Sulfate brines in fluid inclusions of hydrothermal veins: Compositional determinations in the system H 2 O-Na-Ca-Cl-SO 4
Sulfate brines in fluid inclusions of hydrothermal veins: Compositional determinations in the system H 2 O-Na-Ca-Cl-SO 4
复制标题
热液脉流体包裹体中的硫酸盐盐水：H 2 O-Na-Ca-Cl-SO 4 系统中的成分测定
DOI：
10.1016/j.gca.2017.04.027
复制
发表时间：
2017
影响因子：
5
通讯作者：
Markl, Gregor
中科院分区：
文献类型：
--
作者：
Walter, Benjamin F.;Steele-MacInnis, Matthew;Markl, Gregor
硫酸盐是海水中最丰富的离子之一，含硫酸盐的盐水在沉积盆地等环境中很常见。然而，在显微测温含硫酸盐流体包裹体的属性还没有很好的约束，限制了流体包裹体组合物的解释，硫酸盐是一个主要的离子。上莱茵格拉本裂谷东肩的Schwarzwald矿区是以含硫酸盐卤水为特征的地质系统的一个例子，对阴离子丰度（氯化物与硫酸盐）的限制将是理想的，作为区分这些地区热液脉中流体来源的潜在手段。在这里，我们使用Pitzer型的形式主义来计算平衡条件沿着的蒸汽饱和液相线的系统H_2 O-Na-Ca-Cl-SO_4，并构建相图显示预测的相平衡。我们结合联合收割机这些预测的相位关系与微量测温和破碎浸出分析的流体包裹体从静脉中的黑森林和上莱茵河，估计这些盐水的组合物在散装盐度以及阳离子和阴离子负载（钠与钙，氯化物与硫酸盐）。这些数据表明流体包裹体记录的流体成分的系统差异，并展示了详细的低温显微测温法，以确定含硫酸盐卤水的组合物的应用。因此，这些数据提供了新的约束流体来源和古水文这些经典的盆地容矿系统。此外，本文中呈现的相图可直接应用于其它系统中的组成测定。
Sulfate is among the most abundant ions in seawater and sulfate-bearing brines are common in sedimentary basins, among other environments. However, the properties of sulfate-bearing fluid inclusions during microthermometry are as yet poorly constrained, restricting the interpretation of fluid-inclusion compositions where sulfate is a major ion. The Schwarzwald mining district on the eastern shoulder of the Upper Rhinegraben rift is an example of a geologic system characterized by sulfate-bearing brines, and constraints on the anion abundances (chloride versus sulfate) would be desirable as a potential means to differentiate fluid sources in hydrothermal veins in these regions. Here, we use the Pitzer-type formalism to calculate equilibrium conditions along the vapor-saturated liquidus of the system H2O-Na-Ca-Cl-SO4, and construct phase diagrams displaying the predicted phase equilibria. We combine these predicted phase relations with microthermometric and crush-leach analyses of fluid inclusions from veins in the Schwarzwald and Upper Rhinegraben, to estimate the compositions of these brines in terms of bulk salinity as well as cation and anion loads (sodium versus calcium, and chloride versus sulfate). These data indicate systematic differences in fluid compositions recorded by fluid inclusions, and demonstrate the application of detailed low-temperature microthermometry to determine compositions of sulfate-bearing brines. Thus, these data provide new constraints on fluid sources and paleo-hydrology of these classic basin-hosted ore-forming systems. Moreover, the phase diagrams presented herein can be applied directly to compositional determinations in other systems.