ON THE NECESSITY OF SUPPLEMENTING THE SCHEME OF GENETIC CLASSIFICATION OF MINERAL DEPOSITS WITH THE CLASS OF METAMORPHOGENIC-HYDROTHERMAL DEPOSITS OF THE HYDROTHERMAL GROUP

Abstract

The features of the physical and chemical course of the processes of formation of gold ore deposits of the Ukrainian Shield are considered. Their metamorphic-hydrothermal nature is established. This is evidenced by the highest (up to hyperbaric) pressure of mineral formation (200–300–350 MPa), subisochoric trend of ore formation processes and a high degree of thermostatization and geologically the most closed type of deep ore-generating paleohydrothermal systems, where the vertical paleotemperature gradient (ΔT/100 m) ranges from 8–10°C/100 m (Balka Shyroka), 5–8°C/100 m (Balka Zolota) to 3–5°C/100 m (Mayske). A high degree of carbon dioxide density in the fluids (up to 0.944–1.02 g/cm3) was diagnosed during the initial hyper- and high-baric period of the formation of the UC deposits. This is manifested in the obvious dominance of homogenization of complex carbon dioxide-water-salt, water-salt, carbon dioxide-water and substantially water inclusions of the first type – in the liquid. Instead, homogenization into the gas phase of the second type, including partial and complete (for inclusions with CO2), occurs due to phase transitions of CO2 as part of the generation of “boiling” hydrotherms (CO2–G–H2O and CO2–G) during and especially at the end of the formation of gold-bearing paragenesis. The unusually high density of metamorphic fluids due to the particularly high viscosity of the liquid phase of inclusions is manifested in an extremely slow (compressed) process of partial and complete homogenization (heterogenization) of inclusions, which is not typical for magmatogenic-hydrothermal deposits. These and some other features of the thermobarochemical course of ore formation processes, which are exclusively characteristic of metamorphic-hydrothermal deposits, give us grounds to supplement the classification of V. Smirnov's mineral deposits with a new class of hydrothermal group – metamorphic-hydrothermal. Deposits of the metamorphogenic-hydrothermal class of the hydrothermal group are widespread on Archean shields and in the Proterozoic folded border and mostly have an irregular and complex flamelike morphology of ore bodies.