Hydraulic fracturing is applied for the preconditioning of orebodies prior to cave mining. A major project at Northparkes Mines was carried out in 2006 to investigate hydraulic fracture interaction with shear zones in the E48 orebody. The fracture growth was remotely monitored by tiltmeter and microseismic arrays. The mined fractures were then physically mapped and their geometry was compared to that inferred from the remote monitoring. The fractures were found to be subhorizontal, which was consistent with the tiltmeter and in situ stress data. Shear zones, natural fractures, and veins were crossed by the hydraulic fractures, sometimes producing an offset or step in the fracture path at the crossing site. One hydraulic fracture terminated at a shear zone in close proximity to a lithological contact that may be a stress change boundary. Numerical modelling of hydraulic fracture growth with offsets reveals that such fractures require a higher pressure to propagate and grow more slowly than a straight fracture. Results from numerical modelling indicated that the E48 caveability would prove problematic. The E48 orebody was, therefore, preconditioned using hydraulic fracturing and the footprint of the cave was enlarged. PreconditioningMethods to introduce new fractures to weaken the rock mass and enhance its caveability are needed, particularly if less fractured, stronger orebodies, some with smaller footprints, are to be reliably mined by

The tiltmeter described consists of an electrolytic sensor (a glass jar containing an electrolyte and six electrodes) and a portable AC digital conductivity meter, which reads conductivity changes resulting from tilting deflections. The tiltmeter has a sensitivity of 2 to 8 min of arc/cmu (conductivity meter unit), with a measurement range of more than 45°. This tiltmeter measured earth flow subsurface movements reliably. It was easy to install and read.