This contribution is a new multimethod toolset to explore for buried, small-scale (0.01-5 million m3) rare metal and high-purity quartz pegmatites, which was developed as part of the four-and-a-half-year European Union H2020 GREENPEG project. It is underpinned by a complementary suite of existing, revised, and new methodologies, the use of three GREENPEG-developed geophysical exploration devices (EASA-certified, helicoptercompatible nose stinger magnetometer, piezoelectric seismograph, and drone-borne hyperspectral system), and two new databases (spectral library and petrophysical database for pegmatite ores). The toolset is based on the latest understanding of how pegmatites form and become enriched in ore minerals. In this regard, the theoretical component of the toolset resembles that of a comprehensive review article. The toolset has been tested in four active pegmatite exploration areas in a representative range of European surface environments-from coastal Arctic to temperate forest, alpine, and Mediterranean settings. Individual tools or tool combinations can be used to vector toward buried pegmatite-related mineralization, such as for Li, high-purity quartz for silica and metallic Si, ceramic feldspar, rare earth elements, Ta, Be, and Cs, to maximize the success of subsequent more costly exploration such as drilling in ways that optimize environmental, social, and governance outcomes. The tools are optimized for the small size, variable surface environment, depth, geologic setting, mineralogy, chemistry, and often highly variable physicochemical properties of pegmatite ore deposits. They can be used at province, district, and/or prospect scale. This guide is for those who have exploration knowledge and/or experience but who may be new or need updating in the state of the art of pegmatite exploration.

This study presents the results of several GPR surveys conducted at the Bødalen delta, Norway, between 2009 and 2024. Focused on mapping sediment types, studying their internal structure and locating the bedrock surface at the area, these surveys achieved unprecedented GPR travel times - and consequently, penetration depths - in a geological setting. The low loss subsurface along with advancements in GPR equipment and optimized data collection settings, were pivotal in achieving these depths.

In continuation to various ground geophysics conducted at the Åknes unstable rock-slope area during the past 15 years, NVE commissioned additional seismic investigations aimed at helping to determine the thickness of fractured bedrock as well as possible faulting. NGU has done extensive testing on the use of Rayfract® program and obtained knowledge via modeling and real data processing as to the optimized parameters when fracture zones in bedrock are investigated. NVE has provided NGU with the data to undergo such reprocessing and in this sense, we have produced starting models using Hagedoorn's Plus-Minus method and Midpoint Breaks and then implemented Multirun WET inversion using 7 runs of maximum 50 iterations and minimal smoothing. Possible fracture zones were also compared against similar interpretations obtained by ERT to check coherence between methods. Finally, results were delivered to NVE in ASCII format to be part of a multidisciplinary Åknes 3D model built in PETREL.

ABSTRACTGeoelectrical measurements have so far been tested in marine environments worldwide in order to detect subsea fracture zones. However, many of these datasets are processed without considering the extremely high electrical conductivity of seawater and its implications. This study summarizes our efforts to establish the basic rules as to whether marine electrical resistivity tomography can detect weak zones inside a resistive bedrock, a problem which the engineers in Norway usually encounter in tunnel construction sites. This study examines the theoretical response of electrical resistivity tomography in a classic Nordic environment where a highly resistive bedrock is located below the highly conductive seawater, and the capability of electrical resistivity tomography to detect fractured zones, as relevant in a geotechnical study. We performed a large number of synthetic modelling tests examining several factors that marine geoelectrical surveys are particularly sensitive to, such as the depth of the seabed, the seawater conductivity and the bedrock variation, and the survey layout and the inversion scheme. Our results indicate that electrical resistivity tomography surveys for fracture zone detection in geoelectrically demanding marine environments can be promising in case of a limited water depth, and with the use of either dipole–dipole or multiple gradient array and availability of a detailed knowledge of the conductivity distribution in water. However, results of electrical resistivity tomography surveys in such circumstances can be ambiguous since they potentially suffer from reduced resolution and due to the loss of electrical current in water and other artificial effects. Based on the results of modelling, we were able to improve interpretations of electrical resistivity tomography data from a field survey, where marine acquisition was carried at a strait in Kvitsøy, southern Norway.

