伊犁盆地蒙其古尔铀矿床含矿砂岩成岩蚀变特征及其有机—无机流体成岩成矿效应

摘要

伊犁盆地蒙其古尔铀矿床为典型的层间氧化带型铀矿床,虽然前人对该区铀矿的成矿流体进行了较为系统的研究,但对其成矿流体来源依然存在较大的分歧,尤其对该区成矿流体与蚀变特征、铀成矿的内在联系研究较少.本文为了研究蒙其古尔铀矿床成矿流体来源及其与成岩蚀变、铀成矿的内在联系,综合地应用了偏光显微镜、扫描电镜、电子探针等手段,对其含矿目的层砂岩成岩蚀变进行系统的分析,并对蚀变矿物高岭石H—O同位素、碳酸盐胶结物C—O同位素及黄铁矿S同位素进行了研究.研究表明:与砂岩型铀矿有关的成岩蚀变类型主要有黏土化、碳酸盐化、硅化及金属矿化;成矿流体中水8DH2O,V-SMOW为-48.3‰-93‰,δ18OH2O,V-SMOW为-10.3‰-5.1‰,碳酸盐胶结物δ 13C V-PDB为-10.9‰～-7.2‰,818OV-SMOW为17.6‰～24.9‰,黄铁矿δ34SⅤ-CDT为-17.3‰～1.2‰,上述特征揭示蒙其古尔铀矿床成矿流体是由大气降水性质的地表水(无机)和煤系地层有机质脱羟基及热降解作用产生的有机酸及CH4等还原性气体(煤层气)(有机)两部分组成;成岩蚀变和铀成矿效应皆是有机—无机流体及流体与周围砂岩相互作用的结果.%Objectives:The mengqiguer uranium deposit,Ili Basin,was interlayer oxidation zone type uranium deposit.Although its metallogenic fluid was studied systematic by predecessor,the problem about its source still exist,especially about the internal relation between metallogenic fluid and alteration characteristics and uranium mineralization.In this article,we will find out the source of metallogenic fluid,the relationship between metallogenic fluid and diagenetic alteration and uranium metallization.Methods:In order to researching the source of metallogenic fluid and the relationship between metallogenic fluid and diagenetic alteration and uranium metallization,the methods of polarizing microscope,scanning electron microscope,electronic probe was comprehensively utilized to analysis alteration characteristics of sandstone in the ore-bearing layer systematically and the stable isotope of alteration mineral about ite,carbonate cement,pyrite in sandstone of ore-bearing was studied.Results:The diagenetic alteration characteristic relating to sandstone-type uranium deposit mainly include clayzation,carbonation,silication and metal mineralalization;the δD(aq) Ⅴ-SMOWand δ18OⅤ-SMOW of its metallogenic fluid is varies from-93‰ to-48.3‰,-10.3‰ to-5.1‰ respectively,the δ13CⅤ-PDB and δ18OⅤ-SMOW of its carbonate cement from sandstone in ore-bearing is range between-10.9‰ and-7.2‰,17.6‰ and 24.9‰ and the δ34SⅤ-CDT is range from-17.3‰ to 1.2‰ respectively.Conlusions:The above characteristics reveal that the metallogenic fluid of Mengqiguer Uranium deposit is mixed fluid which consists of surface-water stemming from meteoric waters (inorganic) and organic acid,reducing gas (CBM) originating from coal evolution;As a result,the effect of diagenetic and uranium mineralization was result from reciprocity of organic — inorganic fluid and fluid—rock.