THERMOBAROGEOCHEMICAL ZONING AND GENESIS OF GOLD DEPOSITS AT DIFFERENT DEPTHS

Abstract

It is shown that the depth factor affected the mode and the conditions of mineragenesis, so that thermobarogeochemical tests would be just as useful as geologic and mineralogic evidence as reliable indicators of the emplacement depth of gold mineralization. Information on levels of pressure and salt concentration is most important in this respect, as are data on the behavior of alkalies and CO2, whose high content is a typomorphic feature of fluid inclusions in minerals of ores formed at greatest depths. The effect of the depth factor was most marked in the early stage of ore deposition, when temperature differences at different depths were especially contrasting 370° to 245°C at a depth of 1 to 1.5 km below the surface, and 500° to 260°C at medium and relatively great depths. But in the later stages there was much less variation in thermal regime. The principal gold-bearing mineral parageneses were formed between 270° and 190°C at pressures that ranged from 95 to 55 MPa at medium and greater depths and from 9 to 3 MPa nearer the surface. Thermobarogeochemical indicators of the evolution of gold mineralization itself are very specific and, moreover, fairly uniform for deposits emplaced at different depths.