银同位素在行星和地球科学中的研究进展

系统梳理了放射性Pd-Ag体系银同位素在行星科学中的发展概况以及稳定银同位素在环境科学示踪和金银矿床中的研究进展.在太阳星云以及行星核的形成过程中，由于107Ag可由107Pd经β衰变产生，而挥发性元素的耗散又会造成早期Pd/Ag的分异，使得Pd-Ag同位素体系可以用于早期太阳系的活动历史研究，例如定义行星核的形成、限定行星形成时代.在稳定银同位素体系中，已探明银同位素组成（δ109Ag）变化范围为-1.0‰~+2.3‰.稳定银同位素组成在不同环境的样品中具有类似于“指纹”特性，可用于确定污染物来源，追溯污染物环境过程，还原真实的环境系统.在金银矿床研究中，具有显著变化的银同位素组成使其在贵金属矿床的形成及演化机制上具有直接的应用意义.目前银同位素在解答行星科学及地球科学等诸多领域问题上仍存在一些尚未解决的难题，例如放射性Pd-Ag体系中太阳系初期107Pd/108Pd比值的精确限定、环境及矿床中银迁移沉积的物理化学过程的复杂耦合同位素分馏机制的确定等. 

Progress of Silver Isotopes Studies in Planetary and Earth Sciences

The progresses of the radioactive Pd-Ag system in planetary sciences and the stable silver isotope in environmental sciences and ore-deposits are systematically reviewed in this paper. In the formation of solar nebula and planetary nucleus, 107Ag can be produced by 107Pd through β decay, and the dissipation of volatile elements will cause the early Pd/Ag differentiation, which makes the Pd-Ag system applicable to investigate various activities of the early solar system, such as defining the formation of planetary nucleus and the age of planetary formation. In the stable silver isotope system, it has been proved that the wide variation range of δ109Ag is -1.0‰ to +2.3‰ in terrestrial materials. Stable silver isotope has characteristics similar to "fingerprint" in environmental materials, which makes it possible to effectively determine pollutants sources and to track migration paths of pollutants. Much wider variations of δ109Ag in metallic ore-deposits have been observed, showing a great potential of silver isotope in studying the genesis and evolution mode of Au-Ag deposits. However, there are still many concerns remained to be resolved, such as the precise definition of 107Pd/108Pd ratio in the early solar system of radioactive Pd-Ag system, and the quantification of silver isotope fractionation in physiochemical processes (e.g., boiling/phase separation, multistage ore paragenesis, precipitation, redox, adsorption and remobilization etc.) involved in silver migration and deposition in environmental and ore-forming processes.