Mixed & Warehouse Modes

Studio NPVS+ understands two kinds of stockpiling mode: Warehouse and Mixed. This choice is made using the Scheduling Setup: Options screen.

When reclaiming a parcel from a warehouse stockpile, the contents of the parcel are reclaimed exactly as it was stockpiled. When reclaiming a parcel from a mixed stockpile, the properties of the material reclaimed are calculated from the weighted average of all material in the stockpile at the time of reclaim. Mixed stockpiles require additional constraints and are more complex to solve, but are more common at mines.

Warehouse stockpiles can be further simplified by restricting the number of periods that parcels can remain on the stockpile (defined as Maximum periods to reclaim). This reduces the number of variables in the problem at the cost of forcing the model to reclaim from the stockpile when it may be more profitable to process material taken directly from the mine.

Studio NPVS+ solves the mixed stockpile problem by first solving the warehouse problem and converting the solution to a mixed stockpile problem solution. This requires more time and memory, so if the user is finding that it takes too long to obtain a solution, the following options can be considered to obtain a solution more quickly:

Increase the Optimality Gap setting.
Choose Warehouse instead of Mixed stockpiles. See Scheduling Setup: Options.
Choose a small number for Maximum periods to reclaim.
Try increasing the Number of cores.
Reduce the number of periods until the Optimizer switches to Multipass for number of periods...
Remove minimum constraints.
Reduce the number of ore bins.

Note: The Optimizer requires mixed stockpiles with initial tonnage to be empty at the end of the schedule. In rare cases when using mixed stockpiles with large initial tonnage, not enough periods to reclaim, or a low reclaim rate (processing capacity) the Optimizer will show the message "Problem has no solution". This can be avoided by adding more periods or decreasing the initial tonnage.