10
The alternate models show how a small reduction
(IKD) or large reduction (OK) in selectivity can impact the
grade distribution (Figure 14a). If tons sent to the mill are
at 50% of mining capacity, the IKD model shows 3% lower
mill grade and the OK model shows 9% lower mill grade
(Figure 14b).
Planned NPV sensitivity to block models
Plans built with the three models show significantly differ-
ent NPV’s, with the OK based plan showing a 16.8% lower
NPV than the IK plan (which can also be expressed as IK
is 20% higher than OK) and the IKD based plan show-
ing 5.2% lower NPV than the OK plan (Table 4 top sec-
tion). These planning-stage NPV differences are large and
can have a significant impact on project prioritization and
whether projects are executed or not.
Realized NPV sensitivity to plans built from different
block models
If a project is executed, the realized NPV will depend upon
the actual ore control selectivity rather than the selectivity
that is modeled in the block model. A same-ore-control-
selectivity comparison of plans created from alternative
blocks models was analyzed by freezing the mining sequence
from each plan and then reoptimizing the processing
sequence using the IK model (Table 4 middle section). The
mining sequence for the IK and IKD plans are very simi-
lar, so they have very similar NPV’s when evaluated using
the same selectivity (IKD based plan 0.1% lower). The OK
mining sequence is quite different with the final five phases
delayed while stockpiled material is processed however,
when evaluated using the IK model, the NPV reduction is
still small (OK based plan 0.8% lower) because the NPV of
the last five phases is very similar to the NPV of the mate-
rial stockpiled while mining the first five phases.
Figure 12. Creation of OK model from simulations—
example for bench 20
Figure 13. Creation of diluted simulations—example for
simulation #6, bench 20
The alternate models show how a small reduction
(IKD) or large reduction (OK) in selectivity can impact the
grade distribution (Figure 14a). If tons sent to the mill are
at 50% of mining capacity, the IKD model shows 3% lower
mill grade and the OK model shows 9% lower mill grade
(Figure 14b).
Planned NPV sensitivity to block models
Plans built with the three models show significantly differ-
ent NPV’s, with the OK based plan showing a 16.8% lower
NPV than the IK plan (which can also be expressed as IK
is 20% higher than OK) and the IKD based plan show-
ing 5.2% lower NPV than the OK plan (Table 4 top sec-
tion). These planning-stage NPV differences are large and
can have a significant impact on project prioritization and
whether projects are executed or not.
Realized NPV sensitivity to plans built from different
block models
If a project is executed, the realized NPV will depend upon
the actual ore control selectivity rather than the selectivity
that is modeled in the block model. A same-ore-control-
selectivity comparison of plans created from alternative
blocks models was analyzed by freezing the mining sequence
from each plan and then reoptimizing the processing
sequence using the IK model (Table 4 middle section). The
mining sequence for the IK and IKD plans are very simi-
lar, so they have very similar NPV’s when evaluated using
the same selectivity (IKD based plan 0.1% lower). The OK
mining sequence is quite different with the final five phases
delayed while stockpiled material is processed however,
when evaluated using the IK model, the NPV reduction is
still small (OK based plan 0.8% lower) because the NPV of
the last five phases is very similar to the NPV of the mate-
rial stockpiled while mining the first five phases.
Figure 12. Creation of OK model from simulations—
example for bench 20
Figure 13. Creation of diluted simulations—example for
simulation #6, bench 20