt@sisprobe.com; Romeo Corbis, romeo.corbis@sisprobe.com; Richard Lynch, richard.lynch@sisprobe.com
Ensuring the safety of structures like pit slopes, tailings-storage facilities and earthen dams is critical in mining operations. Changes in a structure can cause failure below the surface with no discernable surface expression. Monitoring changes in physical properties within a structure can provide the mine operator with advance warning of potential structural failure, with sufficient time to remedy the cause or take appropriate precautions. An ideal monitoring method would be robust, low-maintenance and low-cost, and would provide 3D images of the subsurface in real time. Ambient seismic noise interferometry (ANI) is a relatively new method for monitoring changes within a structure. ANI uses seismometers or optic fibers and exploits ambient seismic noise generated by natural and human sources to monitor small changes in seismic velocity down to 0.01%. Changes in water content, fracturing and stress within a structure will contribute to changes of seismic velocity that can be detected by the method. We will present theory and practical applications when ANI was used to monitor tailings facilities and pit slopes in Africa, Australia, North America and Europe. Also presented will be a case study demonstrating the instrumentation and monitoring of a pit wall where ANI detected changes in subsurface physical properties that led to subsequent slope failure.
Closure of Mine Physical Hazards in Communities
Houle, Jean-Sebastien, Wsp Canada Inc., jean.sebastien.houle@wsp.com; Paul Palmer, paul.palmer@wsp.com
Mines and communities have been linked throughout our history. One of the many challenges when mines close is they leave behind mine physical hazards such as openings to surface (shafts, raises, adits, etc.) and near surface workings (i.e., crown pillars overlying drifts and tunnel). Safely closing these mine physical hazards can be complex, expensive and often require in perpetuity maintenance requirements. These mine physical hazards can present risks to the general public (i.e., injuries and damage to property and infrastructure) if left un-rehabilitated. These mine physical hazards might have been a “lower-risk” situation during operations or directly after closure but can become a high risk if they are left to degrade over the following years and/or decades often when the community has forgotten about them. Surface rights owners may even be unaware these mine physical hazards are on their property. Over the past several decades our WSP teams have been involved in locating, investigating, assessing long term stability, developing specific risk mitigation and remediation measures for mine physical hazards. Over the years the remediation requirements for mine closure in Canada and many other locations have evolved and became more stringent, often due to past failures and the overall increased knowledge and experience of all parties involved. This presentation will outline successful investigation approaches, stability assessments, and remediation measures implemented for mine physical hazards located in communities.
An Optimized Geotechnical and Geophysical Site Investigation for Derisking Future Mine Tailings Storage at DLM, Canada
McClymont, Alastair, BGC Engineering, Canada, amcclymont@bgcengineering.ca; Eric Johnson, Erin Ernst, Greg Wenger, Caroline Bates, Annie Ruksys, Rita Wang, Andrea Regli, and Simon Dickinson
The Detour Lake Mine (DLM) in northern Ontario is one of the largest gold producing mines in Canada. With an expected mine life of at least 22 years, future tailings storage is required to accommodate expansion plans. The local geology comprises low, flat-lying, poorly exposed bedrock ridges, predominantly covered by glacial sediments and organic soil of variable thickness. Because variation in the thickness of the cover materials impacts the design of proposed future ring-dikes, mapping the variability in the foundation materials is essential to accurately estimate construction costs and ensure that the dikes are built for the safe containment of tailings well beyond the expected life of the mine. Since these subsurface conditions can change markedly over relatively short distances, conventional drilling and test pit programs that sample at discrete locations run the risk of missing anomalous geological features, including deep bedrock channels and faults that may underly the footprint of the ring dikes. Conversely, drilling or test pitting over dense intervals to capture this variability can significantly increase costs for a site investigation. We present the results of a site investigation that utilized multiple geophysical methods to efficiently map and characterize the subsurface and optimize a follow-up test pitting program. A specialized ground-penetrating radar (GPR) system, together with electrical resistivity tomography (ERT) and targeted seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW) profiles were obtained along the proposed footprint of the ring-dike system. The GPR results mapped organic soil thickness variations of up to 4 m, and the ERT and SRT profiles revealed two distinct bedrock troughs intersecting the dike footprint, one as deep as 38 m. 47 test pits were then completed at targeted locations, informed by the geophysical results and to help ground-truth the geophysical interpretations and characterize geotechnical conditions within the foundation soils.
