南岭两类铀矿床的地质地球化学特征及成因探讨

ON THE ORIGIN OF TWO TYPES OF URANIUM-DEPOSITS IN THE NANLING REGION IN SPECIAL REFERENCE TO THEIR GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS

Occurring in the northern part of the Narling region, the deposits under investigation are multimetal sulfide uranium deposits of hydrothermal. (medium to low temperature)origin, which can be divided into two broad types: quartz sulfide and carbonate sulfide.Evidence shows that uranium mineralization is genetically connected with Early Yenshanian granite, quartz porphyry and granodiorite. The author suggests that the regional source-beds may be the main provider Of uranium for such sulfide-type U-deposits (the source-beds include the old metasedimantary rocks, especially those of the Cambrian and Carboniferous). The mechanism of uranium mineralization can be explained as follows: In the process of migmatization, U became highly activated and took its way into granitic magma. In response to the evolution of late orogenic cycle, U was concentrated into the younger small rocks masses, transported in the form of U+^6-F-carbonate complex and uranyl-silicate complex, or complex anions, and finally deposited in favourable structural settings. In the course of U transportation, the interaction took place between wall rocks and hydrothermal solutions containing uranium, leading to the escape of CO2 with decreasing temperatures and pressures. Under such circumstances, the complexes were decomposed and, at the same time, U^+6 was reduced into U^+4, forming pitchblende. Meanwhile, owing to strong silicification, pyritization, hematitization, carbonization and fluoritization, mesothermal and meso-epithermal sulfide-type U-deposits of multimetals were formed.

Occurring in the northern part of the Nanling region, the deposits under investigation are multimetal sulfide uranium deposits of hydrothermal (medium to low temperature) origin, which can be divided into two broad types: quartz sulfide and carbonate sulfide. Evidence shows that uranium mineralization is genetically connected with Early Yenshanian granite, quartz porphyry and granodiorite.The author suggests that the regional source-beds may be the main provider of uranium for such sulfide-type U-deposits (the source-beds include the old metasedimentary rocks, especially those of the Cambrian and Carboniferous). The mechanism of uranium mineralization can be explained as follows:In the process of migmatization, U became highly activated and took its way into granitic magma. In response to the evolution of late erogenic cycle, U was concentrated into the younger small rocks masses, transported in the form of U+6-F-carbonate complex and uranyl-silicate complex, or complex anions, and finally deposited in favourable structural settings. In the course of U transportation, the interaction took place between wall rocks and hydrothermal solutions containing uranium, leading to the escape of COz with decreasing temperatures and pressures. Under such circumstances, the complexes were decomposed and, at the same time, U+6 was reduced into U+4, forming pitchblende. Meanwhile, owing to strong silicification, pyritization, hematitization, carbonization and fluoritization, meso-thermal and meso-epithermal sulfide-type U-deposits of multimetals were formed.