ALS offers a range of individual preparation methods that can be combined as needed to customise a preparation routine to meet a specific project's needs. Samples submitted as rocks (drill core, rock, or chips) generally require drying, crushing, splitting, and pulverisation. All these steps have a range of options available. Samples submitted as soils and sediments can also be prepared by customised methods for variable screen sizes and drying temperature.
Sample drying is required before any crushing, pulverisation or screening as moisture in the sample can cause sample to adhere to the equipment. Drying rock samples is generally performed at temperatures >100°C, but lower temperature options are available if required. Soil and sediment samples are dried at a maximum temperature of 60°C to preserve volatile components, but air-drying is also available.
Methylated Hg, HgCl2 and Hg0 volatise at less than 100°C thus drying temperatures need to be kept low for samples expected to contain mercury. Where mercury is hosted in cinnabar the same temperature limits are not necessary as it is resistant to volatilisation at higher temperatures.
ALS has a crushing method for large diameter samples that need a step to reduce material size before standard crushing. Fine crushing of material is required for samples that need to be split and pulverised. There are numerous methods with a variety of size and passing percentage requirements available.
The choice of a % passing a certain screen size is best identified by test work on for each project. The preparation requirements will be controlled by the grain size of minerals of interest, how large a sample is submitted, and how much sample is separated out for each size reduction step.
ALS offers splitting methods using a riffle or rotary splitter. Rotary splitting can be paired with size reduction using a Boyd crusher. We also offer splitting methods for samples received as pulps.
A rotary splitter involves a vibrating feed chute that delivers crushed material to a divided rotating sample catcher. The amount of sample needed is then combined from the required number of sample compartments. Samples with nuggety or native metals may not be optimally split this way as the vibration in the chute can segregate heavy minerals. A riffle splitter will divide samples into two equal portions. Reducing the amount of material needed after splitting requires multiple passes through a riffle splitter but can be achieved with a single rotary splitter pass.
ALS has pulverisation methods for a range of sample sizes and passing criteria. Larger sample sizes are often needed when a sample contains nuggety gold. The larger sample size will help minimise nugget effect and produce a more representative sample.
A variety of pulverisation bowls constructed from diverse media are available on request. The standard equipment used at ALS preparation laboratories is low Cr-steel, however substitution of bowl material type may be required when specific elements that may be imparted by Cr-steel equipment are of interest. All crushing and pulverising equipment will impart some elements to a rock sample and if the low-Cr steel is likely to add an element of interest, an alternative bowls can be chosen. Bowls available include tungsten carbide, agate, and zirconium.
|DRY-21||Drying of rock samples||Default drying method for most drill core, rock, and chip samples|
|DRY-22||Drying of wet samples in drying oven with a maximum temperature of 60ᵒC||Soil and sediment samples that will be analysed for volatile elements|
|DRY-23||Air-drying of samples||Soil and sediment samples for some selective leach procedures|
|CRU-21||Coarse crushing of rock and drill samples||Used as a preliminary step before fine crushing. Applicable for large dimension samples. There is no QC performed for this method as the full sample is fine crushed. If QC is required please use CRU-21q for >70% passing 6mm|
|CRU-31||Fine crush of rock, chip and drill samples to 70% passing 2mm||Drill core, rock and percussion chip samples|
|CRU-36||Fine crush of rock, chip and drill samples to 85% passing 2mm||Drill core, rock and percussion chip samples|
|CRU-32||Fine crush of rock, chip and drill samples to 90% passing 2mm||Drill core, rock and percussion chip samples|
|SPL-21||Split sample using a riffle splitter||Standard splitting procedure|
|SPL-21X||Split sample using a riffle splitter. Return or archive sample without analysis|
|SPL-22||Split sample using rotary splitter||Rotary splitting procedures|
|SPL-22X||Split sample using rotary splitter. Return or archive sample without analysis|
|SPL-22Y||Split sample using a Boyd crusher/rotary splitter combination|
|SPL-34||Split pulp for various analysis||Pulp splitting procedure|
|PUL-31||Pulverise a split or total sample up to 250g to 85% passing 75 microns||Default procedure for samples that are finely crushed and split to 250g or less|
|PUL-32||Pulverise a 1kg split to 85% passing 75 microns||Large sample size to mitigate nugget effect|
|PUL-32a||Pulverise a 1kg split to 90% passing 75 microns|
|PUL-21||Pulverise entire sample to 85% passing 75 microns||For samples up to 3kg|
|PUL-23||Pulverise up to 3kg to 85% passing 75 microns. For samples >3kg additional costs are incurred to split the sample prior to pulverising and retaining the remainder.||Appropriate for RC drill chip samples that do not require crushing|
|PUL-24||Pulverise up to 3kg to 85% passing 75 microns. For samples >3kg additional costs are incurred to split the sample prior to pulverising and discard the remainder.|
|PUL-51||Pulverise up to 100g concentrate sample to 85% passing 75 microns||This method includes careful cleaning of the pulverising bowl after grinding|
|PUL-34||Pulverise 200g to 85% passing 75 microns||Appropriate for high grade material|
ALS has a variety of bowls available for pulverisation but it is wise to contact the laboratory before submitting samples so they can ensure the required equipment is on hand to process your samples. This will minimise the chance of delays in processing.