大兴安岭西坡二道河子铅锌银矿床银的赋存状态、迁移形式及沉淀机制  

Deposition mechanism,migration and occurrence of silver in the Erdaohezi Pb-Zn-Ag polymetallic deposit in the western slope of the Da Hinggan Mountains

作　　者：刘艳荣 关强兵 刘民武[1,2] 闫晓儒 黄凡 LIU Yanrong;GUAN Qiangbing;LIU Minwu;YAN Xiaoru;HUANG Fan(School of Earth Science and Resources,Chang'an University,Xian,Shaanzi 710054,China;Xi'an Key Laboratory for Mineralization and Efficient Utilization of Critical Metals,Xi'an,Shaanzi 710054,China;Sencin Mining Development Co.Ltd,Genhe,Inner Mongolia 022357,China;Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]西安市关键金属成矿与高效利用重点实验室,陕西西安710054 [3]根河市森鑫矿业开发有限责任公司,内蒙古根河022357 [4]中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2023年第10期3363-3379,共17页Acta Geologica Sinica

基　　金：陕西省自然科学基础研究计划项目(编号2022JM-158);中国地质调查局项目(编号DD20190379-53);国家自然科学基金项目(编号41702062);西安市关键金属成矿与高效利用重点实验室项目(编号300102272502、300102272504);长安大学中央高校基本科研业务费专项资金(编号300102270203)联合资助的成果。

摘　　要：二道河子铅锌银多金属矿床是一个中型浅成热液矿床,它产于大兴安岭西坡得耳布干成矿带中段的晚中生代“双峰式”火山岩区。根椐野外矿脉的穿插关系和室内矿相学研究,将热液成矿期划分为四个成矿阶段,即:石英-黄铁矿阶段(Ⅰ)、石英-多金属硫化物阶段(Ⅱ)、石英-闪锌矿-方铅矿-银矿物阶段(Ⅲ)和石英-方解石-黄铁矿阶段(Ⅳ)。采用显微镜和电子探针(EPMA)微区技术对矿床中的硫化物和银矿物进行分析,结果表明,银的存在形式主要为可见银(>1μm),其次为不可见银(<1μm)。可见银主要以显微包体银和独立银矿物的形式存在,而不可见银主要呈次显微包体银和晶格银;显微(次显微)银常以浑圆状或不规则状分布在硫化物内部或硫化物和石英颗粒间隙,独立银矿物呈脉状或集合体状主要分布于方铅矿(偶见闪锌矿)脉的裂隙和边缘,晶格银赋存在方铅矿中,含量极少。结合前人研究成果,认为成矿早期(石英-黄铁矿阶段)成矿热液中的金属元素(如Ag、Cu、Fe、Pb和Zn元素等)以氯络合物形式运移,伴随着流体不混溶/沸腾作用,硫氢络合物成为主要的迁移形式。随着温度、压力的降低和大气降水的参与,成矿流体自下而上运移,并先后经历了两次银的沉淀富集,分别是:Ⅱ阶段硫氢络合物解体分解后的Ag+与热液中的Cu^(+)、Sb^(3+)、Pb^(2+)、S^(2-等)结合形成显微(次显微)包体银;Ⅲ阶段热液中的Ag(HS)-2直接分解或解离出Ag^(+)与溶液中的Cu^(+)、Sb^(3+)和S^(2-)等离子结合形成独立银矿物(如辉银矿和硫锑铜银矿)。The Erdaohezi Pb-Zn-Ag polymetallic deposit,one of the largest and most representative deposits,is located in the central part of the Derbugan metallogenic belt.The hydrothermal mineralization process is subdivided into four mineralization stages:quartz-pyrite stage(I);quartz-sulfides polymetallic stage(II);quartz-sphalerite-galena-silver minerals polymetallic stage(III);and quartz-calcite-pyrite stage(IV).Microscope observation and electron probe microanalysis(EPMA)analysis suggest that the occurrence of silver in this deposit is mainly visible silver(>1μm),followed by invisible silver(<1μm).Visible silver is mainly microencapsulated silver and independent silver minerals,and invisible silver is mainly super-microencapsulated silver and isomorphic silver.Microencapsulated(super-microencapsulated)silver occurs usually as round or irregular inclusions within sulfides or between sulfides and quartzes.Independent silver minerals are mainly distributed as veinlets or aggregates in microfractures or edges of galena(sphalerite)veins.A very small amount of isomorphic silver exists in the crystal lattices of sulfides.The metal ions in the ore-forming hydrothermal fluids,such as Ag,Cu,Fe,Pb and Zn,are transported as chlorine complex ions in the early mineralization stage(quartz-pyrite stage),and as HS-complex ions after fluid boiling.With decreasing temperature and pressure of the fluids and mixing of meteoric water,the ore-forming fluid has migrated upward and experienced two silver enrichment processes:Ag+released from HS-complex is coprecipitated with Cu^(+),Sb^(3+),Pb^(2+)and S^(2-)to form microencapsulated(super-microencapsulated)silver in stage II;then the instability of Ag(HS)-2 leads to the complete disintegration of silver from its HS-complex and combination with Cu^(+),Sb^(3+)and S^(2-)to form independent silver minerals(such as argentite and polybasite)in stage III.

关 键 词：大兴安岭西坡 得耳布干 铅锌银矿床 赋存状态 沉淀机制 

分 类 号：P618.52[天文地球—矿床学] P618.4[天文地球—地质学]