Torshab Mine Stone

Short Course Introduction to
Quantitative Mineral Resource
Assessments
By Donald A. Singer1
Open-File Report 2007-1434
2007
U.S. Deprtment of the Interior
U.S. Geological Survey
1U.S. Geological Survey, Menlo Park, Calif.
__________________________________________________ _

Short Course Introduction to Quantitative Mineral Resource
Assessments
By Donald A. Singer
This is an abbreviated text supplementing the content of three sets of slides used in a
short course that has been presented by the author at several workshops. The slides
should be viewed in the order of (1) Introduction and models, (2) Delineation and
estimation, and (3) Combining estimates and summary. References cited in the slides
are listed at the end of this text.
The purpose of the three-part form of mineral resource assessments discussed in the
accompanying slides is to make unbiased quantitative assessments in a format needed in
decision-support systems so that consequences of alternative courses of action can be
examined. The three-part form of mineral resource assessments was developed to assist
policy makers evaluate the consequences of alternative courses of action with respect to
land use and mineral-resource development. The audience for three-part assessments is
a governmental or industrial policy maker, a manager of exploration, a planner of
regional development, or similar decision-maker. Some of the tools and models
presented here will be useful for selection of exploration sites, but that is a side benefit,
not the goal.

To provide unbiased information, we recommend the three-part form of mineral
resource assessments where general locations of undiscovered deposits are delineated
from a deposit type’s geologic setting, frequency distributions of tonnages and grades of
well-explored deposits serve as models of grades and tonnages of undiscovered deposits,
and number of undiscovered deposits are estimated probabilistically by type. The
internally consistent descriptive, grade and tonnage, deposit density, and economic
models used in the design of the three-part form of assessments reduce the chances of
biased estimates of the undiscovered resources.
What and why quantitative resource assessments: The kind of assessment recommended
here is founded in decision analysis in order to provide a framework for making
decisions concerning mineral resources under conditions of uncertainty. What this
means is that we start with the question of what kinds of questions is the decision maker
trying to resolve and what forms of information would aid in resolving these questions.
Some applications of mineral resource assessments: To plan and guide exploration
programs, to assist in land use planning, to plan the location of infrastructure, to estimate
mineral endowment, and to identify deposits that present special environmental
challenges.
Why not just rank prospects / areas? Need for financial analysis, need for comparison
with other land uses, need for comparison with distant tracts of land, need to know how
uncertain the estimates are, need for consideration of economic and environmental
consequences of possible development.
Our goal is to provide unbiased information useful to decision-makers.

A short history: 1957 “Method of appraising economic prospects of mining exploration
over large territories—Algerian Sahara case study” by M. Allais, 1974-75 beginning of
three-part assessments in Alaska (Richter et al., 1975, Singer, 1975).
Three-part resource assessments: (1) General locations of undiscovered deposits are
delineated from a deposit type’s geologic setting, (2) Frequency distributions of
tonnages and grades of well-explored deposits serve as models of grades and tonnages
of undiscovered deposits, (3) Number of undiscovered deposits are estimated
probabilistically by type.
The nature of mineral resources: Only a few deposits account for most resources, most
important is tonnage—not grade in estimating total resources, few deposit types account
for most resources.
Required Deposit Models
Integrated mineral deposit models are at the core of three-part assessments because they
reduce uncertainty about locations, amounts, and values of resources.
General modeling: A model is a way in which the human thought process can be
amplified. The way to describe a model is first by thinking about what it is for, about its
function, not the list of items that make up its structure. What is surely needed as a
minimum is an information system that will help the policy makers to make their
decisions (Churchman, 1968). Desirable to define and use the same set of rules for all
deposits in the model, these same set of rules apply to all of the undiscovered deposits
that are estimated.
Descriptive models: Focus on observations, only use theories of origin to guide what to
observe, observations must be available at scale of assessments.
Beginning of digital models: Documented and reproducible, do not miss the obvious
and, can be used in classification and prediction.
Grade and tonnage models: The purpose of grade and tonnage models is to provide
unbiased representations of the grades and tonnages of undiscovered mineral deposits in
a tract or belt. Grade and tonnage models used in three-part assessments represent the
premining grade and tonnage of a deposit. This means that current resources at the
lowest cutoff grade are added to past production.
Grade and tonnage models use resource figures to represent the mineralized material in a
deposit in order to allow for possibly different technologies and mining costs to be
assumed.
Spatial rules for models: For deposit models, a spatial rule should be used to determine
which ore bodies should be combined. For example, ore bodies of both kuroko and
Cyprus type massive sulfides were combined into single deposits based on a 500-m rule
of adjacency. Map scale affects what is called a mineral deposit, for some deposits legal
or geographical boundaries affect what is reported as a deposit

Sources of errors in grade and tonnage models: Mixed geologic environments, poorly
known geology, data recording errors, mixed deposit / district data, mixed mining
methods, incomplete production / resource estimates.
Deposit density models: A robust method to estimate the number of undiscovered
deposits is a form of mineral deposit model wherein numbers of deposits per unit area
from well-explored regions are counted and the resulting frequency distribution is either
used directly for an estimate or indirectly as a guideline in some other method.
Although only three deposit types have detailed density models developed at this time,
the combination of these studies with other density studies shows that the deposit
density relationships can be generalized across deposit types (Singer, in press). The
relationship between size of permissive tract and size of deposit estimated can be used to
estimate the number of deposits for any deposit type.
Cost models: Models of capital and operating costs required to build and operate a mine
and mill, and infrastructure that supports them. Models do not estimate costs of
preproduction exploration, permitting, environmental studies, taxes, corporate overhead,
site reclamation, concentrate transportation, or smelter and refinery charges. Although
not all costs are included and the estimates are rough, these models serve to discriminate
clearly uneconomic from clearly economic deposits at an early assessment stage.
Daily capacity is the key variable in these models, mine life is calculated from capacity,
capital and operating costs are a function of capacit, the equations vary with mining and
milling methods.
Delineation of Tracts and Estimating Number of Deposits


__________________________________________________ _





View HTML

Download PDF