青藏高原东部碳酸岩-正长岩杂岩体型REE矿床成矿模式--以大陆槽REE矿床为例  

The formation model of the carbonatite-syenite complex REE deposits in the east of Tibetan Plateau: A case study of Dalucao REE deposit

作　　者：刘琰[1,2,3] 陈超[4] 舒小超 郭东旭[3] 李自静[3] 赵海璇[5] 贾玉衡[6] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]内生金属矿床成矿机制研究国家重点实验室、南京大学,南京210093 [3]中国地质科学院地质研究所,北京100037 [4]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [5]河北省区域地质矿产调查研究所,廊坊065000 [6]桂林理工大学地球科学学院,桂林541004

出　　处：《岩石学报》2017年第7期1978-2000,共23页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划“973”项目(2015CB452600);中国地质调查局地质调查项目(121201102000150011)联合资助

摘　　要：冕宁-德昌稀土(REE)矿带位于青藏高原东部,受川西一系列走滑断裂控制,大陆槽矿床是矿带中唯一位于南部的大型REE矿床。在前人研究基础上,结合近年来对整个稀土矿带地质填图和室内研究,重点对大陆槽矿床的成矿特征、赋矿围岩及其蚀变、矿石类型、成矿流体来源和流体包裹体演化等方面与同一矿带内的其它矿床进行了详细对比,进一步总结了碳酸岩型(含碳酸岩-正长岩杂岩体)REE矿床的成矿过程。大陆槽矿床的No.1号和No.3号矿体均位于碳酸岩-正长岩杂岩体内,分别由不同隐爆角砾岩筒所控制。以往研究认为两个矿体的碳酸岩-正长岩杂岩体侵位的年龄都在12Ma左右,本次研究发现在26.49±0.63Ma已经存在碳酸岩-正长岩杂岩体岩浆活动。大陆槽REE矿床受隐爆角砾岩构造活动和风化作用的影响,矿石类型以角砾岩型和风化型为主,脉石矿物和矿石矿物在手标本尺度和镜下很难辨认。通过野外观察、镜下矿物共生组合、包裹体显微测温等研究发现,大陆槽矿化过程和牦牛坪矿床相似,只是矿化规模较小,矿化阶段分为岩浆岩阶段-伟晶岩阶段(>600℃)-高温热液阶段(450~350℃)-低温热液阶段(<350℃),氟碳铈矿形成于热液阶段的晚期。根据伟晶岩阶段至热液阶段氟碳铈矿中流体包裹体的特征,发现多期次隐爆角砾活动导致大气降水和碳酸岩中脱出的CO_2的加入,使得成矿流体的密度(0.732~0.631g/cm^3)、压力(2436~101bar)逐渐降低,直至成矿。此外,岩相学观察和拉曼测试分析也表明包裹体从熔融包裹体过渡到含重晶石、萤石、天青石子晶的富CO_2包裹体、气液两相包裹体,显示了成矿流体由岩浆至热液的转化过程。大陆槽矿床中的包裹体阴离子以SO_4^(2-)为主,气体以CO_2为主,成矿流体中阳离子主要为K^+、Na^+、Ca^(2+)、Sr^(2+)、Ba^(2+)和稀土元素阳离子,表明流体属于SO_4^(2-)-CO_2-H_2O体Mianning-Dechang（ MD） REE Belt is located in the east of Tibetan Plateau and western Sichuan Province,southwestern China. It is controlled by a series of cenozoic strike-slip faults. Dalucao REE deposit is the only large deposit identified in the southern part of the MD REE Belt. Detailed comparison including metallogenic characteristics,host rock alteration,ore types,source of oreforming fluids and evolution of fluid inclusions of Dalucao and other deposits within MD REE Belt has been concluded based on latest geological surveys,studies on petrographic features; and the metallogenic process of carbonatite-type（ including carbonatite-syenite complex） REE deposits is summarized. The No. 1 and No. 3 orebodies in Dalucao deposit are both hosted in breccia pipes,located in carbonatite-syenite host rocks. Previous studies suggested that both No. 1 and No. 3 orebody in Dalucao deposit are formed at about12 Ma,but the latest research indicate there had already exist magmatic activity of carbonatite-syenite complexes at about 26. 49 ±0. 63 Ma. And the ores in Dalucao deposit are mainly classified as weathered and breccia type ores; the high levels of brecciation and weathering in the Dalucao deposit make it difficult to recognize the ore veins or gangue minerals from the hand specimen or field of microscope. Based on field observations,study of paragenetic association of minerals and analyses of inclusion in these REE deposits,the total mineralization in Dalucao deposit is similar to that of Maoniuping except for the smaller size of Dalucao REE deposit. The mineralization process can be divided into magmatic stage,pegmatite stage（ 600℃）,high-temperature hydrothermal stage（ 450 -350℃） and low-temperature hydrothermal stage（ 350℃）,the bastnsite precipitated during the later period of low-temperature hydrothermal stage. Based on the geological characteristics of inclusions found in pegmatite and hydrothermal fluids,the multiple episodes of explosive breccia activities leads to the addition of m

关 键 词：大陆槽矿床 碳酸岩-正长岩杂岩体 隐爆角砾岩型稀土矿床 成矿模式 

分 类 号：P611[天文地球—矿床学] P618.7[天文地球—地质学]