Simulation of the merging of two limestone quarries in the Tournai area of Belgium
Nikiema, Tégawendé, University of Mons/ Faculty of Engineering, tegawende.nikiema@umons.ac.be; Nicolas Gonze, nicolas.gonze@umons.ac.be; Fanny Descamps, fanny.descamps@umons.ac.be; Jean-Pierre Tshibangu, katshidikaya.tshibangu@umons.ac.be
Lemay and Antoing quarries near Tournai (Belgium) are two adjacent limestone quarries reaching the limits of their current permit. To extend their life, the owners plan to exploit the rock mass left as a wall between the two quarries, which could constitute a significant part of the reserves still mineable. This work aimed to determine the recoverable reserves within the wall while proposing a mining scenario that meets the production objectives of both quarries. Indeed, the Lemay quarry produces stone blocks and aggregates, while the Antoing quarry produces cement, thanks to the high CaO content of some strata, and aggregates. The first step consisted of creating a 3D geological model of both quarries. This model was built based on drillholes carried out on site and the geological data allowing to take the faults into account in the model. New “virtual” drillholes based on the geology knowledge were implemented to overcome the lack of data in some areas. The 3D model allowed to understand the thickness evolution of geological layers. The second step was to create a block model of the geochemical parameters, which is essential for classifying rocks for cement or aggregate production. Based on geochemical data from drillholes, a discretization of the ore body in blocks, and the application of inverse distance weighing, a 3D geochemical model was created to understand the variation of the content of useful minerals in the ore body. The last step was planning the open-pit exploitation of the wall based on geological and geochemical models. A scenario was proposed to achieve the operating company's objectives while keeping a permanent passage between the two quarries during the exploitation. The proposed new mining scenario extends the life of both operations by 06 years.
Behavior of Solar Farms to Mine Subsidence
Osouli, Abdolreza, Marino Engineering Associates, Inc., aosouli@meacorporation.com; Gennaro Marino, gmarino@meacorporation.com
There are vast areas of undeveloped land across the U.S. that are undermined and can be used for solar farms. These abandoned underground coal mines are many times not stable over the life span of the proposed farm area. These abandoned mines can fail in many different ways resulting in expressions on the ground surface from “pothole” like features to large sinkholes to boarder “bowl-shaped” depressions 100’s of feet across to 1,000 or more feet wide. These boarder depression sags are not only accompanied by vertical movement but horizontal displacement. Depending upon the sensitivity of the proposed farm infrastructure, the amount of damage which occurs will be determined. Typical sag maximum vertical displacement is on the order of 1.5 ft to 3.5 ft. with the corresponding maximum horizontal movement on the order of 1.5 ft. to 2 ft. This presentation will go over the various mechanisms of abandoned underground mine failure, the nature of the resulting subsidence, and how it affects the farm infrastructure.
Automated Detection of Rockfalls with Thermal Imaging
Potter, Julia, University of Arizona, juliajpotter@arizona.edu
Despite significant progress in slope monitoring technologies, limited methods exist to detect rockfalls in real-time in open pit mining environments. Thermal video cameras are commercial-off-the-shelf technology in hardened, weatherproof configurations ready for deployment in harsh environments. Ongoing research conducted by the Geotechnical Center of Excellence (GCE) in collaboration with NIOSH has proven that thermal video cameras can observe rockfalls. Several companies have already deployed thermal video cameras in surface mines as early adopters of the technology. The current focus of this research project includes the development of 1) software to detect, track, recognize, and alarm rockfalls in real time, 2) a standalone system for deployment in both civil and mining environments, and 3) empirical correlations between environmental and rockfall detection data for use in predicting times of heightened risk for rockfall. This presentation includes an overview of the GCE’s findings regarding the use of thermal imaging for rockfall detection in open-pit mining environments and a summary of the development work currently in progress and future research paths both approved and under consideration by the GCE.
