西藏波龙斑岩铜金矿床钾长石和绢云母^40Ar/^39Ar年龄及其地质意义  

^40Ar/^39Ar dating of hydrothermal K-feldspar and hydrothermal sericite from Bolong porphyry Cu-Au deposit in Tibet

作　　者：祝向平[1] 陈华安[1] 马东方[1] 黄瀚霄[1] 李光明[1] 李玉彬 李玉昌 卫鲁杰 刘朝强 

机构地区：[1]成都地质矿产研究所,四川成都610081 [2]西藏地质矿产勘查开发局第五地质大队,青海格尔木816000

出　　处：《矿床地质》2013年第5期954-962,共9页Mineral Deposits

基　　金：国家973项目"青藏高原南部大陆聚合与成矿作用"(编号:2011CB403105);国家自然科学基金项目(编号:41202049;41272091);中国地质调查局地质矿产调查评价专项(编号:1212011086074;12120113037000)联合资助成果

摘　　要：西藏波龙斑岩铜金矿床是新近在青藏高原中部发现的规模最大的斑岩型矿床。文章对该矿床内的蚀变钾长石和蚀变绢云母进行了^40Ar/^39Ar年代学测试,获得蚀变钾长石的^40Ar/^39Ar坪年龄为（118133±0160）Ma,反等时线年龄为（118149±0174）Ma（初始40Ar/36Ar=28611±814）,表明波龙斑岩铜金矿床的钾化蚀变年龄为118-119 Ma;蚀变绢云母的^40Ar/^39Ar坪年龄为（121161±0167）Ma,反等时线年龄为（12111±210）Ma（初始40Ar/36Ar=279±19）。由于蚀变绢云母测试样品内可能混入了斜长石,受其影响,蚀变绢云母测年结果的下限可能代表了该矿床绢英岩化蚀变年龄。这些蚀变钾长石和蚀变绢云母^40Ar/^39Ar测年结果与波龙矿床的成岩年龄值和成矿年龄值在误差范围内基本一致,表明该矿床的钾化和绢英岩化与成岩、成矿同期,该矿床的岩浆-热液活动过程的时限为121-118 Ma。The Bolong porphyry copper-gold deposit is the largest porphyry copper deposit discovered recently in the middle of the Tibetan plateau.Hydrothermal K-feldspar from the potassic alteration zone and hydrothermal sericite from the phyllic alteration zone were analyzed by40Ar/39Ar dating technique.The plateau age of secondary K-feldspar is（118.33±0.60）Ma,which,together with its reverse isochron age of（118.49±0.74） Ma（initial40Ar/36Ar=286.1±8.4）,represents the potassic alteration age of the Bolong deposit.The plateau age of secondary sericite is（121.61±0.67）Ma,and its reverse isochron age is（121.1±2.0）Ma（initial40Ar/ 36Ar=279±19）.The high37Ar/39Ar ratio of the secondary sericite sample indicates that some magmatic plagioclase was mixed in the sample,which increased the dating value.Thus,the phyllic alteration might have occurre d around 119 Ma.Taking the deviation and uncertainties of geochronologic methods into account,the authorshave found that the40Ar/39Ar ages of hydrothermal K-feldspar and hydrothermal sericite are similar to the oreforming and rock-forming agesof the Bolong deposit,suggesting that the potassic alteration and mineralization in the Bolong porphyry deposit were coeval with the intrusion of porphyries and phyllic alteration,and the magmatic-hydrothermal duration was within 121-118 Ma.

关 键 词：地球化学 40AR/39AR年龄 钾长石化 绢英岩化 波龙斑岩铜金矿床 班公湖-怒江成矿带 西藏 

分 类 号：P618.41[天文地球—矿床学] P618.51[天文地球—地质学]