离子选择电极法测定水热气体中的硼含量及硼的气态迁移能力研究

Determination of Boron Content in Hydrothermal Vapor by Ion Selective Electrode Method: Insights into the Gaseous Transport of Boron

火山和成矿地质现象表明硼可以在含水流体和气体中运移,本文应用离子选择电极法测定水热气体中硼的溶解度,以揭示硼的气态迁移能力。使用氟硼酸盐选择电极,测定了经氟硼酸化的硼酸标准溶液和含硼气体凝结水的电位,当硼含量处于地质流体的主要范围内（0.52-524.50 mg/L）时,电极电位与硼浓度的对数呈现出灵敏度很高的能斯特线性关系,标准曲线具有很好的稳定性和重现性。本方法测定硼的检出限为0.13 mg/L,低于饮用水标准规定的硼含量限值,适用于测定水热气体中的硼含量。硼酸挥发实验显示,硼在150℃、0.37 MPa水蒸气中的含量可达0.65%-0.72%,与富硼火山喷气的硼含量相符,显示硼在高温水热条件下可在气相中显著迁移,且H3BO3气态分子是硼的主要迁移形式之一。矿床地质特征和实验表明,硼的气态迁移和电气石化与稀有金属型伟晶岩的形成和矿化以及某些热液-气成型Sn-W、Mo矿床和斑岩型Cu、Au矿床的形成密切相关。

Geological phenomena of volcanism and metallogenesis indicate that boron can be transported significantly in aqueous fluids and gases. In this study,the Ion Selective Electrode Method was used to determine the solubility of boron in hydrothermal vapor in order to determine the ability of gaseous transport of boron. The electric potentials of boric acid standard solutions and boron-bearing condensates of water vapor after conversion to tetrafluoroborate ion with hydrofluoric acid were determined using a fluoroborate selective electrode. When the concentrations of boron change within the main range of geological fluids（ 0. 52-524. 50 mg / L）,the calibration curve reveals a good linear Nernstian relationship between the potential and the logarithm of boron content with high sensitivity,good stability and good reproducibility. The detection limit of this method is 0. 13 mg / L of boron,within uncertainties,which is lower than the upper limit of boron content standard for potable waters. This method is suitable for boron analysis of hydrothermal vapor. The experimental results of boric acid volatilization show that boron content in water vapor reaches 0. 65%-0. 72% at 150℃ and 0. 37 MPa,which is consistent with boron-rich volcanic fumarole gases,demonstrating that boron can be remarkably transported in vapor phase and exists mainly in gaseous molecule species H3BO3 under high-temperature hydrothermal conditions. The geological characteristics of ore deposits and available experimental evidence indicate that boron transport in vapor and subsequent tourmalinization is closely related to the mineralization of rare metal type pegmatites and the formation of hydrothermal-pneumatolytic type Sn-W and Mo deposits and porphyry Cu and Au deposits.