内蒙古赵井沟铌钽矿床燕山期成矿:来自LA-MC-ICP-MS独居石、锆石U-Pb和黑云母^(40)Ar-^(39)Ar年龄的证据

Yanshanian Mineralization of Zhaojinggou Nb-Ta Deposit,Inner Mongolia:Evidences from the Monazite and Zircon LA-MC-ICP-MS U-Pb and Biotite ^(40)Ar-^(39)Ar Geochronology

内蒙古武川县赵井沟铌钽矿是新近取得勘查突破的一例大型铌钽矿床.矿体赋存岩石为含天河石钠长花岗岩,其次为花岗细晶岩、云英岩及天河石花岗伟晶岩.运用LA-MC-ICP-MS法对矿区钠长花岗(细晶)岩脉、正长花岗岩中的独居石、锆石进行了U-Pb同位素年龄测定,同时对石英-黑云母脉中的黑云母进行了^(40)Ar-^(39)Ar定年.4件独居石的LA-MC-ICP-MS U-Pb年龄分别为124±2Ma(MSWD=2.9,n=27)、124±3Ma(MSWD=2.0,n=46)、121±1Ma(MSWD=3.3,n=43)和124±2Ma(MSWD=3.2,n=12),1件锆石的LA-MC-ICP-MS U-Pb年龄为125±1Ma(MSWD=1.6,n=18);黑云母^(40)Ar-^(39)Ar坪年龄为133.84±0.79Ma(MSWD=3.31),40 Ar/36 Ar-39 Ar/36 Ar等时线年龄为134.55±0.79Ma(MSWD=1.93),反等时线年龄为134.58±0.80Ma(MSWD=1.99),这些年龄限定赵井沟铌钽矿形成于早白垩世.综合分析表明,燕山期是内蒙古地区重要的铌钽成矿期,赵井沟铌钽矿是燕山期伸展体制下构造岩浆活动的产物.

The Zhaojinggou Nb-Ta deposit is a newly explored large-scale deposit in Wuchuan County,Inner Mongolia.The NbTa orebody is mainly hosted in the amazonite-bearing albite granite,and partly hosted in the granite aplite,greisen and amazonite granite pegmatite.In this paper,we use monazite and zircon LA-MC-ICP-MS U-Pb and biotite 40Ar-39Ar dating methods to constrain the mineralization age.Monazite LA-MC-ICP-MS U-Pb geochronological dating of four samples from granites yields ages of 124±2Ma(MSWD=2.9,n=27),124±3Ma(MSWD=2.0,n=46),121±1Ma(MSWD=3.3,n=43)and124±2Ma(MSWD=3.2,n=12).One zircon sample from albite granite yields age of 125±1 Ma(MSWD=1.6,n=18).Meanwhile,biotite 40Ar-39Ar dating obtains the plateau age of 133.84±0.79 Ma(MSWD=3.31),isochron age of 134.55±0.79Ma(MSWD=1.93)and reverse isochron age of 134.58±0.80 Ma(MSWD=1.99).Therefore,all these ages constrain that the ore-forming period of Zhaojinggou Nb-Ta deposit is Early Cretaceous.In conclusion,the Zhaojinggou deposit resulted from the tectonic-magmatic activities of extensional setting,and the Yanshanian Period is the main Nb-Ta metallogenic age in Inner Mongolia.