Mining in the production area 'Block 19' in the LKAB Kiirunavaara Mine has resulted in extensive seismic activity and several serious rockfalls. This paper describes a modelling study aimed at quantifying the seismic potential for future mining of Block 19, considering several different mining sequences. A 3D discontinuum model was used, in which geological structures were included explicitly to simulate the development of fault slip seismic events. Four different mining sequences were simulated-three of which involved leaving the whole, or part of, Block 19 as an unmined pillar. Mining was simulated from the current active mining level and for a production period of more than 20 years ahead in time. The results were evaluated in terms of stress influences on critical infrastructure in the footwall of Block 19 and, more importantly, the possible extent of fault slip seismic events due to mining (by calculating seismic moments). The results showed that leaving a pillar in Block 19 may be less desirable as higher seismic moments will develop in the final mining stages. However, continued mining without a pillar will also likely result in an increased seismic activity in Block 19, which needs to be addressed appropriately. Block 19 should be mined prior to the neighbouring production areas, but additional and more detailed numerical modelling may be needed to fine-tune the extraction sequence for each level mined. https://papers.acg.uwa.edu.au/p/1201_26_sjoberg/ Numerical analysis of alternative mining sequences to minimise the potential for J. Sjöberg et al. fault slip rockbursting

Mining in the production area Block 19 in the LKAB Kiirunavaara Mine has resulted in extensive seismic activity and several serious rockfalls. This paper describes a modelling study aimed at quantifying the seismic potential for future mining of Block 19, considering several different mining sequences. A three-dimensional discontinuum model was used, in which geological structures were included explicitly to simulate the development of fault slip seismic events. Four different mining sequences were simulated: three of which involved leaving the whole, or part of, Block 19 as an unmined pillar. Mining was simulated from the current active mining level and for a production period of .20 years ahead in time. The results were evaluated in terms of stress influences on critical infrastructure in the footwall of Block 19 and, more importantly, the possible extent of fault slip seismic events due to mining (by calculating seismic moments). The results showed that leaving a pillar in Block 19 may be less desirable as higher seismic moments will develop in the final mining stages. However, continued mining without a pillar will also likely result in an increased seismic activity in Block 19, which needs to be addressed appropriately. Block 19 should be mined before the neighbouring production areas, but additional and more detailed numerical modelling may be needed to fine-tune the extraction sequence for each level mined.

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LKAB operates two underground iron ore mines located in the northern part of Sweden, both using sublevel caving as the mining method. Common sublevel heights vary between 25-30 m. Tests with 40 m sublevel height is ongoing in a fairly small orebody called Konsuln located close to the main Kiruna orebody. LKAB has developed three sublevels (436, 486 and 536 m) in Konsuln to test sublevel caving with 40 and 50 m sublevel height. The objective with these tests is to assess the applicability of large sublevel heights in some of the LKAB future production areas. The production started in March 2021 at level 436, and it is currently the only level in production. Development work with the ramp started in 2018. Production drilling is ongoing at the second level (486 m) with 50 m sublevel height and drifting is being completed at the third level (50 m sublevel height). About 0.8 Mt has been produced so far from blasted rings at level 436. Preparations necessary for planning and for the assessment of the performance of these large sublevel heights includes:1. Measurements of blasthole and raise hole deviations. Installation and detection of smart markers.3. Measurements of iron grades in selected blastholes. 4. Opening blast tests. 5. Scanning of eventual open cavities. 6. Blast performance assessment.Follow up of the performance of the rings involves collection of data from loaded buckets, recovered markers, blast function (vibrations) and visual inspections as well as laser scanning when appropriate. This paper describes the preparations and the results achieved so far for blasted rings using 40 m sublevel height.

LKAB has been mining iron ore with the sublevel caving mining method in northern Sweden for more than 60 years. Throughout the years, LKAB has improved this mining method to stay competitive in a tough international iron ore market. Improvements in drilling and blasting technology have helped LKAB increase the scale of sublevel caving and therefore decrease its mining costs in development. Today, sublevels at LKAB are up to 30 m high. In recent years, with increasing mining depth LKAB has been experiencing decreased availability of some production areas due to rockfalls induced by seismicity and orepass instabilities. LKAB started a study in 2017 to investigate mining under the current main level both at the Kiruna mine and Malmberget mine. This paper presents part of the results of this study, which is a novel layout for sublevel caving that is more suitable for mining under high horizontal stress and with higher production capacity than the existing layout. This layout has been internally named 'fork layout', since its basic layout looks like a drawing of a fork. This layout divides the orebody into contiguous production areas. A production area is formed by several crosscuts linked together by a transport drift. It is expected that this new layout will have a significantly higher production capacity than the existing transversal sublevel caving layout, and will be more suitable for mining at depth compared with the existing layout. One of the drawbacks of this new layout is the need for more development work than the traditional layout. To decrease the economic impact of this effect on mining costs, a further increase in the sublevel from about 30 to 50 m high is suggested. This layout is being considered for approval by the LKAB board to a full-scale test at Kiruna.