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The FUTURE project aims to enhance seismic surveying in South African mining by integrating advanced acquisition technologies. In this paper, we detail surface and underground seismic surveys at the South Deep gold mine as part of the project. Surface seismic acquisition used co-located broadband micro-electromechanical sensors, one and three component recorders connected to geophones, distributed acoustic sensing using a straight fibre optic cable, along with a 6 ton broadband seismic vibrator operating with 4-180 Hz linear sweeps. In addition, underground surveys employed a combination of straight, and helically wound fibre optic cables, cabled-based and nodal sensors, along with a 500 kg drophammer mounted on a skid steer bobcat. The surface and underground seismic arrays were time synchronised using a GPS-time transmitter to allow for accurate seismic data recording in a GPS-denied environment. Results show the efficacy of these techniques in acquiring high-resolution seismic data, revealing detailed subsurface geological structures and mineralisation down to 3500 m below ground surface. Surface data revealed clear seismic reflections corresponding to the Black Reef and Ventersdorp Contact Reef. An underground P-wave velocity model exhibits low velocity anomalies that are associated with fracturing, while a P-wave reflection stack section shows significant reflections and a degree of faulting below the tunnel floor that was not observed on the surface reflection seismic data. We highlight the potential of these technologies to enhance safety, efficiency, and sustainability in mining. This study sets a benchmark for future reflection seismic surveys, paving the way for safer, more efficient, deep mineral exploration and extraction practices.

In June 2022, an innovative seismic survey was conducted in Bl & ouml;tberget, central Sweden, to evaluate the effectiveness of employing both a broadband seismic source and broadband receivers for mineral exploration in a challenging hardrock setting. The Bl & ouml;tberget mine hosts high-quality iron oxides, predominantly magnetite and hematite, sometimes enriched with apatite. These deposits comprise 10-50 m thick sheet-like horizons with a moderate eastward dip (similar to$\sim$45 degrees) along an NNE-trending zone. The survey employed a combination of co-located micro-electromechanical sensors, three-component recorders, surface and borehole distributed acoustic sensing, along with a 77-kN broadband seismic vibrator operating with 2-200 Hz linear sweeps. A tailored processing workflow was applied to preserve the broadband nature of the recorded data, and a one-dimensional velocity model was derived from the borehole distributed acoustic sensing data for migration and time-to-depth conversion purposes. Compared to the previous seismic surveys, the resulting seismic cross section reveals several well-defined reflections with improved resolution. Notably, a reflection intersecting the main deposits at a depth of approximately 1200 m exhibits a distinct polarity reversal relative to the reflection from the mineralization, providing further evidence for its interpretation as originating from a fault zone. Shallow reflections align with geological boundaries and partially coincide with weak magnetic anomalies. Additional reflections were revealed underneath the known mineralization on both sides of the fault zone and may suggest the presence of potential additional resources. The delineation of these reflections and the fault zone is critical for future mine planning and development in the region. This case study underscores the potential of broadband data in achieving high-resolution subsurface imaging in hardrock environment and its pivotal role in mineral resource assessment processes.

Geologic carbon storage in saline acquirers is a feasible and scalable way of reducing atmospheric carbon dioxide (CO2). Since 2022, Denmark has stepped up site characterization at five suitable onshore locations for this purpose with a particular focus on four-way domal structures. A dual-element recording system incorporating landstreamer and wireless recorders was innovated and upscaled in a cost- and time-effective way for this purpose at the R & oslash;dby structure (one of the five sites). The dual-element recording allows a better imaging of the near-surface structures but also because of its broadband nature, it helps to retain higher resolution for imaging toplap structures and smaller faults in the area. The landstreamer data better image fault structures offsetting the Bunter Sandstone Formation, which is the primary reservoir, and the overlying geological seals such as Fjerritslev, & Oslash;rslev and Falster Formations. The Vedsted Formation, which a secondary seal in the region, appears unfaulted in the landstreamer data. The landstreamer data also reveal glacial valleys, near the surface, which are a source of groundwater. The two complementary datasets, from the landstreamer and nodal data, help to de-risk geological carbon storage in Denmark and is a solution we recommend to be adapted for onshore sites elsewhere in the world specially where the logistical acquisition challenges are not significant.

Understanding the structural intricacies of subsurface halokinetic formations is crucial for various geological applications, including geological capture and storage (geological carbon storage (GCS)). This study focuses on the seismic imaging of the Gassum structure in eastern Jutland, Denmark, employing high-resolution, dual-element acquisition, and processing techniques. The investigation aims to unravel details in the evolution of the salt dome and its implications for GCS potential. High-resolution seismic data processing and interpretation reveals a skewed dome structure with steeper flanks on the western and northern sides, characterized by faults and stratigraphic thinning. The asymmetric growth of the dome suggests uneven salt loading during its genesis, influencing local stress fields and structural development, with evidence of syn-tectonic subsidence that produced salt welds. This is supported by the presence of stratigraphic wedges and an increased depth of imaged horizons within steeper flanks of the dome. A mild piercement of the salt into overlying sediments, onlapping features, and the presence of normal faults that originate from the dome apex and extend radially, all indicate a reactive piercement process in the salt pillow's development stage. This produced an extensional regime in overlying strata, inducing sequence thinning and graben structures. Analysis of reservoir and seal properties unveils adequate conditions for GCS, with a continuous reservoir and thick primary and secondary seals. However, the presence of faults intersecting these formations raises concerns regarding long-term storage stability. Further investigations into reservoir porosity, migration paths, and volumetric analysis are warranted for conclusive GCS assessments.

