川西碱性岩-碳酸岩型稀土矿床成矿模型  

The Metallogenic Model of Alkaline Rocks-carbonatite Related REE Deposits in the Western Sichuan,China

作　　者：翁强 牛贺才[1,3] 杨武斌[1,3] 李宁波[1,3] 单强[1,3] WENG Qiang;NIU He-cai;YANG Wu-bin;LI Ning-bo;SHAN Qiang(Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,China)

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广州510640 [2]中国科学院大学,北京100049 [3]中国科学院深部地球科学卓越研究中心,广州510640

出　　处：《矿物岩石地球化学通报》2022年第3期465-473,I0003,共10页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家重点研发计划项目(2017YFC0602301);国家自然科学基金重点项目(41930424)。

摘　　要：为构建碱性岩-碳酸岩型稀土矿床成矿模型,从源区及岩浆演化角度研究了川西牦牛坪和里庄两个典型稀土矿床。牦牛坪碱性正长岩元素和Sr、Nd、Pb、B同位素以及里庄基性脉岩元素和同位素地球化学研究显示,来自俯冲板片熔/流体的共同交代使地幔源区发生稀土初始富集,切壳拉张性深大断裂引发的脉动式软流圈上涌,诱发富集地幔低程度部分熔融形成富稀土和挥发分的碱性母岩浆。牦牛坪云母原位主、微量元素分析结果显示,在地壳岩浆房中,幔源碱性母岩浆经适度演化后不混溶形成了碱性硅酸盐熔体与富SO_(3)和F的碳酸盐熔体。牦牛坪氟碳铈矿原位Th-Pb定年和单斜辉石、磷灰石成分和方解石C-O、Sr、Pb同位素及组成研究显示,不混溶的硅酸盐熔体与碳酸盐熔体经充分演化,分别形成碱性岩型、霓辉重晶伟晶岩型和碳酸岩型稀土矿体。里庄矿床霓长岩化研究显示,富稀土流体出溶和强烈的水-岩反应有利于稀土元素超常富集成矿。此外,牦牛坪矿床杂岩体中的碱性花岗斑岩锆石U-Pb年代学、元素地球化学及Sr、Nd、Hf同位素研究显示,软流圈上涌导致的区域持续性地热异常对超大型稀土矿床的形成具有重要作用。结合前人研究结果,本文认为源区稀土富集、熔体不混溶、充分的岩浆-热液演化及区域高热状态可能是形成超大型碱性岩-碳酸岩型稀土矿床的重要控制因素,并据此构建了川西碱性岩-碳酸岩型稀土矿床成矿模型。In order to establish the metallogenic model of alkaline rocks-carbonatite related rare earth elements(REE)deposits,two typical REE deposits(Maoniuping and Lizhuang)in the western Sichuan have been studied from the perspective of magma source and magmatic evolution in this paper.The studies of elemental geochemistry and Sr,Nd,Pb,and B isotopes of the Maoniuping alkaline syenite,and elemental and isotopic geochemistry of the Lizhuang mafic dikes show that a coupled metasomatism by melts/fluids derived from the subducted slab had caused the initial REE enrichment in the metasomatised mantle.The pulsating asthenosphere upwelling induced by the crust-cutting and extensional deep strike-slip faults had induced the low degree partial melting of the initial REE-enriched metasomatised mantle to form the REE-and volatiles-rich alkaline parent magmas.In situ analytical results of major and trace elements of micas in the Maoniuping deposit show that the unmixing of mantle-derived alkaline parent magmas,occurred after the moderate magmatic evolution,had subsequently formed the alkaline silicate melt and SO_(3)and F-rich carbonatitic melt in the crustal magma chamber.The results of in-situ bastn?site Th-Pb dating and compositions of clinopyroxenes and apatites,as well as the C-O、Sr and Pb isotopes and compositions of calcites in the Maoniuping deposit show that the strong evolution of immiscible silicate melts and carbonatitic melts resulted in the formation of the alkaline rock type,the aegirine-augite barite pegmatite type,and the carbonatite type REE orebodies.Studies on fenitization of the Lizhuang deposit show that the exsolution of REE-rich fluids and the strong fluid-rock intereactions are favorable for the supernormal enrichment and mineralization of REE.In addition,the studies of zircon U-Pb geochronology,elements and Sr,Nd and Hf isotopes of alkaline granitic porphyry in the Maoniuping deposit show that the regional continuous geothermal anomalies induced by the asthenosphere upwelling have important constraints o

关 键 词：碱性岩-碳酸岩型稀土矿床 源区过程 岩浆演化 成矿模型 川西 

分 类 号：P611[天文地球—矿床学]