CONDITIONS OF FORMATION AND ORIGIN OF RIPHEAN ILMENITE-TITANOMAGNETITE DEPOSITS IN THE URALS

Abstract

Principal compositional features of Riphean gabbroids and associated titanomagnetite deposits on the western slope of the Urals are generally related to P-T conditions and the fluid regime of their formation. At low fluid pressure and high temperature (PH2O = 1-3 kbar, T = 900-1100°C, -logfO2 = 15-10), high-titanium magnetite with 10-15% TiO2 crystallized from an Fe- and Ti-rich basic magma. The magnetite accumulation formed thin extended reeflike bodies (deposits in the Kopan' and Matkal' massifs). In the presence of aqueous (+ chlorine) fluid at a high water pressure and lower temperature (PH2O = 6-7 kbar, T = 600-1000°C, -logfO2 = 18-11), both ilmenite and magnetite crystallized in similar reeflike bodies, resulting in the formation of ilmenite-titanomagnetite ores with magnetite containing 3-9% TiO2 (deposits in the Medvedevka and Kusa massifs).