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Russian Geology and Geophysics

2004 year, number 8


L.B. Damdinova and F.G. Reyf
Geological Institute, Siberian Branch of the RAS, 6a ul. Sakh'yanovoi, Ulan Ude, 670047, Russia
Keywords: Mineralization, beryllium, fluid inclusions, thermometry, microanalysis, role of CO2, Ermakovskoe deposit
Pages: 928-941


Based on geological, mineralogical, and petrographic data and results of thermometric and microanalytical (electron probe microanalysis and atomic-emission spectroscopy) studies of fluid inclusions (FI), the major factors have been established which determined the composition and Be content of various types of veinlet mineralization at the Ermakovskoe F-Be deposit. Despite a great difference in the composition of vein filling (ores of types I and II), the parageneses in all near-fracture metasomatites are the same. In limestones, they form diffusion-metasomatic fringes composed of predominant fluorite, subordinate K-feldspar, calcite, quartz, apatite, spodiophyllite, and phenakite (up to 4%). In aluminosilicate schists, the veinlet fringes are 0.6 cm thick; they are dominated by K-feldspar, albite, and, to a lesser extent, dolomite and calcite, bear minor fluorite, and lack phenakite. These schists bear nearly barren veinlet mineralization of type II, which is due to the effect of the wallrock lithology on the composition of near-fracture metasomatites. Beryllium mineralization of type II occurs only in carbonates, though it is also poorer in Be than the ores of type I because of the low content of phenakite in the vein filling.
As the composition of veinlets does not depend on the lithology of the host rocks (in contrast to the composition of near-fracture metasomatites), the minerals seem to have deposited in fractures as a result of cooling of hydrothermal solutions. But the ores of types I and II are characterized by close temperature ranges of formation ( ~ 300-150 and 360-90