西藏甲玛矿床磁黄铁矿微量元素特征及其与金富集沉淀的耦合机制  

Geochemistry of pyrrhotite in the Jiama deposit, Tibet and its relationship with gold enrichment and precipitation

作　　者：杨征坤 杨阳 张忠坤 林彬[3] 赫健 张泽斌[4] 高福太 唐晓倩 唐攀 祁婧 李怡萱 YANG Zhengkun;YANG Yang;ZHANG Zhongkun;LIN Bin;HE Jian;ZHANG Zebin;GAO Futai;TANG Xiaoqian;TANG Pan;QI Jing;LI Yixuan(Huatailong Mining Development co.LTD,Tibet,Lhasa 850200,Tibet,China;School of Earth Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan,China;MNR key Laboratory of Metallogeny and mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;China Mining Federation of Beijing Consulting Center,Beijing 100044,China;Key Laboratory of Solid Waste Treatment and Recycling,Ministry of Education,School of Environment and Resources,SouthwestUniversity of Science and Technology,Mianyang 621010,Sichuan,China)

机构地区：[1]西藏华泰龙矿业开发有限公司,西藏拉萨850200 [2]成都理工大学地球科学学院,四川成都610059 [3]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [4]中国地质大学(北京)地球科学与资源学院,北京100083 [5]北京中矿联咨询中心,北京100044 [6]西南科技大学环境与资源学院,固体废物处理与资源化教育部重点实验室,四川绵阳621010

出　　处：《中国地质》2022年第4期1198-1213,共16页Geology in China

基　　金：国家重点研发计划-深地专项(2018YFC0604101);中国地质科学院矿产资源研究所基本科研业务费(KJ2102、KK2017);西藏自治区科技计划项目(XZ201901-GB-24);国家自然科学基金项目(419002097);中国地质调查局项目(DD20190167)联合资助。

摘　　要：【研究目的】甲玛矿床是西藏冈底斯成矿带最重要的斑岩成矿系统之一,具有斑岩、矽卡岩、角岩、脉状金矿四位一体矿体结构,形成了丰富的矿物种类和多样的金属矿化。其中,磁黄铁矿作为重要的金属矿物之一,其矿物地球化学特征以及与金矿化的耦合关系一直不明确。【研究方法】此次,以甲玛斑岩成矿系统外围和远端的不同产状的磁黄铁矿为研究对象,基于详细的野外地质调查和镜下鉴定,通过激光剥蚀电感耦合等离子质谱分析方法(LA-ICP-MS)对不同产状的磁黄铁矿开展测点分析和扫描分析,详细揭示其地球化学特征。【研究结果】结果显示,甲玛矿床磁黄铁矿主要富集Co、Ni、Cu、Zn、Ge、Se,弱富集Pb、Bi、Sb、Te、Ag、As,而Mo、Cd、In、Sn、Ba、W、Au、Tl、Th、U等元素含量较低。其中,矽卡岩中的磁黄铁矿具有较高的Co/Ni比值,能有效揭示其岩浆热液成因,而角岩中磁黄铁矿可能继承了一定的沉积特征。【结论】甲玛矿区磁黄铁矿的Cu、Zn、Pb含量变化特征与矿床空间矿化规律一致。矽卡岩中的块状磁黄铁矿与金矿化关系密切,金主要呈他形、不规则的独立金矿物产于磁黄铁矿的孔隙和粒间。同时,金的富集和沉淀可能与富铋的熔体有关。[Objective]As one of the most important porphyry metallogenic systems in Gangdese metallogenic belt in Tibet,Jiama has a four in one orebody structure of porphyry,skarn,hornfels,and vein gold ore-body,forming riched minerals and diverse metal mineralization.Pyrrhotite is one of the important metal minerals,and its mineral geochemistry and relationship with gold mineralization are still obscure.[Methods]The mineralogy and geochemistry of pyrrhotite in different occurrences of the Jiama porphyry system are the main objects for this paper according to detailed field geological survey,petrography,and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)analysis.[Results]The results show that pyrrhotite is obviously enriched in Co,Ni,Cu,Zn,Ge,and Se,and weakly enriched in Pb,Bi,Sb,Te,Ag,and As,and low content of Mo,Cd,In,Sn,Ba,W,Au,Tl,Th,U,relatively.Moreover,the pyrrhotite from skarn has a high ratio of Co/Ni,represent the its magmatic-hydrothermal genesis,while the pyrrhotite hosted in hornfels shows sedimentary characteristics.[Conclusions]The variation of contents of Cu,Zn,and Pb in pyrrhotite are related to the spatial mineralization in the Jiama deposit.The massive pyrrhotite in skarn is closely related to gold mineralization and the gold is mainly anhedral or irregular free gold occurring in the cavity and boundary of pyrrhotite grains.The enrichment and precipitation of gold could be related to bismuth-rich melts in the ore-fluids.

关 键 词：LA-ICP-MS 微量元素 磁黄铁矿 斑岩型铜矿 金矿化 甲玛 西藏 

分 类 号：P618.51[天文地球—矿床学]