Sample preparation

Sample preparation quality

Each sample preparation step requires controls to be in place; from sample submittal, through preparation and return or disposal of samples. Generating a homogeneous sample that adequately represents the material from which it was taken is the goal of all sample preparation. This requires strict control on the particle size at each step of the process, accompanied by representative sub-sampling and splitting.

Calidad de preparación de las muestras

The ALS difference

ALS routinely carries out internal quality control verifications at each sample size reduction stage to ensure that each step meets the size requirements specified by the client’s method choice. This information is essential to ensure high quality sample preparation, and all QC data generated through these verifications is available through Webtrieve™ for routine monitoring.

preparación de muestras: la diferenciación de ALS

Sample submission

Confidence and security in the chain of custody for your samples as they pass through our system is paramount, and a cornerstone of ALS Geochemistry’s proprietary global laboratory management system. Samples are given a barcode and logged into our laboratory information management system on receipt and tracked through all processes. Our LIMS accommodates all major barcode formats, and we encourage clients to barcode samples prior to sending them to our laboratories.

Access to barcode tickets

Barcode ticket books can be purchased from ALS if required.

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Sample storage

Materials submitted for analysis are retained free of charge at ALS laboratories for a limited time, starting from the day the final Certificate of Analysis is issued. Reasonable monthly charges apply to samples archived for longer periods in our facilities.

Secure sample storage

ALS sample storage facilities provide a secure and organised environment protected from the elements, and all archive locations are included in the laboratory tracking system.

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Specific gravity & bulk density

Specific gravity and bulk density of ores are important parameters that are often under-characterised in deposits. The specific gravity of rock is a key parameter for grade and tonnage estimates for deposits. Insufficient or incorrect specific gravity or bulk density estimates can have major economic impacts for companies which makes a quality routine measurement a necessity.

The challenge of weathered rock

Field based estimates of specific gravity often use the water immersion method used for rock samples at the lab. This can be problematic when samples are highly weathered, as immersion will result in the sample disintegrating. Consequently, this can drive a sampling bias from the field technicians responsible for specific gravity measurement, as more solid rock intervals are easier to handle and more likely to be chosen. By submitting samples for specific gravity to an ALS laboratory this sampling bias is removed, and a more representative characterisation achieved.

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Rock preparation

The rock preparation packages offered by ALS are ideal for outcrop, drill core and drill chip samples. These packages represent the most commonly used combinations of crushing size and pulverisation volume, however customisable variations are available to suit all projects.

Choosing a preparation method

The choice of sample preparation methods will depend on the unique mineralogy and texture of a deposit’s rocks. For this reason, there is no single package that will suit all rock types and deposits. Some preliminary test work is recommended to identify the sample preparation steps that will produce a representative sample for deposit characterisation.

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Individual preparation procedures

Individual procedures can be used either separately or combined to meet specific needs required for sample size and composition. Most preparation methods are charged at a rate that is based on sample weight.

Customised sample preparation

ALS offers a range of preparation procedures for each step to allow a fully customisable protocol to suit all sample types.

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Soil & sediment preparation

Drying temperatures for soil and sediment samples are typically kept low (<60ᵒC/140ᵒF) to avoid the loss of mercury and other volatile elements that may be important to interpretation. Samples can be pulverised or sieved to a specified mesh size to remove larger gains, often quartz and lithic fragments. The most common mesh size used is -180 microns, however many other screen sizes are available. If requested, all fractions generated by screening are retained and weights of each fraction can be reported as required.

Clay-sized particle separation

The clay-sized fraction in soils and sediments have been shown to provide the most reproducible precious metal values in regional geochemical surveys. Reproducibility or precision is a key requirement for data to be a reliable geochemical exploration tool. Clay separation may require pre-drying and screening (-180 or -106 micron) before the clay separation procedure can be performed. Please contact ALS to discuss options.

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Miscellaneous procedures

Some procedures may be used when specialised preparation or sample compositing is required. Specialised preparation includes the use of additional washes during preparation, homogenisation, and re-bagging of samples. An hourly labour charge may apply to time-intensive projects.

What are washes?

A preparation wash is the term used when barren material, i.e. a rock that doesn’t contain any economic elements, is prepared between regular samples. These are inserted as a routine part of the ALS procedure at the beginning of each batch, but they can also be added on request after highly mineralised intervals, and are a good way of reducing the potential effect of carry-over between successive samples.

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Frequently asked questions

  • How much clay fraction material is produced with the screen clay separation method?

    The clay-sized material produced by the clay specific separation method is in the range of one to several grams of material. This method is therefore not recommended for preparing samples for a method that requires large aliquots of material. The weight of clay-sized material recovered is also highly dependent on the material being separated – the clay-sized material that is separated can be dominated by actual clay minerals. When sampling high energy fluvial and aeolian environments, the clay fraction has often been washed or blown away prior to sediment deposition. These sample types may not produce enough clay-sized material for analysis, so particular care should be taken to optimise sampling locations to collect field samples from a clay rich location.

Downloads

pdf

ALS Sample Preparation Quality Control Technical Note

21 JUL 2022

Related resources

Fluorescência de raios X portátil (pXRF)

pXRF analysis on prepared samples

A portable XRF (pXRF) scan performed on samples after preparation provides timely geochemical information and is ideally paired with quantitative laboratory data.

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Serração de núcleos

Core sawing and photography

ALS offers a wide range of core services including cutting, sampling and photography.

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Webtrieve

Webtrieve access

Routine internal quality control verifications conducted by ALS to ensure all methods are performing as expected can be viewed within Webtrieve™.

LEARN MORE about Webtrieve access