DISCOVERY OF A PURE RHENIUM MINERAL AT KUDRIAVY VOLCANO

KUDRIAVY volcano on Iturup island in the Kuril are is an active calc-alkaline volcano. It has not erupted this century; its current volcanic activity is characterized by hot (up to 910 degrees C) gas jets which have been stable for at least 30 years. The composition of the gaseous emissions is typical of high-temperature fumaroles, but we report here the discovery of unusual subsurface sublimates associated with one gas jet-a sulphide mineral containing rhenium as the only cation. To our knowledge, this is the first reported occurrence of a pure rhenium mineral. The concentration of rhenium in the fumarole gas is only 2-10 p.p.b., so the condensation of pure rhenium sulphide from this gas requires both enrichment of rhenium by eight orders of magnitude and remarkable selectivity. Rhenium is generally believed to exist in only trace amounts at the Earth's surface, but our findings demonstrate that it can be readily mobilized, dispersed and concentrated by degassing magmas.