Cadmium in Zinc Deposits: Economic Geology of a Polluting Element
Cadmium in Zinc Deposits: Economic Geology of a Polluting Element
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DOI：
10.1080/00206810009465091
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发表时间：
2000-05
影响因子：
2.6
通讯作者：
M. Schwartz
中科院分区：
文献类型：
--
作者：
M. Schwartz
锌矿床中镉的主要赋存形式是闪锌矿，闪锌矿中镉的含量与存款类型有关。来自密西西比河谷型（MVT）矿床的闪锌矿具有高镉浓度，而来自喷流矿床的闪锌矿具有低镉浓度。闪锌矿中Cd含量与Cd/Zn比值、配体活性和成矿流体温度有关。温度，pH值，还原硫的总活性和Cl-的活性的变化的综合影响不能单独占镉耗尽（呼出存款）或镉富集（MVT存款）。流体中Cd/Zn比值的变化对确定闪锌矿的Cd/Zn比值有显著影响。盆地卤水，这可以被认为是MVT流体的最近的等价物，具有高的Cd/Zn比，和活跃的喷流系统的特点是低的Cd/Zn比。不同存款类型之间的闪锌矿组成的差异可能不是温度和配体活性的函数，而是成矿流体的Cd/Zn比。在热液环境中，Cd/Zn比通常不足以使硫化镉（绿硫镉石或钙钛矿）结晶。热液型锌矿床表生蚀变带中绿辉石的富集可从菱锌矿结晶对锌的清除作用来解释。
The chief host of cadmium in zinc deposits is sphalerite, the cadmium content of which depends on the type of deposit. Sphalerite from Mississippi Valley-type (MVT) deposits has high cadmium concentrations whereas sphalerite from exhalative deposits has low cadmium concentrations. The Cd content of sphalerite depends on the Cd/Zn ratio, ligand activities, and temperature of the ore-forming fluids. The combined effect of variation of temperature, pH, total activity of reduced sulfur, and activity of Cl- cannot by itself account for either Cd depletion (exhalative deposits) or Cd enrichment (MVT deposits). Variations in the Cd/Zn ratio of the fluid have a significant effect in determining that of sphalerite. Basinal brines, which can considered to be the recent equivalents of MVT fluids, have high Cd/Zn ratios, and active exhalative systems are characterized by low Cd/Zn ratios. Probably the differences in sphalerite composition between the different deposit types are less a function of temperature and ligand activities than Cd/Zn ratio of the ore-forming fluids. In the hydrothermal environment, the Cd/Zn ratio is generally not high enough to allow crystallization of cadmium sulfides (greenockite or hawleyite). The abundance of greenockite in the supergene alteration zone of hydrothermal zinc deposits can be explained on the basis of Zn scavenging by crystallizing smithsonite.