Physical-chemical conditions of the beryl generation in greisens of Orlovskoe deposit (East Transbaikalia)

Ponomareva N. l., Kruzhalin S. V.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2017. V. 146. N 5. P. 20-30

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Language: Russian

Abstract

Principal physical-chemical parameters of the beryl-topaz-zinnvaldite association have been studied from the points determining generation of beryl in ores of Orlovskoe deposits (East Transbaikalia). Microscopic investigations of beryl and topaz made it possible to detect numerous syngenetic gas-liquid and water—carbonic acid inclusions. The homogenization temperature of gas-liquid inclusions in zonal beryl crystals was determined as 275—350 °C, under pressure of 0.9—1.1 kbar. On the base of calculation techniques for chemical thermodynamics, analysis of mineral equilibrium has been carried out for the system K—Li—Mg—Fe—Al—Si—Be—F—H₂O, with estimation of acidity-alkalinity and activity of main components in the mineral-forming media: pH = 7.2, lga_FeOH  –3.5, lga_Li = –2, lga_H4SiO4 = –2, f_HF = 10 bar. Influences of temperature, pH, activities of participating ions upon stability of zinnwaldite, biotite, protolithionite, lepidolite were estimated and determined in terms of chemical thermodynamics.

Key words: rare-metal granites, greisens, beryl, topaz, Li-Fe micas, fluid inclusions, mineral equilibrium.