西藏古堆地热显示区地热流体化学特征及物源分析

There are various high-temperature geothermal manifestations in Tibet. More than 600 thermal springs are distributed throughout the area. Gobdu geothermal area is a typical high-temperature thermal water system in the South of Tibet. It is situated in Himalayan Geothermal Belt which has been described as a 3000 km long belt from the Pamir terrain through Tibet into Yunnan. It is few untapped geothermal area in Tibet. There are seven high-temperature geothermal manifestations in the area, are Nuo, Buxionglanggu, Chaka, East Chaka, Sagalangga, Babudimi and Tuduo from West to East respectively. According to the fluids geochemistry, it is confirmed five geothermal area belong to a same hydrothermal system, include Buxionglanggu, Chaka, Sagalangga and Babudimi. The study area along the upstream of Xiongqu river in the East-North of Cuomei County, it is about extend for 17km and spread more than 10 km2 around. The types of surface manifestations are various, include many boiling springs, thermal springs, fumaroles, sulfur fumaroles, sulfur flowers, large area of sinter, travertine and alteration zone. It is mainly Cl or Cl-HCO3 type geothermal water and CO2 type geothermal gases after preliminary survey in the study area. However, some geothermal gases samples N2 content are high follow CO2, even to appear N2 type and CO2 content is special low. Especially, the N2 type geothermal gases usually appear to medium-low geothermal water system. Because of it could be comparable with Yangbajing geothermal filed and is another important geothermal area in Tibet, the project choose Gobdu geothermal area for study.. With thermal water chemistry, isotope and geothermal gases composition and isotopic studies, research characteristics of the geothermal fluids chemistry and its sources. Compare with Cuna-Sangri active faults hydrothermal system, Yangbajing and Yangyi high-temperature geothermal fields of hydrothermal systems, base on thermal water chemistry and hydrogen and oxygen isotopes, analysis of the Gobdu unique geothermal fluids type which Cl or Cl-HCO3 water with N2 type geothermal gases, and study its genesis. With thermal water carbon and sulfur isotope data, study geothermal water carbon, sulfur source and its composition; use thermal water strontium isotope research, study thermal water hydrogeochemical processes and its quantitative data of cold water mixing ratio. With compositions of geothermal gases, carbon and nitrogen isotopic, noble gases helium isotopes, combined the parameters of CO2/3He-3He/4He、CH4/3He-3He/4He、δ13CCO2-CO2、δ15N-N2, indicate the sources and genesis of geothermal gases. Comprehensive analysis the geothermal fluid chemical characteristics and genesis, quantitative analysis sources of the geothermal fluids in the study area, not only to provide suggestions for the later depth research and development and utilization provided an important scientific basis, furthermore rich genesis mechanisms of high-temperature geothermal systems.

本项目以古堆地热显示区为研究对象，以地下热水水化学、同位素及地热气体组分及同位素为主要研究手段，开展地热流体化学特征和物源的研究。与错那-桑日活动断裂带水热系统、羊八井及羊易高温地热田等水热系统进行对比，依据地下热水水化学及氢氧稳定同位素，分析古堆地热显示区特有Cl-Na、Cl•HCO3-Na水与N2含量增多的地热气体伴生类型的地热流体成因；利用地下热水碳硫同位素研究地下热水碳源、硫源及其成分组成，用地下热水锶同位素研究地下热水历经的水文地球化学过程，定量分析地热流体中冷水的混合比例；根据地热气体组分及氦同位素碳氮同位素，辅以CO2/3He-3He/4He、CH4/3He-3He/4He、δ13CCO2-CO2、δ15N-N2等综合指标，分析地热气体的来源。综合分析研究区地热流体化学特征及成因、定量分析地热流体物源，不仅为后期研究区地热勘查及开发提供指导意义，同时丰富高温地热系统的成因机制。

西藏山南地区措美县的古堆地热显示区是喜马拉雅地热带上典型的高温地热系统，也是西藏为数不多的未开发的高温地热显示区之一，它包括日若、布雄朗古、茶卡、东茶卡、撒嘎朗嘎、巴布的密和突多7个主要地热显示区。研究区地热水的水化学类型以Cl·HCO3-Na、Cl-Na水为主，TDS、Na、F、Li、SiO2、As与Cl大体上存在正相关关系，指示古堆地热显示区存在深部热流体的混入。通过地热水同位素分析，其主要来源为大气降水，地热水就近接受融雪水补给；地热水中HCO3主要来源于碳酸盐的溶解，硫酸盐主要来源于沉积层的淋滤作用；利用氚同位素值定性判断地热水仍残留一些核爆3H，循环深度不深。通过地热气体主要成分分析，表明CO2为深部无机来源，N2主要为大气成因；利用气体三角图及He同位素比值，揭示了研究区地热气体中氦主要为壳源，地热流体运移到浅部不断有大气成分的混入。利用流体化学地温计估算区内深部最高的热储温度260℃左右。研究成果可用于指导研究区地热资源勘查工作，完善高温地热系统的成因机制。