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Geochemistry /

Base metals analysis

Base metals analysis

Global consumption of base metals is increasing due to expanding populations and increases in technological development, including transition to “green” energy. The increased need is driving exploration in both historically explored and new regions. This exploration requires high-quality analysis to improve geochemical vectoring and interpretation. ALS base metal analyses involve rigorous quality control to ensure confidence in results and therefore interpretation based on those results.

Metal base

Four-acid digestion

Historically, much base metal exploration with soils, rocks, and drill samples has involved an aqua regia digestion as it is effective at digesting sulphides – the primary economic host minerals for most base metals. However, four-acid methods are increasingly popular, and many projects benefit from a higher degree of decomposition such as that produced by a four-acid method. Four-acid digestion produces a near total digestion and offers an advantage of being able to report useable data on many of the rock forming elements along with exploration pathfinder elements.

Cuatro digestiones ácidas

Copper Analysis

ALS Geochemistry has decades of experience with some of the world’s largest copper projects. An extensive range of methods are available that are suitable for all major copper deposit types and project stages ranging from exploration to mining and processing. Methods are available with super trace detection limits as described in the Generative Exploration section of this web page through to single element analysis for ore grades up to 100% Cu.

Copper mineral selective leaches

Mineral-selective leaches for copper can be useful at many different stages in a project’s life. Some understanding of the recovery from common processing methods may be valuable during resource evaluation. Established mines may want to produce early metallurgical characterisation with exploration geochemistry during resource extension or infill drilling.

Nickel Analysis

The mineralisation style will constrain which method is needed for nickel analysis. A nickel laterite sample is best analysed by a fusion method followed by lab based XRF. A disseminated nickel sulphide mineralisation may best be analysed with a four-acid digestion or sodium peroxide fusion and digest followed by ICP-AES, ICP-MS or AAS analysis. ALS has a large range of methods which can deal with all types of nickel ore.

Nickel mineral selective leaches

Determining the proportion of Ni present in sulphide mineral phases associated with oxides or as metallic Ni can be an important step in planning a resource extraction processes. ALS has several methods that target nickel sulphides during digestion but leave the oxides and metallic Ni undigested. In combination with detailed mineralogy studies on a subset of samples these methods can identify geometallurgical domains within a resource.

Other Base Metals

ALS has methods for the analysis of all base metals either as part of multi-element packages or stand-alone analytes. These methods range from the super trace methods described in the generative exploration section of this web page to 100% classical chemistry methods.

Ore hosting mineral

The choice of digestion method for any geological sample depends on the mineralogy of the sample. If elements of interest are hosted in minerals that are resistant to a particular digestion, then the total concentration of that element will not be reported. An example of this is tin hosted in cassiterite, which is resistant to acid digestion, even the strong four-acid digestion. Cassiterite requires a fusion decomposition to fully break the mineral down and enable instrumental analysis and reporting of the Sn concentration.

Base Metal Concentrates

Samples are analysed by XRF following lithium borate fusion including the addition of strong oxidising agents to decompose sulphide mineral concentrates. Because sodium is added as part of the oxidising agent it cannot be reported by this method. A loss on ignition determination is needed for the concentrate base metal determination but is not used to normalise results.

Titration methods

Certain ore deposits can have extremely high-base metal concentrations over very short intervals. Where concentrations exceed the upper detection limits in concentrate methods, titration methods for individual elements are available. These methods use specialised digestions with classic chemistry to enable reporting of concentrations up to 100%.

Frequently asked questions

If my sample has native Cu is any special method needed?

Yes. Native Cu can smear on preparation equipment surfaces during both crushing and pulverisation. For this reason, it is necessary to notify ALS when submitting samples that contain native Cu and it may also be necessary to add extra washes during preparation. The addition of washes is described in the sample preparation section of this web page. Analysis for native Cu should also use the metallic screen method as the distribution of malleable native Cu may not be well represented by the fine fraction of a pulverised sample.

Related topics

Generative exploration

Super trace detection methods

Methods that report super trace detection levels are given in the Generative Exploration section.

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