Most of the rock mechanic challenges at Yara Suomi Oy Siilinjärvi apatite mine are related to several continuing and steeply dipping shear zones almost parallel to the pit slopes. One of the most unstable areas is located in the eastern pit walls near the contact with ore and external waste rock. Due to the nature of the rock mass and the extreme environmental conditions, slope monitoring at Siilinjärvi poses some challenges. Real-time critical slope monitoring at Siilinjärvi is performed by employing two IBIS Synthetic Aperture Interferometric Radars. The IBIS units are used to monitor in real time the entire slope and timely detect impending failure for early warning. High spatial resolution and fast scan time, typical of IBIS technology, allows the radar to pick-up localized fast movements on nearly-vertical benches even at long working distances, providing the mine personnel enough time to issue evacuation alerts.
Yara Siilinjärvi apatite mine is located in eastern Finland, close to the city of Kuopio. Even though Siilinjarvi mine has been ongoing over thirty years, in the past there has been done quite little with rock mechanics and slope monitoring. When the owner of the mine changed in 2007 and production rates increased significantly, rock mechanics and mine safety have been a bigger concern. Yara's mine staff decided to purchase IDS radar systems to start critical safety monitoring of the pit walls. Currently Yara is expanding the pit, and currently mine life is up to 2035. Currently mining rates are around 30 Mt of rock per year. Yearly production rate is about one million tons of apatite concentrate.
The Archean Siilinjärvi carbonatite complex consists of a steeply dipping body roughly 16 km long with a maximun width of 1.5 km. The deposit is located in a major fracture zone where carbonatites were erupted 2.6 Ga ago. On the Sarkijärvi open pit area the mineralization is vertically dipping and N-S striking on the length of 3 km. The majority of the apatite containing mineralization is composed of phlogopite-rich rocks ranging from almost pure glimmerite (phlogopite) and carbonate glimmerite to silicocarbonatites and finally to carbonatites (>50% carbonates). The mineralized body is surrounded in the eastern and the northwestern part by a fenite margin and in the western and southwestern part by a diorite (O'Brien et al. 2015).