Unraveling the Sulfate Sources of (Giant) Gypsum Crystals Using Gypsum Isotope Fractionation Factors
Unraveling the Sulfate Sources of (Giant) Gypsum Crystals Using Gypsum Isotope Fractionation Factors
复制标题
使用石膏同位素分馏因子揭示（巨型）石膏晶体的硫酸盐来源
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
J. García‐Ruiz
中科院分区：
文献类型：
--
作者：
A. V. Van Driessche;À. Canals;M. Ossorio;R. Reyes;J. García‐Ruiz
我们将实验室沉淀的石膏的新确定的同位素分馏因子与天然硬石膏和石膏的同位素组成结合起来，揭示了奈卡矿（墨西哥奇瓦瓦州）巨型亚硒酸盐晶体的硫酸盐来源。在实验室中，石膏在较宽的温度范围内从 CaSO4-NaCl-H2O 溶液中沉淀出来，以建立硫酸盐分子在固相和溶解相之间的同位素分馏行为。氧同位素显示出对温度的显着分馏依赖性，随着温度的降低，固相中的轻同位素更加贫乏。硫同位素仅表现出对温度的微弱但相似的依赖性。在高盐度 (4.5 M NaCl) 下，同位素组成没有发现温度依赖性。基于这种分馏行为，我们试图阐明导致奈卡矿中（巨大）石膏晶体形成的硫酸盐来源的来源。对硬石膏、石膏和水样的同位素组成的详细分析强烈表明，不同类型的硬石膏（深生和沉积成因）溶解形成了这些独特的石膏地层。分析的大多数石膏晶体的均质同位素组成揭示了有效的流体动力混合和来自不同硬石膏来源的硫酸钙溶液的缓慢沉淀动力学。
We combine newly determined isotope fractionation factors of gypsum precipitated in the laboratory with the isotopic compositions of natural anhydrite and gypsum to unravel the sulfate sources of the giant selenite crystals in the Naica mine (Chihuahua, Mexico). Gypsum was precipitated in the laboratory from CaSO4-NaCl-H2O solutions across a broad temperature range to establish the isotopic fractionation behavior of the sulfate molecule between the solid and dissolved phase. Oxygen isotopes show a significant fractionation dependence on temperature, with the solid phase more depleted in light isotopes with decreasing temperature. Sulfur isotopes display only a weak but similar dependence on temperature. At high salinity (4.5 M NaCl) no temperature dependence was found for the isotope composition. Based on this fractionation behavior, we attempt to elucidate the origin of the sulfate source(s) responsible for the formation of the (giant) gypsum crystals in the Naica mine. Detailed analysis of the isotopic composition of anhydrite, gypsum, and water samples strongly suggests that different types of anhydrite (of hypogenic and sedimentary origin) were dissolved to form these unique gypsum formations. The homogeneous isotopic composition of most gypsum crystals analyzed reveals an effective hydrodynamic mixing and a slow kinetics of precipitation fed by solutions of calcium sulfate from different anhydrite sources.