西藏隆格尔铁矿床成岩成矿时代及对区域多期铁成矿作用的启示:地球化学、锆石U-Pb及金云母Ar-Ar同位素定年约束  

Geochronology of Magmatic Intrusions and Mineralization of Lunggar Iron Deposit in Tibet and Its Implications for Regional Multi-Stage Iron Mineralization:Geochemistry,Zircon U-Pb and Phlogopite Ar-Ar Isotopic Dating Constraints

作　　者：高顺宝[1] 郑有业[2] 田坎 陈鑫[2] 姜晓佳[2] 顾艳荣 Gao Shunbao;Zheng Youye;Tian Kan;Chen Xin;Jiang Xiaojia;Gu Yanrong(Institute of Geological Survey,China University of Geosciences,Wuhan 430074,China;Faculty of Earth Resources,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学地质调查研究院,湖北武汉430074 [2]中国地质大学资源学院,湖北武汉430074

出　　处：《地球科学》2021年第6期1941-1959,共19页Earth Science

基　　金：国家地质调查项目(No.DD20190159-33);国家重点研发计划项目(No.2016YFC0600300).

摘　　要：为了查明冈底斯成矿带隆格尔富铁矿床的成矿时代、形成环境及其对区域铁成矿作用的指示,对该矿床开展了岩石地球化学、锆石U-Pb年代学和Lu-Hf同位素及金云母Ar-Ar定年分析,结果表明:(1)矿区存在早白垩世花岗闪长岩(116.3 Ma)和晚白垩世闪长岩(94.3~93.8 Ma)两个阶段的岩浆活动,主矿体金云母^(40)Ar/^(39)Ar等时线年龄为93.71±2.96 Ma,表明该铁矿形成于晚白垩世;(2)与主矿体成矿相关的闪长岩具较低SiO_(2)含量(52.17%~55.32%),富集LREE及Rb、Ba、Pb等大离子亲石元素,亏损HREE和Nb、Ta、Ti等高场强元素,属于高钾钙碱性和准铝质岩石系列,锆石ε_(Hf)(t)介于1.4~3.6,Mg^(#)指数极高(0.59~0.64),暗示成矿岩体有较多的幔源物质加入,具有壳幔混合特征;(3)结合冈底斯带其他铁矿床时代,可以将冈底斯铁成矿作用划分为~115 Ma、~94 Ma和50~65 Ma三期,隆格尔铁矿床属于冈底斯带新一期(晚白垩世)富铁成矿作用;(4)对比冈底斯成矿带多阶段矽卡岩型铁成矿作用发现,隆格尔铁矿成矿岩体与其他时期铁矿具有明显的地球化学差异,幔源物质较多的中基性岩浆相对于酸性岩浆可能更容易形成富铁矿床.To find out the metallogenic age and environment of Lunggar iron-rich ore deposit and its indication of regional iron mineralization in Gangdese Belt,the petrogeochemistry,zircon U-Pb chronology,zircon Lu-Hf isotopes,and Ar-Ar dating of phlogopite have been carried out.The results show that:(1)there are two stages of magmatism:Early Cretaceous granodiorite(116.3 Ma)and Late Cretaceous diorite(94.3-93.8 Ma).The ^(40)Ar/^(39)Ar isochron age of gold mica in the main orebody is 93.71±2.96 Ma,indicating that the deposit was formed in the Late Cretaceous.(2)The diorite related to the mineralization is characterized by low SiO_(2) content(52.17%-55.32%),enrichment of LREE and large ion lithophile elements such as Rb,Ba,and Pb,and depletion of HREE and high field strength elements such as Nb,Ta,and Ti,which belongs to the High-K calcalkaline and metaluminous rock series.The zircon ε_(Hf)(t)is between 1.4 and 3.6,and the Mg^(#)index is very high(0.59-0.64),suggesting that more mantle-derived materials are added to the ore-forming pluton,which has the characteristics of crust-mantle mixing.(3)According to the ages of other iron deposits in Gangdese Belt,the iron mineralization can be divided into three stages,including~115 Ma,~94 Ma and 50-65 Ma.The Lunggar iron deposit suggests that it belongs to a new stage(Late Cretaceous)of iron-rich mineralization in Gangdese Belt.(4)Compared with the multi-stage skarn iron mineralization in the Gangdese metallogenic belt,it is found that there are obvious geochemical differences between the Lunggar iron ore-forming body and other periods of iron ore-forming body.The intermediate-basic magma with more mantle-derived materials may be easier to form ironrich deposits than acid magma.

关 键 词：年代学 矽卡岩型 富铁矿床 壳幔混合 隆格尔 冈底斯 地球化学 

分 类 号：P581[天文地球—岩石学]