Some observations on the determination of gold and the platinum-group elements in black shales

This research compares various ways of applying oxidative chemical decompos ition to the analysis of gold-bearing black shale ores from the Russian Nat alka and Sukhoj Log deposits. This study was conducted as part of the certi fication program for the Russian candidate black shale reference materials SLG-1 and SCHS-1 and also because of the paucity of data available on the d etermination of the platinum group elements (PGE) in analogous sample types . We report direct evidence of PGE volatilisation from black shale material s when processed in the presence of oxygen. We also developed a comprehensi ve analytical scheme for the quantitative determination of PGE in all phase s (gaseous and ash) produced during slow combustion of carbonaceous materia ls in oxygen. This study has shown that during combustion in oxygen at 600 degreesC, PGE contained in the Natalka black shale ores are lost as gaseous reaction prod ucts. Thus, the volatilized PGE (recovered in traps) account for up to 14% pt, 40% Pd, 40% Ru and 10% Ir relative to their total concentrations in a c arbonaceous concentrate. It was also established that in the process of com bustion, Au quantitatively remains in the ash cake. In order to avoid the deleterious effects of oxygen on the volatility of th e PGE, we propose a new comprehensive sample decomposition method based on the application of fluoroxidants such as BrF3 and KBrf(4). This method was validated using samples of black shale ores and their processing products b y comparing our results with those obtained independently using sealed auto clave processing of the same materials. It was shown that PGE in black shal e ores and their processing products not only exist in commercially exploit able quantities but that a small proportion of PGE compounds are soluble in alcohol. We propose that in gold-bearing black share ores, PGE are present as organometallic compounds.