152
(UG) mining option with the required crown pillar, capital and operational developments.
The NPV of the OPUG mining option is about 14.4% better than an independent OP mining option and about 24.1% better than an independent UG mining option. The evaluated
results are shown in Table 4. The copper deposit is therefore best exploited with a combined
open pit and underground (OPUG) mining option for a mine life of 19 years with Level 3
acting as the unmined crown pillar.
With a total ore production of 100.05 Mt from the combined OPUG mining option with
crown pillar, the OP mining operation contributes 64.80 Mt of ore while the UG mining
operation contributes 35.25 Mt of ore. The remaining 15.95 Mt of the available mineral
resource is either left in the crown pillar (5.40 Mt) or left as unmined low-grade stopes (10.55
Mt). In a more practical underground mine, where the crown pillar is recovered (“robbed”)
during the operational life of mine, the 5.40 Mt of ore deposit will be mined to further
improve the total net present value (NPV) of the project if the ore quality is economical.
A sectional view through the ore body showing the open pit limit, location of the required
crown pillar, an unmined low-grade stope and the mineralized zone extending beyond the
bottom of the open pit limit is shown in Figure 4. The crown pillar is located on Level 3;
thus, the first 2 levels (or benches) are extracted by open pit mining while Levels 4 and 5 are
extracted by underground mining.
The ore and rock extraction schedules for the combined open pit and underground mining (OPUG) option with a crown pillar are shown in Figure 5 and Figure 6 respectively. The
ore is extracted by an independent open pit mining option in the first 2 years of the mine life
before underground ore production begins simultaneously from the 3rd year through to the
12th year. The ore production schedule switches completely to an independent underground
mining option in the remaining 2 years of the mine life. In summary, the ore extraction profile for the combined OPUG mining option is a blend of sequential and simultaneous open
pit and underground mining options for a mine life of 14 years. Due to the outcrop of the ore
Table 4. Results from the integrated MILP model for the case study.
Mining option
Net present
value ($b)
NPV of OPUG
compared (%)
Processed ore
tonnage (Mt)
Resource
depletion (%)
Open pit mining
227.73
−14.4
116.00
100.0
Underground mining
201.72
−24.1
103.95
89.6
Combined open pit and
underground mining
265.89
−
100.05
86.3
Figure 4. A sectional view through the block model showing the open pit limit, crown pillar and
underground mining regions for the case study.
Unmined lowgrade stope
Cro\\ n Pillar Location
UG Mine
(UG) mining option with the required crown pillar, capital and operational developments.
The NPV of the OPUG mining option is about 14.4% better than an independent OP mining option and about 24.1% better than an independent UG mining option. The evaluated
results are shown in Table 4. The copper deposit is therefore best exploited with a combined
open pit and underground (OPUG) mining option for a mine life of 19 years with Level 3
acting as the unmined crown pillar.
With a total ore production of 100.05 Mt from the combined OPUG mining option with
crown pillar, the OP mining operation contributes 64.80 Mt of ore while the UG mining
operation contributes 35.25 Mt of ore. The remaining 15.95 Mt of the available mineral
resource is either left in the crown pillar (5.40 Mt) or left as unmined low-grade stopes (10.55
Mt). In a more practical underground mine, where the crown pillar is recovered (“robbed”)
during the operational life of mine, the 5.40 Mt of ore deposit will be mined to further
improve the total net present value (NPV) of the project if the ore quality is economical.
A sectional view through the ore body showing the open pit limit, location of the required
crown pillar, an unmined low-grade stope and the mineralized zone extending beyond the
bottom of the open pit limit is shown in Figure 4. The crown pillar is located on Level 3;
thus, the first 2 levels (or benches) are extracted by open pit mining while Levels 4 and 5 are
extracted by underground mining.
The ore and rock extraction schedules for the combined open pit and underground mining (OPUG) option with a crown pillar are shown in Figure 5 and Figure 6 respectively. The
ore is extracted by an independent open pit mining option in the first 2 years of the mine life
before underground ore production begins simultaneously from the 3rd year through to the
12th year. The ore production schedule switches completely to an independent underground
mining option in the remaining 2 years of the mine life. In summary, the ore extraction profile for the combined OPUG mining option is a blend of sequential and simultaneous open
pit and underground mining options for a mine life of 14 years. Due to the outcrop of the ore
Table 4. Results from the integrated MILP model for the case study.
Mining option
Net present
value ($b)
NPV of OPUG
compared (%)
Processed ore
tonnage (Mt)
Resource
depletion (%)
Open pit mining
227.73
−14.4
116.00
100.0
Underground mining
201.72
−24.1
103.95
89.6
Combined open pit and
underground mining
265.89
−
100.05
86.3
Figure 4. A sectional view through the block model showing the open pit limit, crown pillar and
underground mining regions for the case study.
Unmined lowgrade stope
Cro\\ n Pillar Location
UG Mine