wAbstract
@Since 1975, mineral resource assessments have been made for over
27 areas covering 5~106 km2 at various scales
using what is now called the three-part form of quantitative assessment.
In these assessments, (1) areas are delineated according to the
types of deposits permitted by the geology, (2) the amount of
metal and some ore characteristics are estimated using grade and
tonnage models, and (3) the number of undiscovered deposits of
each type is estimated.
@Permissive boundaries are drawn for one or more deposit types
such that the probability of a deposit lying outside the boundary
is negligible, that is, less than 1 in 100,000 to 1,000,000.
@Grade and tonnage models combined with estimates of the number
of deposits are the fundamental means of translating geologists'
resource assessments into a language that economists can use.
@Estimates of the number of deposits explicitly represent the
probability (or degree of belief) that some fixed but unknown
number of undiscovered deposits exist in the delineated tracts.
Estimates are by deposit type and must be consistent with the
grade and tonnage model. Other guidelines for these estimates
include (1) frequency of deposits from well-explored areas, (2)
local deposit extrapolations, (3) counting and assigning probabilities
to anomalies and occurrences, (4) process constraints, (5) relative
frequencies of related deposit types, and (6) area spatial limits.
In most cases, estimates are made subjectively, as they are in
meteorology, gambling, and geologic interpretations.
@In three-part assessments, the estimates are internally consistent
because delineated tracts are consistent with descriptive models,
grade and tonnage models are consistent with descriptive models,
as well as with known deposits in the area, and estimates of number
of deposits are consistent with grade and tonnage models. All
available information is used in the assessment, and uncertainty
is explicitly represented.
Key words: Mineral resource assessment; Mineral deposit models;
Quantitative assessment; Three-part assessmentsx
Introduction
Mineral deposit models
Delineation
Grades and tonnages
Number of undiscovered deposits
Conclusions
References