Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Consequently, seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration. These methods also can be used with varying degrees of success to directly target mineral deposits at depth. We review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions: Australia, Europe, Canada, and South Africa. A wide range of case studies are covered, including some that are published in the special issue accompanying this article, from surface to borehole seismic methods, as well as petrophysical data and seismic modeling of mineral deposits. At present, high-resolution 2D surveys mostly are performed in mining areas, but there is a general increasing trend in the use of 3D seismic methods, especially in mature mining camps.

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Three-dimensional seismic reflection data from the Halfmile Lake area, New Brunswick, Canada, was reprocessed over an 18- [Formula: see text] grid to improve the seismic signatures of a 5-million-ton volcanic-hosted massive sulfide (VHMS) deposit located at 1200-m depth, known as the deep zone, as well as key host-rock structures. We chose a prestack dip moveout (DMO) and poststack migration processing sequence to preserve the possible diffraction signature of the deep VHMS zone. Despite the high level of source-generated noise and large statics caused by near-surface conditions, our processing results revealed improved 3D seismic images for shallow and deep structures. Many of the imaged structures were easily correlated with known lithological con-tacts constrained by boreholes and petrophysical measurements. A short, flat-lying segment of high-amplitude reflection at about 800-m depth in the unmigrated cube was interpreted to originate from a small portion of the lower VHMS zone. The DMO stack was characterized by a large, high-amplitude asymmetric diffraction signature originating from the deep VHMS zone. The asymmetry of the diffraction hyperbola relative to the location of the deep zone was interpreted as resulting from a shape effect from the zone, with the strongest amplitudes along the diffraction hyperbola found north-northwest of the apex. This indicated that the deep VHMS zone dips in a similar direction. This diagnostic diffraction signature was not preserved with the prestack migration approach previously implemented for processing Halfmile Lake data.

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Unmanned aerial vehicle (UAV)-based geophysical surveys are attractive for land mineral exploration and are gradually opening extraordinary opportunities in providing high-resolution definition of geologic structures and for direct targeting of mineral deposits. There are, however, challenges such as electromagnetic noise from the UAV, limited load capacity, and short flight times. If these are overcome, there will be a new era in using UAV-based geophysical systems for mineral exploration and for a number of mining-related purposes. In this study, we have tested the potential of rotary-wing UAV systems, given their flight flexibility and robustness for direct targeting of iron-oxide deposits in central Sweden. A walking-mode high-precision Overhauser magnetometer was reassembled so that it could be lifted by the rotary-wing system. Successful backyard tests were performed, but during the real experiment several issues related to high UAV noise level and extreme magnetic field from the mineralization delayed data acquisition. At the end, within nearly three hours and 10 sorties, approximately 20 km-line total-field magnetic data were collected covering an area of about 2 km2. Flight lines were designed perpendicular to the strike of the mineralization to maximize data sampling. Two distinct mineralized zones, magnetite- and hematite-rich and only 50–100 m apart, are notable in the magnetic data due to the fine sampling spacing provided by the UAV survey. Historical low-altitude (30 m above the ground) fixed-wing aeromagnetic data are available from the study area and are compared with the UAV data. Both data sets are consistent in delineating the mineralization, therefore demonstrating the potential of UAV-based surveys for mineral exploration in geologically and logistically challenging areas.

We present a preliminary assessment of the potential utility of various geophysical measurements carried out over a quick-clay landslide site in south-west Sweden. The multidisciplinary approach includes active P-and S-wave seismic investigations, including 2D and 3D reflection and refraction surveys, passive single and 3C seismic surveys, electrical resistivity tomography and electromagnetic surveys including controlled-source and radio-magnetotellurics, ground-penetrating radar and potential field studies. The P-wave and particularly S-wave reflection seismic data show a highresolution image of bedrock topography and the stratigraphy of a 100 m thick sequence of sediments that lies on top, which include lightly consolidated quick-clays. Of particular interest is the identification of a layer of relatively coarse-grained material between 10-20 m below the ground surface. Geotechnical investigations indicate that most but not all quick-clays at the site are located above this layer. Further studies are required to determine the importance of their relationship and whether the coarse-grained layer may have had a role in triggering quick-clay landslides in the region. Geoelectrical and electromagnetic methods provide high-resolution images of the unconsolidated subsurface and particularly the normal and leached clays. Radio-magnetotelluric methods proved valuable near the river where traditional geoelectrical methods failed to provide sufficient depth coverage. The study shows that geophysical data are able to image major subsurface structures associated with quick-clay landslides.

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The Bergslagen region is one of the most ore prospective districts in Sweden. Presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the Dannemora mining area. The interpretations are constrained by seismic wave velocity measurements on a series of rock samples, cross‐dip analysis, prestack time migration, and swath 3‐D imaging, as well as by other available geophysical and geological observations. A series of major fault zones is imaged by the seismic data, as is a large mafic intrusion. However, the most prominent feature is a package of east‐dipping reflectors found east of the Dannemora area that extend down to at least 3 km depth. This package is associated with a polyphase, ductile‐brittle deformation zone with the latest ductile movement showing east‐side‐up or reverse kinematics. Its total vertical displacement is estimated to be in the order of 2.5 km. Also clearly imaged in the seismic data is a steeply dipping reflector near the Dannemora mine that extends down to a depth of at least 2.2 km. The geological nature of this reflector is not known, but it could represent either a fluid‐bearing fault zone or a deep‐seated iron deposit, making it an important target for further detailed geophysical and geological investigations.