西藏弄如日金矿床侵入岩锆石SHRIMP U-Pb年龄与地球化学特征  

Zircon SHRIMP U-Pb age and geochemistry of intrusive rocks from Nongruri gold deposit,Gangdese,Tibet

作　　者：刘云飞[1,2] 杨志明[1] 谢玉玲[3] 周平[4] 杜等虎[2] 李应栩[3] 李秋耘[2] 曲焕春[2] 许博[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学地球科学与资源学院,北京100083 [3]北京科技大学土木与环境工程学院,北京100083 [4]中国地质调查局发展研究中心,北京100037

出　　处：《矿床地质》2012年第4期727-744,共18页Mineral Deposits

基　　金：行业基金项目"中国大陆环境典型斑岩型矿床成矿规律和找矿模式"(编号:2010011011);国家重点基础研究发展计划(973计划)"青藏高原南部大陆聚合和成矿作用"(编号:2011CB403100);中国地质调查局地质调查项目"青藏高原碰撞造山及成矿地质背景研究"(编号:1212011121253)的联合资助

摘　　要：弄如日金矿床位于青藏高原南部冈底斯-喜马拉雅构造区的冈底斯构造-岩浆带东段的中部,是该成矿带内首次发现并评价的浅成低温热液型金锑矿床。文章对该矿区出露的钾长花岗岩和二长花岗斑岩进行了锆石SHRIMPU-Pb测年,并对岩石的主量元素、微量元素进行了分析。测试结果显示,钾长花岗岩的加权平均年龄为(66.6±0.7)Ma,属晚白垩世;岩石富硅〔w(SiO2)平均为76.74%〕、富碱(ALK平均为8.21%),A/CNK均大于1.0,属过铝质高钾钙碱性岩石;稀土元素球粒陨石配分模式图表现为右倾型,LREE富集、HREE亏损,ΣREE平均为66.31×10-6,并且具有明显的Eu负异常(δEu平均为0.40);微量元素原始地幔蛛网图表现出LILE富集、HFSE相对亏损的特征,暗示其可能为弧岩浆作用的产物。二长花岗斑岩的加权平均年龄为(18.8±0.3)Ma,属中新世;岩石富硅〔w(SiO2)平均为72.69%〕、富碱(ALK平均为6.73%),A/CNK大于1.0,属过铝质高钾钙碱性岩石;稀土元素球粒陨石配分模式图表现为右倾型,LREE富集、HREE亏损,ΣREE平均为77.33×10-6,Eu异常不明显(δEu平均为1.03);在微量元素原始地幔蛛网图上,具有LILE富集、HFSE相对亏损的特征;同时,该岩石还具有较高的La/Yb比值〔(La/Yb)N平均为18.53〕,显示出一定的埃达克岩亲和性。结合区域地质背景表明:弄如日金矿床形成于陆-陆碰撞后伸展环境,与区域上近SN向正断层系统及裂谷裂陷带有关的冈底斯含矿斑岩的侵位时代相一致,是区域内中新世岩浆活动所形成的斑岩系统外围的浅成低温热液系统的产物。Located in the Riduo town,Maizhokunggar County of Tibet,the Nongruri gold deposit is an epithermal Au-Sb deposit discovered for the first time in the eastern part of southern Gangdese metallogenic belt.In this study,zircon SHRIMP U-Pb age,whole-rock major and trace elements of K-feldspar granite and monzogranite porphyry of this deposit were analyzed.The zircon SHRIMP U-Pb dating of K-feldspar granite shows that the crystallization age is（66.6±0.7） Ma.The major element analyses show that the rock is enriched in silica and alkali（with the average SiO2 being 76.74%,ALK being 8.21% and A/CNK1.0）,and can be classified as high-K calc-alkaline granite with peraluminous.Chondrite-normalized REE patterns are of the rightly-oblique type.The rock is enriched in LREE and LILE and depleted in HREE and HFSE in the primitive mantle normalized multi-element diagram,its ΣREE is 66.31×10-6,exhibiting obvious negative Eu anomalies and showing some characteristics of arc magmatic rocks.The crystallization age of monzogranite porphyry is（18.8±0.3） Ma.The major element analyses of the rock shows the enrichment of silica and alkali（with the average SiO2 being 72.69%,ALK being 6.73% and A/CNK1.0）,and can be classified as high-K calc-alkaline peraluminous granite.Chondrite-normalized REE patterns are of the rightly-oblique type.In the primitive mantle normalized multi-element diagram,the rock is enriched in LREE and LILE and depleted in HREE and HFSE,its ΣREE is 77.33×10-6 and its La/Yb ratios are high（the average of（La/Yb）N being 18.53）,thus showing some typical geochemical characteristics of adakite.Combined with regional geological characteristics,the authors hold that the Nongruri gold deposit was formed in post-collisional extension setting simultaneously with the ore-bearing porphyry intrusive event related to the south-north fault system and rift zone in Gangdese,thus being a product of epithermal system in the periphery of the PCDs（porphyry Cu deposits） system.

关 键 词：地球化学 锆石SHRIMP年龄 弧岩浆 中新世斑岩 弄如日金矿 冈底斯 西藏 

分 类 号：P618.51[天文地球—矿床学] P597[天文地球—地质学]