10 research outputs found

    Deep Controlled Source Electromagnetics for Mineral Exploration: A Multidimensional Validation Study in Time and Frequency Domain

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    The focus of this thesis is the derivation of an independent multidimensional resistivity model utilising land based controlled source electromagnetics (CSEM) with resolution to conductive structures down to 1 km depth. Data is evaluated in both, time and frequency domain. Since the resistivity distribution is strongly multidimensional, besides conventional 1D inversion methods, 2D inversion techniques are applied to the dataset. The objective of the BMBF funded DESMEX (Deep Electromagnetic Sounding for Mineral Exploration) project is the development of an electromagnetic exploration system which can be used for the detection and assessment of deep mineral resources. In order to obtain a high data coverage as well as a high spatial and depth resolution, airborne and ground based methods are combined in a semi-airborne concept. In the framework of the DESMEX project, the University of Cologne conducted large scale ground based long offset transient ­electromagnetic (LOTEM) measurements along an 8.5 km long transect in a former mining area in eastern Thuringia, Germany. Within the LOTEM validation study, an independent multidimensional resistivity model of the survey area was derived, which serves as a reference model for the semi-airborne concept developed within DESMEX and is eventually integrated into a final mineral deposition model. Utilising in total 6 transmitters in broadside configuration, data at 170 electric field stations were recorded during two large scale LOTEM surveys. In addition, a full component magnetic field dataset was acquired with SQUID sensors using a dense station spacing along the transect. For a preliminary evaluation, conventional 1D techniques are applied to the dataset. The individual switch on transients of the electric field can be explained by a 1D approach, the obtained models however indicate a strong multidimensional subsurface with rather large variations in resistivity. For further interpretation, the LOTEM data is analysed in frequency domain. Obtained 1D and 2D inversion models of the electric field component in frequency domain are in a good agreement with the time domain results. Subsequently, a joint multidimensional inversion of the full dataset in frequency domain was carried out, including electric and magnetic field data. Derived 2D inversion models are discussed in terms of sensitivities and resolution capabilities. Shallow high conductive structures are well comparable to inversion results from other conducted reconnaissance surveys and the semi-airborne CSEM model. The dominant conductivity structures can be linked to the occurrence of Silurian graptolite shales

    INFACT technology watch report

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    This research has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement nÂș 776487. Furthermore, some of the authors (B.J. and V.H.-S.) were supported by the Spanish Ministry of Science Innovation and Universities under the framework of the R&D project RTI2018-098966-B-I00.Summary: This report presents a bibliometric study on patents and scientific publications related to the following technologies involved in INFACT: airborne electromagnetic methods, airborne gravity gradiometry, airborne magnetometry and drone-borne hyperspectral imaging. A statistical analysis of the documents reveals the main players, technology trends and collaboration patterns via bibliometric techniques

    Using electromagnetic methods to map and delineate high-grade harzburgite pods within the Ni-Cu mineralised Jacomynspan ultramafic sill, Northen Cape, South Africa

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    A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016.The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion

    Geophysical analysis of an area affected by subsurface dissolution - case study of an inland salt marsh in northern Thuringia, Germany

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    The subsurface dissolution of soluble rocks can affect areas over a long period of time and pose a severe hazard. We show the benefits of a combined approach using P-wave and SH-wave reflection seismics, electrical resistivity tomography, transient electromagnetics, and gravimetry for a better understanding of the dissolution process. The study area, "Esperstedter Ried"in northern Thuringia, Germany, located south of the KyffhÀuser hills, is a large inland salt marsh that developed due to dissolution of soluble rocks at approximately 300 m depth. We were able to locate buried dissolution structures and zones, faults and fractures, and potential fluid pathways, aquifers, and aquitards based on seismic and electromagnetic surveys. Further improvement of the model was accomplished by analyzing gravimetry data that indicates dissolution-induced mass movement, as shown by local minima of the Bouguer anomaly for the Esperstedter Ried. Forward modeling of the gravimetry data, in combination with the seismic results, delivered a cross section through the inland salt marsh from north to south. We conclude that tectonic movements during the Tertiary, which led to the uplift of the KyffhÀuser hills and the formation of faults parallel and perpendicular to the low mountain range, were the initial trigger for subsurface dissolution. The faults and the fractured Triassic and lower Tertiary deposits serve as fluid pathways for groundwater to leach the deep Permian Zechstein deposits, since dissolution and erosional processes are more intense near faults. The artesian-confined saltwater rises towards the surface along the faults and fracture networks, and it formed the inland salt marsh over time. In the past, dissolution of the Zechstein formations formed several, now buried, sagging and collapse structures, and, since the entire region is affected by recent sinkhole development, dissolution is still ongoing. From the results of this study, we suggest that the combined geophysical investigation of areas prone to subsurface dissolution can improve the knowledge of control factors, hazardous areas, and thus local dissolution processes

