Mapping, Sampling, and Testing
Published:January 01, 1995
The Importance of a geologic map in the development of an ore deposit is fairly obvious. Perhaps less obvious is the fact that different kinds of maps may be required at different stages of the project. Table VIII-A presents the sequence of stages in the development of a mineral deposit used by SOQUEM to enable the public to visualize the scope of activities involved at various stages in the life of a project (Vallée, 1986). Table I-A presented a somewhat similar effort by Hanna Mining to relate the degree of risk to the stage of development of a mineral project.
Immediately following the discovery of potentially oregrade mineralization, the question of concern is, “Is there likely to be enough of this mineralization present to warrant further expenditure?”
For this purpose, a fairly generalized map may be sufficient to guide ongoing exploration. By the time a development decision is reached, a map (or maps) defining the relationship between different types of ore in the deposit, their detailed structural settings, the relationship of the deposit to host rocks of varying competence, the distribution of recoverable grades within the various ore types, and any special features of geotechnical interest will be required to guide actual mine layouts. Such maps can be prepared only with input from geological, metallurgical, engineering, and operations personnel—in other words, from all the disciplines associated with a mining operation.
Failure to involve nongeological expertise at an early stage in project development is one of the reasons for the
Figures & Tables
Ore Reserve Estimates in the Real World
In Simplest Terms, the work of the mineral industry may be defined as the search for and production of some naturally occurring mineral substance useful for some specific purpose, and as such, that substance is both a defining element of and the underlying basis for our existence as a species.
The fundamental requirement for any venture designed to extract a mineral substance from the ground is the presence of a reserve of that substance, and the estimation of the quantity and quality of the available reserve is the single most important step in the development of a mineral discovery. In fact, the basic purpose of ore reserve estimation is to provide the first step in the evaluation of a business opportunity:
… all financial calculations can be no more than the transposition of the ore reserve estimate into other terms.
(King et al., 1982, p. 65)
Prior to roughly 1970, there was little or no standardization of nomenclature regarding the various levels of reliability attached to estimates of mineral resources or reserves, and quite frequently the same term was applied to estimates of widely differing reliabilities, made for widely different purposes. It was generally accepted that the term “ore” should be restricted to material having at least a remote possibility of economic viability, and that the terms “proven” or “measured,” “probable” or “indicated,” and “possible” or “inferred” should be used to denote estimates based on progressively less reliable data. In 1980, based on modifications of a standardized system proposed in 1976, the U.S. Bureau of Mines (USBM) and U.S. Geological Survey (USGS) published a revised classification system (Fig. I-1), in which the term “resources” was applied to an overall “concentration of [a] naturally occurring solid, liquid or gaseous material in or on the earth’s crust in such form and amount that economic extraction from the commodity is currently or potentially feasible.” The term “reserves” was restricted to “that part of an identified resource that meets specified minimum physical and chemical criteria ...[and] may encompass those parts of the resources that have a reasonable potential for becoming economically available within planning horizons beyond those that assume proven technology and current economics” (USBM … USGS, 1980, p. 2).
In 1996, the United Nations proposed a three dimensional scheme for the classification of resources and reserves (Fig. I-2) that assigns a numerical degree of reliability to each of three axes, representing economic, feasibility, and geologic elements of the evaluation (United Nations, 1996; Kirk, 1998).