ИСТИНА

Fluid inclusions were studied in quartz from quartz-carbonate gold-bearing veins hosted by metamorphic rocks of six gold deposits in Northern Transbaikalia (Uryakh, Dogaldyn, Pervenets, Verninsk, Sukhoy Log and Irokinda). Generally, 3 types of fluid inclusions are contained in quartz from all deposits, namely, type 1 – high-to medium density, vapor-rich CO2 inclusions, type 2 – aqueous carbonic inclusion and type 3 – aqueous two-phase inclusions. CO2–rich type 1 inclusions homogenize into the liquid phase at temperatures between -32.4 and +30.8 °C and show TmCO2 between -56.9 and -62.3 °C due to additional minor amounts of N2 and CH4 in the inclusions. The densities of type 1 inclusions vary between 0.54 and 1.09 g/cm3. Aqueous carbonic type 2 inclusions show Th between +179 and +380 °C and salinities of 1.4-8.6 wt. % eq. NaCl. Aqueous two-phase type 3 inclusions contain MgCl2 and NaCl and show Te values between -25 and -34 °C and Tmice between -2.2 and -12.0 °C, corresponding to salinities of 3.7 to 16.0 wt. % eq. NaCl. Th values of type 3 inclusions fall into the temperature range between +128 and +385 °C. In addition to the above, there are multiphase H2O-NaCl-CaCl2-rich inclusions hosted in early quartz of the Irokinda deposit. Multiphase inclusions show halite disapearance between +320 and +389 °C and Th between +280 and +453 ºC. The liquid phase of multiphase inclusions has Te values of about -55 °C and salinities of 39.8-46.3 wt. % eq. CaCl2-NaCl. Raman spectroscopy proves there to be nitrogen (0.8-0.6 mole%) and methane (0.1-0.01 mole%) besides CO2 in gas-rich inclusions in quartz of the Irokinda deposit. Calcite, rhodochrosite and siderite were identified in multiphase inclusions as anisotropic phases. High concentrations of Br in the liquid phase of multiphase inclusions were proven by crush-leach analyses. The δ13CCO2 values of fluid inclusion gases of five deposits (Uryakh, Dogaldyn, Pervenets, Verninsk, Sukhoy Log) range between -5.5 to -1.9 ‰ and yield a magmatic and/or metamorphic source for CO2. However, the d13CCO2 of gas-rich inclusions in quartz from the Irokinda deposit are more positive (-0.6 to +0.7 ‰) suggesting that CO2 was probably derived by decarbonization of limestones. The data obtained revealed evidence that fluids of deep crustal origin were the source of gold deposits in Northern Transbaikalian.