Stockpile Algorithm Modelling
Many algorithms can be applied to predict the grade of material reclaimed from stockpiles. Simple algorithms are often best for estimating stockpile grades. Exceptions to this include ore passes or ROM fingers with a specific build strategy. Grade options include First In First Off (FIFO), Last In First Off (LIFO), LIFO-Average, and Average. Be sure to select the algorithm that best matches the real life practices of your stockpiling!
Average
Average modelling algorithm is the default modelling algorithm that does not calculate a stockpiles composition. This means that the composition of the stockpile is never tracked when the stockpile is modelled as Average. As material is removed from the stockpile, it is assigned the average grade of the stockpile. When a stockpile that has been modelled as Average delivers material to a stockpile using another modelling algorithm, the material delivered will be recognised as “Unknown”.
First In First Out (FIFO)
FIFO modelling is a management algorithm that ensures that whatever material or stockpile composition that was delivered to the stockpile first, will be the material that is removed first. This stockpile algorithm is reliant on the order of transactions to and from a stockpile and the accuracy of these transactions. As material is removed from the stockpile, it is assigned the grades of the blocks or composition removed from the stockpile.
The examples below demonstrate the use of the FIFO Algorithm to calculate the composition of the stockpile.
Opening Balance:
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
Add 100t of Block C:
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
| C | 100 |
Remove 50t (from Block A since it was delivered first):
| Block Name | Tonnes |
| A | 50 |
| B | 50 |
| C | 100 |
Add 100t of Block A:
| Block Name | Tonnes |
| A | 50 |
| B | 50 |
| C | 100 |
| A | 100 |
When calculating the grade balance for a FIFO stockpile, the mass average of all the components remaining at the end of the shift is used.
Last In First Out (LIFO)
LIFO modelling is a management algorithm that ensures that whatever material or stockpile composition that was delivered to the stockpile last, will be the material that is removed first. This stockpile algorithm is reliant on the order of transactions to and from a stockpile and the accuracy of these transactions. As material is removed from the stockpile, it is assigned the grades of the blocks or composition removed from the stockpile.
The examples below demonstrate the use of the LIFO Algorithm to calculate the composition of the stockpile.
Opening Balance:
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
Add 100t of Block C:
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
| C | 100 |
Remove 50t (from Block C since it was delivered last):
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
| C | 50 |
Add 100t of Block A:
| Block Name | Tonnes |
| A | 100 |
| B | 50 |
| C | 50 |
| A | 100 |
When calculating the grade balance for a LIFO stockpile, the mass average of all the components remaining at the end of the shift is used.
LIFO Average – This algorithm will apply grades from LIFO modelling back to the beginning of the previous shift before reverting to average weighted grades.
LIFO Configured – The algorithm will use LIFO for a configured period (days) before reverting to Average. The look back period to use when setting the LIFO_configured option should be defined by the frequency of additions to that stockpile. For example, if a stockpile doesn’t have additions for 2 days, then LIFO_configured should have a configured period > 2 days. This avoids incorrect calculation of the depletion grade.
Notes:
The grades for reclaim movements will always be NULL if the closing balance for the corresponding shift is negative. This is the case even if there are deliveries to that stockpile on the same shift that match or exceed the tonnes of the reclaim movement(s). For example, if a stockpile has an opening balance of -5000 tonnes, and there are deliveries of 3000 tonnes and reclaims of 2000 tonnes, the reclaim movement will have NULL grades since the closing balance is -4000 tonnes. The grades associated with the 3000 tonnes delivered are essentially lost (unless the negative balance is corrected via an adjustment).
If there is a delivery with NULL grades to a stockpile, the associated parcel of material will be allocated the current weight average opening grade of the stockpile. When this parcel is reclaimed at later date, the movement grade will be calculated using these weight average grades from a prior shift.
