The Journal of Explosives Engineering - March/April 2013 - 36

Figure 11. Cross section of electronic detonator shot, shown with pyrotechnic profile in the background (all units in feet).

detonators resulted in another increase in the cast-to-final
from 37% to 44%. Evidence of this increase is shown in the
power trench displayed in figure 10 and 11. Both the pyrotechnic and the electronic detonator shots were in the
same pits with very similar bench heights making an accurate and fair engineering assessment of the two blasting
systems possible.
The first cast shots began in January 2010 and full implementation of a cast blast based mine plan was in December 2010. Since December 2010, there have been many
individual cast shots as high as 37% cast benefits and with
several troublesome ramps areas as low as 25% cast-to-final.
Overall Simplot Phosphates has been able to average a 32%
cast-to-final benefit for the past eight months.
After the first few tests using electronic detonators Simplot has been able to increase record cast blast efficiencies
from 37% cast-to-final with pyrotechnic detonators to 44%
cast-to-final with electronic detonators. This 7% increase
in cast-to-final was based upon comparing two closely
matched shots.
Similar increases in efficiencies are expected across the
pit whether or not they are best case scenarios, perfect drill
benches, or multi-terraced irregular shaped benches due to
the more accurate electronic delays. Based on these test
shots, Simplot is now in the conversion process of changing
all of the delay to electronic and phasing out the pyrotechnic delays. Electronic delays have enabled us to accurately
time multi-terraced benches that have utilized both varying
angled holes and vertical holes that would have been nearly
impossible with pyrotechnic delays and still we were able
to achieve over 37% cast to final.

Economic Study of
Conversion to Cast Blasting

Prior to 2007, Simplot Phosphates philosophy was to
strip ahead in order to uncover the upper 21.34 m (70
ft) high cover bench comfortably. It took nearly two and
a half years in order to catch the low cover bench to the
high cover bench. Modeled estimates of cast-to-final were
as optimistic as 36% but in order to be conservative only
30% cast was used in calculations for equipment justifications and engineering proposals. The estimation of cast
gains predicted that the overall cast-to-final benefit would

increase from 10% of the total overburden mined to 30%,
making a 20% overall efficiency gain.The mine knew that it
would take several years until both the high and low cover benches would be caught up until the new mine plan
could be fully implemented, so the work force was allowed
to slowly be reduced by 20% due mainly to attrition.
The average historic powder factor was 0.56 kg/m3
(0.95 lb/BCY) for shooting the two overburden benches
separately. The powder factor increased to 0.77 kg/m3 (1.3
lb/BCY) to cast all the overburden in a single bench. This
was a 37% increase in blasting agent each year yet an 18%
decrease in operating costs due to the reduction of equipment hours. This translates into the fact that now Simplot
can move more for less, increasing their economic reserves.
Additional benefits have been realized due to the increased blasting efforts and care thus providing better shot
rock for the dozers and shorter haul distances for the overburden removal. The dozer production has increased 12%
over previous years along with a 22% reduction in required
truck hours that are required to uncover ore. This truck
hour reduction is above and beyond the simple cast-to-final
benefit and is directly related to a more efficient compact
mine plan that now reduces truck hauls from 1067.5 m to
274.5 m (3,500 ft to 900 ft).
The two unexpected downsides that have been realized
are a 20% increase in dozer work preparing appropriate drill
ramps and drill pads along with the increase in engineering
required to orchestrate a successful cast blast. Overburden
pits are designed for the most part to be perpendicular to
the contour of the ground with the drill ramps running on
contour.The larger drill requires wider drill ramps with everything required to be engineered prior to construction.
The increase in awareness of the importance of the drilling
and blasting program has nearly required the addition of a
full time engineer.

Conclusions

Simplot Phosphates has successfully converted its mining operation from a two bench overburden removal operation into an efficient single bench cast blasting operation.
Simplot has been successful in increasing its overall castto-final overburden at their operation from ~7% to ~32%
annually. During test shots utilizing electronic detonators

The Journal of Explosives Engineers

March/April 2013

http://www.isee.org

The Journal of Explosives Engineering - March/April 2013

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