Synthesis of geochemical techniques to identify the origin and multistage evolution of saline water in a complex geothermal system

• Main Authors: Hao Yinlei, Pang Zhonghe, Huang Tianming, Kong Yanlong, Tian Jiao, Wang Yingchun
• Format: Article
• Language: English
• Published: EDP Sciences 2019-01-01
• Series: E3S Web of Conferences
• Online Access: https://www.e3s-conferences.org/articles/e3sconf/pdf/2019/24/e3sconf_wri-162018_08005.pdf

Elucidating brine origin and evolution is a fundamental but not easy task especially for coastal geothermal systems with possible marine constituents and multistage evolution, as subsequently physical, chemical and biological alteration processes may mask the original and early-stage signatures. Here chemical and isotopic characteristics of water (D and 18O) and dissolved constituents (13C, 14C, 11B and 87Sr/86Sr) have been utilized to investigate the source and multistage evolution of the Jimo coastal geothermal system in eastern China, with dramatic differences of geochemical characteristics observed within a 0.2 km2 area. Results show that geothermal water is derived from paleo-meteoric water and has undergone a 3-stages evolution that involves: (1) Dissolution of marine halite and potash salts in the deep reservoir; (2) Water-rock reactions especially cation exchange produces a Cl-Na-Ca type water as deep geothermal water upwells along the fault zone; (3) A minor (<0.3%) addition of fossil seawater to the shallow aquifer that produces Cl-Na type waters in the west, whereas sulfide oxidation and dissolution of aluminosilicate and carbonates in the east produces Cl-Na-Ca type waters. The methodology utilized in this study offers a means of examining other similar complex geochemical systems having a multistage evolution.