MINERALOGICAL-PETROGRAPHIC FEATURES OF SYENITIC MIGMATITES OF THE ILMENOGORSKY MIASKITE BLOCK (SOUTH URALS)

Abstract

Syenitic migmatites of the contact of the Ilmenogorsky miaskite block are characterized by high (>500 ppm) contents of REEs, which are mainly hosted in fluorapatite and titanite of the leucosome. Apatite exhibits zoned and sectorial composition with decreasing REE and Si contents and increasing Cа, P, and F contents from central parts to the margins indicating the change in physicochemical conditions of mineral formation. The La/Nd ratios of REE-bearing fluorapatite indicate that apatite-1 formed from a F-bearing fluid in contrast to apatite-2 formed from an alkaline, F–CO2–SO3-rich fluid during albitization. The REEs and F released by alkaline metasomatism accumulated in late generation of REE–F-bearing titanite. Migmatization of rocks was accompanied by involvement of an alkaline F–CO2–SO3-bearing fluid.

Keywords

• syenitic migmatites
• alkaline metasomatism
• f–co2 –so3 -bearing fluid
• reebearing fluorapatite
• ilmenogorsky miaskite block