1,720,977 research outputs found
Induced Polarization Effects in Electromagnetic data: the Loupe case study
No full textIt is nowadays accepted, both in industry and in academy, that Induced Polarization (IP) affects electromagnetic (EM) data, when these are collected over a medium characterized by strong IP properties. With this study we want to verify if and how IP effects are detectable also by the new ground-EM system Loupe. The Loupe system is a two-operator walkable transient EM (TEM) profiling system designed to image the electrical properties of the ground with a high lateral and vertical resolution. In order to map the IP effects, we set up a large data space and model space analysis, parametrizing a two-layer synthetic model and calculating thousands of forward responses varying the model’s parameters. We thus compare the forward responses affected by IP with the equivalent purely-resistive ones. We find that significant IP effects are present on most models, also with moderate polarization properties
Modelling the airborne Induced Polarization effects at continental scale: the Tempest case study in the AusEM project
No full textTempest is a very successful AEM system, used over the last 2 decades for mapping changes in subsurface conductivity from tenement to regional scales (Lane et al, 2000). It delivers B field 100 % duty cycle data for X and Z components. It has been the subject of extensive research and development from both internal and third parties (e.g., Mulè and Smiarowski, 2013; Brodie and Ley Cooper, 2019). This paper focuses on a rather novel aspect: its sensitivity to IP effects and the relevance of modelling IP in its data. Airborne IP (AIP) modelling has been researched extensively over recent years, mainly in Helicopter Time Domain EM data. Both the industry and the academic community (Oldenburg and Kang, 2015, Macnae, 2016, Viezzoli et al., 2017, Cox et al., 2022,) have come to accept AIP as an important part of HTEM data. We now wish to take a similar approach for the Tempest Fixed-wing Time Domain EM (FTEM) system.
We focus on the Tempest system given its large application for continental scale mapping, such as for the AusEM project in Australia. Here, this fixed-wing system is used to map the ground resistivity of the entire Australian continent and has already covered an amount of 2millions of flown line-kilometres. In this scenario, being able to extract the ground chargeability from the AEM data would add a high-impact extra layer of information to the continental mapping for mineral purposes
Closing the gap between Airborne EM and Ground Galvanic Induced Polarization for Mineral Exploration
Get PDFIt is demonstrated and nowadays accepted that the Induced Polarization effects can affect inductive measurements and can be a source of artifacts if not proper modelled during inversion process. At the same time, using a dispersive resistivity to model EM data largely expands the model space and expose the inversion procedure to strong equivalencies and ambiguities. These limitations have often brought to over-precautionary modelling approaches of AIP and leaded to the impossibility in interpretation of the airborne-retrieved chargeability models.
With this contribution a novel modelling approach to extract inductive induced polarization from Airborne EM data is proposed. The AEM data are acquired in Spain, for VMS and polymetallic exploration and overlap 17 ground DCIP lines. The modelling approach we propose concerns a re-parametrization of the Cole-Cole model to an equivalent less-correlated parametrization and a split of the spectral parameters during the inversion procedure. To prove the modelling, a comparison with the ground DCIP lines will be shown. This latter one has been modelled with the same parametrization and inversion scheme of the AEM data to provide a robust comparison between the two and reduce ambiguities in the interpretation. Then, to evaluate the AIP sensitivity to ground chargeable bodies, a joint inversion between the two entire datasets will follow and a vertical and lateral resolution-improved chargeability model is retrieved. This shows the AIP information content and contribute in the enhance of data sensitivity during the modelling procedure
Airborne and Ground IP: an integrated approach for exploration
No full textThe Iberian Pyrite Belt (IPB) is one of the oldest and still active mining districts in the world. In the last decade, a renewed mining activity and scientific research have led into a wealth of new data and new geological hints for explorers and for the academic community, making the IPB one of the most important and dynamic mining districts in Europe (Inverno et al, 2015). In this region, the great number of different signatures related to the ore body and to its vectors call for an integrated use of complementary geophysical methods. The sulfides targets show contrast in both density and electrical properties, and historically gravity has played a crucial role for exploring in the IPB. These methods have been later accompanied by EM methodologies, both airborne and ground, given their high sensitivity to conductive targets (Menghini et al, 2022).
With this contribution we will focus on an application of a novel modelling approach that aims to properly extract the Induced Polarization (AIP) effects from the Airborne Electromagnetic (AEM) data. The AEM survey has been acquired in the IPB for mineral exploration to localize the VMS deposit. After the AIP modelling, we will show a comparison between the airborne chargeability and some overlapping ground IP models from the same area. This comparison aims to better understand the potential in the use of AIP for exploration and to attempt an improvement in the definition of the sensitivity field of the airborne technique, as well as its relationships with ground IP. Then, a joint inversion between the two methods will be presented
Joint Inversions of AEM modelling AIP effects: Helicopter-borne, Ground IP and Fixed-Wing systems
No full textIt is nowadays widely accepted that Induced Polarization (IP) effects can affect Airborne Electromagnetic (AEM) measurements. Modelling the AEM data with a dispersive-resistivity allow to properly retrieve the halfspace parameters avoiding high inversion misfits and wrong structures. Even if the Airborne IP (AIP) modelling it is a known and controlled practice, there are still some open questions regarding the complexities of this modelling approach. Most of this lie into the AIP sensitivity to geological targets, others in its capability in integrate with the ground IP and other more about the parametrical management during the inversion process. To contribute on the AEM-IP modelling field of research, with this work we performed two joint inversions on real data modelling AIP effects. For the first experiment we jointly inverted AEM-IP fixed-wing data with helicopter-borne data. For the other experiment, we jointly modelled ground DCIP and helicopter-borne AEM data, modelling AIP parameters. With these experiments we retrieved that inductive airborne IP can contribute, in term of sensitivity, to the ground IP modelling procedure and that fixed-wing airborne data have a good sensitivity to geological targets as well as helicopter-borne platforms. More in general, it has been seen that inductive IP contains complementary information for modelling IP effects
Inductive Induced Polarization: integration with galvanic DCIP and joint inversion
Get PDFWith this contribute we present a case study of integration between ground DCIP and the inductive Induced Polarization extracted from the airborne EM measurements. To do this we worked with data acquired by the PanGlobal mining company, in Spain, constituted by 17 ground DCIP lines overlapped by an airborne EM survey. First, we apply a novel modelling technique to AEM data with a dispersive resistivity that aims to reduce the equivalencies in the inversion procedure. Then, a comparison of the airborne chargeability models with the ground DCIP models will be conducted, to evaluate and ground prove the modelling done. In conclusion, to robustly evaluate the AIP sensitivity, a joint inversion between the two datasets will be done modelling the capacitive phenomena
Airborne IP driven exploration for greenfield exploration: an application in the Horizon SEMACRET project
No full textThe critical raw materials (CRMs) exploration and supply is crucial to achieve the objectives defined by the European Critical Raw Materials Act to reach the green energy transition. In order to reduce the social and environmental impact of the exploration, innovative indirect techniques have to be adopted for the mineral targeting.
