水-岩反应与稀土元素行为

BEHAVIOR OF RARE-EARTH ELEMENTS IN FLUID-ROCK INTERACTION: A REVIEW

大量研究表明 ,水 岩反应过程中REE表现为不同程度的活动性。富含各种络合剂的流体与岩石反应时可活化REE ;水 岩反应过程中既可出现HREE优先活化 ,亦可出现LREE优先活化 ,这取决于流体的化学成分、Eh、pH以及REE的寄主相及其赋存状态 ;水 岩反应过程中的可出现Eu的正异常、负异常或无异常 ,其主要影响因素是流体的氧化 还原状态 ;单矿物组合的REE行为受制于矿物的晶体化学性质 ,而多矿物组合则取决于体系的Eh、pH、水 /岩值和络合剂浓度等 ,目前亟待开展实验工作有 :①流体的化学组成及其性质 ,尤其是各种络合剂的活度及其对REE的活动性的影响 ;②REE在热液矿物与流体相之间的分异机制及控制因素 ;③T、P、pH、Eh和水 /岩比如何影响REE的活动性和分异行为。

As suggested by a great amount of geologic and experimental evidence. The REE in rock sequences may be mobilized during fluid\|rock interaction when solutions are rich in F\+-, Cl\+-, CO\+\{2-\}\-3, HCO\+-\-3, CO\-2, HPO\+\{2-\}\-4, HS\+-, S\+-\-2, and SO\+\{2-\}\-4, though little has been known about the mobilizing mechanism of these anions or ligands. The fractionation of REE resulted from hydrothermal alterations, i. e., fluid\|rock interactions are significantly different. One set of field data implies the preferential mobility of the lighter REE, while another set of field observations demonstrates the dominant mobilization of the heavier REE. This depends upon the composition, Eh and pH of the hydrothermal and REE\|bearing phases involved in reactions. Eu anomalies caused by fluid\|rock interactions are complex. REE distributions of monomineral alteration assemblages are related to chemical\|crystallographic controls of the altered minerals in contrast, REE distributions of polymineral alteration assemblages are related to changes in physico\|chemical conditions during alteration, including pH, Eh, fluid/rock ratio, and complexing agent concentration. To know the exact behavior of REE during fluid\|rock interaction and to solve the contradiction between some theoretical predictions and field observations, the following work needs to be done: (1) Experimental research on REE mobility and fractionation as a function of fluid chemistry, e.g. the activities of F\+-, Cl\+-, CO\+\{2-\}\-3, HCO\+-\-3, CO\-2, HPO\+\{2-\}\-4, HS\+-, S\+-\-2, SO\+\{2-\}\-4, etc.; (2) Experimental determination of REE mobility and fractionation as a function of T, P, pH, Eh and water/rock ratio; (3) Investigation of the mechanism and controlling factors of REE partitioning between hydrothermal minerals and fluids.