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西藏拿若斑岩铜金矿床成矿斑岩年代学、岩石化学特征及其成矿意义
投稿时间:2014-02-28  修订日期:2014-05-23  点此下载全文
引用本文:祝向平,陈华安,刘鸿飞,马东方,李光明,张红,刘朝强,卫鲁杰.2015.西藏拿若斑岩铜金矿床成矿斑岩年代学、岩石化学特征及其成矿意义[J].地质学报,89(1):109-128.
ZHU Xiangping,CHEN Huaan,LIU Hongfei,MA Dongfang,LI Guangming,ZHANG Hong,LIU Chaoqiang,WEI Lujie.2015.Geochronology and Geochemistry of Porphyries from the Naruo Porphyry Copper Deposit Tibet and Their Metallogenic Significance[J].Acta Geologica Sinica,89(1):109-128.
DOI:
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作者单位E-mail
祝向平 成都地质矿产研究所成都, 6100812) 西藏自治区地质调查院, 拉萨, 850000 zhuxiangping3@hotmail.com 
陈华安 成都地质矿产研究所成都, 610081  
刘鸿飞 西藏自治区地质调查院, 拉萨, 850000  
马东方 成都地质矿产研究所成都, 610081  
李光明 成都地质矿产研究所成都, 610081  
张红 成都地质矿产研究所成都, 610081  
刘朝强 西藏地质矿产勘查开发局第五地质大队, 青海格尔木, 816000  
卫鲁杰 西藏自治区地质调查院, 拉萨, 850000  
基金项目:国家重点基础研究发展计划(973计划),国家自然科学基金项目(面上项目,重点项目,重大项目)
中文摘要:西藏拿若矿床位于西藏多龙矿集区北部,是2010年新发现的一个斑岩铜矿。三期花岗闪长斑岩在拿若斑岩铜矿内侵位,前两期花岗闪长斑岩是拿若矿床的主要成矿斑岩;成矿前的闪长岩在拿若矿床东南侧侵位。本文开展了拿若矿床斑岩和闪长岩的锆石U-Pb年龄、全岩岩石地球化学和Sr-Nd-Hf同位素组成分析。锆石U-Pb测年结果显示,三期花岗闪长斑岩在120Ma集中侵位,闪长岩略早于花岗闪长斑岩侵位(121 Ma)。三期花岗闪长斑岩具有相似的岩石化学特征,均富集轻稀土、大离子亲石元素,亏损重稀土、高场强元素,Eu异常不明显,显示出岛弧岩浆岩的特征,均具有高Sr低Y的特征,可能表明三期花岗闪长斑岩形成于同一个岩浆房;三期花岗闪长斑岩均具有高Al2O3、富钠、低镁和高Sr低Y的特征,显示出埃达克岩的特征;前两期花岗闪长斑岩的(87Sr/86Sr)i值分别为0.7054~0.7058和0.7056~0.7057,εNd(t)分别为-3.7~-2.9和-3.5~-3.2,εHf(t)值分别变化于3.6~6.7和3.6~7.4,表明前两期花岗闪长斑岩起源于新生的下地壳角闪岩相,有较多幔源物质混入;第三期花岗闪长斑岩具有较高εNd(t)值(-1.3~1.6)和εHf(t)值(5.1~8.1),表明第三期花岗闪长斑岩也起源于下地壳,但地壳物质混入较少。闪长岩也具有岛弧岩浆岩的特征,具有与花岗闪长斑岩相似的(87Sr/86Sr)i值(0.7052~0.7057)和略高的εNd(t)值(0.2~3.3)与εHf(t)值(1.2~9.5),表明闪长岩也起源于新生的下地壳,源区中壳源物质混入相对更少。闪长岩和成矿的花岗闪长斑岩铜背景值均较高,可能表明成岩源区内Cu丰度较高。含矿斑岩中地壳物质混入较多,可能表明成矿斑岩在侵位过程中从地壳中萃取了较多成矿元素。成矿晚期花岗闪长斑岩中Cu含量明显较低,可能是末期岩浆在岩浆房中释放了较多成矿元素所致;多期岩浆活动释放的成矿元素有利于成矿元素在成矿流体中持续富集成矿,多期岩浆侵位是形成斑岩铜矿的必要因素。
中文关键词:西藏拿若斑岩铜矿  多龙矿集区  班公湖-怒江成矿带  岩浆演化  岩石化学
 
Geochronology and Geochemistry of Porphyries from the Naruo Porphyry Copper Deposit Tibet and Their Metallogenic Significance
Author NameAffiliationE-mail
ZHU Xiangping Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081
Tibet Institute of Geological Survey, Lasa, 850000 
zhuxiangping3@hotmail.com 
CHEN Huaan Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081  
LIU Hongfei Tibet Institute of Geological Survey, Lasa, 850000  
MA Dongfang Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081  
LI Guangming Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081  
ZHANG Hong Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081  
LIU Chaoqiang No. 5 Geological Party, Tibet Bureau of Geology and Mineral Exploration and Development, Golmud, Qinghai, 816000  
WEI Lujie No. 5 Geological Party, Tibet Bureau of Geology and Mineral Exploration and Development, Golmud, Qinghai, 816000  
