Gravity flow research at the Kiruna sublevel caving mine during the last decade and an outlook into the future

Abstract

LKAB operates two underground iron ore mines located in the northern part of Sweden, both using sublevel caving as mining method. Knowledge of the mechanisms of gravity flow is important since it affects both ore recovery and waste dilution. This paper summarizes results from research conducted during a decade at the Kiruna mine with focus on gravity flow. Two large scale field tests have been carried out, both adopting a holistic approach, not only the gravity flow being monitored but also possible factors influencing the flow. The results from these tests clearly shows that the gravity flow in large scale SLC in Kiruna is often of disturbed character. Shallow draw has been documented both in marker trials but also in many hang-up situations. Shallow draw is common especially in the northern part of the orebody and appears to be rock mass dependent. However shallow draw does not necessarily mean poor extraction ratio, in fact there are many examples on the opposite. The results from the two large scale field trials confirm also a relation between fragmentation and the width of the draw, 10-13 m for fine fragmentation (test 1) and 11-16 m for coarser fragmentation (test 2). A stepped ring design has been tested addressing shallow draw issues, the results appear promising. Several other tests are now ongoing to optimize the current SLC parameters based upon the findings from this research. Recently, the industrial development project “SUM” (Sustainable Underground Mining) has been launched. Part of that project are tests on extreme sublevel heights (40 and 50 m) in a dedicated test mine. Gravity flow will be monitored in all these upcoming trials, but a customized approach will be adopted. A very interesting and challenging future is to come.