城山岩体铀的赋存状态及配分研究

利用诱发裂变径迹结合铀浸取分析资料,对城山岩体及围岩的铀赋存状态和配分进行了研究。岩石中的铀按照浸出难易程度可把其分为固定铀和活动铀两大类。岩体中的原生铀主要是铀的简单氧化物和类质同象置换或晶格吸附铀二种,以那种存在形式为主取决于全岩铀含量的高低和付矿物含量的多少。岩体和围岩的铀富集均与铁质有密切的关系,尤其是一些次生氧化物吸附了较多的铀,系原生铀的活化迁移所致。各种围岩(沉积岩)向着接触带,随着其基质的粒度增大,含铀的点状放射源的数目减小,但放射源变得更强。紧靠接触带的固岩,由于受岩浆期后热液的影响,铀含量明显增高。岩体由中心向着接触带铀的浸取率变大。岩体不同侵入阶段从早到晚活动铀的含量增加,铀赋存状态的变化趋势是固定铀→分散的活动铀→集中的活动铀。只有铀含量和浸取率都高的岩石才能提供较多量的活动铀,从第三侵入阶段岩石中淋滤出足够的铀形成矿床的可能性是很小的。铀源主要来自岩浆分异。

A STUDY OF THE EXISTING FORMS OF URANIUM AND ITS DISTRIBUTION IN CHENGSHAN GRANITIC BODY

The existing forms of uranium and its distribution in Chengshan granitic body and country rocks have been investigated by the methods of fission-track and uranium maceration. Uranium can be divided into two groups, mobile and inert, according to the possibility of the maceration from rocks. Primary uranium exists mainly in two forms, simple oxides and solid solution and crystal structural incorporation. Whether it appears chiefly in the former form or latter one depends on uranium abundance and contents of accessory minerals in whole rock. Uranium enrichment, both in granite and country rocks,is closely associated with Fe. It is noteworthy that secondary Fe oxides absorb more uranium because of primary uranium mobilization. From country rocks (sedimentary rocks) to the intrusive contact zone,as the grain in ground mass increases in size,uraniumbearing point sources decrease in number, and the remaining sources become more intense. Uranium contents in the country rocks close to the contact zone increase significantly under the influence of postmagmatic hydrothermal solution. Mean while, the ratio of uranium maceration becomes greater from the centre of the granitic body to the contact zone. Contents of mobile uranium increase from early to lace in different intrusive stages. The change pattern of the existing forms of uranium is inert uranium,dispersive mobile uranium and concentrated mobile uranium. Only the rocks high both in uranium contents and ratio of maceration may produce more mobile uranium. It is little possible to leach enough uranium from the rock of the third stage to form deposits. The source of uranium is mainly due to magmatic differentiation.