Native Iron in Siberian Traps

Abstract

The study of trap intrusions with a large-scale occurrence of native iron allowed us to identify general features in their composition and origin. Intrusive bodies are weakly differentiated and have similar structure and mineralogical, petrochemical and geochemical composition. Two associations of rock-forming minerals were found in all studied bodies: early deep-seated (pre-chamber) and intra-chamber. Native iron forms nodular segregations, with a subordinate amount of cohenite, troilite and magnetite–wüstite. Metallic iron can accumulate Ni, Co, Au, and PGE. Their content in metal increases by hundreds or even thousands of times compared to host silicate rock. The formation of native iron is based on the fluid-magmatic interaction between magma and reducing components of the fluid, mainly of methane–hydrogen composition. As a result, an initially homogeneous basalt liquid is dispersed into silicate and metallic components. In the course of transportation, finely dispersed iron phases form droplet-liquid segregations with a monomolecular gas layer on their surface, thus preventing enlargement of metallic droplets. In the hypabyssal chamber, magma, including metallic spherules, is degassed, and droplets are merged to form nodular segregations of native iron.