Illusory reconciliation: compensation of manual sampling errors

Abstract

In the mining industry, reconciliation can be defined as the practice of comparing the tonnage and average grade of ore predicted by the geological models with the tonnage and grade generated by the processing or metallurgical plant. This practice is of increasing importance, since, if correctly executed, it allows the reliability of short-term planning to be improved and the mining and processing operations to be optimised. However, the usefulness of reconciliation relies strongly on the quality of the input data, which is generated by many different sampling methods across the industry. In fact, successful reconciliation can be illusory-errors generated at one point of the process can be offset by errors generated at other points, resulting in apparently excellent reconciliation. Such a situation will in fact also hide compensating biases in the system that will, unavoidably, surface some other day. When this happens, sampling errors are masked and may lead to an erroneous appreciation of the reconciliation system as a whole, which results in serious consequences for the mine operation, especially when reaching poorer or more heterogeneous areas of the deposit. Since valid estimation is only possible with TOS-correct sampling practices, the reliability of reconciliation results depends critically on the representativeness of the samples that generated them. This contribution a summary of an analysis of the manual sampling practices carried out at a copper and gold mine in Goias, and proposes a more reliable sampling method for reconciliation purposes. Results show that the apparently excellent reconciliation between the mine and the plant was in fact illusory; here a consequence of accidental compensation of many errors due to sampling practices for short-term planning.

Validation of reverse circulation drilling rig for reconciliation purposes

“…The previous work 3 proved that this drilling rig is not able to recover all the material from the hole, especially the coarse and consequently lower grade material. Thus, the fragments sent to the surface piles (finer fragments) are richer than the original lot (all fragments composing the drill hole: fines, medium and coarse).…”

“…In 2013 3 , the authors presented the results of a sampling campaign in the same mine, which demonstrated the tendency of the Furukawa to overestimate both gold and copper grades, especially due to poor recovery (only 80%) coupled with segregation between fines and coarse material. Therefore, a reverse circulation (RC) drilling rig with automatic sampling system (recovery of up to 99%) was recommended, in order to minimise the errors generated by manual sampling, such as the increment delimitation error, the increment extraction error, the increment weighting error and the grouping and segregation error (IDE, IEE, IWE, GSE).…”