S2_12_30_Lorrie_Fava.pdf

Application of an evolutionary solver to the optimisation of an open pit mine

Lorrie Fava, MIRARCO, Laurentian University

Overview

• The evolutionary solver

• Parva Mine

• Integrated optimisation process

• Case Study outcomes:

Optimised schedule, Ultimate pit and Nested pits

• Sensitivity analysis

• Conclusion

• Future Work

An evolutionary solver for optimisation of life-of-mine schedules

• SOT (Schedule Optimization Tool)

• Context of selective underground mining

• Schedules of access development and production activities

• Precedence constraints

• Operational resource constraints

• Maximise NPV (net present value)

Parva Mine • portion of a real, undisclosed mine

• 58,141 blocks; 245 with mineralisation

• 25 × 25 ×25

• Constraints:

precedences

ore: 386,000 tonnes/year

total: 7.8 Mt/year

3 active faces: 1 ore, 2 waste

Integrated Optimisation

• Objective: maximise NPV

• In a single optimisation process, the evolutionary solver generates:

– ultimate pit,

– schedule of individual blocks and

– mineable nested pit shells.

Optimised Life-of-Mine Schedule Year

Ore mined (kilotonnes)

Waste mined (kilotonnes)

Gold production (kilograms)

Discounted cashflow (million $)

NPV (million $)

2013 675.0 14,095.6 2,210.3 4.6 4.60

2014 1,156.6 13,877.5 4,018.0 95.3 99.87

2015 651.4 13,188.0 2,459.8 47.2 147.06

2016 621.6 13,201.4 2,665.6 49.8 196.90

2017 439.2 12,523.6 1,740.2 24.5 221.39

2018 464.1 12,730.0 1,966.6 27.7 249.11

2019 791.7 12,012.4 2,945.3 45.9 295.01

2020 389.5 12,324.3 1,220.0 9.2 304.20

2021 295.3 12,395.9 1,084.5 6.5 310.67

2022 759.4 11,734.2 3,711.2 50.7 361.33

2023 590.6 6,368.6 3,557.3 50.0 411.32

Ultimate Pit

3,364 blocks

162 ore blocks

$411.32 million

Number of pit shells generated = total number of ore blocks

Nested pits are generated without artificially varying the economic value of blocks

Sensitivity Analysis: Number of active faces

Faces active

Waste faces Active

Cost of fleet (million $)

Mine life (years)

NPV (million $)

1 2 9.00 11.0 411.3

1 3 12.38 8.0 463.9

1 4 15.76 6.0 493.6

2 3 14.62 8.0 464.2

2 4 18.00 6.0 494.4

2 5 21.38 5.0 511.0

Future Work

• On-the-fly aggregation of blocks into working faces

• Constraints to limit proximity of working faces

• Application of solver to detailed schedule optimisation after haulage roads have been designed

• Stockpile management

• Grade control blending

Conclusion

• SOT can select the blocks of the ultimate pit and schedule them in one optimisation process

• As part of the same process, nested pits are generated

– No need to artificially vary the economic value of blocks

• Accommodates depth-varying costs and discounted cash flows

Thank you!