Leading Swedish iron ore miner LKAB announced that decision as how the Kiruna mine will be mined at depth has been taken. LKAB has opted for a stable pillar solution in the middle of the mine, in the Block 22 area. This means that one mine will effectively become two. The decision has been taken to leave an approximately 700-metre-broad pillar in place, which corresponds to about 90 million tonnes or about three years’ production. And, although some ten percent of production is lost, the profits are considerably greater.On May 20th 2020 the most dramatic seismic event ever recorded in the Kiruna mine occurred. The event had a magnitude 4.2 on the local magnitude scale, and a relatively widespread area sustained varying degrees of damage. In the days that followed, activity was intensive and all focus was placed primarily on surveying the damage. Over two years have passed since the major seismic event occurred in the Kiruna mine. Since then, however, the mine has been a hive of activity. Enormous efforts have been made to restore the damaged Block 22 area, while considerable resources have been invested in analysis, rock reinforcement damage survey, mining planning and increased instrumentation.The fact is, as mining progresses deeper, rock stresses increase. These stresses can never be eliminated but they can be reduced, for example, by adapting the mine layout, i.e., how production, infrastructure – roads and production areas – are planned and placed in relation to factors including the geology. When an orebody is mined out, rock stresses must find new paths around and under the mined-out area. This is when rock stress concentrations are induced and, if the stresses exceed the strength of the rock mass, the rock mass ruptures. Seismic activity, sudden failures in the rock mass, release enormous amounts of energyIn simplified terms this means that the orebody is reduced in volume in the middle of the mine, in the area in which Block 22 is situated. This means that the hanging wall and the so-called barren rock allow less space for blocking up as areas are mined out. The underground mining method employed by LKAB is based on the hanging wall being blocked up, fragmented and successively caved in to the mined-out areas, but in a highly controlled manner.In a way, the pillar solution enables greater flexibility, since vertical mining and sequencing will be somewhat easier to manage. Production must follow a pattern – a production flow, because all blocks are impacted by one another. In effect, this means that the southern mine will not be affected by operations in the northern mine, and vice versa.