What is a volumetric reconciliation report in mining?
A volumetric reconciliation report ties what the pile physically measures out at to what the books say should be there. It's the document that either confirms your stockpile numbers or tells you where to start asking questions.
The report takes two tonnage figures for the same pile, same period, and lays them side by side. One comes from a physical survey of the pile surface. The other comes from the mine's production and dispatch records, the "book" number built from truck counts, belt scale totals, or mill feed tallies. The report states both, states the difference in tonnes and as a percentage, and gives whoever's reading it, the mine manager, the auditor, the site accountant, enough to decide whether that gap is normal variance or something that needs a closer look.
What goes into the report
A reconciliation report isn't just the two numbers. A proper one includes:
- Survey date and method. How the volume was captured, whether that's an RTK walk, laser scan, or photogrammetric surface model, and when.
- Surface model or volume calculation. The pile's measured volume, converted to tonnage using a density or swell factor specific to that material.
- Book tonnage for the same period. Pulled from whatever system tracks movements in and out of the pile.
- The variance. Expressed in tonnes and percentage, with the sign showing whether the survey came in over or under book.
- Density and conversion factors used. Because a volume-to-tonnage conversion is only as good as the bulk density assumption behind it, and that assumption should be visible, not buried.
- Notes on anything that would explain a gap. Recent rain changing moisture content, a known weighbridge calibration issue, a partial survey that missed part of the pile's toe.
Some sites also track a running cumulative variance across several reconciliation cycles, since a small gap that repeats in the same direction every month points to a systematic error rather than noise.
Survey tonnage vs. book tonnage: why they don't match
They're almost never identical, and that's expected, not a red flag by itself. Survey tonnage measures what's physically sitting on the ground right now. Book tonnage is an accounting figure built from individual movement records added and subtracted over time. Every source of error in those records, a truck count that didn't get logged, a belt scale that's drifted out of calibration, moisture swings that change bulk density between loads, compounds over weeks and months. The pile itself doesn't lie. The paper trail can accumulate small errors that nobody notices until someone puts a number on the physical stock and compares it.
A gap of a percent or two over a quarter is often just measurement noise and density assumptions doing what they do. A gap that's large, or that keeps growing in the same direction cycle after cycle, is the kind of thing that gets flagged in a stock audit and chased back through the dispatch records.
How often should you run one
Cadence depends on the operation, but weekly or monthly is common for active stockpiles that see regular movement, with a more thorough audit-grade survey at quarter or year end. The tighter the cycle, the easier it is to catch a drifting weighbridge or a bad truck count before it turns into a six-figure write-down at year-end stocktake.
Where the survey number actually comes from
The reconciliation report is only as good as the survey tonnage feeding it, and that's where a lot of sites lose time. Putting a crew on top of an active pile with an RTK rover means a day of crew time per round and a person standing on material that might slump underneath them. Stockpile Volume builds that surface from weekly drone or crewed-aircraft photogrammetry instead, differenced against ground control, so the volume side of the reconciliation comes from a flight, not a walked survey.
If your reconciliation reports keep flagging variance you can't pin down, it might be worth checking whether the survey method itself is the weak link.