Reflection Seismic Survey for Characterising Historical Tailings and Deep Targeting at the Blötberget Mine, Central Sweden

Abstract: Iron has been an essential element to human development and iron-oxide deposits are known to host minerals that are labelled as critical raw materials (CRMs), especially in the EU. Therefore, ensuring a sustainable supply of CRMs require access to both primary and secondary sources of their host deposits such as iron oxides. Blötberget is an old mining site in central Sweden rich in both primary and secondary iron-oxide resources (i.e. tailings) from centuries-long mining activities. Thus, this thesis focused on this site, to (1) improve the image of its iron-oxide mineralisation under the historical tailings area through the extraction and processing of 2D data from a wider and sparse 3D dataset, (2) characterise the tailings in terms of geometry delineation and geomechanical property estimation by generating P-wave velocity models of the tailings, and (3) improve the interpretation of existing results in the area through 3D visualisations and comparison. Results from this thesis work suggest possible depth and lateral extensions of the mineralisation for few hundreds of metres beyond what was known previously in the area. It is believed that about 10 Mt of primary iron-oxide resources could arguably be present under the tailing area while the tailings contain an estimated 1 Mt of secondary iron-oxide resources. Also, this thesis work findings indicate that the historical tailings are approximately 10 -12 m thick, 650 m long, and 300 m wide, and has a Vp/Vs ratio between approximately 3-4, indicating a poor geomechanical strength. Additionally, the depth to bedrock in this area was estimated to be 50 m at its deepest parts, with a morphology indicative of complex geological occurrence. Therefore, it is concluded, based on these results, that Blötberget has a good potential to ensure the supply of both iron ore and its constituent CRMs.