斑岩铜矿床成矿流体演化:中甸普朗铜矿床蚀变矿物学与热力学模拟  

Ore-forming fluids evolution of the porphyry Cu deposits:Alteration mineralogy and thermodynamic modeling of the Pulang Cu deposit,Zhongdian district

作　　者：张少颖 和文言[1] 高雪[1] 张宏睿 袁建江 ZHANG ShaoYing;HE WenYan;GAO Xue;ZHANG HongRui;YUAN JianJiang(State Key Laburalary of Gedlogical Preceses and Mineral Resources,China University of Geosciences,Beijing 100083,China;Explorution and Research Instiute,CNAOG,Beijing 100039,China;Key Laburalary of Rare Mineral,Ministy of Naural Resources,Wuhan 430034,China)

机构地区：[1]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 [2]中国煤炭地质总局勘查研究总院,北京100039 [3]自然资源部稀土稀有稀散矿产重点实验室,武汉430034

出　　处：《岩石学报》2020年第5期1611-1626,共16页Acta Petrologica Sinica

基　　金：国家重点研发计划(2019YFA0708603);国家重点基础研究发展计划“973”项目(2015CB452606);高等学校学科创新引智计划(BP0719021);中国地质大学地质过程与矿产资源国家重点实验室专项基金(MSFGPMR201804);中国博士后基金(2019T120121、2018M640161);自然资源部稀土稀有稀散矿产重点实验室开放基金资助项目(KLRM-KF201803)联合资助.

摘　　要：不同阶段热液蚀变矿物的组成是水岩反应过程和成矿流体演化的地球化学"指纹"。三江特提斯义敦岛弧南缘的普朗超大型斑岩铜矿床形成于晚三叠世甘孜-理塘洋西向俯冲的岛弧环境,但具有不同于典型斑岩铜矿的蚀变-矿化分带特征:即在早期钾硅酸盐化蚀变带内常可见晚期脉状(沿裂隙分布的细脉状)青磐岩化或沿破碎带边部发育的绢英岩化,且主要在青磐岩化蚀变带内发育铜(-钼)矿化。为此,本研究选取普朗矿床含矿石英二长斑岩(QMP)中热液黑云母及绿泥石进行矿物产状、共生组合和世代划分研究,并针对不同产状的绿泥石开展电子探针分析研究,以探讨其形成的物理化学条件,并结合热力学模拟结果反演成矿流体演化轨迹。不同于岩浆黑云母(Bt-1)的锯齿状边缘及内部发育磷灰石包体特征,普朗铜矿热液黑云母(Bt-2)多为片状且解理发育、沿其边缘或裂隙多被绿泥石交代。青磐岩化带内发育有两类产状明显不同的绿泥石,即由黑云母蚀变而成的片状绿泥石(Chl-1)和蠕虫状绿泥石(Chl-2),且后者多与黄铜矿、黄铁矿、磁黄铁矿及辉钼矿伴生。电子探针分析结果显示两类绿泥石均为富Mg的三八面体类绿泥石,且具有相似的主量元素组成。石英二长斑岩中Bt-2型黑云母形成温度范围为305-336℃(平均值为321℃),氧逸度位于NNO(Ni-NiO)缓冲线与HM(Fe2O3-Fe3O4)缓冲线之间。Chl-1和Chl-2型绿泥石形成温度分别为284~347℃(平均值为316℃)和278~328℃之间(平均值为310℃)。Chl-1和Chl-2的Log fO2分别在-42.7--37.2(平均值-39.8;ΔFMQ=-5.7)和-41.8^-38.4之间(平均值-40.0;ΔFMQ=-5.5),对应的Log fS2在-14.9^-12.1(平均值-13.5)和-14.5^-12.7之间(平均值-13.6)。不同蚀变阶段矿物组合特征及热力学模拟结果表明,在早期高温的钾硅酸盐化阶段含矿流体具有高氧逸度、中性特征(ΔFMQ=2,pH=7),在中温青磐岩化阶段具有低氧逸度�Compositions of hydrothermal alteration minerals in different generations provide geochemical fingerprints for water-rock interaction processes and evolution of ore-forming fluids.The giant Pulang porphyry Cu deposit,located in the southern segment of the Yidun arc,part of the Sanjiang Tethyan orogenic belt,is the product of the subduction of Garze-Litang oceanic plate during Late Triassic.Different from typical porphyry alteration-mineralization model,the Pulang deposit develops later propylitic alteration Cfine veins along the fissuresD or disseminated phyllic alteration Calong the edge of the fracture zonesD overprinting earlier potassic alteration zone.The Cu mineralization at Pulang mostly occurs at the propylitic zone.In order to discern the physical and chemical conditions for metal deposition at Pulang,different generations of biotites and chlorites from the ore-bearing quartz monzonite porphyry CQMPD have been selected to examine their mineral characteristics.Combined with the electron microprobe analysis CEMPAD of chlorite,the thermodynamic modeling has been managed to explore the evolution path of the ore-forming fluids.Unlike the magmatic biotites CBt-1 D of the QMP,which are associated with serrated edges and apatite inclusions,the hydrothermal biotites CBt-2 D are mostly sheet-like and have been partly altered to chlorite along its margins or cleavages.Two types of chlorites,including biotite-altered sheet-like chlorite CChl-1 D and worm-like chlorite CChl-2 D,have been identified in the QMP,and the later one is mostly associated with chalcopyrite,pyrite,pyrrhotite and molybdenite.These two types of chlorites show similar major element compositions,belonging to the Mg-rich trioctahedral chlorite.The formation temperatures of Bt-2 are among 305~336℃ Caverage of 321℃ D,with the estimated oxygen fugacity plotting at the NNO CNi-ViOD and HM CFe2 O3-Fe3 O4 D buffer line.The Chl-1 and Chl-2 have formation temperatures of 284~347℃ Caverage of 316℃ D and 278~328℃ Caverage of 310℃ D,and the log f

关 键 词：绿泥石 黑云母 矿物共生组合 热力学模拟 普朗斑岩铜矿 

分 类 号：P575.1[天文地球—矿物学] P618.41[天文地球—地质学]