Page 216 - Introduction to Mineral Exploration

10

Evaluation Techniques

Michael K.G. Whateley and Barry C. Scott

As an exploration geologist you will be Finally, to ensure that the maximum
expected to be familiar with mineral deposit amount of information is derived from drill
geology, to understand the implications of core (other than the obvious grade, thickness,
extraction on the hydrology of the mineral rock type, etc.) a basic geotechnical and hydro-
deposit area, to recognize the importance of geological outline is given. This information
collecting geotechnical data as strata control may be used in assessing possible dilution of
problems may have considerable impact on the ore upon mining, or may identify strata
mine viability, to be able to propose suitable control or serious water problems which may
mining methods, and to assess the economic occur during mining.
viability of a deposit. To be able to cope with all
these tasks you will need to be technically
competent particularly in sample collection, 10.1 SAMPLING
computing, and mineral resource evaluation.
The basis of all geological evaluation is the
sample. Poor sample collection results in un- 10.1.1 Introduction to statistical concepts
reliable evaluation.
This chapter will present some of the Population and sample
methods that are used in the field to obtain Sampling is a scientific, selective process
representative samples of the mineralized rock applied to a large mass or group (a population,
that will enable the geologist to undertake as defined by the investigator) in order to
mineral deposit evaluation. This includes the reduce its bulk for interpretation purposes.
various drilling techniques, pitting and trench- This is achieved by identifying a component
ing as well as face and stope sampling. Once part (a sample) which reflects the character-
these data have been collected they are evalu- istics of the parent population within accept-
ated to determine how representative they are able limits of accuracy, precision, and cost
of the whole deposit. This is achieved using effectiveness. In the minerals industry the
statistics, a subject covered in the first part of average grade of a tonnage of mineralized rock
the chapter. (the population) is estimated by taking samples
The geologist prepares and evaluates the which are either a few kilograms or tonnes in
deposit’s geological and assay (grade) data. In weight. These samples are reduced to a few
an early phase of a project, global resource grams (the assay portion) which are analyzed
estimates using classical methods will norm- for elements of interest.
ally be adopted. Later, as more data become Results of analyzed samples plotted as a
available, local estimates are calculated using frequency curve are a pictorial representation
geostatistical methods (often computer based). of their distribution (Fig. 10.1). Distributions
An outline of these evaluation methods is also have characteristics such as mid-points and
presented. other measures which indicate the spread