Combination of Seismic and Log Correlation Methods in Stratigraphic Interpretation – Geosciences and Coal Mining
Püspöki, Zoltán, Supervisory Authority for Regulatory Affairs, zoltan.puspoki@sztfh.hu; Julianna Mekker, julianna.mekker@sztfh.hu; György Tóth, gyorgy.toth@sztfh.hu; Teodóra Szocs, teodora.szocs@sztfh.hu; Andrea Jordán-Szucs, andrea.szucs@sztfh.hu; Ágnes Szalkai, agnes.szalkai@sztfh.hu; Nóra Gál, nora.gal@sztfh.hu; Gábor Markos, gabor.markos@sztfh.hu; Ágnes Cserkész-Nagy, agnes.cserkesz-nagy@sztfh.hu; Márton Bauer, marton.bauer@sztfh.hu; Tamás Lukács, tamas.lukacs@sztfh.hu; Ágnes Kiss-Mezei, agnes.mezei@mert.hu; Sári Katalin, katalin.sari@wbgc.hu; Éva Kun, eva.kun@sztfh.hu
Stratigraphy of coal bearing deposits targeted by mining is mostly focused on correlation of the cultivated seams and the dewatered sand bodies, and restricted for the vicinity of the mines. Contrary to this, basin analyses focus on stratigraphic architectures, considering the coal seams as a complementary facies indicator only. However, in some cases an integrated approach may be necessary e.g. when disentangling the hydrodynamic impacts of coal mine dewatering and groundwater productions of different aims. In the Jászság Basin (North Hungary) a regional scale hydrogeological modelling is planned to interpret the long-term decrease of hydraulic heads, in the context of groundwater production of different aims, mine dewatering and climate change. To establish this hydrogeological modelling procedure, a comprehensive geological model of the Jászság Basin was necessary. At the basin margin an Upper Miocene lignite bearing succession is outcropped and cultivated by open pit mines to 80–120 metres below surface, while deep drillings in the basin centre detected lignite seams down to 1500–1600 metres. It was a basic requirement to clarify the stratigraphic relation between the lignite seams cultivated in the basin margin and those detected in the basin centre. Due to the horizontal and vertical scale limitations of geophysical methods, the lignite bearing succession was investigated by the combination of seismic interpretations and well-to-well log correlations. The investigation revealed three distinct periods of coal formation in the succession, related to different progradations. The mined lignite seams are related to the uppermost lignite bearing stratigraphic unit that is also the main target of the regional groundwater production. The geothermal explorations mostly target the deepest lignite bearing unit. To express the lithological contrast between the lignite-bearing and underlying units, the facies boundary at the base of the coal bearing stratigraphic units was traced basinward, instead of high-frequency quasi-isochronous clinoforms.
Ambient Seismic Noise for Slope Stability Monitoring: Case Study at an Open Pit Mine
Rohwer, Monty, Institute of Mine Seismology, monty.rohwer@imseismology.org; Tjaart de Wit, tjaart.dewit@imsi.org
Landslides directly impact thousands of people every year and cause significant loss of life. Landslides are often triggered by extreme weather events or earthquakes. In the mining context, landslides occur in the form of slope failures in open mining operations and tailings dam failures, and as recent high-profile failures have demonstrated, cause significant economic disruption and in severe cases: loss of life. We explore the possibility of using interferometry of the ambient seismic noise, i.e. without costly active sources, to detect subtle changes in the velocity structure of the subsurface. In particular we investigate the potential for detecting early signs of instability or even precursors to slope failure. While most slope monitoring approaches focus on surface deformation (e.g. using radar), seismic methods are well suited to detect changes in the bulk medium and therefore also at depth. Seismic ambient noise correlation has been successfully applied in landslide monitoring (for a recent review, see Le Breton et al., 2021). We present a case study from an open-pit mine in Australia, where a dense geophone array was installed in boreholes beneath a well- instrumented slope. We monitor changes in ambient noise correlations across a period of several weeks that includes a nearby slope failure event. We measure a decrease in seismic velocity approximately two weeks prior to the initiation of the slope failure. We compare the findings against complimentary data from radar surface-monitoring and microseismic event detection and demonstrate the ambient noise response to seismicity, rainfall and surface-deformation recorded during this period. By using all the available information we build a model of slope failure and show that a decrease in seismic velocity may be the earliest warning sign.
New Solutions for Mining Education and Research
Ross, Brad, University of Arizona, bjr@arizona.edu
The mining industry struggles with attracting the people and skills required to address critical challenges such as tailings, critical minerals, safety, as well as sustainability, and social license to operate. This shortage of talent, which has been building for nearly 40 years, also impacts the daily operations of most mines as well as the ability of companies to implement new technologies to improve their performance. The annual impact is in the billions of dollars. It is time that the mining industry creates a new strategy to build a vision, provide leadership, and invest the resources to solve this long-term crisis. This strategy needs to be led by an industry-wide group that is dedicated to changing the culture of the industry, such as ICMM. A key component of the strategy needs to include the creation of a new institute that is dedicated to:
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Recruiting new talent and increasing the skills of current professionals through world-class professional development training programs, scholarships, and certification.
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Engaging industry and academic experts worldwide to prioritize educational and research topics as well as develop and deliver course content.
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Act as a global facilitator/integrator with mining-related schools and industry partners to share course content, research collaboration/funding, and sharing of resources.
This paper will discuss the strategy for implementing these new solutions as well as methods for companies and industry experts to become involved.
Mine Surveys using the Loupe Transient EM System
Street, Greg, Loupe Geophysics Pty Ltd., gstreet@iinet.net.au
Loupe is a new TEM instrument designed for profiling and mapping electrical conductivity to a depth of around 30 metres below surface. The system is mounted on two backpacks and data acquisition is continuous at walking pace. The transmitter and receiver are carried by separate operators in a ‘moving loop’ or ‘out-of-loop’ mode. Since presentation of the initial results using the Loupe TEM system (Duncan and Street, 2018) field tests have confirmed the applicability of the system to a range of near-surface electrical conductivity mapping applications particularly in and around mine sites.
