ИСТИНА

Core from the Kola super-deep borehole (SG-3, 12262 m depth) contains Archaean age gold-enriched rocks at depths between 9.5 and 11.0 km, originally at c. 17 km. These were overprinted by Proterozoic regional epidote-amphibolite facies metamorphism at 500-650 °C and 3.5-6 kbar. Fluid inclusions (FI) in vein quartz from 9907.5 m, within the gold enriched interval, are 3 distinct types: 1) gas inclusions of dense CO2, salinity c. 4wt. %-eq, 2) L-V aqueous inclusions, with salinities of c. 28 wt. % eq. NaCl2, Th between 137-185°C and 3) L-V-S inclusions (halite) with salinities of c. 31 wt. % eq. NaCl, with Thhalite from 231-123 °C and Thvapour from 107-185 ºC. Elemental ratios (LA-ICP-MS individual FI’s) of the 3-FI types are reasonably consistent and confirm the major cation are Na, K and Ca, with several 100’s to a few thousand ppm of Fe, Cu, Zn, Pb in the higher salinity fluids. There are extremely high concentrations of Au in all FI types, the high salinity FI’s average concentration is c. 300 ppm and as high as 2000 ppm. Thermodynamic simulations indicate such high Au concentrations correspond to a saturated solution of Au as chloride complexes at temperatures above 500 ºC. Metamorphic fluids are produced by releasing small amounts of volatiles from large areas of crust, and there is uncertainty if there is sufficient fluid available to produce the gold deposits. We suggest the fluids here, could be a precursor of “Orogenic gold fluids” which at these Au concentrations would reduce the requirements for large volumes of metamorphic fluids to form such ore deposits.