We have investigated the response of several synthetic models of variable complexity to tomographic inversion using Rayfract®. This software is fairly advanced and complex and offers many different options when inverting refraction seismic data. Using this program to investigate the detection of fracture zones in bedrock, its parameters may be roughly grouped in three categories: the inversion and weighting method used, whether single or multi-run will be employed and the intensity of smoothing. We have discerned that multi-run Conjugate Gradient inversion method, with Cosine-Squared weighting and a 2D Plus-Minus starting model can give fairly good results. Minimal smoothing is also essential for the quantitative characteristics of the detected zones to be accurately calculated, but this is a hyper sensitive procedure which may result in over or underestimations of zone velocity values. Generally, we have concluded that it possible to locate and characterize fractured zones in bedrock albeit with some limitations. It has been found that the imaging of the position and inclination of zones can be problematic especially when the zones are neighboring bedrock areas with small velocity contrast. The detectable depth extent of fracture zones can be followed to a certain depth, but deep zones give the same response as shallow zones due to geological noise. The width of the zone is almost always very accurate and overburden layers can be precisely defined when the interactive picking of branch points prior to inversion is carefully done. The velocity of a zone can be calculated with a good combination of inversion parameters. Moreover, as seen after reprocessing some of the Knappe tunnel data, tomographic inversion can pick up zones that cannot be interpreted traditionally. Finally, denser shot point spacing can bring about a noticeable improvement on the inversion results.

In recent years the types of investigations carried out prior to tunneling have changed in Norway. Resistivity has been introduced as a new method, and refraction seismic data is now processed with the use of tomographic inversion. A comparison between old and new interpretations of refraction seismic data has shown reoccurring inconsistencies when compared with ERT profiling (Rønning et al., 2009). The Geological Survey of Norway (NGU) has re-examined the results from the Knappe-tunnel at the ring-road west of Bergen in collaboration with the Norwegian Public Roads Administration (NPRA) and Geophysix, the Geophysical company that first interpreted the refraction seismic data using traditional techniques. In this work we have compared different interpretations of refraction data with each other, with seismic interpretations, with resistivity and with tunnel data. We have employed traditional interpretation using Hagedoorn's +/- method (Hagedoorn, 1959) and tomographic inversion using the commercial software Rayfract (Rayfract, 2016). The study was supplemented with in-situ observations obtained during the tunnel construction. Our goal is to correlate geophysical anomalies (seismic velocities and resistivity) with weak zones detected during tunneling.

Summary The Geological Survey of Norway (NGU) has reprocessed various geophysical data from the Knappe tunnel in Bergen in collaboration with the Norwegian Public Roads Administration (NPRA) and Geophysix AS, the Geophysical company that originally collected, processed and traditionally interpreted refraction seismic data along the route of the tunnel. In this work we have compared different inversion schemes of refraction seismic data to each other but also to classic interpretations, resistivity profiles, geological mapping and actual observations done after the completion of the tunnel. In connection to the results obtained in the work described above, modeling was planned and carried out to test the efficiency of refraction seismic data inversion when applied to the detection of fracture zones in Norwegian settings (abrupt velocity changes between fracture, bedrock and possible overburden layers). Our goal is not to assess the Rayfract(r) software but instead to try and identify patterns created by known models when moderately knowledgeable inversion schemes are used and in this way attempt to correlate geophysical anomalies (seismic velocities) with weak zones on real refraction seismic data and plan future studies.

A combined geophysical and geotechnical method was carried out at Federal University of Agriculture, Abeokuta for a foundation studies of a proposed New Lecture Theatre of 2,500 capacity. The survey is aimed at evaluating the competence of the subsurface formation as foundation materials. To image the subsurface, Electrical Resistivity imaging (ERI) and soil analysis techniques were adopted. Five (5) traverses and five (5) soil samples from different location within the study area were considered for the work. Four geoelectric layers were delineated from the geophysical results: these are the topsoil, sand clay/clayey sand, weathered rock and fractured rock/fresh basement. The result of the geotechnical method shows that the soil has relatively low clay content. It is concluded from the combined results above, that the subsurface on which the building structures will be located within the study area is safe and fairly competent for any engineering work.

