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Mine Bench-Tunnel Seismic Data Acquisition for Characterizing Shear Zones in the Siilinjärvi Phosphate Mine, Finland
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 25th European Meeting of Environmental and Engineering Geophysics, Sep 2019, Volume 2019, p.1 - 5
Abstract
Siilinjärvi in central Finland, is currently the only phosphate mine with significant phosphorus production in western Europe. Phosphate rock and phosphorus are critical for the EU because of their supply risks and economic importance. The phosphate bearing rocks in Siilinjärvi are within a major Archean alkaline and carbonatite complex deformed and intruded by several shear and dyke systems. By understanding their spatial and temporal relationships an improved exploration and extraction of this critical ore would be possible. The objective of the study was to employ a novel seismic survey using the existing mine infrastructure for better planning and geological understanding. An innovative in-tunnel seismic survey was conducted in the Siilinjärvi open-pit mine in October 2018. A water-drainage tunnel nearly in the bottom of the pit intersecting two major shear zones was used to enable bench-tunnel seismic data acquisition. High-quality data were acquired using 144 receivers inside the tunnel, with the sources located both inside the tunnel (Bobcat-mounted vertical drophammer) and on the surface (combined explosives and Bobcat). Two reflections interpreted to originate from subvertical shear zones intersecting the tunnel were observed illustrating the importance of such surveys for shear-zone imaging and site characterization.