Weight Calculation Algorithm

Pit Optimisation uses the following weight calculation algorithm to convert all costs into a single value for each block in the model.

The formulae below are based on unit rates for mass quantities. Where unit rates are specified relative to volumes, densities are omitted as required.

  • Attempt to process the blocks using every processing method:

    • An element will be extracted only if its grade is within the cutoffs.

    MinedOreMass = Volume * Density * MiningRecovery
    AvailableElementQuantity = MinedOreMass * (ElementGrade - Threshold)
    RecoveredElementQuantity = AvailableElementQuantity * ProcessingRecovery
    RockTypeProcessCost = MinedOreMass * MiningDilution * RockTypeUnitProcessCost * PCAF
    ElementProcessCost = AvailableElementQuantity * ElementUnitProcessCost
    ElementSalesCost = RecoveredElementQuantity * ElementUnitSalesCost
    ElementRevenue = RecoveredElementQuantity * ElementUnitPrice * RAF
    BlockProcessValue = SUM(ElementRevenue - ElementProcessCost - ElementSalesCost) - RockTypeProcessCost

    Select the method with maximum BlockProcessValue.

    If no method is acceptable for a block, classify it as waste.

  • Calculate mining cost:
    • OreMiningCost = Volume * Density(ore) * MCAF(ore) * OreUnitMiningCost * RCAF
    WasteMiningCost = Volume * Density(waste) * MCAF(waste) * WasteUnitMiningCost * RCAF
  • Calculate general and administration cost:
    • GeneralAdminCost = Volume * Density * UnitGeneralAdminCost
  • Calculate rehabilitation cost for waste:
    • RehabilitationCost = Volume * Density(waste) * UnitRehabilitationCost
  • Calculate block value as ore and waste:
    • Value(ore) = BlockProcessValue - OreMiningCost - GeneralAdminCost
    Value(waste) = 0 - WasteMiningCost - RehabilitationCost

    Based on whichever value is greatest, classify the block as ore or waste.

    When all the blocks have been processed, determine the undefined volume in each parent block of the block model and calculate the air volume. If the model is an Ore body model, add the default waste using the parameters on the Defaults tab with the formulae above to determine the “true” undefined volume (undefined volume - air volume).

    If the model is a Full model, all undefined volume is treated as air.