Memoria

NorthParkes was discovered in 1977 near Goonumbia, in NSW Australia. The E26 block ore body is approximately 200metres in diameter and extends from the surface to over 800 metres in depth. The mineralization occurs in stock-work quartz veins and disseminations that have invaded volcanic sedimentary units. This phenomenon does not occur naturally, and for this reason copper-gold mineralizationdecreased gradually.

A 530 m deep, 5.3 m diameter, concrete lined hoisting shaft was designed specifically for the transportation of rock (production ore and development waste). Access to the block cave for all personnel and materials was catered for through a 5.0 m wide by 5.5 m high, 1:7 gradient access decline.

On November 24 1999, a sudden catastrophic accident occurred in the E26 blockcave at NorthParkes Mines (NP), where a cave-back provoked an air-blast that circulated all over the underground mine. The cave-back was connected with the level 1 which was roughly 200m from the surface and 280m from the mineral extraction level. The amount of collapsed material was around 13Mton, and the air volume displaced was approximately 4Mm3.

As a consequence from this accident, fourpeople died and the equipment suffered an extreme damage as well as the entire structure.

Geological and geotechnical characteristics:
The Geotechnical domains are based on core and cuttings of diamond and rotary drilling that were analyzed geologically as well as the drill core which was logged in these three metres. From this information Rosengren (1992) divided the ore-body into ninegeotechnical distinct domains.

On the other hand, the rock mass consist on strong rocks jointed with four to five joint sets. The presence of gypsum mineralization decreases with depth, and the geotechnical quality increases with depth. There are not major faults transecting the ore-body. Due to the nature of the fracture in the rock mass and the stress condition in situ realize an SE dipping mayorprincipal stress. According to Laubscher’s diagram the caveability was predicted to fall well in the Caving Zone, which suggests a hydraulic radius of 20 to 25.

|Depth |Characteristic |
| 0 m – 25 m |Clay |
| 25 m – 45 m|Oxidation zone of poor geotechnical quality |
| 45 m – 155 m |Upper Gypsum |
| |Siliceous zone |
| |Leached zone |
|110 m –175 m |Carbonate |
| |Impregnated zone |
|175 m – 205 m |Lower Gypsum |
| |Leached zone|
|205 m – 335 m |Heavy Gypsum Veining (HGV) |
|335 m – 385 m |Medium Gypsum Veining (MGV) |
|385 m – 485 m |Lower Gypsum Veining (LGV) |
|> 485 m |LIFT 1 – Extraction Level|


Design Characteristic:
Undercut level: An advanced undercut, where all of the lower development was planned to lag behind the stress cover of the upper undercut, was selected to minimise the effects of the high abutment stresses on the extraction level.

Exctraction level: Offset herringbone layout with seven extraction drives and 130 draw points. The spacing...