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What is sampling and how does it apply to mineral exploration?

November 20, 2019

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Sampling is a statistical technique that means extracting from the whole (population) a part (sample) for the purpose of evaluating certain characteristics of this population.

A good mining project is developed in stages that are previously defined on the basis of results obtained from samples of rock, soil, stream sediment, battery concentrate, water, ROM, plant concentrates, etc., which after being collected have their mineralogical content and/or composition, specific weight, porosity, humidity, granulometry determined by various chemical, mineralogical, physical and physicochemical analysis techniques; as well as samples of data obtained through structural and geophysical measurements, for example.

Economic evaluation studies, mining planning and forecasting the performance of a mining project are based on estimates of ore content and quantity. These estimates, in turn, are based on samples selected according to a sampling plan. The more representative the samples, the more precise and accurate the estimates will be. A sample can be defined as a reduced fraction of a body or population that summarises certain characteristics of the whole. For this representativeness to occur, it is necessary to adopt criteria and methods that make it possible to maintain the intrinsic errors of each stage, from collecting the sample to interpreting the data interpretation within acceptable and controlled limits.

What is the sampling process?

The sampling process consists of taking modulated quantities of material from a whole that you want to sample, to make up the primary or global sample, in such a way that it is representative of the whole sampled.

Representativeness in a sample occurs when properties such as mineralogical constituents, content of the various elements, granulometric distribution, specific mass, etc., estimated on the basis of a sample, show statistically acceptable variability.

 

What are the objectives of the sampling process?

The ultimate goal of all sampling is basically to determine a quality parameter, or attribute. The main parameters usually estimated in a sample are:

  • geochemical contents
  • mineralogy
  • humidity
  • porosity
  • density
  • magnetic susceptibility.

 

Sampling in Mineral Prospecting

In the case of a mineral deposit, you have a range of minerals in proportions that vary throughout the body. Consequently, the concentration of elements also varies from one point to another.

As a result, it is extremely unlikely that a single sample will efficiently and accurately represent the overall composition of the deposit. The error related to sampling decreases as the number of samples increases, but does not disappear. All sampling therefore involves an intrinsic error.

The main objectives of sampling in a mining project involve representing the mineral deposits themselves and also the products generated from processing the mineralised rocks contained therein, by determining their physical and chemical properties.

The results obtained from the physical and chemical analyses of the materials in a given deposit are used to:

(a) interpreting the formation processes of the deposit and its geological modelling;

(b) classifying resources and reserves;

(c) assessing economic potential;

(e) defining processes and routes for treatment and industrial transformation;

 

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