Geochemical Study Of The Uranium Ore In Xiazhuang Uanium Ore Fields, Northern Guangdong Province

Granite type, volcanic type, sandstone type and carbon-silicon mudstone type uranium deposits are the four main types of uranium mineralization currently in China. Accounting for about38%of the uranium reserves in China the granite uranium deposit becomes the most important uranium mineralization type in our country. Granite uranium deposit in Xiazhuang uranium ore field, located in the east of the Guidong granite lithosome (pluton) of Nanling Rang which is an important metallogenic belt in South China, is found for the first time in China. In order to start a further uranium deposit prospecting work in the surrounding of the ore field and other granite areas, it is significant to study the uranium mineralization mechanism of the region where some uranium deposits has been detected. The petrology, isotope chronology, isotopic tracing and other related research has been carried out on the ore bearing wall rock, typical uranium ore and the interrelated associated mineral samples collected in the Xiazhuang ore field. Combining with previous research of other researchers, the author proposed the following main points:(1) Through the results of uranium leaching experiment, significant differences can be found regarding to the leaching rate of the granite and the diabase. The leaching rate of the Luxi, Xiazhuang and Maofeng uranium are all above40%, but the leaching rate of diabase uranium is only1.43%, thus it can concluded that the uranium element in Xiazhuang uranium deposit comes from the granite rather than the diabase.(2) Many muscovitization and choritization alteration of the biotite are observed in the granite slices by microscope. It has been proved that the alteration of biotite can release uranium element, which is one of the important uranium sources in this region. Through the microscopic morphology and age characteristic of the uraninite in Xiazhuang and Maofeng lithosome, we can get conclusion that the uraninite is another important uranium source in Xiazhuang area.(3) In this paper, the ages of the uraninite in Xiazhuang and Maofeng are207.8±4.3Ma and197.5±1.9Ma. These formation ages, different from the the host rock’s age, are obviously older than the muscovite age (145Ma) which represents the time of the alkali metasomatism in this area. In addition, comparing with the chemical composition of other uraninites from difference origin, it can get the conclusion that these uraninites may form in the magmatic crystallization stage.(4) Considering the chemical composition and microstructure characteristics of samples in the No.335deposit, the No.335deposit has been affected by other geological events after its formation. But the maximum age (93.5±1.2Ma) obtained in this paper still has significance on behalf of its initial formation age. The similarity of the ore-forming age and the diabase age105Ma, it is the formation time of the crustal extension, shows that they are formed in the same period. What’s more, this relationship is a favorable evidence for the fact that the crustal extension event controlled the formation time of the uranium deposit.(5) The results of the carbon and oxygen isotope study display that the δ13C is mainly between-9.2‰and-3.1‰. And the diagrams of the carbon and oxygen isotope show that the mineralization liquor of the Xiazhuang ore field mainly came from the magmatic hydrothermal and have some atmospheric precipitation in the late stage. This mixed hydrothermal acted on the consolidated granite body with the joining of mantle-derived fluid and contributed to the enrichment of uranium.Finally the pattern of uranium migration, enrichment, precipitation is summarized and a four-stage enrichment metallogenic model of uranium is proposed in this paper based on the geochemical behavior of uranium in various geological bodies, geological evolution in Xiazhuang Ore field and the works in this paper. The conclusion are as follows:The first stage:because of the element geochemical behavior, uranium tended to enrichment in the crust after the initial crust-mantle differentiation.The second stage:Partial melting of the crust-derived material formed the early uranium basal.The third stage:Early uranium basal evolved into the uranium-rich granites through partial melting under the indo-tectonic movement.The fourth stage:part alteration and dissolution occurred in the uranium-rich minerals. This progress released the uranium when the granite was transformed by the post-fluid. The uranium migrated after the further action of the fluid and precipitated in a favorable position to form the uranium deposit at last.