内蒙古孟恩陶勒盖银多金属矿床及其附近侵入岩的年代学

Geochronology of Intrusive Rocks Occurring in and Around the Mengentaolegai Silver-Polymetallic Deposit,Inner Mongolia

孟恩陶勒盖是内蒙古东部地区的一处大型银多金属矿床,铅锌银矿体呈脉状产出,受东西向断裂控制。对孟恩陶勒盖矿区及其外围主要侵入岩体开展了年代学和地球化学研究。LA-MC-ICP-MS锆石测年结果表明:孟恩陶勒盖岩基中黑云母斜长花岗岩的锆石年龄为(240.5±1.2)Ma,MSWD=0.48;白云母斜长花岗岩的锆石年龄为(234.3±3.2)Ma,MSWD=0.21;矿区外围杜尔基岩基中的黑云母正长花岗岩的锆石年龄为(154.5±0.5)Ma,MSWD=0.41;矿区外围的安山玢岩的锆石年龄为(127.5±0.7)Ma,MSWD=1.3;分别代表了中三叠世、晚侏罗世和早白垩世的3期岩浆活动。岩石地球化学分析结果表明:孟恩陶勒盖岩基的黑云母斜长花岗岩和白云母斜长花岗岩与杜尔基岩体的黑云母正长花岗岩均为富SiO2、富碱、准铝的钙碱性岩石,具有轻稀土分异明显、富集大离子亲石元素(LILE)为特征,其中Ba、Nb、La、Sr、P、Ti相对亏损,而Rb、Th、K、Ta、Ce、Nd、Hf、Sm、Y和Yb相对富集。岩体年代学和岩石地球化学特征表明,孟恩陶勒盖岩基和杜尔基岩基分别形成于印支期的碰撞造山和燕山期的伸展构造环境。根据获得的侵入岩的测年数据与前人获得的孟恩陶勒盖银铅锌矿与成矿有关的蚀变白云母的Ar-Ar年龄(179.0士1.5)Ma对比显示,这些侵入岩的侵位年龄与成矿年龄之间差别较大,说明这些岩体不太可能是孟恩陶勒盖银铅锌矿床的成矿母岩。成矿岩体可能在深部尚未出露,或者已被杜尔基岩体改造。

Located in eastern Inner Mongolia,the Mengentaolegai silver-polymetallic deposit is one of large-scale deposits.Ore bodies occur as vein-like,and are controlled by the east-west trending fault.Geochronology and geochemistry of the main intrusive rocks occurring in and around the Mengentaolegai silver-polymetallic ore district are studied.In order to constrain the emplacement age of intrusive rocks,the zircons in four samples from the intrusive rocks were dated by the LA-MC-ICP-MS method.Four reliable weighted mean 206Pb/238U ages of（240.5±1.2） Ma（MSWD=0.48）,（234.3±3.2） Ma（MSWD=0.21）,（154.5±0.5） Ma（MSWD=0.41）,and（127.5±0.7） Ma（MSWD=1.3） were obtained for the biotite plagioclase granite and muscovite plagioclase granite in Mengentaolegai batholiths,biotite K-feldspar granite in Duerji batholiths and andesite porphyry in southern part of the Mengentaolegai deposit,respectively.It is indicated that there were three times of magmatic emplacement in and around the Mengentaolegai silver-polymetallic ore district,during Middle Triassic,Late Jurassic and Early Cretaceous period,respectively.The geochemical analysis of these intrusive rocks show that the biotite plagioclase granite,muscovite plagioclase granite and biotite K-feldspar granite are characterized by the high SiO2,enriched alkali,meta-aluminum and calc-alkaline,with LREE differentiation obviously.They are enriched in LILE elements,characterized by relatively depleted Ba,Nb,La,Sr,P and Ti,and enriched Rb,Th,K,Ta,Ce,Nd,Hf,Sm,Y and Yb.Combined with the dating results of the intrusive rocks,it can be concluded that the Mengentaolegai batholiths and Duerji batholiths were formed under collisional and extensional settings,respectively.The reported Ar-Ar age of the muscovite associated the mineralization is（179.0士1.5） Ma,which is quite different from the emplacement ages of the intrusive rocks studied.It is suggested that these exposed intrusive rocks are not likely related to the silver-polymetallic mineralization in Mengentaolegai area.The intrusive rocks related to the silver-polymetallic mineralization may be buried in the depth,or have been re-melted due to the intruding of the Duerji batholiths.