| Dafushang ore deposit is located in the middle of Dawangshan-Yushan granite uranium metallogenic belt, in the southern of Taoshan uranium ore field. Uranium minerlization is mainly produced in medium-fine grained two-mica moorstone, and is strictly controlled by the tectonic fracture zone. The uranium ore bodies form of vein-group-type, among a single ore body form of lenticular or irregular shape. Texture of ores mainly for colloidal texture and sphaerulitic texture, but a small amount to the banded structure. Structure of ores mainly for micro-vein structure and mesh-vein structure and impregnated structure. The wall-rock alteration characteristics of Dafushang uranium deposit are mainly hematitization, chloritization, fluoritization, carbonatation, albitization, silicification, etc.Based on test samples of Dafushang uranium ore deposit using electron microscope, electron probe, artificial heavy concentrate, X-ray diffraction, laser Raman of modern testing technology, has been found that the occurrence state of U mainly exists in the form of independent uranium ore, such as pitchblende, coffinite, brannerite and uranothorite. These mineral that have forms of granulous, irregular crumby-structure, nebulosity, mottling and disseminated, distributed to the mineral interior gaps of orthoclase, apatite, chlorite, quartz and pyrite, also has distributed along the mineral fracture or micro-fracture with to form vein structure and mesh-vein structure. Second a small amount isomorphism of the occurrence state of U existed in auxiliary mineral- such as apatite and zircon. Otherwise minute quantity adsorption of the occurrence state of U dispersed into mineral surface, such as orthoclase, sericite, chlorite and limonite. It made in ore deposit of alteration zone and oxidation zone, α track-etch measurement micrograph display that the occurrence state of U is adsorption form of disperse.Chloritization is an important alteration type of the metallogenic stage in the Dafushang uranium deposit. It is very close relationship with uranium mineralization, that the forming process is closely related with hydrothermal fluid. Chlorite characteristics of chemical composition can be used as a geological thermometer, that can reflect fluid properties, environment of water-rock reaction and ore-forming physicochemical conditions. The results of electron probe microanalysis showed that,(1) the chlorites from the Dafushang uranium deposit are iron-rich prochlorite,(2) the temperature range of formation of chlorite is 201.48 ~ 224.20 ℃(averagely 213.65℃), which belong to the mesothermal epithermal alteration,(3) formation mechanism are dissolution-crystallization and dissolution-migration-crystallization. Chlorite characteristics shows that medium-low temperature reducing coditions of uranium-forming of granite type in the Dafushang deposit.We can roughly speculate about chloritization of Dafushang uranium deposit relationship with uranium mineralization, namely, U-rich hydrothermal solution transporting along to structural fracture and crushed zone of wall-rock. U-rich hydrothermal solution have happened metasomatism with rock-forming minerals-such as orthoclase and biotite, in a relatively acidic reducing environment, not only form to chlorite, but also prompted inert-U active-U of biotite. Therefore, chloritization provided uranium source for uranium mineralization. Following original physical and chemical equilibrium of U-rich hydrothermal solution constantly destroyed that the uranyl ion in fluid be further revivification and sediment, so that take shaped tetravalent uranium ore-for example pitchblende, also fill in cleavage and fissure of chlorite, which constitute the pitchblende – chlorite – pyrite veins. |
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