THERMOBAROGEOCHEMISTRY OF ORE FORMATION PROCESSES AT THE BALKA SHYROKA GOLD ORE DEPOSIT (UKRAINIAN SHIELD)

Abstract

The article characterizes the morphology, morphometry, and phase composition of fluid inclusions in minerals of the Balka Shyroka gold deposit ores (Middle Dnieper region, Ukrainian Shield). The contrast of the main mineral paragenesises and clear manifestations of the signs of their time relationships are revealed, namely the textures of intersection, replacement, brecciation, and cementation. This gave rise to the identification of a number of sequentially formed mineral associations of stable composition and their complexes, which differ significantly in terms of productivity. The most stable associations of minerals were selected and the temperature of mineral formation was determined with the help of thermobarogeochemical studies. The pre-productive complex is represented by a pyrite–quartz association (with magnetite) and includes three paragenesises – magnetite–quartz (435–390 °С), pyrrhotite–pyrite–quartz with magnetite (395–320) and quartz–siderite with redeposited magnetite (280–240 °C). The productive polysulphide complex is composed of two sequential mineral associations, such as arsenopyrite–pyrite– quartz with gold (385–310 °C, 194–123 MPa) and gold–sulphosalts (290–200 °C, 93–79 MPa). The first of them covers the following paragenesises: tourmaline–quartz (385–300 °C), quartz–pyrrhotite–pyrite (385–310) and gold–arsenopyrite–sphalerite–chalcopyrite–quartz (335–310 °C), the second one – quartz– pyrite (290–210 °C), quartz–chalcopyrite–arsenopyrite–sulphosalts with gold (275–210), cleiophane– chalcopyrite–quartz (245–210), cleiophane–galena–quartz (245–210) and quartz–ankerite (210–200 °C). The post-productive carbonate complex is represented by a quartz–calcite mineral assemblage, which includes calcite–pyrite–quartz (150–110 °C) and quartz–calcite (110–90 °C and below) paragenesises. A model of the staging and thermobarogeochemical regime of the Balka Shtroka deposit formation was developed on the basis of the given data. It reflects the evolution of the mineral composition of ores, aggregate state and chemical composition of solutions. It can be successfully applied during prospecting, evaluation and forecasting of gold mineralization with depth and on the flanks of the Balka Shyroka deposit.