Practical aspects of mineral resources and ore reserves measurement and accounting

Abstract

Mineral resources and ore reserves estimation, mine planning, measurement of mine and plant performance and the reconciliation of production results with original expectations are continuous processes during the operation of a mine. These activities involve members of several disciplines over an extended period. Although operating conditions, policies and personnel may change, estimating and reporting practices must be applied consistently to achieve accuracy in periodic evaluations and reconciliation.Operational practices are considered against the background of refinement of the definitions of 'resources' and 'reserves' in an effort by mining and regulatory institutions to achieve conformity. The examples relate to underground gold mining, but the principles are adaptable to other situations. Many elements of the systems described are in place at some operations, but may not be consistently used. At other mines systems may be modified on an ad-hoc basis, with the result that not everyone understands them or some may misinterpret the data. This may have serious consequences when ownership or key staff changes occur or third parties have to interpret inconsistently stated resources, reserves and production data—for example, during due-diligence studies.The monitoring of resources and reserves estimation efficiency and the effective reporting of trends are discussed. Some standard terms and ratio definitions are noted that can be adapted for most situations, and the verified mineral resource estimate is suggested for use as an internal tool to provide an ultimate mineral resource check from observations made immediately before mining takes place. The importance of realistic planning and tracking of both stoping and development material and their contributions to production is stressed, especially in narrow-vein mines, where planning and control of development ore output and quality can have a major effect on extractive performance. The translation of resources to reserves, the treatment of 'not-in-reserve' ore and the accounting of remnant ore reserves are discussed, as are shaft call and plant call factors, which combine to create the more familiar mine call factor. Ore-reserve reconciliation procedures are outlined that comprise two stages: the results of the ongoing resources and reserves estimation and monitoring, followed by the accounting of additions and depletions from the reserves due to exploration, mining and changing conditions. Procedural flowcharts and suggestions for reporting formats are included.