西藏驱龙铜矿西部斑岩与成矿关系的厘定：对矿床未来勘探方向的重要启示  

Relationship between Western Porphyry and mineralization in Qulong copper deposit of Tibet and its enlightenment to further exploration

作　　者：杨志明[1] 侯增谦[1] 夏代详 宋玉财[1] 李政[3] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]西藏中胜矿业有限公司,西藏拉萨850000 [3]北京科技大学土木与环境工程学院,北京100083

出　　处：《矿床地质》2008年第1期28-36,共9页Mineral Deposits

基　　金：国家自然科学重点基金(编号:40730419);国家基础研究规划973项目(批准号:2002CB412600)资助

摘　　要：对正在勘查中的西藏驱龙斑岩铜矿床,任何关于基础矿床地质认识上的改变,都可能会引发勘查方向上的重大变动。驱龙铜矿的勘探工作是围绕矿区内出露的几套斑岩体进行的。然而,野外调查发现,矿区西部斑岩体(指原Ⅱ、Ⅲ及Ⅳ号斑岩)却表现出与东部斑岩体(原Ⅰ号斑岩)截然不同的蚀变、矿化及岩石学特征:西部斑岩蚀变以石英-绢云母化为主,局部可见青磐岩化;矿化主要为黄铁矿化,黄铜矿很少;通常产于斑岩铜矿外围的黄铁矿D脉发育。这些特征均表明,西部斑岩整体处于斑岩矿化系统的绢英岩化带,局部甚至处于青磐岩化蚀变带内,并非像东部斑岩(出现以斑岩体为中心、呈同心环状分带的蚀变及矿化系统)一样。西部斑岩还发生了明显的韧性变形,经历了比东部斑岩更为复杂的地质演化过程,其形成时间明显早于东部斑岩。因此,推断西部斑岩对成矿的贡献不大。为证实野外观察的正确性,作者对西部斑岩开展了详细的岩石学、岩石地球化学及年代学研究,结果显示,西部斑岩为高钾钙碱性系列,具有明显的Eu负异常,富集大离子亲石元素,亏损高场强元素,但不亏损Ta,其锆石U-PbSHRIMP年龄为(182.3±1.5)Ma,为早侏罗世的产物,明显不同于形成于中新世的东部斑岩。因此,驱龙铜矿床未来的勘探工程布置方案更加清晰,应紧紧围绕东部斑岩所形成的矿化系统进行。由于西部斑岩出露面积较大,与叶巴组火山岩一样,仅为围岩,并没有形成自己的蚀变与矿化系统,建议不要对该斑岩布置太多的勘查工程。在矿床勘探过程中,详细的野外观察,辅以适当的科学分析手段,往往能够避免投入过多无谓的勘查工程,减少浪费。Any change in basic geological knowledge of the Qulong giant porphyry copper deposit, the most important and exploring deposit in the Gandise Porphyry Copper Belt （GPCB）, will result in change of exploration plan. In the past, the western （the original Ⅱ, Ⅲ and Ⅳ porphyries） and the eastern （the original Ⅰ porphyry） por- phyries were both considered to have been formed in Eocene and related to Cu-Mo mineralization. However, based on careful field observation, the authors found that the two kinds of porphyries have different alteration, mineralization and petrologic characteristics. Mineralization in the Western Porphyry, characterized by abundant pyrite veins and quartz-sericite alteration （with minor local epidote alteration）, is obviously controlled by fractures. Sulfide veins in them are typical D type veins at all exposed levels, and usually have sericite alteration halos. Concentric alteration-mineralization systems usually developed in porphyries related to mineralization were not found at the Western Porphyry. In addition, ductile deformation was developed in the Western Porphyry but not seen in the Eastern Porphyry, indicating a more complex evolutionary process of the Western Porphyry. It is thus inferred that the Western Porphyry probably has an older crystallization age than the Eastern Porphyry, and it only served as wall rock during the formation of the ore deposit. To testify the inference, the authors carried out detailed petrological, rock geochemical and radioactive age studies of the Western Porphyry. The analytical results indicate that the Western Porphyry has high K20 content and Aluminum Saturation Index （ASI, 1.6--2.8）, belonging to the strongly peraluminous and high K calc-alkaline series, and is rich in LILE and depleted in HSFE, with enriched light-REE. Zircons from a sample of the porphyry were selected and dated by SHRIMP and, as a result, an age of （182.3 ± 1.5） Ma was obtained. In contrast to the Eastern Porphyry, the Western Porphyry is not depleted

关 键 词：地质学 西部斑岩 U-PB SHRIMP定年 斑岩铜矿 驱龙 冈底斯 西藏 

分 类 号：P618.41[天文地球—矿床学]