Pub. 7 2017 Issue 1

22 AT THE CENTER OF UTAH INDUSTRY STUDY ON CONVERSION TOCAST BLASTING The mining is oriented down a 10 percent grade (Figure 1). An engineering study was performed to assess the feasibility of cast blasting, including the mechanics of the overburden movement, and the anticipated benefits. The mechanics of the overburden movement were evaluated using the computer code, DMC (Distinct Motion Code) (Preece, et al, 1993). See figure 2 for the DMC model that predicted cast performance of the combined benches. ECONOMIC STUDY OF CONVERSION TO CAST BLASTING Modeled estimates of CTF were as optimistic as 36 percent, but in order to be conservative only 30 percent cast was used in calculations for equipment justifications and engineering proposals. The estimation of cast gains predicted that the overall CTF benefit would increase from 10 percent of the total overburdenmined to 30 percent, resulting in a 20 percent overall efficiency gain. The average historic powder factor was .95 lbs/BCY for blasting the two overburden benches separately. The current powder factor of 1.3 lbs/BCY is now used to cast a single bench. This was a 37 percent increase in blasting agent each year yet an 18 percent decrease in operating costs due to the reduction of equipment hours. This translates to more overburden being moved for less capital, increasing economic reserves. Various pit widths were evaluated and it was determined that for this geometry a 180 foot wide pit provided the best overall benefit Additional benefits have been realized due to the increased drilling and blasting efforts. The additional benefits are providing better-fragmented rock for the dozers and shorter haul distances for the overburden removal. The dozer production has increased 12% over previous years and a 22 percent reduction in required truck hours to uncover the phosphate ore. The truck hour reduction is above and beyond the simple CTF benefit and is directly related to a more efficient and compact mine plan. The more compact layout of mining benches has reduced overburden truck hauls from 3,500 feet to 900 feet simplifying the pit layout. During this engineering study, electronic detonators were evaluated and single blast efficiencies increased from 36 percent CTF with pyrotechnic detonators to 44-52 percent CTF with electronic detonators. Electronics detonators will continue to be a strong part of Vernal Mine’s future blasting designs. The two unexpected down sides to cast blasting are a 10 percent increase in dozer work preparing appropriate drill ramps and drill pads, and the addition of a full time engineer required to design a successful cast blast. CONCLUSIONS The Simplot, Vernal Mine has been successful in the implementation of cast blasting, as well as the conversion of their mining method from a two bench overburden removal method into an efficient single bench cast blasting operation. Simplot has been successful in increasing their overall cast to final overburden at their operation from ~7 percent to ~32 percent annually. Simplot is now moving more overburden for less capital, which has increased economic reserves. ACKNOWLEDGEMENTS Mine Manager Mark Krall, Mine Superintendent Vince Christensen, Mine Blast Crew: Brad Davidson, David Kidd, Eric Warren, Rex Howa, Clint Stagg. X Figure 2: DMC modeling of the low cover blast SIMPLOT PHOSPHATES continued from page 21 The two unexpected down sides to cast blasting are a 10 percent increase in dozer work preparing appropriate drill ramps and drill pads, and the addition of a full time engineer required to design a successful cast blast.