Abstract:The Naruo deposit, which is located in the north of the Duolong metallogenic district, is the third newly discovered porphyry copper deposit in the middle of the Tibet plateau. Three granodiorite porphyry phases were emplaced in the Naruo porphyry deposit. The former two granodiorite porphyry phases are mineralized porphyries, while the last granodiorite porphyry phase is a late mineral porphyry and barren. An early diorite pluton intruded in the southeast to the Naruo porphyry copper deposit. Zircon U-Pb dating, bulk rock geochemical compositions and Sr-Nd-Hf isotopic compositions of these porphyries and diorite were analyzed. Zircon U-Pb dating results shows that the diorite intruded at 121 Ma and these ganodiorite porphyries were emplaced at 120 Ma. Three granodiorite porphyry phases have similar ages and geochemical features, which might suggest that they were formed in a same magma chamber. These granodiorite porphyry phases are enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy earth elements and high field-strength elements, with weak Eu anomalies, indicating that these granodiorite porphyries resemble arc magmas in composition. These granodiorite porphyries have high SiO2 (63%~65%), Al2O3 (>16%), Na2O (>3%) and low MgO (<2%) content, together with the high Sr and low Y content, showing the adakitic affinities. (87Sr/86Sr)ivalues of the former two granodiorite porphyry phases are 0.7054~0.7058 and 0.7056~0.7057 respectively, with εNd(t) ranges within-3.7~-2.9 and-3.5~-3.2, εHf(t) varies within 3.6~6.7 and 3.6~7.4 respectively, suggesting that the former two granodiorite porphyry phases were derived from juvenile lower crust and some mantle-derived materials were mixed in the source region. The late mineral granodiorite porphyry also shows arc magma affinities in composition, its higher εNd(t)(-0.7~-0.2) and εHf(t)(1.3~12.2) might suggest that late mineral ganodiorite porphyry was also generate from lower crust with more mantle-derived materials, but less middle or upper crust derived materials were involved into the magmas while pooled in the magmas chamber. The diorite also shows arc magma affinities in geochemical composition, and has the lower (87Sr/86Sr)ivalues (0.7052~0.7057) and slightly higher εNd(t) (0.2~3.3) and εHf(t) (1.2~9.5) values, indicating that the diorite was also generated from lower crust but mixed with less crust-derived materials. The diorite and ganodiorite porphyries are fertile and have high copper concentration, which imply that larger amounts of copper might be concentrated in their source region within the lower crust. Comparing with the late mineral granodiorite porphyry phase, mineralized granodiorite porphyry phases contain more crust-derived materials, suggesting that metals were extracted into the magma chamber within the upper or middle crust. The late mineral granodiorite porphyry phase has lower copper concentration, indicating that the late stage of magmas released metals within the magmas chamber and the former magmas were enriched, and multi-stages of magmatic activities is crucial for the formation of porphyry copper deposits.
keywords:porphyry deposit, the Duolong metallogenic district  the Bangonghu-Nujiang metallogenic belt  magmatic evolution  geochemistry  Naruo Tibet
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