Ore reserves, mining and profit

CIM Bulletin, Vol. 87, No. 983, 1994

Hugh K. Taylor North Vancouver, British Columbia

With some justification, people have long complained about the indefinition of ore reserves. Perhaps they were led to expect too much; from former and easier definition practices in the once common underground mines with exposed and available assets, where the obsolete term 'ore in sight' was at least partly literal. But such mines have become rarer, and their underground development less affordable. For most projects, valuations and its definitions have thus been advanced from actual to prospective mines, leaving a very wide gulf between 'what is there' and 'what may happen to it'. This brings the double challenges of reduced geological and technical assurance and the protraction of economic uncertainties. This paper avoids the popular field of regional resources, being confined to what may possibly be mined within single or closely grouped deposits. For these, many estimates of tonnage and grade must be made, defined and declared long before assessment of feasibility; and the uncertainties of the latter make it an unsound base for defining the earlier quantities. Despite the best of intentions, implied or inferred promises may prove impossible to honour. A simpler framework of definitions is suggested, to some extent reverting to an earlier dependence on supporting work rather than on opinions ofeconomic assurance or future events that are more properly the functions of production and cash flow schedules.

Mots Clés: Ore reserves, Mining economics, Estimation, Ore reserve definition.