(1. 中南大学 有色金属成矿预测与地质环境监测教育部重点实验室，长沙 410083；
2. 中南大学 地球科学与信息物理学院，长沙 410083；
3. 有色金属矿产地质调查中心，北京 100012)
摘 要: 下金宝岩体位于永安－下营坊－毛家沟构造岩浆岩活动带上，与本区金、银、铜等多金属成矿关系密切。对下金宝含矿花岗斑岩的锆石进行LA-MC-ICP-MS U-Pb年代学和微量元素地球化学研究，岩体锆石U-Pb年代学表明，锆石206Pb/238U加权平均年龄为(158.0±2.5) Ma(1σ，MSWD为0.76，n=16)，表明该岩体形成于燕山早期。锆石Ti温度计计算结果显示，下金宝岩体中锆石的结晶温度除一个测点小于700 ℃外，其余测点温度均大于700 ℃，表明锆石结晶于形成深度较深、温度较高的岩浆。锆石εHf(t)为-10.913~-7.5828，均为负值，Hf同位素特征表明，下金宝岩体主要起源于下地壳岩石的部分熔融，形成于由挤压向伸展转换的大地构造环境中。其动力学机制如下：燕山早期华北地块发生岩浆底侵作用，下地壳岩石重熔，并伴有部分地幔物质的参与，形成深部岩浆房，在深部压力作用下，原始岩浆沿深断裂上升，岩浆在演化过程中发生结晶分异作用，导致岩浆出溶流体，形成富水的岩浆热液，在近地表伴随温度和压力的降低，岩浆冷凝形成本区含矿斑岩体。
关键字: 锆石U-Pb年代学；锆石Hf同位素；成岩过程；成岩动力学；下金宝岩体
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitor,
Ministry of Education, Central South University, Changsha 410083, China？
2. School of Geoscience and Info-Physics, Central South University, Changsha 410083, China;
3. China Non-ferrous Metals Resource Geological Survey, Beijing 100012, China）
Abstract:Xiajinbao granite-porphyry body is located in Yong’an-Xiayingfang-Maojinggou tectono -magmatite zone, which is closely related to Au, Ag and Cu polymetallic metallogenic. Zircon U-Pb geochronology and trance element geochemistry of the ore-bearing granite porphyry in the Xiaojinbao was studied first time. The weighted average of 206Pb/238U age of (158.0±2.5) Ma (1σ, MSWD is 0.76, n=16), the result shows that Xiajinbao granite-porphyry body forms in early Yanshanian. Using zircon Ti thermometer, the forming temperature of zircon was calculated and all of them more than 700 ℃ except one point, it shows that zircon crystallized in deep and high temperature magma. The εHf(t) values of zircon ranging from -10.9130 to -7.5828, and all of them are less than 0. The characteristics of Hf isotope show that Xiajinbao granite-porphyry body originates from the partial melting of lower crust, and the formation environment is conversion environment from compression to extension. The geodynamic mechanisms of Xiajinbao granite-porphyry body formation were proposed based on the zircon U-Pb geochronology and trace element. The lower crust remelted under the magma under plating of the North China block in early Yanshanian, at the same time, involving in part of mantle material. Primary magma increases along the deep fault based on the deep pressure, showing a crystallization differentiation. The exsolution fluid from magma forms the water-rich magmatic hydrothermal. The ore-bearing granite porphyry is a product form by condensation of magmatic hydrothermal under the lower temperature and pressure of near-surface.
Key words: zircon U-Pb geochronology; zircon Hf isotope; diagenesis; diagenetic geodynamic; Xiajinbao rock body
