硫酸盐-水体系高温液-液不混溶作用的发生条件、机理及成矿意义

The high-temperature liquid-liquid immiscibility in sulfate-water system is an important mechanism for the accumulation and reduction of sulfate in hydrothermal system and may shed light on the formation of some economically important metal sulfide. However, this special phase behavior has not been well studied. In this study, we will carry out in situ observations on the formation condition, mechanism, and possible geological implications of the liquid-liquid phase separation in sulfate-water system at elevated temperatures and pressures. Firstly, we will observe the stable P-T-x conditions of the liquid-liquid immiscibility, especially the pressure effect on the formation of the two immiscible liquid phases; this will help us to understand the migration and accumulation of sulfate during tectonic decompression. Then, we will analyze the composition and structure of the aqueous solution and immiscible fluids to investigate the formation mechanism of the liquid-liquid immiscibility. At last, a case study of the migration and reduction of sulfate in typical ocean hydrothermal vents will be carried out to improve our knowledge on the formation of some massive sulfide deposits. This study might be of importantly theoretical and practical significance because our experimental results can enhance the knowledge of the migration and accumulation of importantly geological elements under high temperatures, which will help us to better understand the formation of some ore deposits.

近期硫酸盐-水体系的相行为研究逐渐揭示出高温液-液不混溶可能是一种比较重要的现象，这对于认识热液体系中硫的富集、转化与金属硫化物的形成具有重要意义，但缺少系统的实验研究。本项申请拟应用先进的原位观测和分析技术，重点研究硫酸盐-水体系高温液-液不混溶的发生条件、机理及地质意义。首先分析硫酸盐-水体系高温液-液不混溶稳定的温度、压力及流体组分条件，重点是压力对液-液不混溶发生温度的影响，以揭示构造减压对硫酸盐迁移和富集的影响。其次，从揭示液-液不混溶发生前后流体组分和结构特征的差异性入手，探讨硫酸盐-水体系高温液-液不混溶的发生机理。最后，以典型海底热液活动区海水-热液-岩石相互作用为例，探讨液-液不混溶在硫酸盐迁移、聚集以及向低价态硫转化过程中发挥的作用与地质意义。研究结果可望通过新的实验依据深化对高温条件下元素迁移和富集规律的认识，丰富成矿机制和理论研究，具有重要的基础科学与实践应用意义。