Variable Mining Costs

SimSched was conceived with some simplifications for current version, such as the Fixed Mining Costs.

The software considers a fixed mining cost, which is applied beforehand in the economic formulation. This value is inputted in the user interface to make the software able to recognize this variable and fragment the previously calculated economic values in order to apply proper discounts to each block, whether (1) processed, (2) discarded, or (3) stocked and processed — here, mining costs are applied earlier than the processing costs and revenue.

However, mining costs might be defined with some variability for purposes of higher detail.

This article shares some ideas to consider Variable Mining Costs, where some goals are based on different:

• • Haul costs, in function of block's depth and/or the destination site.

  • Blasting costs, in function of the rock type.

  • Loading costs, in function of a selective mine

  • Supplies and materials, labor costs, among others.

How to estimate a Fixed Mining Cost?

• 1. Prior to the model import, create a column of mining costs by block — including whatever costs are applicable: blasting, haul, loading, etc.

  2. Calculate the Average Mining Cost of all of the blocks.

  3. During the model import, assign the Mining Costscolumn to the field type Other; SimSched will export this column along with its output.

  4. Use the Average Mining Cost as the Fixed Mining Cost for the stockpiles.

  5. Run MiningMath.

  6. (OPTIONAL, for more accurate approximation) Analyze the MinedBlocks file (or AllBlocks) and calculate the Average Mining Cost just for the stockpiled blocks (Check out, Tracing Stocked Blocks)

  7. (OPTIONAL) Run SimSched again, now using the new Average Mining Cost (from Step 6) as the Fixed Mining Cost for the stockpiles.

Mining Costs in the stockpile context

For mined blocks in the stockpiles context, the possibilities for the material flow are:

• 1. Mine-to-process.

  2. Mine-to-waste.

  3. Mine-to-stock.

  4. Stock-to-process.

The mining costs for flows (1) mine-to-process and (2) mine-to-waste are already embedded in the economic formulation.

The costs for flow (4) stock-to-process consider an additional cost, represented in the user interface by the re-handling cost.

SimSched assumes the costs for (2) mine-to-waste and (3) mine-to-stock are the same, which might not be always the case due to, for example, different distances at the mine site surface (different haul costs).

How to consider different costs for discarded and stocked blocks?

Option 1: Manual NPV Calculation

For which the steps are:

1. Open the MinedBlocks.csv.

2. Edit the stocked blocks' value to add new costs.

3. Calculate the NPV manually.

Option 2: Iterative Process

1. For the first execution 1, set up SimSched to export the AllBlocks.csv and run.

2. Use the output model (AllBlocks) to update the economic value for stocked blocks. Then, save as a new model.

3. For the execution 2, re-import this model with fixed surfaces for all periods. As in the Figure 1.

Observation

This process does not guarantee solution will not change, i.e. the stocked blocks might change, which might require further iterations for a better approximation.

As stockpiles are treated as a post-processing unit in our algorithm, not being part of the optimization, Option 1 is more suitable for a more assertive NPV calculation.