从热力学角度探讨构造热液中铀的溶存形式、迁移及沉淀机理

DISCUSSION ON SPECIES OF URANIUM AND ITS MIGRATION AND PRECIPITATION MECHANISM IN TECTONO-HYDROTHERMAL SOLUTION IN VIEW OF THERMODYNAMICS

本文从热力学计算入手，以２００℃的Ｕ－Ｃ－Ｏ－Ｈ体系为例，从Ｅｈ，ｐＨ，Ｔ，Ｐｃｏ＿２及∑Ｕ五方面探讨构造热液中铀的溶存形式及其迁移、沉淀机理。结果表明：Ｅｈ，ｐＨ降低不仅改变铀的溶存、迁移形式，而且使其还原成低价态沉淀析出；Ｔ升高会降低构造热液的Ｅｈ，ｐＨ值，使ＵＯ＿（２（ｓ））稳定区间增大，从而控制了溶存、迁移形式的优势分布；Ｐｃｏ＿２降低会使构造热液产生沸腾，逸出ＣＯ＿２，有利于铀的还原析出，而铀矿床的形成离不开丰富的活性铀源，这是维持构造热液具一定浓度的铀，从而使矿化顺利进行的不可缺少的前提。

Based on thermodynamic calculations and taking the U-C-O-H system at 200℃ as an example,the species of uranium and its migrstion and precipitation mechanism in tectono-hydrothermal solution are discussed from such five aspects as Eh,pH,T,Pco_2 and ∑U in this paper. The results indicate that the decrease of Eh and pH not only may lead to the change ofspecies of uranium and its migration,but also cause uranium to be reduced into low valencestate and to be precipitated,the increase of T may lower Eh and pH values in tectono-hydrothermal solution and may result in the increment of stable area of UO_(2(s)), thus,controlling the dominant distribution of existing and migration form of uranium,the decrease of Pco_2may make tectono-hydrothermal solution boiling and CO_2 escaping from the solution,whichare favourable to uranium reduction and precipitation. Anyway,uranium deposits can not beformed without abundant mobile uranium source,which is an indispensable prerequisite forthe tectono-hydrothermal solution to maintain a definite concentration of uranium so that theuranium ore-formation may proceed smoothly.