Summary In the present work we examine the crustal structure in the wider Adriatic Sea region using a newly presented Bouguer database derived from the integration of satellite, marine and inland gravity measurements. The observed large-wavelength Bouguer anomalies clearly correlate with the deeper crustal - upper mantle structural features, revealing new information on the Moho undulations, allowing the quantitative assessments of the Moho geometry in the study area. This task was performed using three different approaches, namely the multiple source Werner deconvolution (MSWD), the isostatic admittance method and the Parker-Oldenburg algorithm. The interpretation of the MSWD estimates was performed along nine selected Bouguer gravity profiles, leading to a pseudo-3D Moho map, as opposed to the other two methodologies from which 3D models are derived. All three maps exhibit similar large scale features but also local differences for the Moho structure in the Adriatic Sea area. Since this region exhibits complex geotectonic features, such as a double plate subduction, the main goal of the present work is to highlight the main areas of crustal thinning and thickening, using the aforementioned results. Moreover, the results provided by the different methods are evaluated against the current geological and geophysical data and models developed for the area.

Resistivity measurements in marine environments have already been tested in Norwegian landscapes in in the detection of subsea fracture zones (Lile et al. 1994; Dalsegg, 2012). Yet, most of the produced data have been processed without taking into account the special conditions created by the presence of seawater. Similar studies outside of Norway (Tsourlos et al., 2001; Satriani et al., 2011; Rucker & Noonan, 2013; Dahlin et al., 2014) have also utilized ERT in marine conditions however, most of these studies had deal with brackish water which is less conductive than pure seawater and therefore more favorable to the method (figure 1). This study summarizes our efforts to establish basic rules when considering whether or not pure sea water ERT can satisfactorily detect weak zones inside resistive bedrock. It is also in close connection to related ERT measuring (Rønning et al., 2009; Ganerød et al., 2006; Dalsegg, 2012) and modeling work (Reiser et al., 2007) carried out at the Geological Survey of Norway (NGU) and funded by the Norwegian Public Roads Administration. All results presented here are part of published NGU reports which were made to supplement the construction of an underwater tunnel in western Norway. Based on the modeling results, we were able to improve interpretations of ERT measurements made across seawater straits at Kvitsøy island but also conduct new marine ERT measurements in a more sophisticated manner. Nevertheless, we were also able to detect further limitations to the method.

The individual abstracts for this session are available to read in the PDF.

The purpose of this paper is the development of a new Bouguer anomaly map for the broader Adriatic Sea area to be used as geo-scientific tool which will answer questions mainly regarding the deep and intermediate depth structure of the Adriatic and its surrounding areas. As a first step, a consistent, high-resolution and accuracy free-air gravity anomaly database is created using all the available terrestrial and satellite altimetry data sources. The least-squares collocation (LSC) method is employed to validate the different gravity data sets through an appropriate covariance analysis and following the remove-compute-restore procedure (RCR) for the detailed study of the gravity spectrum. The finally generated gravity database has a resolution of a 0.0333 degrees (similar to 3.2 km) in both latitude and longitude, while its external and internal accuracy is estimated to about +/- 5 mGal and +/- 0.5 mGal, respectively. Based on the derived free-air gravity database a new Bouguer gravity anomaly database is determined at the same resolution for the wider region of the Adriatic Sea. Comparison with existing results confirms the reliability of the new Bouguer map for the study area, mainly due to the combination of both land and sea data. The derived Bouguer anomaly map can support different kind of geophysical investigations of both local and regional structure of the study region. As an example three density models are constructed along selected cross sections extracted from the Bouguer anomaly database, in order to obtain structural information for the crustal-upper mantle structure of the region and draw relevant conclusions. The obtained results show that the Bouguer map can provide important information for the lower-crustal/upper-mantle depth range but also helps to constrain the 2D geometry of the shallow geological units, in very good agreement with the observed surface geology and the current understanding of the geotectonic setting of the area. (C) 2013 Elsevier Ltd. All rights reserved.

