Hydrogeochemical and isotopic signatures elucidate deep subsurface hypersaline brine formation through radiolysis driven water-rock interaction
Hydrogeochemical and isotopic signatures elucidate deep subsurface hypersaline brine formation through radiolysis driven water-rock interaction
复制标题
水文地球化学和同位素特征阐明了通过辐射分解驱动的水-岩石相互作用深层地下高盐水的形成
DOI：
10.1016/j.gca.2022.11.015
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发表时间：
2023
影响因子：
5
通讯作者：
Whitehouse, M.J.
中科院分区：
文献类型：
--
作者：
Nisson, D.M.;Kieft, T.L.;Drake, H.;Warr, O.;Sherwood Lollar, B.;Ogasawara, H.;Perl, S.M.;Friefeld, B.M.;Castillo, J.;Whitehouse, M.J.
来自南非威特沃特斯兰德盆地Moab Khotsong金矿和铀矿的2.9-3.2 km深、45-55° C温度的高盐度盐水的地球化学和同位素流体特征与辐射分解和水-岩石同位素交换模型相结合，以描绘地质时期的盐水演化，并探索盐水的可居住性条件。莫阿布霍特松卤水是高盐（Ca-Na-Cl），TDS为215-246 g/L，Cl−浓度高达4 mol/L，这表明它们作为高盐端元的位置比任何以前采样的威特沃特斯兰德盆地流体的含盐量都要高。尽管在微氧条件下（Eh= 135-161 mV），卤水中DIC含量较低（0.266- 0.111111] 1/1），DOC含量较高（0.849 - 0.23611111] 1/1），但仍有几种气态物质（H2体积分数高达46%）被还原。α粒子辐解水到H2、H2 O2和O2沿着无水硅酸盐到粘土的蚀变反应，预测在> 1.00 Ga的时间段内，裂缝沃茨中Cl−浓度为4 mol/L，氘富集，与之前报道的该系统40 Ar稀有气体衍生的停留时间1.20 Ga一致。此外，在1-100 μ g/g238 U剂量情景下，预测了7-26 nmol/（L × yr）H2、3- 11nmol/（L × yr）O2和1-8 nmol/（L× yr）H2 O2的辐解产物随着时间的推移，支持辐解作为H2和氧化剂物种的重要来源，进入低生物量系统的深层盐水（10 2-10 3个细胞/mL）。主岩岩性主要为白垩纪石英岩，断裂面上暴露的矿物包括方解石、黄铁矿和方解石。从二次离子质谱（西姆斯）微区分析中获得的δ 18 O方解石、δ 13 C方解石、Δ 33 S黄铁矿、δ 34 S黄铁矿和87 Sr/86 Sr的特征表明，当盆地从绿片岩峰值条件冷却到与现今盐水温度平衡时，发生了几次离散的流体事件。卤水的物理化学，地球化学和细胞丰度显着不同的一个年轻的，浅，在同一个矿山的低盐度的岩石流体，都是不同的矿山服务水。这些结果表明，发现的几个长期孤立的系统，支持地下卤水形成通过延长水-岩相互作用，和地下卤水系统的一个例子，其中非生物地球化学可能支持低生物量的微生物群落。
Geochemical and isotopic fluid signatures from a 2.9–3.2 km deep, 45–55° C temperature, hypersaline brine from Moab Khotsong gold and uranium mine in the Witwatersrand Basin of South Africa were combined with radiolytic and water–rock isotopic exchange models to delineate brine evolution over geologic time, and to explore brine conditions for habitability. The Moab Khotsong brines were hypersaline (Ca-Na-Cl) with 215–246 g/L TDS, and Cl− concentrations up to 4 mol/L suggesting their position as a hypersaline end-member significantly more saline than any previously sampled Witwatersrand Basin fluids. The brines revealed low DIC (∼ 0.266–∼ 1.07 mmol/L) with high (∼ 8.49–∼ 23.6 mmol/L) DOC pools, and several reduced gaseous species (up to 46% by volume H 2) despite microoxic conditions (Eh= 135–161 mV). Alpha particle radiolysis of water to H 2, H 2 O 2, and O 2 along with anhydrous-silicate-to-clay alteration reactions predicted 4 mol/L Cl− brine concentration and deuterium enrichment in the fracture waters over a period> 1.00 Ga, consistent with previously reported 40 Ar noble gas-derived residence times of 1.20 Ga for this system. In addition, radiolytic production of 7–26 nmol/(L× yr) H 2, 3–11 nmol/(L× yr) O 2, and 1–8 nmol/(L× yr) H 2 O 2 was predicted for 1–100 μ g/g 238 U dosage scenarios, supporting radiolysis as a significant source of H 2 and oxidant species to deep brines over time that are available to a low biomass system (10 2–10 3 cells/mL). The host rock lithology was predominately Archaean quartzite, with minerals exposed on fracture surfaces that included calcite, pyrite, and chlorite. Signatures of δ 18 O calcite, δ 13 C calcite, Δ 33 S pyrite, δ 34 S pyrite and 87 Sr/86 Sr obtained from secondary ion mass spectrometry (SIMS) microanalyses suggest several discrete fluid events as the basin cooled from peak greenschist conditions to equilibrium with present-day brine temperatures. The brine physiochemistry, geochemistry, and cellular abundances were significantly different from those of a younger, shallower, low salinity dolomitic fluid in the same mine, and both were different from the mine service water. These results indicate the discovery of one of few long-isolated systems that supports subsurface brine formation via extended water–rock interaction, and an example of a subsurface brine system where abiotic geochemistry may support a low biomass microbial community.