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- Volume 40, Issue 8, 2022
First Break - Volume 40, Issue 8, 2022
Volume 40, Issue 8, 2022
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Semi-Airborne Electromagnetic Exploration Using a Scalar Magnetometer Suspended below a Multicopter
Authors Michael Becken, Philipp O. Kotowski, Jörg Schmalzl, Gregory Symons and Klaus BrauchAbstractSemi-airborne electromagnetic (EM) techniques offer the opportunity to combine lightweight airborne receivers mounted on unmanned aerial vehicles (UAV) with high-moment transmitters on the ground. Owing to their low flying speed, UAVs facilitate recordings of low-frequency signals, which is beneficial for the exploration of deeply seated mineral deposits or other geological targets. However, noise from the electrical components of the aircraft as well as motional noise pose limits on the signal-to-noise ratio at far offsets from the transmitter. Here, we demonstrate the use of an optically pumped magnetometer (OPM) suspended below an UAV to measure scalar EM responses in the frequency range from 1–256 Hz that is nearly unaffected by motional noise. The responses can be identified with the component of the EM signal in the direction of the geomagnetic field, and they can be inverted into resistivity using available software solutions. We illustrate the technique using field data from the Hope deposit, Namibia. Two-dimensional inversion models image the mineralization zone with remarkable resolution from the surface to about 300 m depth, in good agreement with results from previous exploration. This field example suggests that the method is efficient for exploring conductive mineral deposits at depths of several hundred meters.
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On the Development and Application of Airborne GPR Solutions
Authors Jesper Emilsson, Johan Friborg, Jaana Gustafsson, Jimmy Adcock and Andreas VibergAbstractRecent development of ground penetrating radar (GPR) technology, together with effective unmanned aerial vehicles (UAVs), have made it possible to carry out airborne GPR measurements across areas otherwise difficult to access and survey. The interest in airborne GPR studies has therefore been rising steadily in recent years and applications are many, including bathymetry, glaciology, archaeology, near-surface geology, ice- and snow thickness, road planning, peat, and wetland studies.
However, airborne GPR measurements introduce several challenges that affect surface-based measurements to a lesser extent. Some of these challenges are regulatory, others of a more technical nature. In this article, we will discuss the effects an airborne antenna solution has on antenna footprint, unwanted signal input and signal loss. We will also describe a few scenarios where airborne GPR has been successfully used. Throughout the included studies, and depending on the application, different MALÅ GeoDrone antennas (developed and manufactured by Guideline Geo) have been used. At this point, it is also important to remind the reader the importance of adhering to local and regional regulations regarding the use of both UAV and GPR equipment.
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Active and Passive-Source Underground Seismic Data Acquisition
Authors T.-J. Hupe, D. Draganov and D. OrlowskyAbstractAs part of the European research project Seismic Imaging Techniques for Mineral Exploration (SIT4ME), in-mine seismic active-source and continuous noise measurements were performed within an underground mine gallery of a former radioactive waste repository – the Asse II salt mine (Lower Saxony, Germany) to investigate its geological conditions. Inspired by recent underground active-seismic surveys in the Cote Blanche salt mine and former In-seam seismic surveys in the German hard-coal district of the Ruhr area, we apply conventional exploration and processing methods to an image of the subsurface. Among others, these include data sorting, bandpass filtering, normal moveout correction, static correction and depth (distance) conversion. To process the passive seismic data, we perform an illumination diagnosis for the retrieval of body-wave arrivals and apply passive-source seismic interferometry by cross-correlation (PSICC) on noise data dominated by S-waves. We show that active-source seismic measurements can be used from underground mine galleries for the identification of geological structures. Furthermore, we demonstrate that PSICC can be used to produce virtual-source underground seismic surveys resembling an active-source seismic survey.
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Application of 3D Optical Fibre Reflection Seismic in Challenging Surface Conditions
Authors Sasha Ziramov, Andrej Bona, Konstantin Tertyshnikov, Roman Pevzner and Milovan UrosevicAbstractDistributed Acoustic Sensing (DAS), which uses strain-induced optical distortion effects to use optical fibres as multi-channel seismic arrays, enable efficient and inexpensive high-resolution seismic surveying in the challenging surface conditions, such as salt lakes. In this study, we present a first published 3D seismic survey completed with a fibre optic network.
Since DAS cables freely deployed on surface can be sensitive to ambient noise such as strong wind, which is common in many field conditions, we developed an efficient methodology for cable burring by fast ploughing it in both soft and hard ground conditions. Even a standard telecommunication fibre optic cable deployed beneath the surface by this ploughing method delivers reflection seismic recording performance comparable to conventional geophone systems, offering substantial cost savings in practice.
Combined with light and mobile seismic sources such as Betsy gun, DAS technology deployed in 3D surface reflection configuration across a hyper-saline salt-lake environment delivered a performance akin to modern nodal seismic systems. We show that the introduction of DAS technology into seismic surveying practice in the mineral sector could deliver an order of magnitude saving, while substantially increasing the data density and hence allowing optimum performance of modern seismic imaging algorithms.
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Application of the Magnetic Geophysical Method to Exploration of the Potassic Zone in Some Porphyry Copper Deposits (Iran)
Authors Shohreh Hassanpour, Mehmet Salih Bayraktutan and Snežana KomatinaAbstractHaftcheshmeh, Masjeddaghi and Nowchun are three giant porphyry systems located in Iran. Because of the presence of potassic alteration outcrops in the Haftcheshmeh ore deposit (NW Iran), we decided to detect borders of this alteration zone by a ground magnetic method. Goal of exploration is to understand the distribution of concentration in porphyry systems, as the level of magnetization commonly differs across alteration boundaries. Further, 3D interpretation of magnetic data is important to improve our understanding of geology and alteration in the system.
In this paper, qualitative and quantitative results of geophysical surveys are presented in the form of total field intensity, second derivative, upward continuation and pole reduction maps. Comparison of magnetic results with borehole logging provides a good pattern to a field geologist to assign and guide an exploration project. According to this pattern, all drill holes in Haftcheshmeh, Masjeddaghi and nowchun porphyry system were designed.
According to the results for the mentioned copper systems, anomalous magnetic features are related to the sub-volcanic intrusions and high anomaly zones over the potassic alteration probably show the existence of magnetite. The potassic zone pattern can be used as a key in all further exploration of porphyry systems.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)