Among the various geophysical methods, two of the most common techniques for exploration are the Induced Polarization (DCIP) and the Electromagnetic (EM) to map, respectively, chargeable and conductive bodies in depth. Although these techniques have been considered sensitive to different physical properties for a long time, it has been recognized that the effects of a polarizable ground can be measurable by inductive EM measurements (Smith et al., 1996), both airborne and ground. It has then been shown that is possible to model the inductive IP (Viezzoli et al., 2013) to retrieve the ground chargeability distribution and how novel modelling approaches (Dauti et al., 2024) can increase the inductive chargeability sensitivity in depth with good relationships with known mineralized bodies.
In this context, with this contribute we propose a case study for which the retrieved inductive chargeability models have been actively used to define the next steps of the exploration workflow for a real green-field exploration research project (the HORIZON SEMACRET European project) with chargeable targets.
First, two Airborne EM surveys have been flown with different base frequencies (12.5 Hz and 25 Hz) to increase the data sensitivity to IP effects and to improve the near surface resolution. Then, a modelling approach that points to reduce the equivalencies among the parameters of the “IP-expanded” model-space has been applied to the data to define where to follow-up on the ground. In this optic, the benefits of an effective AIP mapping are many, spanning from risk reduction to logistic simplification and increasing the mineral system understanding through the large-scale mapping of the ground resistivity and chargeability.
With this work we also aim to investigate the inductive IP effects from a multi-frequency range prospective: we acquired on the ground different inductive data with different instruments and base frequencies over the AIP localized anomalies and compared the data among them and with overlapping DCIP galvanic lines. With this we aim to improve the understanding of IP effects at different scales of investigation and for different instrumental spectral contents among galvanic and inductive measurements
First attempts to model AIP in fixed-wing EM data
No full textIP effects can distort airborne EM data, usually producing faster decays and, under certain conditions, changes in signal polarity. These effects, if not recognized and treated with a dispersive resistivity model, often lead to artifacts in the resistivities recovered. Commonly, the IP effects in fixed-wing AEM data are not taken into account in the processing and modelling procedure. This mainly because of their geometric configuration (and the system footprint) that does not allow to uniquely relate the negative measurements to the polarization effects. The rapidly accumulating experience on IP effects in helicopter EM systems, however, warrants further research on fixed wing EM and IP modelling for the recorded data. With the current paper we present a first attempt of Airborne Induced Polarization (AIP) modelling for a fixed-wing electromagnetic system and a joint AIP inversion between fixed-wing and helicopter concentric loop platform data. Realistic retrieval of chargeability from fixed-wing data and comparable with VTEM. Joint AIP inversion of these two systems also shows promising results
Joint Inversion of Electrical and Electromagnetic data including IP: a Methodological Breakthrough
No full textThis study focuses on the joint inversion of Electrical and Electromagnetic (EEM) data, specifically galvanic and inductive
measurements, within a unified inversion framework. The proposed joint inversion includes both galvanic and inductive datasets in
the data space, with the modelling accounting for induced polarization (IP) effects.
This joint inversion procedure is first assessed using synthetic models and then applied to a field case study involving AEM and
high-density geophysical coverage. The results consistently show that joint inversion yields models with enhanced resolution,
capturing both high and low electrical conductivity features more precisely compared to independent models.
The joint model is validated using borehole data, including EM geophysical logging and lithological descriptions, confirming the
methodology's effectiveness. This study highlights the potential of joint inversion techniques to provide comprehensive and reliable
subsurface models, crucial for geophysical applications especially in complex geological settings
Airborne and Ground Induced Polarization integration: new insights for exploration
No full textIt is known and recognized that Induced Polarization effects can affect the Airborne Electromagnetic measurements. These effects, if not treated properly, can represent a source of artifacts, bad fitting, and false recovered structures during the inversion process. At the same time, recognize and properly model the polarization effects can provide a mapping of the spectral content of the recorded data, adding extra information to the results, and allows to properly model the EM. With this work, we modelled the spectral content of Airborne EM data and compared the results with ground IP measurements acquired in the same area. For the modelling procedure, we propose to use the same approach, in order to be more consistent in the modelling procedure. The data we used are from the Iberian Pyrite Belt, one of the most important mining districts in Europe and with the highest concentration of VMS worldwide. Given the geological complexity of the area and the different signatures of the mineralisation style, with our data integration we aim to evaluate the potentialities of the AIP modelling and its role for exploration
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