摘要
云南马厂箐斑岩-矽卡岩型铜钼矿床位于金沙江-哀牢山成矿带东部,是与喜马拉雅期富碱斑岩侵入有关的大型多金属矿床。本文以其矽卡岩型矿化中的石榴子石为研究对象,利用电子探针和LA-ICP-MS原位U-Pb定年技术开展了成分和年代学测试分析。根据石榴子石的手标本及镜下特征,将其划分为早(Grt I)、中(Grt II)、晚(Grt III)三个世代,其中SiO_(2)、CaO、Al_(2)O_(3)、FeO含量分别为34.15%~36.97%、32.55%~34.40%、0.03%~10.47%、和15.6%~28.3%,属于钙铝榴石-钙铁榴石固溶体系列(Gro_(1-47)And_(51-99)),Grt I较Grt II和Grt III更富含钙铝榴石。三者均富含高场强元素(Th、U、Nb、Ti等)、亏损大离子亲石元素(Rb、Sr、Sc、Y、Sn等)。稀土配分总体呈现轻稀土相对富集、重稀土相对亏损的右倾型。GrtⅠ从核到边Eu均为负异常,GrtⅡ和GrtⅢ核部显示微弱的Eu负异常而边部显示强烈的Eu正异常。石榴子石化学成分及岩相学特征表明早-中期流体处于一个弱氧化、近中性、相对封闭的体系,以扩散交代为主;晚期流体则处于高氧逸度、酸性、相对开放的体系,以渗透交代为主。LA-ICP-MS原位U-Pb同位素测试获得49个石榴子石的U、Th、Pb含量分别为1.95×10^(-6)~56.85×10^(-6)、0.01×10^(-6)~4.74×10^(-6)和0.10×10^(-6)~9.45×10^(-6),T-W图解获得^(206)Pb/^(238)U下交点年龄为34.77±0.38Ma,限定了矽卡岩矿化的时间。综合研究区已有岩浆活动(38~34Ma)、斑岩型矿化(36~34Ma)时限,认为马厂箐斑岩型矿化和矽卡岩型矿化属于同一个岩浆-热液成矿系统的产物。
The Machangqing porphyry-skarn large-scale Cu-Mo deposit is located in the eastern Jinshajiang-Ailaoshan metallogenic belt in Yunnan Province,whose formation is related to the intrusion of alkaline porphyry in the Himalayan Period.This study takes garnets from skarn mineralization as the research object and carries out a systematic analysis on their composition and geochronology by electron microprobe and LA-ICP-MS in-situ U-Pb dating technology.According to the cutting relationship and optical characteristics,the garnets can be divided into three generations from early to late of Grt I,Grt II and Grt III,respectively.The results show that they have SiO_(2),CaO,Al_(2)O_(3) and FeO contents of 34.15%~36.97%,32.55%~34.40%,0.03%~10.47%and 15.6%~28.3%,respectively.The garnets belong to the andradite-grossularite series(Gro_(1-47)And_(51-99)),and the Grt I has more grossularite endmember than Grt II and Grt III.All samples are strongly enriched in high field strength elements(Th,U,Nb,Ti,etc.),depleted of large ion lithophile elements(Rb,Sr,Sc,Y,Sn,etc.).These garnets show a LREE-enriched and HREE-depleted right-leaning type in general.The Grt I has a negative Eu anomaly in the core and rim,while the Grt II and Grt III show weak negative Eu anomaly in the cores and strongly positive Eu anomaly in the edges.The chemical composition and petrographic characteristics of garnets indicate that the fluids in the early and middle skarnization belong to a relatively closed system with near neutral and weak oxidation,and hydrothermal diffusive metasomatism is dominated.In the late stage,the fluids evolve into a relatively open,acidic and high oxygen fugacity system,and infiltration metasomatism is dominated.The LA-ICP-MS in-situ U-Pb dating results show that the U,Th and Pb contents of garnets are 1.95×10^(-6)~56.85×10^(-6),0.01×10^(-6)~4.74×10^(-6) and 0.10×10^(-6)~9.45×10^(-6),respectively;and the calculated lower intercept ^(206)Pb/^(238)U age is 34.77±0.38 Ma via the Tera-Wasserburg diagram,which limits the skarn mine
作者
王潇逸
张静
边晓龙
佟子达
李登峰
WANG XiaoYi;ZHANG Jing;BIAN XiaoLong;TONG ZiDa;LI DengFeng(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;School of Marine Sciences,Sun Yat-sen University,Guangzhou 510006,China;Guangzhou Provincial Key Laboratory of Marine Resources and Coastal Engineering,Guangzhou 510006,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2022年第1期124-142,共19页
Acta Petrologica Sinica
基金
国家自然科学基金重大研究计划(91855217)
高等学校学科创新引智计划(BP0719021)联合资助。
