滇西北羊拉矽卡岩铜矿床石榴子石原位成分、U-Pb测年及其地质意义  

In situ Chemical and U-Pb Dating Analyses of Garnet from the Yangla Skarn Copper Deposit in Northwest Yunnan Province,and its Geological Implications

作　　者：孙滨[1] 刘益[1] 燕永锋[1] 孔志岗[1] 杨光树[1] 钟军伟[1] 沈畯 SUN Bin;LIU Yi;YAN Yongfeng;KONG Zhigang;YANG Guangshu;ZHONG Junwei;SHEN Jun(Faculty of Land Resources Engineering,Kunming University of Science and Technology,Kunming 650093,Yunnan,China;Hubei Institute of Land Resources,Wuhan 430071,Hubei,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]湖北省国土资源研究院,湖北武汉430071

出　　处：《大地构造与成矿学》2023年第5期1018-1039,共22页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41862007);云南省地球系统科学重点实验室开放课题(ESS2021004)联合资助。

摘　　要：羊拉铜矿床是三江特提斯构造域金沙江缝合带中段的大型矽卡岩型铜矿床,其成矿过程划分为3个期次5个阶段:(1)矽卡岩期:矽卡岩阶段和退化蚀变阶段;(2)石英硫化物期:石英-硫化物阶段和石英-碳酸盐阶段;(3)表生期:主要是表生氧化阶段。里农矿段揭露矽卡岩期的矽卡岩矿物以石榴子石、透辉石为主,根据野外观察、镜下鉴定结合LA-ICP-MS原位微区分析,可将石榴子石分为两个世代:早期石榴子石(GrtⅠ),以钙铝榴石为主(And_(24.81)Gro_(72.40)~And_(57.92)Gro_(30.02));晚期石榴子石(GrtⅡ),以钙铁榴石为主(And_(61.64)Gro_(37.18)~And_(90.96)Gro_(7.81)),发育振荡环带;二者均属于钙铁榴石-钙铝榴石系列。石榴子石稀土元素总量总体较低(ΣREE=3.74×10^(-6)~111×10^(-6)),轻、重稀土元素分异明显(LREE/HREE=0.72~31.7),多呈现正Eu异常(δEu=0.83~8.40)。GrtⅠ亏损轻稀土元素、富集重稀土元素,稀土元素配分模式为左倾型;GrtⅡ整体上富集轻稀土元素、亏损重稀土元素,稀土元素配分模式为右倾型,GrtⅡ中ΣREE、LREE/HREE和δEu值高于GrtⅠ。GrtⅠ、GrtⅡ均呈现出亏损Rb、Ba和Sr等大离子亲石元素,富集Ta、Th和U等高场强元素,GrtⅡ中Cu、Mo、Sn及Pb等成矿元素含量明显高于GrtⅠ。石榴子石主量和微量元素含量及变化特征表明:GrtⅡ形成时氧逸度较GrtⅠ更高,且流体更偏中性或碱性;GrtⅠ交代方式以扩散交代为主,GrtⅡ以渗滤交代为主,与铜钼矿化密切相关。与黄铜矿紧密共生的石榴子石LA-sf-ICP-MS U-Pb进行年代学研究,获得年龄为236±5 Ma(MSWD=0.8,n=23),限定羊拉铜矿床的成岩成矿作用时限为晚三叠世早期,与前人研究的第一期花岗闪长岩锆石U-Pb和辉钼矿Re-Os年龄在误差范围内基本一致,进一步佐证羊拉铜矿床成矿作用与第一期岩浆事件密切相关。The Yangla copper deposit is a large skarn copper deposit in the Jinsha River suture line in the Sanjiang tectonic domain.The mineralization process can be divided into 3 stages and 5 sub-stages:(1)the skarn stage can be further divided into skarn and degeneration alteration sub-stages;(2)the quartz sulfide stage includes the quartz-sulfide and the quartz-carbonate sub-stages;(3)the supergene stage is mainly the supergene oxidation sub-stage.The skarn minerals are mainly garnet and diopside in the Linong section.According to field observation,microscopic identification and LA-ICP-MS in situ microanalysis,garnet in the deposit can be divided into two generations.The early-stage garnet(GrtⅠ)is mainly calcium aluminum garnet(And_(24.81)Gro_(72.40)–And_(57.92)Gro_(30.02)),and the late-stage garnet(GrtⅡ),which has oscillatory rings,is mainly calcium iron garnet(And61.64Gro37.18–And90.96Gro7.81).Both of them belong to the andraditegrossularite series.The garnet has relatively low REE contents(ΣREE=3.74×10^(−6)–111×10^(−6)),high LREE/HREE ratios(LREE/HREE=0.72–31.72),and dominantly positive Eu anomalies(δEu=0.83–8.40).GrtⅠshows depletion of light rare earth elements(LREE)and enrichment of heavy rare earth elements(HREE),showing left inclined REE patterns.GrtⅡshows enrichment of LREE and depletion of HREE as a whole,and right inclined REE patterns.In comparison,theΣREE,LREE/HREE ratios andδEu of GrtⅡare generally higher than those of GrtⅠ,the ratio of LREE/HREE has a clear positive correlation withδEu,theΣREE has a weakly positive correlation with U and Y,but GrtⅠhas no significant correlation.Both GrtⅠand GrtⅡare strongly depleted in large ion lithophile elements including Rb,Ba,and Sr,and enriched in high field strength elements such as Ta,Th and U.The contents of Cu,Mo,Sn and Pb in GrtⅡare significantly higher than those in GrtⅠ.The contents and variations of major and trace elements in garnet indicate that the oxygen fugacity of GrtⅠis higher than that of GrtⅠ,and the f

关 键 词：石榴子石 原位U-Pb测年 LA-ICP-MS 羊拉铜矿床 滇西北 

分 类 号：P611[天文地球—矿床学] P597[天文地球—地质学]