Seismic tomography as an instrument for structural evaluation in the Printzsköld and Alliansen ore bodies, Malmberget

• Main Author: Jonsson, Linus
• Format: Bachelor Thesis
• Language: English
• Published: Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser 2017
• Subjects: Geology; Seismic tomography; LKAB; Geologi; Malmberget; Norrbotten
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64918

The Malmberget deposit is one of the major apatite iron ores in Europe, located in northern Norrbotten. As the mining in Malmberget proceeds deeper more challenges with the stability have been faced. When the stress distribution of a rock mass exceeds the rock strength energy in form of seismic waves is released. In Malmberget, a monitoring system consisting of 200 geophones is installed which detects all seismic waves in the area. Based on data received from the monitoring system, LKAB has achieved to generate a seismic tomography model over the velocity variations of the seismic waves as they propagate in the rock mass. The present study evaluates how the seismic tomography model can be used as a tool for reconstructing the structural characteristics of the two ore bodies Printzsköld and Alliansen. The aim is to clarify how seismic tomography can be combined with structural data to increase the geological knowledge of the Malmberget mining area. Based on structural measurements from the mine in combination with geotechnical data (RQD, Jr, Ja) two structural geological models were constructed. One model visualizing the orientation of the foliation and the other presenting brittle joints and fractures. The models were constructed in order to compare them with the seismic tomography model to outline structures and characteristics in the rock mass. The foliation in Printzsköld has a steep NE-SW orientation. In the eastern part where Printzsköld connects to Alliansen, the orientation changes to NW-SE, indicative of a fold structure. The joints and fractures in the study area appeared as 4 sets. One set appeared parallel to the foliation and one perpendicular to it. The two other sets were oriented E-W almost perpendicular to each other with a shallow dip. The rock quality in Printzsköld shows a pattern of increasing quality deeper down with zones of lower quality following the magnetite ore body. The previous identified deformation zone DZ031 appear as an important structure for unstable zones in Printzsköld. The ...