Complex hydrodynamic and thermodynamic model for a convective hydrothermal system: 2. Self-mixing of solutions

A complex model making allowance for the self-mixing of hydrothermal solutions was developed for a convective hydrothermal system in a mid-ocean ridge. The modeling technique is developed based on the method published in [1] and includes two stages of calculations. The first stage involves the calculation of a hydrodynamic model of the system. Simultaneously, the temperatures, pressures, and the filtration rates of the hydrothermal solution are obtained for any element of the system. In the second stage, the compositions of equilibrium mineral assemblages and hydrothermal solutions are calculated for these elements. The method makes it possible to calculate the spatial distribution of metasomatic and newly formed ore minerals and the volume differences for the metasomatic reactions. A technique is proposed for evaluating local rock/water ratios in a convective system with self-mixing solutions. Our calculations of the spatial distribution of mineral deposition indicate that massive epidosite should form at the roof of an intrusive body and that zones of greenstone metasomatic rocks should develop away from the contact with the intrusion. The simulated distribution pattern is consistent with the those observed in ophiolite sequences. Ore mineralization develops during the early stages of the system evolution in the form of stockworks in the zone of ascending hydrothermal flows. As the process develops, ore-forming elements are actively removed from the system. The largest negative volume differences of metasomatic reactions (porosity increase) were determined to accompany the origin of epidosites in proximity to the intrusive body. The maximum positive volume changes arise as ore minerals are deposited: anhydrite in the zone of the active descending hydrothermal flows and quartz in the areas of the active cooling of the solution.