湘南尖峰岭岩体锆石U-Pb年龄、地球化学特征及成因

香花岭锡多金属矿田处于南岭西段中_晚侏罗世形成的花山_西山_香花岭_骑田岭NE向的富碱侵入岩带上,是湘南地区矿化类型最为完整的锡矿区。尖峰岭岩体为矿田内主要的成矿母岩之一。为了进一步明确尖峰岭黑云母花岗岩的岩石成因及成岩年龄,笔者对尖峰岭黑云母花岗岩开展了LA_ICP_MS锆石U_Pb测年及岩石地球化学特征分析。锆石LA_ICP_MS U_Pb测年获得206Pb/238U年龄介于(158.6±2.3)Ma~(164.8±4.5)Ma之间,加权平均年龄为(160.7±2.2)Ma(MSWD=0.8),这与香花岭锡多金属矿田的成矿时限(154~161 Ma)相吻合,表明岩体的侵位与区内多金属成矿作用均发生于中_晚侏罗世。尖峰岭岩体的主量、微量元素研究显示,尖峰岭黑云母花岗岩具有富硅、富碱及成矿元素,富LILE及Zr、Ga等部分高场强元素(HFSE),贫Ca、Mg、P、Eu特征,指示尖峰岭黑云母花岗岩属于过铝质A型花岗岩(A2型)。综合研究表明,尖峰岭黑云母花岗岩体与其周缘钨锡多金属矿床在时间、空间及成因上有密切关系。结合区域上已有的同位素年代学数据,香花岭矿区的成岩成矿作用与南岭西段同时代的其他钨锡多金属矿床形成于同一岩石圈伸展的地球动力学背景下。

Zircon U-Pb age, geochemistry and petrogenesis of Jianfengling pluton in southern Hunan Province

The Xianghualing tin-polymetallic orefield located in the NE-trending Huashan-Xishan-Xianghualing-Qitianling alkali-rich intrusion belt hosts the most diverse types of ore mineralization in southern Hunan. The Jianfengling pluton is one of the major ore-related granites in this area. In order to further clarify the emplacement age and genesis of the Jianfengling biotite granite, the authors carried out zircon LA-MC-ICP-MS U-Pb dating and major and trace elements analyses of the pluton. The zircon LA-MC-ICP-MS U-Pb dating yielded ²⁰⁶Pb/²³⁸U ages ranging from (158±2.3) Ma to (164.8±4.5) Ma, with a weighted average ²⁰⁶Pb/²⁰⁸U age of (160.7±2.2) Ma (MSWD=0.8), which is well consistent with the mineralization timing (154~161 Ma) of the tungsten-tin polymetallic deposits in the Xianghualing area, indicating that both the granite emplacement and the tin-polymetallic mineralization occurred in the middle-late Jurassic. The major and trace elements compositions of the Jianfengling biotite granite indicate that the intrusion is characterized by high silica, rich alkali, rich LILE and some HFSEs (e.g. Zr, Ga), high concentrations of ore metals and the depletion of Ca, Mg, P and Eu, suggesting that the pluton belongs to the aluminous A-type granite (A2 type). Comprehensive studies show that tin-polymetallic mineralization in the Xianghualing orefield has a close temporal, spatial and genetic relationship with the Jianfengling biotite granite. Combining the new zircon U-Pb age obtained by the authors with previous geochronological data from the other important deposits in the region, the authors hold that the large-scale middle-late Jurassic tungsten-tin polymetallic mineralization in the western Nanling region occurred under the same geodynamic setting of lithospheric thinning and extension.