大兴安岭南段毛登Sn-Cu矿床岩浆作用对成矿制约:年代学、地球化学及Sr-Nd-Pb同位素证据  

Metallogenetic Control of Magmatism on the Maodeng Sn-Cu Deposit in the Southern Great Xing’an Range:Evidence from Geochronology,Geochemistry,and Sr-Nd-Pb Isotopes

作　　者：季根源 江思宏[1] 李高峰 易锦俊 张莉莉[1] 刘翼飞[1] JI Genyuan;JIANG Sihong*;LI Gaofeng;YI Jinjun;ZHANG Lili;LIU Yifei(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;Cores and Samples Center of Natural Resources,Langfang 065201,Hebei,China;Key Laboratory of Orogen and Crust Evolution,Peking University,Beijing 100871,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [2]自然资源实物地质资料中心,河北廊坊065201 [3]北京大学造山带与地壳演化重点实验室,北京100871

出　　处：《大地构造与成矿学》2021年第4期681-704,共24页Geotectonica et Metallogenia

基　　金：科技部深地项目(2017YFC0601303);国家自然科学基金项目(41873051);地科院基本业务费项目(YYWF201715);地质调查项目(DD20190437、DD20190411)联合资助。

摘　　要：毛登Sn-Cu矿床位于大兴安岭南段内蒙古锡林浩特境内,其Sn、Cu储量均达到中型。本文利用LA-ICP-MS锆石U-Pb法测得与成矿关系密切的花岗斑岩成岩年龄为138±0.6 Ma;利用LA-ICP-MS锡石U-Pb法测得锡石‒硫化物‒石英脉型矿石中锡石的Tera-Wasserburg谐和年龄为139±3.2 Ma,表明花岗斑岩体形成年龄与毛登矿床成矿年龄在误差范围内一致,均形成于早白垩世。花岗斑岩富硅(SiO_(2)=73.18%~77.3%)、富碱(Na_(2)O+K_(2)O=8.00%~8.69%)、富钾(K_(2)O=4.80%~5.22%)、贫铝(Al_(2)O_(3)=11.67%~12.83%),贫钙(CaO=0.49%~0.95%)、镁(MgO=0.12%~0.46%),具有较高的FeO^(T)/(MgO+FeO^(T))值(0.74~0.91)、10000×Ga/Al值(3.64~4.28);微量元素亏损Ba、Sr、P、Ti等元素,富集Rb、Th、K、Hf等元素;稀土元素配分模式图呈典型的“海鸥型”以及显著的Eu负异常(δEu=0.05~0.2);锆石饱和温度为817~861℃,以上均说明花岗斑岩具有A型花岗岩特征。全岩Sr-Nd同位素结果显示低初始(^(87)Sr/^(86)Sr)i值(0.702907~0.704506)、较高的ε_(Nd)(t)值(+0.8~+4.4)以及年轻的二阶段模式年龄(t_(DM2)=572~863 Ma),说明花岗斑岩可能为新生地壳经部分熔融后,在上升过程中经历较强烈的结晶分异演化作用而形成。Pb同位素组成指示岩体和矿石的Pb同位素组成接近,说明成矿物质主要来源于岩浆。微量元素特征、构造环境判别图解显示花岗斑岩具有A_(2)型造山后花岗岩特征,成岩环境处于伸展构造背景。结合前人研究成果以及矿区地质特征、成岩(矿)年代学、Sr-Nd-Pb同位素特征,认为毛登矿床成矿物质的富集与花岗斑岩体侵入密切相关,矿床成矿物质的富集规模受花岗斑岩结晶分异演化程度制约。The Maodeng Sn-Cu deposit is a medium-sized deposit in the southern segment of the Great Xing’an Range located in Xinlinhot City of Inner Mongolia.Whole rock geochemistry,LA-ICP-MS zircon and cassiterite U-Pb ages,and Sr-Nd-Pb isotopic compositions of the granite porphyry and Sn-Cu ores in the Maodeng deposit have been studied in detail and are reported in this contribution.The zircon from the ore-related granite porphyry has a weighted mean U-Pb age of 138±0.6 Ma,while the cassiterite from cassiterite-sulphide-quartz vein-type ore has a Tera-Wasserburg concordant U-Pb age of 139±3.2 Ma.These two ages are consistent within error,which indicates that the emplacement of granite porphyry and Sn-polymetallic mineralization in Maodeng took place during the Early Cretaceous.Geochemically,the granite porphyry is characterized by high SiO_(2)(73.18%to 77.3%),(Na_(2)O+K_(2)O)(8.00%to 8.69%),and K_(2)O(4.80%to 5.22%),with low CaO(0.49%to 0.95%),Al_(2)O_(3)(11.67%to 12.83%),MgO(0.12%to 0.46%),and relatively high FeO^(T)/(MgO+FeO^(T))(0.74 to 0.91),and 10000×Ga/Al(3.64 to 4.28)ratios.The rock is enriched in Rb,Th,K,Hf,and depleted in Ba,Sr,P and Ti.The REE distribution patterns of the granite porphyry are of typical gull-wing shape with obviously negative Eu anomalies(δEu=0.05 to 0.2).Zircon saturation temperatures of the granite porphyry vary from 817 to 861.All these show that the granite porphyry exhibits geochemical cha℃ racteristics typical for A-type granite.The granite porphyry has relatively low(^(87)Sr/^(86)Sr)i values(0.702907 to 0.704506),high ε_(Nd)(t)values(+0.8 to+4.4)and young two-stage Nd model ages(t_(DM2)=572 to 863 Ma),suggesting that the rock was dominantly derived from partial melting of a juvenile lower crust,followed by strong fractional crystallization during magma ascent.The Pb isotope compositions of the granite porphyry and ores are similar,indicating that the Pb of the ores could be sourced from the granite porphyry.According to the trace element characteristics,chemical subdivision diagr

关 键 词：大兴安岭南段 毛登锡铜矿床 锡石U-Pb年龄 锆石U-Pb年龄 SR-ND-PB同位素 

分 类 号：P597[天文地球—地球化学] P612[天文地球—地质学]