Mining Mirror May 2018 - Page 18

Mining in focus Downstream impacts of drilling and blasting Drilling and blasting are not always given the full emphasis it deserves, writes Anthony Konya. [16] MINING MIRROR MAY 2018 D rilling and blasting is a complex process and plays a critical role in process development and controlling the cost throughout the mine. For example, the blasting process dictates muck-pile configuration, which affects shovel and loader fill factors. The fill factor of the shovel affects how many trucks are required on site, how fast those trucks can be loaded, and the truck fill factor. The fragmentation of the blast affects the crushing costs and leaching efficiency. The over-break of the blast affects slope stability, slope steepness, pit safety, and scaling costs. The blasting process impacts every aspect of the operation and poor blasting can lead to millions of dollars in direct costs and tens of millions in indirect costs at larger operations, such as copper and gold mines. In many cases, the drill and blast team may not need to understand the haulage, as the haulage does not have an impact on blasting (in a direct cost sense). However, every person responsible for any operation at a mine must at least understand drilling and blasting — enough to explain what they require of the drill and blast team. How stemming can change blast function One variable of blasting is stemming. Stemming is a material that is inserted into a blast hole to help prevent gases from escaping. Incorrectly placed stemming can greatly decrease fragmentation size at a blast. While important, stemming is not nearly as vital as other variables such as burden and stiffness ratio. However, stemming can dramatically change a blast’s function. It can reduce the air overpressure from a blast by over 98%, which dramatically reduces noise. Proper stemming can also decrease the P80 (post primary crush 80% passing size) of a blast by over 10% and reduce mucking cycle times by over 18%. It is incredible to think that a few feet of gravel can really change the blast this much. Poor stemming will blow out, causing poor results for fragmentation,