Stabilitet och säkerhet - hängväggsstabilitet i Kirunavaara

The town of Kiruna is located 150 km north of the polar circle in Sweden. Just west of Kiruna is the Kirunavaara iron orebody. The orebody consists of magnetite, surrounded by quartz porphyry on the hangingwall side and syenite porphyry on the footwall side.

The orebody is about 4000 meters long, 80 meters wide and has an average dip of 60º to the east. As a result of underground mining (sub-level caving), large-scale subsidence is taking place in the hangingwall between the orebody and the town.

As mining proceed to greater depths an increasing volume of rock in the hangingwall is influenced, thereby pushing the deformation front towards the town and its railway.

The geophysical methods used are gravity profiling, seismic velocity studies and anisotropy of magnetic susceptibility (AMS).

Weakness zones occur both in the orebody and the surrounding rock, and a previous study of the geological structures of Kirunavaara concludes that there is a general link between local and regional deformation zones. Brittle deformation is dominant and there appears to be a link between plastic and brittle deformation as the plastic ones are often re-activated. AMS reflects the preferred orientation of magnetic grains and crystals in rocks.

The minerals are also oriented due to deformation of the rock, and AMS is a very good tool for defining width and type of plastic deformation. By determining the rock mechanical properties on samples where the mineral orientations have been defined we also want to test eventual links between the degree, type and orientation of magnetic anisotropy and mechanical properties.

For information on the rockmechanical part of the project, see Tomas Villegas: Hangingwall subsidence.

Mai-Britt Mose Jensen

Telefon: +46 920 491 690

Sten-Åke Elming

Kirsten Holme