西秦岭阳山金矿带安坝矿床热液蚀变作用  

Hydrothermal alteration of the Anba deposit,Yangshan gold belt,western Qinling

作　　者：张志超[1] 李楠[1] 戢兴忠[1] 韩忠[2] 郭耀宇[1] 李在春[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国人民武装警察部队黄金第三总队,成都610000

出　　处：《岩石学报》2015年第11期3405-3419,共15页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(2015CB452605);国家自然科学基金项目(41030423);国家公益性行业科研专项经费项目(201411048);高等学校学科创新引智计划(B07011);中国地质调查局地质调查项目(1212011121090);中国地质大学(北京)基本科研业务费专项资金资助项目(2-9-2014-055)联合资助

摘　　要：安坝金矿床是阳山金矿带内已探明金资源储量最大的金矿床,矿体受NEE向的区域性安昌河-观音坝断裂带及其次级断裂-裂隙系统控制,主要赋存于紧邻断裂带的千枚岩和斜长花岗斑岩中。围绕断裂-裂隙系统的赋矿围岩硫化、硅化、绢云母化、碳酸盐化、绿泥石化、绿帘石化和粘土化蚀变发育,其中前三种蚀变与金成矿作用关系最为密切。论文在厘定安坝金矿床热液蚀变类型、矿物组合特征、以及断裂变形与蚀变空间变化关系的基础上,通过对蚀变岩及其原岩的地球化学分析,剖析了热液蚀变作用过程与机理。研究结果表明,硅化蚀变贯穿发育于成矿前、成矿期和成矿后,绢云母化蚀变为成矿前和成矿期的产物,碳酸盐化蚀变主要发育于成矿晚阶段和成矿后,而粘土化蚀变为成矿后的产物。在长石蚀变为绢云母的过程中,有少量Al2O3带出,而TiO 2在蚀变过程中相对稳定,为此选取TiO 2作为不活动组分,开展质量平衡计算得出:在硅化过程中,明显带入的组分有SiO 2、Fe2O3、FeO、MgO、CaO、C、S、Au、As、Hg、Pb和Zn,而被带出的元素为Rb和Ba;在绢云母化过程中,明显带入的组分为SiO 2、Fe2O3、CaO、C、S、Au、As、Hg、Pb、Zn、Rb和Ba,带出组分为Na2O。稀土元素地球化学特征显示千枚岩原岩稀土元素含量比硅化和绢云母化千枚岩的稀土元素含量高,表明在蚀变过程中有稀土元素的流失。此外,千枚岩原岩的δEu=0.70,δCe=0.95;硅化千枚岩的δEu=0.72,δCe=1.00;绢云母化千枚岩的δEu=0.76,δCe=0.95。硅化、绢云母化千枚岩与千枚岩原岩的REE球粒陨石标准化配分模式曲线变化趋势相似,表现为明显的Eu负异常、无Ce异常的富轻稀土的右倾型曲线。含矿流体沿断裂带运移并与围岩反应,形成了石英和绢云母等蚀变矿物。硅化过程中,含矿流体中还原硫活度降低导致金沉淀;而绢云母化过程中,含矿流体的pThe Anba gold deposit has the largest verified gold reserves in the Yangshan gold belt. The ores are controlled by regional Anchanghe-Guanyinba fracture zones with NEE strikes and its secondary faults and facture system. The ores mainly hosted in phyllite and plagioclase granite porphyry near the fracture zones. Sulfuration, silification, sericitization, carbonatization, chloritization,epidotization and clay alteration develop in the rocks around the secondary faults and facture system. And,the first three types of alteration are critical for mineralization. Based on the type of hydrothermal alteration,the mineral assemblage characteristics and the spatial relationships between fracture transformation and alteration,and combined with the geochemical analysis of the altered rocks and original rocks,the paper studies the alteration process and mechanism. The study results show that silification occurs before,during and after mineralization,while sericitization develops before and during mineralization,carbonatization develops in late stage of mineralization and after mineralization,and clay alteration develops after mineralization. During the process of feldspar turns into sericite,Al2O3 will be brought out slightly,but Ti O2 is relatively stable. And Ti O2 is chosen as inactive component. The mass balance calculations show that： during silification,Si O2,Fe2O3,Fe O,Mg O,Ca O,C,S,Au,As,Hg,Pb and Zn are brought in,contrary with Rb and Ba. During sericitization,Si O2,Fe2O3,Ca O,C,S,Au,As,Hg,Pb,Zn,Rb and Ba are obviously brought in,while Na2 O out. The rare earth elements geochemical characteristics show that the total rare earth elements content in the original phyllite rock is more than that in the silicified phyllite rock and the phyllite rock of sericitization,and it suggests a loss of rare earth elements.δEu and δCe in the original rock are 0. 70 and 0. 95,respectively. δEu and δCe in the silified rock are 0. 72 and 1. 00,respectively,While δEu and δCe in the sericitization rock are 0. 76 and 0. 95,respec

关 键 词：热液蚀变 质量平衡 安坝金矿床 阳山金矿带 西秦岭 

分 类 号：P618.51[天文地球—矿床学]