Native iron (–platinum) ores from the Siberian Platform trap intrusions

Abstract

Native iron occurs in two forms: terrestrial (telluric) and meteoritic. The former was considered to be poor in trace elements, whereas the latter contains varying amounts of Ni–Fe alloys, including kamacite, tanite and awaruite. In the late 1950s, native iron was discovered in the Siberian Platform trap intrusions, although it is only recently that geologists became interested in native iron from the traps. We provide a brief description of intrusions containing native iron and a detailed description of its occurrence, species, mineralogy and geochemistry of ore-forming and accompanying typomorphic chemical elements. A study of Siberian native iron shows wide variations in composition from Ni-free iron to awaruite and its intergrowth with a number of minerals. Globules of glass with a ‘liquid-in-liquid’ structure were recognised in native iron and analysed. Immiscible liquids have the compositions of ferruginous and high-silicon melts which are similar to that of ferrogabbro and granophyre. Isotopic compositions, such as 4He/3He, δ13CPDB, 87Sr/86Sr, 87Rb/86Sr of native iron and host-rocks suggests participation of continental-crust material in ore formation. Native iron was found to contain high concentrations of Cu, Ni, Co, Pt, Pd, Rh and Ge. The existence of a new Fe (–Pt) type of ore is established for the first time. Native iron and related Fe (–Pt) ores formed in feeder columns as a result of the interaction of tholeiite-basalt melt with fluid reservoirs of sedimentary rocks in the platform cover. Hydrocarbon fluids and organometallic compounds play a leading role in ore formation. The finding of Fe (–Pt) ores open up new possibilities for discovering new types of ores in large igneous provinces, in which hydrocarbons are of major importance.