首页|秦岭山前眉县低温地热水及伴生氦气成因机制

秦岭山前眉县低温地热水及伴生氦气成因机制

Genetic mechanisms of low-temperature geothermal water and its associated helium gas in Meixian County in the piedmont of Qinling Mountains

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秦岭山前眉县地热水资源丰富,伴生气中氦气丰度较高,专门针对该区地热流体特征及成因的研究尚未开展.通过对地热流体的化学组分、同位素地球化学分析,结合区域构造断裂分析地热流体特征及成因机制.研究发现:地热水矿化度为 638.96～1 026.83 mg/L,水化学类型为HCO3-Na型;地热水变质程度低,属于未平衡或部分平衡水,溶质主要来自硅酸盐类岩石风化;地热水δD为-77.3‰～-70.8‰,δ18O为-10.9‰～-9.8‰,均位于大气降水线附近;地热水平均补给高程约为1 030 m,补给水源温度 4.9～7.0℃,最大循环深度约为 3 200 m.地热水伴生气以氮气为主,烃类气体含量低,氦气丰度相对较高;地热水伴生气中甲烷δ13C平均值为-52.8‰,δD平均值为-247‰,伴生气具有较小的R/Ra值和较大的4He/20Ne值.研究揭示:秦岭山区的大气降水通过大断裂及其次生断裂下渗并储存于断裂裂隙和砂岩孔隙中,经地温加热后形成地热水;地热水水源近且充足,封闭性差,循环速度快且深度浅,是秦岭山前眉县地热水低温量大的主要原因;地热水伴生气中的氦主要来自壳源,由地壳岩石中铀、钍元素放射性衰变形成.研究成果为开发利用秦岭山前眉县地区的地热资源提供了重要的地球化学证据.
Meixian County in the piedmont of the Qinling Mountains boasts abundant geothermal water resources with high-abundance associated helium gas.However,the characteristics and origin of geothermal fluids in the study area are yet to be studied.By analyzing the chemical composition and isotopic geochemistry of geothermal fluids and combining the distributions of regional structures and faults,this study delved into the characteristics and genetic mechanisms of geothermal fluids in the study area.The results show that the geothermal water exhibits salinity ranging from 638.96 to 1 026.83 mg/L and a hydrochemical type of HCO3-Na.The low-degree metamorphism suggests that the geothermal wa-ter is unbalanced water or partially balanced water,with solutes primarily originating from the weathering of silicate rocks.The geothermal water yielded δD and δ18O values ranging from-77.3‰ to-70.8‰ and from-10.9‰ to-9.8‰,respectively,both of which fell near the meteoric water line.Furthermore,the geothermal water features an average re-charge elevation of approximately 1 030 m,recharge water temperatures ranging between 4.9℃ and 7.0℃ ,and a maxim-um circulation depth of about 3 200 m.The geothermal water-associated gas is dominated by nitrogen gas,exhibiting low hydrocarbon gas concentrations and high-abundance helium gas.The methane in the associated gas showed an aver-age δ13C value of-52.8‰ and an average δD value of-247‰.Besides,the associated gas displayed low R/Ra ratios and high 4He/20Ne ratios.As revealed by this study,the meteoric water from the Qinling Mountains infiltrated downward in-to fault fractures and sandstone pores through deep-seated faults and their secondary faults,ultimately forming geo-thermal water via geothermal heating.The low-temperature and high-volume geothermal water in the study area is primarily formed by the close and sufficient water sources,poor sealing,and fast circulation at shallow depths.The heli-um in the associated gas was principally crust-derived and formed by the radioactive decay of uranium and thorium ele-ments in crustal rocks.The results of this study will provide critical geochemical evidence for the exploitation and utiliz-ation of geothermal resources in the study area.

low-temperature geothermal waterhelium gashydrogen and oxygen isotopesgenetic mechanismpied-mont of Qinling Mountains

韩元红、吕俊、张育平、罗娜宁、李兵、申小龙

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自然资源部煤炭资源勘查与综合利用重点实验室,陕西 西安 710021

陕西中煤新能源公司,陕西 西安 710054

陕西煤田地质勘查研究院有限公司,陕西 西安 710021

低温地热水 氦气 氢氧同位素 成因机制 秦岭山前

国家重点研发计划课题陕西省重点研发计划项目陕西省自然科学基金陕西省自然科学基金

2022YFC29043012021ZDLSF05-122021JLM-142023-JC-QN-0631

2024

10.12363/issn.1001-1986.23.10.0639

煤田地质与勘探
中煤科工集团西安研究院

煤田地质与勘探

CSTPCD北大核心
影响因子：1.079
ISSN：1001-1986
年,卷(期)：2024.52(1)
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