Seismic investigations and physical property studies of natural resources in Finland and Sweden : Efficient exploration of groundwater and mineral resources

Abstract: Natural resources, such as mineral deposits and groundwater in particular, are crucial for our society, as the world prepares itself for a smooth transition towards green technologies and decarbonization. Apart from extraction and use, innovative mineral exploration solutions are needed to complete the full value chain and to achieve the sustainable development goals.  The application of seismic methods for both near-surface environmental and deep mineral exploration investigations is known, but high costs are associated with data acquisition and processing. In order to illustrate the potential of the seismic methods for efficient exploration of groundwater and mineral resources, cost-effective seismic surveys were acquired within two locations in Finland and Sweden, for aquifer delineation and imaging of iron-oxide mineralization in a hardrock environment, respectively. Physical properties, obtained from geophysical downhole logging and laboratory measurements, were analyzed for a complete characterization of the mineralization and its host rocks. 3D ray-tracing and 2D finite-difference forward modeling were carried out for better assessing the seismic response of the mineralization.The effectiveness of these seismic surveys was revealed by the quality seismic data acquired using a low-cost, easily operated seismic source and different sensors, including a broadband seismic landstreamer. In particular, the seismic source provided adequate penetration in two different and challenging environments, namely soft glacial sediments at Virttaankangas, southwest Finland, and swampy glacial cover at Blötberget, south central Sweden. The large-scale units of the Virttaankangas aquifer were successfully delineated and integrated with the hydrogeological units of the groundwater flow model. The mineralization at Blötberget was interpreted to further extend 300-400 m downdip, below the currently known depth from borehole observations. 3D processing of the 2D seismic profiles revealed a lateral extent of least 300 m, providing encouraging results for improved assessments of the mineral resources. The reflection pattern validated through forward modeling, suggested a possible new mineralized horizon below the known deposits. Physical property studies helped characterize the mineralization and its host rocks in terms of seismic attenuation and rock quality. Fracture zones detected through sonic full-waveform logging were associated with high seismic attenuation, suggesting low mechanical competence of the mineralized rocks despite good rock quality designation, providing thus important information for mine planning and exploration.   The studies presented in this thesis illustrate the potential of seismic methods and physical property studies for efficient natural resources exploration in crystalline rocks and in overlying glacial sediments.