FERROHÖGBOMITE-2S2N IN THE DIATEXITES OF WESTERN SANGILEN, SOUTH-EASTERN TUVA, RUSSIA

In the Western Sangilen (Tuva–Mongolia microcontinent, Central Asian Orogenic Belt, Russia) rare mineral ferrohögbomite-2S2N, for first time, was found in a deep-seated contact aureole of early Paleozoic Bayan-Kol gabbro-monzodiorite intrusion. The rocks are diatexites roof pendant, where metamorphics gabbronorite. Diatexites formed as result strong melting and desilication quartz-bearing kyanite-staurolite schists (M1) during progressive thermal metamorphism (M2) near intrusion with peak at 950 °C, 7–8 kbars. Ferrohögbomite-2S2N grains up to 50 μm size ilmenite-corundum-magnetite-hercynite pseudomorphs. later stage M2 after regional staurolite M1 cordierite-gedrite-plagioclase restite blocks diatexites. Ferrohögbomite also appeared thin (1–5 μm) rims around individual hercynite, corundum magnetite rock matrix. According microtextural features ferrohögbomite post-peak metamorphic minerals A univariant reaction ferrohögbomite-2S2N formation calculated quantitatively Fe-Al-Ti-Zn-H 2 O system program Mathematic 9.0 using electron microprobe chemical composition is 0.96Spl+0.194Ilm+0.116Mag+0.036Crn+0.163H O=0.163Hgb. local equilibrium value probably correlated pseudomorphs thus do not transcend 1 mm 3 . Thermobarometry yields temperature pressure T=665 P=5.8 kbar, which correspond late retrograde To present day Russia, högbomite group known only on South Urals Aldan Shield Eastern Siberia.