The Mitsubishi Higashitani limestone mine is a ten million tonne per annum operation located near the city of Kitakyushu on Japan's western island of Kyushu. Higashitani is one of the largest limestone mines in Japan and accounts for about five per cent of national production._x000D_
Blasting practices at the Higashitani mine involve the use of bagged ANFO, dynamite primers and non-electric detonators. Regulations in Japan prohibit the use of site mixed bulk explosives. Blast size is usually around 17 000 tonnes with 20 holes in a single row, two or three blasts are fired per day at a powder factor of between 0.25 and 0.32 kg/m3._x000D_
As part of a program looking at oversize reduction Mitsubishi, Asahi and Orica agreed to conduct a joint project at the Higashitani mine to investigate the relationship between the powder factor and fragmentation._x000D_
The first stage of the project was to benchmark the current blasting performance. Five blasts were monitored in each of the 210 (hard rock) and 220 (soft rock) areas of the mine. Orica's Powersieve software was used to measure fragmentation and total rock breaker hours were also recorded for each blast._x000D_
Orica's computer blasting simulation model Sabrex was used to prepare revised blast designs with a higher powder factor and predict their performance. The performance of these blasts was monitored using the same methods.