Some applications that have been trialled with success include:
• Tailings Storage Facility (TSF) seepage investigations; • Mapping within TSFs;
• Mapping of ground conditions prior to TSF construction; • Mapping of acid mine drainage;
• Mapping sulphides in underground mines;
• Mapping clays and other hazards in iron ore deposits;
• Mapping clay variability for brick making;
• Shallow sulphides and graphite mapping for exploration; and • Groundwater exploration.
The system clearly has many applications in the life of a mine including some that have not been trialled as yet.
MASW and Microgravity – a Novel Approach to Investigating Karstic Features in a Large Tailings Storage Facility
Tomkins, Aaron, GBG Group, aaron@gbgoz.com.au
Multi-channel Analysis of Surface Waves (MASW) is a non-destructive seismic method which uses the elastic properties of subsurface materials to determine the subsurface structure. By analysis of the dispersive properties of varying frequencies from a single seismic source, shear-wave velocity (Vs) and associated geotechnical parameters can be determined. Microgravity is a potential field technique used to accurately record localised variations in the earth’s gravitational field. The variations in gravitational readings are caused by density contrasts of the rocks and sediments beneath the reading location. Both methods are therefore an indicator of low velocity and low-density subsurface units, a common characteristic of karstic features or voiding. When individual readings from both methods are combined, a scientist can interrogate the subsurface in a detailed manner outlining both low velocity and corresponding low-density areas. Through careful interpretation, an accurate image of the subsurface can be inferred. Although both methods have been used independently for karstic investigations, they have not been combined for a large-scale geotechnical investigation and used to constrain the overall 3D geotechnical model. This paper presents an alternative way of using seismic and gravity investigations with the primary objective to target unconsolidated subsurface strata or voiding, within limestone terrains. The way data is collected and combined within this paper is specifically designed and applicable for Tailings Storage Facilities. The paper introduces the reader to automated GPS corrected MASW data collection, while handling large datasets in excess of 85,000 shots. The paper also covers 3D inversion and display of the MASW data, and how modelled data can be interrogated to use results and findings to plan a Gravity campaign over anomalous areas. Finally, the paper will outline how all datasets can then be used to constrain final 3D models for target anomalies associated with unconsolidated subsurface strata or voiding.
Geophysical Solutions for Acid Mine Drainage Assessment
Van Dam, Remke, Southern Geoscience Consultants, remke.vandam@sgc.com.au
Effective site remediation and impact management requires a thorough understanding of the scale of the problem. Unfortunately, only limited site information is typically available. Whilst sampling and drilling efforts do provide detailed information, the information is localized in nature, the approaches are invasive, and the costs are often considerably high. Non-invasive geophysical tools can overcome some of these limitations as they are ideal for the mapping, imaging, and monitoring of site variables over larger areas, albeit at a lower resolution. Information that can be obtained varies with the type of geophysical method employed, and includes detail on structural (e.g., bedrock, soil thickness, fractures), hydrological (e.g., water table depth, soil moisture), and water quality (e.g., salinity, contamination) properties. This contribution will discuss the uses and potential benefits of non-invasive geophysical survey methodologies for Acid Mine Drainage (AMD) assessment programs. Case examples from Western Australia will illustrate the uses of several of these methods in real-world applications. Key take-aways are that geophysical surveys can identify and sometimes quantify the below-ground distribution of AMD and can guide and de-risk sampling and drilling programs.
Mine Infrastructure Planning with Airborne EM
Wijns, Chris, First Quantum Minerals, chris.wijns@fqml.com
Airborne electromagnetic surveys with near-surface vertical resolution provide rapid and comprehensive coverage of a mine site ahead of infrastructure planning. In environments of sufficient electrical conductivity contrast, the data will map variations in the depth to bedrock, providing guidance for expected excavation depths for solid building foundations, or mine pre-strip volumes. Continuous coverage overcomes the severe areal limitation of relying only on drilling and test pits. An AEM survey in northern Finland illustrates the success of this approach for guiding the placement of a mine crusher and related infrastructure. The cost of the EM data collection and interpretation is insignificant in comparison to the US$300 million capital cost of the mine infrastructure. This environment of shallow glacial cover challenges the limits of AEM resolution, yet analysis of subsequently collected three-dimensional surface seismic data and actual pre-strip excavation depths reinforces the predictive, but qualitative, mapping capability of the AEM. It also highlights the need to tune the modelling via petrophysics for the specific goal of the investigation, and exposes the limitations of visual drill core logging.