Ore fragmentation at the DOZ block cave mine is highly variable, both as a function of rock type and column height of draw._x000D_
Initially, the mine was constructed and equipped with limited capability to handle drawpoint oversize material. Significant issues with drawpoint availability and achieving overall mine production targets resulted. A suite of secondary sizing tools was added to the mine equipment fleet over a one-year time frame. Although significant oversize continues to be experienced, use of the correct secondary breakage tool for each particular oversize or hang-up occurrence has resulted in increased drawpoint availability, production rate, draw compliance, and operator safety._x000D_
Currently, a range of secondary breakage techniques is being utilised to size material for delivery to the primary crusher. Run-of-mine material(<1 m3 ) is directly mucked to ore passes fitted with grizzlys that have one-metre square openings. ore containing small boulders(>1 m3, <2m3) is loader-trammed to ore passes fitted with rockbreakers. medium-sized boulders(>2 m3) accessible from the drawpoint are drilled with Sandvik Tamrock Commando drills. Boulders hung-up within the drawbell are drilled and charged with a Sandvik Tamrock Secondary Breakage Unit. Compacted, fine-grained muck is blasted utilising 55 mm cartridge powder concussion bombs._x000D_
FORMAL CITATION:Flint, D C, Sinuhaji, A, Setyoko, T B and Kalangi, H, 2005. Secondary breakage practice at the DOZ Block Cave Mine, in Proceedings Ninth Underground Operators' Conference 2005, pp 53-56 (The Australasian Institute of Mining and Metallurgy: Melbourne).