Metal accounting systems of mining and processing operations are coming under increasing scrutiny, primarily because of poor agreement between the estimates of mined metal and the quantity of metal actually produced by the concentrator, refiner or smelter. This scrutiny comes in the wake of scandals in the financial accounting world, which has put increased pressure on financial accountants to improve accounting transparency and auditability. This has, in turn, put the onus on metal accountants to examine the quality of their systems, since they form the basis of mining company financial accounts and reports. One weakness that has been identified in the area of metal accounting is a lack of continuity between many mine and mill (processing plant) accounting systems, which often show major discrepancies in production estimates (Baker and Giacomo, 2001). Mine-mill reconciliation is the term applied to the area of comparing, balancing and adjusting production estimates between mine and mill for consistency in reporting, and this thesis seeks to evaluate the concerns in this area and to find robust strategies to ameliorate these concerns. A review of metal accounting and mine-mill reconciliation practices reveals a large number of cultural and technical barriers preventing consistent and high-quality mine-mill reconciliation practice. Current measurement technologies and mathematical/statistical techniques available to the mining industry were also reviewed, and it is clear that application of these underutilised tools has the potential to vastly improve the quality and usefulness of mine-mill production measurement and accounting. Thus, in addition to the benefit of better accounting standards compliance, significant operational improvements may be realised through application of many of these tools and techniques. The approach used to achieve the thesis objectives is to collate a wide variety of available tools and techniques (along with some novel techniques developed) into a practical framework/strategy for undertaking mine-mill accounting and reconciliation. This approach is based on the notion that knowledge of measurement sources and uncertainty (error) is essential to control and improve production efficiency of the overall operation (as opposed to individual areas within). As such, a conceptual approach to mine-mill reconciliation is first proposed, which addresses many of the problem areas identified in the review. A detailed, step-by-step methodology applicable to most metal mining operations is then expanded from this framework, illustrated through a fictitious operation. This methodology is divided into two main parts, consisting of a metal accounting site survey followed by the metal balancing, reconciliation and reporting process. One element of particular importance in this process is ore tracking through process hold-ups, and some approaches to examining this issue are discussed in detail and demonstrated. The proposed mine-mill metal accounting and reconciliation methodology was applied to two very different case studies, Northparkes Mines (NPM) and Potgietersrust Platinums Limited (PPRust). The NPM case study showed application of the entire methodology to a mining and processing operation. For PPRust, only particular elements of the methodology were applied to exhibit the flexibility of the methodology and demonstrate its application through example. The product of this methodology is a practical, yet still somewhat conceptual, methodology that can be applied to most metal mining operations in order to maximise the potential of their mine-mill accounting and reconciliation. The strategy proposed has uncovered a number of significant implications to the mining industry, such as: • Better understanding of the sources of and uncertainty in production estimates can lead to better system control, system auditability and reporting integrity, which should elevate operational credibility in the eyes of mining company financial accountants, analysts and stakeholders at a “license to operate” level. • Dissolving the traditional mine-mill boundary and focussing on best utilising the most accurate and precise production information over the entire operation provides an improved basis for operational decision making and economic calculations. • Using an ore tracking system that can link mill production measurements of in-process ore back to its original location in the deposit can provide a robust means of evaluating mine production efficiency, of evaluating mine model performance and, potentially, of updating reported reserve estimates based on statistically sound information. Though this work does not represent a complete solution to mine-mill reconciliation, it provides strong conceptual goals and a solid technical foundation for future work in this area.
