Watson B.P., Milev A.M., Roberts D.P. Presenter: B.P. Watson Unusual fracturing above intermediate to deep level Bushveld platinum workings Watson B.P., Milev A.M., Roberts D.P. Presenter: B.P. Watson
Extent of Bushveld platinum exposure © CSIR 2006 www.csir.co.za
© CSIR 2006 www.csir.co.za
Plan view of a typical Bushveld stope © CSIR 2006 www.csir.co.za
Stope sheet – instrumentation site © CSIR 2006 www.csir.co.za Depth: 1300 m below surface
Stratigraphy © CSIR 2006 www.csir.co.za
Horizontal stress above a Merensky stope © CSIR 2006 www.csir.co.za
Laboratory tests Type II (Wawersik, 1968) Pyroxenite Anorthosite © CSIR 2006 www.csir.co.za
Borehole core showing possible fracture 1 m Borehole core = 1,6 m Camera survey = 1,4 m © CSIR 2006 www.csir.co.za
Interpreted GPR radargram Borehole 2,6 m 1,5 m © CSIR 2006 www.csir.co.za
Ground motion monitor © CSIR 2006 www.csir.co.za
Geophone layout N Scale 15 m Borehole Dip © CSIR 2006 www.csir.co.za
Seismic events during (a) Active mining (b) non mining period Borehole © CSIR 2006 www.csir.co.za
Location of seismic events – section Vertical Scale 4 m © CSIR 2006 www.csir.co.za
Peak particle velocities © CSIR 2006 www.csir.co.za
Results of the GPR survey (dip direction) Borehole © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za
Conclusions Source of most seismic events was from hangingwall fracturing. Most of these events located over the face, during or just after the blast. The larger seismic events occurred in the more brittle anorthosites. Good agreement between the GPR results and the height of the seismic events. Horizontal stress is sometimes higher in the anorthositic rocks than in the pyroxenites. Observed fracturing probably occurred in extension. © CSIR 2006 www.csir.co.za