FEATURES OF COMPOSITION OF IMPURITIES IN BERYL CRYSTALS OF VARIOUS COLORS OF TRANSBAIKALIA

Abstract

The relevance of the work lies in the study of the features of the chemical composition of beryl, which is an important source of beryllium and gemstone, the gemological properties of which are determined by the concentrations and forms of occurrence of impurity chemical elements. The aim of the study is to determine the content of impurity chemical elements in beryl crystals of various colors, the relationships between them and the relationship with the conditions of formation. Objects of the research are crystals of beryl of different colors of greisen (Sherlovaya Gora, Spokoyninskoe) and pegmatite (Orlovskoe, Sachanayskoe) fields. Methods of the research are neutron activation and ICP MS. Results. The authors have established a wide range of concentrations of impurity elements in 31 beryl crystals of various colors, siderophyllite-quartz (Spokoininskoe deposit of tungsten) and mica-beryl-topaz-quartz (Sherlovaya Gora) greisens, as well as rare-metal (Orlovskoe) and chamber pegmatites (Sakhanayskoe). Beryl crystals of mica-beryl-topaz-quartz (Sherlovaya Gora) greisens are characterized by low sodium and cesium contents in comparison with those of siderophyllite-quartz greisens and pegmatites. Rubidium is approximately equally present in beryl crystals of all the studied deposits, regardless of color. For the first time, gold was found in them, the contents of which tend to be associated with cobalt and zinc. The content of arsenic, the isomorphic incorporation of which into beryl is unlikely, also shows a correlation to the bond with zinc and cobalt. The highest iron contents are found in yellow, blue and yellow-green crystals, entering both tetrahedral (blue) and octahedral positions (green, yellow, and yellow-green). The content of uranium and thorium is higher in the crystals of beryl greisens (Sherlovaya Gora, Spokoininskoe) in comparison with pegmatites. Their contents tend to be interdependent when thorium predominates over uranium. Uranium has bonds with iron, the highest concentrations of which are inherent in zonal crystals with breaks in growth. Thorium is associated mainly with zircon, which is confirmed by the positive correlation of its contents with hafnium. A relatively wide range of impurities in beryl crystals is due to differences in the conditions of formation (greisens and pegmatites) and the geochemical features of the mineral-forming fluid systems reflected in the composition of fluid inclusions.

Keywords

• beryl
• trace elements
• relationships between trace elements
• greisens
• pegmatites
• sherlovaaya gora
• orlovskoe deposit
• spokoininskoe deposit
• sakhanayskoe deposit