ON THE BORON CONCENTRATION AND FORMS OF ITS OCCURRENCE IN HYDROTHERMAL ORE-FORMING FLUIDS

Abstract

The boron concentration in relictant hydrothermal ore-forming fluids captured in the mineral fluid inclusions from various hydrothermal deposits (gold, gold-platinum, tin, and some others) was studied. The fluid inclusions, which were captured at various physicochemical parameters (T =550–175°C, P = 3700–110 bar), were studied with atom-emission spectroscopy (with laser unsealing of inclusions) and with aqueous extraction from the inclusions using inductively coupled plasma. The boron concentration varies strongly from 8 to 0.0001 g/kg of water, and in half of the analyses the concentration exceeds 0.5 g/kg of water. Boron occurs in solution mainly as orthoboron acid under 300–100°C, vapor-saturated pressure, and pH less than 9, according to thermodynamic modeling in a system with similar chemical composition. Possible types of soluble borate species of various elements transported by the hydrothermal ore-forming fluids are discussed.