Sampling in Mining - Core Case

Sampling in Mining

One of the major processes in characterizing a mineral deposit is sampling. This is the process of systematic and specialized material collection for analysis.

Sampling of metallic or industrial mineral deposits is performed for several reasons and at various stages of their assessment and exploration 

The mining industry routinely collects samples to help decision-making, whether for exploration, resource estimation, grade control or mine planning. 

In this text, we will address the major characteristics of sampling in mining. Read to the end to find out more!

What is mining sampling?

The sampling process in mining consists of removing certain amounts of material (increments) from a whole to be sampled (population), to make up the primary or overall sample so that it is representative of the population it was taken from.

The sample is, therefore, a representative amount of the whole to be sampled (population) and comprises increments.

Sampling is characterized as a selection and inference process, geared at representing a whole (a mineral deposit, for example) as concretely as possible through the analysis of its parts (samples). 

Samples are prepared and sent for further laboratory analysis, enabling an increase in knowledge on the deposit or ore bed.

The representativeness of the sample is related to the characteristics of the deposit analysis interest characteristics, such as: 

  • Type of rock and minerals in it
  • Density
  • Grade
  • Moisture
  • Porosity
  • Particle size

The importance of ore sampling relates to:

  • Assessment of mineral deposits (quantification, economic feasibility, etc.)
  • Process control (variability, capability, etc.)
  • Product sale (inspection, batch classification, etc.)

Deposit sampling and representativeness

Accurate resource estimates depend on collecting reliable samples during exploration. 

Therefore, sampling programmes must be carefully designed to minimize the chances of collecting biased, unrepresentative or contaminated material. 

Whether for direct and manual collection samples, in trenches or drill cores, the sampling process must be adapted to the target mineralization and soil conditions.

Poorly designed sampling protocols can result in increased project risk due to increasing variability. 

Protocols for sample collection, preparation and testing or test work optimized to suit the ore type, along with QAQC systems, will reduce variability.

Mineral sampling errors

According to GÓES, LUZ e POSSA (2004, p. 19)

“Ill-conducted sampling can result in costly losses or result distortions with unpredictable technical consequences”

“Sampling is, without a doubt, one of the most  complex and error-inducing-prone operations encountered in the mining and 

steelmaking industries”

Mineral sampling error involves a difference between the value of a given characteristic of interest and the estimate of this characteristic in the analyzed sample. 

Techniques to correct these errors in the sampling process are applied in order to obtain satisfactory results.

Types of mineral sampling

The sampling process in a mineral project can be performed in two main ways:

  • Random sampling: It is typically used when little information is available about the material to be sampled. The increments are chosen at random (all parts of the material are equally likely to be selected)
  • Systematic sampling: Increments are collected at regular, preset intervals.

Sampling can be done by several methods, such as:

  • Sampling of existing exposures, manual collections.
  • Use of manual or mechanized excavations (e.g., trenches)
  • Boreholes 

Mineral Project Sampling and Steps

During the exploration phase, sampling is largely confined to the analysis of drilling gravel or drill cores, and is geared at assessing intersections in the deposit. 

Drill cuttings and gravel are broken pieces of solid material removed from a drilled well by rotary, percussion or auger methods and brought to the surface in the drilling slime.

During the exploration phase, sampling is used to define grade over mineable thicknesses, taking into account not only the mineralized zone, but also its potential dilution by low grade material or waste rock. 

Mineral deposit characterization for sampling purposes

A mineral deposit’s occurrence mode and morphology has a considerable impact on sampling type and density and the amount of material required.

Sample type and amount collected depend on a number of factors including:

  • Type of mineral deposit – composition and structure
  • Distribution and particle size
  • Process assessment phase
  • Existence of direct access to mineralization
  • Sampling cost 

Thus, based on prior knowledge on the deposit or ore bed of interest, it is necessary to perform a study on the types, objectives and sampling methods to be used in the mineral project.

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