ИСТИНА

In the drillcore of the Kola super-deep borehole (SG-3, 12262 m depth) gold bearing rocks of Archaean age have been located at depths of 9.5-11.0 km. These rocks were overprinted by Proterozoic regional amphibolite faces metamorphism at 500-650 °C and 3.5-6 kbar. Quartz veins, located between 9052 and 10744 m, within this gold zone, contain fluid inclusions with exceptional gold concentrations as high as 1500 ppm as colloidal particles. There are 4 types of fluid inclusions (FI’s) : 1) gas inclusions of dense CO2, 2) liquid-vapour two-phase aqueous inclusions, 3) three-phase inclusions with NaCl daughter crystals, and 4) CO2 - aqueous inclusions. CO2 FI’s homogenized into the liquid phase at temperatures ranging from +30.8 to -45.0 °C with TmCO2 from -56.7 to -60.3 °C and a density of 0.37-1.14 g/cm3. The salinity of the aqueous phase of vapour FI’s is 3.4-4.1 wt. % eq. NaCl. The composition of the gas phase of these inclusions was determined by Raman spectroscopy indicating a small amount of nitrogen (3.3-1.9 mol %) is present in the carbonic phase of all gas inclusions throughout the section under consideration, but methane and hydrogen sulfide are absent. Microthermometry indicates the two-phase inclusions are brines containing Na, Ca chlorides with Te from -55 to -74 °C and Tmice from -20.7 to -63 °C, corresponding to salinities of 21.6 to 30.2 wt. % eq. CaCl2, Th was between 137-228 °C. Three-phase inclusions have Thhalite between 123-381 °C and Thvapour 137-264 ºC. They also contain Na and Ca chlorides with Te of c. -64 °C and salinities of 25.9-45.4 wt. % eq. NaCl. CO2 aqueous inclusions have Th between 203-356 °C and salinities of 3.6-18.8 wt. % eq. NaCl. Individual FI’s analysed by LA-ICP MS, indicates the elemental ratios of the 4-FI types are reasonably consistent and confirm the major cations are Na, K and Ca, with several 100’s to a few thousand ppm of Fe, Cu, Zn, Pb in the higher salinity fluids. However, there are extremely high concentrations of Au in all FI types analysed. In the high salinity FI’s the average concentration is c. 300 ppm and as high as 1500 ppm. These measurements are consistent with results of an experimental study of gold in synthetic fluid inclusions by Hanley et al. (2005), that at 600 °C and 1.5 kbar may exceed 1000 ppm. We suggest these fluids could be a precursor of “Orogenic gold fluids” which, at the Au concentrations detremined, would reduce the requirements for large volumes of metamorphic fluids to form such ore deposits. The gold is currently present as colloids and may be proof that such a state can transport greater amounts of gold than true solution.