Innovative Blasting - Oversize Reduction at the Timbarra Gold Mine in Australia

The Timbarra opencut gold mine is located about 30 km(19 miles) southeast of Tenterfield in northern NSW some 4 hours by car from Brisbane, the capital city of Queensland in Australia. It was a small operation designed to produce about 40000 ounces of gold per annum utilising contract mining and company owned crushing plant feeding heap leach pads. This is a standard setup except that the mine owner was in charge of all aspects of drill & blast design even though a contract drilling & blasting (shotfiring) service was being provided. The major problem was that the blasting operations were yielding massive amounts of oversize due to the jointed partially weathered nature of the granite. This was adversely affecting all downstream aspects of the operation as well reducing gold output as ore boulders were being dozed over the side of the mine as they were impinging on mining productivity. The oversize problem had to be solved as the mine was struggling to achieve design gold output. Significant design & trialing effort using minesite resources were utilised to reduce the oversize but this failed even when powder factors up to 1kg/bcm(1.68lb/yd) were used. Dyno Consult from Dyno Nobel were therefore called to investigate, review & trial options to reduce oversize from the top flitch.