YU Chi-da1, WANG Kai-xing1, LIU Xiao-dong1,2, ZHANG Zhi-qiang1, WANG Gang3, WANG Ya-di4
(1. State Key Laboratory of Nuclear Resources and Environment, ECUT, Nanchang 330013, China;
2. JiuJiang University, JiuJiang 332000, China;
3. No. 203 Research Institute of Nuclear Industry, Xianyang 712000, China; 4. Research Center of the Oriental Geophysical Prospecting INC. PetroChina, Zhuozhou 072750, China)
Abstract: The Jiling uranium deposit of Gansu Province, one of the typical alkali metasomatic type uranium deposits in China, is located in the middle part of the Longshoushan Uranium Metallogenic Belt. The commonly occurred chloritization is a type of crucial alteration and one of prospecting indicators in the Jiling uranium deposit. The previous studies of chlorite are mainly concentrated on the estimation of the mineralization temperature and discussion of the mineralization environment by using the chlorite geothermometer. Based on the field investigation, microscopic and SEM petrographic observations, and electron probe microanalysis (EPMA) of chemical compositions of the chlorite in mineralized rocks of the Jiling uranium deposit, we have classified types of chlorites, estimated the formation temperatures and related characteristic indexes of chlorites, and discussed the relationship between chloritization and uranium mineralization in this paper. Several important points have been obtained: (1) Chlorites of the Jiling uranium deposit were mainly classified into four types including the fissure infilling (vein/veinlet), disseminated distribution, biotite altered, and feldspar altered types. The fissure infilling and disseminated distribution types of chlorites are related to the uranium mineralization, but other two types of chlorites are not related to the uranium mineralization; (2) Based on the classification diagram of (Fetotal / Fe+Mg) / Si, chlorites in the Jiling uranium deposit all belong to diabantite; (3) The formation temperatures of chlorites in the deposit obtained by using the Semi-empirical geothermometer, vary from 129 to 297 ℃ with an average of 242 ℃ for the chlorites which are not related to uranium mineralization, , and from 112 to 264 ℃ with an average of 190 ℃ for the chlorites which are closely related to the uranium mineralization. They were all formed in a range of medium to low temperatures; (4) The hydrothermal activity of chlorites which have no directly relationship with the uranium mineralization caused the change of physicochemical property of host rocks and promoted the activation of uranium in uranium-rich accessory minerals within biotite. The hydrothermal activity of chlorites, which were related to the uranium mineralization and were formed due to the emigration of Fe and Mg from the hydrothermal fluid, resulted in the change of chemical properties and broken of the stability of the ore-forming fluid, and promoted the enrichment and precipitation of uranium from the ore-forming fluid.
Keywords: chlorite; geothermometer; uranium mineralization; Jiling uranium deposit；Longshoushan uranium metallogenic belt
ACTA MINERALOGICA SINICA Vol. 40, No.5, 2020, page 628-638
