AGE, COMPOSITION, AND SOURCES OF ORE-BEARING MAGMATISM OF THE OROT BERYLLIUM DEPOSIT IN WESTERN TRANSBAIKALIA, RUSSIA

Abstract

The Orot bertrandite deposit is one of the largest deposits in the Western Transbaikalian beryllium metallogenic province. The deposit is associated with alkaline granitoids of the Malokunalei complex and volcanic rocks of the Orot paleovolcano. According to Rb-Sr isotope data, the age of the Orot volcanic edifice is 236.4 ± 3.9 Ma and the age of granitoids of the Malokunalei complex, the host rocks for ore mineralization, is 224.8 ± 1.3 Ma. The formation of bertrandite ores of the deposit occurred in the age framework of granitoids of the Malokunalei complex (about 225 Ma). Magmatic and ore processes at the Orot deposit, as well as graben formation area, were associated with intracontinental rifting. The Western Transbaikalian beryllium metallogenic province and all known Be deposits and occurrences are also related to intracontinental rifting. The positive value of ENd(T) = +2.4 of the granitoids of the Malokunalei complex suggests the existence of a depleted mantle as a protolith source. The magmatic rocks and Be ores of the Orot deposit were formed with the participation of the N-MORB and EMII sources and some addition of rocks of the continental crust made up of granitoids of the Angaro-Vitim batholith and crystalline schists framing the batholith. In comparison with the volcanics, the sources of alkaline granitoids of the Orot bertrandite deposit are more enriched with the EMII components and with crystalline schists. The isotope and geochemical data obtained suggest that the Be mineralization of the deposit is genetically associated with alkaline granitoids.