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Throughout the foregoing, we have stressed the fact that very few mines operate exactly as forecast, that in most instances the actual results are below original expectations, and that this fact is usually due to a failure to anticipate geologic complexities in the orebody, rather than to the computational techniques employed in the reserve estimation process. Mason (1993) has suggested that the two main reasons for incorrect reserve estimates are (1) a lack of detailed mine geology (including a fundamental geologic understanding of the deposit), and (2) “advances” in computer skills and technology.

It has been pointed out to us that on occasion, a property has been brought into production simply because the company involved is anxious to become an active producer, even though the deposit in question is clearly uneconomic—a situation that seems especially prevalent with small gold occurrences. There is a legal term for this sort of action (“fraud”), and further discussion of this sordid subject is beyond the scope of this text.

The intent of this chapter is not to present a detailed list of “horror stories,” but is, rather, to summarize some general observations that can be drawn from the literature. This literature contains a great many studies comparing predevelopment ore reserve projections with actual production (e.g., Section B, CIM Special Vol. 9, 1968; Blackwell 1992; Manns and Ellingham, 1992).

In many of these studies, the mine staff takes pride in the fact that the operation has produced more metal units than forecast. A study

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