福州盆地地热水微量元素特征

Characteristics of Trace Elements of Geothermal Water in Fuzhou Basin

福州地热田是以燕山晚期侵入岩为主要热储层的中低温对流型地热系统。通过对福州盆地不同类型地下水的取样分析发现,福州盆地不同类型地下水中微量元素质量浓度变化关系较复杂。研究表明,地热水微量元素质量浓度主要受含水介质的岩性控制,也与地下水温度有关。对所检测的19个微量元素,除个别元素外,第四系孔隙水微量元素质量浓度均大于基岩裂隙水;Ga、Rb、Sb、Se、Sr、Tl元素质量浓度随水温的升高而增高。基岩裂隙热水与第四系孔隙水混合形成的第四系热水中,As、Cd、Cu、Mo、Pb、Sb、Se、Sr等元素质量浓度明显增高,说明在混合过程中这些元素又发生了溶解作用。根据地热水微量元素与盆地周围不同期次侵入岩体微量元素质量浓度的聚类分析,得出福州地热水形成的地球化学环境主要与福州岩体、魁岐岩体和文笔山岩体的岩性有关。地热水微量元素是地热水在形成过程中与这些岩体的岩石接触发生水-岩相互作用形成的。

Fuzhou geothermal field is a low-medium temperature geothermal system of convective type and its geothermal reservoir is the intrusive rocks of Late Yanshanian stage. The sample analysis of different types of groundwater in Fuzhou Basin indicates that it contains different amount of trace elements . It is shown that the trace elements content is related to the lithology of aquifer, and also to the temperature of groundwater. The content of trace elements in Quaternary pore water is higher than that in bedrock frac- ture water except for some trace elements, while some elements, such as Ga, Rb, Sb, Se, Sr and T1, are increasing with the temperature in groundwater. In Quaternary geothermal water, formed by the mixing of bedrock geothermal water and Quaternary pore water, the contents of As, Cd, Cu, Mo, Pb, Sh, Se and Sr are increased remarkably. This implies that these elements have been dissolved during mixing process. Clustering analysis, among the contents of trace elements in geothermal water and in intrusive rocks formed different period around the Fuzhou Basin, shows that the geochemistry environment of geothermal water is main related to Fuzhou intrusive rock, Kuiqi intrusive rock and Wenbishan intrusive rock, and the trace elements in geothermal water are originated from the interactions between the geothermal water and the intrusive rocks.