地幔去气与铀成矿的关系——以江西相山火山岩型铀矿为例

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	地幔去气与铀成矿的关系——以江西相山火山岩型铀矿为例
其他题名	The relationship between the mantle degassing and uranium metallogenetism-a case of the Xiangshan U deposit
	刘磊
学位类型	硕士
	2005
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	地球化学
关键词	Co_2地慢去气矿化剂构造特征流体包裹体铀成矿作用相山铀矿床
摘要	江西相山铀矿床，位于中生代赣一杭火山岩带相山火山塌陷盆地内，是中国目前发现的最大的火山岩型铀矿床，其独特的成矿环境及成矿机理为国内外地质界所瞩目。本论文主要运用岩石学、构造学寸流体包裹体地球化学、同位素地球化学、热力学方法，从相山铀矿床的成矿构造演化、成矿流体、岩石蚀变特征、成矿物质同位素组成特征以及热力学计算等方面对地慢去气特征、过程以及其与铀矿化的关系进行了详细的研究。本研究取得了以下主要认识：1、构造活动对成矿过程起到重要作用。区域深大断裂构造、慢源岩浆活动和碱交代蚀变作用，是相山铀矿田地（量去气作用产生的地慢流体参与成矿作用的有利条件和证据。2、热力学计算表明成矿期前成矿热液pH值为9．50，呈碱性；成矿期前，UO2（CO3）22-、UO2（Coa）44-两种形式迁移的U占总U的99.96％，即矿床中成矿期前的铀主要是以这两种形式迁移的。3、氦一氢同位素研究表明，相山铀矿床的成矿流体由富CO2和3He的慢源流体与贫CO2的大气成因流体混合而成。相山铀矿床成矿热液中的CO2总体属于慢源碳，主要是由地慢或分布在铀矿床中的漫源基性脉岩提供的，而且大部分是在地壳拉张作用期间由地慢去气作用产生而上升形成了成矿热液。4、相山铀矿田成矿期前的流体包裹体中气泡较大，气体含量较高，表明包裹体捕获时压力较大；成矿期和成矿后的包裹体中气泡较小，并存在大量的纯气相包体，通过激光拉曼分析测得的物相峰值极低，表明包体中所包含组分的含量极低。而且大量成矿期纯气相包体的发现也说明其是在去气过程中捕获的从成矿热液中释放出的气体。从成矿期前到成矿期后，CO2含量减小的变化。也说明了成矿作用中发生了减压去气过程。5、在铀成矿过程中，共发生了两次去气作用。第一次地慢去气作用产生并把C仇带入到成矿热液中，第二次成矿流体去气作用正好相反把CO2从成矿热液中带出。地慢去气作用产生富CO2+H2O的地慢流体运移到地壳浅部与大气降水混和，富含矿化剂的成矿溶液由此可以有效地从赋矿围岩（中酸性火山岩和盆地基底地层）中萃取出成矿所需的U。第一次地慢去气作用产生的富CO2+H2O的地慢流体为成矿提供了最充足的矿化剂（CO2），是成矿作用得以发生的最基本最重要的条件。
其他摘要	The Xiangshan uranium deposit , Jiangxi province, located in Xiangshan volcanic collapse basin of Mosezoic Gan-Hang volcanic rock belt, is the largest volcanic rock-hosted uranium deposit in China. The petrology, tectonics, fluid inclusions, isotope geochemistry, thermodynamics were used to determine the characteristics of uranium mineralization at the Xiangshan uranium deposit and discuss the process of mantle degassing and the relationship between mantle degassing and uranium mineralization. The main conclusions are listed as follow: 1. The field observations suggest that the structure control is one of important factors associated with uranium mineralization. 2. The thermodynamic calculation shows that 99.96% of total U in the solution is transported as UO2(CO3)22" and UO2(CO3)34" under alkalic condition (pH=9.5) in the early stage. Regional deep rift, mantel-derived magma movement, and alkali-metasomatic alteration are favorable condition and evidence that mantle-derived fluid, produced by degassing process, joined metallogenesis. 3.The carbon and He isotopes indicate that the ore-forming fluid of Xiangshan uranium deposit is composed of CO2-3He-rich mantle-derived fluid and CO2-poor meteoric fluid. CO2 of Xiangshan uranium deposit was provided by mantle or mantle-derived mafic dike-rock, which may be produced by mantle degassing process during crust pull-apart extension, then moved up and formed metallogenetic solution. 4.The bubble of fluid inclusion, is much bigger and the gas content is much higher at premetallogenetic period. Bubble of fluid inclusion is much smaller and a lot of pure gas inclusion existing at metallogenetic and postmetallogenetic A mass of pure gas inclusion existing indicates the inclusion formed during degassing by capturing gas released from metallogenetic solution. From the early stage to the late stage, the reduce of CO2 content also indicates degassing process existing during metallogentism. 5.There were two stages degassing. Firstly, mantle degassing produced CO2 and took it into metallogenetic solution; secondly) metallogenetic fluid degassing brought CO2 out of the metallogenetic solution. The mantle degassing produced the CO2-H2O-rich fluid, the fluid moved to crust shallow and mixed with meteoric water. So mineralizer-rich (CO2) metallogenetic solution could effectively extract U from wall rock (middle-acid volcanic rock and basement metamorphic rock). The first degassing produced CO2-H2O-rich mantle-derived fluid and provided the enough mineralizer (CO2) for metallogenesis, is the most base and important condition of metallogenesis.
页数	79
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3726
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	刘磊. 地幔去气与铀成矿的关系——以江西相山火山岩型铀矿为例[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2005.

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