Mining-Induced Deformation in the Malmberget Mine

Abstract

The Norra Alliansen orebody of the Malmberget sublevel caving mine consists of iron ore interspersed with biotite schist and granitic inclusions. The schist is squeezed between the ore and the host rock and in direct contact with the ore along the majority of the length of the footwall. The schist exhibits high deformation when exposed to stress. SMART cable bolt roof deformation measurements are re-analyzed to draw conclusions regarding the patterns of deformation in the mine. Each bolt's head is placed at the origin of a spherical coordinate system and the radius and inclination angle between the bolt and every production blast occurring during the bolt's recorded lifetime are calculated. The deformation experienced by each instrument is investigated by comparing the long-term recorded movements with the developed geometric variables. Patterns of deformation magnitude and rate are found with respect to production-blast distance and inclination angle, instrument location, rock quality designation, and likely mining-induced stresses. Results show that deformation magnitude tends to be higher when driven by production blasting occurring on the production level above the instrumentation when accounting for the effects of distance, but average deformation magnitude for very-near production blasts tends to be higher than that for production blasts occurring directly above the instrument. Correlations also exist between the measured RQD, estimated rockmass parameters, and the measured deformation. Empirical evidence allows the identification of six scenarios which account for 91% of the recorded high-deformation-rate events. These scenarios help determine which production activities are most likely to cause high deformation rates.

Empirical damage prediction in sublevel cave crosscuts at the Malmberget mine

“…This matches well with the findings of the deformation measurements from the extensometers which showed a crosscut location tended to remain relatively stable for long periods after development until redistributed stresses became high enough to cause increased deformation rates (Jones & Saiang 2022a). The same type of trend was identified in previous extensometer research in the same mining area (Jones et al 2019).…”

“…The main gangue minerals are amphibole, pyroxene and biotite and granitic intrusions often cross the ore (Bergman et al 2001). The thickness of the orebodies ranges between 20 m and 100 m. The volcanic host rock consists of grey (GLE), grey-red (GRL), red-grey (RGL) and red leptites (RLE) with increasing strength (Jones et al 2019), along with granite (GRA).…”

Damage mapping and monitoring in sublevel caving crosscuts at the Malmberget mine

“…The main gangue minerals are amphibole, pyroxene and biotite and granitic intrusions often transect the ore (Bergman et al 2001). The thickness of the orebodies ranges between 20 and 100 m. The volcanic host rock consists of grey, grey-red, red-grey, and red leptites with increasing strength (Jones et al 2019).…”

Mining-induced deformation for a haulage drift of the hanging wall at Jinshandian iron mine in China

“…A deformation model needs to be developed with relationships linking rock mass data, distance to undercut front, mining depth, relative position of the mining activity and the type of researched roadway, geotechnical indexing, support pattern, etc. (Fernandez et al, 2012;Jones et al, 2019;Lai et al, 2020). In the Malmberget mine, blast-instrument vectors were established in a spherical coordinate system to represent the spatial geometric relationship between mining blast and monitoring instrument.…”

“…In the Malmberget mine, blast-instrument vectors were established in a spherical coordinate system to represent the spatial geometric relationship between mining blast and monitoring instrument. The typical patterns of accumulated deformation were revealed with respect to production-blast distance and inclination angle (Jones et al, 2019). However, in reality the deformation patterns of roadways were investigated only when situated at the same level or above the active mining level.…”