西藏改则多龙矿集区地堡那木岗矿床钾玄质二长花岗斑岩锆石LA-MC-ICP-MSU-Pb年龄、地球化学特征及其地质意义

发布时间：2018-08-21 12:23

【摘要】：西藏班公湖—怒江结合带已经成为我国重要的斑岩铜金矿成矿带,改则县多龙斑岩—浅成低温热液型铜(金)矿集区是近几年班公湖—怒江成矿带最为瞩目的找矿发现。本文首次对多龙矿集区地堡那木岗矿床二长花岗斑岩进行全岩地球化学分析及锆石LA-MC-ICP-MS U-Pb测年。二长花岗斑岩SiO_2为66.31%~67.31%,Al_2O_3为15.16%~15.33%,MgO为1.30%~1.47%,CaO为1.53%~1.65%,TFe_2O_3为3.29%~3.74%,K_2O为3.72%~3.98%,Na_2O为4.48%~4.96%,K_2O/Na_2O为0.80~0.89,铝饱和指数为1.00~1.07,里特曼指数为2.82~3.43,属于为高钾钙碱性弱过铝质岩石。其明显富集轻稀土及大离子亲石元素(Th、U、K、Pb及Rb),亏损重稀土及高场强元素(Ta、Nb、Ti及Zr),稀土总量为131.81×10~(-6)~151.59×10~(-6)之间,轻稀土与重稀土比值为10.67~10.97,(La/Yb)_N为14.03~15.23,δEu为0.75~0.78,具有中等负铕异常,显示出典型岛弧岩浆岩的特征,表明二长花岗斑岩可能是处于俯冲带背景下由洋壳俯冲板片脱水产生流体交代地幔楔发生部分熔融形成。二长花岗斑岩La/Nb值为3.36~3.50,La/Ta值为40.71~42.79,指示了岩浆在上升的过程中可能遭受到地壳物质的混染作用。其锆石具有明显的岩浆结晶环带,锆石U-Pb测年显示,Th/U值为0.56~1.10,岩石成岩年龄为112.6±1.3Ma。结合前人资料可知,多龙矿集区内岛弧岩浆岩存在117~124 Ma和107~112 Ma两个明显的主要成岩期,地堡那木岗矿床二长花岗斑岩形成于矿集区岩浆动活后期。综合分析认为,班公湖—怒江特提斯洋在早白垩世晚期(112.6±1.3Ma)尚未关闭,仍正在向北俯冲于羌塘地块之下。
[Abstract]:The Bangong Lake-Nujiang combined belt in Tibet has become an important porphyry copper-gold metallogenic belt in China. The Dulong porphyry and epithermal hydrothermal copper (gold) ore concentration area is the most prominent prospecting discovery in the Bangong Lake-Nujiang metallogenic belt in recent years. In this paper, the whole rock geochemistry analysis and zircon LA-MC-ICP-MS U-Pb dating of the Erchang granitic porphyry of the Guinamugang deposit in the Dulong ore concentration area have been carried out for the first time. The SiO_2 of Erchang granitic porphyry is 66.31 / 1 / 66.31and the number of Al2O3 is 15.160.33mg / m = 1.30300.477.33mg / MGO = 1.30300.470.45CaO = 1.53530.65Co = 1.53531.65TFe2O3 = 3.290.29K2O = 3.722.98Na2O = 4.484.96K _ 2O = 0.800.89, Al saturation = 1.001.077.707, Ritman's index 2.82n 3.43, belonging to high calcareous alkaline-weakly overaluminous rock. The number of K _ 2O / Na _ 2O / Na _ 2O is 0.80 0.89, the aluminum saturation index is 1.001.07, the Ritman's index is 2.82 ~ 3.43, and the value of K _ 2O / Na _ 2O is 0.80 0.89, and the value of Al saturation is 1.001.07 and 2.82 ~ 3.43. The contents of LREE and large ion lithophile elements (Rb), heavy rare earths and high field strength elements (Ta-Nb-Ti and Zr),) are 131.81 脳 10 ~ (-6) ~ (-6) and 151.59 脳 10 ~ (-6), respectively. The ratio of light to heavy rare earth is 10.67 ~ (10.97), (La/Yb) N is 14.03 ~ (15.23), 未 EU is 0.75 ~ (0.78), and it has moderate negative europium anomaly. The characteristics of typical island arc magmatic rocks indicate that the Erchang granitic porphyry may be formed by partial melting of fluid metasomorphic mantle wedge due to the dehydration of oceanic crust subduction plate in the background of subduction zone. The La/Nb value of Erchang granitic porphyry is 3.36 ~ 3.50% La / Ta = 40.71 ~ 42.79, which indicates that magma may be subjected to the mixing of crustal materials in the process of rising. The zircon has an obvious magmatic crystallization ring. The U-Pb dating of zircon shows that the U value of the zircon is 0.561.10 and the diagenetic age of the rock is 112.6 卤1.3 Ma. According to previous data, there are two main diagenetic periods in the island arc magmatic rocks in the Dulong ore concentration area: 11712Ma and 107112Ma, and the Erchang granitic porphyry formed in the late stage of magmatic activity in the ore concentration area. The comprehensive analysis shows that the Tethys ocean of Bangong Lake and Nujiang River was not closed (112.6 卤1.3Ma) in the late early Cretaceous and is still subducting north under the Qiangtang block.
【作者单位】：中国地质大学(北京)地球科学与资源学院;中国地质科学院矿产资源研究所;成都理工大学;中铝西藏金龙矿业股份有限公司;
【基金】：中国地质调查局公益性行业科研专项(编号:201511017) 中国地质科学院基本科研业务费项目(编号:YYWF201608) 国家自然科学基金青年基金资助项目(编号:41402178) 中铝资源公司项目(编号:ZLXZ-2013-JS03)的成果~~
【分类号】：P597.3;P618.41;P618.51

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