The Henty Mine uses bench, and flatback mining as the principle means of ore extraction. A modified Avoca mining method has been successfully used in selected places where development allows. The mining method selection is based on the following:
• Width and grade of the ore.
• Regularity along strike and up dip.
• Proximity to the Henty Fault zone.
• General ground conditions.
In bench stoping, heights are limited to 12-15 m. Where it is economical to do so, development is completed top and bottom. The choice of uphole or downhole drilling is based on the geometry of the ore. Extraction is bottom up.
In general, the mining areas in the lower section of the mine are wider with more modest grades and are spatially removed from the Henty Fault. Conversely, the upper areas of the mine tend to be higher grade, narrow and occasionally interact with the Henty Fault.
For the modified Avoca style bench stoping, waste rock is tipped over the advancing ore face until the void is filled. If the strike of the ore is longer than the maximum allowable stope length, the placed waste is dug out to create a sufficient void to blast the following ore rings. The next ore firing is blasted against the remaining waste causing mixing of ore and rockfill. The dilution is considered in the stoping and recovery factors applied to the stoping tonnes.
Production drilling uses a long hole drill rig equipped with a Minnovare Production O ........