    Hochtemperatursupraleitende Quanteninterferenz-Detektoren mit Stufenkontakten fĂŒr neue geophysikalische Messinstrumente

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    Die Dissertation beschĂ€ftigt sich mit der Erforschung und der Optimierung von HTS-SQUID-Magnetometern auf Basis von Stufen-Josephson-Kontakten fĂŒr die Anwendung in TEM-Systemen fĂŒr die geophysikalische Exploration. FĂŒr Entwicklung und Optimierung wurden sowohl der Fabrikationsprozess analysiert, um eine zeit- und ressourcenschonende Fabrikation mit hoher Ausbeute und hoher Reproduzierbarkeit zu ermöglichen. Zudem wurden Methoden zur Verringerung des Rauschens im niederfrequenten Bereich und zur VergrĂ¶ĂŸerung der SensitivitĂ€t untersucht, um eine möglichst große Explorationstiefe zu erreichen. Im Rahmen der Fabrikationsanalyse wurden LackhomogenitĂ€t und -höhe sowie der Einfluss der Ätzwinkel auf die entstehenden MgO-Stufen beim IonenstrahlĂ€tzen untersucht. Zudem zeigte sich, dass YBCO/STO/YBCO-Schichtsysteme beschichtet mit in situ gepulster Laserablation bessere morphologische und supraleitende Eigenschaften aufweisen als einzelne YBCO-Schichten. Basierend auf diesen Ergebnissen wurden integrierte HTS-SQUID-Magnetometer hergestellt. Sie haben große AufnehmerflĂ€chen, die direkt an vier SQUIDs gekoppelt sind, sowie integrierte Heizer und Feedback-Spulen. Diese Magnetometer erzielen hohe IcRn-Produkte und hohe SpannungshĂŒbe und ein weißes magnetischen Feldrauschen von BN < 30 fT/√Hz. Ihre LangzeitstabilitĂ€t konnte durch ein Passivierungsschichtsystem deutlich verbessert werden. Um das Rauschen im niederfrequenten Bereich ausgelöst durch Flussschlauchbewegung zu verringern, wurden zwei separate Methoden untersucht: Einerseits die Verringerung der supraleitenden FlĂ€chen, andererseits die Implementierung von Gold-Nanopartikeln in die supraleitenden Strukturen. Beide Methoden zeigen signifikante Verringerungen des niederfrequenten Rauschens mit BN ≈ 200 fT/√Hz bei f = 1 Hz. ZusĂ€tzlich wurden Magnetometer mit vergrĂ¶ĂŸerter effektiver FlĂ€che hergestellt. Sie haben eine höhere SensitivitĂ€t und dadurch ein verringertes magnetisches Feldrauschen mit BN ≈ 17 fT/√Hz

    Modeling and inversion of airborne full tensor magnetic gradiometry data in the Thuringian basin and forest

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    The recent development of airborne full tensor magnetic gradiometer (FTMG) systems, based on superconducting quantum interference devices (SQUID), allows to obtain the full magnetic gradient tensor of the Earth's magnetic field of large areas (10x10 km). This system allows acquiring all components of the magnetic gradient tensor. This tensor exhibits some advantages over conventional airborne magnetic field data, e.g. a higher spatial resolution and additional directional sensitivity. In this work a FTMG system was applied in the framework of the multidisciplinary INFLUINS project (Integrated fluid dynamics in sedimentary basins) in order investigate different areas in the Thuringian Basin and the neighboring highlands. Main goal was to map magnetic lineaments along major fault zones and to demonstrate the advantages of airborne FTMG. Full tensor data sets have been acquired with very low system noise of only 60 (pT/m). Two different case studies are presented: In the first case study a strong magnetic anomaly in the center of the Thuringian Forest, caused by the magmatic intrusion of the Höhenberger dolerite is analyzed, which exhibits indications of a significant remanent magnetization. Multiple magnetization vector inversions were performed using either the full magnetic gradient tensor or only the total field anomaly data. The inversion results are evaluated using magnetization directions acquired by paleomagnetic sampling and available geological information. In the second case study, a small magnetic anomaly was investigated. It was discovered while mapping magnetic anomalies along the Eichenberg-Gotha-Saalfeld fault zone, which is one of the major fault zones in the Thuringian Basin. The detected lineament is interpreted using the components of the magnetic gradient tensor, additional ground based geo-electrical data and available geological information. The inversion of the magnetic gradients revealed a steeply dipping zone of mostly induced magnetization

    Magnetic Hybrid-Materials

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    Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

    Magnetic Hybrid-Materials

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    Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

    GSI Scientific Report 2016

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    PLEASE GO TO FILES TO SELECT YOUR DOWNLOAD SECTION. Lience: https://creativecommons.org/licenses/by/4.0
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