Journal of the Southern African Institute of Mining and Metallurgy
On-line version ISSN 2411-9717
HUDYMA, M.; POTVIN, Y. and ALLISON, D.. Seismic monitoring of the Northparkes Lift 2 block cave - Part 2 production caving. J. S. Afr. Inst. Min. Metall. [online]. 2008, vol.108, n.7, pp. 421-430. ISSN 2411-9717.
Production caving started for Lift 2 at Northparkes in August 2004. In a period of less than 3 months, more than 10 000 seismic events were recorded. Events up to local magnitude +2.9 were induced near the mine during caving, with event rates of up to 500 per day. This paper documents the seismicity related to cave initiation and cave propagation during the initial production of Lift 2. The seismogenic zone of events initially moved at a rate of about 0.5 metres per day, accelerating to 2 to 3 metres per day after a few months of cave production. Seismic data analysis infers that the crown pillar between Lift 1 and Lift 2 was destressed over a vertical height of about 100 metres. As the seismogenic zone approached the crown pillar, a macroseismic episode occurred, with more than 20 events of at least local magnitude +1 occurring in a two-week period. Based on the seismicity recorded for Lift 2 at Northparkes Mines, a caving mechanics model is proposed. Comments and suggestions are made for seismic data analysis and design of seismic monitoring systems in block caving mines.