西藏冈底斯南缘雄村铜金矿床成矿斑岩厘定及其锆石U-Pb和黑云母Ar-Ar年龄分析  

Identification of porphyry genetically associated with mineralization and its zircon U-Pb and biotite Ar-Ar age of the Xiongcun Cu-Au deposit,southern Gangdese,Tibet

作　　者：邹银桥[1,2] 黄文婷[1] 梁华英[1] 伍静[3] 林书平[1,2] 王秀璋[1] 

机构地区：[1]中国科学院广州地球化学研究所、中国科学院矿物学与成矿学重点实验室,广州510640 [2]中国科学院大学,北京100049 [3]广西大学资源与冶金学院,南宁530004

出　　处：《岩石学报》2015年第7期2053-2062,共10页Acta Petrologica Sinica

基　　金：中国科学院战略性先导科技专项(B类)(XDB03010302);国家自然科学基金项目(41121002;41172080;40772054)联合资助

摘　　要：雄村特大型斑岩铜金矿床主要以细脉浸染状产于强烈蚀变岩石中,赋矿岩石原岩成因类型存在争议。本文对多个赋矿蚀变岩石作了系统光薄片显微鉴定,在多个蚀变较弱的矿化样品中发现赋矿岩石具斑状结构,其基质主要为钾长石,斑晶主要为斜长石、钾长石及少量石英,显示石英正长斑岩及二长斑岩（少量）矿物组成特征。结合前人工作,可以认为雄村铜金矿床赋矿岩石为正长斑岩、火山岩及少量二长斑岩。正长斑岩发育斑岩铜金矿床成矿早期常见的钾硅化蚀变及磁铁矿化蚀变,锆石具高的Ce4＋/Ce3＋比值（334~3084,平均值为1169）,显示高氧逸度岩浆特征,和世界斑岩铜金矿床成矿岩体一致;这表明石英正长斑岩为雄村铜金矿床成矿岩体。石英正长斑岩锆石LA-ICP-MS U-Pb年龄为173.7±2.1Ma（MSWD=0.23）,石英正长斑岩钾化阶段形成的黑云母40Ar/39Ar坪年龄为48.3±0.9Ma（MSWD=1.58）,远小于锆石U-Pb年龄却与矿区东北部始新世花岗岩基的年龄一致,显示Ar-Ar年龄受后期地质事件影响而发生重置。通过上述研究,可以认为雄村铜金矿床为与石英正长斑岩有关的斑岩型矿床,形成时代约173Ma,和新特提斯洋洋壳向北俯冲诱发的岩浆事件有关,矿区内云母受后期地质事件影响重置,不能记录其形成时代。The Xiongcun super-large Cu-Au porphyry deposit occurs as veinlet and disseminated mineralization in strongly altered rocks. There are different opinions on the type of ore bearing rock due to that the rocks underwent strongly alteration and therefore, protolith could not easily be recognized. The mineral assemblage and structure of the ore-hosted rocks are systematically studied through thin section identification at the relatively weakly altered domains. It is found at the weakly domain of the thin section that the protolith was characterized by porphyritic texture. The phenocrysts are dominantly plagioclase, K-feldspars, and minor quarts, while matrix is consist of K-feldspar and plagioclase. The petrology features indicate they are mainly of quartz syenite porphyry and a small amount of monzonite porphyry. Based on our work, together with previous work, it is concluded that the strongly altered ore bearing rocks include mainly quartz syenite porphyry, volcanic rocks and some monzonite porphyry. The Xiongcun quartz syenite porphyry underwent potassic alteration, silication, and magnetic alteration, which is common in the early stage alteration of Cu-Au porphyry deposits all over the world. The Xiongcun quartz has high zircon Ce4＋/Ce3＋ ratios, with an average of 1169, suggesting that the magma of the Xiongcun syenite porphyry was formed under high oxygen fugacity, which was the same as those found in most of the porphyry Cu-Au deposits in the world. The alteration assemblage in the quartz syenite porphyry and the high oxygen fugacity of the magma of syenite porphyry suggest that the quartz syenite porphyry is genetically related to the Xiongcun Cu-Au mineralizatoin. Quartz syenite porphyry has zircon LA-ICP-MS U-Pb age of 173.7 ＋ 2. 1Ma, with MSWD = 0. 23 and Ar-Ar age of biotite formed by potassic alteration in the quartz syenite porphyry is 48. 3 ＋0. 9Ma, with MSWD = 1.58. The biotite Ar-Ar age is much younger than the zircon U-Pb age and on the other hand, is coeval with the age of granitic batholith

关 键 词：雄村 锆石U-Pb年龄 斑岩型铜金矿床 新特提斯 冈底斯南缘 

分 类 号：P588.133[天文地球—岩石学] P597.3[天文地球—地质学]