1. 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

2. Extent of Bushveld platinum exposure
© CSIR

3. © CSIR

4. Plan view of a typical Bushveld stope
© CSIR

5. Stope sheet – instrumentation site
© CSIR
Depth: 1300 m below surface

6. Stratigraphy
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7. Horizontal stress above a Merensky stope
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8. Laboratory tests Type II (Wawersik, 1968) Pyroxenite Anorthosite
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9. Borehole core showing possible fracture
1 m
Borehole core = 1,6 m
Camera survey = 1,4 m
© CSIR

10. Interpreted GPR radargram
Borehole
2,6 m
1,5 m
© CSIR

11. Ground motion monitor
© CSIR

12. Geophone layout N
Scale
15 m
Borehole
Dip
© CSIR

13. Seismic events during (a) Active mining (b) non mining period
Borehole
© CSIR

14. Location of seismic events – section
Vertical Scale
4 m
© CSIR

15. Peak particle velocities
© CSIR

16. Results of the GPR survey (dip direction)
Borehole
© CSIR

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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