5
pre-split holes can directly affect the area where the trim
holes will be drilled in the future by creating a pre-fractured
surface that can work as an “energy-loss conduit.” The sec-
ond case is the most common sequence of events that takes
place at the Pinto Valley mine.
The behavior observed in Figure 5 matches two impor-
tant behaviors observed:
1. what was observed in Figure 1, where the non-
broken knobs on the wall were generally observed
on the bottom 45ft (13.7m) of the 90ft (27.4m)
full bench, and less frequent but yet possible on
the top 45ft.
2. occurrences of pre-split holes venting out of trim
row holes when the pre-split lines were drilled after
trim blast holes had already been drilled ahead of
them.
From this point forward, the team working on the proj-
ect identified that two paths could be pursued to mitigate
the issue of unrecovered material being left on the walls:
a. Adjust trim-blast designs to accommodate inherent
pre-split drilling accuracy limitations.
b. Improve pre-split hole drilling quality (i.e., minimize
drill hole deviation) as much as possible.
The focus of the team involved on this project was to
create an alternate design option while coaching the pre-
split drillers on how important the drilling quality was for
the overall results achieved. The new design created for the
trim blasts is shown in Figure 6.
Figure 7 shows a visual comparison of results achieved
where the new design was used with the previous results
obtained in multiple benches above with the traditional
designs.
To quantify the monetary impact of the improvements,
the final wall shown in Figure 7 was used as a sample. The
volume and average copper grades of the knob-like shapes
were extracted with the aid Maptek’s Vulcan mine planning
software. The results showed an average 71.2% decrease in
unrecoverable underbreak on the benches where the new
design was used.
For an average of 60 final-wall blasts per year recorded
in the recent years at the mine, we estimated unrecoverable
tons to be near 380,000 per year. With that, the estimated
amount of extra material to be recovered with the alternate
design tested was of approximately 270,000 tons of ore at
average grade of 0.187% Cu (average grade of the knobs
quantified in the study).
Figure 6. Alternate cross-section design to accommodate drill-hole deviation
pre-split holes can directly affect the area where the trim
holes will be drilled in the future by creating a pre-fractured
surface that can work as an “energy-loss conduit.” The sec-
ond case is the most common sequence of events that takes
place at the Pinto Valley mine.
The behavior observed in Figure 5 matches two impor-
tant behaviors observed:
1. what was observed in Figure 1, where the non-
broken knobs on the wall were generally observed
on the bottom 45ft (13.7m) of the 90ft (27.4m)
full bench, and less frequent but yet possible on
the top 45ft.
2. occurrences of pre-split holes venting out of trim
row holes when the pre-split lines were drilled after
trim blast holes had already been drilled ahead of
them.
From this point forward, the team working on the proj-
ect identified that two paths could be pursued to mitigate
the issue of unrecovered material being left on the walls:
a. Adjust trim-blast designs to accommodate inherent
pre-split drilling accuracy limitations.
b. Improve pre-split hole drilling quality (i.e., minimize
drill hole deviation) as much as possible.
The focus of the team involved on this project was to
create an alternate design option while coaching the pre-
split drillers on how important the drilling quality was for
the overall results achieved. The new design created for the
trim blasts is shown in Figure 6.
Figure 7 shows a visual comparison of results achieved
where the new design was used with the previous results
obtained in multiple benches above with the traditional
designs.
To quantify the monetary impact of the improvements,
the final wall shown in Figure 7 was used as a sample. The
volume and average copper grades of the knob-like shapes
were extracted with the aid Maptek’s Vulcan mine planning
software. The results showed an average 71.2% decrease in
unrecoverable underbreak on the benches where the new
design was used.
For an average of 60 final-wall blasts per year recorded
in the recent years at the mine, we estimated unrecoverable
tons to be near 380,000 per year. With that, the estimated
amount of extra material to be recovered with the alternate
design tested was of approximately 270,000 tons of ore at
average grade of 0.187% Cu (average grade of the knobs
quantified in the study).
Figure 6. Alternate cross-section design to accommodate drill-hole deviation