Abstract Fluids in geothermal reservoirs can be affected by the interaction with host rocks. To determine solute sources and water-rock interaction processes, this study collected water samples from the Upper Cretaceous to Lower Eocene strata of the Jiangling Basin, South China. Their chemical and isotopic (hydrogen, oxygen, strontium, boron) characteristics and the mineralogy of corresponding reservoir rocks were investigated. Five high-salinity water samples (343–359 g/L) were collected from deep boreholes tapping Paleocene to Eocene formations in the central basin. Seven water samples (four oilfield and three saline waters) were collected from boreholes tapping Upper Cretaceous formations in the northwestern part of the basin and had salinities of 23.1–81.4 g/L. These water samples showed depletion of Mg and SO4 and enrichment of K, Na, Ca and Cl, compared with the ion trajectories of evaporated seawater. The observed Cl/Br mass ratios (709–1390), Na/Cl molar ratios (0.79–1.01), Ca excess and Na deficit imply contributions of halite dissolution and multiple diagenetic processes of albitization, dolomitization, and calcite and anhydrite cementation, which are consistent with the reservoir rock mineralogy. Chemical geothermometers of these geothermal fluids estimated temperatures of around 200 ± 20 °C and 125 ± 10 °C for hot brines and saline waters, respectively. Compared with the chemical compositions of Upper Cretaceous saline waters, the hot brines are enriched in K, Li, B, Sr, Rb, Cs, Br, Ba and transition metals such as Co, Ni, Cu, Zn, V, Ti and Mn. Correlations of δ18O-Li, δ18O-Rb, δ18O-Cs and δ18O-K values indicate that equilibrium with rocks caused enrichments in K, Li, Rb and Cs. Variations in 87Sr/86Sr ratios (0.706954–0.711249) and δ11B values (+8.7‰–+23.1‰) were used to find many discrepancies due to water-rock interactions involving basalt and clastic rocks. The integration of chemical and isotope data suggests that the geothermal waters in the Jianging Basin are derived from water-rock interactions and recharge of meteoric waters. In addition, the boron isotope data are consistent with traditional hydrogen, oxygen and strontium isotopes in terms of explaining water-rock interaction processes. Multi-isotopic characterization of Upper Cretaceous to Lower Eocene geothermal waters indicates that the isotopic compositions of water from the Jiangling Basin are consistent with a fluid signature of interactions involving basalt and clastic rocks with water derived from primary brine diluted by meteoric waters. The combined water chemistry and multi-isotope approach shows that high-temperature water-rock interaction is a major influence on the mineralization of hot brines in the Jiangling geothermal system.

中文翻译：

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江陵盆地上白垩统至下始新统地热水的成因：多同位素示踪剂和水岩相互作用的约束

摘要 地热储层中的流体会受到与母岩相互作用的影响。为了确定溶质来源和水-岩相互作用过程，本研究收集了华南江陵盆地上白垩统至下始新统地层的水样。研究了它们的化学和同位素（氢、氧、锶、硼）特征以及相应储层岩石的矿物学。五个高盐度水样 (343–359 g/L) 从挖掘中央盆地的古新世至始新世地层的深钻孔中收集。从盆地西北部上白垩统地层的钻孔中收集了七个水样（四个油田和三个咸水），其矿化度为 23.1-81.4 g/L。这些水样显示出 Mg 和 SO4 的消耗以及 K、Na、Ca 和 Cl，与蒸发海水的离子轨迹进行比较。观察到的 Cl/Br 质量比 (709–1390)、Na/Cl 摩尔比 (0.79–1.01)、Ca 过量和 Na 不足意味着岩盐溶解和钠长石化、白云石化、方解石和硬石膏胶结的多种成岩过程的贡献，其中与储集岩矿物学一致。这些地热流体的化学地温计估计热盐水和咸水的温度分别约为 200 ± 20 °C 和 125 ± 10 °C。与上白垩统咸水化学成分相比，热卤水中富含K、Li、B、Sr、Rb、Cs、Br、Ba和过渡金属Co、Ni、Cu、Zn、V、Ti、Mn . δ18O-Li、δ18O-Rb、δ18O-Cs 和 δ18O-K 值的相关性表明，与岩石的平衡导致了 K、Li、Rb 和 Cs。由于玄武岩和碎屑岩的水-岩相互作用，87Sr/86Sr 比值 (0.706954–0.711249) 和 δ11B 值 (+8.7‰–+23.1‰) 的变化被用来发现许多差异。化学和同位素数据的整合表明，江宁盆地的地热水来源于水-岩相互作用和大气水的补给。此外，硼同位素数据在解释水岩相互作用过程方面与传统的氢、氧和锶同位素数据一致。上白垩统至下始新世地热水的多同位素特征表明，江陵盆地水的同位素组成与玄武岩和碎屑岩与被大气水稀释的原生卤水衍生的水相互作用的流体特征一致。