Conditions of the Formation of Iron–Manganese Mineralization at the Poperechny, Kostenga and Kaylan Deposits in the Lesser Khingan Ore District (Jewish Autonomous Region, Russian Far East)
摘要
The article discusses the magmatic–hydrothermal model for the formation of iron ore (with manganese) mineralization within three large (Poperechny, Kostenga, Kaylan) deposits in the Lesser Khingan ore district of the Russian Far East. Iron–manganese ores in these deposits form pseudostratified lodes in the Vendian–Cambrian carbonates and are associated with magmatic breccias (fluidolites), magnetite lavas, and mineralized tuffs. The ore-magmatic complex is significantly younger (125 ± 21 Ma 190Pt–4He age of isoferroplatinum from magmatic breccias) than host carbonates and is characterized by a complex mineralization: in some cases, magmatic rocks crosscut hydrothermal ores and form pseudolaminated members with the latter, while in the other cases, they have been subjected to hydrothermal alteration and ore formation themselves. Both magmatic rocks and ores contain numerous silicate, iron-oxide, and Cu–Ag–Au microspherules, suggesting involvement of explosive processes in the formation of these deposits. Host carbonates are locally altered with the formation of skarn minerals and partial melting of dispersed material, which we interpret as the result of local breakthroughs of high-temperature fluid associated with ore formation. Geochemical characteristics indicate a general postsubduction character of the explosive magmatic rocks in these deposits, while Nd–Sr isotope systematics suggests their contamination by continental crust. The proposed model for the iron ore (with manganese) mineralization in the studied deposits is based on the possible existence of a magmatic–hydrothermal ore-forming system in the Lesser Khingan district during the Hauterivian–Aptian, characterized by intense explosive activity against the background of hydrothermal ore formation. This system formed above the slab breakoff after cessation of the Jurassic–Neocomian flat subduction of the oceanic plate beneath the Bureya–Jiamusi–Khanka superterrane and intensification of tectonic movements along the Tan-Lu strike-slip fault system.