相山铀矿田云际矿床碱交代型铀矿化蚀变作用及组分迁移规律研究  

Mineralization characteristics and geochemical elements migration during alkali metasomatized hydrothermal process of Yunji deposit in Xiangshan uranium ore field

作　　者：王勇剑[1,2,3] 聂江涛 林锦荣[1] 庞雅庆[1] 王正庆[4] 秦克章[2,3] WANG YongJian;NIE JiangTao;LIN JinRong;PANG YaQing;WANG ZhengQing;QIN KeZhang(Beijing Research Institute of Uranium Geology,Beijing 100029,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;School of Nuclear Resources Engineering,University of South China,Hengyang 421001,China)

机构地区：[1]核工业北京地质研究院,北京100029 [2]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049 [4]南华大学核资源工程学院,衡阳421001

出　　处：《岩石学报》2022年第9期2865-2888,共24页Acta Petrologica Sinica

基　　金：国家重点研发计划专项(2017YFC0602600);国家自然科学基金项目(41772082);中国铀业有限公司地勘项目(地D2002、地D2210)联合资助.

摘　　要：云际矿床是江西相山火山岩型铀矿田内最典型的碱交代型铀矿床,其矿体主要赋存于碎斑熔岩中。本文以两个典型矿化剖面为研究对象,系统研究了碱交代型铀矿化的蚀变分带特征、蚀变和矿石矿物组合以及热液蚀变过程中元素迁移变化规律。详细的岩相学观察表明,碱交代型铀矿化发育明显的侧向水平分带,由内到外可细分为矿化中心带、近矿强蚀变带、远矿蚀变带和新鲜围岩,各蚀变带之间并无明显的界线;发育的主要蚀变类型为钠长石化、赤铁矿化、碳酸盐化、绿泥石化和磷灰石化;铀赋存状态主要以独立铀矿物(钛铀矿和铀石为主)、类质同象和吸附状态3种形式存在。Isocon标准化图解法表明,从远矿弱蚀变带到矿化中心带,CaO、Na_(2)O、P_(2)O_(5)、MgO、TiO_(2)、Fe_(2)O_(3)、U、HREE、Sr、Cr、Co、Ni、Zr、Hf的迁入量呈逐渐升高的趋势,其中CaO、P_(2)O_(5)、MgO、U、Sr在矿化中心带表现为强烈的富集,而SiO_(2)、K_(2)O、LREE、Ba、Rb、Cs则呈明显的迁出趋势;各蚀变带均呈现Na_(2)O的大量富集和K_(2)O的极度贫化,且均不伴有钍富集和钼富集。矿石中显著升高的Y/Ho值、δEu值以及Fe_(2)O_(3)/(Fe_(2)O_(3)+FeO)值暗示碱交代铀成矿流体具有较高的氧逸度,可能为多来源流体混合形成的复杂成因流体;矿石中强烈的“去硅”作用、Zr的富集以及极高的Na^(+)/K^(+)值和Zf/Hf值表明碱交代成矿流体具有较高的碱度。综合岩相学、蚀变带元素迁移特征及前人研究成果,本文认为碱交代铀成矿流体在演化过程中呈现氧逸度、pH值和温度逐渐降低的趋势,流体中的铀可能主要以碳酸铀酰络合物的形式迁移,CO_(2)挥发分的大规模逸散可导致铀矿物和大量磷灰石、碳酸盐的共同沉淀富集并形成富大矿体;此外,铀磷络合物可能也是本矿床成矿流体中铀的赋存、迁移形式之一。Yunji deposit is the most typical alkali-metasomatized uranium deposit in Xiangshan volcanic-related uranium ore field in Jiangxi Province,and its ore bodies are mainly hosted within porphyroclastic lava.Exemplified by two typical uranium mineralization sections,we systematically studied the alteration zoning and mineral assemblage of alkali metasomatic uranium mineralization,as well as the elements migration regularity during hydrothermal process.Detailed petrographic observations indicated that the uranium mineralization is characterized by laterally horizontal zoning,which can be subdivided into mineralized central zone,near-ore altered zone,distant-ore altered zone and fresh wall rock outwardly,and the dominant alteration types include albitization,hematitization,carbonation,chloritization and apatitization.The occurrence of uranium is mainly composed of independent uranium minerals(brannerite and coffinite),isomorphism and adsorption.The result of standardized Isocon graphical method showed that,from the distant-ore zone to the central zone,the contents of CaO,Na_(2)O,P_(2)O_(5),MgO,TiO_(2),Fe_(2)O_(3),U,HREE,Sr,Cr,Co,Ni,Zr and Hf gradually increase,of which CaO,P_(2)O_(5),MgO,U and Sr are strongly enriched in the central zone,while SiO_(2),K_(2)O,LREE,Ba,Rb and Cs decrease dramatically.All three altered zones are enriched in Na_(2)O and extremely depleted in K_(2)O,and not accompanied by enrichment in Th and Mo.The significantly increased Y/Ho,δEu and Fe_(2)O_(3)/(Fe_(2)O_(3)+FeO)values in the mineralized zone suggest that the alkali metasomatic ore-forming fluid is characterized by a relatively high oxygen fugacity,which may be caused by mixing of multi-source fluids.The intense desiliconization,enrichment of Zr,and extremely high Na^(+)/K^(+) and Zf/Hf values indicate that the ore-forming fluid has a high alkalinity.Combined with petrography,elements migration characteristics and previous studies,it is believed that the oxygen fugacity,pH values and temperatures of ore-forming fluid might gradually decre

关 键 词：碱交代型铀矿化 热液蚀变 元素迁移 成矿流体 云际矿床 相山铀矿田 

分 类 号：P619.14[天文地球—矿床学]