Carbonates and sources of fluids in ores and metasomatites of the Ermakovka fluorite-bertrandite-phenacite deposit (western Transbaikalia)

We present results of isotope-geochemical study of the Ermakovka F-Be deposit, including data on the oxygen and carbon isotope compositions in dolomite and calcite marbles and in carbonates accompanying skarns, of early and late stages of ore formation and of post-ore parageneses. To elucidate the sources of fluids participated in the ore formation, we calculated the oxygen isotope composition in water and the hydrogen isotope composition in hydroxyl-containing minerals. Phlogopite in marbleized dolomites, vesuvianite and amphibole in skarns, eudidimite and bertrandite in ore parageneses, and bavenite formed during post-ore processes are analyzed. Most of the ore-stage minerals are depleted in heavy oxygen. Their 5¹⁸O values are lower than 5-6%c (SMOW). Oxygen in carbonate minerals of the initial stage (dolomite and bastnaesite) is heavier (1.3-4.9%c) than that in calcite (+ 2 to -3.7%c). The 5¹⁸O values of water in equilibrium both with carbonate and with silicate minerals (-4 to -14%c) suggest the contribution of meteoric water to the mineral formation. A magmatic fluid (5¹⁸O from + 6 to + 9%c) participated in the skarn formation at the initial stage, and a meteoric fluid, at the final stage (5¹⁸O from -1 to -9%c). A meteoric source is confirmed by the depleted hydrogen isotope composition in minerals (5D from -119 to -192%c).