Metal content of ore-forming solutions of the Ermakovka beryllium deposit (Western Transbaikalia)

Thermometry and atomic-emission spectroscopy of individual fluid inclusions (FI) unsealed by laser pulse were used to study the salt and metal content s of solutions responsible for the formation of rich phenakite-bertrandite- fluorite ores and K-feldspar-fluorite rocks with poor Be mineralization. Th ese rocks form vein zones in aluminosilicate rocks and metasomatic zones in limestones. Results of study of fluid inclusions In fluorite from hydrothe rmalites enriched in phenakite and/or bertrandite allow the following concl usions. At the contact with aluminosilicate rocks and earlier deposited hyd rothermal minerals, ore-forming solutions were enriched in Be (to 2 g/kg so lution), F (to 4.5 wt. %), and B (6-0.9 g/kg), had elevated contents of Na and K (to 2.5 and 9 wt. %, respectively), traces of Ca, Cl, and S, and a va rying amount of Cu (2-0.02 g/kg solution). The concentration of Be under th ese conditions was, as a rule, within 2-0.3 g/kg and could remain at this h igh level mainly at the cost of complexes BeF42- and BeF3-, stable at high activity of F- and K+. Under the conditions of intense interaction with lim estones accompanied by the formation of fluorite and release of CO2, the so lutions became enriched in Ca and CO2 (in places, up to saturation). The ac tivity of their F-, obviously, decreased below the level ensuring stability of the most soluble fluorine complexes of Be. This led to crystallization of phenakite and/or bertrandide and a decrease in Be concentration in the s olution below 0.3 g/kg (down to 0.03 g/kg). At least part of microcline-flu orite deposits and veins with poor Be mineralization was formed by such ,,n onmetaliferous" solutions. The reaction of fluorine-bearing solutions with limestones played a more important role in the formation of rich F-Be ores than a decrease in temperature.