摘要
根据花岗岩铀成矿作用的"铀预富集系"和沉淀等理论进行一系列实验模拟。对华南产铀花岗岩及其母岩进行"部分熔融实验",可知其寒武系等下古生界是形成产铀花岗岩重要母岩之一。实验表明,岩浆温度下产铀花岗岩流体(f)与共存相熔体(m)铀分配系数Kf/m测定值明显<1,这说明铀强烈趋向熔体,不断重熔会使花岗岩更富铀。岩浆结晶过程中流体(f)与结晶熔体(c)铀分配系数Kf/c随结晶作用加强而增长,说明对形成热液铀矿床有利。岩浆结晶过程中晶体与晶体共存相间铀的分配系数中,以含铁物质与铀矿物共存相间铀的分配系数为最大。此结果与产铀花岗岩含晶质铀矿,黄铁矿含铀较高,黑云母结晶捕获一定量铀的地质事实相一致。成矿前的"前提蚀变"阶段的铀活化实验得出,黑云母在白云母化时铀释出约达3%~30%;花岗岩白云母化过程中,全岩将有30%~60%的铀释出。在花岗岩白云母化时锆石迁出铀可达1.4%~21%。晶质铀矿在花岗岩白云母化时发生崩解和部分溶蚀,实验得出转入溶液的w(U)为(1.04~1.30)×10-6。大量水-岩反应的热液实验表明,在封闭体系统的溶液中,随压力(pH2O)降低,产铀花岗岩中的铀溶解增加(最高可增达2~3个数量级),从而打破了"压力降低铀沉淀"的一般传统说法。对热液铀矿成矿机理进行多次实验取得如下新认识:(1)适度脱碳酸(或脱CO2)对铀沉淀有利;也可使铀-硅-碳酸盐体系中的"铀-硅分离"沉淀;(2)成矿溶液"pH显著降低(落差)"是铀沉淀几大因素中的关键。这些实验结果证实和发展了"地层、岩石等预富集系"理论,并有重要找矿意义。
Based on the theory of "uranium pre-concentration system" and the theory of precipitation, the author has conducted the "partial fusion experiment" of uranium productive granite and its mother rock. The result shows that the mother rocks for forming uranium productive granite are originated from the sedimentary rocks of Cambrian and the Lower Palaeozoic, etc. The test indicated that the uranium distribution coefficient (K^f-m) between the uranium productive granite fluid (f) and the co-existing fused mass (m) at magma temperature is remarkably smaller than 1, showing that the uranium is intensively concentrated in the fused mass, and the continuous re-melting can make the uranium content increase in granite. During the period of magma crystallization, the distribution coefficient (K^f-c) between fluid (f) and crystalline fused mass (c) increases with the advance of crystallization, indicating it is favourable for forming the hydrothermal uranium deposit. By analyzing the uranium distribution coefficients of different crystals, we found that the uranium distribution coefficient is the largest, when ferruginous material and uranium mineral crystals are co-existing. The experiment results are concordant with the fact that uranium content is higher when the uranium productive granite contains more uraninite and pyrite, which is consistent with the fact that biotite captures uranium during the crystallization. The experiment of uranium mobilization in the period of pre-ore alteration before mineralization shows that about 3%-30% uranium is released when the biotite is converted into muscovite (muscovitization). During the granite muscovitization, about 30%-60% uranium will be released from the total rock and 1.4%-21% uranium will be released from zircon; the uraninite is disintegrated and parts of them are dissolved. The experiment indicates that the total uranium which migrated into the solution is (1.04-1.30) × 10^-6. Hydrothermal experiments of water-rock reaction exhibit that in the solution of a sealed system, the dissolution of uranium increases (up to 2-3 orders) with pressure decreasing. This conclusion smashed the traditional view point that the uranium will precipitate when pressure is decreased. New conclusions have been drawn from the experiments of hydrothermal uranium mineralization: (1) Moderate decarbonation is favourable for uranium precipitation and also favourable for "uranium-silicon separation" from the "uranium-silicon-carbonate" system. (2) The key factor for uranium precipitation is the remarkable decrease in the pH of the mineralization solution. The experiments have confirmed and developed the theory of the pre-concentration system of strata and granite masses, and have a great significance for uranium prospecting.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2009年第1期99-113,共15页
Earth Science Frontiers
基金
国家自然科学基金项目(49903004
4860075)
关键词
花岗岩
铀成矿作用
部分熔融
分配系数
活化迁移
成矿机理
模拟实验
granite
uranium mineralization
partial fusion
distribution coefficient
mobilization migration
mineralization mechanism
simulation test