广东元湾金矿床成因:来自稀土元素和流体包裹体的证据  

Genesis of the Yuanwan Gold Deposit in Guangdong Province:Evidence from Rare Earth Elements and Fluid Inclusions

作　　者：陆一敢 肖益林[1,3] 周奇明[4] 陶明荣[4] 王晓霞 余成龙 LU Yigan;XIAO Yiin;ZHOU Qiming;TAO Mingrong;WANG Xiaoxia;YU Chengong(CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,Anhui,China;School of Natural Resources and Surveying,Nanning Normal University,Nanning 530001,Guangxi,China;CAS Center for Excellence in Comparative Planetology,Hefei 230026,Anhui,China;China Nonferrous Metals Mining(Group)Co.,Ltd,Guilin Research Institute of Geology for Mineral Resources,Guilin 541004,Guangxi,China)

机构地区：[1]中国科学技术大学地球和空间科学学院,中国科学院壳幔物质与环境重点实验室,安徽合肥230026 [2]南宁师范大学自然资源与测绘学院,广西南宁530001 [3]中国科学院比较行星学卓越创新中心,安徽合肥230026 [4]中国有色桂林矿产地质研究院矿产地质研究所,广西桂林541004

出　　处：《大地构造与成矿学》2023年第4期810-823,共14页Geotectonica et Metallogenia

基　　金：国家重点研发计划项目(2018YFA0702701);国家自然科学基金项目(42073003、41729001);广西科技基地和人才专项(2022AC21002)联合资助。

摘　　要：广东元湾金矿床是近年新发现且有潜力的金矿床,为了揭示成矿物质来源和矿床成因,对该矿床的黑云二长花岗岩、花岗闪长岩、含碳质泥岩、石英脉等进行稀土元素和流体包裹体研究。分析结果显示,稀土元素总量(∑REE)平均含量由高到低依次为:含碳质泥岩(182×10^(-6))>黑云二长花岗岩(105×10^(-6))>花岗闪长岩(95.1×10^(-6))>石英脉(19.0×10^(-6))。其中,含碳质泥岩与华南黑色岩系的稀土元素组成相近,是金矿的主要源岩。黑云二长花岗岩的LREE/HREE为1.2~6.8,δEu为0.01~0.24,整体表现为强烈的Eu负异常和四分组效应,属于高分异演化花岗岩,与华南燕山期重熔花岗岩类的稀土元素特征一致,可能为金矿提供必要的成矿物质。δCe负异常反映了寒武系牛角河组(Є1n)形成于相对氧化的滨海‒浅海环境,有利于金矿初始富集。Eu、Ce呈负异常,反映黑色岩系形成于气候干燥的陆棚边缘浅海氧化环境。岩相学观察、显微测温指示流体包裹体类型主要为气‒液两相包裹体和少量含CO_(2)三相包裹体,属于中‒低温(均一温度181.4~204.3℃)的CO_(2)-NaCl-H_(2)O体系,具有低盐度(0.18%~24.46%NaCleqv),且在成矿过程中,含矿流体可能经历了流体不混溶作用。在中‒低温和剪切带相对还原条件下,金矿在构造有利部位发生沉淀是该矿床成矿的关键。The newly discovered Yuanwan gold deposit in Guangdong province,situated in the Qin-Hang metallogenic belt,has significant gold resource potential.In order to reveal the source of the ore-forming materials and genesis of the deposit,rare earth elements(REEs)and fluid inclusions of the biotite monzogranite,granodiorite,carbonaceous mudstone,and quartz veins were analyzed.Our results show that the average∑REE contents of the samples decrease from carbonaceous mudstone(182×10^(-6)),biotite monzogranite(105×10^(-6)),granodiorite(95.1×10^(-6)),to quartz(19.0×10^(-6)).The mudstones have REE patterns similar to those of the black shales in South China,and are considered to be the main source of gold.The biotite monzogranites are highly evolved S-type granite with LREE/HREE ratios of 1.2 to 6.8,showing significant negative Eu anomalies(δEu ranges from 0.01 to 0.24)and tetrad effect.The biotite monzogranites may provide necessary ore-forming materials for the Au deposit.The negative Eu and Ce anomalies of the Cambrian Niujiaohe Formation(Є1n)indicate that the black rock-series was formed in relatively oxidized litoral-shallow marine environment,which was conducive to the initial enrichment of gold.In addition,the fluid inclusions mainly consist of two-phase gas-liquid inclusions and a small amount of CO_(2)-bearing three-phase inclusions,and the fluid belongs to mid-low temperature(181.4–204.3℃)CO_(2)-NaCl-H_(2)O system with low salinity(0.18%–24.46%NaCleqv).Moreover,the ore-bearing fluids might have experienced fluid immiscibility during the mineralization.Thus,under these favorable conditions of mid-low temperature and relative reductive in shearing zones,the Yuanwan gold deposit ultimately formed in a unique structural location.

关 键 词：粤西‒桂北 元湾金矿 稀土元素 流体包裹体 钦‒杭成矿带 

分 类 号：P611[天文地球—矿床学] P595[天文地球—地质学]