Post pillar case study

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The following article documents the use of post pillar mining at the Agnew Nickel Mine in Western Australia.

Introduction and Geology

The Agnew Nickel Mine in Western Australia is found in the Perseverance orebody. This orebody has a wide variety of geological settings which justified the application of several different mining methods. This article will focus on the integration of post pillar mining at the mine.

The geology of the orebody is a highly jointed and sheared serpentinite and a disseminated sulfide, hosted in a metasediment country rock. The joints in the disseminated ore are weakly cemented and cause ground control issues. Due to the poor quality of the ground conditions, a highly supportive mining method had to be employed.[1]

Mining and Development

The Agnew Mine combined the beneficial supportive properties of cut and fill with room and pillar to create a highly productive and safe mining method for poor ground conditions. The pillars provide support for the hanging wall for the entire extraction period. A drawback to cut and fill is that large unsupported spans must be opened up before the backfill is able to support the hanging wall. The use of the intact pillars is able to alleviate this problem by providing support throughout the entire mining cycle. The backfill provides support for the hanging wall and keeps the rock mass stable. With the backfill in place, there is also a lateral pressure exerted on the pillars which improves load bearing capacity. The backfill allowed the pillars to be long and slender rather than short and squat which helped to increase ore recovery.

The post pillar stopes at Agnew mine were accessed by finger ramps from the decline which progressively moved upwards as the stope was mined out from bottom to top. On the lowest level of the stope, an ore pass draw point and a truck loading bay was constructed. As mining moved upwards, the ore pass was extended up using bricks to hold the backfill in place.

The ground support used at Agnew Mine consisted of pillars, backfill, mesh and rock bolts. The backfill was either dry waste rock fill or hydraulically placed deslimed tailings. Split sets with bearing plates were used and mesh and strapping were added in poorer ground conditions.

The drifts and crosscuts in the stopes were advanced forward using full face slicing. The advancing face measured 5m wide by 4.5m high. Each round usually advanced 3.7m forward using 35 45mm bore holes. A two boom jumbo was used to drill these holes. The holes were primed with one stick of AN60 and filled with ANFO. The broken ore from blasting was mucked by LHDs, which hauled the ore to the ore pass.[1]

Applications

The operating procedures learned in this case study have potential applications to other similar deposits worldwide. Canada is home to a number of different massive sulphide deposits, some of which could have similar ground control problems to the ones experienced by Agnew Mine. Based on some preliminary research, there are no Canadian deposits with direct parallels but given the diversity of Canadian geology, it is very possible that a post pillar mining could be applicable to a Canadian deposit sometime in the future. This study also helps exemplify the potential opportunity for achieving high production rates in very poor rock conditions when it is feasible to use the post pillar mining method.
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References

  1. 1.0 1.1 Jones, T., Cannings, W., Myers, P., Lawrence, J., & Noble, M. (1985). Mining Methods at Agnew Nickel Mine, Western Australia. Underground Operator's Conference (pp. 69-74). The Aus.I.M.M. Kalgoorlie Branch.

Created by Group 5 2012: Chris Cameron, Lucas Dale, Kain Petterson, Scott Simpson, Courtney Squires