Evolution of Seismicity at Malmberget Mine

The Malmberget iron ore mine owned by LKAB (Sweden) is one of the largest iron underground mines in the world. At present 10 orebodies are being mined, with seismicity being a known issue for several of them. The seismic system consists of 143 geophones, of which 36% are triaxial. They are a mix of 4.5 and 14 Hz geophones installed underground and in crown pillars. On the ground surface five 1 Hz geophones have been installed to estimate seismic source parameters. The mine seismic system records on average 440 events monthly with ML > 0. The largest seismic event recorded until the end of 2023 is with ML 2.9. The study was carried out in order to identify some trends in seismicity as the mining goes deeper and to find a correlation with some main controlling parameters – volume and depth of the production in order to obtain information for future seismic hazard and risk analysis. Another purpose of the study was to identify trends and behaviors for different orebodies (mining areas). The seismicity correlates strongly with the production depth, but there are differences between the orebodies. 1. INTRODUCTION The Malmberget iron ore mine owned by LKAB (Sweden) is one of the largest iron underground mines in the world. Mining in the area started by the official records in the mid-18th century, but in a small scale. The railroad was finished in the 1890s, which meant an upswing in the mining activities. Already in 1914 underground mining dominated the production. The Malmberget underground mine consists of about 20 orebodies, of which 11 are mined at present (December 2023), covering a surface area of about 4 × 8 km. The orebodies vary in size, shape and dip in addition to having different rock mechanics issues related to geology and extraction sequence. Some orebodies have been mined by surface mining, while mining in others started some distance below the ground surface, leaving a crown pillar. At present the mine uses the sublevel caving mining method.