CRITICAL INCLUSION AND ITS APPLICATION IN GOLD DEPOSIT GEOLOGICAL STUDY

Critical inclusions are formed in ultra-critical fluid only when the critical volume is definite.Their gas/liquid ratio is invariant till it becomes homogeneous fluid in thermodynamic process.They occur in all kinds of magmatic, igneous and hypometamorphic rocks and iron, copper, gold and other multi-metal deposits.By studying the critical homogeneous temperature and the phase graph of the fluid system, we can obtain the physicochemical information about the thermodynamic state of minerogenetic fluid system, the basic composition of fluid, critical pressure, salinity, density etc.Through years' research, the authors discover that many gold deposits occurred in hypometamorphic rocks in North China contain critical inclusions whose critical homogeneous temperature is lower than the pure water's (374. 2℃), indicating that the ultra-critical fluid in early minerogenetic stage is composed of a low salinity CO₂-H₂O system and derived from ancient hypometamorphic rock.The other mineralization hydrothermal, with higher salinity, comes from Mesozoic acid-intermediate rock bodies near the deposits. The ultra-critical fluid has then formed gold deposits with multi-stage, multi-origin and multi-genesis features, which is proved by inclusion refrigeration, composition analysis and the H and O isotopic analysis for the water from inclusions.