AU-197 MOSSBAUER STUDY OF AU2S AND GOLD ADSORBED ONTO AS2S3 AND SB2S3 SUBSTRATES

Au-197 Mossbauer spectra were measured for crystalline Au2S and for gold adsorbed onto colloidal As2S3 and Sb2S3 substrates. The spectrum for Au2S is characterised by a quadrupole split doublet which has been deconvoluted into two overlapping doublets. The spectra for adsorbed gold on colloidal As2S3 and Sb2S3 are similar in appearance to that of Au2S and have isomer shifts (IS) and quadrupole splitting (QS) values which are characteristic of gold in the +1 oxidation state, coordinated to two sulphur electron donors in an approximately linear geometry. The Au-197 Mossbauer data confirm that the gold occurs on the As2S3 and Sb2S3 substrates as a surface complex and has not been electrochemically reduced to elemental gold (Au0). These data further emphasize the role of surface chemistry in the scavenging and concentrating of gold by sulphide mineral surfaces from hydrothermal fluids in high-temperature ore-forming systems (e.g., epithermal environments), as well as in seafloor hydrothermal systems, where sulphide minerals are precipitating near the seafloor-seawater interface.