On the possibility of analytical determination of structurally bound gold in sulfide minerals

The idea of a statistical analysis of the distribution of hydrothermally sy nthesized single sulfide crystals using their gold contents is developed sp ecifically to distinguish the structurally bound gold component. Mercury wa s taken as a model example. Similar to gold, mercury shows reduction-aided chemosorption on sulfides, but its speciation can be directly determined by thermal atomic absorption analysis. It was ascertained that the structural ly bound component is best characterized by a set of the lowest values of e lement concentrations with a variation coefficient no higher than 20% (not accounting for the random error of determination). Proceeding from this res ult and from previous data on Au distribution, a scheme was elaborated to p rocess the analytical results for individual crystals in order to character ize the structurally bound Au component. The main requirement for the analy tical method-a combination of a low detection limit and high accuracy-is me t by atomic absorption spectrometry with electrothermal atomization of liqu id or solid samples. The optimum conditions of analysis were determined for sulfide minerals (pyrite, galena, and greenockite). Some modifications of the method were compared, which demonstrated a reasonable agreement for bot h low and high Au contents. The application of the method of direct Au dete rmination in solid samples revealed difficulties in the determination of th e structurally bound Au component at high Au concentrations close to the sa turation limit, and it was necessary to analyze fragments of crystalline in dividuals. A more promising variant of the experimental procedure includes the investigation of phase correspondence in gold-bearing systems with Au-u ndersaturated minerals. The perspectives of the direct determination of Au speciation by the method of a stepwise increase of atomization temperature of solid samples are discussed.