Causes, implications and control of oversize during blasting

Rock Fragmentation by Blasting – Sanchidrián (ed) © 2010 Taylor & Francis Group, London, ISBN 978-0-415-48296-7

Causes, implications and control of oversize during blasting
S.P. Singh & R. Narendrula
School of Engineering, Laurentian University, Sudbury, Canada

ABSTRACT: Profitability of a mine depends upon the ability of a mining engineer to produce a fragment size distribution as closeas possible to the optimal range for downstream operations. From the practical standpoint, oversize is defined as a size, which needs secondary breakage before further handling. The generation of oversize during blasting has a detrimental effect on the economy and productivity of the downstream operations. A study was conducted in several operating surface operations to examine the effects ofdifferent blast design parameters on the production of oversize. Blast design parameters for each blast were documented and the pre as well as post blasting conditions of the faces were photographed. Fragmentation was monitored and analyzed by the Wipfrag system. It was found that the uniformity index varies inversely with the hole size, stemming length, burden and spacing. It was also observed thatninety percent passing size (D90) varies directly with the hole size, burden, spacing and stemming length. Strategies to determine the exact locations and sources of the oversize have been outlined in this paper. Causes and control of oversize found at the following locations in a muckpile have been discussed: (a) On top of the muckpile near the blasted face, (b) At the floor level near the face,(c) In the interior of the muckpile and (d) At the front of the muckpile. The implications of oversize on the economy and productivity of mines have also been discussed in this paper. 1 INTRODUCTION typical mining operation, the blasted material after digging and hauling is fed to the primary crusher, followed by a secondary and tertiary crusher. Hence, the optimal fragmentation from the point ofthe crushing unit/circuit will be that which will maximize the output of the crusher and at the same time minimizes the power consumed in the size reduction process. If the crusher is fed with material that is not optimum, the power consumption increases along with other problems like jamming, excessive wear and tear, etc. The details of the main causes that contribute towards formation ofoversized boulders are discussed in Section 3. 2.1 What is oversize

In most hard rock mines, drilling and blasting is the most widely used method of breaking/fragmenting the rock. As the end result of the blast directly affects the subsequent operations such as loading, crushing and grinding, the performance of drilling and blasting operations carries significant importance in the overall profitabilityof the mining operations. High level of mechanization and the integrated nature of the production systems adopted in the mining industry demands that all the units must function with designed reliability and capacity to achieve the planned production targets. The presence of oversize boulders in the blasted muck causes not only loss in production, but also increases the cost of its handlingsystems. In other words, the cost and efficiency of loading, crushing and grinding operations are very seriously affected by the outcome of blasting operations. In heap leaching operations, the efficiency of operations are influenced by the size distribution of the ore on the leach pad. This paper describes the implications, causes, sources and control of oversize in surface mines. 2 OVERSIZE IN MINESIn any mining operation, blast fragmentation is the first element in the rock size reduction process. In a

The term oversize may be defined as any boulder produced from primary blasting, which cannot be adequately handled by the standard loading, hauling and crushing equipment used in an operation. From the practical standpoint, oversize may also be defined as a size, which needs secondary...