Recon #16 of 17. F3 - The Procrustean Bed of Reconciliation

Hi everyone and thanks for your interest in mining geology!

In Greek mythology, Procrustes was a rogue smith and bandit from Attica who, after inviting passing guests to his house, tried to force them to fit the size of an iron bed. If the person was too short or too tall, the malicious host would either stretch them or cut off their legs to ensure a perfect fit. Nobody ever fit the bed exactly. Procrustes continued his reign of terror until he was captured by Theseus, who, while traveling to Athens along the sacred way, "fitted" Procrustes to his own bed.

I always thought that a Procrustean bed, serving as an arbitrary standard to which exact conformity is forced, is a perfect metaphor for F3 applied as a single reconciliation metric. But let me explain.

One of the unfortunate features of F3, which is calculated as Mill Reconciled / Resource (or Reserve) Model (or simply F1 x F2), is that, when disconnected from the overall reconciliation framework, it provides little value for evaluating ore control performance. It is very common, for example, to see long-term models being overly conservative (intentionally or unintentionally?). Then, you observe a substantial spike in the in situ grade control model, lose this extra material due to poor ore control, and end up with a perfect F3. Or, you might see a reasonable higher grade resource model presented as a scapegoat in a mine with a severely punished grade control model that was forced to match the mill numbers, resulting in poor F1 and a great but fake F2. Sometimes, there may even be a very positive F3 that keeps everyone calm and out of trouble, but this result also indicates a lack of understanding of what is actually going on. This ignorance may cost the company a fortune, either from direct losses or untapped potential value that ends up on the waste dump.

That’s why it is paramount to delve deeper into the details of the mining operation instead of trying to simplify it with a good-looking but not very helpful F3 metric, which only serves as a derivative of the rest of the data and not the definitive answer. The good news, however, is that it is not necessary to have an intricate understanding of all the small ore control procedures to derive a meaningful conclusion. If you need to quickly assess ore control performance and reconciliation, the following steps may prove handy.

• Start with ore control (F1), not the mill (F2). Problems in mining will affect both the numerator and denominator in F1 and the numerator in F2, while mill issues only affect the denominator in F2.
• Ensure that the Grade Control model makes sense. This is the key starting point and the most informed piece of information you will ever have.
• Perform an in situ check of the Grade Control model vs. the Resource Model. This ensures the quality of the long-term prediction and determines the need for adjustments.
• Compare the Grade Control model to Dispatch numbers. This step will encompass all polygon development, blasting, and mining issues at once. If you have time, you can go into more detail later.
• Review F2 in detail, keeping in mind everything you discovered in the previous steps. This may provide insights into both mining issues and plant performance simultaneously.

This may add a bit more work to the general audit; however, those hours will definitely be well-spent. The truth is that a poorly performing F3 will likely not provide any insights into the source of the problem (the convention is usually to model and remodel resources until they fit rather than focusing on ore control), while a well-behaved F3 will not prove that everything is okay. The problem becomes even more serious when, on top of the reconciliation, one tries to analyze compliance with the mine plan, which can also change during the mining process. My preference is to keep the classy reconciliation exercise separate from the budget-actuals analysis because of the overlapping effects.

Today’s post completes the technical-related component of the reconciliation journey. In the next post, I plan to touch on some lesser-discussed aspects of the duties and responsibilities of the chief operational geologist and their position in the mining framework, which will complete the full series on reconciliation topics. As always, please feel free to share your thoughts and experiences in the comments.

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