Editorial focus by Harold Hough

As mineral and metals prices drop, most mines are finding their profit margins disappearing. And, while the road to improved productivity and profits is multifaceted, drilling and blasting is the first step and can have a major impact on the rest of the mining, milling, prepping, and concentrating process.

The first step to improving drilling and blasting productivity is to have good drill operators. Poorly trained operators have a major impact on the efficiency of drilling equipment. If a blast hole drill is only operated by a fair operator (90 percent as good as an experienced one), than the mine is not only operating at 90% efficiency, it is impacting maintenance because the drill is only doing 90% of the work it could do between overhaul cycles. That’s one to two percent of the initial cost of the equipment for every 2,000 hours of operation. Compare that to a highly skilled professional operator who can get an extra 10% more out of the equipment than the skilled operator. He is helping produce 10% more ore per rebuild cycle, which equates to 25 extra shifts of work per every 2,000 hours of operation.

Use Explosives to Reduce Equipment Wear

The best way to reduce the cost of operating and overhauling your drill is to rely more on the wide variety of explosives that have been designed for a multitude of mining applications.

Many mines and quarries are discovering that high explosives are an excellent way to improve productivity and lower costs. The Newton County Aggregate Quarry in Georgia, discovered a few years ago that a fresh look at their blasting requirements gave them a 33% improvement in productivity.

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 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, drilling costs, 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.