The theory of water phase transitions controlling hydrothermal mineralization

Based on the researches of water physicochemical properties, hydrothermal deposits and solubility experiments, the sketch of the ore-controlling theory of water phase transition in hydrothermal deposit was given ago. Now the following shows the latest version of this theory: (1) the water phase transition may cause some mutations of physicochemical properties, such as the heat capacity, mineral solubility in water, compressibility coefficient and expansion coefficient. Especially the second-order phase transition at the critical point induces the critical singularity which some physicochemical parameters tend to be the infinity. The significant changes of physicochemical properties at water phase transitions are obviously different from small- amplitude and gradual change at the district without phase transition. The differences will significantly influence the dissolution, migration and depositing of ore-forming materials in the lithosphere. The water phase transition and its type depend on the structure, magmatic activity and the geothermal gradient. According to normal geothermal curves in the lithosphere, the pressure reducing from fracture or fold or ductile shear is essential to induce the water phase transition. Therefore, the study of hydrothermal mineralization can also give some valuable information on the regional tectonic evolution. (2) There are 3 key steps in this theory. Firstly, the significant differences of water physicochemical properties between phase transition area and no-phase transition area in phase diagram, can give the probability to carry the ore-forming materials into or out of water-bearing system in the lithosphere. Secondly, the geological environment with the temperature and pressure near to water phase transition is essential for the thermal geo-fluid to dissolve a large amount of ore-forming materials. Lastly, it is also necessary that reducing pressure in some parts of the lithosphere induces the phase transition of water, in which the ore-forming materials in thermal geo-fluid can be released to form the hydrothermal deposits. Overall, the theory studies physicochemical property of water-bearing system and its relative geological response under temperature and pressure in the lithosphere, and it belongs to the content of tectono-physicochemistry.