Investigation of Influential Contexts on Mining-front Seismicity at Kiirunavaara Mine

Sammanfattning: Mining at great depths has become the reality for the mining industry in Sweden, that faces challenges in terms of increasing seismic events and sometimes intrinsically related rock mass failure. Kiirunavaara mine is owned by LKAB (located at north Sweden) and the company has been dealing with seismicity in a daily basis once the mine has been regarded as seismically active since 2007-2008 and presently has the largest seismic monitoring system in the world. Several authors have studied the characteristics of seismicity at Kiirunavaara mine, but still a closer look into the factors that influence mining-front related seismicity has yet not been performed. In this sense, the present master thesis aimed to investigate the influential contexts on mining-front seismicity in Kiirunavaara mine from a production point of view (mucking data, mining-front geometry and mining sequence) and to point out probable triggers to seismic events and practical guideline measures to partly mitigate the seismic risk. For this the large seismic events (local magnitude ML ≥ 1.5) from 2011 to 2021 classified by previous studies as mining-front related have been analyzed. 63 events were initially investigated individually, combining mucking data, production data and mine geometry from GironPlot 2D and 3D views and the seismic data from software mXrap. The aim was to find patterns of contexts (in terms of mucking data, mining-front geometry and mining sequence) that are likely influential to the occurrence of large seismic events. The results allowed to reclassify the number of mining-front related seismic events to 52, and these were pointed to be probably triggered by blasting (25 events) or mucking (27 events). The events were further classified in 7 categories of probable influential contexts. Most of the events were categorized as related to the Longitudinal Mining category (19 events) and to the Stage I category (17 events). The Stage I category presents a critical scenario of stress concentration in the intact rock pillar that exists between sublevels on the initial stage of production of a level, when no connection to the cave above has been established yet. The high number of events related to the Longitudinal Mining category reinforces the suggestion of not using this type of geometry in the mine. Other categories show the relevance of having proper strategies in terms of mining sequence and mining rate between production blocks. The work brings forward relevant discussions for the future of mining in high stressed environments, e.g. how to enhance the early production stage in terms of providing better preconditioning to the cave and also highlight the importance of investigating and developing tools that could allow to increase the understanding of mucking on the mining-front related seismicity at Kiirunavaara mine.