地学前缘 ›› 2010, Vol. 17 ›› Issue (2): 185-197.

• 论文 • 上一篇    下一篇

西藏尼木地区岗讲斑岩铜钼矿床地质特征及锆石U-Pb年龄

 冷成彪, 张兴春, 周维德   

  1. 1中国科学院 地球化学研究所 矿床地球化学国家重点实验室, 贵州 贵阳 550002
    2中国科学院 研究生院, 北京 100049
    3四川省冶金地质勘查院, 四川 成都 610051
  • 收稿日期:2010-02-05 修回日期:2010-03-04 出版日期:2010-03-15 发布日期:2010-04-05
  • 作者简介:冷成彪(1982—),男,博士,助理研究员,主要从事斑岩铜矿床研究。E-mail: lcb8207@163.com
  • 基金资助:

    国家自然科学基金项目(40873039);矿床地球化学国家重点实验室专项基金项目

A primary study of the geological characteristics and the zircon UPb age of the Gangjiang porphyry coppermolybdenum deposit in Nimu, Tibet.

 LENG  Cheng-Biao, ZHANG  Xin-Chun, ZHOU  Wei-De   

  1. 1State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guizhou  550002, China
    2Graduate University of the Chinese Academy of Sciences, Beijing 100049, China
    3Sichuan Institute of Metallurgical Geology and Exploration, Chengdu 610051, China
  • Received:2010-02-05 Revised:2010-03-04 Online:2010-03-15 Published:2010-04-05

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摘要：

岗讲铜钼矿床位于冈底斯中段尼木矿田之中,是近年新发现的一个储量在大型以上的典型斑岩型铜钼矿床。含矿岩体为复式岩体,其中铜、钼矿化主要产于黑云石英二长岩、石英二长斑岩和流纹英安斑岩之中。热液蚀变类型有钾化、硅化、绢英岩化、绿泥石化和局部泥化,从岩体中心向外主要发育钾化带和绢英岩化带。矿体主要分布在钾化带与绢英岩化带叠加部位,矿区次生氧化富集带也比较发育。文中利用二次离子探针质谱(SIMS)对主要含矿岩体进行了锆石UPb定年研究,获得黑云石英二长岩和流纹英安斑岩的结晶年龄分别为(1473±013) Ma(MSWD=13,N=16)和(1201±029) Ma(MSWD=23,N=8),与尼木矿田其他斑岩铜(钼)矿床含矿斑岩体的形成年龄基本一致,表明岗讲铜钼矿床形成于印度欧亚大陆板块碰撞后的伸展阶段。鉴于矿区缺失青磐岩化带,且钾化带主体已出露地表,因此该区的剥蚀深度至少应该在2～3 km,这与结合青藏高原的剥蚀速率(013～023 mm/a)估算的剥蚀深度一致。

关键词: 矿床地质, SIMS锆石UPb年龄, 剥蚀程度, 岗讲斑岩铜钼矿床, 尼木, 西藏

Abstract:

Gangjiang coppermolybdenum deposit is located in the Nimu ore field in the middle section of the Gangdese porphyry copper belt. It is a typical porphyrytype deposit discovered in recent years, with more than half million tons of contained copper and molybdenum resources. The Gangjiang complex is composed of biotite quartz monzonite, quartz monzonite porphyry, rhyodacite and dacite. There are many types of hydrothermal alteration including patassic, silicific, phyllic, propylitic, chloritic and argillic alterations. There are obvious potassic and phyllic alteration zones from the central to the outward part of the complex. The copper and molybdenum mineralization occurs mainly in the overlapped part of the potassic and phyllic alteration zones. The supergene oxidation enrichment zone is developed in the top part of the ore bodies. In this paper, the zircon UPb dating method by secondary ion microprobe mass spectrometer (SIMS) is applied to study the intrusion ages of the main orebearing porphyries. The zircon UPb dating ages of the biotite quartz monzonite and rhyodacite are (14.73±0.13) Ma (MSWD=1.3, N=16), and (12.01±0.29) Ma (MSWD=2.3, N=8), respectively. They are in accordance with the ages of orebearing porphyry from other porphyry coppermolybdenum deposits in the Nimu ore field, so the Gangjiang porphyry coppermolybdenum deposit was formed in the extensional tectonic setting posterior to the collision between the Indian and Eurasian plates. On account of the missing of large propylitic alteration zone and the exposure of the main potassic zone, it is inferred that the depth of erosion in the Gangjiang area could be 23 km. This is similar to the estimation based on the published denudation rate (013023 mm/a) of the Tibetan Plateau.

Key words: ore deposit, SIMS zircon UPb age, denudation, Gangjiang porphyry coppermolybdenum deposit, Nimu, Tibet

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