Why Reinvent the Wheel? Maximising Efficiency in Life-of-Mine Scheduling
These days, everyone seems to be overburdened and short on time, so we need to be as efficient as possible in our work. Why waste time reinventing the wheel when a solution already exists? It makes no sense to start a task from scratch when the groundwork has already been laid.
This is particularly important when developing a strategic Life-of-Mine (LOM) schedule. Your model will be used for years, guiding major decisions, so it is crucial to get the setup right from the beginning.
To help mining engineers think through this process, I have compiled a list of key questions to consider when creating a new strategic LOM schedule. Each question is followed by a brief explanation, and you can download a handy checklist for future reference.
The Five Key Areas to Consider:
- Material in the Pit
- Material Destinations
- Moving Material to Destinations
- Processing of Material at Destinations
- Reporting
Material in the Pit
1. What’s your reserve data?
Strategic schedules are spatially based at the block level, where a block model defines the material in the pit. While specifics may vary, at a minimum, block models should include:
- The pit and/or phase where the block will be mined
- Geographic location (X, Y, Z)
- Spatial dimensions (x-width, y-width, z-height)
- Mass (tonnage or density)
- Grades (metal content, contaminants, etc.)
Material Destinations
2. Is ore and waste pre-determined, or will the model calculate your cut-off grade?
If ore and waste blocks are pre-defined for processing or waste dumping, then your model operates on a fixed cut-off grade. Here, the cut-off grade is an input.
If the model selects which blocks to process and discard, then it operates on a variable cut-off grade, making the cut-off grade an output. Variable cut-off grade models generally produce higher-value schedules than fixed cut-off grade models.
For more information, read: How Much Value is Your Cut-Off Grade Devouring?
3. What processing options are available for ore material?
Ore is often processed at multiple destinations, such as a mill or leach pad. While multiple processing options increase complexity, they can also unlock significant value, improving overall profitability.
4. Are processing options fixed, or will optimisation determine them?
If each block’s processing destination is pre-determined, then the optimisation model cannot take advantage of varying processing recoveries, costs, and capacities.
However, if the model is allowed to choose each block’s destination, it can maximise value by optimising trade-offs between different processing scenarios.
5. Are intermediate stockpiles available?
Stockpiles can provide strategic advantages, such as:
- Setting aside material to achieve optimal blends for processing or sale
- Prioritising higher-grade ore, improving discounted profit
6. Will you consider capital expenditure to expand capacity?
Expanding processing or mining capacity (e.g., increasing mill capacity or purchasing additional trucks) can enhance schedule value.
To maximise value, the optimisation model should include all feasible options, allowing it to explore the most profitable use of resources.
Moving Material to Destinations
7. Will tonnage or trucking constrain material movement?
Mining capacity can be constrained by tonnes or trucking, with associated costs applied.
- Tonnage constraints require an approximation approach to variable costs (e.g., incremental bench mining cost).
- Trucking constraints allow for direct haulage cost calculations.
For more details, read: Why Accurate Trucking in a Mine Plan is Essential.
8. What are your truck cycle times?
Truck-based constraints and cost calculations require accurate cycle times for each block-to-destination movement. If waste dumps are included, cycle times should be measured to either:
- An average location per lift
- The centroid of each dump block
It is essential to account for congestion effects in haul roads, particularly at intersections and around loading and dumping points.
9. Will additional trucks have varying capacity based on truck life?
Fleet capacity can be:
- Fixed, or
- Expanded through capital expenditure
When modelling fleet expansions, consider the declining annual capacity of ageing trucks due to increased maintenance requirements.
For further insights, read: Truck Purchase or Rebuild: An Optimal Approach.
10. What are the requirements for your waste dump(s)?
If waste dumps are modelled at an aggregate level, an average dumping location can be assumed for haulage calculations.
For more precise scheduling, waste placement should be block-specific, particularly if dealing with different waste types (e.g., acid-forming, soil, or hard rock waste).
Processing of Material at Destinations
11. What are your processing requirements and capacities?
Processing facilities may have:
- Minimum grade requirements
- Blending constraints
- Mill hour limits
- Tonnage limits per period
These restrictions define operationally feasible schedules.
12. Do your processing plants have blending requirements?
Blending constraints may be:
- Grade-based
- Rock type-based
Stockpiles can help manage these requirements.
13. Is your processing throughput constant for all ore types?
Throughput may be:
- Constant across all ore types
- Variable based on ore type or other attributes
14. What are the recoveries and processing costs at different destinations?
Do recoveries and costs vary based on:
- Rock type?
- Grade?
- Other factors?
Recoveries, costs, capacity, and ore availability influence processing profitability. Accurately modelling costs and recoveries is critical for schedule optimisation.
Reporting
15. What reporting requirements do you have?
How will you break down reports? Possible categories include:
- By pit or phase
- By rock type
Beyond key performance indicators (KPIs), you may also need reports on:
- Optimal mill capacity
- Optimal leach pad location
- Waste dump requirements
- Fleet expansion decisions
Final Thoughts: Maximising the Value of Your LOM Schedule
Each operation is unique, and not all of these factors will apply to your mine. However, many of them will.
The challenge with cut-off grades is that there is no simple formula to determine whether a block should be processed or discarded.
To truly maximise project value, all block interactions must be considered. The only way to achieve this is through mathematical modelling and optimisation using a solver such as Minemax Scheduler.
The solver evaluates all possible options to determine the highest-value destination for each block while respecting:
✅ Equipment constraints
✅ Customer requirements
✅ Operational logistics
If your cut-off grade model does not consider blending opportunities or the discount rate, it may be worth investigating how optimisation can uncover hidden value.
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