On the ore-formational affiliation of gold deposits of the Beltau-Kuramin volcano-plutonic belt in Eastern Uzbekistan (according to thermobarogeochemical data)

Abstract

Gold deposits in the Beltau-Kuramin volcano-plutonic belt (Eastern Uzbekistan) are traditionally considered mineral products of the volcanogenic-hydrothermal class of shallow formations. However, geological, geochemical, isotope-geochemical and precise thermo- barogeochemical studies of the physical and chemical conditions of their formation give reason to question their shallow nature. Comparison of the thermobaric conditions of ore-genesis, the chemical composition of the fluid’s aqueous and gas phases, the value of the paleotemperature gradient (ΔT/100 m) of the hydrothermal solutions of the Kochbulak and Kyzil-Alma deposits with those belonging to the medium-depth formation of the plutonic-hydrothermal class (Lyahov, 1988; Lyahov, Pavlun, Piznyur, Popivnyak, 1995) shows that there are much more similarities than differences with genotypic deposits of medium depths. Signs that call into question the shallow nature of gold deposits in the Beltau-Kuramin volcanic-plutonic belt include the following: interspersion of gold ore process and dike magmatism; high-medium temperature level of hydrothermal processes (> 390–200 °С); relatively high pressure in the mineral formation system (from 40 to > 58 MPa); a high content of Na+ and Cl– ions in solutions of fluid inclusions according to the data of triple water extractions and a significant predominance of Na+ over K+ (by two to five times); high and predominant content in the gas phase of the productive stage solutions of CO2 (up to 97 %) and CH4 (up to 45%); the presence in fluid inclusions at room temperature of a liquid phase of CO2 of relatively high density (up to 0.560 g/cm3); high purity of native gold of early generations; exclusively electronic electrical conductivity of galena; relatively insignificant paleotemperature gradient (ΔТ/100 m) in ore bodies of different morphology (15–20 °С/100 m for vein structures and 9–12 °С/100 m for ore-explosive ones). Geological data indicate a large erosion section of ore-conjugated morphostructures, which is at least 2000–2500 m, depending on the depression or domed nature of the volcanic morphostructures. At shallow depths of the formation of the syn-ore paleosurface, the gold deposits would have been completely eroded, while in the modern erosion section there is a large scale of vertical mineralization. Ore-formation correlation of gold deposits in Eastern Uzbekistan increases the prospect of deep horizons of these deposits, as well as gold-bearing areas and ore occurrences, where prospecting and evaluation work will be carried out.