Platinum Group Elements
The platinum group elements (PGE) or metals (PGM) – ruthenium, rhodium, palladium, osmium, iridium, and platinum – have similar chemical characteristics and behave as a group during geochemical processes. They are strongly siderophile (iron-loving) and chalcophile (sulfur-loving) and are therefore concentrated in the core of the Earth and in iron meteorites, in sulfide ore deposits, and to a lesser extent in the Earth’s mantle. An important geological application of the PGE is the use of iridium as a tracer of meteoritic material, most famously in the development of the meteorite impact hypothesis for the origin of the Cretaceous-Tertiary mass extinction. The isotopic system rhenium-osmium is used to date mafic-ultramafic rocks and as a tracer of processes in the Earth’s mantle. The occurrence of small excesses of PGE in the mantle has been often indicated as evidence of a late contribution of chondritic material to the Earth (Late Veneer hypothesis).