Stockpile reconciliation usually starts with a disagreement: the survey says one thing and the production records say another. A stockpile survey is often the first figure questioned, but it is rarely the best place to start looking.
Quick Answer
Where a surveyed tonnage and a production record disagree, the two figures are usually built on different bases before either one is wrong. Check five things in order: the dates each figure applies to, the extent of the pile, the base surface, the density basis, and any movement between the two dates. Question the measurement last. If one figure has no recorded basis, the difference cannot be settled by measuring again.
This article is the investigation procedure. The arithmetic of converting volume to tonnage is covered in our article on survey volume and tonnage.
A stockpile reconciliation procedure in five steps
The steps below run in a fixed order, from the quickest checks to the slowest, so the survey is questioned only after the more common causes have been ruled out.
| Step | Check | What a difference here means |
|---|---|---|
| 1 | The date each figure applies to | The two figures describe different moments |
| 2 | The extent of the pile | The two figures describe different ground |
| 3 | The base surface | The volume was measured against a different floor |
| 4 | The density basis | The same volume was converted differently |
| 5 | Movements between the dates | Material moved and was not recorded |
Step 1: dates
A survey figure applies to the day the pile was captured. A production figure may run to the end of a shift, a week or a month. Line the two up before comparing them. If the survey was taken mid-week and the production record runs to month end, the material moved in between belongs to one figure and not the other.
Step 2: extent
Two figures for "the stockpile" can describe different footprints. Confirm that both cover the same area, and note any edge one of them excluded. A pile that has spread into a neighbouring area, or merged with another pile, is a common source of a difference that looks like a measurement problem.
Step 3: base surface
A volume is measured against a base surface. If the survey and the production model assume different floors, they will disagree with no material moving at all. Ask which base each figure used, and when it was last surveyed.
Key point
Most stockpile reconciliation questions are settled in the first three steps. Dates, extent and base surface are quick to check and often responsible.
Survey and production records disagree?
Send us both figures and how each was produced. We will start at step 1.
Ask us to reconcile the figuresDensity and movement: the last two checks
Density and movement are the two checks that need information from outside the survey, which is why they come after the survey's own basis has been confirmed.
Step 4: density
A survey measures volume, not mass. A tonnage is obtained by applying a density, and that density comes from sampling the material, not from the survey. Density varies with material type, particle size, moisture, and how recently the pile was placed or reworked. Confirm which density each figure used, where it came from and when it was taken. If the survey report and the production system used different densities, the two tonnages will differ even when the volumes agree exactly. A density from one part of the pile, or from one time, may not represent the whole pile.
Step 5: movement
Material can be added, removed or reshaped between two dates. Check deliveries, reclaim, and any pushing or reshaping. Weighbridge records, loader logs and conveyor totals can each show movement that the stockpile figures do not, so gather them for the same period before drawing a conclusion. Where no record exists for a movement, note that gap rather than estimating around it. Movement that was not recorded can account for part or all of the difference. Our article on stockpile volume measurement covers how to keep repeat surveys comparable so that a real change stands out.
Then the measurement
If all five checks agree and a difference remains, the measurement deserves a closer look. That might mean a repeat survey by the same method, or an independent check where the figures are commercially significant.
Whatever the outcome, write it down. A stockpile reconciliation that records which step explained the difference makes the next one faster, and over a few months it shows whether one cause keeps returning. A cause that keeps returning is usually a process to fix, not a figure to argue about.
Key point
Stockpile reconciliation checks the basis of each figure before it checks the figure. A disagreement on basis is not a disagreement on fact.
Need monthly figures you can reconcile?
Tell us the piles and the reporting cycle. We will record the basis every time.
Get a stockpile survey quoteWhere survey cannot help you
A careful stockpile reconciliation can usually find the cause, but some gaps cannot be closed by measuring again.
Survey cannot recover the basis of a figure that was never recorded, and it cannot settle which of two undocumented figures is right. It cannot determine density, which depends on sampling. It cannot reconstruct movement nobody logged, and it cannot measure a pile that has since been reclaimed. On larger sites, the same procedure applies to volumetric surveys generally, including those captured from the air by aerial survey. Mine survey practice in the region has its own professional body, the Institute of Mine Surveyors of Southern Africa.
A dispute that needs an independent view?
An independent check can test both figures against their stated basis.
See survey auditsLet's Build With Accuracy.
Stockpile figures recorded with their date, extent, base surface and method, so reconciliation starts from the records.
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