BLASTING IMPROVES PRODUCTIVITY AT NEWTON GEORGIA QUARRY

While many companies look at new management techniques, larger heavy equipment, and new facilities for improved productivity, many forget that something as mundane as blasting materials offer a serious way to improve production. There's no better proof of that than the LaFarge aggregate quarry in Newton County, Georgia, where a fresh look at their blasting requirements a few years ago gave them a 33% improvement in productivity.

The Newton County Quarry is one of the Georgia quarries that LaFarge didn't sell earlier this year. Joelle Lipski-Rockwood, director of communications for LaFarge in the U.S., said the Newton Quarry was not been sold, but that the company is looking to focus its geographic footprint in the Great Lakes and Mississippi River regions. "We will likely look to divest them over time," she said. "For the buyer we were talking to, they didn't really fit with what they wanted to do."

The Newton County Quarry started operations in 1978. It covers about 80 acres and before it changed its blasting system, only produced 3,000 tons per day of an all-granite aggregate. Unlike many quarries, Newton County is lucky in that there is no overburden. All they have to do is mow the grass and mine.

The answer to their productivity came a few years ago when an explosives sales representative asked the quarry if they wanted to see how their costs per ton could be reduced by switching blasting agents. The blasting specialist noted that the all-granite nature of the quarry had a major impact on the blasting conditions and picking the right type of blasting agent could dramatically reduce cost.

According to blasting experts the geology is the most important factor in picking a blasting agent. In the case of the Newton County Quarry's solid granite, the shock waves easily travel to other explosive filled holes and can either set them off prematurely or even prevent an explosion (dead pressing). Since granite is more abrasive than other materials and wears out the drilling tools. The easy answer is to change the drillhole patterns and drill fewer holes with more explosive in each hole.

Naturally, reducing the number of holes also changes the requirements for explosives and the results. Some explosives like ammonium nitrate and fuel oil (ANFO) will not detonate in small holes one inch in diameter, but can be used in larger ones. Also fewer holes placed further apart will create larger rocks than smaller holes placed closer together. While the blasted rock can be crushed in a crusher, the smaller the rock can be broken in the blasting process, the lower the overall cost.

The Newton Quarry needed smaller crushed rock, so larger, wider blasthole placement wasn't the whole answer. There was also a problem with ground water that prevented the use of ANFO, which was desensitized by water. The result was high blasting costs that ruined operational cost projections.

The answer was an explosive called Apex Gold, which is produced by Orica and is designed for surface mines and quarries. This explosive is less sensitive and requires a larger shock to set it off. This in turn, eliminates the shockwave problems associated with operating in granite. It also allowed closer, smaller drill holes that make smaller chunks of rock. Since it has varying water resistance, depending on the blend, water conditions downhole were not a factor.

The blended explosive also offered other benefits. It could be blended with the cheaper ANFO to reduce costs. The explosive could be blended to increase shock value in order to increase fragmentation or increase gas to better throw the rock and give the maximum transfer of energy from the explosive to the rock.

The change in explosives increased rock production by 33% a day. It also made the cost per blast more predictable, which made operational costs more manageable.

Many mine and quarry managers think that explosives are just another cost that needs to be controlled. Picking the right agent for your operation can have dramatic effects on productivity and the bottom line. Rather than focusing on new heavy equipment or more crushers, it pays to check out the ways a better blasting system can impact your mine's profit picture.