For geochemical exploration of the base metals, we recommend aqua regia digestion of the sample and multi-element analysis by ICP-OES (Method 511P). The package can be upgraded by ICP-MS- analysis to include larger set of elements and lower detection limits (Method 511PM).
Although aqua regia is a powerful leaching agent, it still produces a partial dissolution for many elements. The dissolution of silicates and refractory minerals (e.g. baryte, chromite and other spinelles, zircon, cassiterite, tourmaline) varies depending on various factors. Most of the sulphide and oxide minerals (ore forming minerals) are, however, dissolved. The data will also give information on alteration and weathering of rock and till samples.
When precious metal data is required the option is a multi-element package using ICP-OES and ICP-MS analysis (515PM). The method uses larger subsample size giving more representative sample for analysis. This package will give totally 39 elements.
Rare elements including rare earth elements can be analysed using multi-acid total digestion and ICP-OES and ICP-MS –analysis (307PM).
If only precious metal analysis (Au ,Pd, Te) is required for geochemical exploration, we recommend aqua regia leach, followed by pre-concentration by Hg co-precipitation and analysis by GFAAS (Method 521U; 5 g subsample). Sub-ppb detection limits can be attained for Au and Pd giving meaningful anomaly contrasts. Alternatively a larger sample weight of 20 g can be used (Method 522U). The methods are applicable to non-mineralised samples (till, weathered bedrock, stream sediments, humus, rock).