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 investigatsed 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, uranium bearing point sources decrease in number, and the remaining sources become more intense. Uraniumm 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 late in different intrusive stages. The change pattern of the existing forms of uranium is inert uranium, dispersive mobile uramium and concentrated mobile uranium. Only the rock high both in uranium contents and ratio of maceration may produce more mobile uranium. There is a little possibility to leach enough uranium from the rock of the third stage to form deposits. The source of uranium is mainly due to magmatic differentiation