A Study on Existing Forms and Migration Process of Uranium at Shazhou Deposit, Jiangxi Province, China : Evidences from Induced Fission Tracks

Shazhou uranium deposit occurs in the porphyritic biotite monzonitic granite. Existing forms and distribution characteristics of uranium in the granitic wall rocks and the alteration process at the Shazhou deposit are studied by means of induced fission tracks in this paper. Five existing forms of uranium in the altered granitic wall rocks are identified: i.e., isomorphic uranium in accessory minerals, microscopic-ultramicroscopic uranium mineral grains, adsorbed uranium in rock-forming minerals, uranium in fluid inclusions, and simple uranium oxside minerals. According to the uranium sources in the altered granitic wall rocks, the uranium in the alterated rocks can be subdivided into two categories: i.e., inherited uranium derived from original granite and superimposed uranium derived from ore-forming hydrothermal solutions. During hydrothermal alteration, uranium contents in major rock-forming minerals significantly decreased, and most uranium-bearing accessory minerals disappeared after metasomatism. Metasomatic alteration could move uranium out from granitic wall rocks to hydrothermal fluids, and the activated uranium could be at last concentrated nearby and in the fissures of the alterated minerals, or be adsorbed by the newly formed minerals. Metasomatic alteration changed the existing forms and caused migration and preliminary concentration of uranium, which would be favorable for uranium mineralization.