Chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings, Woodsreef Asbestos Mine, Australia
Chemical and isotopic signatures of waters associated with the carbonation of ultramafic mine tailings, Woodsreef Asbestos Mine, Australia
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DOI：
10.1016/j.chemgeo.2016.04.014
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发表时间：
2016-10
期刊：
影响因子：
3.9
通讯作者：
H. Oskierski;B. Dlugogorski;T. Oliver;G. Jacobsen
中科院分区：
文献类型：
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作者：
H. Oskierski;B. Dlugogorski;T. Oliver;G. Jacobsen
在伍兹礁砷矿的尾矿上形成了广泛的碳酸盐结壳，直接从大气中吸收了大量的二氧化碳。与尾矿和相关碳酸盐沉淀物相互作用的沃茨的物理化学（pH、T、电导率）、化学（阳离子、溶解无机碳（DIC））和同位素（δ 2 H、δ 18 O、δ 13 CDIC、F14 C）特征提供了对控制碳酸化过程的深入了解。我们观察到两个不同的演化路径的一组流和大气来源的水样，分别与这两个群体一般被描述为中度碱性，碳酸氢盐为主，镁丰富的沃茨。溪流水样品过饱和与CO2，因此容易脱气，这与蒸发相结合，驱动碳酸盐过饱和和沉淀。同位素特征表明土壤CO2作为进入尾矿堆的流沃茨中的主要碳源，而尾矿堆下游出现的水也可能含有来自同位素轻基岩菱镁矿在相对于土壤CO2的开放系统中溶解的碳。另一方面，大气生成的沃茨的演化部分发生在CO2限制条件下，这是由于CO2进入深度减少和/或流体碱化和CO2进入碱性溶液的动力学阻碍吸收之间的时间滞后造成的。高pH值、富镁的大气降水在排放到尾矿堆内的隧道后吸收大气CO2，导致具有大气碳同位素特征的高DIC浓度。在隧道中的排放点处的水的蒸发驱动水菱镁矿（Mg 5（CO 3）4（OH）2·4 H2O）的沉淀，显示出清晰的大气同位素特征，与先前对水合碳酸镁沉淀期间的碳和氧同位素分馏的估计大致一致。
Extensive carbonate crusts have formed on the tailings of the Woodsreef Asbestos Mine, sequestering significant amounts of CO2directly from the atmosphere. The physico-chemical (pH,T, conductivity), chemical (cations, dissolved inorganic carbon (DIC)) and isotopic (δ2H,δ18O,δ13CDIC,F14C) signatures of waters interacting with the tailings and associated carbonate precipitates provide insight into the processes controlling carbonation. We observe two distinct evolutionary pathways for a set of stream and meteoric-derived water samples, respectively, with both groups generally being characterised as moderately alkaline, bicarbonate-dominated and Mg-rich waters. Stream water samples are supersaturated with CO2and therefore prone to degassing, which, in combination with evaporation, drives carbonate supersaturation and precipitation. Isotopic signatures indicate soil CO2as the main carbon source in the stream waters entering the tailings pile, whereas water emerging downstream of the tailings pile may also contain carbon from the dissolution of isotopically light bedrock magnesite in an open system with respect to soil CO2. The evolution of meteoric-derived waters on the other hand, partly occurs under CO2-limited conditions, which results from reduced CO2ingress at depth and/or a temporal lag between fluid alkalisation and kinetically hindered uptake of CO2into alkaline solution. A high pH, Mg-rich meteoric water absorbs atmospheric CO2after discharging into a tunnel within the tailings pile, resulting in high DIC concentrations with atmospheric carbon isotope signature. Evaporation of the water at the discharge point in the tunnel drives precipitation of hydromagnesite (Mg5(CO3)4(OH)2·4H2O), displaying a clear atmospheric isotope signature, broadly consistent with previous estimates of carbon and oxygen isotope fractionation during precipitation of hydrated Mg-carbonate.