含矿流体混合反应与成矿作用的动力平衡模拟研究

The numerical modelling of the reactive fluids mixing and the dynamic equilibrium of mineralization.

本文在约定热液体系中成矿元素成矿速率(成矿过程中单位时间内单位体积所含成矿元素重量的变化)的基础上,借助于物质-热-化学-成矿四重全耦合的研究思路,构建了均匀热液体系、层状热液体系、岩浆侵入热液体系下成矿元素的迁移、富集、溶解与沉淀作用数值模型。模拟结果表明:(1)硫化物(H_2S)和硫酸盐(SO_(42-))流体的混合反应是成矿热液体系中铅、锌、铁成矿元素成矿的重要控制因素;(2)均匀介质、岩浆侵入或地质构造的存在,对成矿元素在成矿流体运移的速度、流线、温度分布和成矿元素的溶解与沉淀分布都有着各自的特征,不同的成矿环境或成矿背景制约了成矿元素的迁移与富集以及矿体的产出定位。暗示成矿环境及成矿速率对热液体系中成矿元素的沉淀与溶解具重要作用;成矿流体的混合反应是成矿作用发生的重要机制之一。在成矿理论研究中必须充分考虑不同地质构造因素的约束。

We have deduced the concept of mineralization rate of a mineral in a hydrothermal system from the strict scientific point of view. The mineralization rate of a mineral is defined as the variation in the mineral weight per unit volume rock at per unit time during the mineralization. The mineralization rate of a mineral is a function of the equilibrium concentration of the mineral. In order to maintain the dynamic equilibrium state of a mineral in a pore-fluid flow regime, the precipitation and/or dissolution of the mineral must take place in the hydrothermal system. From this point of view, the dynamic equilibrium theory presented here is the core part of the modern mineralization theory in hydrothermal system. This is the major contribution of this study. Also presented in this study is the finite element simulations of reactive mineral-carrying fluids mixing and mineralization in pore-fluid saturated hydrothermal system. Particular consideration is given to explore the mixing of reactive sulfide and sulfate fluids and the relevant patterns of mineralization for lead, zinc and iron minerals in the regime of temperature-gradient-driven convective flow. We have modelled the distribution of the pore-fluid velocity, streamline and temperature as well as the distribution of the precipitation/dissolution of the aqueous minerals under different geological situations. Through applying the present mineralization theory to three examples in hydrothermal system, the related numerical resulte have demonstrated that: (1) The present mineralization rate is useful for the prediction of the precipitation and dissolution regions of a mineral in hydrothermal systems. (2) The mixing of fluids is one of the effective mechanisms for the mineralization of lead,zinc and iron minerals in the hydrothermal system. (3) The locations of both the injected reactive fluids and geological structures can significantly affect the distributions of pore-fluid flow and temperature as well as the zonation of minerals in hydrothermal systems. Therefore, grological structures need to be considered as an important constraint to control the ore body formation and mineralization.