珊瑚岛礁地下含水层的水-岩作用研究

Study on water-rock interaction of underground aquifer in coral islands

珊瑚岛礁地下含水层的水-岩作用研究对于岛礁地下水资源开发和保护意义重大。基于西沙珊瑚岛礁水文地质勘察和野外样品采集工作,运用PHREEQC模拟软件初步探讨了地下水水化学组分形成的水文地球化学作用,获得了珊瑚岛礁含水层岩土化学特征并建立了水-岩作用概念模型。研究结果表明:含水层碳酸盐类矿物质量分数占总体97%以上,从上部砂砾沉积层到不整合面下部的珊瑚礁灰岩地层,文石和高镁方解石占比减小,方解石占比增加,出现方解石化。地下水中文石、方解石、白云石的饱和指数与深度呈负相关性,而生石膏的饱和指数和深度具有一定的正相关性。地下含水层的上部水体对碳酸盐矿物的溶蚀作用强于下部高TDS水体。

The study of water-rock interaction in the underground aquifer in coral islands is of great significance to the exploitation and protection of groundwater resources in coral island. Based on the hydrogeological survey and field sample collection from Xisha Coral Island in South China Sea, the hydrogeochemical process of Groundwater Hydrochemical Composition formation was preliminarily discussed by using PHREEQC simulation software. The geochemical characteristics of the aquifer in Xisha Coral Island were obtained and the conceptual model of water-rock interaction was established. The results showed that the mass fraction of carbonate minerals in aquifers accounted for more than 97% of the total. From the upper gravel sediments to the lower part of the unconformity, the proportion of aragonite and high magnesium calcite decreased, while the proportion of calcite increased and calcification occurred. The saturation index of quartz, calcite and dolomite in groundwater was negatively correlated with depth, while the saturation index and depth of gypsum had a certain positive correlation. The dissolution of carbonate minerals in the upper water body of underground aquifer is stronger than that in the lower high TDS water body.