Abstract The underground spaces of the former mines in Jachymov, Czech Republic and Rotgulden, Austria house diverse assemblages of secondary minerals, mostly arsenates. The formation conditions and processes involved with the secondary minerals were deciphered using field observations, sampling of both solids and co-existing aqueous solutions, calorimetric measurements on Ca Mg arsenates, forward thermodynamic modeling, and X-ray absorption spectroscopy. In Jachymov, the sampled solutions have pH values from 0.3 up to 7.4 and are moderately to strongly oxidized. The acidic solutions precipitate arsenolite and kaatialaite, and originate by the weathering of native arsenic and sulfides. When these solutions encounter hydrothermal carbonates they are slowly neutralized and precipitate the Ca Mg arsenates picropharmacolite, pharmacolite, haidingerite, brassite, and rosslerite. Measured enthalpies of formation and standard entropies were combined to Gibbs free energies of formation (all in kJ/mol) for picropharmacolite [Ca4Mg(AsO3OH)2(AsO4)2·11H2O, −8139.2 ± 12.4], pharmacolite [Ca(AsO3OH)·2H2O, −1762.0 ± 3.1], haidingerite [Ca(AsO3OH)·H2O, −1522.8 ± 3.1], rosslerite [Mg(AsO3OH)·7H2O, −2849.7 ± 2.5], and brassite [Mg(AsO3OH)·4H2O, −2139.9 ± 2.7]. Forward thermodynamic modeling and the calculation of temperature-relative humidity phase diagrams using these values agreed with field observations. In Rotgulden, secondary Ca Mg minerals are restricted to gypsum and hornesite, and no aqueous solutions were sampled there. The Mg arsenates brassite and rosslerite are typical for systems which initially develop substantial acidity and metal load in the aqueous phase, and afterwards are neutralized, whereas the Mg arsenate hornesite is typical for systems which maintain circumneutral or mildly basic pH, and are slowly enriched in As. Evaluation of the saturation indices in almost 900 chemical analyses of pristine water and acidic/neutral mine drainage showed that they are all undersaturated with respect to Ca Mg arsenates. Therefore, these minerals control the As solubility only in specific (carbonate-rich, Fe-poor, S-poor) mine drainage systems that are progressively neutralized.

中文翻译：

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酸性和碱性流体中 Ca-Mg 砷酸盐形成的预测和观察：捷克共和国 Jáchymov 和奥地利 Rotgülden 的热力学性质和矿物组合

摘要 捷克共和国 Jachymov 和奥地利 Rotgulden 的前矿山的​​地下空间包含多种次生矿物，主要是砷酸盐。通过实地观察、固体和共存水溶液的取样、砷酸钙镁的量热测量、正向热力学模型和 X 射线吸收光谱，破译了与次生矿物有关的形成条件和过程。在 Jachymov，采样溶液的 pH 值在 0.3 到 7.4 之间，并且被中度到强氧化。酸性溶液会沉淀亚砷酸盐和 kaatialaite，并且起源于天然砷和硫化物的风化作用。当这些溶液遇到热液碳酸盐时，它们会被缓慢中和并沉淀出砷酸钙镁 黄铜矿和 rosslerite。将测得的生成焓和标准熵与苦味药石 [Ca4Mg(AsO3OH)2(AsO4)2·11H2O, -8139.2 ± 12.4]、药用石 [Ca(AsO3OH)· 2H2O, -1762.0 ± 3.1], 海丁格石 [Ca(AsO3OH)·H2O, -1522.8 ± 3.1], 红橄榄石 [Mg(AsO3OH)·7H2O, -2849.7 ± 2.5], 和黄铜矿 [Mg(AsO3OH)·H2O, -1522.8 ± 3.1] ± 2.7]。正向热力学建模和使用这些值计算温度-相对湿度相图与现场观察一致。在 Rotgulden，次生 Ca Mg 矿物仅限于石膏和角铁矿，并且没有在那里对水溶液进行采样。镁砷酸盐黄铜矿和红锰矿是典型的体系，最初在水相中产生大量的酸度和金属负载，然后被中和，而 Mg 砷酸盐菱镁矿对于保持环中性或弱碱性 pH 值的系统来说是典型的，并且在 As 中缓慢富集。对原始水和酸性/中性矿井排水的近 900 次化学分析中饱和度指数的评估表明，就砷酸钙镁而言，它们都是不饱和的。因此，这些矿物仅在逐渐中和的特定（富碳酸盐、贫铁、贫硫）矿井排水系统中控制砷的溶解度。