Observations on new approaches for the determination of platinum-group elements, gold and silver in different geochemical samples from Siberia and the Far East

Some recent experiments on the determination of Au and the platinum-group e lements (PGE) in geochemical samples ore reviewed. Emphasis is given to the determination of ultra-low levels of PGE concentrations in resistant matri ces, including chromites, molybdenites and ultrabasic ores. The problems an d features of PGE determination in samples of various chemical composition are considered. For each sample type studied, a series of sample preparatio n techniques are proposed. These techniques included acid digestion, fusion with sodium peroxide, cold sintering with an oxidizing mixture of Na2O2 Na2CO3 and also oxidizing fluorination with bromine trifluoride. A new appr oach for preparing geochemical material prior to digestion, based on mechan o-chemical activation with simultaneous hyperfine grinding, is proposed and studied. The instrumental determination of PGE contents was carried out di rectly by AAS from extracted organic phases. If was found that a combinatio n of digestion processes was required to achieve geochemical background lev els of Au and PGE concentrations with the following detection limits: Pd, P h - 1 ng g(-1), Pt, Ru - 10 ng g(-1), Au - 0.2 ng g(-1), Ag -0.1 ng g(-1). The uncertainty in PGE and Au determination in geochemical samples is depen dent on metal concentration, and also on their distribution in samples. The total analytical uncertainty of the proposed method is between 15-30%.