西藏龙根铅锌矿床二长花岗斑岩锆石U-Pb年代学和微量元素地球化学特征
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摘要
西藏龙根铅锌矿床位于中拉萨地体西部,是继查个勒铅锌多金属矿床之后,念青唐古拉铅锌银铜铁成矿带西段又一重要找矿突破。对龙根二长花岗斑岩进行了LA-ICP-MS锆石U-Pb年代学和微量元素地球化学研究,获得锆石~(206)Pb/~(208)U加权平均年龄为(62.9±0.8)Ma(MSWD=2.4,n=17),与念青唐古拉铅锌银铜铁成矿带东段亚贵拉铅锌钼矿床、中段纳如松多铅锌矿床和勒青拉铜钼铅锌矿床、以及西段的查个勒铅锌多金属矿床成岩年代相一致,均为印-亚板块同碰撞初期的产物。锆石Ti温度计估算出二长花岗斑岩中绝大部分锆石的结晶温度小于或等于680℃,推测岩浆来源于水近饱和条件下古老地壳的部分熔融。锆石微量元素特征表明龙根二长花岗斑岩形成于陆缘弧环境,具陆缘弧岩浆的特征。
The Longgen Pb-Zn deposit, located in the west of central Lhasa terrane,belongs to another important ore prospecting breakthrough after Chagele Pb-Zn pollymetallic deposit in the Nyainqentanglha Pb-Zn-Ag-Cpy-Py metallogenic belt. This paper studies zircon LA-ICPMS U-Pb geochronology and trace element, geochemistry of the monzonitic granite porphyry in Longgen deposit. Zircon U-Pb dating yielded weighted mean ages of(62.9±0.8)Ma(MSWD=2.4,n=17),which consists with the age of Yaguila Mol-Pb-Zn deposit in the eastern part of the belt,the ages of the Narusongduo Pb-Zn deposit and the Leqingla Cpy-Mol-Pb-Zn deposit in the middle part of the belt,the age of Chagele Pb-Zn pollymetallic deposit in the western part of the belt. The calculation by using zircon Ti thermometer reveals that the crystallization temperature of most zircons is lower than 680℃ in the monzonitic granite porphyry,which states its origin from partial melting of the ancient crust near the saturation of water. Based on the detailed study of the zircon REE,it is concluded that the monzonitic granite porphyry of Longgen deposit was formed in continental arc,with the characteristics of the continental margin arc magma. Combining with the previous research results about the typical Pb-Zn polymetallic ore deposits in the Nyainqentanglha metallogenic belt,we can infer preliminarily that the western part with low exploration degree owns great prospecting potential as the eastern and middle part.
The Longgen Pb-Zn deposit, located in the west of central Lhasa terrane,belongs to another important ore prospecting breakthrough after Chagele Pb-Zn pollymetallic deposit in the Nyainqentanglha Pb-Zn-Ag-Cpy-Py metallogenic belt. This paper studies zircon LA-ICPMS U-Pb geochronology and trace element, geochemistry of the monzonitic granite porphyry in Longgen deposit. Zircon U-Pb dating yielded weighted mean ages of(62.9±0.8)Ma(MSWD=2.4,n=17),which consists with the age of Yaguila Mol-Pb-Zn deposit in the eastern part of the belt,the ages of the Narusongduo Pb-Zn deposit and the Leqingla Cpy-Mol-Pb-Zn deposit in the middle part of the belt,the age of Chagele Pb-Zn pollymetallic deposit in the western part of the belt. The calculation by using zircon Ti thermometer reveals that the crystallization temperature of most zircons is lower than 680℃ in the monzonitic granite porphyry,which states its origin from partial melting of the ancient crust near the saturation of water. Based on the detailed study of the zircon REE,it is concluded that the monzonitic granite porphyry of Longgen deposit was formed in continental arc,with the characteristics of the continental margin arc magma. Combining with the previous research results about the typical Pb-Zn polymetallic ore deposits in the Nyainqentanglha metallogenic belt,we can infer preliminarily that the western part with low exploration degree owns great prospecting potential as the eastern and middle part.
引文
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[9] 孟祥金,侯增谦,叶培盛,等.西藏冈底斯银多金属矿化带的基本特征与成矿远景分析[J].矿床地质,2007,26(2):153-162.
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[20] 黄瀚霄,李光明,曾庆高,等.西藏查个勒铅锌矿床成矿时代研究及地质意义[J].中国地质,2012,39(3):750-759.
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[22] 段志明,李光明,李应栩,等.中冈底斯成矿带龙根铅锌矿床成矿斑岩年代学与地球化学特征[J].矿床地质,2014,33(3):625-638.
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[24] 李应栩,谢玉玲,陈伟,等.西藏恰功铁矿二长花岗斑岩锆石的U-Pb年代学与地球化学特征及意义[J].岩石学报,2011,27(3):2023-2033.
[25] 于玉帅,杨竹森,多吉,等.西藏加多捕勒铁铜矿成矿岩体时代与成因:锆石U-Pb年龄、Hf同位素与稀土元素证据[J].矿床地质,2011,30(3):420-434.
[26] Zhu D C,Zhao Z D,Niu Y L,et al.The Lhasa Terrane:Record of a microcontinent and its histories of drift and growth[J].Earth and Planetary Science Letters,2011,301(1/2):241-255.
[27] Liu Yongsheng,Zong Keqing,Kelemen P B,et al.Geochemistry and magmatic history of eclogites and ultramafic rocks from the Chinese continental scientific drill hole:Subduction and ultrahigh-pressure metamorphism of lower crustal cumulates[J].Chemical Geology,2008,247(1/2):133-153.
[28] Liu Yongsheng,Hu Zhaochu,Zong Keqing,et al.Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J].Chinese Science Bulletin,2010,55(15):1535-1546.
[29] Andersen T.Correction of common lead in U-Pb analyses that do not report 204Pb[J].Chemical Geology,2002,192(1):59-79.
[30] 吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1604.
[31] Hoskin P W O.Trace-element composition of hydrothermal zircon and the alteration of Hadean zircon from the Jack Hills,Australia[J].Geochimica et Cosmochimica Acta,2005,69(3):637-648.
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