The applicability of marine ERT surveys into the detection of underwater fracture zones is studied in this work. Various marine fracture zones models and measuring modes were tested using synthetic data which were subsequently subjected to inversion. In particular factors such as the effect of the sea water layer, the resistivity contrast, the overburden layer in both floating and submerged electrode modes are examined and compared. Among others, results indicate that the exact inclusion of the water layer into the inversion models is extremely important and that ERT surveys can be successful only for the first 10 meters of sea water.

This study is attempting to create a tool which will answer questions mainly aiming at the deep but also shallow structure of the Adriatic Sea and its surrounding areas. The most vital parameter for the accomplishment of this task is the production of gravity from geodetic data coming from satellite missions. Quintessential to this goal is the successful compilation of a total gravitational database consisting of gridded Bouguer anomalies for the wider region of the Adriatic, empowered by the correct binding of heterogeneous data such as field gravity measurements (both land and shipborne) and altimetric data. These data are consolidated through the application of least squares collocation, an interpolation method which uses the statistical properties of the gravitational field and predicts its values on grid points of our choice. The whole procedure is based on the notion of the covariance function, which is normally used for geodetic applications. The completion of the Bouguer anomaly map generates the desired tool which aids and supports all kind of geophysical investigation of the deep and shallow structure of the region at hand.

(1) NCSR Demokritos, Institute of Materials Science, Aghia Paraskevi, Attiki, Greece (david.psomiadis@gmail.com), (2) Aristotle University of Thessaloniki, Department of Physical and Environmental Geography, School of Geology, Thessaloniki, Greece, (3) Aristotle University of Thessaloniki, Department of Geophysics, School of Geology, Thessaloniki, Greece, (4) Aristotle University of Thessaloniki, Department of Geology, School of Geology, Thessaloniki, Greece

The magnetic difference, the quantity measured by magnetic gradiometers, is considered to be the convolution between a function that controls the anomaly pattern and another that controls the strength signal. These are called shape and amplitude functions, respectively. They are distinct and analytically determined; thus, after the assessment of a suitable model, its shape function can be inverted to serve as a filter. If this filter is next convolved with the measured field, a series of amplitude functions is recovered, provided that the subsurface structures can be simulated by a combination of a number of models similar to the one whose anomaly was inverted. The recovered series is essentially the subsurface distribution of the amplitude function.Alternatively, the scheme can be viewed as a transformation of the original field of magnetic differences. The signals, transformed in this context, comprise rectified monopolar versions of the originals, positioned directly above the centre of the targets. Furthermore, their amplitude is a measure of the magnetization of the targets. Thus, the new anomalies can be viewed as a kind of magnetization or susceptibility mapping. Inversion filters are computed in the Wiener mode by inverting the shape function of the anomalies caused by vertical sided finite prisms. This particular model is appropriate for a wide variety of targets that are commonly met in archaeological prospecting. Converting the magnetic signal from the dual lobe pattern to single monopolar anomalies cause them to resemble the usual outcome of resistivity exploration. In this context, this work aims to form a scheme that makes the magnetic gradiometry outcome directly comparable to the outcome of resistivity mapping. Furthermore, it can be applied without contradicting or excluding any other processing operation.The method is implemented in a FORTRAN program that is reasonably user-friendly. The efficiency of the scheme is tested both on synthetic and real data sets.

The convolutional model is considered for a particular type of magnetic gradiometry data. On the basis of a model, its anomaly is considered as the convolution of a shape and an amplitude function. The first one is inverted and forms the filter, which is next convolved with the data to recover the distribution of the subsurface magnetization. Tests on synthetic and real data explore the applicability and efficincy of the scheme.