Geological structure, mineralogy, and genesis of the Zhelannoe quartz deposit (Pripolyarnyi Urals, Russia)

The Zhelannoe vein quartz and rock crystal deposit are unique in their geol ogical structure, scale and high quality of ore mineralization and mineral product. The economic ores of the deposit are enclosed in monomineralic qua rtzite-sandstones of Early Ordovician age. At the base of giant quartz vein s, almost monomineralic serieitic rock bodies (serieitoliths) containing la rge amounts of rutile, zircon, and REE minerals occur. The origin of seriei toliths is not metasomatic according to some geological and mineralogical e vidence. A model of synchronous deposition of the serieitoliths and vein qu artz is proposed based on detailed geological, mineralogical, and geochemic al study of the deposit. The model implies a liquation of the hydrothermal solution and consequent sedimentation of some of mineral substance in tecto nic cavities. The consequent crystal formation was not accompanied by addit ional introduction of hydrothermal solution, but was caused by decreasing p ressure in reopened cavities and by reactions between minerals and undersat urated solution that was residual after deposition of the vein quartz and s erieitoliths. The economic concentration of rutile, zircon, and REE mineral s and the high concentrations of Cr, W, Th, and Nb are determined for the f irst time in the serieitoliths.