Technical innovations in geochemistry
By Brenda Caughlin, vice-president, Technical Services – ALS Minerals, Vancouver
Technical innovation is one of the cornerstones of the ALS Group. The ALS geochemistry team continues to exemplify this value through several recent initiatives aimed at improving service to our clients.
In the coming year, there is an expectation that clients in mineral exploration will be focused on soil analysis and will require lower detection limits on routine methods to define targets for further work. Recognizing this coming trend, the geochemistry group put in place a coordinated development plan to meet clients’ needs.
First, to improve sample preparation turnaround time, new soil preparation stations were installed in several laboratories.
These stations are necessary to prevent cross-contamination from higher-grade rock samples received in the laboratory.
The gold detection limit from an ICP-MS method designed for soils was lowered by rapid development of a graphite block heating and shaking system, and by improved sample introduction to the ICP-MS. The graphite block fits disposable plastic bottles which reduce carryover contamination between samples during digestion, and the block shaking system is robust, providing reliable productivity and automation on a previously labour-intensive task. Syringe pump systems coupled to the ICP-MS reduce background noise and improve precision.
Detection limits for other key elements in soils by ICP-MS analysis were reduced by factors of 10 to 100. The ICP-MS is operated in collision cell mode to remove spectral interferences, and fitted with a thermally controlled spray-chamber utilizing online dilution in order to significantly reduce background signal and memory effects in the instrument. This has the added benefit of reducing the time required to analyze each sample.
Finally, ALS Geochemistry has developed a rapid, high-quality clay-size fraction separation on screened soils. The clay fraction in soils may be analyzed to enhance subtle geochemical signals, or used in other cutting-edge exploration techniques. The screened soil is combined with water, sonicated to suspend very fine particles in solution, and centrifuged in two steps to isolate the clay fraction. The increase in signal for a few key elements can be seen in the accompanying graph.
This work represents a co-ordinated plan of service delivery through improvements on existing facilities and methods, and implementation of new technologies to benefit our clients. And most importantly, this work was done by a global team with members from labs around the world.