COMPOSITION AND TRANSFORMATIONS OF THE Os-Ir-Ru SYSTEM MINERAL MICROINCLUSIONS IN ANCIENT GOLD JEWELRY
Morphology, composition and transformations of Os-Ir-Ru mineral micro-inclusions have been examined in jewelry gold of archaeological artifacts related to the Early Iron Age. Burial mounds - sources of studied artifacts are located at the South Urals and the Azov Sea region, both near ultramafic belts which served as a primary source of metal for the gold-platinum-bearing placers. In five studied cases, micro-inclusions as large as 15-50 mkm in size (the primary ones) are surrounded by a halo of smaller nano-scale particles. These secondary nano-inclusions are distinguished by the lowered content of osmium (10-20 %), as compared with primary micro-particles containing 30-50 % of osmium. It is assumed that formation of the halo of fine particles was caused by cracking of micro-inclusions while the gold melting. Decrease of the osmium content in these scattered particles may be explained by Os oxidizing under effect of overheat air in numerous pores of the gold melt.