粤东金坑Sn-Cu矿成岩成矿年代学格架与Sn-Cu共生成矿作用

Geochronological framework and coexisting Sn-Cu mineralization of Jinkeng Sn-Cu deposit in eastern Guangdong,China

金坑Sn-Cu矿床是粤东地区新发现的典型Sn-Cu共生矿床。矿区发育花岗闪长斑岩、中粗粒黑云母花岗岩和细粒花岗岩等多种侵入岩以及高基坪组火山岩,而这些岩石的年代学格架,及其与成矿过程关系还不清楚。因此,本文以粤东地区新发现的金坑铜锡矿床为研究对象,系统开展不同岩性侵入岩锆石和矿石锡石的U-Pb年龄测定,旨在浅析Sn-Cu共生成矿机制和成矿背景。结果表明,矿区中粗粒黑云母花岗岩和细粒花岗岩的锆石U-Pb年龄为145.2±1.2Ma和144.1±2.2Ma,这些年龄与该矿床的锡石U-Pb年龄(144.2±5.6Ma)在误差范围内一致,表明区内中粗粒黑云母花岗岩和细粒花岗岩与锡矿成矿关系密切。此外,获得花岗闪长斑岩U-Pb年龄为147.4±1.1Ma,且花岗闪长斑岩和高基坪组火山岩具有较高Cu含量,表明Cu可能来自于这两类岩石。结合前人研究成果,我们认为早白垩世矿区内发生了含锡中粗粒黑云母花岗岩和细粒花岗岩的侵位,其分异出富锡的还原性流体由于物理化学条件的变化析出了锡石;随着水岩反应的进行,流体萃取了围岩中的Cu、Pb、Zn等成矿元素,随着流体温度、盐度的持续下降,Cu、Pb、Zn和剩余的Sn在构造带内析出沉淀,从而造成了Sn-Cu共生成矿。

The Jinkeng Sn-Cu deposit is a typical coexisting Sn-Cu deposit newly discovered in the eastern Guangdong Province.Volcanic rocks of Gaojiping Formation and various intrusive rocks including granodiorite porphyry,biotite granite and fine-grained granite are developed in the mining area.However,the geochronology of these rocks and their relationship with mineralization are still unclear.In this paper,we systematically determined the U-Pb ages of zircon and cassiterite from different intrusive rocks or ore body from the Jinkeng Sn-Cu deposit,in order to investigate the mechanism of coexisting Sn-Cu mineralization and metallogenic setting.Zircon U-Pb dating of the biotite granite and fine-grained granite in the Jinkeng deposit yielded concordant ages of 145.2±1.2 Ma and144.1±2.2 Ma,consistent with the cassiterite U-Pb age(144.2±5.6 Ma),indicating a genetic link between the biotite granite and fine-grained granite and the Sn mineralization.In addition,the granodiorite porphyry with a U-Pb age of 147.4±1.1 Ma and the volcanic rocks of the Gaojiping Formation having high Cu contents,likely suggesting a Cu source.Combined with the previous studies,we propose the Sn-bearing granite intruded during the Early Cretaceous in the mining area,and then evolved high-Sn fluids resulted in cassiterite precipitation due to the change of physicochemical conditions.With the progress of fluid-rock reactions,Cu,Pb and Zn were extracted from the surrounding rock by fluid.Cu,Pb,Zn and remaining Sn precipitated coevally in the structures with the decrease of fluid temperature and salinity,which resulted in coexisting Sn-Cu mineralization.