ALS provides a wide range of methods that are useful when non-standard preparation is required. These methods include compositing samples, adding washes between samples, screening samples with multiple sieve sizes, and performing other non-routine work.
Compositing is the process of combining two or more sample into a single sample. This can be done by volume, core length, or by weight. This method will be performed using instructions provided to ALS.
Carryover is the contribution of elements of interest to a sample from the previous sample prepared (crushed and/or pulverised). The form in which elements of interest occur in a sample will affect the amount of carryover between samples. Smearing of samples caused by highly malleable minerals such as native copper and gold increases the likelihood of carryover significantly more than samples where metals occur within a mineral structure. Even without the presence of highly malleable native copper and gold, there can be some carryover between samples prepared using the same equipment. As part of our standard quality control procedures to minimise carryover, washes (barren material run through the equipment) are added to the crusher and pulverising bowls at the start of each new batch of samples to clean the equipment. The crusher and pulverising bowls are also cleaned with compressed air or a vacuum between every sample to remove any remaining loose material from the equipment. A request to add barren material washes between mineralised samples within a batch can be accommodated and will reduce or eliminate carryover.
When washes are used between samples there is the option to retain the pulp produced, or have it analysed at the same time as the original samples. This can provide useful information about how much carryover is likely occur between mineralised samples and those following.
ALS provides a range of methods for transferring sample to drying trays or new bags, bagging large pulps for storage, and light pulverisation for homogenisation. If any other specialised work is needed this can be performed to your specifications as needed.
ALS preparation laboratories have a large range of screen (sieve) sizes available. These can be used individually or in sequence to characterise the grain size distribution of samples or to use multiple fractions for analysis. Please contact your preparation laboratory before submitting samples for uncommonly used screen sizes so that the lab can ensure the screens are available when samples arrive.
Sieve sizes are referred to in several ways. They can be identified by the diameter of the openings in the sieve in millimetres or microns, or as a Tyler or US number. The numbers of screens in the Tyler and US series are generally not the same so it is important to specify which numbering convention you are using, or preferably identify them by the metric opening size.
The most commonly used sample preparation methods for rock samples offered by ALS are packaged together for convenience.MORE INFORMATION