Salt pillow growth leads to the deformation of the suprasalt strata and can affect geological carbon storage in saline aquifers. A concern for storage sites on land is the drinking water because the impact of the deformation on fluid pathways and groundwater systems needs to be studied. Here, we present new seismic data from a potential carbon storage site in Denmark. A high-resolution seismic dataset was acquired using a strategically deployed nodal array and a landstreamer to assess the effects of the Permian Zechstein salt migration on the layers above a salt pillow. We create a geological model of the subsurface through correlation of reflection data with borehole data and investigate the main Upper Triassic Gassum Formation reservoir. Our findings reveal a fault system linked to salt diapirism and evidence of salt pillow growth from the Triassic into the Miocene. We image up to 2 km-wide Quaternary palaeovalleys, which incise the deformed overburden and serve as key groundwater aquifers. These results have implications for fluid transport in deep saline aquifers above the salt pillow, and for clarifying the deformation impact on the shallower groundwater systems.

In Denmark, Geological Carbon Storage (GCS) has been prioritized as an immediate solution for climate action. The Havns & Oslash; domal structure has been identified as one of the most promising locations for GCS because its size and properties are believed to be suitable for GCS. However, the preliminary assessments, based mainly on old, sparse, and low-quality seismic data, are uncertain regarding the prospective storage resource and the integrity of the structure. To enable informed decisions and planning of the storage operations and as part of a large-scale acquisition campaign targeting several similar onshore structures throughout Denmark, a seismic data acquisition work was conducted in 2022 in the area. The purpose of the survey was to delineate the structural closure and map possible geologic features, such as faults, that could jeopardize GCS operations. In total, 132 km of highfold and high-resolution 2D profiles were acquired using an innovative dual-element recording system for both deep and shallow subsurface imaging purposes. The recording comprises two vibrating sources and a combination of nodal recorders spaced at 10 m, and 2-m-spaced microelectromechanical systems (MEMS)-based recorders attached to a moving landstreamer. The seismic data contain information on all horizons of interest for GCS. The structure is estimated as a well-defined four-way closure, where the reservoir is continuous. A thick, mostly uniform sealing rock is interpreted and no large-scale faults are found in the near surface. The results, supported from existing background information, provide crucial information to assist further decisions and actions related to future storage operations in Havns & Oslash;.

The advancement of seismic methods is vital for mineral exploration in the ongoing energy transition. In this study, we investigate the application of ambient noise seismic interferometry and surface-wave analysis to characterize the subsurface in a mineral exploration context. We then confirm the results of the passive seismic investigation through an active source experiment. We collected ambient noise data using a 2-D seismic line initially deployed for an active source reflection seismic study. By cross-correlating the signals, we retrieved the surface waves and constructed a 2-D shear-wave velocity profile using conventional surface-wave analysis. We utilized the active source data to establish initial assumptions about the surveyed medium and then validated the passive seismic experiment. The passive seismic results are concordant with the active source results and allow for the interpretation of geological contacts and fault zones. Our work demonstrates the potential of passive seismic methods for investigating local tectonic settings and their role in hardrock mineral exploration.

Strong global actions for climate change include carbon capture and storage (CCS) as a feasible solution to reach carbon neutrality and raise opportunities for detailed subsurface investigations. An acquisition set-up designed for onshore-offshore zones was maximized for wide-scale high-resolution structural imaging and implemented to cover a domal structure of interest for CCS utilization close to the town of Havns & oslash; (Denmark). The challenges of the combined acquisition and processing of land and marine multisensor data along a 42 km seismic profile are analyzed, the suggested solutions are applied, and the limitations are discussed. On the onshore side, a nodal array and a seismic landstreamer system were simultaneously used, whereas along the transition zone, a marine seismic streamer and ocean-bottom seismometers were added to record the seismic response generated by two seismic vibrator sources. The adopted sensing domains (velocity, acceleration, and pressure) were studied, and different processing steps were evaluated to enable their processing and subsequent data set merging. Results suggest, as the best approach, a separate prestack processing of the different data sets and the computation of new geometries and new surface-consistent residual static correction after their merging. The data acquired in the transition zone illuminate, for the first time, the subsurface geology of the region, delineating an expected domal closure. The final seismic section shows high continuity of the reflections with good resolution along the entire profile, identifying the main reservoir structure and the surrounding areas, which are important to ensure reservoir integrity and safe exploitation over longer time scales. Shallow and deep reflections are consistent with the stratigraphic column from a well log near the profile. The presented study shows a comprehensive workflow for processing such a multisensor data set in onshore and transition zone settings.