浙江地热田的地球化学体系及其热能潜力评估

The geochemical system of Zhejiang geothermal fieldsand their heat energy potential

浙江位于中国东南活动大陆边缘，与粤闽高温地热带毗连。目前，浙江主要有武义（鱼形角－塔山）、宁海（南溪）及泰顺（会甲溪）等三个地热田。为了评估热能潜力和开发前景，本文着重对它们进行了较系统的水化学和同位素示踪研究。应用ＳｉＯ２、Ｎａ／Ｋ及 Ｏ（ＳＯ４／Ｈ２Ｏ）地热温标，估算出热储温度大致为８０～１１０℃，热储深度大致为８５０～９５０ｍ。此结果与地热田中微量元素和Ｓｒ同位素特征一致。地热水的Ｈ、Ｏ同位素示踪表明，它们的来源与现代大气降水有关，但不是区内当地的地表水，而是各个地热田外围较高山区（相对高程大于３ｍｍ或大于５００ｍ）的大气降水。它们沿着断裂带渗流至地下深处，并借助于地热增温和循环补给成为热水涌出地表。

Zhejiang Province locates in the active continent margin of southeastern China, andadjoins the high geothemial anomalous zone of Guangdong-Fujian provinces. There are mainlythree geothermal fields in Zhejiang Province, i.e. Wuyi (Yuxingue-Tashan), Ninghai(Nanxi) and Taishun (Huijiaxi) thermal fields. Hydrochemistry and isotopic tracing studieshave been carried out for the geothermal fields in order to assess the heat energy potentials andthe exploitation prospect. The temperatures and depths of the geothermal reservoir are estimatedat 80￣ 110 ℃ and 850￣950 m, respectively, using SiO2, Na/K and 18 O(SO4/H2O)geothermometers. They are in agreement with the results obtained from the characteristics oftrace element and strontium isotope in geothermal fields. The hydrogen and oxygen isotopiccompositions show that the source of geothermal water is related to the present meteoricwater. However, it is derived from the meteoric water on the higher hill (with relative altitude of> 300 m or > 500 m) out of the geothermal fields, rather than the local surface water. Themeteoric water might permeated deep level along the fracture zone, be heated by geothermalgradient and supplied by circulating water, and become heat water to gush out on the surface.