Lea Gyger: Advancing Subsurface Imaging for Mineral Exploration Through Broadband Acquisition, Surface DAS, and SWD in Blötberget, Sweden

Abstract

The increasing demand for critical raw materials, driven by the energy transition and digitalization, has highlighted the European Union’s reliance on external suppliers and the need to enhance domestic mineral exploration. Seismic methods provide high-resolution subsurface imaging but remain underutilized in hardrock environments due to cost and technical challenges. This thesis investigates how seismic data acquisition and processing techniques can improve imaging quality and cost efficiency in mineral exploration. Three approaches are evaluated using field data from the Blötberget iron-oxide deposit in central Sweden: broadband seismic acquisition, surface-deployed distributed acoustic sensing (DAS), and drilling-related seismic energy for seismic-while-drilling (SWD). Broadband seismic data show improved resolution and depth penetration, enabling better delineation of known mineralization, clearer imaging of geological structures, and identification of deeper reflectors with exploration potential. Surface DAS is assessed as a seismic receiver array and, despite challenges such as noise and variable coupling, successfully images the main ore body and associated faults. Although data quality is lower than that of conventional recorders, DAS demonstrates potential as a cost-effective and scalable alternative when acquisition and processing are optimized. In addition, drilling-related seismic sources are investigated. While drill-bit signals are too weak for reliable imaging, rig-induced vibrations generate coherent seismic energy that can be used to extract surface-waves and reflections consistent with known structures, indicating potential for passive seismic applications. This thesis demonstrates that combining broadband acquisition, emerging sensing technologies, and unconventional seismic sources can significantly enhance seismic imaging in hardrock environments. These developments contribute to making seismic methods more effective and accessible for mineral exploration, supporting efforts toward a more secure and sustainable supply of critical raw materials.