Postorogenic Granitoids of the Polousny Range (North-East of the Verkhoyansk-Kolyma Orogenic Region)

Abstract

The article considers the petrology of postorogenic Albian subvolcanic granites of the North-Elikchan and Upper-Elikchan massifs of the South-eastern part of the Polousny synclinorium, which involved Au-Ag and Sn-W mineralization. Structural and textural features of magmatic rocks indicate a multievent pulsation intrusion of a granite melt. Typomorphic features of minerals of the rocks: the presence in rhyolite and granite porphyry of restites of pyroxenes, identical to pyroxenes of derivatives of basite - hyperbasite associations, chromium-containing native iron, zircons of crust-mantle morphotypes D and J, and the presence of globules of rhyolite composition in the matrix of dikes of trachidolerites formed after subvolcanic granites, indicate the interaction of crustal granite melt and alkaline-basic mantle melt in the process of evolution of magmatism. Crystallization of the granite melt at the early magmatic stage under conditions of high activity of oxygen, water and chlorine caused the formation of Au-Ag ore occurrences. During the late-magmatic stage, the crystallization proceeded from water-saturated melt under conditions favorable for the formation of rare-metal mineralization with the leading part of the borum. Subvolcanic and host rocks are transformed into quartz-tourmaline greisen with topaz and fluorite, tourmaline-containing exogreisens and tourmalinites, and are penetrated by quartz veins with cassiterite, wolframite, and arsenopyrite. The sharp increase of the borum content is presumably related to the supply of volatiles from an external mantle source.