The Fabian orebody is a non-daylighting iron orebody in the LKAB Malmberget Mine in northern Sweden. The orebody was mined using slot caving and sublevel stoping during the 1970s and 1980s, resulting in a large open stope under a 250 m thick crown pillar. The orebody has since been mined using sublevel caving beneath the open stope, which has caused progressive caving and a corresponding continuous reduction of the crown pillar thickness toward the ground surface.
During 2010, a prognosis of the cave development in the Fabian area was developed, based on compilation and analysis of all available material. At this time, the crown pillar had a minimum thickness of 77 m. The prognosis was presented at the end of 2010, and predicted a slow, progressive caving of the crown pillar and the formation of a cave crater on the ground surface within the previously fenced-off area, and with minor disturbance to the surrounding municipality.
The cave development was followed up continuously through laser scanning, visual observations and seismic monitoring. In March 2012, a new cave crater formed on the ground surface above the Fabian orebody, similar to what was predicted. The crater developed in the morning of March 20, with no disturbances to nearby residents or municipal functions.
The prognosis is compared with observations of the caving and the differences and implications quantified. A program for continued monitoring of mining-induced deformation in Malmberget is also described and a criterion for allowable mining-induced surface deformations is proposed.